Anti-scouring and reinforcing method for silt roadbed slope

Abstract

The invention discloses an anti-scouring and reinforcing method for a silt roadbed slope, and belongs to the technical field of roadbed protection. In order to solve the technical problems that an existing silty soil side slope is scoured and damaged due to high permeability, and a traditional reinforcement measure is difficult to consider structural stability and ecological restoration at the same time, trapezoidal grooves are excavated to be filled with graded quartz sand, an alkaline silicate curing agent is sprayed to form an anti-seepage layer, and a mechanical framework is constructed in combination with a pre-tensioning geogrid and a gravel mixed layer; a drainage pipe wrapped with a filter material is arranged to be communicated with a slope drainage system, and finally a vegetation concrete layer is sprayed to plant drought-enduring plants. The anti-seepage layer and the drainage system synergistically reduce the scour risk, the geogrid and the gravel layer improve the shear strength, the plant root system penetrates through the grid to achieve surface layer anchoring, meanwhile, the vegetation concrete layer is adopted to restore ecology, the structure is suitable for protection engineering of silty soil roadbed slopes of roads, railways and the like, and structural stability and ecological sustainability are both considered.

Description

Technical Field

[0001] The invention belongs to the technical field of roadbed protection, and more specifically, relates to a method for preventing scour and reinforcing a silt sand roadbed slope. Background Art

[0002] When silt soil is used as roadbed filler, its particle size composition is between silt soil and fine sand, with weak bonding between particles and high permeability coefficient. Under conditions of rainfall or groundwater level changes, slope runoff easily penetrates along the pores of the soil, causing fine particles to migrate and lose, leading to the gradual formation of erosion gullies on the surface of the slope. The three-dimensional vegetation net slope protection and concrete skeleton slope protection measures used in existing projects have the problem of disconnection between surface protection and deep reinforcement: the former has a limited root system soil fixing depth and is difficult to resist deep seepage erosion; the latter hardened structure affects ecological recovery and is prone to cracks due to temperature stress.

[0003] The application of ecological protection measures is limited by the particularity of silt soil. The bonding strength between ordinary sprayed vegetation concrete and silt soil slopes is insufficient, and rainfall erosion can easily cause the substrate to peel off; plant roots are difficult to form effective anchors in loose silt soil, and the survival rate is low. At the same time, the drainage system and reinforcement structure of conventional ecological slope protection lack connection design, which is difficult to drain and increases the risk of structural instability. The root cause of these problems is that silt soil has the dual characteristics of clay soil penetration damage and sandy soil loose structure. The protection system must simultaneously solve the contradictions in the four dimensions of surface anti-scouring, internal drainage, structural reinforcement and ecological restoration. It is urgent to develop a composite protection system that takes into account both mechanical properties and ecological functions. Summary of the invention

[0004] An object of the present invention is to address at least the above-mentioned disadvantages and to provide at least the advantages which will be described hereinafter.

[0005] The present invention provides a method for preventing scour and reinforcing a silt roadbed slope. Aiming at the technical problems that the existing silt soil slope is damaged by scour due to high permeability and that traditional reinforcement measures are difficult to balance structural stability and ecological restoration, a trapezoidal trench is excavated and filled with graded quartz sand and an alkaline silicate curing agent is sprayed to form an impermeable layer, a mechanical skeleton is constructed by combining a pre-tensioned geogrid and a crushed stone mixed layer, a drainage pipe with an external filter material is arranged to connect the slope drainage system, and finally a vegetation concrete layer is sprayed to plant drought-resistant plants. The present invention also reduces the risk of scour by synergistically reducing the risk of scour through the impermeable layer and the drainage system, the geogrid and the crushed stone layer improve the shear strength, the plant roots penetrate the grid to achieve surface anchoring, and the vegetation concrete layer is used to restore the ecology. The present invention is suitable for protective engineering of silt soil roadbed slopes such as highways and railways, and balances structural stability and ecological sustainability.

[0006] The present invention provides a method for preventing scour and reinforcing a silt sand roadbed slope, which comprises the following steps: Excavating a plurality of parallel trapezoidal trenches on the surface of the silt soil slope, wherein the bottom width of the trenches is smaller than the top width, and the top surfaces of adjacent trenches are connected; Fill the groove with graded sand and gravel materials and vibrate and compact them until the density is not less than 90%, and the maximum particle size of the graded sand and gravel materials does not exceed 1 / 5 of the filling thickness; Spray alkaline silicate curing agent solution on the surface of the compacted sand and gravel layer. The curing agent penetrates to a depth of 0.5-1.2 times the thickness of the sand and gravel layer and then forms an impermeable layer. A geogrid is laid on the surface of the impermeable layer, and the geogrid is stretched to a preload force and then fixed to an anchor structure at the top of the slope; Covering the surface of the geogrid with a crushed stone mixed layer and compacting it, wherein the crushed stone mixed layer comprises crushed stone of a predetermined particle size and water-absorbent mineral powder; A drainage channel penetrating the impermeable layer is arranged in the gravel mixed layer, a drainage pipe wrapped with filter material is arranged in the drainage channel and is connected to the slope drainage system; A vegetated concrete layer is sprayed on the surface of the gravel mixture layer, and drought-resistant plants are planted on the vegetated concrete layer. The plant roots can extend into the anti-seepage layer.

[0007] Preferably, the pH value of the alkaline silicate curing agent solution is 8-9, the penetration depth of the curing agent solution in the sand and gravel layer after spraying is 0.8-1.2 times the thickness of the sand and gravel layer, and the calcium-silicon molar ratio in the aluminosilicate gel generated by the reaction of the curing agent solution and silt sand is 1:2-1:3.

[0008] Preferably, the alkaline silicate curing agent solution is prepared by mixing sodium silicate solution and calcium silicate powder in a mass ratio of 3:1-5:1, wherein SiO 2 / Na 2 O molar ratio is 2.5-3.0, the particle size of calcium silicate powder is ≤0.075mm; the water-soluble calcium ion content in the silt soil is not less than 0.5%, and the clay content is 8-15%.

[0009] Preferably, the method further comprises the following steps: Before construction, the composition of the silt soil on the slope is tested. If the water-soluble calcium ion content is lower than 0.5%, powdered dihydrate gypsum is added to the silt soil in an amount of 0.3-0.8% of the dry mass of the silt soil. After mixing evenly, let it stand for 24 hours. If the clay content is lower than 8%, sodium bentonite powder with a particle size of less than 0.002mm is added to the silt soil in an amount of 3-5% of the dry mass of the silt soil. After mixing, a rotary tiller is used to stir the soil to a depth of not less than 300mm. If the clay content is higher than 15%, river sand with a particle size of 0.1-0.5mm is added to the silt soil in an amount of 10-15% of the dry mass of the silt soil. After layered paving, a roller is used to compact the soil to a compaction degree of ≥90%.

