Seasonal frozen area salinized soil body improvement and slope collaborative reinforcement method based on microbial mineralization and layered grouting

Abstract

The invention relates to the technical field of stable reinforcement of side slopes, in particular to a seasonal frozen area salinized soil body improvement and side slope collaborative reinforcement method based on microbial mineralization and layered grouting. According to the method, environmental pollution caused by traditional cement spraying and other methods is avoided by using microorganisms to reinforce and improve the salinized soil slope, meanwhile, damage to the environment caused by calcium carbonate precipitation induced by microorganisms is small, the generated calcium carbonate precipitation can serve as a cementing way between soil particles, the cohesive force of a soil body is increased, and the soil quality is improved. The grouting pressure is controlled according to'graded grouting pressure-depth coupling ', layered grouting is performed according to the sequence of surface layer cementing shell construction, middle layer mineralization reinforcement and deep layer structure consolidation, and the problem of top surface slurry channeling is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of improving the stability of soil slopes, and particularly relates to a method for improving saline soil and synergistically reinforcing a slope in a seasonal freezing region based on microbial mineralization and layered grouting. BACKGROUND

[0002] High-salt saline soil is widely distributed in the coastal areas of North China and the northwest region of China. The salt content of the saline soil is usually as high as 1% to 25%. Under the combined action of temperature fluctuation of-20℃ to 40℃ and water content change of 10% to 30%, the soil is prone to salt crystallization-dissolution cycle, which leads to a volume expansion and contraction rate of more than 15%, causing uneven settlement of the foundation. Such deformation directly causes road subgrade cracking with a crack width of 5 to 10 cm, bridge pier tilting with a maximum inclination of more than 3%, and other engineering disasters. The freeze-thaw cycle in winter, with a freeze-thaw ratio of more than 0.8, further aggravates the deterioration of the soil structure, increases the pore ratio by 0.2 to 0.4, and reduces the shear strength by 40% to 60%, forming a vicious cycle of geological disaster chain.

[0003] At present, the reinforcement technology for saline soil slopes mainly has three major bottlenecks. Firstly, chemical grouting methods (such as cement slurry and polyurethane) are prone to replacement reactions with sodium salts in high-salt environments. The effective diffusion radius of the slurry is less than 60% of the design value (actual measurement data show that it is only 0.8 to 1.2 m), which cannot penetrate more than 1.5 m thick saline soil layer, resulting in weakly cemented deep soil. Secondly, the traditional grouting body is salt-analyzed (the amount of NS2SO4 crystal precipitation is more than 12%) under dry-wet cycles, causing the dissolution rate of the cemented body to exceed 25%, and the strength decay rate to reach 50% within three years. Thirdly, the excessive use of chemical additives leads to excessive Cr6+ and Ss3+ in groundwater, causing surrounding vegetation to wither and die and groundwater pollution.

[0004] Therefore, in recent years, the microbial-induced calcium carbonate precipitation technology has shown revolutionary potential in the field of geotechnical engineering reinforcement due to its characteristics of "biological energy replacing mechanical energy and metabolic products replacing chemical reagents". Through the metabolic activity of urease-producing microorganisms such as Bacillus pasteurii, stable CSCO3 precipitates are formed to realize the cementation between soil particles. Compared with traditional grouting technology, this technology does not require large-scale mechanical disturbance and has ecological friendliness and long-term stability.

[0005] However, the existing grouting technology still has significant limitations: existing researches focus on the reinforcement of dry sandy soil or unsaturated soil body, and there is no matching microbial group for the saline soil slope in the seasonal frozen region, and the microbial liquid is easily inhibited by salt during grouting, resulting in insufficient slurry diffusion radius; if the conventional grouting process is used, the following problems exist: the deep soil body is in a weakly cemented state for a long time, which is difficult to meet the engineering requirements; the grouting pressure is difficult to accurately control, which often causes the problem of surface slurry channeling, seriously affecting the deep soil reinforcement effect.

[0006] To solve the above problems, the present application provides a solution. SUMMARY

[0007] The present application aims to provide a method for improving and reinforcing the saline soil slope in the seasonal frozen region based on microbial mineralization and layered grouting, which can effectively reinforce the saline soil slope in the seasonal frozen region under different conditions for a long time without polluting the environment; the method of "microbial slurry formula screening" plus "sleeve type layered grouting-microbial mineralization" is innovatively proposed, which realizes uniform reinforcement of deep soil body through step-by-step cemented shell layer construction and pressure gradient control, completely solves the problem of surface slurry channeling in traditional grouting process, inhibits salt migration under freeze-thaw cycle, and effectively improves the diffusion radius of MICP slurry; and provides a green and sustainable solution for the reinforcement of saline soil slope in the seasonal frozen region.

[0008] To achieve the above-mentioned purpose, the present application adopts the following technical scheme: a method for improving and reinforcing the saline soil slope in the seasonal frozen region based on microbial mineralization and layered grouting, comprising the following steps:

[0009] S1: sampling the saline soil in the seasonal frozen region by the ring knife method, and then determining the physical and chemical properties of the saline soil in the seasonal frozen region;

[0010] S2: preparing a liquid culture medium, inoculating the liquid culture medium with Bacillus pasteurii to prepare a microbial liquid, and preparing a cementing liquid for standby;

[0011] S3: inoculating the saline soil sample in the seasonal frozen region: evenly placing the saline soil sample in the seasonal frozen region into multiple inoculation pots; adding Bacillus pasteurii liquid into the inoculation pots in a 1%-3% inoculation ratio for stirring and mixing, then adding 1-2 times the volume of the cementing liquid relative to the Bacillus pasteurii liquid, the concentration of the cementing liquid is 1-1.75 mol / L, stirring and mixing to obtain multiple improved saline soil samples in the seasonal frozen region; the stirred multiple saline soil samples in the seasonal frozen region are placed in a mold for soil curing;

