Construction method for expansive soil slope ecological protection

Abstract

The invention discloses a construction method for expansive soil side slope ecological protection, and relates to the technical field of side slope protection, and the construction method comprises the following steps: testing basic physical indexes of a soil body, preparing a culture medium and a microbial solution, preparing a cementing solution, preparing a mixture, preparing spraying slurry, laying a vegetation net, preparing a grass seed mixture, spraying the slurry, and performing covering maintenance. According to the construction method, the requirements for ecological greening of the expansive soil side slope, rain wash resistance and prevention of shallow landslide of the side slope can be met, meanwhile, the granulated blast furnace slag powder solid waste resources are recycled, environmental and ecological friendliness is achieved, cost and land resources can be saved, harmony and unity with the surrounding ecological environment are formed, and the construction method is suitable for large-scale popularization and application. The culture medium with low price is adopted for microbial culture, so that the cost is low, and the granulated blast furnace slag powder subjected to microbial improvement can be used for curing harmful elements, so that the influence on the ecological environment is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of slope protection, and in particular relates to a construction method for ecological protection of expansive soil slopes. Background Art

[0002] Expansive soil is a highly plastic clay composed primarily of hydrophilic clay minerals such as montmorillonite and illite. Its core characteristics are swelling upon water absorption and shrinking upon water loss. This repeated expansion and contraction can lead to structural damage. In its natural state, expansive soil is typically hard or hard-plastic, possessing high bearing capacity and low compressibility. However, upon contact with water, its strength drops dramatically, with an expansion force of up to 50-550 kPa. Expansive soil slopes, containing hydrophilic clay minerals such as montmorillonite and illite, exhibit these properties, leading to repeated expansion and contraction, which can cause slope instability, landslides, and other disasters. Therefore, a construction method for the ecological protection of expansive soil slopes is needed.

[0003] Traditional methods for reinforcing expansive soil slopes, such as replacement, lime improvement, pile foundation reinforcement, and chemical improvement, include mixing lime and cement with expansive soil, a commonly used method in engineering. These methods can cause certain environmental problems, produce greenhouse gases, and increase the pH value of the treated soil, causing soil erosion and hindering plant growth. Vegetation is an effective way to prevent soil erosion, but it cannot meet people's needs. Summary of the Invention

[0004] The present invention aims to solve the technical problems existing in the prior art; to this end, the present invention proposes a construction method for ecological protection of expansive soil slopes.

[0005] A construction method for ecological protection of expansive soil slopes, the specific steps are as follows: Phase 1: Detecting basic physical indicators of soil and conducting test analysis; Phase II: Preparation of culture medium and microbial solution containing yeast extract, ammonium sulfate and buffer; The third stage: preparation of cementing fluid mainly composed of calcium chloride and urea; Stage 4: preparing a mixture containing slag powder, fly ash and soil; Stage 5: Mixing the mixture, microbial solution and cementing fluid to prepare the spraying slurry; Phase 6: Laying vegetation nets, setting up drainage systems, and laying nylon vegetation nets; Stage 7: preparing a mixture containing grass seeds, adhesive, moisturizer and water; The eighth stage: spraying construction, mixing the slurry and grass seed mixture evenly and spraying it onto the slope surface; The ninth stage: covering and maintenance, covering the slope surface with non-woven fabric after construction.

[0006] As a further solution of the present invention: in the first stage, the basic physical indicators of the soil of the slope to be reinforced are tested according to the test specifications in the "Highway Geotechnical Test Code" (JTCE4-2007), mainly including the basic indicators of the soil's natural moisture content, density, pH value, liquid limit, plastic limit, plasticity index and free expansion rate.

[0007] As a further embodiment of the present invention: in the second stage, the solutes of the culture medium mainly include 20 g / L yeast extract, 20 g / L ammonium sulfate, and 0.13 mol / L Tris buffer; in parts by mass, 10 parts yeast extract, 5 parts ammonium sulfate, and 1.55 parts Tris buffer are weighed, and the above solutes are mixed with water in a mass ratio of 1:5 to prepare a liquid culture medium, and then a certain amount of sodium hydroxide solution is added to the liquid culture medium to adjust the pH value to about 9, and the liquid culture medium is sealed and sterilized at high temperature in a high pressure sterilizer at 120°C, and then cooled to about 28°C; As a further embodiment of the present invention, the microbial solution is prepared by vacuum-preserving the purchased freeze-dried bacterial strain in an ampoule for bacterial activation. One volume fraction of Bacillus pasteurianus is inoculated into the prepared culture medium mixture under a sterile clean bench. The microbial solution is placed in a constant temperature (28°C) incubator and shaken at 220 rpm for 36 hours or more, until the 0D of Bacillus pasteurianus in the solution reaches 0. 600 is 3.5.