[0010] Preferably, the geogrid is a biaxially stretched polypropylene grid, whose longitudinal and transverse tensile strength is not less than 50kN / m, the mesh size is 15-25mm×15-25mm, and the grid thickness is 1.2-1.5mm; the particle size of the crushed stone in the crushed stone mixed layer is 4-12mm, and the proportion of crushed stone with a particle size ≤6mm does not exceed 30%, and the water-absorbing mineral powder is sodium bentonite or attapulgite clay powder, and the addition amount is 2%-4% of the total mass of the crushed stone mixed layer; before paving the crushed stone mixed layer, a cement-based interface agent with a thickness of 1-2mm is sprayed on the surface of the geogrid, and after the interface agent is initially set, the crushed stone mixed layer is covered and compacted.

[0011] Preferably, the method for opening the drainage channel is as follows: before covering the crushed stone mixed layer and compacting it or before filling the graded quartz sand and compacting it, a hard casing is pre-buried at intervals of 1.5-2m along the slope surface longitudinally, the casing has an outer diameter of 60mm and a wall thickness of 3mm, and the bottom of the casing penetrates the anti-seepage layer and extends to 50-80mm inside the silt sand; after the crushed stone mixed layer is compacted, the casing is removed to form a drainage channel, and a drainage pipe wrapped with a non-woven geotextile is inserted into the channel, the drainage pipe has an outer diameter of 50mm, and a plurality of holes are opened on the upper wall of the drainage pipe, and the hole diameter is 2-3mm; the gap between the outer wall of the drainage pipe and the inner wall of the drainage channel adopts a particle size of 1-3mm quartz sand backfill, the thickness of the backfill sand layer is uniform and the compaction degree is ≥85%; the front end of the drainage pipe is flush with the outside of the crushed stone mixed layer, and a polypropylene non-woven filter element is set in the front end of the drainage pipe. The filter element density is 400-450g / m³ and the length is 50-80mm. The outer surface of the filter element and the inner wall of the pipe mouth are sealed and fixed by hot melt adhesive; the end of the drainage pipe is connected to the water collection well of the drainage system at the bottom of the slope. An anti-filter layer is set in the water collection well. The anti-filter layer is composed of gravel with a particle size of 20-40mm, crushed stone with a particle size of 5-10mm and non-woven geotextile from bottom to top.

[0012] Preferably, when the hard casing is pre-buried, it is arranged to be inclined downward at an angle of 5°-30° along the longitudinal direction of the slope surface, and the bottom end of the casing penetrates the anti-seepage layer and extends to the inside of the silt sand, and the distance between the bottom end of the casing and the lower interface of the anti-seepage layer is 20-30mm; the opening area of ​​the pipe wall at the bottom end of the drainage pipe covers the lower interface of the anti-seepage layer, and a layer of stainless steel wire mesh with a pore size of 0.1-0.3mm is added outside the opening area; the permeability coefficient of the polypropylene non-woven geotextile is 0.2-0.5cm / s, and a gap of 1-2mm is reserved between the stainless steel wire mesh to form a secondary filtration cavity, and the gap is filled with activated carbon particles with a particle size of 0.5-1mm, and the filling rate is 60%-70% of the gap volume.

[0013] Preferably, when the hard PVC casing is pre-buried, the outer surface of the casing is evenly coated with a paraffin-based release agent with a thickness of 0.1-0.2mm, and the top of the casing is 50-80mm higher than the elevation before the gravel mixture layer is paved; before the casing is pre-buried, a circular hole with a diameter of 70-80mm is opened at the mesh of the geogrid corresponding to the casing position, and the edge of the hole is coated by hot-melt welding so that the gap between the geogrid mesh and the outer wall of the casing is ≤5mm; when removing the casing, a hydraulic jacking device is used to slowly pull out the casing with a vertical pulling force of 0.5-1.0kN, and after pulling out, the inner wall of the hole in the anti-seepage layer penetrated by the casing is sprayed with silicate curing agent repair liquid, and the spraying amount of the repair liquid is 0.3-0.5L per meter.

[0014] Preferably, the vegetation concrete contains 12-18% cement, 25-35% silt, 8-12% plant fiber, 1.5-2.5% water retaining agent, 5-8% organic humus and the rest water in mass percentage, and the plant fiber is coconut shell fiber with a length of 10-30 mm and straw fiber mixed in a mass ratio of 1:1-1:2.

[0015] Preferably, when spraying the vegetation concrete layer on the surface of the gravel mixed layer, a wet sprayer is used for two-layer construction, the first layer is sprayed with a thickness of 30-40 mm, and the second layer is sprayed 2-3 hours after the first layer is initially set to a total thickness of 80-100 mm; the drought-resistant plant is a mixture of Bermuda grass and tall fescue in a weight ratio of 1:1, and seeds are sown on the initially set surface of the sprayed vegetation concrete layer, and covered with 100g / m² non-woven fabric, and watered twice a day for maintenance, with a water spraying amount of 1.0-1.5L / m² each time. After 7 days of maintenance, the non-woven fabric is removed and seeds are re-sown.

[0016] The present invention has at least the following beneficial effects: The present invention forms an anti-seepage layer by excavating a trapezoidal trench, filling it with graded quartz sand and spraying an alkaline silicate curing agent, constructs a mechanical skeleton by combining a pre-tensioned geogrid with a crushed stone mixed layer, arranges a drainage pipe wrapped with a filter material to connect to the slope drainage system, and finally sprays a vegetation concrete layer to plant drought-resistant plants.

[0017] The present invention reduces the risk of scouring through the synergistic effect of the anti-seepage layer and the drainage system, improves the shear strength of the geogrid and the gravel layer, and allows plant roots to penetrate the grid to achieve surface anchoring. At the same time, a vegetation concrete layer is used to restore the ecology. It is suitable for protective projects of silt sand roadbed slopes such as highways and railways, and takes into account both structural stability and ecological sustainability.

[0018] The present invention cooperates with water drainage to form aluminosilicate gel by curing agent reaction, making the permeability coefficient of the anti-seepage layer ≤1×10⁻ 6cm / s, and cooperate with drainage pipes (water conduction capacity ≥0.5cm³ / s) to reduce internal water pressure and reduce the risk of scouring; the present invention can also improve structural stability, pre-tension geogrid to increase the shear strength of the slope, and mechanical bite between the gravel layer and the grid mesh to enhance the overall anti-slip ability; and improve ecological compatibility, the 28-day compressive strength of vegetation concrete ≥4MPa, pH8-9 to reduce the impact on the growth of dogtooth grass and tall fescue, the plant root system extends to the inside of the impermeable layer, improve the survival rate, and achieve synchronization of engineering protection and ecological restoration.

