Transverse passages in the development of soil. Reference encyclopedia of the road builder (volume I) Construction and reconstruction of highways. Ed. Vasilyeva A.P. - file n1.doc. Excavation work by graders
General provisions. The construction of the subgrade of roads in mountainous areas is complicated, as a rule, by the fact that in the places where the route is laid, there are steep slopes with an intense manifestation of exogenous processes (landslides, landslides, falls, screes) in a certain area of small length. In connection with this, it is recommended when drawing up a project performance of work (PPR) take into account the engineering and geological features of a site or group of sites that differ in the indicated characteristics. It is recommended to assign the technology for the construction of the subgrade, taking into account the design features of the embankment or excavation, the construction region as a whole, the structure of the slope (slope) and the properties of the constituent rocks.
It is necessary to provide for a set of technological measures in the WEP to ensure the stability of natural slopes and slopes of excavations during the construction and subsequent operation of the road.
When developing a PPR, choosing a technology, machines and method of drilling and blasting, the presence of cracks in the developed massif and the nature of the layering of sedimentary rocks are taken into account.
Availabilitycracks in rocky igneous rocks reduces the stability of slopes and slopes of excavations. The fall of cracks at an angle of more than 35° towards the road contributes to the occurrence of landslides, collapses, falls already in the process of work. Safe is the fall of cracks in the direction of the array.
Layering leads to a weakening of the array in the slopes and slopes, especially when they are pruned or undermined.
With an increase in the angle of meeting of the strike of the layering with the longitudinal axis of the road, the stability of slopes and slopes increases sharply. The most stable position of the bedding meeting angle with respect to the road axis will be 90°. If the azimuth of the strike of the layering coincides with the direction of the axis of the road, the cut or undermined slopes and slopes of the cuts are destroyed only along the bedding planes.
During the construction of roads in mountainous conditions, the main difficulties are associated with the development of rocks, a reduction in the scope of work, limited transport accessibility working area, moving, leveling, compaction of coarse soils, finishing works.
If the working area is not available for the direct operation of machines, the first stage of construction should include the laying of a pioneer road along the planned route. If the laying of a pioneer road along the planned route is impossible, it is arranged as close as possible to it with approaches to the work area of individual structures. In this case, a hiking trail is laid along the route itself.
Loosening and development of rock, belonging to the difficulty of development to group V and above, is carried out by the explosive method. The explosive method is also recommended for the formation of deep cuts by mass ejection explosions or targeted explosions for the construction of embankments in hard-to-reach places in the mountainous terrain.
At all stages of work, measures must be constantly taken on slopes and slopes to prevent geodynamic phenomena (landslides, scree, avalanches, etc.) that may pose a danger to working people, equipment, structures. To this end, prior to the start of work, as well as in the process of developing mountain slopes, constant monitoring of the stability of both individual rock fragments and the entire slope from the upper side should be organized. If signs of instability are found, safety measures must be taken immediately, such as undermining and removing overhanging boulders. In the presence of active landslides, intense landslides, large falls, drilling and blasting operations are carried out only for loosening with small-hole charges.
Works on the construction of a subgrade on slopes, stable and landslide slopes include: a preparatory complex associated with marking work, removing vegetation; arrangement of a construction drainage system, parking lots for equipment placement, special anti-landslide structures; the main work on the construction of a subgrade located on various elements of the slope relief or in its environment and a set of anti-landslide measures.
It should be borne in mind that the choice of technology is also associated with the need to develop deluvial, rocky or semi-rocky rocks, as well as their use in the form of coarse soils for filling embankments. The latter depends on the passage of the route in conditions of rugged terrain.
Construction of embankments and excavations. The construction of a subgrade in a mountainous area includes the installation of the following structures, depending on the conditions for laying the route in a particular region and region of a mountainous area, their hypsometric, geomorphological and engineering-geological features: a subgrade in a ledge, a half-fill-half-cut, a cut in a rock mass, an embankment of rocky or coarse soils.
The choice of technology for the development of excavations and the construction of embankments is determined design features subgrade, category of rocks according to the difficulty of their development, sources of obtaining rocky or coarse-grained soil for the subgrade of embankments.
Construction of subgrade in shelves in pressure areas with a slope steepness of more than 1:3 in rocks, they are carried out by blasting, followed by excavation of the blasted mass, its transportation to the areas of the embankment. If there are deluvial deposits on the slopes, the subgrade in the shelf is developed by initially cutting the slope with powerful bulldozers of the 250-300 tf class, followed by refinement by excavators and transportation of coarse soils by dump trucks.
Construction of embankments and excavations on slopes with a steepness of 1:3 or more is carried out by the method of successive cutting of shelves for recesses or half-pits or ledges at the base of the embankment. Cutting ledges (shelves) is performed, as a rule, starting from the upper tier. With the provided stability of the slope and the need to create a passage for drilling operations, the first shelf is produced at the level of the lower edge of the excavation (shelf).
Development of excavations in rocks are carried out immediately with a small enumeration in order to avoid subsequent difficult and costly work to remove an under-selected thin layer of rocky soils. The subgrade is leveled to the design marks with small torn stone and rubble.
The development of excavations in deluvial soils, softened and highly weathered collapsible, fractured rocks is recommended to be carried out according to the “sliding shelf” scheme, when, after the implementation of the pioneer trench-face necessary for the placement and safe operation of the excavator, the soil is developed from top to bottom and moved by powerful bulldozers of the class 250-300 tf. With the help of an excavator, the subsequent refinement of the soil and its loading into vehicles with movement to the construction sites of embankments takes place.
To form smooth surfaces of slopes during the construction of cuts and half-cuts in favorable engineering and geological conditions (poor crack resistance of rocks, separation into rectangular parts with a vertical direction of the interface planes, the ability of rocks to brittle chipping, etc.), contour blasting is used.
The choice of the method and parameters of loosening rocky and coarse-grained soil should be carried out in accordance with the soil group according to the difficulty of development, with the area and conditions of its application. If the calculated number of oversized items in the loosened soil and their maximum size are exceeded, it is necessary to make appropriate changes to the loosening scheme and parameters.
Prior to drilling and blasting, the vegetation cover, topsoil and overburden are removed and removed. When the thickness of overburden is not more than 1/3 of the working depth, loosening of rocky soil is allowed without their removal.
Drilling and blasting and loading of loose rock by excavators can be carried out in parallel. In this case, the first work must be carried out ahead of time. If the method of blasthole charges is used for loosening in recesses or ledges up to 5 m deep, drilling and blasting operations should be carried out ahead of time, providing at least a replaceable supply of blasted rock. In this case, the minimum lead distance must be maintained in accordance with the Uniform Safety Rules for Explosive Operations (M.: Nedra, 1985).
Before the start of the excavator, oversized items located in the upper layer of the blasted soil are crushed by additional explosions. In the process of excavation development, oversized pieces are rolled off to the side and then also crushed by explosions, moving the exploded rock with a bulldozer to the excavator face.
When developing half-holes on rocky slopes, they first arrange a shelf for a working passage 3.5 m wide, which makes it possible for the main machines (drilling rigs, excavators, bulldozers, dump trucks, etc.) to pass. Then the shelf is widened, bringing the subgrade to the design outline.
When developing excavations loosening of rocks to the required particle size must be ensured by the proper drilling and blasting technology and proceed from the required compaction conditions provided for by SNiP 2.05.02-85. Crushing of large oversized fragments is carried out by overhead charges. This method is used with limited compressor capacity or in the absence of drill hammers and a small amount of oversized. The ledges of rocky soil remaining on the slopes and the main excavation site are also crushed.
With explosive methods of development and loosening, shortfalls at the base of the excavations are not allowed. Shortfalls on the surface of the slopes should not exceed 0.2 m, provided that their stability is ensured. The value of the searches after the final cleaning of the bottom and slopes of the excavations should not exceed the values \u200b\u200bspecified in Table. one.
When finalizing excavations in rocky soils after explosions for ejection, the following work procedure should be observed:
crushing of oversized objects located on the surface, formed during the explosion of the trench;
leveling loosened soil heaps with a bulldozer;
removal of blasted soil from slopes by an excavator (slope trimming);
removal of non-hanging stones and visors with an excavator and small explosions;
finalization of the excavation to the design outline by explosions; leveling of the main platform.
Table 1
Note. During drilling operations under water and in offshore areas and roadsteads, the size of the searches is established by the construction organization project.
In the case of tiered excavation, each tier must be completed to the design contour and cleaned before work begins on the next tier.
When constructing embankments from coarse-grained soils, which are the product of loosening or weathering of rocks, maximum size particles of the blocky fraction should be assigned depending on the thickness of the compacted layer, the type and technical parameters of the compacting means and the physical and mechanical characteristics of the soil, but should not exceed 2/3 of the thickness of the compacted layer.
Oversized fragments, the dimensions of which do not meet the specified requirements, are allowed to be laid in the side (slope) parts and in the lower layer of the embankment in one row so that they do not fall into the working layer of the embankment.
When laying oversized debris in the base of the embankment, in order to exclude uneven settlement due to spillage of fine-grained aggregate from the overlying layers into the underlying layers, interrupting layers of crushed stone (pebble), sandy or clayey soils should be arranged.
The filling of the embankment from coarse-grained soils is carried out by a bulldozer using the “push” method in such a way that the largest fragments are located in the lower parts of the embankment. The most rational is the use of a bulldozer with a universal blade, which allows during the distribution process to produce a rejection of oversized items with their subsequent placement in the side of the embankment.
There are two patterns of distribution of coarse-grained soil: longitudinal and diagonal. Depending on the method of filling the soil, the longitudinal and diagonal distribution patterns can be one-sided or two-sided.
For axial dumping, a two-sided distribution scheme is used, for lateral dumping - one-sided.
It is rational to use specially equipped dumps with a mixed sorting device according to the type of ripper for rejecting oversized items.
Before compaction, the side parts of the embankment, including slopes made of oversized, are leveled with soil of smaller fractions. When arranging a subgrade on slopes with a steepness of more than 1: 3, it is advisable to arrange alignment from soils with sandy filler according to the wedging method.
The development of coarse-grained soils after blasting should be carried out with an excavator with a bucket capacity of 0.65-1 m 3 with loading into vehicles. If it is necessary to hill up the soil of an oversized dump on horizontal surfaces and slopes with a steepness of up to 1: 3, bulldozers are used.
With a layered occurrence of easily weathered softening rocks, interspersed with layers of clay soils, the development is carried out for the entire thickness of the face, taking into account that the developed soils contain 30-40% (by weight) of clayey fine earth. Otherwise, the development is carried out in separate layers.
Layingand compaction of coarse soils. Coarse-grained soils of frame and imperfect-frame structure from durable water-resistant rocks should be compacted, as a rule, by vibration. Coarse clastic soils containing more than 30% clay aggregate are compacted at a moisture content not exceeding the allowable values for heavy sandy loams and light loams, and with a clay aggregate content of less than 30% - at a moisture content not exceeding the allowable values for light and silty sandy loams.
Compaction of coarse soils, the strength of which is less than 5.0 MPa (50 kg / cm 2), should be carried out in two stages: at the first - with lattice rollers; on the second - rollers on pneumatic tires weighing at least 25-30 tons. When using softened coarse-grained soils, work should be carried out in dry weather with minimal time gaps between individual technological operations.
Methods and technical means of compaction of easily weathered, non-water-resistant coarse-grained soils are prescribed from the condition of ensuring the destruction of aggregates until the pores are filled with fine earth. To improve the efficiency of the destruction of aggregates, they are periodically moistened.
Good results are obtained by the technological scheme of compaction in two stages: at the first (immediately after leveling and moistening) - by lattice rollers, which carry out additional crushing of the soil, at the second - by heavy rollers on pneumatic tires. The required degree of soil compaction is achieved after 10-12 passes along one track of rollers on pneumatic tires weighing 25-30 tons. For coarse-grained soils of low strength, compaction by tamping is effective.
If it is impossible to ensure the destruction of aggregates of non-water-resistant rocks, their protection in the embankment from the effects of weather and climatic factors should be provided. When constructing protective layers from clay or loamy soils, the latter are filled up to a given thickness in layers, level with a layer of clastic soil and compacted together with it.
When constructing a protective layer with a thickness of 15-20 cm from soils reinforced with organic binders, the soil is pre-mixed with binders in stationary or mobile units and transported by dump trucks to the place of laying. Bulldozers or leveling excavators are recommended for spreading the mixture on slope surfaces. Site vibrators or vibrating slats moving along the slope from top to bottom or from bottom to top can be used as sealing means.
Quality control of works when constructing a subgrade on slopes, stable and landslide slopes, in addition to the general requirements provided for by SNiP 3.06.03-85, it includes: control over the restoration, fixing and breakdown of the subgrade on the marked relief elements; quality control of ledge cutting (in compliance with the design geometric parameters), compliance with the technology for developing slopes and slopes when constructing a subgrade in a shelf and the sequence of a set of anti-landslide measures (drainage, drainage and retaining structures).
Organization of work on the construction of roads in the presence of landslides, it includes two independent issues: the construction of a subgrade and the construction of a complex of anti-landslide structures established by the project. The sequence of these works is determined by the specific conditions of the territory, the location of the subgrade, the composition and types of anti-landslide structures and should be specified in the design and calculation documentation. In practice, there are several options for organizing the sequence of earthworks and the installation of anti-landslide structures: the construction of a complex of anti-landslide structures before the construction of the subgrade; implementation of anti-landslide structures in the process of its construction; construction of anti-landslide structures after the construction of embankments or excavation.
As a rule, the first scheme is the most appropriate for the construction of a road on landslide slopes, when the construction of the subgrade is possible only under the direct protection of supporting structures or after measures have been taken to regulate surface and underground runoff. The second scheme is used when the subgrade is located in deep excavations and high embankments. For example, as each tier is developed, excavations strengthen slopes and construct drainage structures. The third scheme is used in many cases in the construction of roads in mountainous conditions, when, in particular, after the construction of the subgrade in the shelf, upper retaining walls or anchor structures are constructed.
Undoubtedly, the variety of complex conditions for the construction of roads in landslide or potentially landslide areas requires the creative application of these schemes with subsequent development to specific technological and organizational solutions in work projects. This section only deals with general issues organization of construction in landslide areas and does not cover the specifics of the construction of specific types of anti-landslide structures, which is reflected in other chapters.