[0008] As a further solution of the present invention: in the third stage, the solutes of the binder mainly include calcium chloride and urea. According to the formula calculated by mass, 2 parts of urea and 2 parts of calcium chloride are weighed and dissolved in 1L of water, and stirred and mixed evenly to obtain a binder with a concentration of 2 mol / L. Since the dissolution of urea in water is an endothermic reaction and the dissolution of calcium chloride in water is an exothermic reaction, the reaction liquid is generally exothermic when mixed. After the exotherm ends and the temperature returns to room temperature, it is mixed with the microbial solution for use.

[0009] As a further solution of the present invention: in the fourth stage, the main components of the mixture include granulated blast furnace slag powder, fly ash and soil. The granulated blast furnace slag powder, fly ash and soil are all considered in terms of mass fractions in a dry state. 18 parts of granulated blast furnace slag powder, 2 parts of fly ash and 40 parts of soil are weighed, mixed and stirred evenly to form a mixture. The soil in the mixture is one or more of expansive soil, silt soil, clay soil or planting soil.

[0010] As a further solution of the present invention: in the fifth stage, according to the formula calculated by volume, 500-1200 parts of the mixture, 1 part of the microbial solution and 10 parts of the binder are weighed respectively, the mixture, the microbial solution and water are first mixed and stirred evenly in a certain proportion, and then the binder is added and stirred evenly with water to prepare an improved spray slurry.

[0011] As a further solution of the present invention: in the sixth stage, the excavated slope is first leveled and debris and other obstacles are cleared, and drainage ditches are set on the slope, intercepting ditches are set on the top of the slope, and drainage ditches are set at the bottom of the slope. The nylon vegetation net is laid on the expansive soil slope from top to bottom. When the nylon vegetation net is laid on the top of the slope, it needs to be extended 40 to 80 cm, buried in the soil and compacted. The nylon vegetation net and the slope surface are smoothly connected, and U-shaped steel bars with a diameter of 6 mm or more are used to fix the vegetation net. The U-shaped steel bars are about 15 to 30 cm long and about 8 mm wide. The spacing between the U-shaped steel bars is about 1.5 to 2.5 m, and U-shaped iron nails or bamboo nails are used in the middle for auxiliary fixation.

[0012] As a further solution of the present invention: in the seventh stage, grass seeds, adhesives that promote their growth, wood fibers, fertilizers, growth hormones, moisturizers and water are mixed and stirred in a certain proportion to form a uniform grass seed mixture, wherein the grass seeds are sprayed at about 25 grams per square.

[0013] As a further solution of the present invention: in the eighth stage, after the nylon vegetation net is laid, the improved slurry and the grass seed mixture are evenly mixed, and then hydraulically sprayed to the slope surface. The thickness of the slurry sprayed each time is 4±1 cm, and a total of 3 sprays are performed. The total thickness of the slurry sprayed on the slope is not less than 12 cm. The construction of the slurry spraying is carried out in the order of upper part first, lower part later, and from left to right.

[0014] As a further solution of the present invention: in the ninth stage, after the slurry spraying construction is completed, the slope surface is covered with non-woven fabric to retain moisture on the slope surface and reduce the erosion of seeds by rainfall, thereby promoting seed growth; if the temperature is too high, there is no need to cover it to avoid the occurrence of pests and diseases. When the lawn grows to about 5 cm, the non-woven fabric can be uncovered.

[0015] Compared with the prior art, the present invention has the following beneficial effects: (1) The construction method adopted by the present invention achieves a triple breakthrough in engineering durability, ecological self-healing and economic feasibility of expansive soil slope protection through the coordinated innovation of material modification, microbial mineralization and ecological protection. It can meet the requirements of ecological greening of expansive soil slopes, resistance to rainwater erosion and prevention of shallow landslides on the slopes. At the same time, the solid waste resources of granulated blast furnace slag powder are recycled, which is environmentally friendly and can save costs and land resources, forming a harmonious unity with the surrounding ecological environment. The microbial culture uses an inexpensive culture medium, which is not only low in cost, but also the granulated blast furnace slag powder improved by microorganisms can achieve the solidification of harmful elements, reducing the impact on the ecological environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a flow chart of the construction method of the present invention. DETAILED DESCRIPTION

