Method and device for improving MICP foundation reinforcement uniformity

Abstract

The invention belongs to the technical field of geotechnical engineering soil body improvement, and relates to a method and device for improving MICP foundation reinforcement uniformity. According to the grouting method, a urease solution of bacillus pasteurii is firstly subjected to enlarged culture in an LB culture medium, and then grouting is conducted in a multi-round mode with the concentration of a cementing solution changed. According to the method, the initial activity of the urease solution is improved, and the reaction rate and the calcium carbonate crystallization position of the MICP technology are effectively regulated and controlled in combination with a multi-round variable cementing liquid concentration grouting process, so that the problem of non-uniform soil reinforcement caused by a traditional grouting mode is solved. The matched grouting device integrates the in-situ investigation function and the grouting function and comprises a grouting pump, a slurry box, a connecting pipe, an end cap, a center penetrating hammer, a grouting rod and a drop hammer blocking buckle. According to the device, the characteristics of the soil body can be evaluated through in-situ investigation, and grouting parameters are dynamically optimized according to the characteristics. According to the method, the foundation reinforcement uniformity and reliability can be remarkably improved, meanwhile, the engineering cost is reduced, and the construction period is shortened.

Description

Technical Field

[0001] This invention relates to the field of soil improvement technology in geotechnical engineering, and in particular to a method and apparatus for improving the uniformity of MICP foundation reinforcement. Background Technology

[0002] In the global trend towards green, low-carbon, and sustainable development, microbial-induced calcium carbonate precipitation (MICP) technology has demonstrated outstanding application potential in geotechnical engineering due to its significant environmental friendliness, low carbon footprint, and process controllability. Bacillus pasteurellii is a commonly used urease-producing microorganism in MIP technology. It synthesizes urease through metabolism, catalyzing the hydrolysis of urea in the cementing solution to produce CO3. 2- Then with Ca 2+ A biochemical reaction occurs, producing calcium carbonate (CaCO3) precipitate. CaCO3 precipitate can fill the pores between soil particles, coat soil particles, and connect adjacent particles, thereby improving the overall structural stability of the soil and ultimately achieving soil reinforcement.

[0003] In the cultivation of *Sporosarcina pasteurii*, inorganic nitrogen sources such as urea and ammonium chloride are typically added to the culture medium to promote its growth and reproduction. The supply of nitrogen sources effectively increases bacterial biomass and significantly enhances urease activity. Studies have shown that the urease activity of the bacterial solution is positively correlated with the mineralization reaction rate; the higher the urease activity, the faster the mineralization reaction rate, the greater the deposition of CaCO3 near the grouting port, and the higher the probability of grout blockage. Grout blockage not only wastes grouting materials and increases construction costs, but also leads to uneven diffusion of the reinforcing grout in the soil, significantly weakening the overall compressive strength and bearing capacity of the soil.

[0004] To address the issue of uneven soil reinforcement using MIP technology, patent publication number CN 113774897A discloses a method for solidifying sandy soil using low-pH mixed grouting. The core of this method is to delay the formation of calcium carbonate precipitation by adjusting the pH value of the grout. Patent publication number CN114592498A and patent authorization number CN 111441337 B respectively employ the introduction of urease inhibitors to slow down the reaction rate and prevent premature clogging of the grouting port. While these methods alleviate the grouting clogging problem to some extent, they increase operational complexity and material costs. Furthermore, acidic reagents may disrupt the soil's microecological balance, and exogenous inhibitors pose a risk of bioaccumulation. In addition, existing MIP foundation reinforcement technology requires prior geological surveys to locate the reinforcement area, followed by the installation of grouting devices using external power equipment to carry out soil reinforcement, resulting in long construction cycles, complex operations, and high costs. Summary of the Invention

[0005] To address the problems of grout blockage, uneven reinforcement effect, and complex construction and high installation cost of supporting devices in existing MIP technology, this invention provides a method and device for improving the uniformity of MIP foundation reinforcement.