In addition to the features associated with the sequence of earthworks and the construction of anti-landslide structures, it should be noted that the technology of earthworks largely depends on the design principles (in relation to the relief) of roads. There are the following types of individual technological schemes for organizing earthworks: the development of deep excavations and the construction of high embankments; construction of embankments on slopes with crossing of landslide areas; arrangement of subgrade in the shelves. One of the most difficult cases of work performance is their implementation at emergency facilities, when sections of operated roads are destroyed by landslides.
The fact established by repeated surveys of the violation of the stability of natural slopes and slopes of the subgrade during the construction of roads in various regions of our country convincingly shows that the influence of technological factors can be significant, and in some cases prevailing.
In this case, technological factors include: the method and time of excavation or construction of embankments, the method and time of construction of anti-landslide structures. These factors can be combined into a general technological system for the construction of individual subgrade structures, which, during its implementation, will have certain effects on the stability of the slopes of the subgrade and the slopes adjacent to it, especially landslides.
An analysis of the construction of roads in landslide areas showed that the impact of the technological system on the stability of slopes and slopes is manifested in the following.
An unsuccessfully chosen direction of work in the development of deep excavations can lead to the development of landslides in the slopes. The degree of intensity of earthworks affects the stability parameters of slopes during the construction process. So, with a short front of work and a high speed of excavation in slopes (at the working depth of development), deformations leading to landslides do not have time to occur, which makes it possible to give the slopes of the working tiers steeper angles. The construction of high embankments and embankments on slopes (including landslides), on the contrary, requires a slower soil dumping mode, due to the need for thorough compaction of the soil, as well as the gradual transfer of the load from the weight of the embankment to the slope base, which ensures its stability and further stability.
The order and timing of their design configuration have a significant impact on the development of landslides in slopes and slopes. The most common mistake in this regard is associated with the installation of berms, tiers, drainage structures and strengthening works on slopes not during the development of excavations and the construction of embankments, but after their completion. Of particular importance is the technological sequence of the construction of embankments on the slopes. In the projects for the production of work, such a principle of conducting work should be laid down, which would guarantee the stability of the inclined base during the construction of the subgrade. In particular, for example, in many cases, the stability of embankments on slopes was violated due to an incorrect method of work: instead of the consistent construction of an embankment from the downstream side of the slope, work was carried out from the upstream side, which led to the development of uncompacted zones in the sloping parts, overstressing the slope base, the development of landslides both in the slopes and in the slopes of embankments.
Very importance acquire technological factors during earthworks on landslide slopes or in their environment. Proper placement of earth-moving equipment, determination of the required pace, maintaining the required depth of development or steepness of the slope provide not only the possibility of implementing design solutions, but also their further reliability during the operation of the road section, as well as the degree of preservation of the landslide slope itself in a stable state.
The foundation of the building transfers the load it perceives to the base plane. bearing soil it is necessary to withstand this load without destruction. For foundations, two types of soil are usually used: with high cohesion (clay, silt) and loose (sand, gravel). More rarely, rocky soils are used that provide a high bearing capacity; there are soils with a low bearing capacity, such as peat, backfill, macroporous loess. Among cohesive and loose soils, there are also transitional types.
Before calculating the foundation, it is necessary to study the basic properties of the soil. It is best to conduct an examination of the site, on the basis of which to calculate the depth of the foundation. It is possible, however, to obtain sufficient information on the basis of a soil sample from one pit. The most common mistake in the construction of foundations is the option when part of it falls on dense soil, and the other on loose soil. As a rule, this happens when building a house on a slope, in a recess or on an embankment. In this case, the foundation sags more on loose soil than on dense soil, and a difference in subsidence occurs (Fig. 25). Under the influence of this difference, cracks appear in the walls; with large subsidence, there may be a danger of loss of stability of the entire structure. The correct solution is to excavate the soil in steps 0.5 m wide to build a foundation on a slope so that the structure does not fall into the embankment zone, remaining on compact soil. To correct errors, they proceed in the same way, but now with a higher cost of funds. Subsidence can only be stopped when the sole of the structure is completely on solid ground.
Scrapers are usually used on soft and dense soils, in areas with a short winter period. Scrapers are widely used in earthworks: removing the vegetation layer and moving it to cavaliers; stripping operations in non-metallic quarries building materials; construction of embankments and excavations for various purposes; performance of planning work with cutting off elevated places and laying soil in low places; arrangement of irrigation canals, reservoirs and ponds.The best filling of the bucket with soil occurs when the scraper moves down a slope of 5 ... 12 °. When developing cohesive soils, it is advisable to use a pusher tractor in the process of collecting soil. This increases the filling of the bucket and reduces the duration of the set.
The length of the soil collection path depends on the nature of the soil being developed, the size of the scraper and the adopted work scheme.
They cut the soil and fill the bucket only with the rectilinear movement of the tractor and the scraper. To reduce the time for collecting soil into the bucket of the scraper and its maximum filling, the soil is cut in first gear (speed 2.5 ... 3.5 km / h), elongated knives are used and teeth, lead downhill cutting, loosen dense soils, install cheeks to the bucket, use pusher tractors and adjust the position of the damper during cutting the soil.
When developing soft soils (vegetable, loess, soft solonchak, etc.), wedge-shaped chips are cut off - thicker at the beginning and thinner towards the end of the bucket set. When developing dry sandy soils, cutting is carried out with comb profile chips with variable depth of the bucket and a gradual decrease in chip thickness.
With all cutting methods, the soil is collected with the maximum possible chip thickness (Table 1).
Note. To the line - without a pusher, beyond the line - with a pusher.
Dense soils are preliminarily loosened to the thickness of the cut chips. For loosening weak clay soils, a ripper with five racks is used, and loamy soils with three racks. For better filling of the bucket, dry soils are moistened with the help of watering machines to the optimum moisture content, and waterlogged soils are dried.
When developing ground light scrapers should: perform layer-by-layer loosening of dense soils to the cutting depth of the scraper; do not allow movement and set of soil on slopes greater than those indicated in the vehicle's passport; use pusher tractors when collecting soil; use scrapers with forced filling; unload the soil on the embankment when the scraper moves parallel to the longitudinal axis of the embankment; pour the soil in the embankment in layers from the slopes to the axis in longitudinal strips; erect embankments alternately on the maps, on each of which operations are carried out for unloading, leveling, moistening (drying) and compacting the soil.
Scraper traffic patterns
Depending on the size of the earthwork, the location of cuts, embankments, cavaliers or dumps, the following schemes of their movement are most often used during the operation of scrapers: elliptical, "eight", spiral, zigzag, shuttle-transverse and shuttle-longitudinal.Work "on an ellipse" (Fig. 1, a) and "eight" (Fig. 1, b) is applicable when erecting embankments from one- and two-sided reserves, when arranging excavations with laying soil in embankments, dams and caves, when planning work in industrial and civil construction. When working with the "eight" in one pass, the scraper performs two operations of loading the bucket and two operations of its unloading, which shortens the path of the idle run and, as a result, increases the productivity of the scraper.
Fig.1. Scraper movement scheme
a - along an ellipse; b - eight; in - in a spiral; g - zigzag; e - according to the shuttle-transverse scheme; e - according to the shuttle-longitudinal scheme; rectangles show loading areas; shaded rectangles - unloading areas
The spiral scheme (Fig. 1, c) is used in the construction of wide embankments from bilateral reserves or wide excavations with a height or depth of up to 2.5 m. At the same time, work is carried out without the arrangement of exits and exits.
Work "in a zigzag" (Fig. 1, d) is carried out during the construction of embankments up to 6 m high from reserves with a grip length of 200 m or more.
The shuttle-transverse scheme (Fig. 1, e) is used more often when erecting embankments and dams with a height of less than 1.5 m when working from bilateral reserves or when constructing canals and excavations up to 1.5 m with laying soil in dams or cavaliers. The productivity of the scraper along the zigzag is 15% higher, and with the shuttle-transverse - by 30% compared to the elliptical scheme.
The shuttle-longitudinal scraper movement pattern (Fig. 1, f) is used in the construction of embankments 5 ... 6 m high with slopes not steeper than 1: 2 ° with soil transportation from bilateral reserves.
The traffic pattern for each specific case should be chosen taking into account local conditions so that the traffic paths are the smallest. The greatest slopes of earth-carrying roads should be for scrapers: in the freight direction - when lifting - 0.12 ... 0.15, and when descending - 0.2 ... 0.25; in an empty direction - when lifting 0.15 ... 0.17, and when descending 0.25 ... 0.3.
Innovate experience
In construction, trailed scrapers DZ-20 with a capacity of 7 m 3 aggregated with tractors T-100M and T-130 are widely used. Theoretical and techno-economic analyzes of the operation of these machines have shown that in order to reduce the reduced costs in the development of soil, the bucket capacity of serial scrapers can be increased to 10-12 m 3 .For this purpose, designs of increased-capacity scraper buckets with a movable bottom have been developed, the filling of which does not require an increase in the traction force of the tractor.
Long-term tests have shown that the use of buckets of increased capacity with a movable bottom provides an increase in the productivity of scrapers due to a larger volume of soil transported per cycle by 2.9 ... 3.8 m 3 with a slightly changing speed of transportation. The productivity of scrapers increases by an average of 30...35%, and the specific reduced costs are reduced by 15...20%.
Safety
Before moving the scraper, make sure the path is clear. When working on a freshly poured embankment, the tractor caterpillars and the wheels of the machine must be no closer than 1 m from the edge of the embankment.After work, the machine must be braked. It is forbidden to leave the car unbraked on a slope or slope.
Do not troubleshoot the machine, adjust or lubricate the machine, or get on or off the machine while the scraper is moving.
Scrapers must not be used: when developing clay soils in rainy weather; when driving uphill with a longitudinal slope of more than 25 ° and descending with the ground with a slope of more than 30 °; when working on slopes with a transverse slope of more than 30 ° or steep slopes.
The scraper driver should not make sharp turns of the unit, especially when working on slopes, which often leads to the tractor slipping; it is also forbidden to turn the machine with a buried bucket.
Before starting a turn, the scraper driver must shift to a lower gear (first or second) and only then start the turn.
When moving the unit under its own power to another place of work at a distance of not more than 1 km, the bucket should be raised and fixed with a transport suspension to the scraper frame, turning off the winch or hydraulic drive. In this case, special attention should be paid to the state of the braking device, and when driving downhill, the tractor engine unit should be additionally braked.
Bulldozer Application
Bulldozers are designed to perform various earthworks: they erect embankments up to 2 m high from one-sided or two-sided reserves (Fig. 2); soil is developed in excavations with its displacement at a distance of 50 ... 150 m; develop the soil of pits for foundations and trenches; cut the soil on the slopes (for cutting ledges, the device of semi-dredging-half-fills, etc.); cut ditches and shallow drainage ditches; fall asleep sinuses, pits, trenches, reserves, pits and ravines; planning sites, etc. (Fig. 3).
Fig.2. Erection of a bulldozer embankment
a - from a unilateral reserve; b - from bilateral reserves
Fig.3. The layout of the bottom of the pit with a bulldozer
a - movement of soil to the place of excavation of the excavation with a dragline; b - moving the soil to the place of subsequent development with a straight shovel
The rational range of soil movement by bulldozers depends mainly on the power of the bulldozer: on tractors DT-54 - up to 30 ... 50 m, DT-75 and T-100 - up to 50 ... 70, T-130 and T-180 up to 100 , DET-250M and T-330 up to 150...160m.
The cycle of the bulldozer consists of set, move, level the ground and reverse.
Soil collection (digging) can be done in the following ways:
chips of constant thickness. This is how all types of soils of groups I ... III are developed when they are collected on the rise or soils with significant digging resistance;
comb method - chips of variable thickness, with a transverse deepening of the blade. This is how dense and dry soils are developed;
wedge method - chips of variable thickness, moving from the largest to the thinner chips. This is how soils with low digging resistance are usually developed.
When developing a recess, the most productive work of a bulldozer is achieved when it moves down a slope of 10 ... 15 °. The largest slopes overcome by bulldozers of classes up to 40, from 40 to 100 and from 150 to 250 kN are: when moving up, respectively, 20, 25 ... .30 and 25 °; when descending with the ground, respectively, 20, 25 ... 35 and 35 °; at a cross slope of 20, 30 and 30°.
Fig.4. Ways to reduce soil loss during transportation by a bulldozer
a - creating a trench; b - multiple penetrations along one track; in - paired work of bulldozers; g - the creation of intermediate shafts
Depending on the nature of the structure being erected, the relative position of the sites for excavation and backfilling of soil, and local conditions, various schemes for the movement of bulldozers are used. At the same time, there are three main schemes for developing and moving soil with bulldozers: straight, lateral and stepped.
The direct scheme is used when digging trenches and excavations, the width of which slightly exceeds the width of the bulldozer blade; when arranging entrances, when soil dumping is allowed in one place, with this scheme the bulldozer reciprocates without turns, therefore the scheme is often called shuttle or pendulum. When moving forward, the bulldozer cuts the soil and transports it to the dump site (working stroke). Then he reverses back to the place where the cutting of the soil began.
The side scheme of the bulldozer is used when moving previously developed soil from dumps or bulk materials (sand, gravel, etc.) from bunkers, when developing light soils cut in thick layers, and also when working on slopes. At the same time, the developed soil is located on the side of the path along which the bulldozer transports it to the place of backfilling. The bulldozer captures the soil with a dump, makes a turning movement, moves the soil to the transport path, then transports it to the dumping site. Only a qualified bulldozer operator can work according to this scheme, since with insufficient experience in driving a bulldozer, a significant part of the soil can be lost during the turn of the bulldozer.
The stepwise scheme of development and movement of soil is mainly used in the construction of embankments, overburden operations and vertical planning of areas, when it is allowed to pour the developed soil over the entire width of the excavation. The work is carried out in parallel penetrations. Having moved the soil from one penetration, the bulldozer idles at an angle to the axis of the working stroke and begins to develop and move the soil at a nearby penetration (see Fig. 2, a).
Depending on the width of the embankment, soil development is carried out in one- and two-sided (see Fig. 2, b) lateral reserves. Before starting work, a geodetic breakdown of the embankment and lateral reserves is carried out, the purpose of which is to outline the axis and boundaries of the base of the embankment, the boundaries of the berm and reserves. Reserves are laid mainly on the upland side of the embankment with a transverse two-sided bottom slope of 0.02 to the middle of the reserve. The longitudinal slope of the bottom of the reserve should be at least 0.002 and not more than 0.008. For the convenience of work, the filling of the embankment is carried out with grippers 50 ... 100 m long.
