An expansive soil slope ecological protection structure and method

Abstract

A kind of expansive soil slope ecological prevention and control structure and method, the expansive soil slope ecological prevention and control structure includes a plain expansive soil layer, an ecological protection layer and a water-proof layer; the ecological protection layer includes a biological matrix improvement layer, lateral root type plants and main taproot type plants, and the water-proof layer includes a MICP technology solidification layer and a sand and gravel hole; the biological matrix improvement layer, the MICP technology solidification layer and the plain expansive soil layer intersect in a stepped manner from the surface to the inside, and the lateral root type plants and the main taproot type plants are planted alternately in a herringbone shape, and the sand and gravel holes connect the biological matrix improvement layer and the plain expansive soil layer. The present invention also includes a kind of expansive soil slope ecological prevention and control method. The present invention can effectively prevent seepage and moisturize, improve the reinforcement and anchoring ability of vegetation roots, suppress the cracking of the surface layer of the expansive soil slope and its strength attenuation after alternating sunny and rainy weather, ensure the long-term stability of the expansive soil slope, and provide a reasonable way to process agricultural waste at the same time, which is of great significance to ecological environment protection.

Description

Technical Field

[0001] The present invention relates to the technical field of soil erosion and slope control engineering, and in particular to an expansive soil slope ecological protection structure and method. Background Art

[0002] Expansive soils are primarily composed of highly hydrophilic minerals such as montmorillonite, illite, and kaolinite. They exhibit typical characteristics such as swelling and softening upon water absorption, and shrinkage and cracking upon water loss. Expansive soils have extremely poor engineering properties, leading to the saying that "every cut is sure to collapse, and every embankment is sure to collapse." Currently, the main engineering technologies for preventing and controlling expansive soil embankment slopes include stone masonry, concrete retaining walls, anti-slide piles, and flexible reinforcement. Flexible reinforcement offers the most effective and economical results, but the materials used are mostly synthetic fibers, which can cause irreversible environmental pollution.

[0003] With growing awareness of ecological and environmental protection, low-cost, resilient ecological slope protection technologies are gaining increasing attention. Plants significantly enhance the shear strength and stability of slopes through the hydrological effects of their stems and leaves, the reinforcement effect of their fibrous roots, and the anchoring effect of their taproots and coarse roots, playing a role in controlling and preventing shallow landslides. However, ecological slope protection technologies for expansive soil slopes still have some limitations: ① During their early growth phase, plant roots are short, shallow, and sparse, failing to provide reinforcement. ② Expansive soils are extremely low in nutrients and are very poor in fertility, leading to slow root growth. Even roots of plants that have grown for two years cannot penetrate the fissures and potential sliding surfaces of expansive soil slopes. ③ Long-term wetting and drying cycles cause strain softening of the soil within the slope due to repeated changes in cracks, stress, and strength, ultimately leading to slope instability during rainfall. Therefore, to further expand the application of ecological slope protection technologies in engineering practice, new ecological protection structures and methods for expansive soil slopes are urgently needed. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an ecological protection structure and method that can effectively prevent seepage and retain moisture, improve the soil consolidation and slope protection ability of vegetation roots, and ensure the long-term stability of expansive soil slopes, in response to the drawbacks and shortcomings of existing ecological slope protection technologies for expansive soil slopes.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] An expansive soil slope ecological protection structure comprises a plain expansive soil layer, an ecological protection layer and an aquiclude; the ecological protection layer comprises a biological matrix improvement layer, lateral root plants and main taproot plants; the aquiclude comprises a MICP technology solidification layer and sand and gravel holes; the biological matrix improvement layer, the MICP technology solidification layer and the plain expansive soil layer intersect in sequence in a stepped manner from the surface to the inside; the lateral root plants and the main taproot plants are planted alternately in a herringbone pattern; and the sand and gravel holes connect the biological matrix improvement layer and the plain expansive soil layer.

[0007] Furthermore, the biomatrix improvement layer is composed of 80-90% expansive soil, 3-8% bio-organic fertilizer, 5-10% biochar, 0.4-0.5% plant fiber and 0.5-0.7kg / m 3 The slow-release fertilizer is composed of, the "%" is the mass percentage, and the sum of the percentages of the components is 100%; its thickness is 15-25cm.