[0019] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A schematic structural diagram of an implementation form of a roadbed slope constructed by the silt sand roadbed slope anti-scouring and reinforcement method of the present invention; Figure 2 for Figure 1 A schematic diagram of the enlarged structure of part A; Figure 3 It is a structural schematic diagram of another implementation form of the slope; Figure 4 It is a structural schematic diagram of another implementation form of the slope; Figure 5 The present invention provides a flow chart of the silt sand roadbed slope anti-scour and reinforcement method.

[0021] Among them, the top surface of the roadbed 1; the slope 2; the drainage system 3; the anti-seepage layer 4; the crushed stone mixed layer 5; the vegetation concrete layer 6; the lower interface 7; the non-woven geotextile 8; the drainage pipe 9; and the filter element 10. DETAILED DESCRIPTION

[0022] The present invention is further described in detail below in conjunction with embodiments so that those skilled in the art can implement the invention with reference to the description.

[0023] It should be noted that the experimental methods described in the following embodiments are conventional methods unless otherwise specified, and the reagents and materials can be obtained from commercial sources unless otherwise specified; in the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "set" should be understood in a broad sense, for example, they can be fixedly connected, set, or detachably connected, set, or connected and set in one piece. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood in specific circumstances. The orientation or position relationship indicated by the terms "lateral", "longitudinal", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc. is based on the orientation or position relationship shown in the accompanying drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present invention.

[0024] The silt sand roadbed slope anti-scouring and reinforcement method of the present invention comprises the following steps: A plurality of parallel trapezoidal grooves are excavated on the surface of the silt soil slope 2, wherein the bottom width of the grooves is smaller than the top width, the top surfaces of adjacent grooves are connected, and the remaining unexcavated surfaces are protected by a concrete skeleton; See also Figure 1-2 As shown, the groove is filled with graded sand and gravel materials and vibrated and compacted to a density of not less than 90%, and the maximum particle size of the graded sand and gravel materials does not exceed 1 / 5 of the filling thickness; the graded sand and gravel materials can specifically be graded quartz sand with a particle size of 0.5-2 mm; Spray an alkaline silicate curing agent solution on the surface of the compacted sand and gravel layer, the curing agent penetrates to a depth of 0.5-1.2 times the thickness of the sand and gravel layer, and let it stand to form an impermeable layer 4; A geogrid is laid on the surface of the impermeable layer 4, and the geogrid is stretched to a preload force and then fixed to an anchor structure at the top of the slope; Covering the surface of the geogrid with a crushed stone mixed layer 5 and compacting it, wherein the crushed stone mixed layer 5 comprises crushed stones of a predetermined particle size and water-absorbent mineral powder; A drainage channel penetrating the impermeable layer is provided in the crushed stone mixed layer 5, and a drainage pipe 9 wrapped with filter material is provided in the drainage channel and communicated with the slope drainage system 3; A vegetation concrete layer 6 is sprayed on the surface of the crushed stone mixed layer, and drought-resistant plants are planted on the vegetation concrete layer, so that the plant roots can extend into the interior of the impermeable layer.

[0025] One embodiment includes the following steps: Slopes 2 are set on both sides of the top surface 1 of the silt sand roadbed. Trapezoidal grooves with a depth of 300 mm are excavated on the slope surface. The bottom width of the grooves is 500 mm and the top width is 800 mm. The top surfaces of adjacent grooves are connected. The remaining non-excavated surfaces are protected by concrete skeletons. Fill the groove with graded quartz sand with a particle size of 0.5-2mm to a thickness of 100mm, and use a vibrating compactor at a frequency of 40Hz to compact until the density reaches 93%; Spray a silicate curing agent solution with a pH value of 8-9 on the surface of the compacted quartz sand layer. The spraying amount is 2.5L per square meter. The penetration depth of the curing agent solution is not less than 100mm. Let it stand and solidify to form an impermeable layer. A geogrid is laid on the surface of the anti-seepage layer, wherein the mesh size of the geogrid is 20 mm×20 mm, and the tensile strength is not less than 50 kN / m. When laid, the geogrid is stretched longitudinally along the slope until the preload force is 10 kN and then fixed to the anchor piles at the top of the slope; The surface of the geogrid is covered with a 200mm thick gravel mixture layer with a gravel particle size of 5-10mm. Sodium-based bentonite powder accounting for 3% by weight is added to the gravel mixture layer. After layered paving, it is compacted with a plate compactor until the porosity is less than 15%; A drainage channel with an aperture of 50-60 mm is excavated or preset on the surface of the gravel mixed layer. The drainage channel deeply penetrates the gravel mixed layer and the anti-seepage layer. A PVC drainage pipe 9 wrapped with a non-woven geotextile 8 is inserted into the drainage channel. The end of the drainage pipe 9 extends to the drainage system 3 at the bottom of the slope; A vegetated concrete layer with a thickness of 80 mm is sprayed on the surface of the gravel mixture layer, and then drought-tolerant herbaceous plants with a root system depth of more than 200 mm are planted on the surface of the vegetated concrete layer. The planting density can be 30-40 plants per square meter, which is conducive to the plant roots penetrating the geogrid mesh and extending to the inside of the anti-seepage layer.

[0026] In another example, the pH value of the alkaline silicate curing agent solution is 8-9, and the penetration depth of the curing agent solution in the sand and gravel layer after spraying is 0.8-1.2 times the thickness of the sand and gravel layer, and the calcium-silicon molar ratio in the aluminosilicate gel generated by the reaction of the curing agent solution and silt sand is 1:2-1:3. Silicate curing agent (such as sodium silicate solution) itself is alkaline (pH≈11-12) and can be adjusted to pH8-9 by dilution. Penetration depth verification method: pre-embed a dye tracer (such as methylene blue) in the sand and gravel layer during construction, and measure the depth of the dyed area after curing to reach 0.8-1.2 times the thickness of the sand and gravel layer (for example, when the sand and gravel layer is 100mm thick, the penetration depth is 80-120mm, and the reference dosage range can be obtained, such as spraying 2.0-3.0L per square meter). Natural calcium-containing minerals (such as calcite and gypsum) in silt sand provide a calcium source, which is transferred to the sand and gravel layer through the sodium silicate (Na 2 SiO 3) and calcium ions (Ca²⁺) in a molar ratio of 1:2-1:3 to generate the target aluminosilicate gel (CaO·2SiO 2 ·Al 2 O 3 ).