Soil development starts from the field edge of the reserve. The bulldozer moves at the first speed, cuts off the soil in layers up to 30 cm and moves it towards the embankment. When approaching the berm, the bulldozer blade is gradually raised so as not to cut the soil on the berm. Soil is laid in the body of the embankment with rollers, placing them along the width of the embankment. The idling of the bulldozer to the reserve is carried out at the maximum reverse speed.
From each penetration in the reserve, the soil is laid into the body of the embankment, placing it along the width of the embankment. Then the bulldozer starts working the soil in the next tunneling. After filling the first layer of embankment along the entire length of the grip, the bulldozer rises to the embankment, moves along it, while leveling the soil laid with rollers and compacting it with caterpillars. The filling of subsequent layers of the embankment with a bulldozer is carried out in the same sequence. After filling the embankment to a predetermined height, the bulldozer levels the top layer of soil, plans the berms and the bottom of the reserve, bringing the longitudinal and transverse slopes to the design marks.
Backfilling of an embankment with a height of 1.5 ... 2 m can be carried out without layer-by-layer leveling of the poured soil immediately to full height. At the same time, the working level of the embankment should be increased by 10 ... 15% compared to the design level, since the embankment will settle for a long time.
The layout of the bottom of the pit and the cutting of the slopes are carried out by bulldozers after the excavation of the soil by excavators. If the bottom of the pit is the basis for foundations, the soil, depending on the type and capacity of the excavator bucket, is not reached by 0.1 ... 0.3 m. The bottom of the pit is cleaned with a bulldozer that moves the soil to the excavator (see Fig. 3, b) , and at small distances of movement and the depth of the pit, it removes it itself.
When cleaning slopes with bulldozers, soil dumps are located mainly along the lower edge of the slope being cleaned. This allows you to move the soil from top to bottom (the steepness of the slopes does not exceed 1: 2.5).
The backfilling of trenches by a bulldozer is carried out with soil from a dump located along the trench. After laying the pipeline, cable or device of another structure, in order to avoid damage to them, they are manually backfilled simultaneously from both sides to a height of 0.25 ...
Safety
The bulldozer operator must inspect the place of work. Oversized pieces of soil, stumps and other objects must be removed. Near the places of underground structures, the administration is obliged to put up warning signs. At the same time, it is allowed to work near underground structures only in the presence of a foreman or foreman.The development of soils by a bulldozer near live electrical cables is prohibited.
When moving longitudinally on freshly poured soil, it is not allowed to approach the edge of the slope closer than 1 m in order to avoid the bulldozer sliding down the slope. It is forbidden to extend the bulldozer blade beyond the edge of the slope when dumping soil.
At night time workplace should be illuminated.
When working on a bulldozer, it is prohibited:
during engine operation, regulate, fasten and lubricate mechanisms;
leave the control platform and enter it while driving;
be within the prism of the collapse of the bottom of the braced pits and trenches.
During blasting, the bulldozer must be removed to a safe distance and returned to the place of work only after the all-clear signal.
Soil compaction
Soil compaction is carried out when planning sites, erecting embankments, backfilling trenches and foundation sinuses, arranging foundations for floors, etc. Soils are compacted in layers of the same thickness, for which the dumped soil is leveled with bulldozers or graders. The thickness of the layers to be leveled depends on the conditions of work, the type of soil and must correspond to the capabilities of the compacting machines used.The required degree of soil compaction is achieved at the lowest cost with optimal soil moisture, so dry soils must first be moistened, and waterlogged soils must be drained.
The recommended moisture content for soils is, % clay - 23..28; heavy loams - 22...25; medium loams - 21...23; light loams and sandy loams - 15...17; chernozem - 25 ... 35; loess - 19...21, fine and dusty sands - 8...14.
Artificial soil compaction increases the modulus of deformation and soil shear resistance, thereby increasing the stability of slopes and embankments. The compacted soil becomes more impermeable and water resistant.
Layer-by-layer compaction of soil in bulk structures and backfilling of pits and trenches is carried out:
rolling - using self-propelled, semi-trailed and trailed rollers, Vehicle(cars and dredger trailers), as well as earth-moving vehicles (bulldozers and scrapers);
tamping - special tamping machines; mounted tamping - special tamping machines, mounted tamping plates, as well as pneumatic rammers (for cramped conditions);
vibration - suspended, trailed and self-propelled vibrators; in a combined way - vibrorollers-aggregates.
The main parameters characterizing the compaction process depend on the properties of the soil, the methods of compaction, and the types of soil-compacting machines and equipment used.
For rolling, rollers of static and vibration action are used. Rollers of static action are designed for soil compaction during the construction of road embankments, dams and dams of irrigation facilities and reservoirs, during the construction of excavations, etc.
The depth of the compacting effect, which determines the thickness of the layer being dumped, depends on the mass of the roller, the type of its working body and the number of passes along one track.
The scope of rollers according to the types of soil is determined by the type of working body. According to the type of working body, static rollers are divided into rollers with cam, ribbed, lattice, and smooth rollers. According to the method of setting in motion, rollers are trailed and self-propelled.
Cohesive and lumpy soils are compacted with cam rollers (Fig. 5, a), which transfer pressure to the soil that significantly exceeds its tensile strength (Table 2). Such machines weighing up to 5 tons compact a layer of soil 10 ... trace.
Fig.5. Soil compaction schemes
a - cam rollers; b - pneumatic wheel roller; in - a smooth self-propelled roller; g - tamping board suspended from the boom of the E-652B excavator; 1 - overlapping bands; 2 - the direction of rolling from the edges of the embankment to its middle; 3 - width of the rolled strip; 4 - loose layer of soil; 5 - compacted soil layer; 6 - soil compaction zone with manual rammers; 7 - soil layer compacted by a roller; 8 - the axis of the excavator penetration; 9 - tamping plate; 10 - compacted strip; 11 - excavator parking place
table 2
Technical characteristics of trailed cam rollers
When using cam and ribbed rollers, the upper part of the soil layer is loosened to a depth of 1/3 ... 1/2 of the height of the cam or rib. These rollers are not applicable for non-cohesive soils due to the large depth of loosening of the surface of the soil layer.
Clumpy cohesive soils are rolled with rollers, since the roller loosens the lumps and at the same time compacts the layer of loose soil.
Pneumatic trailed rollers are produced in two types: with a rigid attachment of the wheel axles to the frame and a common ballast body, as well as with a balancing axle attachment to the traction frame and with sectional boxes.
Rollers with balancing wheels are constantly provided with contact of all wheels with an uneven rolling surface and all wheels transfer to the ground a given load due to ballast. Skating rinks with rigid wheel mounts do not have these qualities.
Rollers on pneumatic wheels of medium weight (up to 10 tons) compact layers with a thickness of 10 ... the number of penetrations in one track.
With cam rollers and rollers on pneumatic wheels, compaction is carried out by successive closed penetrations of the roller over the entire area of the embankment with each penetration overlapping the previous one by 0.15 ... 0.25 m (see Fig. 31, a). Having finished rolling the entire area, the process is repeated as many times as required to achieve the design density of the soil.
Rollers with smooth metal rollers compact cohesive soils with a layer of up to 15 cm and sand and gravel mixtures with a layer thickness of 5 to 15 cm. The use of such rollers is advisable when the top layer of the embankment is the base of foundations or access roads, as well as when filling the upper part of the sinuses in cramped conditions (see Fig. 31, c). The lower layers of the sinus with a thickness of 15 ... 20 cm around the foundation are compacted with pneumatic or electric rammers.
Vibratory rollers (Table 3) are designed for compaction of non-cohesive backfilled soils and are available in self-propelled and trailed versions with smooth rollers.
Table 3
Technical characteristics of rollers with smooth rollers
The working body of the vibratory roller is a smooth roller, inside which is mounted a shaft with unbalances - vibration exciters. The drum is placed inside a rectangular frame equipped with a drawbar with a hitch. An engine is installed on the rear cross member of the frame, driving the unbalance shaft using a flexible (usually V-belt) transmission.
To balance the engine, a counterweight is attached to the front of the frame. From below, on the crossbars of the frame, spring-loaded scrapers are mounted, cleaning the rollers from the soil. To protect the frame and the engine from vibrations, the bearing housings of the drum and the unbalance shaft are attached to the side beams of the frame with the help of rubber-metal shock absorbers.
Ramming machines and equipment are used to compact cohesive and clayey soils, backfilled in layers of up to 1 ...
In construction, tamping plates are used on single-bucket excavators and cranes, as well as continuous tamping machines.
Tamper plates, hung on the rope of a dragline excavator (see Fig. 5, d), are usually used to compact soils in places with a narrow front of work that are inaccessible to compacting machines of other types.
Tamper plates weighing 2 ... 7 tons or more, suspended from excavators or cranes, compact sandy and clay soils with a number of strokes of 1 ... 5. The disadvantage of this method is the increased wear of the crane or excavator, as well as their relatively low productivity, which limits the use of this method.
Ramming machines are produced in two modifications - DU-12B and DU-12V for aggregation with caterpillar tractors T-100M and T-1Z0.
The working body of the machine is two plates suspended side by side on lifting ropes behind the tractor. The slabs are alternately lifted by ropes and fall freely onto the soil surface, ramming it on a strip equal in width to the capture of both slabs.
During operation, the tractor moves at a speed slowed down by a creeper, which is selected according to the required number of plate strikes in one place. During transport movements of the machine, the plates rise to the upper position, where they are held by hooks. During operation, the hooks are moved to the non-working position by means of a mechanism controlled from the driver's cab.
Table 4
Technical characteristics of the rammer DU-12
| Technical specifications | Machine brand | |
| DU-12B | DU-21V | |
| Basic Tractor | T-100M | T-130 |
| Number of plates | 2 | 2 |
| Plate weight, t | 1,3 | 1,3 |
| Plate size in plan, mm | 1000x1000 | 1000x1000 |
| Height of falling plates, m | 1,3 | 1,3 |
| Capture width of plates, m | 2,5 | 2,5 |
| Impact frequency, min | 2x16 | 2x16 |
| Number of hits in one place | 3…6 | 3…6 |
| Energy of one blow, J | 14300 | 14300 |
| Forward operating speed | 80…200 | 80…200 |
| Compaction depth, m | Up to 1.2 | Up to 1.2 |
| Weight, t | ||
| machines with a tractor | 18 | 18 |
| attachments | 1,3 | 1,3 |
Soil compaction in embankments
The technology of laying and compacting cohesive soils is based on the breakdown of the embankment into maps - sections of small length, on which operations are sequentially performed to unload the soil, level it and compact it.The number of sites simultaneously used for laying the soil depends on the scope of work, the availability of equipment, the season of work and can vary within 4-2. In summer, the highest productivity is achieved when working on 4 sections, in winter - no more than two.
The dimensions of the cards are determined by the specific production conditions and the mechanisms used, but their length must be at least 200 m.
The following dimensions are recommended for cam rollers 250 ... 300 m, for rollers on pneumatic tires - 200 m, for vibratory rollers - 200 ... 250 m; for vibro-compacting and tamping machines when compacting loess, subsidence and gravel soils at least 50 m.
The width of the embankment, as well as the width of the sections, is taken from the conditions of safe work by the compacting machine, which should be at a distance from the edge of the embankment that prevents it from sliding down the slope.
To reduce excess moisture, the soil should be dried in layers in natural conditions before compaction. To speed up this process, the soil on the site must be loosened by harrowing or plowing. With a soil layer thickness in a loose state of 30...40 cm, drying in hot summer weather requires at least 2...3 days.
When compacting a layer of loose soil, filled, for example, with a dragline or a grader-elevator, you should first roll with a light-type roller without loading it with ballast. This operation is not required when backfilling soil layers with dump trucks, scrapers or tractor carts. In this case, the soil is compacted to the required density rate by soil-compacting machines.
In the case of vertical planning of large areas and on embankments where the roller can turn, it is recommended to use the scheme of movement of the rollers in a closed circle. On embankments where it is impossible to turn the rink, a shuttle traffic pattern should be used, when the tractor at the end of the section is unhooked from the rink and joins it from the other side.
When rolling with trailed rollers, the first and second strokes of the roller are performed at a distance of 2 ... 2.5 m from the edge of the embankment, and then, by shifting the moves by 1/3 ... 1/4 of the width of the roller towards the edge, the edges of the embankment are compacted. After that, the rolling is continued by circular penetrations from the edge to the middle of the embankment with the overlap of each passage by 1/3 ... 1/4 of the width of the rink.
For uniform soil compaction, the air pressure in the roller tires must be the same (check with a pressure gauge). Recommended pressure in tires of rollers on pneumatic wheels: for sands 200 kPa, sandy loam 300...400, loams and clays 500...600 kPa. In this case, the number of passes of the rink in one lane is usually taken: for sandy soils 2 ... 3, for sandy soils 3 ... 4 and for loamy and clayey 5 ... 6.
Soil compaction by rolling should be carried out at a rational high-speed operation of the rollers. The speeds of the roller are different, and the first and the last two are made at low speeds (2 ... 2.5 km / h), and all intermediate moves - at high, but not exceeding 8 ... 10 km / h. With a rational high-speed operation of the rink, its productivity is approximately doubled, and total cost work is reduced by 50%.
When erecting an embankment from a reserve with a dragline, work should be carried out on two adjacent grips: on one of the grips, the poured soil layer is leveled by a bulldozer, and on the other, it is compacted by soil-compacting machines. With a decrease in the thickness of the poured layer from 1 to 0.3, the productivity of the dragline decreases by 11%.
When erecting an embankment from reserves with bulldozers, work should also be carried out alternately in two adjacent sections.
For compacting sandy bases under foundations and raising bearing capacity soils under various engineering structures, the hydrovibration method is used. It is based on the use of vibration transmitted to the soil from a hydraulic vibrator, with simultaneous moistening of the compacted soil.