[0008] Furthermore, the bio-organic fertilizer is derived from the composting and fermentation of local livestock and poultry manure and agricultural waste, and has an organic matter content greater than 30% and a nitrogen, phosphorus and potassium content greater than 3%, where the "%" refers to mass percentage.

[0009] Furthermore, the biochar is a type of carbon-rich solid substance produced by pyrolysis of local agricultural and forestry residual waste or animal manure under anoxic conditions at a temperature less than 700°C. The oxides, carbonates and alkaline functional groups contained in the biochar can reduce the thickness of the bound water film through ion exchange and gelation, thereby reducing the expansion rate of the expansive soil.

[0010] Furthermore, the plant fiber is local agricultural waste, such as straw fiber, sugarcane fiber or coconut shell fiber, which can inhibit the expansion and cracking of expansive soil through reinforcement. Its length is 1-3 cm, width is 0.1-0.3 mm, thickness is less than 0.1 mm, and tensile strength is greater than 100 MPa.

[0011] Furthermore, the lateral root type plants can be bermudagrass, tall fescue or Manila etc., and suitable plants are selected according to local climate conditions and environment. The root system thereof grows parallel to the slope surface and the root system depth is 15-20 cm.

[0012] Furthermore, the main taproot plant can be alfalfa, Alocasia glabra, Sapium sebiferum or Camellia oleifera, etc. Suitable plants are selected according to local climatic conditions and environment, and their roots grow vertically to the ground with a root depth of more than 2m.

[0013] Furthermore, the MICP technology solidified layer is made by mixing the following materials in proportion: spraying 45-55 mL of concentrated microbial liquid and 140-160 mL of cementing liquid per 1 kg of expansive soil; after curing for 7 days, the expansive soil cohesion of the solidified layer is greater than 70 KPa, the internal friction angle is greater than 25°, and the saturated permeability coefficient is less than 10 -9 cm / s; its thickness is 10-20cm.

[0014] Furthermore, the concentrated microbial liquid is obtained by further centrifuging and concentrating the microbial liquid after culturing for 48 hours, thereby increasing the bacterial concentration to 2 times; the microbial liquid is formed by culturing Bacillus pasteurianus (No. ATCC11859) in a constant temperature shaking incubator at a temperature of 30°C and a rotation speed of 150 r / min for 48 hours.

[0015] Furthermore, the cementing fluid is composed of calcium chloride and urea in a mass ratio of 1:1, the cementing fluid concentration is 1 mol / L, and each 100 mL of the cementing fluid contains 21.91 g of CaCl26H2O and 6.01 g of urea.

[0016] Furthermore, the radius of the sand and gravel holes is 15-20 cm, the height is consistent with the thickness of the MICP technology solidified layer, and the radius of the filled sand and gravel is 1-3 cm.

[0017] An expansive soil slope ecological protection method comprises the following steps:

[0018] S1: Fill the plain expansive soil layer according to the optimum moisture content and maximum compaction degree of the plain expansive soil;

[0019] S2: Mark the location of the gravel hole on the slope of the plain expansive soil layer, that is, the location where the main taproot plant roots take root, and press a PVC pipe into the marked location, and fill the PVC pipe with gravel;

[0020] S3: MICP technology is used to improve expansive soil. The MICP-improved expansive soil is compacted on top of the plain expansive soil layer with a compaction degree of more than 95%, forming a MICP-solidified layer. The plain expansive soil layer and the MICP-solidified layer intersect in a stepped manner.

[0021] S4: After the MICP technology solidified layer is stable, the pre-buried PVC pipe is pulled out to form a sand and gravel hole;

[0022] S5: preparing biomatrix-modified expansive soil, compacting the biomatrix-modified expansive soil on the MICP technology-cured layer at a compaction degree of 88-90% to form a biomatrix-modified layer, wherein the biomatrix-modified layer and the MICP technology-cured layer intersect in a stepped manner;

[0023] S6: Select local stress-resistant lateral root plants and main taproot plants and plant them alternately in a herringbone pattern on the bio-substrate improved layer;

[0024] S7: Set up drainage ditches at the bottom of the slope and set up longitudinal drainage channels every 8-10m on the slope surface.