[0027] When the pH of silicate curing agent is ≥8, the silicate ions (SiO 3 ²⁻) activity is enhanced, reacting with aluminum and calcium ions in silt sand to form aluminosilicate gel, filling the soil pores to form a dense impermeable layer; if pH <8, the curing reaction rate is significantly reduced, and the impermeable layer is difficult to reach the designed penetration depth (≥110mm); if pH>9, the alkalinity is too strong and will destroy the plant fiber and water retaining agent structure, affecting the stability of the subsequent vegetation concrete layer. The design of the present invention also takes into account the compatibility with drought-tolerant plants. pH8-9 is the tolerable range of drought-tolerant herbaceous plants (such as tall fescue, bermudagrass, etc.), avoiding soil alkalinization and inhibiting plant growth; there are micropores (pore size <0.1mm) inside the impermeable layer formed by the penetration of the curing agent, so that the root system can extend into the impermeable layer to form biological anchoring. Traditional silicate curing agents blindly increase the alkalinity (pH>10) to accelerate the reaction, but it causes soil compaction and vegetation to be unable to survive; the present invention limits pH8-9 to balance the efficiency of impermeable layer formation and plant growth requirements, and achieves the unity of engineering performance and ecological function.

[0028] In another embodiment, the alkaline silicate curing agent solution is prepared by mixing a sodium silicate solution and a calcium silicate powder in a mass ratio of 3:1-5:1. 2 / Na 2 O molar ratio is 2.5-3.0, the particle size of calcium silicate powder is ≤0.075mm; the water-soluble calcium ion content in the silt soil is not less than 0.5%, and the clay content (particle size <0.005mm) is 8-15%. When spraying the curing agent solution, a spraying device with a pressure of 0.3-0.5MPa is used, and the single spraying volume is 1.5-2.5L per square meter.

[0029] In another embodiment, the method further comprises the following steps: Before construction, the composition of the silt soil of the slope is tested. If the water-soluble calcium ion content is less than 0.5%, powdered dihydrate gypsum is added to the silt soil in an amount of 0.3-0.8% of the dry mass of the silt soil, and the mixture is evenly mixed and left to stand for 24 hours; if the clay content is less than 8%, sodium-based bentonite powder with a particle size of less than 0.002mm is added to the silt soil in an amount of 3-5% of the dry mass of the silt soil, and a rotary tiller is used to stir the mixture to a depth of not less than 300mm after mixing; if the clay content is higher than 15%, river sand with a particle size of 0.1-0.5mm is added to the silt soil in an amount of 10-15% of the dry mass of the silt soil, and a roller is used to roll the silt soil to a compaction degree of ≥90% after layered paving. The present invention adopts the differentiated processing logic of "calcium deficiency supplementation with gypsum, clay deficiency supplementation with bentonite, and clay supplementation with river sand" for the insufficient or excessive calcium and clay content of the silt soil, rather than blindly and uniformly improving. Solve the problem that the calcium ion and clay content of silt sand in the natural state often does not meet the reaction requirements of the curing agent (calcium <0.5% or clay <8%), resulting in incomplete formation of the anti-seepage layer or insufficient penetration depth.

[0030] In another example, the geogrid is a biaxially stretched polypropylene grid, the longitudinal and transverse tensile strength of which is not less than 50 kN / m, the mesh size is 15-25 mm × 15-25 mm, and the grid thickness is 1.2-1.5 mm; when laying the geogrid, a tensioner is used to apply a preload to 15%-20% of the ultimate tensile strength of the geogrid along the longitudinal direction of the slope, and after tensioning, the ends of the grid are fixed to the concrete anchor beams at the top of the slope by U-shaped anchors, and the anchor beams are pre-buried with straight The threaded steel bar has a diameter of 16mm and the anchor spacing is 0.8-1.2m; the particle size of the crushed stone in the crushed stone mixed layer is 4-12mm, and the proportion of crushed stone with a particle size ≤6mm does not exceed 30%, and the water-absorbing mineral powder is sodium-based bentonite or attapulgite clay powder, and the addition amount is 2%-4% of the total mass of the crushed stone mixed layer; before paving the crushed stone mixed layer, a cement-based interface agent with a thickness of 1-2mm is sprayed on the surface of the geogrid, and the crushed stone mixed layer is covered and compacted after the interface agent is initially set.

[0031] The present invention meets the shear stress requirements of silt soil slopes (measured slope shear force peak value ≤ 40kN / m) through tensile strength ≥ 50kN / m; the mesh size is 15-25mm to ensure that the gravel particles with a particle size of 4-12mm are partially embedded in the mesh (embedding depth ≥ 1 / 3 particle size) to form a mechanical bite; the thickness is 1.2-1.5mm to balance the tensile strength and flexibility (bending radius ≤ 50mm) to fit the irregular ups and downs of the slope. Preload force = ultimate strength 15%-20%: for example, 50kN / m grid is preloaded to 7.5-10kN / m to offset the late compression deformation of silt soil (estimated deformation 3%-5%); the anchor diameter is 8mm and the length is 300mm, the anchor beam size is 200mm×200mm, and the pre-embedded steel bars enhance the pull-out resistance (single anchor pull-out force ≥ 5kN). The particle size of ≤6mm accounts for ≤30%, which can prevent fine particles from clogging the pores (the porosity is controlled at 18-22%), while ensuring the support of the coarse skeleton; the addition of sodium bentonite / attapulgite clay uses a water absorption expansion rate of ≥200% (bentonite) or ≥150% (attapulgite clay), and the volume expands after absorbing water to fill the pores and inhibit water penetration. The cement-based interface agent with a spray thickness of 1-2mm is an ordinary silicate cement slurry with a water-cement ratio of 0.4, which can enhance the friction coefficient between the grid and the gravel layer (from 0.3 to 0.6); the initial setting time of the interface agent is 30-60 minutes, ensuring that the interface agent is semi-solid when the gravel is paved to avoid slurry loss.

[0032] In another example, see Figure 3 As shown in the figure, the method for opening the drainage channel is as follows: before covering the crushed stone mixed layer and compacting it or before filling the graded quartz sand and compacting it, a hard PVC casing is pre-buried along the slope surface at an interval of 1.5-2m longitudinally or obliquely. The casing has an outer diameter of 60mm and a wall thickness of 3mm. The bottom of the casing penetrates the anti-seepage layer and extends to 50-80mm inside the silt sand. After the crushed stone mixed layer is compacted, the PVC casing is removed to form a drainage channel, and a PVC drainage pipe wrapped with a 300g / m² polypropylene non-woven geotextile is inserted into the channel. The drainage pipe has an outer diameter of 50mm, a wall porosity of 15%-20%, and a hole diameter of 2-3mm. The outer wall of the drainage pipe is connected to the drainage channel. The gaps on the inner wall of the drainage pipe are backfilled with quartz sand with a particle size of 1-3mm. The thickness of the backfill sand layer is uniform and the compaction degree is ≥85%; the front end of the drainage pipe is flush with the outer side of the crushed stone mixed layer, and a polypropylene non-woven filter element 10 is arranged in the front end pipe mouth of the drainage pipe. The filter element density is 400-450g / m³ and the length is 50-80mm. The outer surface of the filter element is sealed and fixed to the inner wall of the pipe mouth by hot melt adhesive; the end of the drainage pipe is connected to the water collection well of the drainage system at the bottom of the slope. An anti-filter layer is arranged in the water collection well. The anti-filter layer is composed of gravel with a particle size of 20-40mm, crushed stone with a particle size of 5-10mm and polypropylene non-woven geotextile from bottom to top.

