Breathable anti-seepage structural layer suitable for roadbed slope protection

Abstract

The invention discloses a breathable anti-seepage structure layer suitable for roadbed slope protection. The breathable anti-seepage structure layer comprises a coarse grain layer, a fine grain layer, plant straw and a drainage ditch. The coarse-grained layer is laid on the roadbed slope, the fine-grained layer is laid on the coarse-grained layer, the plant straws are inserted into the fine-grained layer and are inserted into the interface of the fine-grained layer and the coarse-grained layer, and the drainage ditch is arranged at the position where the toe of the roadbed slope is in contact with the interface of the fine-grained layer and the coarse-grained layer; according to the invention, through two special methods of inserting the plant straws into the fine grain layer and doping the expansion material particles into the coarse grain layer, high air permeability and ultra-strong seepage prevention of the structural layer are realized, the problems of'pot cover effect 'and capillary retardation failure are effectively prevented, and the method has good economic, environment-friendly and social benefits.

Description

Technical Field

[0001] The present invention belongs to the technical field of slope protection, and particularly relates to a breathable and impermeable structural layer suitable for subgrade slope protection. Background Art

[0002] Under the action of continuous rainfall and heavy rainfall, soil subgrades are prone to failures such as collapses, landslides, and collapses of retaining structures. Therefore, impermeable treatment is an important means to prevent subgrade damage during the rainy season. The breathable and impermeable structural layer is an impermeable structure constructed from natural materials. Compared with other impermeable materials (such as impermeable geomembranes, coatings, and concrete), the breathable and impermeable structural layer has better environmental protection and durability, and is currently widely used in slope impermeability, but there are the following two problems:

[0003] 1. The breathable and impermeable structural layer has poor air permeability and forms a sealing layer on the slope surface; when water vapor in the soil migrates towards the boundary, it condenses into water under the breathable and impermeable structural layer, resulting in the so-called "lid effect"; as the water in the slope soil accumulates, the slope stability is significantly reduced, and the risk of landslide instability increases significantly.

[0004] 2. When rain falls on the breathable and impermeable structural layer, the water is blocked at the interface between fine particles and coarse particles, and flows down the slope and drains out of the slope; when the gravity of the water is greater than the capillary force, the capillary blocking effect fails, and the rainwater penetrates through the breathable and impermeable structural layer and infiltrates into the subgrade soil, thereby reducing the slope stability.

[0005] In view of the above two problems, the present invention proposes a breathable and impermeable structural layer for impermeable treatment of subgrade slopes in humid and rainy areas, and keeps the slopes stable for a long time. Summary of the Invention

[0006] The present invention aims to overcome the deficiencies of the prior art and proposes a breathable and impermeable structural layer suitable for subgrade slope protection.

[0007] The innovative points of the present invention include:

[0008] (1) Insert plant straws into the fine-grained layer to the interface between the fine-grained layer and the coarse-grained layer, providing a channel for water vapor in the slope soil to be discharged into the atmosphere, thereby eliminating the "lid effect" and achieving the purpose of air permeability.

[0009] (2) Achieving the purpose of impermeability through the capillary blocking effect between the fine-grained layer and the coarse-grained layer. At the same time, expandable material particles are incorporated into the coarse-grained layer. When the rainfall reaches the heavy rain level and the capillary blocking effect fails, the expandable material particles quickly absorb water and expand to dozens of times their original volume, blocking the pores between the coarse-grained layers (blast furnace slag), thereby forming an impermeable layer to prevent rainwater from penetrating through the coarse-grained layer into the slope soil, achieving the purpose of slope impermeability under any rainfall, and preventing the phenomenon of capillary blocking effect failure.

[0010] The technical solution of the present invention is as follows:

[0011] A breathable and anti-seepage structural layer suitable for subgrade slope protection, comprising: a coarse-grained layer, a fine-grained layer, plant straws, and a drainage ditch; the coarse-grained layer is laid on the subgrade slope, the fine-grained layer is laid on the coarse-grained layer, the plant straws are inserted into the fine-grained layer and inserted to the interface between the fine-grained layer and the coarse-grained layer, and the drainage ditch is arranged at the position where the subgrade slope toe contacts the interface between the fine-grained layer and the coarse-grained layer.

[0012] The coarse-grained layer is composed of blast furnace slag and expansion material particles, and the mass ratio of blast furnace slag to expansion material particles is 2:1 to 4:1.

[0013] The particle size of the blast furnace slag is 20 - 60 mm, and the grading composition is similar to that of coarse gravel, which is obtained by mechanical crushing, screening, and particle size sorting.