[0025] Furthermore, in step S2, the radius of the PVC tube is 15-20 cm, the length is 15-20 cm, and the pressing depth is 3 cm; the radius of the sand and gravel is 1-3 cm.

[0026] Furthermore, in step S3, the MICP technology for improving the expansive soil refers to spraying 45-55 mL of concentrated Bacillus pasteurianus liquid and 140-160 mL of cementing liquid per 1 kg of expansive soil. The concentrated Bacillus pasteurian liquid is obtained by centrifugation and concentration of the Bacillus pasteurian liquid after culturing for 48 hours, and the bacterial concentration is increased to 2 times to accelerate the formation speed of the solidified layer and reduce the curing time. The Bacillus pasteurian liquid is formed by culturing Bacillus pasteurian (No. ATCC11859) in a constant temperature shaking incubator at a temperature of 30°C and a rotation speed of 150 r / min for 48 hours; the cementing fluid is composed of calcium chloride and urea in a mass ratio of 1:1, and the cementing fluid concentration is 1 mol / L. Each 100 ml of the cementing fluid contains 21.91 g of CaCl2·6H2O and 6.01 g of urea; after curing for 7 days, the expansive soil cohesion of the solidified layer is greater than 70 KPa, the internal friction angle is greater than 25°, and the saturated permeability coefficient is less than 10 -9 cm / s; the thickness of the solidified layer is 10-20cm.

[0027] In order to improve the construction efficiency and quality of the MICP technology curing layer, the MICP technology curing layer is carried out according to the following steps:

[0028] S31, strain selection: Bacillus pasteurianus (Sporosarcina pasteurii) was purchased from the China General Microbiological Culture Collection Center (CGMCC), with the strain number ATCC11859.

[0029] S32, Bacterial culture and bacterial solution preparation: Bacillus pasteurianus was cultured in liquid culture medium composed of 20 g urea, 15 g casein peptone, 5 g sodium chloride, and 5 g soy peptone per 1 L of distilled water. The culture medium inoculated with Bacillus pasteurianus was incubated in a constant temperature shaking incubator (model SPX-250B-Z) at 30°C and 150 rpm for 48 h. The bacterial solution reached its maximum concentration when the culture medium became turbid. The OD value was 0.001. 600 The value is equal to 1;

[0030] S33, concentrate the bacterial solution by centrifugation: OD 600 The bacterial solution with a value of 1 is placed in a centrifuge (model DHZ500). After centrifugation, the bacteria and culture solution are separated into layers, with the culture solution on top and the bacteria on the bottom. 1 / 2 of the culture solution is aspirated, and the bacterial solution is concentrated by 2 times.

[0031] S34, cementing fluid preparation: The cementing fluid is composed of calcium chloride and urea in a mass ratio of 1:1, with a cementing fluid concentration of 1 mol / L, and contains 21.91 g of CaCl2·6H2O and 6.01 g of urea per 100 ml of cementing fluid;

[0032] S35, expansive soil improvement: During the improvement process, first spray 150 mL of cementing liquid on every 1 kg of expansive soil, stir evenly, then spray 50 mL of concentrated Bacillus pasteurianus liquid and mix evenly;

[0033] S36, solidification layer construction: The expansive soil improved by MICP technology is compacted on the plain expansive soil layer with a compaction degree of more than 95%. After curing for 7 days, a MICP technology solidification layer is formed. The plain expansive soil layer and the MICP technology solidification layer intersect in a stepped manner.

[0034] Further, in step S5, the composition is 80-90% expansive soil, 3-8% bio-organic fertilizer, 5-10% biochar, 0.4-0.5% plant fiber and 0.5-0.7kg / m 3 The slow-release fertilizer is used to prepare a biomatrix to improve expansive soil, where the "%" is the mass percentage, and the sum of the percentages of the components is 100%; the thickness is 15-25 cm.

[0035] Among them, the biological organic fertilizer is derived from the composting and fermentation of local livestock and poultry manure and agricultural waste, with an organic matter content greater than 30% and a nitrogen, phosphorus and potassium content greater than 3%, where the "%" represents mass percentage; the biochar is a type of carbon-rich solid substance produced by pyrolysis of local agricultural and forestry residual waste or animal manure under anoxic conditions at a temperature less than 700°C, which contains a large amount of oxides, carbonates and alkaline functional groups, and has the characteristics of high adsorption, high pH and water and fertilizer retention; the plant fiber is local agricultural waste, such as straw fiber, sugarcane bagasse fiber or coconut shell fiber, with a length of 1-3 cm, a width of 0.1-0.3 mm, a thickness of less than 0.1 mm, and a tensile strength greater than 100 MPa.