[0033] The present invention reserves a 10mm gap for quartz sand backfilling through the outer diameter of the casing of 60mm (larger than the outer diameter of the drainage pipe of 50mm); the bottom end of the casing penetrates the anti-seepage layer by 50-80mm to ensure that the drainage pipe directly extracts the infiltrated water inside the silt soil. The casing is also removed to form a hole to avoid direct drilling to disturb the structure of the gravel mixed layer; the present invention is wrapped with 300g / m² non-woven geotextile to intercept the silt with a particle size of more than 0.075mm; the opening diameter is 2-3mm, the hole spacing is 10mm, and the opening rate is 15%-20% to balance the water flow and structural strength. The compaction degree of the sand layer with a particle size of 1-3mm is ≥85%, forming a high permeability transition zone to guide the water flow to the drainage pipe; the thickness of the sand layer is uniform to avoid local seepage concentration and scouring around the pipe. The water collection well has a three-stage filtration structure, with a 20-40mm gravel layer (200mm thickness) for coarse filtration, a 5-10mm crushed stone layer (100mm thickness) for fine filtration, and a non-woven geotextile surface interception (the same material as the drainage pipe filter cloth) to prevent sediment backflow in the drainage system. The non-woven geotextile is arranged on the top layer for easy replacement and dredging.

[0034] In another example, when the hard PVC casing is pre-buried, it is arranged downwardly at an angle of 5°-30° along the longitudinal direction of the slope surface, and the bottom end of the casing penetrates the impermeable layer and extends to the inside of the silt sand, and the distance between the bottom end of the casing and the lower interface 7 of the impermeable layer is 20-30 mm, see Figure 4 As shown, the opening area of ​​the bottom end of the PVC drainage pipe wall covers the lower interface 7 of the anti-seepage layer, and a layer of stainless steel wire mesh with a pore size of 0.1-0.3mm is added outside the opening area; the permeability coefficient of the polypropylene non-woven geotextile is 0.2-0.5cm / s, and a 1-2mm gap is reserved between the stainless steel wire mesh to form a secondary filtration cavity, and the gap is filled with activated carbon particles with a particle size of 0.5-1mm, and the filling rate is 60%-70% of the gap volume.

[0035] The implementation form of the present invention sets the drainage channel at a downward inclination angle of 5°-30°, uses gravity to enhance the drainage potential energy, and the drainage flow rate is increased by 40% when the inclination angle is 5°, thereby solving the problem of insufficient hydraulic gradient caused by the flat paving of the drainage channel.

[0036] By placing the bottom of the casing close to the lower interface of the impermeable layer (20-30mm from the interface), it is beneficial to directly intercept the seepage water at the bottom of the impermeable layer and avoid water retention at the interface between the impermeable layer and the silt sand. The lower interface of the impermeable layer refers to the boundary between the impermeable layer (a low permeability barrier formed by graded quartz sand + silicate curing agent) and the untreated silt sand below.

[0037] By covering the lower interface of the impermeable layer with the opening area, it is ensured that the opening of the drain pipe simultaneously penetrates the bottom of the impermeable layer and the top of the silt soil to form a two-way drainage path, solving the problem that it is difficult for water in the impermeable layer to enter the drain pipe. The stainless steel wire woven mesh (pore size 0.1-0.3mm) is conducive to intercepting gel debris with a particle size of > 0.1mm (the weathering product of the silicate gel in the impermeable layer) to prevent it from clogging the non-woven fabric, solving the problem that the single filtration of the non-woven fabric is prone to failure. After long-term use, a single non-woven fabric is easily clogged by fine particles. The present invention also uses activated carbon to adsorb colloidal organic matter (reducing the risk of clay agglomeration), and its porous structure delays clogging, and the permeability of the activated carbon layer is ensured through a gap of 1-2mm. The drain pipe and the stainless steel wire mesh are connected by a snap, and the activated carbon can be disassembled and cleaned or replaced regularly.

[0038] In another example, when the rigid PVC casing is pre-buried, the outer surface of the casing is evenly coated with a paraffin-based release agent with a thickness of 0.1-0.2mm, and the top of the casing is 50-80mm higher than the elevation before the gravel mixture layer is paved; before the casing is pre-buried, a circular hole with a diameter of 70-80mm is opened at the mesh of the geogrid corresponding to the casing position, and the edge of the hole is coated by hot-melt welding to make the gap between the geogrid mesh and the outer wall of the casing ≤5mm; when removing the casing, a hydraulic jacking device is used to slowly pull out the casing with a vertical pulling force of 0.5-1.0kN, and after pulling out, the inner wall of the hole in the anti-seepage layer penetrated by the casing is sprayed with silicate curing agent repair liquid, and the spraying amount of the repair liquid is 0.3-0.5L per meter.

[0039] In another example, the vegetation concrete comprises, by mass percentage, 12-18% cement, 25-35% silt soil, 8-12% plant fiber, 1.5-2.5% water retaining agent, 5-8% organic humus soil and the rest water, and the plant fiber is a mixture of coconut shell fiber with a length of 10-30 mm and straw fiber in a mass ratio of 1:1-1:2.

[0040] The present invention ensures the initial strength (7-day compressive strength ≥3MPa) by configuring 12-18% cement while avoiding excessive hardening, allowing the root system to be squeezed and expanded; by configuring 8-12% plant fiber, the coconut shell fiber and straw fiber are limited to be mixed in a ratio of 1:1-1:2, which is conducive to forming a three-dimensional mesh reinforcement structure and improving the tensile strength; by configuring 5-8% organic humus soil, nitrogen and phosphorus nutrients are slowly released, and humic acid reacts with silicate aluminate gel to form a cement, which enhances the interface bonding between the impermeable layer, the crushed stone mixed layer and the vegetation concrete. The fiber length of 10-30mm avoids fiber winding and pipe blocking during the spraying process, and ensures that the fiber is evenly dispersed in the concrete; the water retaining agent uses polyacrylamide-starch graft copolymer, the water absorption rate is ≥200 times and the water release period is 7-10 days, which meets the water demand characteristics of drought-resistant plants. It solves the problem of excessively high cement content (>20%) in traditional mixes, which results in high brittleness after hardening, inability of roots to penetrate, and insufficient water retention to sustain plant growth under drought conditions, leading to cracking of the vegetation concrete layer and low plant survival rate, thereby improving the anti-scour and reinforcement effects of the slope.

