Precise grouting reinforcement method based on MICP

Abstract

The invention discloses a precise grouting reinforcement method based on MICP, which comprises the following steps: S1, a grouting conduit is arranged in a soil body, the soil body is silty soil, and the permeability coefficient of the silty soil is (1.15-1.25) * 10 <-5 > m / s; s2, the prepared bacterial liquid and cementing liquid are mixed to obtain slurry, then the slurry is injected into the soil body through a grouting guide pipe, and the injection process comprises the steps that grouting is conducted for 0.15-0.25 min at the pressure of 0.22-0.26 MPa, so that a to-be-reinforced area with the pore pressure gradually decreased in the peripheral diffusion direction with the grouting guide pipe as the center within a certain range is formed in a target reinforcing layer of the soil body, and the to-be-reinforced area with the pore pressure gradually decreased in the peripheral diffusion direction with the grouting guide pipe as the center is formed; and then secondary grouting is conducted on the area to be reinforced at the pressure of 0.14-0.16 MPa. The problems of slurry loss and non-uniform distribution in a traditional MICP technology can be solved, the retention rate of bacterial liquid in the soil body is larger than 95%, the calcium carbonate distribution CV is smaller than or equal to 0.12, and the strength of the soil body is improved to about 50%.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering reinforcement technology, and in particular to a precise grouting reinforcement method based on MICP. Background Technology

[0002] Microbial-induced calcium carbonate precipitation (MICP) is an emerging green soil and rock reinforcement technology. It utilizes the metabolic activity of microorganisms to produce calcium carbonate precipitates, which cement loose soil particles, thereby improving the mechanical properties of the soil. Traditional MIP reinforcement methods often involve directly injecting the bacterial solution and nutrients (cementing agents) into the soil at constant injection parameters or transporting them into the soil through pre-buried pipelines. This method has significant drawbacks: the slurry containing the bacterial solution is easily lost with groundwater, resulting in low utilization; and the constant injection pressure easily creates dominant seepage channels in the soil, further exacerbating the problems of slurry loss and uneven distribution.

[0003] In view of this, it is necessary to design a precision grouting reinforcement method based on MICP to solve the above problems. Summary of the Invention

[0004] The purpose of this invention is to provide a precise grouting reinforcement method based on MICP to solve the problems of grout loss and uneven distribution in traditional MICP technology.

[0005] To achieve the above-mentioned objectives, this invention provides a precise grouting reinforcement method based on MICP, comprising the following steps: S1. The grouting pipe is laid in the soil, which is silty sand with a permeability coefficient of (1.15-1.25)×10. -5 m / s; S2. After mixing the prepared bacterial solution and cementing solution to obtain grout, inject it into the soil through the grouting pipe. The injection process is as follows: first, grout at a pressure of 0.22-0.26 MPa for 0.15-0.25 minutes to form a certain range of the area to be reinforced in the target reinforcement layer of the soil, with the pore pressure gradually decreasing in the direction of diffusion from the grouting pipe as the center. Then, grout the area to be reinforced a second time at a pressure of 0.14-0.16 MPa.

[0006] As a further improvement of the present invention, the grouting conduit is specifically installed in the soil as follows: the distance between the bottom end of the grouting conduit and the bottom surface of the target reinforcement layer is 1 / 2 to 2 / 3 of the thickness of the target reinforcement layer.

[0007] As a further improvement of the present invention, the grouting conduit is provided with a plurality of grouting holes at intervals on the pipe section into which the target reinforcement layer is inserted.

[0008] As a further improvement of the present invention, the diameter of the grouting hole is 1-2 mm.

[0009] As a further improvement of the present invention, the bacterial solution is a suspension of Bacillus pasteurellii spores with a concentration of 1×10⁻⁶. 8 -5×10 8 CFU / mL; the cementing solution contains 0.5-1.0M urea and 0.5-1.0M calcium chloride.

[0010] As a further improvement of the present invention, the mixing ratio of the bacterial solution and the cementing solution is 1:0.9-1.1.

[0011] As a further improvement of the present invention, the bacterial solution is stored in a constant-temperature bacterial solution storage tank to maintain the activity of the bacterial solution.

[0012] As a further improvement of the present invention, the constant temperature storage temperature of the bacterial solution is 18-22℃.

[0013] As a further improvement of the present invention, the pressure control accuracy during the grouting process is not less than ±0.01MPa.

[0014] The beneficial effects of this invention are: This invention establishes a two-stage grouting method of "high-pressure short-time activation followed by low-pressure steady-state diffusion." This method first forms a certain area in the soil to be reinforced, with the pore pressure gradually decreasing in the direction of diffusion from the grouting conduit. The pressure change field provides the driving force for the grout to diffuse outward from the center of the grouting conduit. Then, low-pressure grouting allows the grout to continuously and uniformly fill the pores of the soil under the driving force of the pressure gradient. This avoids the situation where the dominant seepage channels caused by the existing constant grouting pressure affect the uniformity of grouting and cause grout loss. As a result, the grouting method of this invention can effectively improve the bacterial solution retention rate, the uniformity of calcium carbonate distribution, and the soil strength, resulting in a bacterial solution retention rate of >95%, a calcium carbonate distribution CV ≤0.12, and a soil strength increase of approximately 50%. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of precision grouting reinforcement based on MICP.