[0012] S4: The maintenance of a variety of improved seasonal frozen region saline soil samples, respectively, compression test, and compared with the original soil compression performance; Determine the value of the inoculation ratio of bacillus pasteurii liquid suitable for the seasonal frozen region saline soil, the value of the volume ratio of the cementing liquid relative to the bacillus pasteurii liquid, the value of the concentration of the cementing liquid;

[0013] S5: In the seasonal frozen region saline soil slope, a plurality of sleeve grouting pipes are arranged; the grouting pipe is inserted into the soil vertically to the surface of the saline soil slope, the grouting pipe is composed of multiple sleeves and gradually narrows from top to bottom, each sleeve is 100 cm long, the bottom of the grouting pipe is sealed, and the pipe wall of the buried part of the grouting pipe is uniformly provided with grouting holes; a layer of mesh cloth is wrapped outside the outer wall of the grouting pipe to prevent the soil from entering the grouting pipe and causing blockage; a joint is arranged on the upper part of the grouting pipe and connected with the peristaltic pump;

[0014] S6: The surface of the soil is uniformly sprayed with bacillus pasteurii liquid; the cementing liquid with a concentration verified to be suitable for the seasonal frozen region saline soil in step S3 is mixed with bacillus pasteurii liquid to form a mixed solution according to the suitable volume ratio multiple; the mixed solution is sprayed onto the surface of the seasonal frozen region saline soil slope using an atomizing nozzle; after the spraying is completed, a plastic film is used for covering and curing;

[0015] S7: After the surface of the soil is solidified, the first stage of grouting treatment is carried out; in order to prevent the rapid formation of calcium carbonate precipitate at the grouting hole when the mixed solution is injected, causing the grouting hole to be blocked, the bacillus pasteurii liquid verified in step S3 is injected separately from the cementing liquid, the liquid is injected first through the grouting pipe, and then the cementing liquid is injected immediately; and the grouting pressure in the soil sample is controlled by the peristaltic pump in a "graded grouting pressure-depth coupling" mode;

[0016] The "graded grouting pressure-depth coupling formula" is as follows:

[0017]

[0018] Wherein, P n represents the n-layer grouting pressure (MPa); P0 represents the initial grouting pressure (MPa); λ represents the depth gain coefficient (0.05-0.2); h n represents the grouting depth (m); α represents the microbial activity coefficient (0.8-1.2); q u represents the triaxial undrained shear strength of the soil (MPa);

[0019] After injection, cover the geotextile to keep it moist and maintain the soil layer, which can withstand subsequent grouting pressure without cracking, effectively preventing top surface grouting;

[0020] S8: Start the second stage of the grouting process, put the sleeve of the grouting pipe into the soil by 100 cm, and inject the bacteria solution and the cementing solution separately according to step S7, control the grouting pressure in the soil sample by using the "stage grouting pressure-depth coupling" method through the peristaltic pump; after the injection is completed, maintenance;

[0021] S9: Repeat the grouting process of step S8, put the sleeve of the grouting pipe down by 100 cm each time until the soil sample at all depths is reinforced.

[0022] S10: After the overall reinforcement of the slope is completed, arrange the geological radar to scan the continuity of the grouting body, detect the grouting coverage, and perform secondary grouting reinforcement for the defect area.

[0023] Further, the method for preparing the Bacillus pasteurii bacteria solution in step S2 is as follows:

[0024] S21: Configure the liquid medium: weigh 10g beef extract, 15g casein peptone, 5g soybean peptone, 5g sodium chloride, and 50ml 20% urea solution into a 1L capacity bottle, add 950ml pure water and shake for 3min, put it into a high-pressure sterilization pot, sterilize at 121℃ for 20min, after sterilization, treat it on the operation table for 30min, then on the operation table, the medium is divided into a flask, sealed with tin foil paper;

[0025] S22: Prepare Bacillus pasteurii bacteria solution: inoculate Bacillus pasteurii freeze-dried powder into the liquid medium in the flask, place the inoculated flask in a constant temperature incubator at 30℃ and 5% CO2, shake culture for 20-50h at a speed of 150rpm, and obtain Bacillus pasteurii bacteria solution after culture.

[0026] Further, the mass ratio of Bacillus pasteurii freeze-dried powder to medium in step S2 is 6:100.

[0027] Further, the physicochemical properties of the saline soil in the seasonal frozen region include salt content, initial density, saturated density, dry density, specific gravity, saturated water content, initial porosity ratio, saturation, and compaction degree; the improved saline soil in the seasonal frozen region is periodically sampled by the cutting ring method, the physicochemical properties are determined, and the improvement effect is verified.

[0028] Further, the volume ratio of the Bacillus pasteurii bacteria solution to the cementing solution in step S3 is 1:2; the concentration of the cementing solution is 1.5mol / L; and the inoculation ratio of the Bacillus pasteurii bacteria solution to the saline soil in the seasonal frozen region is 3%.

[0029] Further, the step S6 uses the atomizing nozzle to spray the mixed solution to the surface of the saline soil slope in the seasonal freeze region, the spraying is divided into three times, each spraying interval is 2h, after the spraying is completed, the plastic film is used for covering and curing, the curing time is 24h; the step S7, S8, S9 and S10 are covered with geotextile for moisture curing for 48h after each grouting is completed.

[0030] Further, the cementing fluid in the step S2 is composed of the following components with the mass ratio: 6%-12% of sodium alginate, 6%-12% of xanthan gum, 1.5%-3% of gypsum, 1.5%-3% of bentonite, 3%-5% of sodium chloride, 2%-5% of acetic acid and 60%-80% of pure water.

[0031] Further, in the step S5, the distance between each sleeve of the grouting pipe is 500mm, the diameter of the sleeve is set according to the depth of the soil sample, the diameter d of the outermost sleeve is x / 10+10, mm, wherein x is the depth of the soil sample, cm, d is rounded up to the whole ten, and 10 is the radius of the innermost sleeve, the length of each sleeve of the grouting pipe is 100cm, the grouting pipe is embedded in the soil, and grouting holes with a diameter of 5mm are arranged every 50cm on the pipe wall of the embedded grouting pipe, and the grouting holes are uniformly arranged around the pipe wall.