Two hoses are connected to the hydraulic vibrator suspended from the crane boom: for supplying water to the lower and upper nozzles. The hydraulic vibrator is removed from the ground with stops every 30...40 cm with continuous water supply to the upper nozzle. The immersion depth of the hydraulic vibrator is determined by the required depth of soil compaction. The rate of immersion depends on the pressure and amount of water supplied. The mass of the hydraulic vibrator, density and granulometric composition of the soil and is taken on average 1 ... 2 m / min. When compacted with moistening with water, the soil settles, and a funnel forms around the hydraulic vibrator within a radius of 0.4 ... 1 m, which must be covered with sand.
On weak water-saturated soils, in many cases it is advisable to apply pre-construction compaction of such soils with a live load using vertical drains (sand, paper, etc.).
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Chapter 6 Slope planning and strengthening
6.1. The main types of subgrade structures on slopes and landslide slopes
The laying of the road route in a highly rugged mountainous area, taking into account the rejection of a sharp section of the relief as the main type of subgrade, includes embankments on the slopes, as well as a subgrade in the ledge. The location of the subgrade on the slopes in many cases is associated with the intersection of landslide areas and is arranged according to the requirements SNiP 2.05.02-85.Subgrade structures on slopes are substantiated by calculations taking into account the stability of the slope (slope) both in the natural state and after construction is completed.
On stable mountain slopes with a steepness of more than 1: 3, the subgrade, as a rule, is located in a shelf embedded in the slope. Under certain conditions, which depend on the engineering and geological features of the slope (slope) and the complex of engineering solutions of the highway route itself (approaches to artificial structures, special structures, etc.), the embankment is located on the slope under the protection of retaining structures.
On slopes with a steepness of 1:10-1:5, the subgrade is designed in the form of an embankment without ledges at the base. When the slopes are steep from 1:5 to 1:3, it is recommended to construct the subgrade, depending on the specific conditions for laying the route, in the form of an embankment, half-fill-semi-dredging, or in a ledge. At the base of the embankment and half-fill-semi-dredging, ledges 3-4 m wide and up to 1 m high should be arranged.
The complex of general requirements at the same time includes coordination with the landscape and aesthetic requirements; preservation and protection of the surrounding geological environment; ensuring the stability of slopes and especially slopes, which, in fact, determine the possibility and nature of the placement of embankments on them.
On stable slopes, the embankment should not reduce their stability both during construction and during operation. This requirement can only be met on the basis of an engineering-geological assessment of the embankment-slope system. The design of the subgrade must be designed in such a way as to prevent the destruction of the downstream slopes; the possibility of embankment displacement along the slope surface; the destructive effect of surface and groundwater from the upper side of the embankment on its general water regime and the regime of the slope itself. From the point of view of aesthetic requirements, it is advisable, providing for the architectural appearance of the entire road consistent with the specific landscape, to place the subgrade (in the presence of a dividing strip) at different levels (staggered arrangement of carriageways). Such a rational and economical solution provides not only an aesthetically perceived appearance of the road, but also makes it possible to significantly increase the stability of the subgrade against slipping along slopes and slopes; reduce the susceptibility to erosion of the slopes of the subgrade; reduce the overall volume of earthworks.
In mountainous areas, where the subgrade located in the shelf becomes the main type, the requirements for the stability of slopes increase, since when they are destroyed, not only traditional cases of reducing traffic safety (for example, reducing the width of the carriageway, speed limiting) are possible, but emergency and even catastrophic situations. The following tasks should be solved here: placement of the subgrade on the most favorable relief elements in terms of stratification and fall of bedrocks and with a minimum thickness of deluvial and eluvial deposits on them; ensuring the durability of upstream and downstream slopes; reliable articulation of the bulk and natural parts of the entire subgrade structure. In the case of a wide subgrade for multi-lane highways, it is advisable to place them separately within one or more relief elements. In this case, a significant shift in height is possible. Satisfying the requirements for the stability and reliability of the subgrade of roads in mountainous areas is practically impossible without considering the principles for choosing rational types of anti-landslide structures (retaining and dressing walls, reinforced soil compositions, bored piles and other types). Aesthetic requirements are in the coordination of mountain roads with the landscape, in the design of exposed rock and soil slopes and elements of retaining anti-landslide structures that ensure the stability of the subgrade and the geological environment.
The most difficult case is the location of the subgrade, when the road route inevitably crosses landslide slopes. In practice there are three possible options landslide crossings: near the sole (lingual part) of the landslide; its middle and upper parts. It is expedient to consider trestle solutions as a competing option in relation to subgrade structures on a landslide slope, especially in cases where the road crosses a small landslide perpendicular to its axis with the possibility of deepening the supports into stable bedrock. Crossing landslides with overpasses is very convenient way the passage of active landslides, but does not provide (practically excludes) protective measures to stabilize the slope itself and road objects located on it or near it. For this reason, in some cases, the overpass option is not widely used.
This does not preclude the use of an overpass option for crossing landslides, the stabilization of which by known methods is impractical and inefficient (for example, large landslide flows).
The principles and nature of the location of the subgrade on landslide slopes primarily depend on the type of landslide, its mechanism, dynamics and design sphere of interaction with the participation of the road. The main requirement is that the subgrade on the landslide slope during construction and operation does not cause active slope movements, contributes to its stability and stability. In addition, the composition and volume of the most expensive retaining anti-landslide structures largely depend on the rational location of the subgrade and its type (embankment, excavation) on the landslide slope, without which it is almost impossible to ensure the stability of either the road or the landslide slope. There are no general recommendations for very diverse landslide conditions here, but it is advisable to be guided by the following basic requirements.
It is unacceptable to place high embankments in the upper and middle parts of the landslide slope, as this is associated with its significant surcharge, reduced stability and subsequent activation. The design and arrangement of the embankment at the base will play a positive role in landslide stabilization - the stability of the slope increases dramatically. In this case, it is necessary to take into account the nature of the displacement surface in the zone of its exit near the sole (steepness, depth) and the strength characteristics in this zone, especially the values of the angle of internal friction. It should be noted that it is in those cases when it is impossible to avoid the location of the embankment in the upper and middle parts of the landslide slope, it is advisable to provide overpasses or viaducts (if it is possible to ensure the stability of their supports).
Excavations are undesirable in any part of a landslide slope, but they pose the greatest danger in its lower and middle parts, as they will inevitably cause landslide activation. The device of recesses in the upper part of the landslide slope is less reflected in the decrease in its stability, but requires increased attention to ensuring the stability of the slopes and the lower part of the slope.
Sustainability principles are determined by the type and nature of the location of the subgrade on the ground, its planned and high-altitude interaction with the relief elements in the area of the route and the stability of these elements.
The variety of options for the location of the subgrade on the relief elements or in their environment, as well as the degree of their stability, requires a certain approach to the appointment of the principle of ensuring the stability of the system in question as a whole and its individual elements. It is advisable to single out the following basic principles for ensuring sustainability:
The stability of the "subgrade - relief element" system does not require ensuring the stability of the relief elements both during the construction process and during the further operation of the road;
The stability of the system can be ensured only if the stability of the relief elements interacting with it is ensured;
For the required stability and operational reliability of the system, it is necessary to ensure the stability of the subgrade structural elements and the relief elements interacting with it.
In the practice of designing and building roads in landslide areas, one of these principles or their combination can be used.
The choice of the principle of ensuring the stability of the "subgrade - relief element" system should be based on the analysis of the results of the stability assessment, when the main causes and factors that have already caused landslide processes or may contribute to their manifestation are identified, the value of landslide pressure is determined.
The role of each of the factors identified in the process of engineering and geological surveys and stability assessment can be established by finding the dependence K = f(a i). TO- coefficient of stability of the system "subgrade - relief element"; a i - factor under study, for example, groundwater level, humidity in the soil shear zone on the proposed displacement surface, seismic factor, distance of the embankment location from the edge of the landslide failure. Based on graphical dependency analysis K = f(a i) and if it is necessary to interpolate it to the values a i , when the overall stability coefficient of the system becomes equal to 1, determine the critical value of the factor under study and its value when TO = TO req.
At the same time, the role of force, climatic and geological factors in the stability of the "roadbed - relief element" system and in the choice of the principle of its provision is established separately in quantitative terms.
When choosing the principle of ensuring stability, it is necessary first of all to take into account the specific type of subgrade construction and the nature of its location on the relief elements. Based on the main features of the location of the subgrade on the relief elements or in their environment, it is advisable to differentiate the considered principles for ensuring stability. During the construction of roads, the following cases of the location of the subgrade on the ground occur: a high embankment on a horizontal base; embankment on a stable slope; deep excavation in the soil massif with a horizontal day surface; deep recess cut into the slope; shelf in a stable or landslide slope; embankments on a landslide slope with different location them on the slope surface (along the length of its generatrix). In each case, an integrated approach to the design of anti-landslide structures is needed to ensure the stability of the subgrade based on a system analysis and the results of a general assessment.
The choice of anti-landslide structures should be carried out within the framework of the main groups of measures to ensure the stability of the systems under consideration. Three groups of such measures can be distinguished: warning; aimed at reducing shear forces; associated with an increase in holding forces.
preventive measures, assigned during the design process of the road should be based on recommendations obtained as a result of engineering and geological analysis and reflecting the possibility of ensuring the stability of slopes and slopes with fairly simple solutions and structures, while guaranteeing the stability of the entire system for a long period. Such decisions also include proposals on the expediency of crossing landslide sections by the route or refusing to build on them, or the possibility of passing them with the help of flyovers and viaducts. In some cases, protective and preventive measures may turn out to be technically and economically more acceptable than constructive solutions, however, on condition that they fully satisfy the required principle of ensuring the stability of the system as a whole. The use of preventive measures is largely determined by the skill and experience of the designer and geological engineer, who must be well aware of the specific conditions of the construction area, know the nature and causes of landslides in it or possible forms slope stability violations, as well as to have data on the effectiveness of the proposed solutions on operated roads in similar conditions.
Reducing shear forces in most cases, both in domestic and foreign practice, it is based on reducing the steepness of the slopes and slopes of the subgrade; the use of drainage; reducing the weight of the soil as a material for the construction of embankments; rational location of the embankment on the slope area, including the landslide. Such solutions are based on the predominantly gravitational nature of the shear forces, since they depend on the weight of the soil and the water contained in it. These solutions are specified in the form individual projects for each individual case, depending on the type of subgrade, the degree of stability of the slope (as a relief element), and the general landslide situation. Without dwelling in detail on the nature of the decisions associated with changing the steepness of slopes and slopes (positioning, unloading the landslide body, setting up berms, etc.) and the arrangement of drainage, we point out the use in foreign practice of road construction of methods based on reducing the weight of the soil (for reducing shear forces by using lightweight materials).
For example, the expediency of building embankments on landslide slopes and unstable foundations from boiler slag, various ashes, encapsulated sawdust, weathered shale, and shell rock has been established. Recently, to reduce the weight of embankments and reduce stresses in their bases, polystyrene plates are used, which prevents the development of landslide movements in the slopes and ensures the stability of the base.
Increase in holding forces is used as the main group of activities, especially in cases where the "subgrade - relief element" system is presented as an "embankment - landslide slope" system. Domestic and foreign sources indicate that the development of landslides, leading to violations of the stability of slopes and slopes, may be due to: an increase in active shear forces; reduction of resistance forces (including strength and rheological characteristics of the soil); the simultaneous influence of these factors. In this regard, within the framework of the third group of measures, there are two options that can be used to fundamentally solve the problems that arise in the design and construction process: the use of external restraining forces to compensate and balance shear stresses in slopes and slopes, as well as to actively counteract them; increase in soil strength.
The choice of one of them or a reasonable and expedient combination constructive solutions are carried out on the basis of consideration, analysis and technical and economic comparison of options. Such options include, regardless of the specific ways to increase the holding forces, two main directions: the application of holding external forces in the passive zones of the slope or slope and increasing the strength of the soil in the active zones, including the zone of actual active mixing of landslide soils. In the first case, anti-landslide structures of the retaining type are used, and in the second case, drainage, chemical fixation, electroosmosis, heat treatment and other solutions are used.
As an example of combining design solutions from among these methods, one can cite options for anti-landslide containment structures in combination with drainage, heat treatment, and surface strengthening.
6.2. Features of the construction of subgrade on slopes and landslide slopes
General provisions. The construction of the subgrade of roads in mountainous areas is complicated, as a rule, by the fact that in the places where the route is laid, there are steep slopes with an intense manifestation of exogenous processes (landslides, landslides, falls, screes) in a certain area of small length. In connection with this, it is recommended when drawing up a project performance of work (PPR) take into account the engineering and geological features of a site or group of sites that differ in the indicated characteristics. It is recommended to assign the technology for the construction of the subgrade, taking into account the design features of the embankment or excavation, the construction region as a whole, the structure of the slope (slope) and the properties of the constituent rocks.It is necessary to provide for a set of technological measures in the WEP to ensure the stability of natural slopes and slopes of excavations during the construction and subsequent operation of the road.
When developing a PPR, choosing a technology, machines and method of drilling and blasting, the presence of cracks in the developed massif and the nature of the layering of sedimentary rocks are taken into account.
Presence of cracks in rocky igneous rocks reduces the stability of slopes and slopes of excavations. The fall of cracks at an angle of more than 35° towards the road contributes to the occurrence of landslides, collapses, falls already in the process of work. Safe is the fall of cracks in the direction of the array.
Layering leads to a weakening of the array in the slopes and slopes, especially when they are pruned or undermined.
With an increase in the angle of meeting of the strike of the layering with the longitudinal axis of the road, the stability of slopes and slopes increases sharply. The most stable position of the bedding meeting angle with respect to the road axis will be 90°. If the azimuth of the strike of the layering coincides with the direction of the axis of the road, the cut or undermined slopes and slopes of the cuts are destroyed only along the bedding planes.
During the construction of roads in mountainous conditions, the main difficulties are associated with the development of rocks, the reduction of the scope of work, the limited transport accessibility of the working area, the movement, leveling, compaction of coarse soils, and finishing work.
If the working area is not available for the direct operation of machines, the first stage of construction should include the laying of a pioneer road along the planned route. If the laying of a pioneer road along the planned route is impossible, it is arranged as close as possible to it with approaches to the work area of individual structures. In this case, a hiking trail is laid along the route itself.
Loosening and development of rock, belonging to the difficulty of development to group V and above, is carried out by the explosive method. The explosive method is also recommended for the formation of deep cuts by mass ejection explosions or targeted explosions for the construction of embankments in hard-to-reach places in the mountainous terrain.