[0017] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0018] Example 1 See also Figure 1 As shown, this application provides a construction method for ecological protection of expansive soil slopes, the specific steps are as follows: Phase 1: Detecting basic physical indicators of soil and conducting test analysis; Phase II: Preparation of culture medium and microbial solution containing yeast extract, ammonium sulfate and buffer; The third stage: preparation of cementing fluid mainly composed of calcium chloride and urea; Stage 4: preparing a mixture containing slag powder, fly ash and soil; Stage 5: Mixing the mixture, microbial solution and cementing fluid to prepare the spraying slurry; Phase 6: Laying vegetation nets, setting up drainage systems, and laying nylon vegetation nets; Stage 7: preparing a mixture containing grass seeds, adhesive, moisturizer and water; The eighth stage: spraying construction, mixing the slurry and grass seed mixture evenly and spraying it onto the slope surface; The ninth stage: covering and maintenance, covering the slope surface with non-woven fabric after construction.

[0019] In the first phase, based on the testing specifications of the Highway Soil Testing Code (JTC E4-2007), the basic physical parameters of the slope soil to be reinforced were analyzed. These parameters primarily covered basic indicators such as natural moisture content, density, pH, liquid limit, plastic limit, plasticity index, and free expansion rate. These parameters are crucial for evaluating the engineering properties of soils, as they provide crucial information on their stability and bearing capacity. These tests provide an understanding of the soil's physical state, providing a scientific basis for subsequent reinforcement design.

[0020] In the second stage, during the preparation of the culture medium and the microbial solution, the solutes of the culture medium mainly include 20 g / L yeast extract, 20 g / L ammonium sulfate, and 0.13 mol / L tris buffer solution; in terms of mass, 10 parts of yeast extract, 5 parts of ammonium sulfate, and 1.55 parts of tris buffer solution are taken, and the above solutes are mixed with water in a mass ratio of 1:5 to prepare a liquid culture medium, and then an appropriate amount of sodium hydroxide solution is added to the liquid culture medium to adjust the pH value to about 9, and then the liquid culture medium is sterilized in an autoclave at 120°C. The culture medium is sealed and sterilized at a temperature of 28°C, and then cooled to about 28°C; this process ensures the sterility of the culture medium and provides a suitable environment for the growth of microorganisms. The preparation of the microbial solution involves vacuum storage of the purchased strains in the form of freeze-dried powder in an ampoule, bacterial activation, and inoculation of 1 portion of Bacillus pasteurianus into the prepared culture medium mixed solution under the aseptic environment of a clean bench, placing the microbial solution in a constant temperature (28°C) incubator and shaking and culturing at a speed of 220 rpm for 36 hours or more, until the 0D of Bacillus pasteurianus in the solution reaches 0. 600 Reaching 3.5, this process is a key step in microbial growth, ensuring the activity and quantity of microorganisms and laying a solid foundation for the subsequent bioreinforcement process.

[0021] In the third stage, the solutes of the cementing fluid mainly include calcium chloride and urea. According to the formula calculated by mass, 2 parts of urea and 2 parts of calcium chloride are weighed and dissolved in 1L of water, and stirred to mix evenly to obtain a cementing fluid with a concentration of 2 mol / L. Since the dissolution of urea in water is an endothermic reaction and the dissolution of calcium chloride in water is an exothermic reaction, the reaction liquid is generally exothermic when mixed. After the exotherm ends and the temperature returns to room temperature, it is mixed with the microbial solution for use. This process is a key link in the preparation of the cementing fluid. By controlling the reaction temperature, the performance of the cementing fluid can be effectively controlled, thereby affecting the reinforcement effect.

[0022] In the fourth stage, the main components of the mixture include granulated blast furnace slag powder, fly ash, and soil. The percentages of these components are calculated by weight in a dry state. 18 parts granulated blast furnace slag powder, 2 parts fly ash, and 40 parts soil are weighed and mixed uniformly to form a mixture. The soil in the mixture can be one or more of expansive soil, silt, clay, or planting soil. This mixing process is critical to ensuring the uniformity and stability of the mixture, as different soil compositions directly affect the engineering performance of the mixture.

[0023] In the fifth stage, according to the formula calculated by volume, 500-1200 parts of the mixture, 1 part of the microbial solution and 10 parts of the binder are weighed respectively. The mixture, microbial solution and water are first mixed and stirred evenly in a certain proportion, and then the binder is added and stirred evenly with water to form an improved spray slurry. This process integrates the results of the previous stages to form the final spray slurry used for slope reinforcement.