[0014] The particle size of the expansion material particles is 0.075 - 0.25 mm, and the grading composition is similar to that of fine sand. The free expansion rate of the expansion material particles is required to be 65% - 90%, and the linear expansion rate is 1.50 - 1.70.

[0015] The expansion material particles are artificially prepared materials with the characteristics of water absorption expansion and water loss shrinkage, and are uniformly mixed by the mass ratio of expansive soil: steel slag: nano-SiO 2 in a ratio of 80:18:2. The montmorillonite content in the expansive soil is 70% - 80%, and after drying and grinding, the particle size is 200 meshes and below; the particle size of the steel slag is 100 meshes and below.

[0016] When expansive soil is used as a foundation or subgrade filler, its properties of swelling when encountering water and shrinking when losing water will cause additional deformation of the foundation or subgrade, thus threatening the stability of the foundation or subgrade and adjacent structures. In the present invention, it is used in the slope structural layer. The property of the expansive soil swelling in volume when encountering water during rain can block pores and thus prevent water seepage; when the sun shines, water is lost under the drying effect, the volume shrinks, and the pores open to play a breathable role. Using the expansive soil to prepare expansion material particles and applying them to the subgrade slope protection layer enables the poor geotechnical properties of the expansive soil of swelling when encountering water and shrinking when losing water to play a positive role in the breathable and anti-seepage of the subgrade slope protection layer, producing unexpected effects.

[0017] Before laying the coarse-grained layer, the blast furnace slag and the expansion material particles are fully mixed to make the porosity of the mixture of the two reach 15% - 20%.

[0018] Under field conditions, the laying thickness of the coarse-grained layer is 0.20 - 0.30 m, and the compaction degree is 90% - 95%.

[0019] Function of the coarse-grained layer: Under working conditions such as continuous rainfall and heavy rainstorms, the capillary blocking effect fails and rainwater seeps into the coarse-grained layer. At this time, the swelling material particles in the pores between the blast furnace slag absorb water and expand to fill the remaining pores, and the rainwater will be blocked in this layer and will no longer seep into the slope soil, playing a further anti-seepage role. Under the working conditions of the weather turning cloudy or sunny after the rain stops, due to the surface evaporation effect, water vapor is continuously discharged, the volume of the swelling material particles shrinks continuously as they lose water, the pores between the blast furnace slag return to their original state, and the water vapor in the slope soil can also be discharged outward through the plant straw at the interface between the coarse-grained layer and the fine-grained layer, playing a ventilation role. In addition, the coarse-grained layer can be used as a drainage layer, and the rainwater at the interface between the coarse-grained layer and the fine-grained layer can flow along the slope into the drain ditch at the slope foot and then be discharged outside the subgrade range.

[0020] The fine-grained layer is composed of silt, and the particle size of the silt is 0.005 - 0.075 mm.

[0021] Under the on-site conditions, the laying thickness of the fine-grained layer is 0.40 - 0.60 m, and the top 15 cm of the fine-grained layer is used as the vegetation layer to reinforce the topsoil. The compaction degree of the top 15 cm is 60 - 65%, and the compaction degree of the following fine-grained layer is 90 - 95%.

[0022] Function of the fine-grained layer: First, under the working conditions of short-term and heavy rain, the coarse-grained layer and the fine-grained layer form a breathable and anti-seepage structural layer, and the capillary force at the interface between the two is used to prevent rainwater from seeping into the coarse-grained layer, playing an anti-seepage role. Second, during the rainfall intermission period, the water vapor in the breathable and anti-seepage structural layer is discharged by using the plant transpiration effect, so that it returns to the unsaturated state and the capillary blocking effect.

[0023] The plant straw can be selected from the straw of sorghum, wheat or other crops, with a diameter of 2 - 5 mm and a length of the thickness of the fine-grained layer + 2 - 5 cm.

[0024] Under the on-site conditions, after laying the fine-grained layer, the plant straws are vertically inserted, and the insertion depth reaches the interface between the fine-grained layer and the coarse-grained layer, and the insertion interval is 0.25 - 0.50 m.

[0025] Function of the plant straw: By inserting the plant straws to the interface between the fine-grained layer and the coarse-grained layer, a channel is provided for the water vapor in the soil to be discharged into the atmosphere, thereby eliminating the "lid effect" and achieving the purpose of ventilation.

[0026] The construction process of the breathable and anti-seepage structural layer applicable to the subgrade slope protection of the present invention is as follows:

[0027] (1) Level the subgrade slope and reinforce the subgrade slope foot;

[0028] (2) Bury the precast channel components, and fill the channel with crushed gravel to form a longitudinal and transverse channel structure on the slope surface;

[0029] (3) In the rectangular compartments formed by vertical and horizontal ditches, a coarse-grained layer and a fine-grained layer are laid in layers from the toe of the slope to the top of the slope; after laying the fine-grained layer, plant straws are vertically inserted.