[0016] Figure Labels 10. Surface compacted soil layer; 20. Target reinforcement layer; 30. Underlying layer; 40. Area to be reinforced; 50. Grouting pipe. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0018] It should also be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and / or processing steps closely related to the present invention are shown in the accompanying drawings, while other details that are not closely related to the present invention are omitted.

[0019] Additionally, it should be noted that the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0020] Example 1 like Figure 1 As shown, this embodiment provides a precise grouting reinforcement method based on MICP. Taking the reinforcement of weak silty sand subgrade as an example, a soil trench is prepared with dimensions of 1.0m × 1.0m × 2.8m and an internal filling permeability coefficient of 1.2 × 10⁻⁶. -5 The soil is silty sand with a density of m / s. Three layers are formed in the trench: a 0.5m thick surface compacted soil layer 10, a 1.0m thick reinforcement layer 20, and a 2.0m thick underlying layer 30. Includes the following steps: S1. The grouting pipe 50 is laid in the soil such that the distance between the bottom end of the grouting pipe 50 and the bottom surface of the target reinforcement layer 20 is 0.4m; wherein, multiple grouting holes are provided at intervals on the pipe section of the grouting pipe 50 inserted into the target reinforcement layer 20, and the diameter of the grouting holes is 1-2mm. S2, Prepare a concentration of 1×10 8 CFU / mL Bacillus pasteurellii spore suspension and a cementitious solution containing 0.5M urea and 0.5M calcium chloride were mixed in a 1:1 ratio and injected into the soil through grouting pipe 50. The injection process was as follows: first, grouting was carried out at a pressure of 0.24MPa for 0.2min to activate the area to be reinforced 40 under high pressure, and then grouting was carried out at a pressure of 0.15MPa to achieve low-pressure steady-state diffusion in the area to be reinforced 40. The total amount of grout injected in the two-stage grouting process was 12mL.

[0021] Examples 2-7 and Comparative Examples 1-8 Examples 2-7 and Comparative Examples 1-8 provide a precise grouting reinforcement method based on MICP. Compared with Example 1, Examples 2-7 and Comparative Examples 1-8 have adjusted the grouting pressure and time during the grouting process. The specific adjustment parameters are shown in Table 1. The remaining steps are the same as in Example 1 and will not be repeated here.

[0022] Comparative Examples 9-10 Comparative Examples 9 and 10 respectively provide a precise grouting reinforcement method based on MICP. Compared with Example 1, Comparative Example 9 only uses a constant pressure of 0.2MPa to grout 12mL, and the remaining steps are the same as those in Example 1, which will not be repeated here.

[0023] Compared with Example 1, Comparative Example 10 used grouting at a pressure of 0.2 MPa for 5 intervals, with each grouting time being 0.25 min and an interval of 5 min between adjacent groutings. The total grouting volume was 12 mL. The remaining steps were the same as in Example 1, and will not be repeated here.

[0024] Seven days after grouting was completed, the soil from the reinforcement zone 40 of Examples 1-7 and Comparative Examples 1-10 was taken out for relevant performance tests. Some test results are shown in Table 1. Among them, the bacterial solution retention rate is the ratio of the grout in the reinforcement zone 40 to the total grout after grouting was completed seven days later. The cv value is the cv value of calcium carbonate distribution in the reinforcement zone 40. The strength improvement is (strength of the reinforcement zone 40 after grouting was completed seven days later - strength without grouting) / strength without grouting. The initial influence radius is the radius of the reinforcement zone 40 formed by high pressure short-term activation. The reinforced body is the soil after two-stage grouting.

[0025] Table 1. Relevant parameters and test results of Examples 1-7 and Comparative Examples 1-8

[0026] As shown in Table 1, in Examples 1-3, when the grouting pressure during the high-pressure short-time activation stage was controlled at 0.22-0.26 MPa, the bacterial solution retention rate was above 95%, the calcium carbonate distribution CV value was below 0.12, and the strength increased by 45-52%. The initial influence radius in the soil was 15 cm, and no dominant seepage channels were formed in the soil. In Comparative Examples 1-4, when the grouting pressure during the high-pressure short-time activation stage was controlled at less than 0.22 MPa or greater than 0.26 MPa, the CV value increased, and the corresponding bacterial solution retention rate decreased. The grouting rate decreased to varying degrees, and the strength improvement also decreased to varying degrees. In Comparative Example 1, when the grouting pressure during the high-pressure short-time activation stage was 0.18 MPa, the initial influence radius was only 8 cm, and the grouting effect was poor. When the grouting pressure during the high-pressure short-time activation stage was 0.28 MPa, slight scouring signs appeared in the soil, that is, the particles in the soil moved slightly, indicating that there was slight channelization in the soil. When the grouting pressure during the high-pressure short-time activation stage was 0.30 MPa, obvious channelization appeared in the soil.

