Microorganism-based method for reinforcing swelling soil slope sliding surface

Abstract

The application discloses a swelling soil slope sliding surface directional reinforcement method based on a microbial technology, relates to the technical field of geotechnical engineering, and comprises the following steps: S1, sliding surface position analysis: numerical analysis software is used to calculate the stability of a slope, and the position of the sliding surface of the slope under the action of gravity stress is predicted; S2, swelling soil preparation: swelling soil samples are selected, and first swelling soil and second swelling soil are prepared; the first swelling soil is swelling soil treated by a microorganism, and the shear strength and impermeability of the first swelling soil are higher than those of the second swelling soil; S3, layered filling and directional reinforcement: in the process of filling the slope model, the slope model is filled in layers; the first swelling soil is used to fill the region above the sliding surface, and the second swelling soil is used to fill the region below the sliding surface, so as to solve the problems in the prior art, through analysis of the position of the sliding surface, the swelling soil with higher shear strength and impermeability is used to fill the key region, and the optimization and improvement of the stability of the slope are realized.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering technology, and in particular to a method for directional reinforcement of the sliding surface of expansive soil slopes based on microbial technology. Background Technology

[0002] Expansive soil, as a typical environmentally sensitive soil and rock material, exhibits engineering properties significantly affected by changes in moisture content. Its composition, rich in highly hydrophilic clay minerals such as montmorillonite, gives it unique swelling and shrinking characteristics: when absorbing water, the interlayer water film thickens, generating swelling stress; when losing water, the attractive forces between particles cause volume shrinkage. This repeated volume deformation creates a non-uniform stress field within the soil, promoting the initiation and expansion of fracture networks and significantly weakening the soil's structural integrity.

[0003] Under the influence of climatic factors, expansive soil slopes undergo a dynamic process of water transport. Rainfall infiltration not only causes the dissipation of matrix suction but also generates expansion pressure through mineral interlayer hydration, altering the soil stress state. Subsequent evaporation leads to the development of shrinkage cracks, forming dominant seepage channels. This positive feedback mechanism formed by alternating wet and dry conditions continuously exacerbates the deterioration of the mechanical properties of slope soil and rock materials, ultimately inducing progressive failure. That is, expansive soil, rich in hydrophilic clay minerals such as montmorillonite, exhibits significant wet-swell and dry-shrinkage characteristics, making it prone to cracking under wet-dry cycles, leading to a decrease in slope stability. Traditional slope reinforcement methods include frame beams, anchor bolts, and grouting, but these methods are often applied globally, resulting in material waste and uneven reinforcement effects.

[0004] Microbial induced calcium carbonate precipitation (MICP) technology, as a novel bio-based geotechnical reinforcement method, utilizes urease-producing bacteria to decompose urea into calcium carbonate crystals, effectively cementing soil particles and improving soil shear strength and impermeability. It has been applied in soil solidification and foundation reinforcement. However, existing MIP technologies mostly employ post-grouting or surface spraying methods, limiting their engineering application effectiveness. Summary of the Invention

[0005] The purpose of this invention is to provide a method for directional reinforcement of the sliding surface of expansive soil slopes based on microbial technology, in order to solve the problems existing in the prior art. By analyzing the location of the sliding surface, expansive soil with stronger shear strength and impermeability is used to fill the key areas, thereby optimizing and improving the stability of the slope.

[0006] To achieve the above objectives, the present invention provides the following solution: The present invention provides a method for directional reinforcement of the sliding surface of expansive soil slopes based on microbial technology, comprising the following steps: S1. Sliding surface location analysis: Numerical analysis software is used to calculate the stability of the slope and predict the location of the sliding surface of the slope under the action of self-weight stress. S2. Preparation of expansive soil: Select expansive soil samples and prepare the first expansive soil and the second expansive soil. The first expansive soil is expansive soil that has been treated with microorganisms, and the shear strength and impermeability of the first expansive soil are higher than those of the second expansive soil. S3. Layered filling and directional reinforcement: During the slope model filling process, the slope model is filled in layers. The area above the sliding surface is filled with the first expansive soil, and the area below the sliding surface is filled with the second expansive soil.