[0006] To achieve the above objectives, this invention provides a method for improving the uniformity of MIP foundation reinforcement. *Bacillus pasteurellii* is activated in LB liquid medium containing an inorganic nitrogen source, and then transferred to LB medium at a volume ratio of 0.5%–2%. The culture is then carried out at a constant temperature of 25–30°C with shaking at 150–200 rpm for 18–24 hours until the bacterial OD600 reaches 1.0–1.8, completing the expansion culture. No additional inorganic nitrogen source needs to be added during the expansion culture process. By limiting the inorganic nitrogen source in the expansion culture medium, the urease activity of bacteria in the early stage of grouting can be effectively reduced, delaying the formation rate of calcium carbonate precipitation, thereby forming more extensive and uniformly distributed calcium carbonate nucleation sites.

[0007] Furthermore, the method also includes a multi-round variable-concentration grouting process. Specifically, the grout is prepared by mixing urea solution and calcium chloride solution of equimolar concentration in a 1:1 volume ratio, with both urea and calcium chloride concentrations ranging from 0.25 to 3 mol / L. The grouting process employs 3 to 7 rounds of variable-concentration grouting, with the grout concentration ranging from 0.5 to 1.5 mol / L. First, a low-concentration grout of 0.5 to 0.7 mol / L is injected to achieve initial uniform penetration and reinforcement of the soil. Subsequently, a high-concentration grout of 1.3 to 1.5 mol / L is injected to induce a rapid solidification effect. This process avoids the grouting blockage and material waste problems caused by traditional single high-concentration grout, and also solves the defects of insufficient calcium carbonate production and limited reinforcement strength caused by single low-concentration grout. This invention, through multi-round, staged concentration control, can significantly reduce engineering costs while ensuring reinforcement effectiveness.

[0008] A method for improving the uniformity of MICP foundation reinforcement includes the following steps:

[0009] The first step is bacterial activation culture: Sporosarcina pasteurii is inoculated into LB liquid medium (LBU medium) with urea added and activated culture is carried out under the condition of pH 6-9.

[0010] The second step is to expand the bacterial culture: the activated bacterial culture from step 1) is inoculated into LB liquid expansion medium at a volume ratio of 0.5% to 2%, and expanded under the condition of pH 7 to 9 to prepare the required bacterial culture.

[0011] The third step is the preparation of the cementing solution: Equimolar concentrations of urea solution and calcium chloride solution are mixed at a 1:1 volume ratio. The urea concentration is 0.25–3 mol / L, and the calcium chloride concentration is 0.25–3 mol / L.

[0012] The fourth step is the positioning and installation of the grouting device: the predetermined grouting point is located; the grouting device is assembled; and the grouting device is driven into the soil using the impact energy of the hammer (5). At the same time, the number of hammer blows and the penetration depth of each blow are recorded to assess the soil compaction, strength and uniformity.

[0013] Step 5, grouting preparation: Remove the end cap and mandrel from the top of the grouting device, and connect the grout tank and grouting pump to the grouting rod via connecting pipes; select the reinforcement mode according to the reinforcement requirements. If only axial reinforcement is required, pressurized grouting can be prepared directly, and then the grout will be injected into the soil through the grouting port at the end of the conical probe. If axial and radial reinforcement are required simultaneously, the grouting rod must be rotated first to move the sliding structure on the turntable, thereby pushing the telescopic segment into the soil.

[0014] Step 6, when the grouting operation is performed in stages:

[0015] Add the bacterial solution obtained in step 2) to the grout tank; start the grouting pump and inject the bacterial solution into the soil at a flow rate of 0.5-5 mL / min. The injection volume of the bacterial solution is 1-2 times the pore volume of the soil in the expected reinforcement area; after the bacterial solution injection is completed, let it stand for 1-3 hours; inject a cementing liquid of the same volume as the bacterial solution at the same flow rate of 0.5-5 mL / min; this process is one round of grouting.