[0036] Furthermore, in step S6, the lateral root type plants may be bermudagrass, tall fescue or Manila ferns, etc. Suitable plants are selected according to local climate conditions and environment, and their roots grow parallel to the slope surface with a root depth of 15-20 cm.

[0037] Furthermore, in step S6, the main taproot plant can be alfalfa, Alocasia glabra, Sapium sebiferum or Camellia oleifera, etc. Suitable plants are selected according to local climatic conditions and environment, and their roots grow vertically to the ground with a root depth of more than 2m.

[0038] The beneficial effects of the present invention are as follows:

[0039] (1) The biomatrix improvement layer can not only provide nutrients for plant growth, but also inhibit the cracking of the expansive soil on the slope surface and reduce the impact of dry-wet cycles on the expansive soil in the slope. The slow-release fertilizer provides short-term (0-3 months) nutrients, and the biological organic fertilizer provides long-term (3-24 months) nutrients, ensuring that plants have sufficient nutrients during the growth stage. The biochar significantly reduces the expansion rate of the expansive soil through ion exchange, and plant fibers such as straw and sugarcane bagasse through reinforcement, thereby inhibiting the cracking of the expansive soil.

[0040] (2) The lateral root plants in the ecological protection layer have roots that grow parallel to the slope surface. On the one hand, they make the horizontal permeability coefficient much greater than the vertical permeability coefficient, effectively slowing down the infiltration rate of water in the expansive soil slope. On the other hand, they increase the shear strength of the surface layer through reinforcement, reducing soil erosion.

[0041] (3) The main taproot plants in the ecological protection layer have roots that penetrate through the holes in the sand and gravel and are anchored in the expansive soil layer. This not only enhances the overall stability of the biomatrix improved layer and the slope, but also drains excess water from the expansive soil layer in the slope through transpiration, thereby improving its matrix suction and shear strength.

[0042] (4) The expansive soil improved by MICP technology not only has a significantly reduced expansion rate and a greatly increased strength, but also has a significantly reduced permeability, less than 10 -9 cm / s, can effectively block water infiltration;

[0043] (5) The pores in the sand and gravel can not only form a capillary water barrier with the biomatrix improved layer to block water infiltration, but also provide root growth channels for taproot plants, thereby improving the overall stability of the slope;

[0044] (6) The biomatrix improvement layer, MICP technology solidification layer and plain expansive soil layer are all intersected in a stepped manner, which effectively improves the tightness of the connection between the layers;

[0045] (7) The present invention provides a reasonable way to treat agricultural waste, which can be made into bio-organic fertilizer, biochar and plant fiber for treating expansive soil slopes, effectively broadening its utilization methods, turning waste into treasure, and generating significant economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a schematic diagram of the ecological protection structure of the expansive soil slope of the present invention;

[0047] Figure 2 is the relationship curve between biochar content and no-load expansion rate of expansive soil;

[0048] Figure 3 is the relationship curve between rice straw dosage and no-load expansion rate of expansive soil;

[0049] Figure 4 The crack development of plain expansive soil after 5 drying and wetting cycles;

[0050] Figure 5 The cracks in the expansive soil improved by the biomatrix after 5 drying and wetting cycles;

[0051] Figure 6 This is the relationship curve between the crack rate of expansive soil improved by biomatrix and the number of drying and wetting cycles;

[0052] Figure 7 The relationship curve between the saturated permeability coefficient and time of expansive soil improved by MICP technology;

[0053] In the figure: 1-plain expansive soil layer, 2-MICP technology solidification layer, 3-biological matrix improvement layer, 4-lateral root type plants, 5-main taproot type plants, 6-sand and gravel holes, 7-drainage ditch. DETAILED DESCRIPTION

[0054] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0055] The protection of expansive soil slope at a certain location on the XX to XX Expressway is used as an example.

