Strengthening the subgrade. Method of strengthening the slopes of the subgrade

STATE EDUCATIONAL INSTITUTION

HIGHER PROFESSIONAL TRAINING

FAR EASTERN STATE UNIVERSITY

COMMUNICATION ROUTES

Department “Railway track, foundations and foundations”

ABSTRACT No. 2

METHODS FOR PROTECTING SCOPE OF SUBGRAD FROM INFLUENCE OF RAIN AND FLOOD WATER

Head Polevichenko A.G.

Developed by Envaev A.V.

2007

1 Methods for protecting embankment slopes and excavations from rainwater

To protect the roadbed from the effects of atmospheric, including flood waters, from its erosion and infiltration of water into the ground, first of all, plan all surfaces of the roadbed, right-of-way, berms, reserves, cavaliers, drainage and drainage devices, etc. Therefore, all these surfaces must have such transverse and longitudinal slopes that ensure rapid outflow of surface water from the roadbed. If necessary, the territory adjacent to the roadbed is leveled, all depressions and drainless hollows are eliminated, this is especially necessary on the surface of unstable slopes.

Properly designed measures to prevent erosion are at the same time protection against harmful infiltration of water into the ground. The type of strengthening and type of protection are assigned depending on the significance and size of the structure, topographical, climatic, soil and hydrological conditions, the availability of local materials, timing of construction and other factors.

Fortifications reduce or prevent the infiltration of atmospheric precipitation into the soil, protect the roadbed from erosion by flowing water or wave breakers, and protect sandy slopes and roadsides from wind erosion.

The slopes of embankments and excavations (except for slopes composed of rocky, non-softening and coarse-grained soils), the sides of embankments and excavations in sandy or waterlogged clayey soils, and berms are strengthened.

1.1 Sowing slopes with perennial grasses

Sowing with grass is the main type of strengthening of slopes of excavations and non-floodable embankments. For seeding, mixtures of local perennial loose-bush grasses (for example, timothy), rhizomatous (for example, awnless brome) and taproot or legumes (for example, alfalfa) are used at different seeding rates. As experiments have shown, the turf formed on a slope is capable of providing significant resistance to tearing. The role of grass cover is also great in relation to soil drainage. The evaporation of water from soil with grass cover is 2 times greater than with a bare surface. Water consumption for transpiration by grasses is 230 x 250 mm/year. Up to 3×5 mm of liquid precipitation per rain is consumed to wet well-leafed grass.

Thus, grass cover increases mechanical resistance drifts and similar deformations of slopes, reduces the amount of surface water entering the soil of the slope, and significantly contributes to the drainage of the soil. In addition, grass cover prevents direct exposure sun rays on the soil and the formation of shrinkage cracks as a result of intense evaporation of water from the surface layers of the soil.

For grass sowing, a TsNIIS mounted unit or a hydroseeder is used. The TsNIIS mounted unit is suspended from the dragline boom. He applies mineral fertilizers, embeds them in the plant soil, then sows the seeds, embeds them in the soil and rolls the slope after sowing the seeds.

The slope can be sown to an almost unlimited height, provided that the seeds are not washed away by flowing water along the slope during rains and with the possibility of mechanized sowing. For the latter purpose, the All-Russian Research Institute of Transport Construction recommends constructing high slopes with shelves (berms) of such width (at least 5 m) that a car can fit on them. Rapid and reliable drainage of water from the shelves must be ensured, including during snow melting; To do this, they are given a slope of at least 2% and, if required, ditches or trays are installed, reinforced against erosion and harmful infiltration of water into the ground.

To sow grass, the slopes are covered with a 10 cm thick layer of plant soil, using organomineral fertilizers if necessary. When hydroseeding, a mixture of water, grass seeds, fertilizers, mulch and film-forming emulsion is applied to slopes in several stages using a hydromonitor of a hydroseeder. Mulch (sawdust, chopped straw, etc.) protects the slope soil from drying out and cracking; Decomposing over time, it helps fertilize the surface root layer. Film formers latex (an intermediate product in the production of synthetic rubber, produced in the form of an aqueous emulsion) or bitumen emulsion when the working mixture dries on a slope, they form a thin (up to 0.1 mm) film that can resist the erosive effect of precipitation and creates a greenhouse effect that accelerates germination of grass seeds.