At all stages of work, measures must be constantly taken on slopes and slopes to prevent geodynamic phenomena (landslides, scree, avalanches, etc.) that may pose a danger to working people, equipment, structures. To this end, prior to the start of work, as well as in the process of developing mountain slopes, constant monitoring of the stability of both individual rock fragments and the entire slope from the upper side should be organized. If signs of instability are found, safety measures must be taken immediately, such as undermining and removing overhanging boulders. In the presence of active landslides, intense landslides, large falls, drilling and blasting operations are carried out only for loosening with small-hole charges.
Works on the construction of a subgrade on slopes, stable and landslide slopes include: a preparatory complex associated with marking work, removing vegetation; arrangement of a construction drainage system, parking lots for equipment placement, special anti-landslide structures; the main work on the construction of a subgrade located on various elements of the slope relief or in its environment and a set of anti-landslide measures.
It should be borne in mind that the choice of technology is also associated with the need to develop deluvial, rocky or semi-rocky rocks, as well as their use in the form of coarse soils for filling embankments. The latter depends on the passage of the route in conditions of rugged terrain.
Construction of embankments and excavations. The construction of a subgrade in a mountainous area includes the installation of the following structures, depending on the conditions for laying the route in a particular region and region of a mountainous area, their hypsometric, geomorphological and engineering-geological features: a subgrade in a ledge, a half-fill-half-cut, a cut in a rock mass, an embankment of rocky or coarse soils.
The choice of technology for the development of excavations and the construction of embankments is determined by the design features of the subgrade, the category of rocks according to the difficulty of their development, the sources of obtaining rocky or coarse-grained soil for the subgrade of embankments.
Construction of subgrade in shelves in pressure areas with a slope steepness of more than 1:3 in rocks, they are carried out by blasting, followed by excavation of the blasted mass, its transportation to the areas of the embankment. If there are deluvial deposits on the slopes, the subgrade in the shelf is developed by initially cutting the slope with powerful bulldozers of the 250-300 tf class, followed by refinement by excavators and transportation of coarse soils by dump trucks.
Construction of embankments and excavations on slopes with a steepness of 1:3 or more is carried out by the method of successive cutting of shelves for recesses or half-pits or ledges at the base of the embankment. Cutting ledges (shelves) is performed, as a rule, starting from the upper tier. With the provided stability of the slope and the need to create a passage for drilling operations, the first shelf is produced at the level of the lower edge of the excavation (shelf).
Development of excavations in rocks are carried out immediately with a small enumeration in order to avoid subsequent difficult and costly work to remove an under-selected thin layer of rocky soils. The subgrade is leveled to the design marks with small torn stone and rubble.
The development of excavations in deluvial soils, softened and highly weathered collapsible, fractured rocks is recommended to be carried out according to the “sliding shelf” scheme, when, after the implementation of the pioneer trench-face necessary for the placement and safe operation of the excavator, the soil is developed from top to bottom and moved by powerful bulldozers of the class 250-300 tf. With the help of an excavator, the subsequent refinement of the soil and its loading into vehicles with movement to the construction sites of embankments takes place.
To form smooth surfaces of slopes during the construction of cuts and half-cuts in favorable engineering and geological conditions (poor crack resistance of rocks, separation into rectangular parts with a vertical direction of the interface planes, the ability of rocks to brittle chipping, etc.), contour blasting is used.
The choice of the method and parameters of loosening rocky and coarse-grained soil should be carried out in accordance with the soil group according to the difficulty of development, with the area and conditions of its application. If the calculated number of oversized items in the loosened soil and their maximum size are exceeded, it is necessary to make appropriate changes to the loosening scheme and parameters.
Prior to drilling and blasting, the vegetation cover, topsoil and overburden are removed and removed. When the thickness of overburden is not more than 1/3 of the working depth, loosening of rocky soil is allowed without their removal.
Drilling and blasting and loading of loose rock by excavators can be carried out in parallel. In this case, the first work must be carried out ahead of time. If the method of blasthole charges is used for loosening in recesses or ledges up to 5 m deep, drilling and blasting operations should be carried out ahead of time, providing at least a replaceable supply of blasted rock. In this case, the minimum lead distance must be maintained in accordance with the Uniform Safety Rules for Explosive Operations (M.: Nedra, 1985).
Before the start of the excavator, oversized items located in the upper layer of the blasted soil are crushed by additional explosions. In the process of excavation development, oversized pieces are rolled off to the side and then also crushed by explosions, moving the exploded rock with a bulldozer to the excavator face.
When developing half-holes on rocky slopes, they first arrange a shelf for a working passage 3.5 m wide, which makes it possible for the main machines (drilling rigs, excavators, bulldozers, dump trucks, etc.) to pass. Then the shelf is widened, bringing the subgrade to the design outline.
When developing excavations loosening of rocks to the required particle sizes should be ensured by proper drilling and blasting technology and proceed from the required compaction conditions provided for SNiP 2.05.02-85. Crushing of large oversized fragments is carried out by overhead charges. This method is used with limited compressor capacity or in the absence of drill hammers and a small amount of oversized. The ledges of rocky soil remaining on the slopes and the main excavation site are also crushed.
With explosive methods of development and loosening, shortfalls at the base of the excavations are not allowed. Shortfalls on the surface of the slopes should not exceed 0.2 m, provided that their stability is ensured. The value of the searches after the final cleaning of the bottom and slopes of the excavations should not exceed the values \u200b\u200bspecified in Table. 6.1.
When finalizing excavations in rocky soils after explosions for ejection, the following work procedure should be observed:
Crushing of oversized items located on the surface, formed during the explosion of the trench;
Leveling loose soil heaps with a bulldozer;
Removal of blasted soil from slopes by an excavator (slope trimming);
Removal of non-hanging stones and visors with an excavator and small explosions;
Refinement of the excavation to the design outline by explosions; leveling of the main platform.
Table 6.1
Note. During drilling operations under water and in offshore areas and roadsteads, the size of the searches is established by the construction organization project.
In the case of tiered excavation, each tier must be completed to the design contour and cleaned before work begins on the next tier.
When constructing embankments from coarse-grained soils, which are the product of loosening or weathering of rocks, the maximum particle size of the blocky fraction should be assigned depending on the thickness of the compacted layer, the type and technical parameters of the compacting means and the physical and mechanical characteristics of the soil, but should not exceed 2/3 of the thickness of the compacted layer.
Oversized fragments, the dimensions of which do not meet the specified requirements, are allowed to be laid in the side (slope) parts and in the lower layer of the embankment in one row so that they do not fall into the working layer of the embankment.
When laying oversized debris in the base of the embankment, in order to exclude uneven settlement due to spillage of fine-grained aggregate from the overlying layers into the underlying layers, interrupting layers of crushed stone (pebble), sandy or clayey soils should be arranged.
The filling of the embankment from coarse-grained soils is carried out by a bulldozer using the “push” method in such a way that the largest fragments are located in the lower parts of the embankment. The most rational is the use of a bulldozer with a universal blade, which allows during the distribution process to produce a rejection of oversized items with their subsequent placement in the side of the embankment.
There are two patterns of distribution of coarse-grained soil: longitudinal and diagonal. Depending on the method of filling the soil, the longitudinal and diagonal distribution patterns can be one-sided or two-sided.
For axial dumping, a two-sided distribution scheme is used, for lateral dumping - one-sided.
It is rational to use specially equipped dumps with a mixed sorting device according to the type of ripper for rejecting oversized items.
Before compaction, the side parts of the embankment, including slopes made of oversized, are leveled with soil of smaller fractions. When arranging a subgrade on slopes with a steepness of more than 1: 3, it is advisable to arrange alignment from soils with sandy filler according to the wedging method.
The development of coarse-grained soils after blasting should be carried out with an excavator with a bucket capacity of 0.65-1 m 3 with loading into vehicles. If it is necessary to hill up the soil of an oversized dump on horizontal surfaces and slopes with a steepness of up to 1: 3, bulldozers are used.
With a layered occurrence of easily weathered softening rocks, interspersed with layers of clay soils, the development is carried out for the entire thickness of the face, taking into account that the developed soils contain 30-40% (by weight) of clayey fine earth. Otherwise, the development is carried out in separate layers.
Laying and compaction of coarse soils. Coarse-grained soils of frame and imperfect-frame structure from durable water-resistant rocks should be compacted, as a rule, by vibration. Coarse clastic soils containing more than 30% clay aggregate are compacted at a moisture content not exceeding the allowable values for heavy sandy loams and light loams, and with a clay aggregate content of less than 30% - at a moisture content not exceeding the allowable values for light and silty sandy loams.
Compaction of coarse soils, the strength of which is less than 5.0 MPa (50 kg / cm 2), should be carried out in two stages: at the first - with lattice rollers; on the second - rollers on pneumatic tires weighing at least 25-30 tons. When using softened coarse-grained soils, work should be carried out in dry weather with minimal time gaps between individual technological operations.
Methods and technical means of compaction of easily weathered, non-water-resistant coarse-grained soils are prescribed from the condition of ensuring the destruction of aggregates until the pores are filled with fine earth. To improve the efficiency of the destruction of aggregates, they are periodically moistened.
Good results are obtained by the technological scheme of compaction in two stages: at the first (immediately after leveling and moistening) - by lattice rollers, which carry out additional crushing of the soil, at the second - by heavy rollers on pneumatic tires. The required degree of soil compaction is achieved after 10-12 passes along one track of rollers on pneumatic tires weighing 25-30 tons. For coarse-grained soils of low strength, compaction by tamping is effective.
If it is impossible to ensure the destruction of aggregates of non-water-resistant rocks, their protection in the embankment from the effects of weather and climatic factors should be provided. When constructing protective layers from clay or loamy soils, the latter are filled up to a given thickness in layers, level with a layer of clastic soil and compacted together with it.
When constructing a protective layer with a thickness of 15-20 cm from soils reinforced with organic binders, the soil is pre-mixed with binders in stationary or mobile units and transported by dump trucks to the place of laying. Bulldozers or leveling excavators are recommended for spreading the mixture on slope surfaces. Site vibrators or vibrating slats moving along the slope from top to bottom or from bottom to top can be used as sealing means.
Quality control of works when constructing a subgrade on slopes, stable and landslide slopes, in addition to the general requirements provided for SNiP 3.06.03-85, includes: control over the restoration, fixing and breakdown of the subgrade on the marked relief elements; quality control of ledge cutting (in compliance with the design geometric parameters), compliance with the technology for developing slopes and slopes when constructing a subgrade in a shelf and the sequence of a set of anti-landslide measures (drainage, drainage and retaining structures).
Organization of work on the construction of roads in the presence of landslides, it includes two independent issues: the construction of a subgrade and the construction of a complex of anti-landslide structures established by the project. The sequence of these works is determined by the specific conditions of the territory, the location of the subgrade, the composition and types of anti-landslide structures and should be specified in the design and calculation documentation. In practice, there are several options for organizing the sequence of earthworks and the installation of anti-landslide structures: the construction of a complex of anti-landslide structures before the construction of the subgrade; implementation of anti-landslide structures in the process of its construction; construction of anti-landslide structures after the construction of embankments or excavation.
As a rule, the first scheme is the most appropriate for the construction of a road on landslide slopes, when the construction of the subgrade is possible only under the direct protection of supporting structures or after measures have been taken to regulate surface and underground runoff. The second scheme is used when the subgrade is located in deep excavations and high embankments. For example, as each tier is developed, excavations strengthen slopes and construct drainage structures. The third scheme is used in many cases in the construction of roads in mountainous conditions, when, in particular, after the construction of the subgrade in the shelf, upper retaining walls or anchor structures are constructed.
Undoubtedly, the variety of complex conditions for the construction of roads in landslide or potentially landslide areas requires the creative application of these schemes with subsequent development to specific technological and organizational solutions in work projects. This section deals only with general issues of organizing construction in landslide areas and does not cover the specifics of the construction of specific types of anti-landslide structures, which is reflected in other chapters.
In addition to the features associated with the sequence of earthworks and the construction of anti-landslide structures, it should be noted that the technology of earthworks largely depends on the design principles (in relation to the relief) of roads. There are the following types of individual technological schemes for organizing earthworks: the development of deep excavations and the construction of high embankments; construction of embankments on slopes with crossing of landslide areas; arrangement of subgrade in the shelves. One of the most difficult cases of work performance is their implementation at emergency facilities, when sections of operated roads are destroyed by landslides.
The fact established by repeated surveys of the violation of the stability of natural slopes and slopes of the subgrade during the construction of roads in various regions of our country convincingly shows that the influence of technological factors can be significant, and in some cases prevailing.
In this case, technological factors include: the method and time of excavation or construction of embankments, the method and time of construction of anti-landslide structures. These factors can be combined into a general technological system for the construction of individual subgrade structures, which, during its implementation, will have certain effects on the stability of the slopes of the subgrade and the slopes adjacent to it, especially landslides.
An analysis of the construction of roads in landslide areas showed that the impact of the technological system on the stability of slopes and slopes is manifested in the following.
An unsuccessfully chosen direction of work in the development of deep excavations can lead to the development of landslides in the slopes. The degree of intensity of earthworks affects the stability parameters of slopes during the construction process. So, with a short front of work and a high speed of excavation in slopes (at the working depth of development), deformations leading to landslides do not have time to occur, which makes it possible to give the slopes of the working tiers steeper angles. The construction of high embankments and embankments on slopes (including landslides), on the contrary, requires a slower soil dumping mode, due to the need for thorough compaction of the soil, as well as the gradual transfer of the load from the weight of the embankment to the slope base, which ensures its stability and further stability.
The order and timing of their design configuration have a significant impact on the development of landslides in slopes and slopes. The most common mistake in this regard is associated with the installation of berms, tiers, drainage structures and strengthening works on slopes not during the development of excavations and the construction of embankments, but after their completion. Of particular importance is the technological sequence of the construction of embankments on the slopes. In the projects for the production of work, such a principle of conducting work should be laid down, which would guarantee the stability of the inclined base during the construction of the subgrade. In particular, for example, in many cases, the stability of embankments on slopes was violated due to an incorrect method of work: instead of the consistent construction of an embankment from the downstream side of the slope, work was carried out from the upstream side, which led to the development of uncompacted zones in the sloping parts, overstressing the slope base, the development of landslides both in the slopes and in the slopes of embankments.