[0056] Reference Figure 1 , an expansive soil slope ecological protection structure, comprising a plain expansive soil layer 1, an ecological protection layer and a water-proof layer; the ecological protection layer comprises a biological matrix improvement layer 3, lateral root plants 4 and main taproot plants 5, the water-proof layer comprises a MICP technology solidification layer 2 and sand and gravel holes 6, the biological matrix improvement layer 3, the MICP technology solidification layer 2 and the plain expansive soil layer 1 intersect in a stepped manner from the outside to the inside, the lateral root plants 4 and the main taproot plants 5 are planted alternately in a herringbone shape, and the sand and gravel holes 6 connect the biological matrix improvement layer 3 and the plain expansive soil layer 1.

[0057] In this embodiment, the biomatrix improved layer 3 is composed of 85% expansive soil, 4.5% bio-organic fertilizer, 10% biochar, 0.5% plant fiber and 0.6 kg / m 3 The slow-release fertilizer is composed of , wherein the "%" is the mass percentage, and the sum of the percentages of the components is 100; and the thickness is 20 cm.

[0058] Among them, the bio-organic fertilizer is derived from the composting and fermentation of local livestock and poultry manure and agricultural waste, and its organic matter content is greater than 30%, and its nitrogen, phosphorus and potassium content is greater than 3%, and the "%" is the mass percentage.

[0059] The biochar is a type of carbon-rich solid substance produced by pyrolysis of local agricultural and forestry residual waste or animal feces under oxygen-deficient conditions at temperatures below 700°C. The oxides, carbonates and alkaline functional groups it contains can reduce the thickness of the bound water film through ion exchange and gelation, thereby reducing the expansion rate of expansive soil.

[0060] The plant fiber is local agricultural waste, such as straw fiber, sugarcane fiber or coconut shell fiber, which can inhibit the expansion and cracking of expansive soil through reinforcement. It has a length of 1-3 cm, a width of 0.1-0.3 mm, a thickness of less than 0.1 mm, and a tensile strength of greater than 100 MPa.

[0061] In this embodiment, the lateral root type plants 4 include Bermuda grass, tall fescue or Manila, etc. Suitable plants are selected according to local climate conditions and environment. The roots grow parallel to the slope surface and the root depth is 15-20 cm.

[0062] In this embodiment, the main taproot plants 5 include alfalfa, Alocasia glabra, Sapium sebiferum or Camellia oleifera, etc. Suitable plants are selected according to local climatic conditions and environment. Their roots grow vertically to the ground and the root depth exceeds 2m.

[0063] In this embodiment, the lateral root type plants 4 and the main taproot type plants 5 are planted alternately in a herringbone pattern, the planting density of the main taproot type plants is 150 cm plant spacing × 200 cm row spacing, and the planting density of the lateral root type plants is 40 cm plant spacing × 60 cm row spacing.

[0064] In this embodiment, the MICP technology solidified layer 2 is made of the following materials mixed in proportion: 50 mL of concentrated microbial liquid and 150 mL of cementing liquid are sprayed on every 1 kg of expansive soil; after curing for 7 days, the expansive soil cohesion of the solidified layer is greater than 70 KPa, the internal friction angle is greater than 25°, and the saturated permeability coefficient is less than 10 -9 cm / s, and its thickness is 15 cm.

[0065] Among them, the concentrated microbial liquid is obtained by further centrifugation and concentration of the microbial liquid after culturing for 48 hours, and the bacterial concentration is increased to 2 times to accelerate the formation speed of the solidified layer and reduce the curing time; the microbial liquid is formed by culturing Bacillus pasteurianus (No. ATCC11859) in a constant temperature shaking incubator at a temperature of 30°C and a rotation speed of 150 r / min for 48 hours.

[0066] The cementing fluid is composed of calcium chloride and urea in a mass ratio of 1:1. The cementing fluid concentration is 1 mol / L, and each 100 mL of the cementing fluid contains 21.91 g of CaCl2·6H2O and 6.01 g of urea.

[0067] In this embodiment, the radius of the sand and gravel holes 6 is 15-20 cm, the height is consistent with the thickness of the MICP technology solidified layer, and the radius of the filled sand and gravel is 1-3 cm.