[0024] In the sixth stage, the excavated slope is first leveled and debris and other obstacles are cleared. Drainage ditches are set on the slope, intercepting ditches are set on the top of the slope, and drainage ditches are set at the bottom of the slope. The nylon vegetation net is laid from top to bottom on the expansive soil slope. When the nylon vegetation net is laid on the top of the slope, it needs to be extended 40 to 80 cm, buried in the soil and compacted. The nylon vegetation net and the slope surface are smoothly connected, and U-shaped steel bars with a diameter of 6 mm or more are used to fix the vegetation net. The U-shaped steel bars are about 15 to 30 cm long and about 8 mm wide. The spacing between the U-shaped steel bars is about 1.5 to 2.5 m, and U-shaped iron nails or bamboo nails are used in the middle for auxiliary fixation. This stage is the on-site construction preparation for the slope reinforcement project, which ensures the close connection between the vegetation net and the slope surface and provides a good foundation for the subsequent vegetation growth.

[0025] In the seventh stage, grass seeds, growth-promoting adhesives, wood fibers, fertilizers, growth hormones, moisturizers, and water are mixed and stirred in a certain proportion to form a uniform grass seed mixture. Grass seeds are sprayed at a concentration of about 25 grams per square meter. This process is a key step in vegetation restoration. By precisely controlling the amount and mixing ratio of grass seeds, the uniform distribution and good growth of vegetation can be ensured.

[0026] In the eighth stage, after the nylon vegetation net is laid, the improved slurry and grass seed mixture are evenly mixed, and then hydraulically sprayed onto the slope surface. The thickness of the slurry sprayed each time is 4±1cm, and a total of 3 sprays are performed. The total thickness of the slurry sprayed on the slope is not less than 12cm. The slurry spraying construction is carried out in the order of upper part first, lower part later, and from left to right. This process is the on-site construction stage of slope reinforcement and vegetation restoration. By precisely controlling the spraying thickness and sequence, the reinforcement effect and uniform coverage of vegetation can be ensured.

[0027] In the ninth stage, after the slurry spraying is completed, the slope surface is covered with non-woven fabric to retain moisture and reduce erosion of seeds by rainfall, thus promoting seed growth. If temperatures are too high, covering is not necessary to prevent pests and diseases. Once the lawn reaches approximately 5 cm in thickness, the non-woven fabric can be removed. This stage is the final maintenance phase of slope vegetation restoration. Proper covering and management can effectively promote vegetation growth, ensuring long-term slope stability and ecological restoration.

[0028] The present invention is applicable to the reinforcement of general railway projects, highway projects and other common types of slope projects as well as slopes with ecological greening protection requirements.

[0029] In summary, this construction method uses microbial mineralization to generate calcium carbonate crystals that form a symbiotic network with the grass seed roots, achieving dual protection of "rigid reinforcement-flexible soil consolidation". When the vegetation coverage rate reaches more than 85%, it can resist runoff erosion. The laying of the three-dimensional vegetation net enables the plant roots and the soil to form a reinforced structure, improving the shallow anti-slip ability. The combination of granulated blast furnace slag powder and microbial metabolites can reduce the free expansion rate of expansive soil by more than 40%. At the same time, the silicon and aluminum components in the slag react with the soil to generate gelling substances, improving the pore structure of the soil. Microbial agents can also adjust the soil pH value, promote the secretion of organic acids by plant roots, and further stabilize the soil. The sprayed slurry forms a 12 cm thick rigid-flexible composite layer, and its shear strength is increased by 30-50%. The nylon vegetation net Shallow reinforcement can block 97.5% of slope erosion. Microbial-induced calcium carbonate deposition fills cracks and effectively inhibits the shrinkage and swelling cycle of expansive soil. The combination of slope top intercepting ditch, slope drainage trough and three-dimensional vegetation net can control the soil moisture content fluctuation within ±3%, reducing the risk of uneven cracking. The low permeability of clay layer and slag-based materials can isolate water infiltration. The spray slurry and vegetation net are laid in a standardized ratio. Workers can operate without special training, which saves costs compared with traditional mortar-laid stone slope protection. High-pressure sterilization culture medium and prefabricated mixture shorten site preparation time and improve construction efficiency. The flexible protective layer allows 3-5cm slope deformation, avoids structural damage by releasing expansion stress, and reduces maintenance frequency by 80% compared with rigid slope protection. The microbial active layer has a pH of 1. Continuous mineralization within the range of 7.3-9.0 can achieve long-term protection for more than 3 years. The mixture is adaptable to various matrices such as expansive soil, silt, and clay soil. The different expansion potential levels can be adapted by adjusting the amount of slag powder. The combination of ryegrass and alfalfa in the grass seed mixture can achieve rapid coverage in 30 days in soil with a pH of 6.5-8.5. Non-woven fabric covering and maintenance can increase the grass seed survival rate to more than 90% in the rainy season. In the hot season, the exothermic reaction can be controlled by adjusting the urea concentration of the binder to avoid microbial inactivation.