[0016] When grouting operations employ mixed injection:

[0017] The bacterial solution obtained in step 2) is premixed with the cementing liquid to form a mixed slurry; the volume of the mixed slurry is 2 to 4 times the pore volume of the soil in the expected reinforcement area; the mixed slurry is added to the slurry tank; the grouting pump is started, and the mixed slurry is injected into the foundation from the top of the grouting device at a flow rate of 0.8 to 5 mL / min.

[0018] Step 7, Repeat grouting: After an interval of 12-36 hours, repeat the grouting process of step 6); in subsequent grouting rounds, the concentration of the binder is 0.5-1.5 mol / L, and the concentration of the binder increases with each grouting round, gradually increasing from low concentration to high concentration; a total of 3-7 rounds of grouting are performed.

[0019] Step 8, Secondary Measurement After Reinforcement: Three days after grouting is completed and cured, remove the grouting pump and grout tank, rotate the grouting rod to retract the telescopic segment, reinstall the end cap and mandrel, and extend the grouting rod. Perform post-reinforcement soil strength measurement according to the in-situ soil parameter measurement method.

[0020] Step 9: Remove the grouting device: Gradually remove the grouting device by striking it in the opposite direction with a hammer, and clean the grouting pipe.

[0021] A grouting device for improving the uniformity of MICP foundation reinforcement includes: a grouting pump, a grout tank, a connecting pipe, an end cap, a through hammer, a grouting rod, a drop hammer stop, a connecting sleeve, a turntable, a turntable drive component, a sliding structure, a telescopic segment, a segment grouting port, a probe, and a probe grouting hole.

[0022] During the installation phase, the mandrel weighs 8–64 kg, is raised to a preset height of 0.50–0.78 m, and then released. It falls freely, impacting the drop hammer stop, which drives the probe into the soil. Based on the relationship between the number of hammer blows (N) and the penetration depth (H), the in-situ soil strength parameters can be calculated. This process not only enables the dynamic installation of the grouting device but also simultaneously measures the in-situ soil strength parameters.

[0023] The grouting rod has a diameter of 25mm to 45mm and is made of high-carbon steel, alloy steel, or stainless steel. After entering the grouting stage, the end cap and mandrel are removed first, and the grouting rod is connected to the grout tank and grouting pump; axial and radial grouting can be performed simultaneously.

[0024] (I) Axial grouting: Grout is injected into the soil below through the grouting port of the cone probe to achieve end soil reinforcement; the probe diameter is 40mm to 75mm, and it is made of high carbon steel, alloy steel or stainless steel, etc. The grouting holes of the probe are arranged in a circumferential array at 2 / 3 of the length from the cone tip.

[0025] (II) Radial grouting: Rotating the grouting rod drives a turntable fixed to it, which in turn moves the sliding structure on the turntable, thus pushing the telescopic segment into the soil. During this process, the grouting hole of the grouting rod and the grouting branch pipe of the sliding structure are dynamically connected. Subsequently, grout is injected into the soil through the grouting port on the side wall of the telescopic segment, completing the soil reinforcement on the side of the device. The relationship between the torque of the grouting rod and the soil strength is as follows:

[0026]

[0027] In the formula, T is the torque, θ is the rotation angle, L is the extension / retraction displacement, and s is the displacement. u Where A is the undrained shear strength of the soil, and N is the area of ​​the expansion joint segment. c This is the bearing capacity coefficient.

[0028] After grouting is completed and cured for 3 days, the grouting pump and grout tank are removed, the grouting rod is rotated to retract the telescopic segment, the end cap and the mandrel are reinstalled, and the grouting rod is extended. Subsequently, according to the in-situ soil parameter measurement method, the soil strength of the reinforced area at the bottom of the probe is measured a second time using the hammering energy of the mandrel.

[0029] The beneficial effects of this invention are:

[0030] 1. This invention can improve the uniformity of foundation reinforcement and effectively alleviate the problem of grout blockage;

[0031] 2. The grouting device of the present invention does not require an external power source for installation, reducing the difficulty of operation and construction cost of the grouting device;

[0032] 3. The grouting device of the present invention integrates an in-situ survey module, which can adjust the concentration of the grout used for soil reinforcement and the grouting pressure in real time based on the obtained in-situ soil parameters. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of grouting at the end of the grouting device.