[0032] Further, the preparation method of the cementing fluid in the step S3 comprises the following steps:

[0033] B1: weigh the sodium alginate and add it into the pure water, set the speed of the magnetic stirrer to 600-800rpm, the temperature to 35-40℃, and mix and stir for 25-30min, then add the xanthan gum, sodium chloride and acetic acid, set the speed of the magnetic stirrer to 1000-1200rpm, the temperature to 40-45℃, and continue to stir for 15-20min to obtain the initial cementing fluid;

[0034] B2: add the bentonite and the gypsum into the pulverizer respectively, set the pulverizing particle size to 200 mesh, and pulverize for 5-10min, repeat twice to obtain the bentonite powder and the gypsum powder;

[0035] B3: add the bentonite powder and the gypsum powder into the initial cementing fluid, set the speed of the stirrer to 400-600rpm, the temperature to 60-65℃, and mix and stir for 30min, then transfer to the homogenizer, homogenize for 30min to obtain the cementing fluid.

[0036] Further, the compression performance measured by the compression test includes the void ratio, the compression coefficient and the compression index, and the calculation formula is as follows: the void ratio is calculated according to formula (1), the void ratio after the consolidation under each level of pressure is stable is calculated according to formula (2), the compression coefficient in a certain level of pressure range is calculated according to formula (3), and the compression index is calculated according to formula (4);

[0037]

[0038] In the formula, represents the initial porosity ratio at the initial water content, represents the density of water (g / cm 3 ), represents the saturated water content, represents the initial density (g / cm 3 ) ;

[0039]

[0040] In the formula, represents the porosity ratio at a certain level of pressure, represents the total deformation amount of the height of the sample at a certain level of pressure (cm), represents the initial height of the sample (cm) ;

[0041]

[0042] In the formula, represents the compression coefficient (MPa -1 ), represents the pressure value at a certain level (kPa) ;

[0043]

[0044] In the formula, represents the compression index.

[0045] In summary, due to the adoption of the above technical scheme, the beneficial effects of the present application are:

[0046] (1) The present application uses microorganisms to reinforce and improve saline soil slopes without chemical pollution, and the damage to the environment by microbial induction of calcium carbonate precipitation is small. The generated calcium carbonate precipitation can be used as a cementing way between soil particles, increase the cohesion of the soil body, reduce the looseness of the soil body and enhance the shear strength of the soil body, and can adjust the growth mode of plant roots to help the soil body resist the damage caused by frost heaving and thawing, and has good long-term stability.

[0047] (2) According to the physicochemical properties of saline soil in seasonal frozen region, the ratio and dosage of bacillus pasteurii and cementing liquid are adjusted, and the surface is treated by "surface cementing shell construction", "middle layer mineralization strengthening" and "deep layer structure consolidation". After the surface treatment, a calcium carbonate solidification layer is formed, which can improve the strength of the soil and reduce the downward permeability of the soil. It can effectively reduce the downward infiltration of rainwater and other water, and reduce the salt expansion and frost heaving phenomenon. The segmented and layered grouting can ensure that the slurry has enough time to penetrate into the soil in each treatment stage, so that the calcium carbonate precipitated by the microbial mineralization reaction is evenly distributed in each layer of soil, and the solidification layer generated by the layered generation can effectively prevent the downward infiltration of water, reducing the salt expansion and frost heaving effect of saline soil due to water absorption. And through the peristaltic pump, the "graded grouting pressure-depth coupling" method is used to control the grouting pressure of the slurry in the soil sample, which can ensure that the slurry can be fully injected, and also ensure that the injected slurry is not enough to break through the top solidification when layered injection; completely solve the top grouting problem of traditional grouting process.

[0048] (3) The "graded grouting pressure-depth coupling" is used to control the pressure gradient, realize the construction of the shell layer by stages, realize the uniform reinforcement of the deep soil, completely solve the top grouting problem of traditional grouting process, and inhibit the salt migration under freeze-thaw cycle; and the grouting pressure is adjusted according to the depth, that is, the speed of grouting is accelerated, the deeper the stratum, the greater the pressure, and the stability of the grouting effect can be ensured through the gradient control of pressure.

[0049] (4) According to the method, the grouting pipe is inserted into the soil vertically to the surface of the saline soil slope, the distance between each grouting pipe is 500 mm, the diameter of the sleeve is set according to the depth of the soil sample, the diameter of the outermost circle is d=x / 10+10, unit: mm, wherein x is the depth of the soil sample, unit: cm, d is rounded to the nearest ten, and 10 is the radius of the innermost circle. The length of each section of the sleeve grouting pipe is 100 cm, the pipe wall of the buried part of the soil is provided with grouting holes with a diameter of 5 mm every 50 cm, the grouting holes are arranged in four directions along the pipe wall, the bottom of the grouting pipe is sealed, a layer of mesh cloth is wrapped outside the outer wall of the grouting pipe to prevent the soil from entering the grouting pipe and causing blockage, and a connector is arranged on the upper part of the grouting pipe and connected with the peristaltic pump to control the flow rate of the slurry in the soil sample. The grouting pipe according to the method is more suitable for the construction of saline soil in seasonal frozen region, effectively solidifies the soil near the potential sliding surface, and increases the feasibility of practical engineering application.

[0050] (5) Verification of biological improvement of saline soil in seasonal frozen region, wherein the freeze-thaw cycle and standard compression test ensure that the most suitable bacteria liquid and cementing liquid for local saline soil in seasonal frozen region can be selected, and the stability of the reinforcement effect is ensured.

[0051] (6) Spraying the mixed solution of the verified proportion of the bacillus pasteurii liquid and the cementing liquid on the surface of the saline soil slope in the seasonal frozen region; the saline soil slope in the seasonal frozen region can be divided into multiple areas, and the grouting in other areas can be carried out during the maintenance period of the layered grouting, so that the construction time is saved under the condition of ensuring the effect of the solidified soil.

[0052] (7) The method has high operation efficiency and strong controllability, is suitable for the special situation of the saline soil in the seasonal frozen region, can solve the characteristics of repeated freezing and thawing, high salt content, salt expansion and frost heaving of the saline soil in the seasonal frozen region, and has stronger pertinence.