[0030] The laying thickness of the coarse-grained layer is 0.20 - 0.30 m, and the compaction degree is 90 - 95%.

[0031] The laying thickness of the fine-grained layer is 0.40 - 0.60 m, and the top 15 cm of the fine-grained layer is used as the vegetation layer to reinforce the topsoil; the compaction degree of the top 15 cm is 60 - 65%, and the compaction degree of the following fine-grained layer is 90 - 95%.

[0032] The insertion depth of the plant straws reaches the interface between the fine-grained layer and the coarse-grained layer, and the insertion interval is 0.25 - 0.50 m.

[0033] (4) Vegetation is planted on the slope surface; a drainage ditch is set at the toe of the slope.

[0034] The basic principle of the present invention includes:

[0035] The plant straws are cylindrical and hollow. Inserting them into the silt at intervals of 0.25 - 0.50 m can well enhance the air permeability of the capillary barrier layer (fine-grained layer + coarse-grained layer), timely discharge the water vapor rising in the soil from the slope, avoid its condensation, and prevent the occurrence of the "lid effect" resulting in water accumulation on the slope and slope sliding instability. Therefore, the plant straws play a role in ventilation.

[0036] The fine-grained layer and the coarse-grained layer form a capillary retardation layer. Under medium to large rainfall conditions, the capillary action at the interface is used to prevent rainwater from infiltrating into the coarse-grained layer; at the same time, the accumulated water at the interface flows along the slope through the coarse-grained surface, converges into the drainage ditch at the toe of the slope, and is discharged outside the subgrade range, so as to achieve the purpose of anti-seepage.

[0037] When the rainfall reaches the heavy rain level, the capillary retardation effect fails, and rainwater infiltrates into the coarse-grained layer. The swelling material particles in it quickly absorb water and expand to dozens of times their original volume, blocking the pores between the blast furnace slag, thus forming an impermeable layer and further playing an anti-seepage role. After the rainfall ends, the swelling material particles will lose water and shrink due to water vapor evaporation, and the pores between the blast furnace slag will open again, and the water vapor in the slope soil can pass through the coarse-grained layer and be discharged into the atmosphere by the plant straws.

[0038] The beneficial effects of the present invention are reflected in:

[0039] The present invention overcomes the deficiencies of the prior art and proposes a breathable and anti-seepage structural layer for the subgrade slope. During service, through two special methods of inserting plant straws into the fine-grained layer and mixing swelling material particles into the coarse-grained layer, high air permeability and super anti-seepage of the structural layer are realized, effectively preventing the occurrence of the "lid effect" and capillary retardation failure problems.

[0040] The present invention uses the waste discharged from the blast furnace during the smelting of pig iron (i.e., blast furnace slag) as the main material of the coarse-grained layer, which can consume a large amount of this type of solid waste, achieve reuse, save natural resources, reduce economic costs, and reduce environmental pollution. Using plant straw as the water vapor discharge channel in the soil produces a green environmental protection effect. Therefore, the present invention has good economic, environmental and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 : Schematic diagram of the air-permeable and anti-seepage structure layer; 1 - plant straw; 2 - fine-grained layer; 3 - coarse-grained layer; 4 - slope soil; 5 - drainage ditch. DETAILED DESCRIPTION OF THE INVENTION

[0042] The present invention will be further described below through specific embodiments, but the protection scope of the present invention is not limited thereto.

[0043] Embodiment 1

[0044] Build a two-way 8-lane high-grade highway in the mountainous and hilly areas of Taizhou. The maximum height of the subgrade fill in a section reaches 8.5 m. The air-permeable and anti-seepage structure layer is used to prevent seepage of the subgrade slope to prevent disasters such as subgrade collapse during the rainy season.

[0045] In this embodiment, the air-permeable and anti-seepage structure layer from top to bottom is successively the fine-grained layer 2 and the coarse-grained layer 3. The fine-grained layer 2 is composed of silt soil, and reed poles 1 are inserted into the fine-grained layer. The coarse-grained layer 3 is composed of blast furnace slag and expanded material particles.

[0046] The laying construction is carried out in sequence from bottom to top.

[0047] First, lay the coarse-grained layer 3. Blast furnace slag is a solid waste discharged during iron and steel smelting. It should be mechanically crushed first, and then blast furnace slag with a particle size in the range of 20 - 60 mm is screened; the expanded material particles are selected with a particle size of 0.075 - 0.25 mm; the two materials are fully mixed by a forced mixer. After mixing, the coarse-grained layer 3 is laid, with a laying thickness of 0.30 m, a compaction degree of 90%, and a porosity of 16%.