Technological factors become very important in excavation work on landslide slopes or in their environment. Proper placement of earth-moving equipment, determination of the required pace, maintaining the required depth of development or steepness of the slope provide not only the possibility of implementing design solutions, but also their further reliability during the operation of the road section, as well as the degree of preservation of the landslide slope itself in a stable state.
6.3. Layout of the subgrade of embankments and cuts, cones and slopes
Space planning. The composition and types of work on the planning of soil surfaces at given elevations are established by the project, depending on the purpose of the planned areas in the general geometric parameters of roads and airfields, their infrastructure.When planning ground areas for structural elements directly working under loads (ground coverings of airfields, ground elements of the road complex, ground parts of the airfield), the planning work includes the following technological operations: leveling stage), compaction with rollers and simultaneous leveling with a motor grader (final leveling). If it is necessary to arrange sod-grass coverings on a planned surface, the application and processing of the soil layer is carried out taking into account the agrotechnical requirements for the planned planting material.
When planning soil surfaces for the purposes of landscaping, improving runoff (reclamated workings, territories between structures, reserve areas), the scope of work includes: leveling with a bulldozer or grader, applying, if necessary, a soil layer of a given thickness provided by the project.
Planning work during the construction of the subgrade includes: laying out the foundation before the start of backfilling; laying out the layers to be poured before compaction and after compaction with the addition of transverse slopes; the layout of roadsides, cones and slopes.
On the preliminary planning stage bulldozers of thrust class 100-150 kN are used. The working marks of the preliminary planning should be assigned taking into account the margin of soil volumes for settlement during compaction, the value of which is assigned based on the results of a test compaction. In areas where soils, due to the difficulty of development, do not correspond to bulldozer work, the soil is first loosened with the help of rippers.
Final layout carried out after the completion of all earthworks and communications. Grading is carried out by graders or long-range planners in a single flow with compaction by rollers. Permissible deviations from design marks are set in accordance with the requirements SNiP 3.06.03-85 depending on the purpose of the planned surfaces and sites.
Slope planning. The main effective measure aimed at ensuring the local stability of slopes and slopes is to strengthen their surface. The selected structures must prevent or prevent (and in some cases provide a consistent joint effect) the development of local slip deformations, slush, slips, erosion.
The type of fortification design must be chosen primarily depending on the general tasks that are being solved to implement the intended principle of ensuring the stability of the geotechnical system "subgrade - relief element". The choice of design is determined by the working elevation of the subgrade, the steepness of the slope or slope, the indicators of the physical and mechanical properties of soils, the most dangerous weather and climatic influences, as well as the hydrological regime of flooding in the case of flooded slopes and slopes.
All structures for strengthening slopes and slopes, depending on their function of protecting the soil from external force and weather-climatic influences, can be divided into three groups:
biological types designed to protect slopes and slopes from erosion, slips, slush in areas with favorable soil and climatic conditions;
bearing structures designed to compensate for shear forces arising in the soil of the surface layers of slopes and slopes, as well as the force effects of flood and surface waters;
protective and insulating structures, which should isolate the surface layers of the soil of the slope or slope from temperature effects, absorption of precipitation, and drain groundwater.
To protect the slopes and slopes of non-flooded embankments, dry (non-rocky) excavations in favorable climatic and soil conditions, as well as flooded embankments at a flow rate of less than 0.6 m/s and in the absence of waves, structures of the first group are recommended as the main type of fortification. Sod cover should be used to strengthen slopes only if it is available in close proximity to building object and if it makes economic sense.
To strengthen the slopes and slopes of non-flooding embankments, composed of clay soils, easily weathered rocks, soils of special varieties, waterlogged soils, slopes of flooded embankments, as well as cuts and slopes with aquifers, structures of three groups can be used. They are combined with each other depending on the engineering and geological conditions of construction on the basis of a technical and economic comparison of options, taking into account the duration of protection.
The basic principle of using all reinforcement structures is to ensure the stability and stability of the soil within the core by controlling the intensity of its formation and the final value with the help of protective or insulating structures, load-bearing types of structures that compensate for the decrease in soil strength within the core; a combination of these methods.
Each of these types of structures has its own scope, depending on the type of slope, its history, the slope of the subgrade and the effect of protection. When it comes to strengthening slopes, especially high embankments, deep cuts or cuts formed as a result of slope trimming, it is necessary to create a grass cover on their surface as soon as possible using complex and combined solutions, for example, lattice structures with hydroseeding of grasses while planting shrubs, synthetic mesh materials, etc.
Lattice structures are a very effective type of reinforcement, providing an immediate protective effect. At the same time, it should be borne in mind that the choice of structures and the technology of their construction should be aimed at creating conditions that prevent erosion and weathering.
The final leveling of the subgrade surface at the elevations of the working layer (the bottom of the pavement) with the addition of transverse slopes and additional compaction of the surface layer, as well as the leveling and strengthening of the slopes of the embankments, is carried out after the design outline of the embankment or excavation is fully completed.
Depending on the working level, leveling is carried out by cutting the soil with a 100 kN traction bulldozer or a heavy-duty motor grader with a slope and blade extension, a slope planer or an excavator with a double-blade scraper (leveling frame, bucket). The choice of machines for planning and compaction of the surface is made according to the table. 6.2. Layout by filling on a loosened surface is carried out as an exception in small areas and subject to the subsequent compaction of these places.
When planning with simultaneous cutting of the soil and moving it down, at the first stage, the sloping sites are leveled, berms are made in accordance with the layout. The conjugation of the slope surface with the upper platform of the subgrade is performed at the final stage.
The laying of slopes of embankments or excavations up to 1.5 m is carried out with 2-4 passes of a heavy motor grader or bulldozer with slopes and blade extensions. The soil cut from the slope is used for reclamation of lateral reserves or it is collected in piles for moving to the sides of the embankment, at ramps and for other purposes. In this case, the cut soil should not interfere with drainage.
Table 6.2
| Cars | Slope height, m | slope steepness | Productivity per shift, m 2 | |
| Slope layout |
||||
| Bulldozer universal | 1-3,5 | 1:1,5 (1:2) | 7000 | 0,14 |
| Bulldozer universal thrust class 100 kN | 6-12 | 1:2 (1:3) | 8900-10000 | 0,10 |
| Heavy Duty Motor Grader with Slope and Blade Extension | 3,5 | 1:1,5 (1:2) | 5000 | 0,20 |
| Planner excavator | up to 12 | 1:1,5 | 2400 | 0,42 |
| 6-10 | 1:1,5 | 3200 | 0,31 |
|
| Soil compaction |
||||
| Vibratory roller or vibrating plate mounted on an excavator boom | until 6 | 1:1,5 (1:3) | 4250-5000 | 0,20 |
| Also | 12 | 1:1,5 (1:2) | 5000-5300 | 0,20 |
The layout of the slopes of embankments or cuts up to 6 m is carried out by a slope planer from the lower parking lot, and slopes up to 12 m from the upper and lower parking lots. The width of the planned slope section from one parking lot should be no more than 2 m, and the overlap - 0.5 m. Slope planning from 6 m to 12 m is carried out using an excavator-planner. The layout of slopes with a height of more than 12 m is carried out during the construction of each tier.
Gentle slopes (steepness 1:2 and more flat) are planned with the help of bulldozers moving along the slope from top to bottom with a forcibly lowered blade (with hydraulic control) or reverse from bottom to top with a blade freely lowered to the ground (with cable control). At the same time, its dump should not be filled with soil more than 2/3 of the height.
To ensure the compaction of the sloping part of the embankments with a height of more than 6 m, it is recommended during its construction to increase the width of the compacted technological layers by 0.3-0.5 m on each side, followed by cutting off the excess soil from the slope during the planning process and moving it to subsequent grips.
6.4. Strengthening cones and slopes of earthworks
The organization of strengthening the slopes of embankments, cones and recesses should provide the possibility of mechanization of work and minimal labor costs. It is recommended to carry out strengthening work using a detachment of vehicles (Table 6.3). Indicators of labor intensity of typical structures for strengthening slopes are given in Table. 6.4.Table 6.3
| Cars | Operations in progress | The need for machines per 1000 m 2 slopes, machine-shifts |
| Excavator-planner or bulldozer of thrust class 100 kN | slope preplanning | 0,4 |
| vegetation layer distribution | 0,3 |
|
| digging a trench under a thrust prism (when reinforced with a prefabricated grating) | 0,1 |
|
| Grass Hydro Seeding Machine | grass hydroseeding | 0,2 |
| Automobile crane with a lifting capacity of 6 t | Loading and unloading. Installation of lattice elements and reinforced concrete blocks. Supply to the slope of materials to fill the cells | 2,9 |
| Road transport (on-board vehicles - for reinforced concrete products, dump trucks - for soil and building materials) | Transportation of materials (vegetable or reinforced soil, crushed stone), reinforced concrete blocks, lattice elements | 10 |
To create a grass cover on the slopes, which is the main way to strengthen soil surfaces, it is recommended to use the method of hydroseeding, sowing on vegetable soil manually or mechanized, as well as laying turf strips.
The main technological processes of the device for strengthening slopes by hydroseeding include: preparation (if necessary) of soil; its distribution and layout on the slope surface; preparation of a working mixture from grass seeds and astringent fertilizer; putting it on a slope; watering after applying the mixture and in subsequent periods.
Table 6.4
The working mixture (mulch) for hydroseeding is prepared at a specially organized base, where there should be warehouses for storing seeds and fertilizers, containers for storing film-forming materials, vibrating screens with cells of 10x10 mm for sifting sawdust or a plant for crushing straw, scales for seeds and fertilizers, lifting equipment for filling the working mixture of a hydraulic seeder. Refueling with a mixture of hydroseeders is carried out with the mixing system turned on.
Soil soil is distributed to the thickness established by the project immediately after the leveling of the slope surface, as a rule, with the help of machines and equipment used in planning work. A scheme of work is also used, according to which soil (vegetation) soil is brought to the roadside and distributed from top to bottom.
Dry slopes must be pre-moistened using watering machines before spreading the soil.
In case of expected erosion of the subgrade slopes during the formation of the sod cover, it is recommended to lay burlap or grids of geosynthetic materials on the surface of the slopes before the distribution of the vegetative soil. Laying of mesh rolls is carried out by rolling them from top to bottom along the slope with an overlap of 10-20 cm and fixing them with pegs within the curbs. Fixing the ends of the canvases in the ground is carried out by cutting with a motor grader at a distance of 0.3-0.5 m from the edge of the slopes of the groove with a depth of 0.2-0.3 m, laying the ends of the canvases into the groove and filling it with soil during the repeated passage of the motor grader or by other methods, specified in the project.
Hydroseeding of grasses with a machine of the DE-16 type (or another type) is carried out in two passes of the machine along the bottom of the slope or berm.
The speed of the machine is selected empirically, depending on the length of the slope generatrix. On slopes with a height of 10-12 m, the mixture is distributed during short stops of the machine after 20-25 m; on slopes with a height of 12-24 m - from the upper and lower parking lots of the machine, turning the hydromonitor in a horizontal plane along an arc of 80 ° - 100 °; and in the vertical plane - within ±40° from the horizontal, providing hydroseeding along the entire length of the slope to a width of 10-12 m. It is advisable to place the places for filling the machine with a mixture in the middle of the reinforced area with a radius of action of the machine no more than 10 km.
If it is necessary to protect against the penetration of atmospheric precipitation through the surface of the slopes, hydroseeding, carried out without the use of film-forming agents as part of the applied mixture, is recommended to be carried out on a protective layer previously laid on the surface of the slope, for example, on geotextile material in the form of grids, or by subsequent application of a binder.
The main technological processes for strengthening slopes with artificial materials include: preparation of working mixtures (cement concrete, soil treated with a binder, fine-grained dry concrete mix, etc.); removal of working mixtures, crushed stone, reinforced concrete blocks for a thrust prism, plastic geogrids, prefabricated concrete, reinforced concrete and asphalt concrete slabs, elements of lattice structures, biomats to slopes; laying and compaction of working mixtures or crushed stone; installation of slab blocks, geogrids and prefabricated lattice structures; filling cells, plastic geogrids, lattice structures with working mixtures, vegetable soil, crushed stone, hydroseeding of grasses, etc.
Before the slope reinforcement earthworks concrete slabs or prefabricated lattice structures of industrial manufacture at the foot of the slope arrange a monolithic or prefabricated concrete stop. The prefabricated emphasis is arranged by laying blocks of the accepted size in a trench on a crushed stone base.
Concrete blocks of the thrust prism are distributed in advance along the trench by a crane of the appropriate load capacity at a distance of 1.5 m from it. Crushed stone for building a base for blocks is unloaded from vehicles at a distance of 1.0-1.5 m from the edge of the trench every 12-13 m.
Crushed stone is distributed in the trench manually with a layer of 11-12 cm and is planned along the sighting rail, controlling the layer thickness with a template, and then compacted in layers with manual rammers of the IZ-4502 type.
The installation of blocks in each section with a length of 10-15 m should be finally verified in terms of the cord and in the profile using sights placed at both ends of the block.
The seams in the joints between the blocks are filled with a cement-sand mortar with a composition of 1: 2. Every 10-15 m, it is necessary to arrange expansion joints, into which planed boards 15-20 mm thick are laid. Mounting loops on the blocks are bent or cut off.
After the installation of prefabricated reinforced concrete blocks, the sinuses of the thrust prism are covered with crushed stone of a fraction of 40-70 mm in layers of 10 cm thick with its layer-by-layer compaction with manual rammers.
When installing a thrust prism, the following tolerances are adhered to with respect to design dimensions: trench depth ± 10%, its width ± 5 cm; layer thickness of crushed stone preparation ±10%; the position of the blocks in the plan after installation, the excess of one block over the other at the joints and the gap between the blocks is ± 5 mm.
After installing the concrete stop, it is necessary to apply the dimensions of the prefabricated elements of the structure to be laid on it and transfer them to the surface of the slope along the generators perpendicular to the reference line with the designation of the axial lines with stakes. For lattice structures with a diagonal arrangement of elements, the breakdown is carried out along the diagonal of the cells. Structural elements should be laid from the bottom up. The interchangeable grip should correspond to the section of the slope, reinforced to its full height.
When installing lattice structures of a triangular configuration, the elements are built up in rows. The necessary elongation of the upper rows on curved sections (cones of overpasses) is compensated by increasing the gaps at the joints. The rhombic structure is mounted in a diagonal direction from the bottom up.