[0053] (8) The method provides the calculation formula of the compression coefficient and the compression index, so that the reinforcement effect of the improved saline soil in the seasonal frozen region can be more reflected, and the suitable inoculation ratio of the bacillus pasteurii liquid, the volume ratio of the bacillus pasteurii and the cementing liquid and the concentration of the cementing liquid can be more efficiently screened out. BRIEF DESCRIPTION OF DRAWINGS

[0054] Figure 1 It is a method flow chart of the application;

[0055] Figure 2 It is a bacillus pasteurii growth curve chart of the application;

[0056] Figure 3 It is a bacteria liquid concentration change curve under different inoculation amounts of the application;

[0057] Figure 4 It is a urease activity change curve under different inoculation amounts of the application;

[0058] Figure 5 It is a field process schematic diagram of the application;

[0059] Figure 6 It is a reinforcement effect diagram of 120cm depth in the application;

[0060] Figure 7 It is a reinforcement effect diagram of 220cm depth in the application;

[0061] Figure 8 It is a reinforcement effect diagram of 320cm depth in the application;

[0062] Figure 9 It is a structure diagram of the overlapping saturator in the compression test in the application;

[0063] Figure 10 It is a structure diagram of the overlapping saturator in the compression test in the application. DETAILED DESCRIPTION

[0064] In order to make the technical means, creative features, purposes and effects of the present application easy to understand, the present application is further described below in combination with specific embodiments.

[0065] The experimental methods in the following examples are all conventional methods, which are carried out according to the techniques or conditions described in the literature in the art or according to the product instructions, unless otherwise specified. The materials, reagents and the like used in the following examples can be obtained from commercial channels, unless otherwise specified.

[0066] Example 1

[0067] The preparation method of the cementing fluid is as follows:

[0068] 1: 60 g of sodium alginate was weighed into 780 g of pure water, the magnetic stirrer was set to rotate at 600 rpm and the temperature was set to 35℃, and the mixture was stirred for 25 min, then 60 g of xanthan gum, 30 g of sodium chloride and 20 g of acetic acid were added, the magnetic stirrer was set to rotate at 1000 rpm and the temperature was set to 40℃, and the stirring was continued for 15 min to obtain the initial cementing fluid;

[0069] 2: The bentonite and gypsum were respectively added into a pulverizer, the pulverizing particle size was set to 200 mesh, and the pulverizing was repeated for 5 min twice to obtain bentonite powder and gypsum powder;

[0070] 3: 25 g of bentonite powder and 25 g of gypsum powder were added into the initial cementing fluid, the stirrer was set to rotate at 400 rpm and the temperature was set to 60℃, and the mixture was stirred for 30 min, then it was transferred to a homogenizer and homogenized for 30 min to obtain the prepared cementing fluid; the bentonite is a yellow calcium-based bentonite powder.

[0071] Table 1, reagent parameter table used in example 1

[0072]

[0073] Example 2

[0074] Sample preparation

[0075] 1: The seasonal frozen area saline soil was sampled by the cutting ring method: the cutting ring method was used to sample the seasonal frozen area saline soil, and the saline soil sample slope was located in the seasonal frozen area test area 2 in Cangzhou City, Hebei Province, then the salt content, initial density, saturated density, dry density, specific gravity, saturated water content, initial pore ratio, saturation and compactness of the seasonal frozen area saline soil were determined;

[0076] 2: Configuration of liquid medium: weigh 10 g of beef extract, 15 g of casein peptone, 5 g of soybean peptone, 5 g of sodium chloride and 50 ml of 20% urea solution into a 1 L volumetric flask, add 950 ml of pure water and shake for 3 min, put into a high-pressure sterilization pot, 121 ℃, sterilize for 20 min, after sterilization, ultraviolet treatment operation table for 30 min, then in the operation table, the medium is divided into triangular bottles, 100 g per bottle, sealed with tin foil paper;

[0077] 3: Preparation of Bacillus pasteurii liquid: inoculate 6 g of Bacillus pasteurii freeze-dried powder into a triangular flask, and place the inoculated triangular flask in a constant temperature incubator at 30 ℃, 5% CO2, shake culture for 20-50 h at a speed of 150 rpm, and obtain Bacillus pasteurii liquid after culture;

[0078] 4: Inoculation of Bacillus pasteurii liquid into saline soil: put 5 kg of saline soil in the seasonal frozen area into a stirring basin, add 100 g of Bacillus pasteurii liquid for stirring, set the speed of the magnetic stirrer to 600 rpm, and stir for 15 min, then add 200 g of the cementing liquid prepared in Example 1, set the speed of the magnetic stirrer to 800 rpm and the temperature to 35 ℃, and continue stirring for 45 min;

[0079] 5: Improved saline soil culture in the seasonal frozen area: the stirred saline soil in the seasonal frozen area is loaded into a mold, the compaction degree of the soil column is adjusted to 95% using a vibrator, then the soil column is wrapped with double-layer water-impermeable plastic film, and transferred to a constant temperature curing room at 18 ℃, the humidity of the constant temperature curing room is adjusted to 95%, and the soil column is cured for 24 h to obtain the improved saline soil in the seasonal frozen area by biological method.