[0068] An expansive soil slope ecological protection method comprises the following steps:

[0069] S1: Fill the plain expansive soil layer 1 according to the optimum moisture content and maximum compaction degree of the plain expansive soil;

[0070] S2: Mark the location of the gravel hole 6 on the slope of the plain expansive soil layer, that is, the location where the main taproot plant roots take root, and press a PVC pipe into the marked location, and fill the PVC pipe with gravel;

[0071] S3: The expansive soil is modified using MICP technology. The MICP-modified expansive soil is compacted on the plain expansive soil layer with a compaction degree of more than 95%, forming a MICP-solidified layer 2. The plain expansive soil layer 1 and the MICP-solidified layer 2 intersect in a stepped manner.

[0072] S4: After the MICP technology solidified layer 2 is stabilized, the pre-buried PVC pipe is pulled out to form the gravel hole 6. The pulled out PVC pipe can also be recycled;

[0073] S5: preparing biomatrix-modified expansive soil, compacting the biomatrix-modified expansive soil on the MICP technology-cured layer at a compaction degree of 88-90% to form a biomatrix-modified layer, wherein the biomatrix-modified layer and the MICP technology-cured layer intersect in a stepped manner;

[0074] S6: Select local stress-resistant lateral root plants and main taproot plants and plant them alternately in a herringbone pattern. The planting density of main taproot plants is 150 cm plant spacing × 200 cm row spacing, and the planting density of lateral root plants is 40 cm plant spacing × 60 cm row spacing.

[0075] S7: Set up drainage ditches at the bottom of the slope and set up a longitudinal drainage channel every 10m on the slope surface.

[0076] In step S2, the radius of the PVC tube is 15 cm, the length is 20 cm, and the pressing depth is 3 cm; the radius of the sand and gravel is 1-3 cm.

[0077] In step S3, the MICP technology for improving expansive soil involves spraying 50 mL of concentrated Bacillus pasteurianus liquid and 150 mL of a binder solution per kg of expansive soil. The concentrated Bacillus pasteurianus liquid is obtained by centrifugation and concentration of a 48-hour culture of Bacillus pasteurianus liquid, increasing the bacterial concentration to twice that of the original to accelerate the formation of the solidified layer and reduce the curing time. The Bacillus pasteurianus liquid is formed by culturing Bacillus pasteurianus (ATCC No. 11859) in a constant temperature shaking incubator at a temperature of 30°C and a rotation speed of 150 r / min for 48 hours. The binder solution consists of calcium chloride and urea in a mass ratio of 1:1, with a binder solution concentration of 1 mol / L, containing 21.91 g of CaCl2·6H2O and 6.01 g of urea per 100 ml of the binder solution. After seven days of curing, the expansive soil in the solidified layer has a cohesion greater than 70 kPa, an internal friction angle greater than 25°, and a saturated permeability coefficient less than 10 -9 cm / s; the thickness of the solidified layer is 15 cm.

[0078] In order to improve the construction efficiency and quality of the MICP technology curing layer, the MICP technology curing layer is carried out according to the following steps:

[0079] S31, strain selection: Bacillus pasteurianus (Sporosarcina pasteurii) was purchased from the China General Microbiological Culture Collection Center (CGMCC), with the strain number ATCC11859.

[0080] S32, Bacterial culture and bacterial solution preparation: Bacillus pasteurianus was cultured in liquid culture medium composed of 20 g urea, 15 g casein peptone, 5 g sodium chloride, and 5 g soy peptone per 1 L of distilled water. The culture medium inoculated with Bacillus pasteurianus was incubated in a constant temperature shaking incubator (model SPX-250B-Z) at 30°C and 150 rpm for 48 h. The bacterial solution reached its maximum concentration when the culture medium became turbid. The OD value was 0.001. 600 The value is equal to 1;

[0081] S33, concentrate the bacterial solution by centrifugation: OD 600 The bacterial solution with a value of 1 is placed in a centrifuge (model DHZ500). After centrifugation, the bacteria and culture solution are separated into layers, with the culture solution on top and the bacteria on the bottom. 1 / 2 of the culture solution is aspirated, and the bacterial solution is concentrated by 2 times.