[0034] Figure 2(a) is a schematic diagram of grouting on the side of the grouting device.

[0035] Figure 2(b) shows the power installation diagram of the grouting device.

[0036] Figure 3 This is a detailed diagram of the probe structure.

[0037] Figure 4(a) shows a detailed diagram of the turntable shrinkage structure.

[0038] Figure 4(b) shows a detailed view of the turntable extension structure.

[0039] Figure 5(a) is a side view of the turntable shrinkage structure.

[0040] Figure 5(b) is a three-dimensional view of the turntable's shrinkage structure.

[0041] Figure 6 This is a schematic diagram of the grouting hole for the grouting rod.

[0042] In the diagram: 1-grouting pump, 2-grout tank, 3-connecting pipe, 4-end cap, 5-through hammer, 6-grouting rod, 7-falling hammer stop, 8-connecting sleeve, 9-turntable, 10-turntable drive component, 11-sliding structure, 12-telescopic segment, 13-segment grouting port, 14-probe, 15-probe grouting hole, 16-grouting rod grouting hole. Detailed Implementation

[0043] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings and technical solutions:

[0044] Example 1:

[0045] This invention provides a method for improving the uniformity of MICP foundation reinforcement, comprising the following steps:

[0046] 1) Inoculate Bacillus pasteurellii into LB liquid medium supplemented with urea and activate it at pH 7.

[0047] 2) Inoculate the activated bacterial solution into LB liquid medium at a volume ratio of 1%, and carry out scale-up culture at pH 7 to obtain the desired bacterial solution.

[0048] 3) Mix urea solution and calcium chloride solution with a concentration of 1 mol / L in a 1:1 volume ratio and set aside.

[0049] 4) Locate the grouting point; assemble the grouting device; lift the 10kg core hammer to a height of 0.5m and release it. The impact energy generated by its free fall will drive the grouting device into the soil; repeat the lifting and releasing until the installation depth of 5m is reached. Record the number of hammer blows N and the penetration depth per blow, calculate the penetration resistance, and evaluate parameters such as soil strength.

[0050] 5) Remove the end cap and the hammer at the top of the grouting device, and connect the grout tank and grouting pump to the grouting rod; rotate the grouting rod to move the sliding structure on the turntable, thereby pushing the telescopic segment into the soil to prepare for grouting.

[0051] 6) Add the bacterial solution obtained in step 2) to the grout tank; start the grouting pump and inject the bacterial solution into the silty sand at a flow rate of 1 mL / min. The injection volume of the bacterial solution is 1 times the pore volume of the soil in the expected reinforcement range; after the bacterial solution injection is completed, let it stand for 1 hour; then inject an equal volume of cementing liquid at the same flow rate.

[0052] 7) After a 24-hour interval, repeat the grouting process in step 6) for a total of 5 rounds of grouting. The concentration of the cementing solution increases from low to high: 0.5 mol / L → 0.75 mol / L → 1 mol / L → 1.25 mol / L → 1.5 mol / L.

[0053] 8) Three days after grouting is completed and cured, remove the grouting pump and grout tank, reinstall the end caps and through-hole hammer, and extend the grouting rod. Measure the soil strength in the reinforced area at the bottom of the probe a second time, following the in-situ soil parameter measurement method.

[0054] 9) End grouting and measurement: Gradually withdraw the grouting device by striking in the opposite direction with a through hammer, and clean the grouting pipe.

[0055] Example 2:

[0056] This invention provides a method for improving the uniformity of MICP foundation reinforcement, comprising the following steps:

[0057] 1) Inoculate Bacillus pasteurellii into LB liquid medium supplemented with urea and activate it at pH 7.5.

[0058] 2) Inoculate the activated bacterial solution into LB liquid medium at a volume ratio of 1%, and carry out scale-up culture at pH 7.5 to obtain the desired bacterial solution.