[0080] Table 2, reagent parameter table used in Example 2

[0081]

[0082] Table 3, physicochemical properties of saline soil selected in Example 2

[0083]

[0084] Standard freeze-thaw compression test

[0085] The freeze-thaw cycle parameters are set as follows: freezing at -20 ℃ for 12 h and thawing at room temperature for 12 h as one freeze-thaw cycle, and the number of freeze-thaw cycles is set to 1, 3, 5, 7, 9, 11 and 13 to simulate the freeze-thaw conditions under natural conditions;

[0086] The compression test operation includes the following steps:

[0087] Put filter paper on both sides of the sample, then put two water-permeable plates on the filter paper, and then fix them on the overlapping saturator; Figure 9 and Figure 10As shown, the top of the superimposed saturator is a pressurized upper cover and water-permeable stone, and the middle of the base is provided with a cavity for placing soil samples, the inside of the cavity is provided with water-permeable stone, rigid guard ring and ring knife; the soil sample is placed into the cavity of the superimposed saturator, and the pressurized upper cover is closed; the saturator with the sample is placed into a vacuum cylinder, the cylinder cover is covered, and vaseline is applied to the joint to prevent air leakage;

[0088] The air extractor is started, and when the value of the vacuum gauge approaches-100 kPa, the air extraction is continued for one hour, and then water is slowly injected into the vacuum cylinder through the water pipe, and the pipe clamp is adjusted at all times during the water injection process to ensure that the value of the vacuum gauge is basically unchanged;

[0089] When the superimposed saturator is completely submerged in water, the air extraction and the injection of saturated liquid are stopped, the pipe clamp is opened to allow air to enter the vacuum cylinder, and the soil sample is fully saturated after being placed for 12 hours, and the saturated liquid is prepared according to the salt concentration of the sample pore liquid, and in this sample, a solution of 27.8 g / L of sodium chloride and 9.4 g / L of sodium sulfate is used as the saturated liquid;

[0090] After the saturated sample is placed in the consolidation container and a pressure of 50 kPa is applied, the saturated liquid is immediately injected into the water tank, and then the standard compression test is carried out according to the pressure gradient setting of 50 kPa, 100 kPa, 200 kPa and 400 kPa.

[0091] The initial void ratio of the sample is calculated according to formula (1), the void ratio after consolidation under each level of pressure is calculated according to formula (2), the compression coefficient within a certain level of pressure is calculated according to formula (3), and the compression index is calculated according to formula (4).

[0092]

[0093] In the formula, represents the initial void ratio under the initial moisture content, represents the density of water (g / cm 3 ), represents the saturated moisture content, represents the initial density (g / cm 3 ).

[0094]

[0095] In the formula, represents the void ratio under a certain level of pressure, represents the total deformation amount of the height of the sample under a certain level of pressure (cm), represents the initial height of the sample (cm).

[0096]

[0097] wherein, represents the compression coefficient (MPa -1 ), represents the pressure value of a certain stage (kPa).

[0098]

[0099] wherein, represents the compression index.

[0100] Table 4, standard freeze-thaw compression test results

[0101]

[0102] By analyzing Table 4, it can be seen that the soil sample pore ratio of the soil sample modified by Bacillus pasteurii decreases, because the calcium carbonate produced by the modification of Bacillus pasteurii fills the pores in the original soil sample, and the salt in the soil sample increases the salt concentration of the pore liquid, further compressing the double electric layer between the soil particles, so that the soil pore ratio decreases, and the soil pore ratio decreases under the combined action of the two; the soil sample pore ratio of the soil sample modified by Bacillus pasteurii also decreases under different freeze-thaw cycle times, but the decrease is smaller than that without freeze-thaw cycle; this is because Bacillus pasteurii consumes water in the soil sample, and part of the salt cannot form ice salt and mirabilite when frozen, but rather the salt is precipitated, which strengthens the soil particle structure and reduces the compressibility.

[0103] The saline soil sample in the seasonal frozen region is evenly placed in multiple inoculation pots; Bacillus pasteurii bacterial liquid is added to the inoculation pots in a 1% to 3% inoculation ratio, stirred and mixed, then 1 to 2 times the volume of cementing liquid relative to the Bacillus pasteurii bacterial liquid is added, the concentration of the cementing liquid is 1 to 1.75 mol / L, and the mixture is stirred and mixed evenly to obtain multiple improved saline soil samples in the seasonal frozen region; the multiple seasonal frozen region saline soil samples after stirring are placed in molds for soil curing; the cured multiple improved seasonal frozen region saline soil samples are subjected to compression tests, and the compression performance of the original soil is compared; the value of the inoculation ratio of the Bacillus pasteurii bacterial liquid, the value of the volume ratio of the cementing liquid relative to the Bacillus pasteurii bacterial liquid, and the value of the concentration of the cementing liquid suitable for the seasonal frozen region saline soil are determined.

[0104] The inoculation of Bacillus pasteurii liquid in the step of changing saline soil is divided into 1%, 2%, and 3% according to the inoculation ratio of Bacillus pasteurii liquid, the volume ratio of the liquid to the cementing liquid is divided into 1:1, 1:1.5, and 1:2, the concentration of the cementing liquid is divided into 1 mol / L, 1.5 mol / L, and 1.75 mol / L; a plurality of biological method improved saline soil samples in the seasonal frozen region are formed as a control group; the standard freeze-thaw compression test is also conducted on the control group, and the test results are compared, so as to screen the suitable Bacillus pasteurii liquid and the cementing liquid ratio.

[0105] The optimal liquid inoculation ratio, cementing liquid ratio, and volume ratio are determined.

[0106] Example 3

[0107] In order to find the most suitable Bacillus pasteurii liquid inoculation amount and the volume and concentration of the cementing liquid required by the saline soil in the seasonal frozen region, the following steps are also conducted:

[0108] The activity detection test under different inoculation ratios is set, the bacterial concentration (OD600 value) and urease activity of Bacillus pasteurii are measured under the inoculation ratios of 1%, 2%, and 3%; it can be known from FIG. 2 that the culture time of Bacillus pasteurii liquid is optimal at 20-50 hours; it can be known from FIG. 3 that when the inoculation ratio is 3%, the concentration of the bacteria and the urease activity are the highest, so the inoculation ratio of 3% is selected; under the same environment, the platform stable period of the urease activity is shorter than that of the liquid concentration, and the urease activity decreases faster, which may be because the urease is a macromolecular protein substance, a large amount of toxic substances produced by the bacteria in the early stage greatly change the environment of the liquid, the protein structure is more easily destroyed, and thus the urease activity rapidly decreases after reaching the maximum value.

