A slurry for reinforcing the interface of loess excavation and filling and a preparation method thereof

Abstract

The application provides a slurry for reinforcing a loess excavation-filling interface and a preparation method thereof, and belongs to the field of soil reinforcement. The components B obtained from silicate cement, standard sand, fly ash and a polycarboxylate-based water reducing agent play a preliminary reinforcing role, and the A components obtained from the subsequent load bacillus pasteurii bentonite, urea, calcium chloride, a surfactant, an antioxidant and methyl cellulose further fill gaps and enhance the reinforced soil through microbial mineralization deposition of calcium carbonate, improve the shear strength and reduce the strength loss after immersion, and have a small impact on the environment and are convenient to construct.

Description

Technical Field

[0001] This invention belongs to the field of soil reinforcement, specifically relating to a slurry for reinforcing the excavation and filling interface of loess and its preparation method. Background Technology

[0002] Currently, soil reinforcement technology has been using traditional soil improvement methods, such as drainage consolidation and chemical grouting. These traditional methods are costly, energy-intensive, and prone to environmental pollution.

[0003] Loess, in its natural state of low moisture content, possesses high strength and low compressibility. However, when the soil is soaked with water, its structure is disrupted, its strength rapidly decreases, and its compressibility increases. Under the same foundation load, this results in greater additional settlement, posing a significant threat to building safety. The loess excavation-fill interface typically refers to the area within the soil where excavation and filling occur. This interface may present several problems, such as structural instability: the different physical properties of the excavated and filled soil can lead to instability in the soil structure at the interface, making it prone to sliding or collapse; and poor permeability: differences in permeability between the fill and the original soil can result in uneven water penetration, potentially causing soil wetting and softening.

[0004] During excavation and backfilling, the stability of the cut-fill interface is crucial, as these interfaces are often susceptible to soil slippage, collapse, or settlement. Therefore, reinforcing the cut-fill interface to enhance its stability is essential for ensuring project safety and sustainability. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a grout for reinforcing the loess excavation-fill interface and its preparation method. This invention combines traditional grouting technology to produce a grout with fewer organic compounds and less environmental harm. At the same time, it combines the mineralization effect of microorganisms to further enhance the solidification effect on the loess excavation-fill interface, improve compressive strength and reduce strength loss after immersion in water.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a grout for reinforcing the excavation-fill interface of loess, comprising the following raw materials in parts by weight:

[0007] 225-300 parts silicate cement, 900-1350 parts standard sand, 500-800 parts fly ash, 50-100 parts bentonite loaded with Bacillus pasteurella, 20-30 parts urea, 30-50 parts calcium chloride, 1-5 parts surfactant, 1-5 parts antioxidant, 1-10 parts pH adjuster, 300-500 parts water, 30-50 parts methylcellulose, and 10-30 parts polycarboxylate superplasticizer.

[0008] Furthermore, the raw materials are in the following weight proportions: 250-280 parts silicate cement, 1150-1200 parts standard sand, 600-700 parts fly ash, 75-80 parts bentonite loaded with Bacillus pasteurellii, 25-30 parts urea, 35-45 parts calcium chloride, 3-4 parts surfactant, 3-4 parts antioxidant, 1-10 parts pH adjuster, 350-450 parts water, 35-45 parts methylcellulose, and 15-25 parts polycarboxylate superplasticizer.

[0009] Preferably, the raw materials are in the following weight proportions: 275 parts silicate cement, 1175 parts standard sand, 625 parts fly ash, 78 parts bentonite loaded with Bacillus pasteurellii, 28 parts urea, 40 parts calcium chloride, 4 parts surfactant, 4 parts antioxidant, 5 parts pH adjuster, 375 parts water, 40 parts methylcellulose, and 20 parts polycarboxylate superplasticizer.

[0010] The cement and skeleton materials in the grout can provide some reinforcement at the loess excavation and filling interface, initially bonding the interface; the fly ash can promote the fluidity of the grout, making it easier to operate during construction and filling the gaps at the interface; moreover, the Bacillus pasteurellium in the grout contains urea, calcium chloride, and free calcium ions in the soil. Bacillus pasteurellium produces urease, which hydrolyzes urea to produce NH4 under the action of urease. + and HCO3 - Then Ca 2+ and HCO3 - The calcium carbonate precipitate is formed and gradually fills the voids after the slurry solidifies, extending to both sides of the interface, thus enhancing the reinforcement effect and reducing the collapsibility.

[0011] Furthermore, the standard sand has a mesh size of 50-80 mesh; preferably, it has a mesh size of 65 mesh. Sand with a certain mesh size can form pores that facilitate the mineralization and binding of Bacillus pasteurellii.

[0012] Furthermore, the fly ash is Class II fly ash, and the density of the fly ash is 2.8-3.2 g / cm³. 3 .

[0013] Furthermore, the surfactant is Tween 80 or Span 80.

[0014] Surfactants can reduce the surface tension of cell membranes and increase their permeability, thereby improving the penetration ability and survival rate of Bacillus pasteurellii in cement. Simultaneously, surfactants can also increase the wettability of cement, which is beneficial for the adsorption and colonization of Bacillus pasteurellii on the cement surface.

[0015] Furthermore, the antioxidant is 2,6-di-tert-butyl-p-cresol or diethylhydroxylamine.

[0016] Antioxidants can protect Pasteurella from oxidative damage and improve its tolerance in cement. Some substances in cement may generate free radicals that cause oxidative damage to cells, while antioxidants can scavenge these free radicals and reduce the oxidative stress on cells.

[0017] Surfactants and antioxidants can both improve the mineralization ability of Bacillus pasteurellii, increase its activity and survival time, and improve the firmness of the cut-fill interface.