[0007] Optionally, in step S2, the first expansive soil is expansive soil treated with MICP or expansive soil treated with EICP.

[0008] Optionally, the first expansive soil is expansive soil treated with MICP. In the process of preparing the first expansive soil, the moisture content of the expansive soil sample is first measured, and bacterial solution and cementing solution are prepared according to the difference between the optimal moisture content and the actual moisture content. The bacterial solution and cementing solution are added to the expansive soil sample and stirred thoroughly to obtain the expansive soil treated with microorganisms.

[0009] Optionally, in step S2, the second expansive soil is expansive soil mixed with deionized water.

[0010] Optionally, in the process of preparing the second expansive soil, the moisture content of the expansive soil sample is first measured, and deionized water is prepared according to the difference between the optimal moisture content and the actual moisture content. The deionized water is added to the expansive soil sample and stirred thoroughly to obtain expansive soil mixed with deionized water.

[0011] Optionally, in step S2, the selected expansive soil sample is first dried, and then crushed and sieved.

[0012] Optionally, after completing step 3, the slope model is cured: after the slope model is filled, it is left to stand still.

[0013] Optionally, after completing the maintenance steps, the slope model can be verified: the changes in the sliding surface position and stress distribution can be verified using the numerical analysis software.

[0014] Optionally, in the step of validating the slope model, a wet-dry cycle test is also conducted on the slope model to evaluate the reinforcement effect.

[0015] Optionally, during the wet-dry cycle test on the slope model: an artificial rainfall device is used to simulate rainfall on the slope model, and the time required for static setting is recorded to indicate crack development; then a drying device is used to dry the slope model, and the time required for drying is recorded to indicate crack changes during the drying process; the number of cycles required is then compared with the crack development of the reference slope model.

[0016] The present invention achieves the following technical effects compared to the prior art: This invention discloses a method for directional reinforcement of the sliding surface of expansive soil slopes based on microbial technology. The method uses numerical analysis software to predict the location of the sliding surface and, during the filling process, uses first expansive soil with stronger shear strength and impermeability to fill the area above the sliding surface, and second expansive soil with relatively lower shear strength and impermeability to fill the area below the sliding surface. By directionally reinforcing key areas, the method ensures a uniform increase in soil strength of the slope model, improves the overall stability of the slope model, and reduces material waste and environmental impact. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the sliding surface location of the slope model before MICP reinforcement, as disclosed in one example of the present invention. Figure 2 This is a schematic diagram of the sliding surface location of a slope model reinforced with MICP, as shown in one example disclosed in this invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] The purpose of this invention is to provide a method for directional reinforcement of the sliding surface of expansive soil slopes based on microbial technology, in order to solve the problems existing in the prior art. By analyzing the location of the sliding surface, expansive soil with stronger shear strength and impermeability is used to fill the key areas, thereby optimizing and improving the stability of the slope.

[0021] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0022] like Figures 1 to 2 As shown, this invention provides a method for directional reinforcement of the sliding surface of expansive soil slopes based on microbial technology, comprising the following steps: S1. Sliding surface location analysis: Numerical analysis software is used to calculate the stability of the slope and predict the location of the sliding surface of the slope under the action of self-weight stress. S2. Preparation of expansive soil: Select expansive soil samples and prepare the first expansive soil and the second expansive soil. The first expansive soil is expansive soil that has been treated with microorganisms, and the shear strength and impermeability of the first expansive soil are higher than those of the second expansive soil. S3. Layered filling and directional reinforcement: During the slope model filling process, the slope model is filled in layers. The area above the sliding surface is filled with the first expansive soil, and the area below the sliding surface is filled with the second expansive soil; thus achieving directional reinforcement of the sliding surface area.

[0023] Among them, the stability calculation of the slope and the prediction of the location of the sliding surface of the slope under the action of self-weight stress can be carried out using, but not limited to, OptumG2 numerical analysis software.