[0030] The above embodiments are only used to illustrate the technical method of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical method of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical method of the present invention.

Claims

1. A construction method for ecological protection of expansive soil slopes, comprising the following steps: Phase 1: Detecting basic physical indicators of soil and conducting test analysis; Phase II: Preparation of culture medium and microbial solution containing yeast extract, ammonium sulfate and buffer; The third stage: preparation of cementing fluid mainly composed of calcium chloride and urea; Stage 4: preparing a mixture containing slag powder, fly ash and soil; Stage 5: Mixing the mixture, microbial solution and cementing fluid to prepare the spraying slurry; Phase 6: Laying vegetation nets, setting up drainage systems, and laying nylon vegetation nets; Stage 7: preparing a mixture containing grass seeds, adhesive, moisturizer and water; The eighth stage: spraying construction, mixing the slurry and grass seed mixture evenly and spraying it onto the slope surface; The ninth stage: covering and maintenance, covering the slope surface with non-woven fabric after construction.

2. A construction method for ecological protection of expansive soil slopes according to claim 1, characterized in that: In the first stage, the soil's natural moisture content, density, pH value, liquid limit, plastic limit, plasticity index and free expansion rate were tested in accordance with the "Highway Geotechnical Test Code".

3. A construction method for ecological protection of expansive soil slopes according to claim 1, characterized in that: In the second stage, the solutes of the culture medium mainly include 20 g / L yeast extract, 20 g / L ammonium sulfate, and 0.13 mol / L Tris buffer solution. 10 kg of yeast extract, 5 kg of ammonium sulfate, and 1.55 kg of buffer solution are weighed and mixed with water in a ratio of 1:5 to form a liquid culture medium. The pH is adjusted to 9, and the medium is sterilized by autoclaving at 120° C. and then cooled to 28° C. The microbial solution is prepared by activating the freeze-dried powdered bacteria, inoculating one portion of Bacillus pasteurianus into the culture medium, and culturing the culture medium at 220 rpm in a 28°C constant temperature box for more than 36 hours until the temperature reaches 3.50D. 600 Up to 3.

5.

4. A construction method for ecological protection of expansive soil slopes according to claim 1, characterized in that: In the third stage, the solutes are calcium chloride and urea, and 240 kg of urea and 240 kg of calcium chloride are weighed and mixed with water to prepare a 2 mol / L cementing fluid.

5. A construction method for ecological protection of expansive soil slopes according to claim 1, characterized in that: In the fourth stage, the main components include 18 tons of granulated blast furnace slag powder, 2 tons of fly ash, and 40 tons of soil, which are mixed and stirred evenly, and are suitable for expansive soil, silt soil, clay soil or planting soil.

6. A construction method for ecological protection of expansive soil slopes according to claim 1, characterized in that: In the fifth stage, 500-1200 cubic meters of mixed material, 1 cubic meter of microbial solution, and 10 cubic meters of binder are weighed, mixed and stirred evenly, and then the binder and water are added to prepare the improved spray slurry.

7. A construction method for ecological protection of expansive soil slopes according to claim 1, characterized in that: In the sixth stage, the slope is leveled, debris is cleared, drainage channels and intercepting ditches are set, and nylon vegetation nets are laid from top to bottom, extending 40 to 80 cm from the top of the slope and fixed with U-shaped steel bars at intervals of 1.5 to 2.5 m.

8. A construction method for ecological protection of expansive soil slopes according to claim 1, characterized in that: In the seventh stage, the grass seeds are mixed with the adhesive, wood fiber, fertilizer, growth hormone, moisturizer and water to form a uniform grass seed mixture, wherein the grass seeds are 25 grams per square meter.

9. A construction method for ecological protection of expansive soil slopes according to claim 8, characterized in that: In the eighth stage, after the vegetation net is laid, the improved slurry and grass seed mixture are mixed and hydraulically sprayed onto the slope surface, 4 cm each time, for a total of 3 times, with a total thickness of not less than 12 cm, and construction is carried out in sequence.

10. The construction method for ecological protection of expansive soil slopes according to claim 1, characterized in that: In the ninth stage, after the spraying construction, the non-woven fabric is covered to retain moisture and reduce rainfall erosion. When the temperature is high, there is no need to cover it to avoid pests and diseases. When the lawn grows to 5 cm, the non-woven fabric is uncovered.

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