[0041] In another example, when spraying a vegetation concrete layer on the surface of a crushed stone mixed layer, a wet sprayer is used for construction in two layers, the first layer is sprayed with a thickness of 30-40 mm, and the second layer is sprayed 2-3 hours after the first layer is initially set to a total thickness of 80-100 mm; the drought-tolerant plants are Cynodon dactylon and Festuca arundinacea mixed in a weight ratio of 1:1, and seeds are sown on the initially set surface of the sprayed vegetation concrete layer, and covered with 100g / m² non-woven fabric, and watered twice a day for maintenance, with a water spraying volume of 1.0-1.5L / m² each time. After 7 days of maintenance, the non-woven fabric is removed and seeds are re-sown.

[0042] The specific implementation method is as follows: when spraying the vegetation concrete layer on the surface of the crushed stone mixed layer, a wet sprayer is used for two-layer construction, the first layer is sprayed with a thickness of 30-40 mm, the spraying pressure is 0.3-0.5 MPa, the spraying angle is ≤10° vertical to the slope surface, and the second layer is sprayed 2-3 hours after the first layer is initially set to a total thickness of 80-100 mm; the drought-resistant plants are Cynodon dactylon and Festuca arundinacea mixed in a weight ratio of 1:1, sown on the initially set surface of the sprayed vegetation concrete layer, and covered with 100 g / m² non-woven fabric, sprayed with water twice a day, each spraying amount of water is 1.0-1.5 L / m², and the non-woven fabric is removed after 7 days of maintenance and seeds are re-sown. The present invention reduces the self-weight stress of a single spraying by spraying the first layer of 30-40mm thinly, avoiding sagging and cracking; spraying again after an interval of 2-3 hours, after the first layer initially sets to form a skeleton, the bonding force of the second layer spraying is increased by 40%; the vertical spraying angle reduces the waste of rebound material and ensures the density of concrete. The present invention adopts mixed sowing of bermudagrass + tall fescue, and utilizes the deep root system of bermudagrass (≥300mm) and strong drought resistance (critical water content of survival 5%); utilizes the dense fibrous root system of tall fescue (root surface area ≥200cm² / plant), enhances surface anchoring, and facilitates deep anchoring.

[0043] In another example, see the process Figure 5 As shown, the composition of the silt soil on the slope is tested before construction. If the water-soluble calcium ion content is less than 0.5%, powdered dihydrate gypsum is added to the silt soil in an amount of 0.3-0.8% of the dry mass of the silt soil. After mixing evenly, let it stand for 24 hours; if the clay content is less than 8%, sodium-based bentonite powder with a particle size of less than 0.002mm is added to the silt soil in an amount of 3-5% of the dry mass of the silt soil. After mixing, a rotary tiller is used to stir the soil to a depth of not less than 300mm; if the clay content is higher than 15%, river sand with a particle size of 0.1-0.5mm is added to the silt soil in an amount of 10-15% of the dry mass of the silt soil. After layered paving, a roller is used to roll the soil to a compaction degree of ≥90%; A trapezoidal trench with a depth of 300mm is excavated on the surface of the silty soil slope. The bottom width of the trench is 500mm and the top width is 800mm. The top surfaces of adjacent trenches are connected, and the other unexcavated surfaces are protected by a concrete skeleton. The trench is filled with graded quartz sand with a particle size of 0.5-2mm and a filling thickness of 100mm. A vibrating compactor is used to compact the sand at a frequency of 40Hz until the density reaches 93%. A sodium silicate solution with a pH value of 8-9 is sprayed on the surface of the compacted quartz sand layer. The spraying amount is 2.4L per square meter. The curing agent solution penetrates to a depth of 100mm and is left to solidify to form an impermeable layer. A geogrid is laid on the surface of the impermeable layer. The mesh size of the geogrid is 20mm×20mm, and the tensile strength is not less than 50kN / m. When laid, it is stretched longitudinally along the slope to a preload of 10kN and then fixed to the anchor piles at the top of the slope; A 200mm thick gravel mixed layer is covered on the surface of the geogrid. The gravel particle size is 5-10mm. Sodium-based bentonite powder accounting for 3% by weight is added to the gravel mixed layer. After layered paving, it is compacted with a plate compactor until the porosity is less than 15%; A drainage channel with a pore size of 50-60mm is preset on the surface of the gravel mixed layer (preset before filling with graded quartz sand). The drainage channel penetrates the gravel mixed layer and the anti-seepage layer. A PVC drainage pipe wrapped with non-woven geotextile is inserted into the drainage channel, and the end of the drainage pipe extends to the drainage system at the bottom of the slope; A vegetation concrete layer with a thickness of 80mm is sprayed on the surface of the gravel mixed layer, and then drought-resistant herbaceous plants with a root system depth of more than 200mm are planted on the surface of the vegetation concrete layer. The planting density can be 30-40 plants per square meter, which is conducive to the extension of plant roots into the impermeable layer. Among them, the vegetation concrete contains 12% cement, 25% silt soil, 8% plant fiber, 1.5% water retaining agent, 5% organic humus soil and the rest is water in mass percentage, and the plant fiber is a mixture of coconut shell fiber with a length of 10-30mm and straw fiber in a mass ratio of 1:1. When spraying the vegetation concrete layer on the surface of the gravel mixed layer, a wet sprayer is used for construction in two layers. The thickness of the first layer is 30mm. After the initial setting of the first layer, the second layer is sprayed at an interval of 2-3 hours to a total thickness of 80mm.

[0044] During the construction process of the present invention, the composition of silt soil is detected by using the Thermo Fisher ARLQUANT'X X-ray fluorescence spectrometer, and the improved material is selected according to the test results: when calcium ions are insufficient, 325 mesh dihydrate gypsum powder produced by Hubei Xinjinhong Chemical is added, and when clay particles are insufficient, sodium-based bentonite (montmorillonite content ≥ 85%) produced in Lingshou County, Hebei Province is used. The trench excavation uses a Sany Heavy Industry SY245H excavator equipped with a customized trapezoidal bucket tooth (top width 800mm / bottom width 500mm), and the vibration compaction uses an Ingersoll Rand SD175 single steel wheel roller (frequency 40Hz). The graded quartz sand uses 0.5-2mm washed sand produced in Zhangzhou, Fujian, and the silicate curing agent uses a sodium silicate solution with a modulus of 2.8 from Shandong Dongyue Chemical and a 600 mesh calcium silicate powder produced in Xinji, Hebei Province, mixed in a ratio of 3:1. The geogrid uses the PP50 biaxially stretched polypropylene grid (tensile strength 50kN / m) of Tai'an Lude Engineering Materials Co., Ltd., and the tensioning equipment uses a general hydraulic tensioning equipment. The drainage pipe is made of Φ50PVC-U pipe from Liansu Group and outsourced with 300g / m² polypropylene non-woven fabric produced by Jiangsu Oriental Filter Bag. The vegetation concrete is sprayed using Zoomlion Heavy Industry HPS30 wet spraying machine. The plant seeds are a 1:1 mixture of bermudagrass and tall fescue from Jiangsu Zhongjiang Seed Co., Ltd.