[0082] S34, cementing fluid preparation: The cementing fluid is composed of calcium chloride and urea in a mass ratio of 1:1, with a cementing fluid concentration of 1 mol / L, and contains 21.91 g of CaCl2·6H2O and 6.01 g of urea per 100 ml of cementing fluid;

[0083] S35, expansive soil improvement: During the improvement process, first spray 150 mL of cementing liquid on every 1 kg of expansive soil, stir evenly, then spray 50 mL of concentrated Bacillus pasteurianus liquid and mix evenly;

[0084] S36, solidification layer construction: The expansive soil improved by MICP technology is compacted on the plain expansive soil layer according to its maximum dry density. After curing for 7 days, a MICP technology solidification layer is formed. The plain expansive soil layer and the MICP technology solidification layer intersect in a stepped manner.

[0085] In step S5, the composition is 85% expansive soil, 4.5% bio-organic fertilizer, 10% biochar, 0.5% plant fiber and 0.6kg / m 3 The slow-release fertilizer is used to prepare a biomatrix-modified expansive soil, where the "%" is the mass percentage, and the sum of the percentages of the components is 100%; the thickness is 20 cm.

[0086] Among them, the biological organic fertilizer is derived from the composting and fermentation of local livestock and poultry manure and agricultural waste, and its organic matter content is greater than 30wt%, and its nitrogen, phosphorus and potassium content is greater than 3wt%, and the "%" is the mass percentage; the biochar is a type of carbon-rich solid substance produced by pyrolysis of local agricultural and forestry residual waste or animal manure under oxygen-deficient conditions at a temperature less than 700°C. It contains a large amount of oxides, carbonates and alkaline functional groups, and has the characteristics of high adsorption, high pH and water and fertilizer retention; the plant fiber is local agricultural waste, such as straw fiber, sugarcane bagasse fiber or coconut shell fiber, etc., with a length of 1-3cm, a width of 0.1-0.3mm, a thickness of less than 0.1mm, and a tensile strength greater than 100MPa.

[0087] In step S6, the lateral root type plants 4 include Bermuda grass, tall fescue or Manila, etc. Suitable plants are selected according to local climate conditions and environment. The roots grow parallel to the slope surface and the root depth is 15-20 cm.

[0088] In step S6, the main taproot type plants 5 include alfalfa, smilax glabra, Chinese tallow tree or camellia sinensis, etc. Suitable plants are selected according to local climatic conditions and environment, and their roots grow vertically to the ground with a root depth of more than 2m.

[0089] Research has shown that the biomatrix-modified layer of the present invention can not only provide nutrients for plant growth, but also inhibit cracking of expansive soil on the slope surface and reduce the impact of dry-wet cycles on the expansive soil within the slope. The slow-release fertilizer provides short-term nutrients (0-3 months), while the bio-organic fertilizer provides long-term nutrients (3-24 months), ensuring that plants have sufficient nutrients during their growth stage. The biochar significantly reduces the expansion rate of expansive soil through ion exchange, and plant fibers such as straw and sugarcane bagasse significantly reduce cracking of expansive soil through reinforcement. Figure 2 、 Figure 3 、 Figure 4 、 Figure 5 and Figure 6 shown.

[0090] The study also showed that the expansive soil improved by the MICP technology of the present invention not only has a significantly reduced expansion rate and a greatly increased strength, but also has a significantly reduced permeability, less than 10 -9 cm / s, can effectively block the infiltration of water, such as Figure 7 shown.

Claims

1. An expansive soil slope ecological protection structure, characterized by: The invention comprises a plain expansive soil layer, an ecological protection layer and an aquiclude; the ecological protection layer comprises a biological matrix improvement layer, lateral root plants and main taproot plants; the aquiclude comprises a MICP technology solidification layer and sand and gravel holes; the biological matrix improvement layer, the MICP technology solidification layer and the plain expansive soil layer intersect in a stepped manner from the outside to the inside; the lateral root plants and the main taproot plants are planted alternately in a herringbone shape; the sand and gravel holes connect the biological matrix improvement layer and the plain expansive soil layer; the biological matrix improvement layer is composed of 80-90% expansive soil, 3-8% biological organic fertilizer, 5-10% biochar, 0.4-0.5% plant fiber and 0.5-0.7 kg / m 3 The "%" is the mass percentage, and the sum of the percentages of the various components is 100%.