Strengthening using hydroseeding is effective for slopes of excavations, non-floodable embankments, ditches with a steepness of 1: 1.5 and in sandy and clayey soils, with the exception of fatty and swelling clays, mudstones, siltstones, marls, etc. rocks. In the arid regions of the south of the European part of the USSR, in Kazakhstan and Central Asia, as well as in areas with a harsh climate, hydroseeding can only be used on a trial basis, taking into account the experience of operating structures and the recommendations of local agricultural authorities. The height of the slopes to be strengthened is limited by the method of applying the working mixture: up to 12 m when processing from the base or from the edge and up to 25 m when applying the mixture from top to bottom and bottom to top. The intensity of application of the working mixture is selected experimentally, preventing it from flowing off the slope and monitoring the uniformity of the treatment.

A team consisting of a hydraulic seeder operator, two drivers and two workers preparing the working mixture can consolidate up to 4 thousand m 2 slopes per shift.

Figure 1 Reinforced concrete lathing for sowing grass: 1 lathing; 2 sowing of herbs; 3 reinforced concrete pile

1.2 Covering slopes with coarse soil or small stones

Covering slopes with coarse soils (pebble-gravel, crushed stone-wood, etc.) is used where sowing grass is impossible due to soil, climatic, technical specifications or economically unjustified. In addition, embankment slopes in the permafrost zone are enclosed in “cages” of coarse soils as cooling agents to prevent thawing of the permafrost layer under the embankment.

In the absence of coarse soils, peat soil mixtures or clay soils can be used to cover the dispersible slopes.

Figure 2 Coating arrangement with coarse soils

1.3 Lattice coverings (reinforced concrete and polymer gratings)

Lattice coatings are made with cards of unlimited sizes, the cells of which are 0.75 in size x 0.75 m deep 5 30 cm filled with crushed stone, stone. The coverings are assembled from blocks with a side of 3 4.5 m, connected by welding. The blocks are assembled by weaving from flexible reinforced concrete garlands, the length of which is equal to the side of the block, and the height of their section is 5 × 30 cm. The garlands are manufactured at the factory in packages weighing 1 ton, stored and transported in dense stacks, and the spatial structure is carried out at the construction site. On an underwater slope, the cells may not be filled with stone. In this case, geotextiles are placed under the grate.

Figure 3 Arrangement of lattice coverings

1.4 Planting shrubs on a slope

Shrub and tree protection. When installing all types of coverings in fences, as well as in all cases when the covering is sewn to the slope with stakes, measures are taken to ensure their germination. By the time the fence service ends, there should be thick shrub vegetation on the slope; for this purpose, for stakes, take rocks that grow easily in given specific conditions and install them with their butts down in pre-prepared holes. The stakes must be provided with care, and, if necessary, watering and protection from weeds.

Shrub and woody vegetation is also used in the form of strips of forest plantations that protect the slopes of floodplains, periodically flooded embankments from the impacts of ice floes and sharply reduce the effect of the breakwater on the slopes.

For successful growth of forest plantations, they cannot be subjected to prolonged, even partial flooding in height. It is known, for example, that even the most moisture-loving species, willows, allow flooding for no more than 2.5 months during the winter dormancy stage and 5 to 6 days during the summer growing season.

1.5 Covering slopes with turf

Artificial turf (grass seeding) is formed by sowing seeds of perennial cereals and leguminous grasses (mixtures of loose bush, rhizomatous and taproot grasses). Turf is able to protect the surface of the subgrade from erosion during v r < 1,5 м/с в зависимости от глубины потока и даже защитить от небольшого волнового воздействия при h i % < 0,20 м (в соответствии с требованиями СТНЦ-01-95 при выборе типов укреплений расчетная величина ветровых волн для скоростных, особо-грузонапряженных линий и линий I III categories is determined according to SNiP 2.06.04-82 with a 1% supply, for lines IV category and access roads 2%).

The turf immediately provides sufficient resistance to erosion by water flowing at a speed of up to 0.9 m/s at a flow depth of 0.4 m, up to 1.20 m/s at a flow depth of 1 m and up to 1.3 m/s at a flow depth 2 m. Solid turf can withstand waves with a wave height of up to 0.2 m for no more than 20 days. Solid turf is used to strengthen the slopes of excavations in clayey soils of high humidity.

To carry out turfing, high-quality turf must grow in the area of ​​construction of the facility, suitable for the conditions of its existence on slopes (for example, lowland and meadow turf is usually of little use for embankment slopes).

The labor intensity and cost of continuous sod are 6 10 times higher than the cost of mechanized grass sowing.

2 Methods of protecting embankment slopes (river banks) from surf and flowing water

2.1 Methods using local materials

2.1.1 Planting strips of trees and shrubs at the bottom of slopes

The main advantage of forest plantations for wave damping is the low cost of construction and operation. The disadvantages include long term from the moment of planting to the start of effective operation of the strips (from 2 to 5 years or more) and the limitation of application to certain specific conditions.