[0109] In order to explore the most suitable cementing liquid concentration and the volume ratio of the liquid to the cementing liquid, the control test of different cementing liquid concentrations and different volume ratios of the liquid to the cementing liquid is set, the calcium carbonate content in the soil is detected by using the acid-base neutralization titration method after the test is completed, and the experimental group setting and the calcium carbonate content in the soil are shown in Table 5.

[0110] Table 5: Reaction liquid mixing ratio test setting and calcium carbonate content in soil

[0111]

[0112] As can be seen from Table 5, when the concentration of the cementing fluid changes from 1 mol / L to 1.5 mol / L, the calcium carbonate content in the sample increases significantly, at this time the microbial induced calcium carbonate precipitation reaction is more sufficient; while increasing from 1.5 mol / L to 1.75 mol / L, the calcium carbonate content in the sample decreases, because when the concentration of the cementing fluid is higher, it will inhibit the activity of urease, which is the most important substance in the microbial induced calcium carbonate precipitation reaction, and the activity is inhibited, which leads to the decrease of the rate of urea hydrolysis, and cannot provide enough carbonate ions, thereby affecting the content of calcium carbonate precipitation; By comparing the calcium carbonate content produced by different ratios of bacteria liquid and cementing fluid, it can be found that when the volume ratio of bacteria liquid to cementing fluid is 1:2, the content of calcium carbonate precipitation produced is the most; Therefore, the calcium ion concentration of the cementing fluid selected in this test is 1.5 mol / L, and the volume ratio of bacteria liquid to cementing fluid is 1:2.

[0113] Example 4

[0114] A plurality of sleeve grouting pipes are arranged at corresponding positions in the saline soil slope soil sample in the seasonal frozen region, the grouting pipes are inserted into the soil vertically to the surface of the saline soil slope, the depth is 220 cm, the grouting pipe is composed of 3 sleeves, the length of each sleeve of the sleeve grouting pipe is 100 cm, the diameter of the first sleeve is 40 mm, the diameter of the second sleeve is 30 mm; the diameter of the third sleeve is 20 mm; the spacing between each grouting pipe is 500 mm, the pipe wall of the soil body part of the grouting pipe is provided with a grouting hole with a diameter of 5 mm every 50 cm, the grouting holes are uniformly arranged along the pipe wall, the bottom of the grouting pipe is sealed, a layer of mesh cloth is wrapped outside the outer wall of the grouting pipe to prevent the soil from entering the grouting pipe and causing blockage, a connector is arranged on the upper part of the grouting pipe and connected with a peristaltic pump, the flow rate of the slurry injected into the soil sample is controlled by the peristaltic pump; as shown in Figure 5 ;

[0115] A mixed solution of bacteria liquid and cementing fluid is sprayed on the surface of the saline soil slope soil body in the seasonal frozen region, the mass ratio of the bacteria liquid to the cementing fluid is 1:2, the next spraying is carried out after 2 hours of interval after the completion of the first spraying, and the spraying is carried out three times, after the completion of the spraying, a plastic film is used for covering and curing, and the curing time is 24 hours; after the surface treatment is completed, a calcium carbonate solidified layer is formed, the soil body strength is improved, and the soil body permeability downward is reduced, which can effectively reduce the downward penetration of rainwater and the like, and reduce the salt heaving and frost heaving phenomena.

[0116] At the same time, the grouting pressure is controlled according to the "graded grouting pressure-depth coupling formula", and the grouting is carried out in layers in the order of "surface cementing shell construction", "middle layer mineralization strengthening" and "deep layer structure consolidation".

[0117] The first stage of grouting treatment is performed after the surface of the soil body is solidified; in order to prevent the rapid formation of calcium carbonate precipitate at the grouting hole when the mixed solution is injected, thereby causing the grouting hole to be blocked, the bacteria solution verified in step S5 is injected separately from the cementing solution; the bacteria solution is first injected through the grouting pipe, and then the cementing solution is immediately injected; and the grouting pressure of the slurry in the soil sample is controlled by the peristaltic pump in a "graded grouting pressure-depth coupling" manner.

[0118] Example 5

[0119] If the depth of the grouting pipe embedded in the slope soil body is 120 cm, 220 cm and 320 cm respectively, the "graded grouting pressure-depth coupling formula" is as follows:

[0120]

[0121] wherein Pn represents the n-th layer grouting pressure (MPa); P0 represents the initial grouting pressure (MPa); λ represents the depth gain coefficient (0.05-0.2); hn represents the grouting depth (m); α represents the microbial activity coefficient (0.8-1.2); and qn represents the triaxial undrained shear strength of the soil body (MPa). n n u

[0122] The calculation results are as follows: when h1=1.2 m, P1=1.56 MPa; when h2=2.2 m, P2=1.85 MPa; and when h3=3.2 m, P3=2.06 MPa.

[0123] The first layer grouting pressure is set to 1.56 MPa, 20 L of Bacillus pasteurii bacteria solution is injected into each grouting pipe, 40 L of cementing solution is injected after the injection is completed, the grouting pressure of the slurry in the soil sample is controlled by the peristaltic pump in a "graded grouting pressure-depth coupling" manner, and the grouting is completed after 48 h of maintenance; since the surface of the soil body has been solidified to reduce the permeability of the soil body, the evaporation loss of the bacteria solution and the cementing solution in the soil body is greatly reduced, the microbial calcification precipitation reaction time in the soil body is effectively increased, and a dense cementing shell layer with a thickness of ≥2 cm is formed.

[0124] After the first stage of grouting treatment is completed, the second stage of grouting treatment is started, the sleeve is lowered by 100 cm, the grouting pressure is set to 1.85 MPa, 20 L of Bacillus pasteurii bacteria solution is injected into each grouting pipe, 40 L of cementing solution is injected after the injection is completed, the grouting pressure of the slurry in the soil sample is controlled by the peristaltic pump in a "graded grouting pressure-depth coupling" manner, and the grouting is completed after 48 h of maintenance.