[0024] This invention discloses a method for directional reinforcement of the sliding surface of expansive soil slopes based on microbial technology. The method uses numerical analysis software to predict the location of the sliding surface and, during the filling process, uses first expansive soil with stronger shear strength and impermeability to fill the area above the sliding surface, and second expansive soil with relatively lower shear strength and impermeability to fill the area below the sliding surface. By directionally reinforcing key areas, the method ensures a uniform increase in soil strength of the slope model, improves the overall stability of the slope model, and reduces material waste and environmental impact.

[0025] To ensure the shear strength and impermeability of the first expansive soil, based on the above implementation method, in step S2, the first expansive soil is either MICP-treated or EICP-treated. MICP treatment utilizes live bacteria to induce the generation of calcium carbonate and cementing soil particles; EICP treatment utilizes free urease to catalyze the generation of calcium carbonate and cementing soil particles. This enables directional reinforcement using microbially treated expansive soil. Utilizing microbial mineralization technology reduces the use of chemical reinforcing agents, lowering environmental impact and engineering costs. Furthermore, wet-dry cycle tests have verified that areas filled with pre-mixed MICP or pre-mixed EICP expansive soil show significantly reduced crack development and enhanced slope stability.

[0026] In some cases, the first expansive soil is expansive soil treated with MICP. In the process of preparing the first expansive soil, the moisture content of the expansive soil sample is first measured. Based on the difference between the optimal moisture content and the actual moisture content, the bacterial solution and cementing solution are prepared. The bacterial solution and cementing solution are added to the expansive soil sample and stirred thoroughly to obtain expansive soil treated with microorganisms.

[0027] For the addition of bacterial solution and cementing solution, they can be added all at once and thoroughly stirred to bring the expansive soil sample to its optimal moisture content. Alternatively, they can be added in multiple batches, again with thorough stirring, to achieve the same optimal moisture content. This multiple-batch addition avoids the inhibition of microbial activity caused by a single high concentration of substrate, maintaining continuous and efficient microbial metabolism, and preventing rapid clogging of pores in the early stages of the reaction, thus ensuring uniform distribution of the cementing material. Furthermore, to further guarantee the uniformity of the bacterial solution and cementing solution addition, they can be added via spraying.

[0028] In a specific example, the bacterial solution and cementing solution can be, but are not limited to, *Pasteurella multocida* bacterial solution and urea-calcium chloride cementing solution. The MICP technique involves injecting *Pasteurella multocida* bacterial solution and urea-calcium chloride cementing solution into an expansive soil sample. The bacteria secrete urease, which catalyzes the hydrolysis of urea, generating carbonate ions, which then combine with calcium ions to form calcium carbonate crystals. These calcium carbonate crystals firmly bind the loose particles of the expansive soil and effectively fill the pores, thereby significantly improving the shear strength and impermeability of the expansive soil.

[0029] In other cases, the first expansive soil is EICP-treated expansive soil. During its preparation, the moisture content of the expansive soil sample is first measured. The EICP reaction solution is then prepared based on the difference between the optimum and actual moisture content. The EICP reaction solution mainly consists of three parts: free urease as a catalyst, urea as a reaction substrate, and calcium chloride solution as a calcium source. The prepared EICP reaction solution is uniformly injected or mixed into the expansive soil sample. Curing is carried out under suitable temperature conditions. During this period, urease continuously catalyzes the hydrolysis of urea, and the generated carbonate ions combine with calcium ions to form calcium carbonate crystal precipitates in the soil pores. These crystals gradually grow and encapsulate and bridge soil particles, effectively cementing the soil and inhibiting its water absorption and swelling capacity, ultimately obtaining EICP-treated expansive soil with high shear strength and impermeability.

[0030] Based on the above implementation method, in step S2, the second expansive soil is expansive soil mixed with deionized water, i.e., ordinary expansive soil. It can be understood that directional filling is achieved by filling the area above the sliding surface with microbially treated expansive soil and the area below the sliding surface with ordinary expansive soil, and then compacting them in layers.