[0027] In Examples 1 and 4 and 5, when the grouting time of the high-pressure short-time activation stage was controlled at 0.15-0.25 min, the CV value was below 0.1 and the initial influence radius was above 13 cm, while no channeling was formed in the soil. In Comparative Example 5, when the grouting time of the high-pressure short-time activation stage was controlled at 0.1 min, the initial influence radius was small and the CV value increased. In Comparative Example 6, when the grouting time of the high-pressure short-time activation stage was controlled at 0.3 min, although the initial influence radius increased, slight channeling began to appear in the soil, and the CV value increased.

[0028] In Examples 1 and 6 and 7, when the grouting pressure during the low-pressure steady-state diffusion stage is controlled at 0.14-0.16 MPa, the grout forms a stable laminar flow in the soil, the solidified body in the soil is nearly spherical or uniformly spherical, and the cv value is below 0.11, and the distribution of grout in the soil is relatively uniform. In Comparative Example 7, when the grouting pressure during the low-pressure steady-state diffusion stage is 0.12 MPa, the solidified body in the soil develops vertically into an ellipsoid, and the cv value increases. In Comparative Example 8, when the grouting pressure during the low-pressure steady-state diffusion stage is 0.20 MPa, the solidified body in the soil exhibits a significantly non-uniform shape, and the cv value reaches 0.28. At the same time, the particles in the soil begin to transfer and gradually form channels, and the grout is unevenly distributed and has a certain degree of loss.

[0029] In Comparative Example 9, when single-stage constant-pressure grouting was used, dominant channels were rapidly formed in the soil, with a cv value of 0.24, a bacterial solution retention rate of only 86.5%, and a limited strength increase of 31%. In Comparative Example 10, when multiple intermittent grouting was used, although the cv value decreased to 0.20, and the bacterial solution retention rate increased compared to single-stage constant-pressure grouting (bacterial solution retention rate of 90.2% and strength increase of 37%), the same pressure each time still strengthened the original channels, resulting in a lower bacterial solution retention rate and strength increase than the method of this invention.

[0030] The two-stage grouting method of the present invention, which is "high pressure short-time activation followed by low pressure steady-state diffusion", utilizes high pressure to quickly establish a pore pressure gradient, and then achieves uniform diffusion through low pressure. This avoids the formation of channels in the soil, effectively improves the retention rate of bacterial solution in the soil, the uniformity of calcium carbonate distribution, and the soil strength, resulting in a significant soil reinforcement effect.

[0031] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A precise grouting reinforcement method based on MICP, characterized in that, Includes the following steps: S1. The grouting pipe is laid in the soil, which is silty sand with a permeability coefficient of (1.15-1.25)×10. -5 m / s; S2. After mixing the prepared bacterial solution and cementing solution to obtain grout, inject it into the soil through the grouting pipe. The injection process is as follows: first, grout at a pressure of 0.22-0.26 MPa for 0.15-0.25 minutes to form a certain range of the area to be reinforced in the target reinforcement layer of the soil, with the pore pressure gradually decreasing in the direction of diffusion from the grouting pipe as the center. Then, grout the area to be reinforced a second time at a pressure of 0.14-0.16 MPa.

2. The precise grouting reinforcement method based on MICP according to claim 1, characterized in that: The grouting conduit is installed in the soil in such a way that the distance between the bottom end of the grouting conduit and the bottom surface of the target reinforcement layer is 1 / 2 to 2 / 3 of the thickness of the target reinforcement layer.

3. The precise grouting reinforcement method based on MICP according to claim 2, characterized in that: The grouting conduit has multiple grouting holes spaced apart on the pipe section into which it is inserted to reinforce the target layer.

4. The precise grouting reinforcement method based on MICP according to claim 3, characterized in that: The diameter of the grouting hole is 1-2 mm.

5. The precise grouting reinforcement method based on MICP according to claim 1, characterized in that: The bacterial solution is a suspension of Bacillus pasteurellii spores with a concentration of 1×10⁻⁶. 8 -5×10 8 CFU / mL.

6. The precise grouting reinforcement method based on MICP according to claim 1, characterized in that: The cementing solution contains 0.5-1.0M urea and 0.5-1.0M calcium chloride.

7. The precise grouting reinforcement method based on MICP according to claim 1, characterized in that: The mixing ratio of the bacterial solution and the cementing solution is 1:0.9-1.

1.

8. The precise grouting reinforcement method based on MICP according to claim 1, characterized in that: The bacterial solution is stored in a temperature-controlled bacterial solution tank to maintain its activity.

9. The precise grouting reinforcement method based on MICP according to claim 8, characterized in that: The bacterial solution is stored at a constant temperature of 18-22℃.

10. The precise grouting reinforcement method based on MICP according to claim 1, characterized in that: The pressure control accuracy during the grouting process shall not be less than ±0.01MPa.

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