[0048] Secondly, lay the fine-grained layer 2. The particle size of the silt soil is 0.005 - 0.075 mm, and the laying thickness is 0.50 m. First, lay a 0.35 m thick silt soil layer with a compaction degree of 95%; then lay a 0.15 m thick silt soil layer with a compaction degree of 60%; again, insert reed poles with a diameter of 5 mm vertically into the silt soil layer, with a length of 0.54 m and an interval of 0.30 m in each direction.

[0049] Finally, spray seeding and grass planting are carried out on the slope surface, and a drainage ditch is set at the slope foot.

Claims

1. A breathable and anti-seepage structural layer suitable for roadbed slope protection, characterized in that: The breathable and anti-seepage structural layer comprises: a coarse-grained layer, a fine-grained layer, plant straws, and a drainage ditch; the coarse-grained layer is laid on the roadbed slope, the fine-grained layer is laid on the coarse-grained layer, the plant straws are inserted into the fine-grained layer and driven to the interface between the fine-grained layer and the coarse-grained layer, and the drainage ditch is arranged at the foot of the roadbed slope and in contact with the interface between the fine-grained layer and the coarse-grained layer; in, The coarse-grained layer is composed of blast furnace slag and expanded material particles; the particle size of the blast furnace slag is 20 to 60 mm; the particle size of the expanded material particles is 0.075 to 0.25 mm; The fine-grained layer is composed of silt with a particle size of 0.005 to 0.075 mm.

2. The breathable and anti-seepage structural layer suitable for roadbed slope protection as claimed in claim 1, characterized in that: In the coarse-grained layer, the mass ratio of blast furnace slag to expanded material particles is 2:1 to 4:

1.

3. The breathable and anti-seepage structural layer suitable for roadbed slope protection as claimed in claim 1, characterized in that: The expansive material particles are obtained by uniformly mixing expansive soil, steel slag and nano-SiO2 in a mass ratio of 80:18:

2.

4. The breathable and anti-seepage structural layer suitable for roadbed slope protection as claimed in claim 1, characterized in that: Before laying the coarse-grained layer, the blast furnace slag and the expanded material particles are fully mixed so that the porosity of the mixture reaches 15-20%.

5. The breathable and anti-seepage structural layer suitable for roadbed slope protection as claimed in claim 1, characterized in that: The coarse-grained layer is laid with a thickness of 0.20 to 0.30 m and a compaction degree of 90 to 95%.

6. The breathable and anti-seepage structural layer suitable for roadbed slope protection as claimed in claim 1, characterized in that: The thickness of the fine-grained layer is 0.40 to 0.60 m, and the top 15 cm of the fine-grained layer is used as a vegetation layer to reinforce the topsoil; the compaction degree of the top 15 cm is 60 to 65%, and the compaction degree of the fine-grained layer below is 90 to 95%.

7. The breathable and anti-seepage structural layer suitable for roadbed slope protection as claimed in claim 1, characterized in that: The diameter of plant straw is 2 to 5 mm, and its length is the thickness of the fine particle layer + 2 to 5 cm.

8. The breathable and anti-seepage structural layer suitable for roadbed slope protection as claimed in claim 1, characterized in that: After laying the fine-grained layer, plant straw is inserted vertically to a depth that reaches the interface between the fine-grained layer and the coarse-grained layer, with an interval of 0.25 to 0.50 m.

9. The construction process of the breathable and anti-seepage structural layer suitable for roadbed slope protection as claimed in claim 1, characterized in that: The construction process is as follows: (1) Level the roadbed slope and reinforce the roadbed slope foot; (2) Bury the prefabricated ditch parts and fill the ditch with crushed gravel to form the longitudinal and transverse ditch structures on the slope; (3) In the rectangular cells formed by the longitudinal and transverse ditches, coarse-grained layers and fine-grained layers are laid in layers from the foot of the slope to the top of the slope; after laying the fine-grained layer, plant stalks are inserted vertically; The thickness of the coarse-grained layer is 0.20 to 0.30 m, and the compaction degree is 90 to 95%; The fine-grained layer is laid with a thickness of 0.40 to 0.60 m, and the top 15 cm of the fine-grained layer is used as a vegetation layer to consolidate the topsoil; The compaction degree of the top 15cm layer is 60-65%, and the compaction degree of the fine grain layer below is 90-95%; The depth of plant straw insertion is to the interface between the fine grain layer and the coarse grain layer, with an insertion interval of 0.25 to 0.50 m. (4) Plant vegetation on the slope and set up drainage ditches at the foot of the slope.

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