The distance between rows is usually about 0.8 m, and in rows for tree-like willows 0.8 1 m and for shrubs 0.4 0.5 m.

2.1.2 Brushed coverings and fascine coverings

Fascines are arranged: light from freshly cut brushwood without filling with stone with a diameter of 25 30 cm and a length of 1.0 2.5 m and heavy (filled 1/3 2/3 of the diameter with stone) with a diameter of 45 60 cm. Lay fascines in a spread or in a wall and sewn to the ground with stakes. From fascines knit fascines or brushwood mattresses, consisting of upper and lower nets woven from brushwood ropes (diameter 10 × 15 cm and length 10 × 40 m); Layers of brushwood are laid between the nets in different directions, and stone is placed inside heavy mattresses. The thickness of the mattresses is 30 75 cm, width 8 30 m and length up to 50 m.

Tashtured masonryIt is a wall of alternating layers of brushwood and stone.

Usually brushwood and fascine mattresses and heavy fascines are used when they are constantly flooded. Fascines on a spread, fascinated and tashtug masonry is used for permanent or temporary flooding. In the latter case, conditions must be provided for the successful germination of stakes attaching brushwood to the ground.

2.1.3 Stone paving (single, double)

To strengthen flooded slopes of embankments at water flow speeds depending on the flow depth from 2 to 6 m/s or at a wave height of up to 1.5 m, a single (Fig. 4) or double paving (simple or in wattle cages) orriprap.

Paving made of stone measuring 0.15 x 0.3 m, laying it face to face on a layer of material that would be quite durable and would not only not be washed out by water, but would also protect the soil under the pavement from washing away. More often paving produced on a layer of crushed stone or gravel with a thickness of at least 0.10 m, slightly decomposed, fibrous peat or moss (if they are protected from drying out and rotting) with a thickness of 0.05 x 0.1 m, and if necessary, protect the slope from water infiltration on a layer oiled sand or gravel 0.1 m thick.

Strengthening with paving is difficult to mechanize and is very labor-intensive. As experience shows, double paving under the influence of waves is destroyed almost in the same way as single paving, only somewhat slower, since first the upper and then the lower row of stones are destroyed sequentially.

Figure 4 Paving slopes with stone

2.1.4 Riprap

To protect slopes from wave action, they are widely used.riprap(Fig. 5).

RiprapThe wattle fence has now almost fallen out of use as it is difficult to mechanize.

The dimensions of the stones of the top row during paving and the stones of the top layer of the riprap are determined based on the permissible speeds of water flow along these protections and depending on the wave break (according to the condition of stability against ascent and capsizing).

Riprapfrom loosened, slightly weathered rocky soils (rock mass) are made in the form of protective prisms (Fig. 5) or sketch different shapes(Fig. 6,7). They can be single-layer or multi-layer (mostly two-layer) from layers of stones of different sizes (larger in the upper layers). The sketches shown in Fig. 5,6, are used in the presence of constant flooding, in Fig. 7 periodic flooding by floodplain waters.

Figure 5 Reinforcement with protective prisms

Figure 6 Reinforcement with riprap on the return filter

Figure 7 Strengthening the slope with a two-layer rock riprap on geotextile

Figure 8 Tetrapods

2.1.5 Gabions and types of gabion slope protection

To strengthen flooded slopes of embankments and the banks of mountain rivers, they are also used. gabions (Fig. 9), from which, as from separate blocks, protective walls are laid out. Gabions are boxes made of galvanized wire mesh filled with stone. They are arranged with a length of 2 6 m, a width and height of 0.5 2 m. The diameter of the wire is 2 6 mm. For larger gabions, they are reinforced with additional transverse and longitudinal walls made from the same mesh.

If gabions operate correctly, by the time the wire is destroyed, the gabion masonry should be completely sealed (clogged with sediment) and be a strong monolithic masonry. With a flow depth of 0.4 3 m, gabion reinforcement allows a flow speed of 4 6 m/s.

Figure 9 Gabion

2.2 Methods using industrial elements

2.2.1 Reinforced concrete slab coverings (prefabricated, monolithic, flexible)

Reinforced concrete coverings are installed at water flow velocities exceeding 3 3.5 m/s, as well as under strong wave action. Coverings are made from prefabricated elements in the form of slabs, mutually unconnected or hinged to each other or monolithic in strips or cards large sizes. The hinged connection of the slabs is usually made by releasing reinforcement or special anchor rods to the outside, which are welded to each other at adjacent slabs. Free-lying slabs with open seams are allowed for a wave height of no more than 0.7 m, and hinged slabs are allowed for a wave height of up to 1.5 m. The dimensions of open seams for prefabricated slabs should be minimal (usually about 1 cm).