2. The expansive soil slope ecological protection structure according to claim 1, characterized in that: The thickness of the biomatrix improved layer is 15-25 cm.

3. The expansive soil slope ecological protection structure according to claim 2, characterized in that: The bio-organic fertilizer is derived from the composting and fermentation of local livestock and poultry manure and agricultural waste, with an organic matter content greater than 30% and a nitrogen, phosphorus and potassium content greater than 3%, where "%" represents mass percentage; the biochar is a type of carbon-rich solid substance produced by pyrolysis of local agricultural and forestry residual waste or animal manure at a temperature less than 700°C under anoxic conditions; the plant fiber is local agricultural waste, including straw fiber, sugarcane fiber or coconut shell fiber, with a length of 1-3 cm, a width of 0.1-0.3 mm, a thickness of less than 0.1 mm, and a tensile strength greater than 100 MPa.

4. The expansive soil slope ecological protection structure according to claim 1, 2 or 3, characterized in that: The lateral root type plants are bermudagrass, tall fescue or Manila clover. Suitable plants are selected according to local climate conditions and environment. The root system grows parallel to the slope surface and the root system depth is 15-20 cm.

5. The expansive soil slope ecological protection structure according to claim 1, 2 or 3, characterized in that: The main taproot plant is alfalfa, Alocasia glabra, Sapium sebiferum or Camellia oleifera. Suitable plants are selected according to local climate conditions and environment. The root system grows vertically above the ground and the root system depth exceeds 2m.

6. The expansive soil slope ecological protection structure according to claim 1, 2 or 3, characterized in that: The MICP technology solidification layer is made by mixing the following materials in proportion: spraying 45-55 mL of concentrated microbial liquid and 140-160 mL of cementing liquid for every 1 kg of expansive soil; after curing for 7 days, the expansive soil cohesion of the solidified layer is greater than 70 KPa, the internal friction angle is greater than 25°, and the saturated permeability coefficient is less than 10 -9 cm / s; its thickness is 10-20cm.

7. The expansive soil slope ecological protection structure according to claim 6, characterized in that: The concentrated microbial liquid is obtained by further centrifuging and concentrating the microbial liquid after culturing for 48 hours, thereby increasing the bacterial concentration to 2 times; the microbial liquid is formed by culturing Bacillus pasteurianus in a constant temperature shaking incubator at a temperature of 30°C and a rotation speed of 150 r / min for 48 hours; the binder liquid is composed of calcium chloride and urea, with a mass ratio of 1:1 and a binder liquid concentration of 1 mol / L, and each 100 mL of binder liquid contains 21.91 g of CaCl2·6H2O and 6.01 g of urea.

8. The expansive soil slope ecological protection structure according to claim 1, 2 or 3, characterized in that: The radius of the sand and gravel holes is 15-20 cm, the height is consistent with the thickness of the MICP technology solidified layer, and the radius of the filled sand and gravel is 1-3 cm.

9. An ecological protection method for expansive soil slopes using the structure described in any one of claims 1 to 8, characterized in that: The following steps are involved: S1: Fill the plain expansive soil layer according to the optimum moisture content and maximum compaction degree of the plain expansive soil; S2: Mark the location of the gravel hole on the slope of the plain expansive soil layer, that is, the location where the main taproot plant roots take root, and press a PVC pipe into the marked location, and fill the PVC pipe with gravel; S3: MICP technology is used to improve expansive soil. The MICP-improved expansive soil is compacted on top of the plain expansive soil layer with a compaction degree of more than 95%, forming a MICP-solidified layer. The plain expansive soil layer and the MICP-solidified layer intersect in a stepped manner. S4: After the MICP technology solidified layer is stable, the pre-buried PVC pipe is pulled out to form a sand and gravel hole; S5: preparing biomatrix-modified expansive soil, compacting the biomatrix-modified expansive soil on the MICP technology-cured layer at a compaction degree of 88-90% to form a biomatrix-modified layer, wherein the biomatrix-modified layer and the MICP technology-cured layer intersect in a stepped manner; S6: Select local stress-resistant lateral root plants and main taproot plants and plant them alternately in a herringbone pattern on the bio-substrate improved layer; S7: Set up drainage ditches at the bottom of the slope and set up drainage channels every 8-10m on the slope surface.

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