[0125] ​​​After the second stage of grouting treatment is completed, the third stage of grouting treatment is started, the sleeve is continuously lowered by 100 cm, the grouting pressure is set to 2.06 MPa, 20 L of bacillus pasteurii liquid is injected into each grouting pipe, after the injection is completed, 40 L of cementing liquid is injected, the grouting pressure in the soil sample is controlled by using the "step grouting pressure-depth coupling" mode through the peristaltic pump, and after the grouting is completed, the curing is also maintained for 48 h.

[0126] A control test is set, the reinforcement effects of the ordinary grouting and the three depth layered grouting with h1 of 120 cm, h2 of 220 cm and h3 of 320 cm are compared, the ordinary grouting does not use a sectional grouting pipe, the injected slurry is a mixed liquid of bacillus pasteurii liquid and cementing liquid, the mass ratio of the bacillus pasteurii liquid to the cementing liquid is 1:2, and the surface is not pre-solidified, and the standard compression test is carried out on the sample in the laboratory.

[0127] As shown in Figure 6 , 7 , 8; in the three depths of the soil sample, the void ratio of the soil sample after the layered grouting reinforcement is smaller than that of the soil sample after the ordinary grouting, which indicates that the reinforcement of the layered grouting is better than that of the ordinary grouting for the saline soil slope; in the process of the ordinary grouting, the MICP reaction is started after the bacillus pasteurii liquid and the cementing liquid are mixed, which may cause the calcium carbonate precipitation to block the further injection of the slurry at the grouting hole, and the surface is not solidified, which may cause part of the slurry to evaporate after penetrating into the surface and be lost.

[0128] After the overall reinforcement of the slope is completed, the geological radar is arranged to scan the continuity of the grouting body, the grouting coverage is detected, and the secondary grouting reinforcement is carried out for the defect area.

[0129] In addition, the saline soil slope in the seasonal frozen region can be divided into multiple areas, and each area is constructed in stages; in this way, during the curing period of the layered grouting in one area, personnel and equipment can be dispatched to carry out grouting in other areas, and the construction time is also saved under the condition of ensuring the effect of the solidified soil body.

[0130] The above shows and describes the basic principles and main features of the present application and the advantages of the present application. Those skilled in the art should understand that the present application is not limited to the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the present application, and various changes and improvements can be made without departing from the spirit and scope of the present application, and these changes and improvements all fall within the scope of the present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for improving saline soil and strengthening slopes in seasonally frozen areas based on microbial mineralization and layered grouting, characterized in that: The following steps are involved: S1: Sampling of saline soil in seasonally frozen areas by ring knife method, followed by determination of the physical and chemical properties of saline soil in seasonally frozen areas; S2: preparing a liquid culture medium, inoculating Bacillus pasteurianus into the liquid culture medium to prepare a bacterial solution, and preparing a binding liquid for later use; S3: Inoculating seasonally frozen saline soil samples: The seasonally frozen saline soil samples are evenly placed in multiple inoculation basins; a Bacillus pasteurianus bacterial solution is added to the inoculation basins at an inoculation ratio of 1% to 3%, and the mixture is stirred and mixed. Subsequently, a binder solution is added at a volume ratio of 1 to 2 times the volume of the Bacillus pasteurianus bacterial solution, wherein the concentration of the binder solution is 1 to 1.75 mol / L, and the mixture is stirred and mixed to obtain multiple improved seasonally frozen saline soil samples; the multiple seasonally frozen saline soil samples after stirring are placed in a mold for soil curing; S4: Conduct compression tests on various samples of improved seasonally frozen saline soil and compare their compression properties with those of the original soil. Determine the values ​​of the inoculation ratio of the Bacillus pasteurianus bacterial solution, the volume ratio of the cementing solution to the Bacillus pasteurianus bacterial solution, and the concentration of the cementing solution suitable for the saline soil in the frozen zone this season; S5: Arrange multiple sleeve grouting pipes in saline soil slopes in seasonally frozen areas. Insert the grouting pipes perpendicular to the surface of the saline soil slope into the soil. The grouting pipes consist of multiple sleeve sections that gradually narrow from top to bottom. Each sleeve section is 100 cm long. The bottom of the grouting pipe is sealed, and grouting holes are evenly distributed on the wall of the grouting pipe buried in the soil. Wrap a layer of mesh on the outer wall of the grouting pipe to prevent soil from entering the grouting pipe and causing blockage. A joint is installed on the top of the grouting pipe and connected to a peristaltic pump. S6: Evenly spraying the soil surface with a Bacillus pasteurianus bacterial solution; mixing a binder solution having a concentration verified as suitable for saline soil in the seasonally frozen zone in step S3 with the Bacillus pasteurianus bacterial solution in an appropriate volume ratio to form a mixed solution; spraying the mixed solution onto the surface of the saline soil slope in the seasonally frozen zone using an atomizing nozzle; and covering the soil with plastic film for maintenance after spraying is completed; S7: After the soil surface solidifies, the first stage of grouting is performed. To prevent the rapid formation of calcium carbonate precipitation in the grouting holes when the mixed solution is injected, which may cause clogging of the grouting holes, the Bacillus pasteurianus solution verified in step S3 is injected separately from the cementing solution. The bacterial solution is first injected through the grouting pipe, and then the cementing solution is immediately injected. The grouting pressure of the slurry injected into the soil sample is controlled by a peristaltic pump using a "graded grouting pressure-depth coupling" method. The "graded grouting pressure-depth coupling formula" is as follows: ； Among them, P n represents the grouting pressure of the nth layer (MPa); P0 represents the initial grouting pressure (MPa); λ represents the depth gain coefficient (0.05~0.2); h n represents the grouting depth (m); α represents the microbial activity coefficient (0.8-1.2); q u represents the triaxial undrained shear strength of soil (MPa); After the injection is completed, cover with geotextile to keep it moisturized; S8: Start the second stage of grouting treatment. Lower the sleeve of the grouting pipe 100 cm into the soil. Inject the bacterial solution and the cementing solution separately according to step S7. Use a peristaltic pump to control the grouting pressure of the slurry in the soil sample using the "graded grouting pressure-depth coupling" method. After the injection is completed, perform curing. S9: Repeat the grouting process of step S8, lowering the sleeve of the grouting pipe by 100 cm each time until the soil samples at all depths are reinforced; S10: After the overall reinforcement of the slope is completed, a geological radar is arranged to scan the continuity of the grouting body, detect the grouting coverage, and perform secondary grouting reinforcement on the defective areas.