[0031] In the process of preparing the second expansive soil, the moisture content of the expansive soil sample is first measured. Deionized water is prepared according to the difference between the optimal moisture content and the actual moisture content. The deionized water is added to the expansive soil sample and stirred thoroughly to obtain expansive soil mixed with deionized water.

[0032] The addition of deionized water can be done all at once, with thorough mixing to bring the expansive soil sample to its optimal moisture content; alternatively, it can be added in multiple batches, with thorough mixing, to bring the expansive soil sample to its optimal moisture content. It is understood that adding water in multiple batches can improve the uniformity of the expansive soil mixed with deionized water.

[0033] Furthermore, in step S2, the selected expansive soil sample is first dried, then crushed and sieved to ensure the dryness and fineness of the expansive soil sample before preparing the first and second expansive soils. By controlling its dryness, the uniformity and sufficiency of its crushing can be ensured. In turn, by controlling its sieving, its fineness can be ensured, thereby improving the quality of the first and second expansive soils.

[0034] In this embodiment, the selected expansive soil sample can be dried using a drying device or by natural drying.

[0035] More preferably, the selected expansive soil sample should be able to pass through a 5mm sieve.

[0036] Based on the above implementation method, after completing step 3, the slope model is cured: after the slope model is filled, it is left to stand still, which allows the internal stress distribution of the slope model to be uniform. It can be understood that in the example where the first expansive soil is expansive soil treated with microorganisms, the standing slope model can also ensure that its MIP and EICP reactions are sufficient.

[0037] Based on the above implementation methods, after completing the maintenance steps, the slope model is validated: the changes in the sliding surface position and stress distribution are verified using numerical analysis software. Taking expansive soil treated with EICP as an example, software analysis reveals that: firstly, combined with... Figure 1 and Figure 2 illustrate, Figure 1 and Figure 2 The diagrams show the changes in the sliding surface position of the slope model before and after MIP reinforcement. The sliding surface position did not change significantly, but the stress distribution at the junction of the slope crest and slope surface became more concentrated. This indicates that MIP reinforcement can improve the shear strength of expansive soil, slightly increasing the slope gravity multiplier, without significantly changing the sliding surface position. However, the stress distribution at the junction of the slope crest and slope surface changed, becoming more concentrated. Experiments show that the depth and number of cracks in the MIP-reinforced area were significantly reduced, the sliding surface position was stable, and the stress distribution was more concentrated, verifying the effectiveness and engineering applicability of this method.

[0038] To verify the changes in the sliding surface position and stress distribution, the Optum G2 numerical analysis software can be used, but is not limited to.

[0039] Based on the above implementation methods, in the step of verifying the slope model, the reinforcement effect is also evaluated by conducting wet-dry cycle tests on the slope model.

[0040] The process of conducting a wet-dry cycle test on the slope model is as follows: An artificial rainfall device is used to simulate rainfall on the slope model at an intensity of 60 mm / h for approximately 1 hour. The time required for settling is recorded to document crack development; this can be done for approximately 12 hours. Then, a drying device is used to dry the slope model for approximately 12 hours, and crack changes during the drying process are recorded. The number of cycles required is then compared with the crack development of a reference slope model, including the crack development process and depth, to demonstrate the effectiveness of the method of this invention.

[0041] The reference slope model can be a slope model that has not undergone directional reinforcement of key areas, or it can be an unreinforced area within the same slope model.

[0042] Furthermore, the drying device can use fluorescent lamps, etc., to simulate sunlight drying, but is not limited to fluorescent lamps.

[0043] Furthermore, to assess the development of cracks, a time-lapse camera can be placed above the slope model to record the crack development process on the slope model surface during water infiltration or drying.