[0059] 3) Mix urea solution and calcium chloride solution of the same concentration at a 1:1 volume ratio and set aside. In the cementing solution, the urea concentration is 1 mol / L and the calcium chloride concentration is 1 mol / L.

[0060] 4) Locate the grouting point; assemble the grouting device; lift the 10kg mandrel to a height of 0.52m and release it. The impact energy generated by its free fall will drive the grouting device into the soil; repeat the lifting and releasing until the installation depth of 3m is reached. Record the number of hammer blows N and the penetration depth per blow, calculate the penetration resistance, and evaluate parameters such as soil strength.

[0061] 5) Grouting preparation: Remove the end cap and through hammer at the top of the grouting device, and connect the grout tank and grouting pump to the grouting rod of the power grouting device through the connecting pipe; only perform axial reinforcement preparation.

[0062] 6) Premix the bacterial solution obtained in step 2) with the cementing solution to form a mixed slurry; the volume of the mixed slurry is twice the pore volume of the soil in the expected reinforcement area; add the mixed slurry to the slurry tank; start the grouting pump and inject the mixed slurry into the sandy soil foundation from the top of the grouting device at a flow rate of 5 mL / min.

[0063] 7) After a 24-hour interval, repeat the mixing and grouting operation in step 6); a total of 3 rounds of grouting are performed, with the concentration of the cementitious liquid in the mixture increasing from 0.5 mol / L to 1 mol / L to 1.5 mol / L.

[0064] 8) Three days after grouting is completed and cured, remove the grouting pump and grout tank, reinstall the end caps and the mandrel, and extend the grouting rod. Based on the in-situ soil parameter measurement method, the soil strength of the reinforced area at the bottom of the probe is measured a second time using the hammering energy generated by the falling mandrel.

[0065] 9) End grouting and measurement: Gradually withdraw the grouting device by striking in the opposite direction with a through hammer, and clean the grouting pipe.

Claims

1. A method for improving the uniformity of MICP foundation reinforcement, characterized in that, Includes the following steps: Step 1, bacterial activation culture: Bacillus pasteurellii was inoculated into LB liquid medium supplemented with urea and activated culture was carried out under conditions of pH 6-9; The second step is to expand the bacterial culture: the activated bacterial culture from step 1) is inoculated into LB liquid expansion medium at a volume ratio of 0.5% to 2%, and expanded under the condition of pH 7 to 9 to prepare the required bacterial culture. The third step is the preparation of the cementing solution: urea solution and calcium chloride solution of equal molar concentration are mixed at a volume ratio of 1:1; wherein the concentration of urea is 0.25-3 mol / L and the concentration of calcium chloride is 0.25-3 mol / L. Step 4, grouting device positioning and installation: Position the predetermined grouting point; assemble the grouting device; use the impact energy of the through hammer (5) to penetrate the grouting device into the soil; at the same time, record the number of hammer blows and the penetration depth of each blow to evaluate the soil density, strength and uniformity. Step 5, grouting preparation: Remove the end cap (4) and the through hammer (5) at the top of the grouting device, and connect the grout tank (2) and the grouting pump (1) to the grouting rod (6) through the connecting pipe (3); select the reinforcement mode according to the reinforcement requirements. If only axial reinforcement is required, pressurized grouting can be prepared directly, and then the grout will be injected into the soil through the grouting port at the end of the conical probe; if axial and radial reinforcement are required at the same time, the grouting rod (6) needs to be rotated first to drive the sliding structure (11) on the turntable (9) to move, thereby pushing the telescopic segment (12) into the soil. Step 6, Grouting operation: When grouting is performed in stages: Add the bacterial solution obtained in step 2) to the grout tank; start the grouting pump (1) and inject the bacterial solution into the soil at a flow rate of 0.5-5 mL / min. The injection volume of the bacterial solution is 1-2 times the pore volume of the soil in the expected reinforcement area; after the bacterial solution injection is completed, let it stand for 1-3 hours; inject a cementing liquid of the same volume as the bacterial solution at the same flow rate of 0.5-5 mL / min; this process is one round of grouting. Step 7, Repeat grouting: After an interval of 12-36 hours, repeat the grouting process in step 6); in subsequent grouting rounds, the concentration of the binder is 0.5-1.5 mol / L, and the concentration of the binder increases with each grouting round, gradually increasing from low concentration to high concentration; a total of 3-7 rounds of grouting are performed; Step 8, secondary measurement after reinforcement: After grouting is completed and cured for 3 days, remove the grouting pump (1) and grout tank (2), rotate the grouting rod (6) to retract the telescopic segment (12), reinstall the end cap (4) and the through hammer (5), and extend the grouting rod (6); measure the strength of the reinforced soil according to the in-situ soil parameter measurement method. Step 9, remove the grouting device: gradually remove the grouting device by striking it in the opposite direction with a through hammer (5), and clean the grouting pipe.