2. The method for improving saline soil and strengthening slopes in seasonally frozen areas based on microbial mineralization and layered grouting according to claim 1, characterized in that: The method for preparing the liquid culture medium and the Bacillus pasteurianus liquid in step S2 is as follows: S21: Prepare liquid culture medium: Weigh 10 g beef extract, 15 g casein peptone, 5 g soy peptone, 5 g sodium chloride, and 50 ml of 20% urea solution into a 1 L volumetric flask. Add 950 ml of pure water and shake for 3 min. Place in an autoclave at 121°C for 20 min. After sterilization, treat the workbench with UV light for 30 min. Then, divide the culture medium into Erlenmeyer flasks on the workbench and seal them with tin foil. S22: Preparation of Bacillus pasteurianus liquid: inoculate the freeze-dried powder of Bacillus pasteurianus into the liquid culture medium in a conical flask, place the inoculated conical flask in a constant temperature incubator at 30°C and 5% CO2, and culture with shaking for 20 to 50 hours at a rotation speed of 150 rpm. After the culture is completed, the Bacillus pasteurianus liquid is obtained.

3. The method for improving saline soil and strengthening slopes in seasonally frozen areas based on microbial mineralization and layered grouting according to claim 2, characterized in that: The mass ratio of the Bacillus pasteurianus freeze-dried powder to the culture medium in step S2 is 6:

100.

4. The method for improving saline soil and strengthening slopes in seasonally frozen areas based on microbial mineralization and layered grouting according to claim 1, characterized in that: The physical and chemical properties of the saline soil in the seasonally frozen area include salt content, initial density, saturated density, dry density, specific gravity, saturated moisture content, initial porosity, saturation and compaction degree.

5. The method for improving saline soil and strengthening slopes in seasonally frozen areas based on microbial mineralization and layered grouting according to claim 1, characterized in that: The volume ratio of the Bacillus pasteurianus liquid to the cementing liquid in step S3 is 1:2; the concentration of the cementing liquid is 1.5 mol / L; and the inoculation ratio of the Bacillus pasteurianus liquid to the saline soil in the seasonally frozen area is 3%.

6. The method for improving saline soil and strengthening slopes in seasonally frozen areas based on microbial mineralization and layered grouting according to claim 1, characterized in that: In step S6, the mixed solution is sprayed onto the surface of the saline soil slope in the seasonally frozen area using an atomizing nozzle. The spraying is divided into three times, with an interval of 2 hours between each spraying. After the spraying is completed, a plastic film is used to cover and maintain the soil for 24 hours. In steps S7, S8, S9, and S10, after each grouting is completed, the geotextile is covered and maintained for 48 hours of moisture retention.

7. The method for improving saline soil and strengthening slopes in seasonally frozen areas based on microbial mineralization and layered grouting according to claim 1, characterized in that: The binder fluid described in step S2 is composed of the following components in mass ratio: 6% to 12% sodium alginate, 6% to 12% xanthan gum, 1.5% to 3% gypsum, 1.5% to 3% bentonite, 3% to 5% sodium chloride, 2% to 5% acetic acid and 60% to 80% pure water.

8. The method for improving saline soil and strengthening slopes in seasonally frozen areas based on microbial mineralization and layered grouting according to claim 1, characterized in that: In step S5, the spacing between each sleeve of the grouting pipe is 500 mm, the diameter of the sleeve is set according to the depth of the soil sample, the diameter of the sleeve of the outermost circle is d=x / 10+10, the unit is mm, where x is the soil sample depth in cm, d is rounded to the nearest ten, where 10 is the radius of the innermost sleeve, the length of each sleeve section of the grouting pipe is 100 cm, and grouting holes with a diameter of 5 mm are set every 50 cm on the pipe wall of the grouting pipe buried in the soil, and the grouting holes are evenly arranged around the pipe wall.

9. The method for improving saline soil and strengthening slopes in seasonally frozen areas based on microbial mineralization and layered grouting according to claim 7, characterized in that: The method for preparing the cementing fluid described in step S3 comprises the following steps: B1: Weigh sodium alginate and add it to pure water. Set the magnetic stirrer speed to 600-800 rpm and the temperature to 35-40°C. Mix and stir for 25-30 minutes. Then add xanthan gum, sodium chloride and acetic acid. Set the magnetic stirrer speed to 1000-1200 rpm and the temperature to 40-45°C. Continue stirring for 15-20 minutes to obtain the initial cementing solution. B2: Add bentonite and gypsum into a grinder, set the crushing particle size to 200 mesh, and crush for 5-10 minutes. Repeat twice to obtain bentonite powder and gypsum powder. B3: Add bentonite powder and gypsum powder to the initial binder, set the stirrer speed to 400-600 rpm and the temperature to 60-65°C, mix and stir for 30 minutes, transfer to a homogenizer after stirring, and homogenize for 30 minutes to obtain the binder.

10. The method for improving saline soil and strengthening slopes in seasonally frozen areas based on microbial mineralization and layered grouting according to claim 1, characterized in that: The compression properties measured by the compression test include porosity, compressibility, and compressibility index. The calculation formulas are as follows: the porosity is calculated according to formula (1), the porosity after consolidation stabilization at each level of pressure is calculated according to formula (2), the compressibility within a certain pressure range is calculated according to formula (3), and the compressibility index is calculated according to formula (4). ； Where, represents the initial porosity at the initial water content, Indicates the density of water (g / cm 3 ), represents the saturated moisture content, Indicates the initial density (g / cm 3 ); ； Where, Indicates the porosity ratio at a certain pressure level, Indicates the total height deformation of the sample under a certain level of pressure (cm), represents the initial height of the sample (cm); ； Where, Indicates the compression coefficient (MPa ～1 ), Indicates a certain level of pressure value (kPa); ； Where, Indicates the compression index.

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