After laying the elements of lattice structures, they are combined in knots with bitumen-coated metal pins with a diameter of at least 10 mm and a length of at least 0.5 m or staples that are hammered in by hand. For reinforced concrete piles, holes of a given diameter and depth are pre-drilled with a D-10 motor drill or other drilling tool. Joints must be monolithic with cement mortar (composition 1: 2) after completion of installation work. Concrete surfaces at the joints are pre-moistened with water, then compacted with a bayonet and the surfaces are smoothed with a trowel. After the installation of the lattice structures, the cells must be filled with the material provided for by the project, which is supplied by a truck crane.
Soil, crushed stone and cement soil on slopes up to 6 m high and with a steepness of 1: 1.5 should be moved from the roadside and leveled with a slope planer, then add the necessary material or select the excess manually. The thickness of the layer of cement soil and crushed stone in the cell should be 2-3 cm higher than the height of the prefabricated element (margin for compaction). After planning, the cement soil and crushed stone must be compacted with manual rammers or vibrating platforms.
When hydroseeding grasses directly on the soil of the slope, the prefabricated elements of the lattice structure must be sunk into the previously loosened surface of the slope to a depth equal to 0.9-1.0 of the element thickness.
The slabs are laid on a layer of geotextile non-woven material or a crushed stone base, depending on the design features determined by the project, which is arranged by distributing and compacting a layer of crushed stone on the surface of the slope, previously harvested at the edges of embankments and cuts. With the help of bulldozers, the rubble is pushed down and evenly distributed.
The crushed stone layer is compacted with rollers, platform vibrators or mechanical rammers. Laying of crushed stone at negative temperatures is allowed only on a slope of non-frozen non-cohesive soils. In this case, crushed stone must be laid in a loose state.
To lift the slabs, truck cranes are equipped with traverses with pairwise different-shouldered mounting cables or chains with steel hooks.
The installation of plates is carried out in rows from bottom to top along the surface of the slope in a certain sequence. The slab is removed from the car with a crane or taken from a stack and roughly pointed at the installation site with an arrow. Then it is lowered down so that the sole is 3-5 cm below the top of the laid adjacent slabs. By moving the boom, the slab is directed so that its transverse face is in contact with the transverse face of the laid slab. By moving the boom “towards itself”, the gap in the longitudinal seam between the stacked and stacked slabs is reduced to a minimum. Then the slab is lowered onto a layer of geotextile or a crushed stone base so that it touches them simultaneously with the entire sole.
When using geotextile materials instead of a crushed stone base or a reverse filter device made of granular material under concrete slabs on flooded slopes, sheets of geotextile materials are laid parallel to the edge of the slope from the bottom up, and the lower sheet of geotextile is laid under the concrete blocks of the resistant prism with the end of the sheet outside the block on 0.2 m. Geotextile sheets are laid on the surface of the slope with its edges fixed with wooden or metal pins. When laying geotextiles under lattice coverings in areas of temporary flooding, adjacent sheets are connected with bituminous mastic, welding or stitching.
Strengthening of slopes with monolithic concrete coatings is carried out according to crushed stone or sand preparation. For filing concrete mix cranes equipped with hoppers with gates are used on the slope surface. The mixture is distributed over the slope surface by slope planners working from the upper and lower parking lots.
Mixtures are compacted with two or three passes of a vibrating screed, advanced along guides set with the help of geodetic instruments.
Working mixtures for strengthening slopes by pneumatic spraying are prepared from cement, sand, crushed stone or gravel. Dry mixes should be used within 2-4 hours from the moment of their preparation. Mixes are unloaded from dump trucks into storage bins or onto metal sheets (to avoid soil or rock) with subsequent reloading into the hoppers of a concrete syringe machine, which ensures their mixing with water supplied from the pumping station, laying and compacting. Additives-accelerators of setting and hardening of cement in working mixtures for pneumatic spraying should be introduced together with mixing water.
Due to the linear nature of strengthening work at road construction sites, it is recommended to place a set of machines and mechanisms for pneumatic spraying on a trailer, providing for the possibility of obtaining electricity and air from power plants and mobile compressor units.
The main operations on the surface of a rocky or soil slope are performed by workers, being in a special suspended cradle on an outrigger boom of articulated auto-hydraulic lifts. The worker controls the nozzle, hinged in the cradle.
The process of pneumatic spraying must be started with moistening the prepared rocky surface through the mesh using an air-water jet. The distance from the nozzle exit to the surface to be strengthened should be 0.9-1.1 m, and the concrete jet should be directed perpendicular to the slope surface. To evenly distribute the layer of protective coating, the operator during the spraying process must move the nozzle simultaneously in a circular and horizontal direction. The thickness of the formed layer is inversely proportional to the speed of such movements. First of all, the recesses on the surface are filled and the "torn" recess profile is leveled.
Strengthening the surface of slopes from rocky, easily weathered, weathered rocks, coarse-grained softened rocks (for example, mudstones, siltstones, shale, etc.) must be carried out using a metal mounting grid, the assortment of which is established by the project. Mounting mesh is attached outside the edge of the slope with load-bearing anchors, and on the surface of the slope - with mounting pins.
After applying the material, the mounting mesh must be sunk into the sprayed material. The thickness of the cladding layer above the grid is at least 20 mm. Air spray should be carried out as continuously as possible.
Sand slopes and roadside strips in areas of sandy deserts are strengthened by pouring liquid binders in the following order: preparation of liquid binders at a stationary base; delivery of binding materials to the place of work; preparation of the working composition; distribution of the working composition (slowly disintegrating bitumen emulsion) over the fixed surface.
The unit for pouring the emulsion consists of a tractor, a sprinkler placed on it in the form of a sprinkler and a motor pump (a fire truck with replaceable hoses up to 250 m long and a hose), a receiving tank with a capacity of 10-15 m 3 mounted on a pneumatic wheel cart coupled to the tractor. The bottling area from one parking lot is about 3 hectares.
7.8.1 Prior to the commencement of earthworks on the slope above the upper edge of the excavation being developed, upland drainage ditches should be arranged to prevent the possibility of water flow along the slope into the excavation being developed.
7.8.2 To ensure the stability of the embankment, backfilled on the slope, ledges 2-3 m wide should be cut on the area of the foot of the embankment before it is backfilled by a bulldozer with a rotary blade moving longitudinally parallel to the road axis, starting from the lower ledge.
After cutting the lower ledge, the soil from the cut overlying ledge, transferred to the finished lower ledge, is distributed in an even layer and compacted before the next layer of embankment is filled. If the slope soil collapse is possible, the development can be started from the upper ledge with the soil moving down the slope.
On gentle slopes with a steepness of less than 20 °, instead of cutting ledges, it is allowed to loosen with a multi-furrow plow.
7.8.3 Excavations on gentle slopes with a steepness of less than 20 ° should be developed by bulldozers with a rotary blade, passages at an angle of 45 ° to the road axis. In this case, the soil moves into the embankment, starting from its lower part, and its layer-by-layer leveling and compaction is ensured.
On slopes with a steepness of more than 20 °, excavation and filling of soil into an embankment is carried out by bulldozers with universal dumps, passages parallel or at an angle of less than 45 ° to the axis.
Earthworks using hydromechanization
7.9.1 The use of hydraulic mechanization is effective with sufficiently large concentrated volumes of earthworks (at least 50,000 m 3 per kilometer of embankment), conveniently located quarries of sandy and sandy loam soils, and the possibility of using industrial electricity to power the earth with pine and hydromonitor installations.
7.9.2 Works on hydraulic filling of the subgrade of roads should be carried out by a specialized production organization. Preparatory work on hydraulic filling of the embankment can be carried out by a road construction organization. Such works include uprooting forests and other
The intensity of soil alluvium into the embankment should ensure the return of water from the soil. Depending on the type of soil to be washed, it should be within the range of values given in Table 7.7.
Table 7.7 - Intensity of alluvium into the embankment
7.9.3 A drainage well should be arranged in the center of the "map". The cross section of the well should be designed for the maximum flow rate of the pulp supplied to the "card".
To drain water from the well, an adit is arranged with a bottom slope of at least 5% to the downstream side; the adit and the drainage well must have walls made of waterproof materials, and also must not let water into the junctions.
Embankments must be washed with a margin for settlement, taken at 1.5% of the height of the embankment when alluvium from mixed soils and 0.75% - when alluvium from sandy soils.
7.9.4 In order to reduce labor costs for preparatory work, laying slurry pipelines, dike, as well as to reduce the cost of timber, it is recommended to use a non-trestle end method of alluvium when filling in an embankment with a height of more than 2 m (Figure 7.10). The use of this technology of alluvial subgrade is feasible with the obligatory use of machines to perform all auxiliary work, etc. first of all, for the device of a dike and re-laying of pipes.
1 - working slurry pipeline; 2- cream with a carrying capacity of 2.5 tons (specific pressure on the ground 0.017 MPa); 3 - catchment wells; 4 - switch 5 - subsequent positions of the slurry pipeline; 6 - the position of the slurry pipeline when moving "forward"; 7 - the position of the slurry pipeline when moving "back". Q - the direction of movement of the pulp
a - plan, b - cross section
Figure 7.10 - Scheme of the non-trestle end method of alluvial subgrade
The use of trestle or non-trestle methods of soil reclamation must be justified in the work organization project by appropriate technical and economic calculations.
When acquiring approaches to large bridge structures using a non-trestle method, it is necessary to prevent the possibility of pulp spreading along a long slope at the junction with the abutments, for which various arresting devices should be created at the abutment (side and end openings-walls, dikes, etc.).
7.9.5 The hydraulic filling of the subgrade should be linked to the process of building an artificial structure through a water barrier.
7.9.6 If, according to local conditions, it is not possible to develop a pioneer trench or a pioneer pit with filling with water from a watercourse and then putting a dredger afloat into the face, then the development of a quarry is advisable using hydraulic monitors.
If at the point where the route crosses the water barrier, the shore is sandy and it is necessary to cut it off or arrange a jet-directing embankment, then hydraulic monitors should also be used to wash out the shore with pumping the pulp from the receiving sump by suction dredgers.
By its size, the sump should ensure uninterrupted operation of the dredger for 1-2 minutes in the event of a break in the supply of pulp.
7.9.7 To develop excavations with hydromonitors, water is supplied under pressure.
When operating hydraulic monitors, the following should be used:
Direct water supply - in cases where the source has a flow rate equal to or greater than the flow rate of water monitors;
Water supply with reuse - in cases where more water is required than the source can provide; Waste water must be clarified in a settling basin for reuse.
SOIL COMPACTION
General provisions
8.1.1 The compaction of soils from which the subgrade is constructed is a technological process, as a result of which the design strength, stability and stability of the road structure are achieved.
The construction of embankments without layer-by-layer compaction of soils (rollers, rammers, etc.) is allowed in special cases: in swamps (below the surface of the swamp), in reservoirs (underwater); by the hydraulic method. In the listed cases, the project should indicate which method, instead of layer-by-layer compaction, ensures the required stability of the bulk soil.
8.1.2 Soil density is estimated by the compaction factor ( TO s). In the subgrade of highways, the soil compaction coefficient should not be lower than the values \u200b\u200bgiven in TCP 45-3.03-19 (Appendix L).
Soil filling into the embankment is carried out, as a rule, from the edges to the middle of the entire width of the canvas, including the sloping parts. In order to compact the soil in the edge parts adjacent to the slope, the width of the poured layer may be 0.3-0.5 m more than the design outline of the embankment on each side. Immediately before the start of work to strengthen the slope, the excess soil is removed when planning the slopes and moved to fill the roadsides, the arrangement of congresses, and the reclamation of the road strip. If, after removal of excess soil, undercompaction of the soil on the slope is detected, then additional compaction is carried out in accordance with 8.5.3-8.5.5. the sufficiency of which is determined by repeated measurements.
The embankment is not widened when backfilling from coarse-grained and sandy soils that do not significantly change the volume during compaction, as well as when constructing high embankments or embankments with slopes of 1: 2 or more gentle. For these cases, slope compaction should be provided as a separate operation.
8.1.3 Each layer is leveled taking into account the longitudinal slope of the embankment surface. In cross section, the surface of the layer is planned for a single-pitched or double-pitched profile with a slope of 20% to the crest for sandy soils. 40% o - for clay. The surface of each layer must be leveled so that after compaction there are no depressions or elevations of more than 50 mm on it and that puddles do not form during rain. The evenness of the surface of the layers is checked by viziers or leveling.
8.1.4 Each subsequent pass of the compacting machine on one track should not be done until then. until the entire width of the subgrade is blocked by the traces of the previous pass of the compacting machine (on embankments with a width of more than 20 m, a longitudinal division of the grips is allowed). Particular attention should be paid to compaction of the soil at the exits and entrances to the road (over a length of 15 - 20 m on both sides) and at the end sections, at their junction with areas filled during concentrated work.
8.1.5 For compaction of cohesive soils, it is advisable to use rollers on pneumatic tires, cam and lattice trailed rollers; for compaction of non-cohesive soils, vibration and vibro-impact machines, rollers on pneumatic tires should be used.
Compaction of loose, especially clayey, soils should be carried out with two types of rollers: preliminary compaction (rolling) - weighing 6-12 tons and final compaction - weighing more than 25 tons.
During pre-compaction with lighter rollers, up to 30%-40% of the total required number of passes should be performed.
8.1.6 The highest density of the soil can be achieved by using rollers that provide the maximum allowable contact pressure on the surface of the layer (Table 8.1), which is permissible under the conditions of the strength of this soil (Table 8.1). The contact pressure throughout the compaction process should be close to the tensile strength of the soil. If the strength limit of the soil is exceeded, phenomena of local softening may occur (wave formation in front of the wheels of the rollers, extrusion of the soil to the sides during compaction). With insufficient contact pressure, high density can also not be achieved either by reducing the layer thickness or by increasing the number of repeated loads.
Table 8.1 - Soil strength limits
8.1.7 The required density of soils can be achieved with a moisture content that differs from the optimum by no more than indicated in Table 8.2.
8.1.8 If the humidity is less than acceptable (see Table 8.2), non-cohesive and slightly cohesive soils are recommended to be moistened in the backfilled layer shortly before compaction. Cohesive soils, in which the redistribution of moisture is slower, are recommended to be moistened at the development site (in a quarry, excavation, reserve) after they have been loosened.