[0045] During implementation, the soil is first improved according to the test results: when calcium ions are less than 0.5%, 0.3-0.8% dihydrate gypsum powder is added; when clay particles are less than 8%, 3-5% bentonite is added during rotary tillage; when clay particles are greater than 15%, 10-15% river sand is spread in layers and rolled to 90% compaction. A 300mm deep trapezoidal trench is excavated, filled with quartz sand, and vibrated and compacted to 93% density, and pH8.5 curing agent solution (2.5L / m²) is sprayed. After laying the geogrid, a 10kN preload force is applied and anchored, and a crushed stone mixed layer (particle size 5-10mm) mixed with 3% bentonite is covered. After the Φ60PVC casing is pre-buried to form a drainage channel, a drainage pipe wrapped with non-woven fabric is inserted, and 1-3mm quartz sand is backfilled around the pipe. Finally, vegetation concrete (total thickness 80mm) is sprayed in two layers, and grass seeds are sown after initial setting and covered with non-woven fabric for maintenance.

[0046] Verification of permeability coefficient of impermeable layer Experimental method: The variable head permeability test (ASTMD5084) was used to test the cured anti-seepage layer sample (100 mm thick), and the head gradient was controlled to be 10.

[0047] Test results: Initial permeability coefficient: 8.4×107 days after curing -7 cm / s; Long-term stability: After exposure to natural climate (simulated 5-year cycle), the permeability coefficient is stable at 1.1×10 -6 cm / s, basically meeting the design requirements (≤1×10⁻ 6 cm / s).

[0048] Comparative data: The permeability coefficient of the traditional cement solidification layer is 1×10 -5 cm / s, the anti-seepage performance of the present invention is improved by about 10 times.

[0049] Compressive strength test of vegetation concrete Experimental method: According to the Technical Specifications for Application of Shotcrete, the test blocks (80mm×80mm×80mm) were tested after curing for 28 days.

[0050] Test results: Standard mix ratio (cement 15%, silt soil 30%, plant fiber 10%, water retaining agent 2%, organic humus soil 6%): compressive strength is 4.8MPa; Extreme mix ratio (cement 12%, silt sand 25%, plant fiber 8%, water retaining agent 1.5%, organic humus soil 5%): compressive strength is 4.1MPa, which still meets the engineering requirements (≥3MPa).

[0051] Compared with traditional spraying substrates: the compressive strength of ordinary vegetation concrete is only 1.5-2.0MPa, and the strength of the present invention is increased by 60%-120%.

[0052] Plant root penetration depth observation Experimental method: Bermuda grass and tall fescue were planted on a simulated slope (slope 1:1.5), and root growth was observed by regular sectioning.

[0053] Test results: After 6 months: the roots penetrated the geogrid (mesh size 20mm×20mm) and extended into the impermeability layer, with an average depth of 180mm; After 12 months: The roots and the anti-seepage layer aluminosilicate gel form a symbiotic structure, and the pull-out resistance is increased by 35% (compared with the rootless area).

[0054] The results of verification and testing show that the aluminosilicate gel generated by the curing agent of the present invention makes the permeability coefficient of the impermeable layer ≤1×10 -6 cm / s, the present invention cooperates with drainage to reduce internal water pressure and reduce the risk of scouring through the coordination of anti-seepage and drainage, and cooperates with drainage pipes (water conduction capacity ≥0.5cm³ / s); the present invention can also improve structural stability, pre-tension geogrid to increase the shear strength of the slope, and mechanical bite of the gravel layer and the grid mesh to enhance the overall anti-slip ability; and improve ecological compatibility, the 28-day compressive strength of vegetation concrete ≥4MPa, pH8-9 reduces the impact on the growth of dogtooth grass and tall fescue, the plant roots extend to the inside of the anti-seepage layer, the survival rate reaches more than 85%, the root system is anchored, and the synchronization of engineering protection and ecological restoration is achieved.

[0055] Although the embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and the embodiments. They can be applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily realized.

Claims

1. A method for preventing scour and reinforcing a silt sand roadbed slope, characterized in that: The following steps are involved: Excavating a plurality of parallel trapezoidal trenches on the surface of the silt soil slope, wherein the bottom width of the trenches is smaller than the top width, and the top surfaces of adjacent trenches are connected; Fill the groove with graded sand and gravel materials and vibrate and compact them until the density is not less than 90%, and the maximum particle size of the graded sand and gravel materials does not exceed 1 / 5 of the filling thickness; Spray alkaline silicate curing agent solution on the surface of the compacted sand and gravel layer. The curing agent penetrates to a depth of 0.5-1.2 times the thickness of the sand and gravel layer and then forms an impermeable layer. A geogrid is laid on the surface of the impermeable layer, and the geogrid is stretched to a preload force and then fixed to an anchor structure at the top of the slope; Covering the surface of the geogrid with a crushed stone mixed layer and compacting it, wherein the crushed stone mixed layer comprises crushed stone of a predetermined particle size and water-absorbent mineral powder; A drainage channel penetrating the impermeable layer is arranged in the gravel mixed layer, a drainage pipe wrapped with filter material is arranged in the drainage channel and is connected to the slope drainage system; A vegetated concrete layer is sprayed on the surface of the gravel mixture layer, and drought-resistant plants are planted on the vegetated concrete layer. The plant roots can extend into the anti-seepage layer.

2. The method for preventing scour and reinforcing the silt sand roadbed slope according to claim 1, characterized in that: The pH value of the alkaline silicate curing agent solution is 8-9, the penetration depth of the curing agent solution in the sand and gravel layer after spraying is 0.8-1.2 times the thickness of the sand and gravel layer, and the calcium-silicon molar ratio of the aluminosilicate gel generated by the reaction of the curing agent solution and silt sand is 1:2-1:

3.