When monolithing slabs, the width of the joints can be quite large (up to 6 cm); however, in this case, reinforced concrete boards about 25 cm wide are laid under the seams parallel to the water’s edge, the slabs are connected to each other by welding the released rods; placed in seams reinforcing mesh, after which the seams are filled with cement mortar.

Fastening with monolithic cards (slabs) manufactured on site often becomes advisable when the wave height is over 2 m, large fastening surfaces, the ability to perform work in the warm season and when the bases under the slabs do not have uneven settlements; It is especially advisable to carry out work on site with a curved slope.

Flexible reinforced concrete slab and lattice industrial coverings were developed at the All-Russian Research Institute of Transport Construction (invention 251463, author L.N. Yudin). They follow well the sedimentation of soil foundations and deformations of the underwater slopes of watercourses and protect them from the effects of water flow. Practical momentlessness 1 design makes it possible to produce prefabricated elements of minimal thickness and large dimensions in plan, ensuring their efficiency and the use of complex mechanization, including when laying them under water. Coatings are used at flow speeds of up to 6 m/s and exposure to waves up to 1 m high.

The flexibility of the structure (Fig. 11) is created by cutting concrete, linear hinges into elements connected by steel-polymer plastic bonds. The connection consists of steel rods 3 with a diameter of 5 mm, enclosed in the hinge area in polyethylene shells 2 2 mm thick, which expand the area of ​​plastic deformation of steel, reduce the bending curvature of rods, and protect them from corrosion. Slab coverings are used with a thickness of 5 15 cm with cards of 500 1000 m 2 , mounted on a slope of prefabricated blocks welded to each other measuring 10 20 m 2 . The concrete of the block is cut by orthogonal linear hinges (node A given in Fig. 11) in increments of 0.5 0.75 m. The soil tightness of the hinges, if necessary, is increased by sealing with strips of synthetic filter fabric (geotextile), while maintaining the drainage properties of the structure.

Figure 10 Construction of reinforced concrete slab covering

Figure 11 Bonding with steel-polymer plastic bonds

2.2.2 Asphalt concrete slabs

For waterproof sealing of joints in reinforced concrete pavements, including temperature and shrinkage ones, as well as in some cases for sealing joints in pavements, asphalt concrete is used, which has the ability to deform plastically, especially at high temperatures. Asphalt is also used for pouring and cementing layers of rock fill (USA, Holland, etc.).

Well-knownasphalt pavementsin the form of mats 5 × 10 cm thick, from 2 m to tens of meters wide (66 m when strengthening the banks of the Mississippi River), up to 100 × 200 m long. The mats are reinforced with wire mesh, cables are embedded in them, the ends of which are released outward and are used for securing mats or interconnecting them. Mats size 3 x 8 x 0.06 m were used to strengthen the underwater part of the slope of the Suez Canal (1953 - 1954), measuring 2 x 7 x 0.06 m to strengthen the banks of the Seine, Missouri rivers. There were cases of unsuccessful use of mats of short length, when the soil was washed out from under them and the mats, when agitated, rinsed in water, undergoing rapid mechanical destruction.

Teams undergo experimental testingasphalt concrete slabs(dimensions 3 x 5 m in plan and 10 cm thick, reinforced with wire mesh with a diameter of 3 4 mm), laid using vacuum grips on the slope with appropriate preparation of the latter.

Slope of the road bed - lateral inclined surface of the road bed

(Bulgarian language; Български) - slope to the ground for a fee

(Czech language; Čeština) - svah zemniho tělesa

(German; Deutsch) - Dammböschung

(Hungarian; Magyar) - alépítmeny rézsű

(Mongolian) - shoroon dalangiin naluu

(Polish language; Polska) - skarpa torowiska ziemnego

(Romanian language; Român) -taluz de rambleu

(Serbo-Croatian language; Srpski jezik; Hrvatski jezik) - nagib zemljanog trupa

(Spanish; Español) -talud del terraplen

(English language; English) - road embankment slope; road sub-soil slope

(French; Français) - talus de la plate - form; talus d'assiette de la route

the surface connecting the shoulder with the surface of the roadside strip or drainage structures.

Construction dictionary.

See what a “GROUND SLOPE” is in other dictionaries:

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