Table 8.2 - Permissible soil moisture during compaction
| soils | Permissible humidity (W add) in fractions of the optimal (W 0) at the required soil compaction coefficient | |||
| St. 1.0 | 1,0 – 0,98 | 0,95 | 0,90 | |
| The sands are silty; sandy loam, light, large; sandy loam, light and silty; sandy loam, heavy, silty; light and light silty loams Heavy and heavy silty loams, clays | 0,85 – 1,30 0,85 – 1,20 0,90 – 1,10 0,90 – 1,00 | 0,80 – 1,35 0,80 – 1,25 0,85 – 1,15 0,90 – 1,05 | 0,75 – 1,60 0,75 – 1,35 0,80 – 1,30 0,85 – 1,20 | 0,75 – 1,60 0,70 – 1,60 0,75 – 1,50 0,80 – 1,30 |
| Notes 1 When building embankments from non-silty sands in summer conditions, the permissible humidity is not limited. 2 These restrictions do not apply to embankments built by hydraulic fill. 3 During the construction of embankments in winter conditions, soil moisture should not, as a rule, be more than 1.3W 0 for sandy and non-silty sandy loamy, 1.2W 0 for sandy loamy silty and light loams and 1.1W 0 for other cohesive soils. 4 The value of the permissible soil moisture can be specified taking into account the technological capabilities of the specific sealing agents available in accordance with TKP 059. |
Watering machines can be used to moisten the soil, pouring water in several stages. When irrigating in situ, the upper moistened layer should be mixed until compacted by loosening or transshipment with a motor grader or bulldozer.
8.1.9 With intense short-term rains, leading to waterlogging of soils,. dumping and compaction of cohesive soils should be stopped before they dry out. In this case, measures are taken to accelerate the drying of soils (loosening, transshipment by graders, bulldozers, etc.). It is allowed to remove the upper layer of soil, waterlogged after rain, into a dump with its subsequent use in other places.
Before a break in work, the surface and slopes of embankments should be compacted and planned so as to prevent waterlogging of soils from stagnant water on the surface of an unfinished embankment. In case of waterlogging in some places, the soil must be dried before the resumption of work or replaced with soil of optimal moisture.
8.1.10 When widening the subgrade of existing highways by adjoining the newly erected part of the embankment to the old one, it is necessary to first remove the vegetable soil from the slope and the sole, fill in the old cuvettes and compact the freshly poured soil in layers in order to avoid subsequent subsidence of the carriageway due to the unevenness of the subgrade in density. The degree of compaction of the backfill of old ditches and other workings should not be less than the degree of compaction of the widened part of the embankment at a given level from the surface.
8.1.11 The thickness of the backfill layer should be set in accordance with the technical parameters of the compacting machines, based on the requirement of a constant density of the soil over the depth of the layer. The layer thickness can be preliminarily assigned according to Table 8.3 with subsequent refinement based on the results of the test soil compaction in accordance with Appendix M.
8.1.12 Test rolling results (Appendix M) are included in technological maps for the construction of earthworks.
The use of test rolling allows, in some cases, to replace operational control by instrumental measurements of density and moisture technological control, which includes determining the conformity of indicators of the composition and condition of soils and monitoring compliance with the layer thickness, the number of passes and the uniformity of the distribution of passes. Acceptance of the compacted layer must be carried out by instrumental methods in accordance with 13.
Rolling
8.2.1 A layer of loose soil is recommended to be compacted in two stages. First, in order to avoid shifts and the formation of soil waves in front of the working bodies of the compacting machine, it is necessary to perform rolling with a light roller weighing from 6 to 12 tons, and then the main rolling with a heavier roller weighing 25 tons or more.
8.2.2 Pre-rolling is not required when the soil layer is backfilled with the regulation of the movement of transport and earthmoving vehicles across the entire width of the embankment. Earth-carrying transport performs the first stage of rolling to a density of about 0.9 of its maximum value according to standard compaction. In this case, heavy-duty compacting machines are immediately used. A clear organization of the joint work of earthmoving-transport and soil-compacting machines makes it possible to ensure complete and uniform soil compaction across the entire width of the subgrade at minimal cost.
Table 8.3 - Data for setting the thickness of the poured layers
| The thickness of the soil layer in a dense body, cm | The method of filling the subgrade | Name of compacting machine | Number of passes (strokes) of the compacting machine | Recommended combination of compacting machines | ||||||||||||||
| Pre-compaction | final compaction | |||||||||||||||||
| Sealing agent | Cohesive soils | Cohesive soils | Sealing agent | Required compaction factor | Cohesive soils | Cohesive soils | ||||||||||||
| Weight, t | A type | Weight, t | A type | Cohesive soils | Cohesive soils | |||||||||||||
| 0,95 | 0,98 | 1,00 | 1,02 | 0,95 | 0,98 | 1,00 | 1,02 | |||||||||||
| 20-40 | dump trucks | 12-15 | A | 2-3 | 1-2 | I | 3-5 | 5-7 | 7-9 | 10-12 | 5-7 | 7-9 | 9-11 | 12-14 | A and I B and I | A and I B and I | ||
| - | - | - | - | 9-18 | II | - | - | - | - | 6-8 | 8-10 | 10-12 | 13-15 | - | II | |||
| - | - | - | - | 6-18 | III | 1-2 | 2-4 | 4-6 | 7-9 | - | - | - | - | III | - | |||
| Trailed lattice roller | 14-15 | B | 2-3 | 2-3 | 25-30 | IV | 3-5 | 5-7 | 7-9 | - | 5-7 | 7-9 | 9-11 | - | IV | IV | ||
| 20-40 | Scrapers | Pneumatic tire roller trailed or semi-trailed | - | - | - | - | I | 3-5 | 5-7 | 7-9 | 10-12 | 5-7 | 7-9 | 9-11 | 12-14 | I | I | |
| Trailed or combined cam roller | - | - | - | - | 9-18 | II | - | - | - | - | 5-7 | 7-9 | 9-11 | 12-14 | - | II | ||
| Roller vibratory trailed or combined | - | - | - | - | 6-18 | III | 1-2 | 2-4 | 4-6 | 7-9 | - | - | - | - | III | - | ||
| 40-50 | dump trucks | 12-15 | A | 3-4 | 2-3 | 40-50 | V | 4-6 | 6-8 | 8-10 | 11-13 | 6-8 | 8-10 | 10-12 | 14-16 | A and V B and V | A and V B and V | |
| 40-50 | dump trucks | Cam roller | 5-9 | V | - | 3-4 | - | - | - | - | - | - | - | - | - | - | ||
| Lattice roller | 14-15 | B | 3-4 | 2-3 | 25-30 | IV | 4-6 | - | - | - | 6-8 | - | - | - | IV | IV | ||
| Vibratory roller | - | - | - | - | 8-18 | VI | 3-4 | 4-6 | 6-8 | 9-11 | - | - | - | IV | - | |||
| rammer | - | - | - | - | VII | 1-2 | 2-3 | 3-4 | 4-6 | 1-2 | 2-3 | 3-4 | 4-6 | VII | VII | |||
| 70-80 | dump trucks | Roller with pneumatic tires | 12-15 | A | 4-5 | 3-4 | 40-50 | V | 6-8 | 8-10 | 10-12 | - | - | - | - | - | A and V B and V | - |
| Lattice roller | 14-15 | B | 3-4 | - | - | - | - | - | - | - | - | - | - | - | - | - | ||
| Trailed vibratory roller | - | - | - | - | 10-18 | VIII | 4-6 | 6-8 | 8-10 | - | - | - | - | - | VIII | - | ||
| 100-120 | dump trucks | Trailer vibrating roller (semi-trailer) | 3-6 | G | 2-3 | - | 15-18 | IX | 6-8 | 8-10 | 10-12 | - | - | - | - | - | B and IX | - |
8.2.3 Rollers on pneumatic tires are the most versatile means of soil compaction. A gradual increase in specific pressure is one of the main requirements for the compaction of cohesive soils, which ensures that a dense and strong soil structure is obtained throughout the entire thickness of the layer. The pressure in the tires of the rink at the initial stage of compaction of cohesive soils should not exceed 0.2-0.3 MPa. The pressure in the tires at the final stage of compaction should correspond to 0.3-0.4 MPa when compacting sandy loam, 0.6-0.8 MPa for loam. When compacting sands, the tire pressure at all stages of compaction should not exceed 0.2-0.3 MPa.
8.2.4 When pre-compacting the soil with a lighter roller, the load on each wheel should be approximately 2 times less than the load on the wheel of the main, heavier roller.
The first and last passes along the rolling strip should be made at a low speed of the roller (2-2.5 km/h); intermediate passes - at high speed (8-12 km / h).
8.2.5 To achieve uniform soil compaction, the pressure in all tires of the roller wheels must be the same. The most uniform density of the compacted layer of the embankment is provided by sectional rollers, in which pneumatic wheels with separate sections for ballast have an independent suspension.
8.2.6 Padfoot compaction is effective in cohesive soils where the soil is loose or lumpy at the start of compaction.
Sandy loams are heavy silty, light loams - from 0.7 to 1.5;
Light silty loams, heavy loams - from 1.5 to 4.0;
Heavy silty loams, clays - from 4.0 to 6.0.
The specified values of specific pressures refer to soils of optimal moisture content.
8.2.7 Trailed lattice rollers are most effective in compacting coarse and gravelly soils with frozen clods, as they provide crushing and uniform density throughout the entire thickness of the compacted layer. However, heavy duty rollers with pneumatic tires and vibratory rollers should be used for final compaction.
8.2.8 Soil compaction with trailed cam and lattice rollers is carried out by circular passages along the working area. Rolling is carried out from the edges of the embankment to its middle (Figure 8.1) with the overlap of the compaction strips by 0.15-0.23 m. 0.3 m
1-8 - sequence of passes;
h is the thickness of the soil layer; b - width of the rolled strip
a - a diagram of the movement of a tractor with cam rollers; b - cross section;
c - overlapping of rolling strips
Figure 8.1 - Scheme of trailed cam rollers
When rolling the upper layers of the embankment with a height of more than 1.5 m with trailed rollers on pneumatic wheels, the first and second passes should be carried out at a distance of 2 m from the edge of the embankment, and then, shifting the moves by 1/3 of the width of the roller towards the edge, compact the edges of the embankment (Figure 8.2). After that, rolling is continued in circular passes from the edge to the middle of the embankment.
1-10 - sequence of passes
Figure 8.2 - Scheme of operation of a trailed roller on pneumatic tires
The approach of the working bodies of compacting machines to the crest of the embankment closer than 0.3 m (Figure 8.3) is not allowed for safety reasons with any compaction methods (except for mounted rammers).
Figure 8.3 - Scheme of compaction of the embankment, taking into account safety regulations
8.2.9 For the operation of trailed rollers, the optimal dimensions of the grip should be at least 200 m across the entire width of the embankment. An increase in the rolling front increases the productivity of trailed rollers. However, with an increase in the length of the area prepared for rolling, it should be taken into account that in dry and hot weather there is an intense loss of soil moisture.
8.2.10 With the intensification and increase in the rate of construction of the subgrade, soil compaction can be carried out by the same rollers, but moving at a speed of 10-15 km/h. This requires more powerful (by 50% -70%) basic or traction means, a decrease in the thickness of the poured layers by 30% -40% and an increase in the number of passes along one track by at least 1/3.
tamping
8.3.1 Compaction is used to compact soils of natural foundations when additionally compacting existing embankments without dismantling them, in cramped places. In this way, it is possible to compact soils in layers of large thickness in one or two passes of the machine. The tamping method makes it possible to obtain a density of soils significantly higher than the maximum standard density, to compact soils with moisture above and below the permissible limits. Compaction can be used to compact solid cloddy soils, including coarse-grained ones.
8.3.2 When choosing a compacting machine, continuous self-propelled machines should be preferred. Tamping plates suspended from the excavator-crane can be used if there are no other machines (Figure 8.4).
When compacting layers of large thickness from 1 to 2 m, to compact soils of low humidity, as well as to achieve soil density above the standard maximum density, tamping plates freely falling from a height of 2-3 to 5-6 m are used, weighing from 2-3 to 12- 15 tons, which are suspended from the boom of an excavator-crane of the appropriate carrying capacity. For a slab weighing 2-3 tons, an excavator with a bucket capacity of at least 0.5-0.7 m 3 is required, for a slab of 12-15 g - at least 1.25 m 3. In this case, the thickness of the compacted soil layer is approximately equal to the diameter of the slab base.
Specification of technological parameters of ramming is carried out according to the test compaction data.
1 - spring shock absorber; 2 - rammer; 3-compacted soil layers; 4-sealed strip;
W- step of moving the excavator (the arrow shows the direction of the working stroke of the excavator
Figure 8.4 - Scheme of operation of a heavy (weighing 12-15 tons) tamping plate suspended from an excavator boom
In order to reduce dynamic loads on the excavator and prevent premature wear of its main mechanisms, a spring suspension is installed between the tamper plate and the lifting rope.
8.3.3 The operating speed of a rammer with free-falling plates on a backhoe crane depends on the type and moisture content of the soil, as well as on the thickness of the compacted layer. Soil with optimal moisture and a layer thickness approximately equal to the diameter of the sole of the slab is recommended to be compacted in one pass of the machine at a speed of about 150 m/h.
8.3.4 When using tamping plates on excavator cranes, the width of the compaction strip should be taken within no more than 1.5 of the radius of the boom.
Compaction of loose clay soil is carried out in two stages: preliminary and main compaction. It is expedient to carry out preliminary compaction by reducing the mass of the rammer by a factor of 2 or by reducing the fall height by a factor of 4. Preliminary compaction of the soil, in which no more than two or three blows are applied on one track, is carried out simultaneously on three or four strips over their entire width. until the specified number of strokes has been made on each strip. During ramming, it is necessary to maintain a constant lifting height of the rammer at the moment of dropping. You can only move to a new compaction strip after compacting the previous strip.
When choosing the operating mode of tamping plates, preference should be given to dropping plates of a larger mass from a lower height. For excavators with buckets with a capacity of 0.5 to 1 m 3, this height is usually 2 to 4 m.
8.3.5 Upon completion of compaction, the top layer of soil 10-15 cm thick, loosened by tamping, should be compacted with light impacts of the tamper from a height of 0.5 miles by rolling with rollers.