3. The method for preventing scour and reinforcing the silt sand roadbed slope according to claim 2, characterized in that: The alkaline silicate curing agent solution is prepared by mixing sodium silicate solution and calcium silicate powder in a mass ratio of 3:1-5:1, the SiO2 / Na2O molar ratio of the sodium silicate solution is 2.5-3.0, and the particle size of the calcium silicate powder is ≤0.075mm; the water-soluble calcium ion content in the silt sand is not less than 0.5%, and the clay content is 8-15%.

4. The method for preventing scour and reinforcing the silt sand roadbed slope according to claim 3, characterized in that: The following steps are also included: Before construction, the composition of the silt soil on the slope is tested. If the water-soluble calcium ion content is lower than 0.5%, powdered dihydrate gypsum is added to the silt soil in an amount of 0.3-0.8% of the dry mass of the silt soil. After mixing evenly, let it stand for 24 hours. If the clay content is lower than 8%, sodium bentonite powder with a particle size of less than 0.002mm is added to the silt soil in an amount of 3-5% of the dry mass of the silt soil. After mixing, a rotary tiller is used to stir the soil to a depth of not less than 300mm. If the clay content is higher than 15%, river sand with a particle size of 0.1-0.5mm is added to the silt soil in an amount of 10-15% of the dry mass of the silt soil. After layered paving, a roller is used to compact the soil to a compaction degree of ≥90%.

5. The method for preventing scour and reinforcing the silt sand roadbed slope according to any one of claims 1 to 4, characterized in that: The geogrid is a biaxially stretched polypropylene grid, and its longitudinal and transverse tensile strength is not less than 50kN / m, the mesh size is 15-25mm×15-25mm, and the grid thickness is 1.2-1.5mm; the particle size of the crushed stone in the crushed stone mixed layer is 4-12mm, and the proportion of crushed stone with a particle size of ≤6mm does not exceed 30%, and the water-absorbing mineral powder is sodium-based bentonite or attapulgite clay powder, and the addition amount is 2%-4% of the total mass of the crushed stone mixed layer; before paving the crushed stone mixed layer, a cement-based interface agent with a thickness of 1-2mm is sprayed on the surface of the geogrid, and after the interface agent is initially set, the crushed stone mixed layer is covered and compacted.

6. The method for preventing scour and reinforcing the silt sand roadbed slope according to claim 1, characterized in that: The method for opening the drainage channel is as follows: before covering the crushed stone mixed layer and compacting it or before filling and compacting the graded quartz sand, a hard casing is pre-buried at intervals of 1.5-2m along the slope surface longitudinally, the casing has an outer diameter of 60mm and a wall thickness of 3mm, and the bottom end of the casing penetrates the anti-seepage layer and extends to 50-80mm inside the silt sand; after the crushed stone mixed layer is compacted, the casing is removed to form a drainage channel, and a drainage pipe wrapped with a non-woven geotextile is inserted into the channel, the drainage pipe has an outer diameter of 50mm, and a plurality of holes are opened on the upper wall of the drainage pipe, and the hole diameter is 2-3mm; the gap between the outer wall of the drainage pipe and the inner wall of the drainage channel adopts a particle size of 1 -3mm quartz sand backfill, the thickness of the backfill sand layer is uniform and the compaction degree is ≥85%; the front end of the drainage pipe is flush with the outside of the crushed stone mixed layer, and a polypropylene non-woven filter element is set in the front end of the drainage pipe. The filter element density is 400-450g / m³ and the length is 50-80mm. The outer surface of the filter element and the inner wall of the pipe mouth are sealed and fixed by hot melt adhesive; the end of the drainage pipe is connected to the water collection well of the drainage system at the bottom of the slope. An anti-filter layer is set in the water collection well. The anti-filter layer is composed of gravel with a particle size of 20-40mm, crushed stone with a particle size of 5-10mm and non-woven geotextile from bottom to top.

7. The method for preventing scour and reinforcing the silt sand roadbed slope according to claim 6, characterized in that: When the hard casing is pre-buried, it is arranged downwardly at an inclination angle of 5°-30° along the longitudinal direction of the slope surface. The bottom end of the casing penetrates the anti-seepage layer and extends to the inside of the silt sand, and the distance between the bottom end of the casing and the lower interface of the anti-seepage layer is 20-30mm; the opening area of ​​the pipe wall at the bottom end of the drainage pipe covers the lower interface of the anti-seepage layer, and a layer of stainless steel wire mesh with a pore size of 0.1-0.3mm is added outside the opening area; the permeability coefficient of the polypropylene non-woven geotextile is 0.2-0.5cm / s, and a gap of 1-2mm is reserved between the stainless steel wire mesh to form a secondary filtration cavity, and the gap is filled with activated carbon particles with a particle size of 0.5-1mm, and the filling rate is 60%-70% of the gap volume.

8. The method for preventing scour and reinforcing the silt sand roadbed slope according to claim 7, characterized in that: When the hard casing is pre-buried, the outer surface of the casing is evenly coated with a paraffin-based release agent with a thickness of 0.1-0.2mm, and the top of the casing is 50-80mm higher than the elevation before the crushed stone mixed layer is paved; before the casing is pre-buried, a circular hole with a diameter of 70-80mm is opened at the mesh of the geogrid corresponding to the casing position, and the edge of the hole is coated by hot-melt welding to make the gap between the geogrid mesh and the outer wall of the casing ≤5mm; when removing the casing, a hydraulic jacking device is used to slowly pull out the casing with a vertical pulling force of 0.5-1.0kN, and after pulling out, a silicate curing agent repair liquid is sprayed on the inner wall of the hole in the anti-seepage layer penetrated by the casing, and the spraying amount of the repair liquid is 0.3-0.5L per meter.

9. The method for preventing scour and reinforcing the silt sand roadbed slope according to any one of claims 1 to 4 or 6 to 8, characterized in that: The vegetation concrete comprises, by mass percentage, 12-18% cement, 25-35% silt, 8-12% plant fiber, 1.5-2.5% water retaining agent, 5-8% organic humus and the rest water, and the plant fiber is a mixture of coconut shell fiber with a length of 10-30 mm and straw fiber in a mass ratio of 1:1-1:

2.

10. The method for preventing scour and reinforcing the silt sand roadbed slope according to claim 9, characterized in that: When spraying the vegetation concrete layer on the surface of the gravel mixed layer, a wet sprayer is used for two-layer construction. The thickness of the first layer is 30-40mm. After the first layer is initially set, the second layer is sprayed at an interval of 2-3 hours to a total thickness of 80-100mm. The drought-resistant plant is a mixture of Bermuda grass and tall fescue in a weight ratio of 1:

1. Seeds are sown on the initially set surface of the sprayed vegetation concrete layer and covered with 100g / m² non-woven fabric. Water is sprayed twice a day for maintenance, and the amount of water sprayed each time is 1.0-1.5L / m². After 7 days of maintenance, the non-woven fabric is removed and seeds are re-sown.

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