[0044] In a specific example, during the wet-dry cycle test on the slope model, an artificial rainfall device was used to simulate rainfall of 60 mm / h for 1 hour. After the rainfall, the slope was left to stand for 12 hours to allow sufficient water runoff and infiltration. During this period, a time-lapse camera was placed above the slope model to record the development of cracks on the slope surface during water infiltration. After the standing period, a fluorescent lamp was used to simulate the drying process for 12 hours, and a time-lapse camera was used to record the development of cracks on the slope during the drying process. This constituted one wet-dry cycle, which was repeated 5 times. By comparing the crack development with that of a reference slope model, the effectiveness of the method of the present invention was demonstrated.

[0045] Any adaptive changes made according to actual needs are within the scope of protection of this invention.

[0046] It should be noted that, for those skilled in the art, it is obvious that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0047] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for directional reinforcement of the sliding surface of expansive soil slopes based on microbial technology, characterized in that, Includes the following steps: S1. Sliding surface location analysis: Numerical analysis software is used to calculate the stability of the slope and predict the location of the sliding surface of the slope under the action of self-weight stress. S2. Preparation of expansive soil: Select expansive soil samples and prepare first expansive soil and second expansive soil. The first expansive soil is expansive soil treated with microorganisms, and the shear strength and impermeability of the first expansive soil are higher than those of the second expansive soil. S3. Layered filling and directional reinforcement: During the slope model filling process, the slope model is filled in layers. The area above the sliding surface is filled with the first expansive soil, and the area below the sliding surface is filled with the second expansive soil.

2. The method for directional reinforcement of the sliding surface of expansive soil slopes based on microbial technology according to claim 1, characterized in that, In step S2, the first expansive soil is expansive soil treated with MICP or expansive soil treated with EICP.

3. The method for directional reinforcement of the sliding surface of expansive soil slopes based on microbial technology according to claim 2, characterized in that, The first expansive soil is expansive soil treated with MICP. In the process of preparing the first expansive soil, the moisture content of the expansive soil sample is first measured. Based on the difference between the optimal moisture content and the actual moisture content, bacterial solution and cementing solution are prepared. The bacterial solution and cementing solution are added to the expansive soil sample and stirred thoroughly to obtain the expansive soil treated with microorganisms.

4. The method for directional reinforcement of the sliding surface of expansive soil slope based on microbial technology according to claim 2, characterized in that, In step S2, the second expansive soil is expansive soil mixed with deionized water.

5. The method for directional reinforcement of the sliding surface of expansive soil slope based on microbial technology according to claim 4, characterized in that, In the process of preparing the second expansive soil, the moisture content of the expansive soil sample is first measured. Deionized water is prepared according to the difference between the optimal moisture content and the actual moisture content. The deionized water is added to the expansive soil sample and stirred thoroughly to obtain expansive soil mixed with deionized water.

6. The method for directional reinforcement of the sliding surface of expansive soil slope based on microbial technology according to claim 2 or 4, characterized in that, In step S2, the selected expansive soil sample is first dried, then crushed and sieved.

7. The method for directional reinforcement of the sliding surface of expansive soil slopes based on microbial technology according to claim 1, characterized in that, After completing step 3, the slope model is cured: after the slope model is filled, it is left to stand still.

8. The method for directional reinforcement of the sliding surface of expansive soil slope based on microbial technology according to claim 7, characterized in that, After completing the maintenance steps, the slope model was verified: the changes in the sliding surface position and stress distribution were verified using the numerical analysis software.

9. The method for directional reinforcement of the sliding surface of expansive soil slope based on microbial technology according to claim 8, characterized in that, In the step of validating the slope model, the reinforcement effect is also evaluated by conducting wet-dry cycle tests on the slope model.

10. The method for directional reinforcement of the sliding surface of expansive soil slope based on microbial technology according to claim 9, characterized in that, During the wet-dry cycle test on the slope model: an artificial rainfall device was used to simulate rainfall on the slope model, and the time required for static setting was recorded to indicate crack development; then a drying device was used to dry the slope model, and the time required for drying was recorded to indicate crack changes during the drying process; the number of cycles required was recorded, and the crack development was compared with that of the reference slope model.

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