2. The method for improving the uniformity of MIP foundation reinforcement as described in claim 1, characterized in that, In the sixth step, when the grouting operation uses mixed injection: The bacterial solution obtained in step 2) is premixed with the cementing liquid to form a mixed slurry; the volume of the mixed slurry is 2 to 4 times the pore volume of the soil in the expected reinforcement range; the mixed slurry is added to the slurry tank; the grouting pump (1) is started and the mixed slurry is injected into the foundation from the top of the grouting device at a flow rate of 0.8 to 5 mL / min.

3. The method for improving the uniformity of MIP foundation reinforcement as described in claim 1, characterized in that, The grouting device includes: a core hammer (5), a grouting rod (6), a telescopic tube segment (12), and a probe grouting hole (15); During the installation phase, the core hammer (5) is raised to a preset height of 0.50 to 0.78m and then released. It falls freely and impacts the drop hammer stop (7), causing the probe to penetrate into the soil. After entering the grouting stage, first remove the end cap (4) and the through hammer (5), and connect the grouting rod (6) to the grout tank (2) and the grouting pump (1); it can simultaneously perform axial grouting and radial grouting: After grouting is completed and cured for 3 days, the grouting pump (1) and grout tank (2) are removed, the grouting rod (6) is rotated to retract the telescopic tube segment (12), the end cap (4) and the through hammer (5) are reinstalled, and the grouting rod (6) is extended. Subsequently, according to the in-situ soil parameter measurement method, the soil strength of the reinforced area at the bottom of the probe is measured a second time using the hammering energy of the through hammer (5).

4. The method for improving the uniformity of MIP foundation reinforcement as described in claim 1, characterized in that, The weight of the core hammer (5) is 8-64 kg, and the diameter of the grouting rod (6) is 25 mm-45 mm. The material is high carbon steel, alloy steel or stainless steel.

5. The method for improving the uniformity of MICP foundation reinforcement as described in claim 3, characterized in that, The axial grouting is as follows: grout is injected into the soil below through the grouting port of the cone probe to reinforce the soil at the end; the grouting holes (15) of the probe are arranged in a circumferential array at a distance of 2 / 3 of the length from the cone tip.

6. The method for improving the uniformity of MICP foundation reinforcement as described in claim 3, characterized in that, The radial grouting is as follows: the rotating grouting rod (6) drives the turntable (9) fixed to it, thereby causing the sliding structure (11) on the turntable (9) to move, thus pushing the telescopic segment (12) into the soil; in this process, the grouting hole of the grouting rod (6) and the grouting branch pipe of the sliding structure (11) are dynamically connected, and then the grout is injected into the soil through the grouting port on the side wall of the telescopic segment (12) to complete the soil reinforcement on the side of the device; the relationship between the torque of the grouting rod (6) and the soil strength is as follows: In the formula, T is the torque, θ is the rotation angle, L is the extension / retraction displacement, and s is the displacement. u Let A be the undrained shear strength of the soil, A be the area of ​​the expansion joint segment (12), and N be the shear strength of the soil. c This is the bearing capacity coefficient.

7. The method for improving the uniformity of MIP foundation reinforcement as described in claim 1, characterized in that, The probe has a diameter of 40mm to 75mm and is made of high-carbon steel, alloy steel, or stainless steel.

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