[0018] Furthermore, the preparation method of the bentonite loaded with Bacillus pasteurization is as follows: 1×10 5 A CFU / mL solution of Bacillus pasteurellii was mixed with bentonite at a ratio of 2 mL: 1 g, allowed to stand for 2 hours, and then filtered and naturally dried to obtain Bacillus pasteurellii-loaded bentonite. Bentonite, being porous, can serve as a reinforcing material and a carrier for Bacillus pasteurellii, extending the survival time of the bacteria and enhancing its mineralization.

[0019] Secondly, the present invention provides a method for preparing the above-mentioned slurry for reinforcing the loess excavation and filling interface, comprising the following steps:

[0020] 1) Weigh the raw materials according to the stated weight proportions;

[0021] 2) Mix the bentonite loaded with Bacillus pasteurization, urea, calcium chloride, surfactant, antioxidant, methylcellulose and 20% water and let stand to obtain component A;

[0022] 3) Mix the silicate cement, standard sand, fly ash, polycarboxylate superplasticizer and the remaining water to obtain component B;

[0023] 4) After mixing components A and B, adjust the pH of the system to 7.0-8.0 using a pH adjuster to obtain a slurry for reinforcing the loess excavation and filling interface.

[0024] Furthermore, in step 2), the settling temperature is 30-35℃ and the settling time is 30-120 min.

[0025] Furthermore, the mixing rate in step 4) is 30-40 r / min, and the mixing time is 5-10 min.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. This invention uses cement and skeleton components to create a certain bonding and reinforcement effect on the excavation and filling interface. Then, through the mineralization effect of microorganisms, it extends to both sides of the interface to achieve a strengthening and reinforcement effect. By filling the gaps, it further improves the compressive strength, which can reduce sliding and collapse and reduce the strength loss after immersion in water.

[0028] 2. The slurry prepared by this invention for reinforcing the loess excavation and filling interface has good fluidity, can fill cracks, is easy to construct, and is environmentally friendly. Detailed Implementation

[0029] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention. Unless otherwise specified, the experimental methods used in the embodiments are all conventional methods; the materials and reagents used are all commercially available.

[0030] The raw materials used in the following examples are as follows:

[0031] Preparation method of bentonite loaded with Bacillus pasteurization: 1×10 5 A CFU / mL solution of Bacillus pasteurellii was mixed with bentonite in a ratio of 2 mL: 1 g, allowed to stand for 2 hours, and then filtered and naturally dried to obtain bentonite loaded with Bacillus pasteurellii.

[0032] Example 1

[0033] The preparation method of the grout for reinforcing the loess excavation and filling interface in this embodiment is as follows:

[0034] 1) Weigh out the following components by weight: 275 parts silicate cement, 1175 parts standard sand, 625 parts grade II fly ash, 78 parts bentonite loaded with Bacillus pasteurellii, 28 parts urea, 40 parts calcium chloride, 4 parts Tween 80, 4 parts 2,6-di-tert-butyl-p-cresol, 375 parts water, 40 parts methyl cellulose, and 20 parts polycarboxylate superplasticizer.

[0035] 2) Mix the bentonite loaded with Bacillus pasteurization, urea, calcium chloride, methylcellulose and 75 parts of water and let stand at 33°C for 100 min to obtain component A;

[0036] 3) Mix the silicate cement, standard sand, Class II fly ash, polycarboxylate superplasticizer and the remaining water to obtain component B;

[0037] 4) Mix component A and component B at a rate of 35 r / min for 5 min, and then adjust the pH of the system to 7.5 using a pH adjuster to obtain a slurry for reinforcing the loess excavation and filling interface.

[0038] Example 2

[0039] The preparation method of the grout for reinforcing the loess excavation and filling interface in this embodiment is as follows:

[0040] 1) Weigh out the following components by weight: 225 parts silicate cement, 900 parts standard sand, 500 parts grade II fly ash, 50 parts bentonite loaded with Bacillus pasteurellii, 20 parts urea, 30 parts calcium chloride, 1 part Span 80, 1 part 2,6-di-tert-butyl-p-cresol, 300 parts water, 30 parts methylcellulose, and 10 parts polycarboxylate superplasticizer.

[0041] 2) Mix the bentonite loaded with Bacillus pasteurellium, urea, calcium chloride, methylcellulose and 60 parts of water and let stand at 30°C for 120 min to obtain component A;

[0042] 3) Mix the silicate cement, standard sand, Class II fly ash, polycarboxylate superplasticizer and the remaining water to obtain component B;

[0043] 4) Mix component A and component B at a rate of 30 r / min for 8 min, and then adjust the pH of the system to 7 using a pH adjuster to obtain a slurry for reinforcing the loess excavation and filling interface.

[0044] Example 3

[0045] The preparation method of the grout for reinforcing the loess excavation and filling interface in this embodiment is as follows:

[0046] 1) Weigh out the following components by weight: 300 parts silicate cement, 1350 parts standard sand, 800 parts grade II fly ash, 100 parts bentonite loaded with Bacillus pasteurellii, 30 parts urea, 50 parts calcium chloride, 5 parts Tween 80, 5 parts diethylhydroxylamine, 500 parts water, 50 parts methylcellulose, and 30 parts polycarboxylate superplasticizer.

[0047] 2) Mix the bentonite loaded with Bacillus pasteurization, urea, calcium chloride, methylcellulose and 100 parts of water and let stand at 35°C for 40 min to obtain component A;

[0048] 3) Mix the silicate cement, standard sand, Class II fly ash, polycarboxylate superplasticizer and the remaining water to obtain component B;

[0049] 4) Mix component A and component B at a rate of 40 r / min for 10 min, and then adjust the pH of the system to 8 using a pH adjuster to obtain a slurry for reinforcing the loess excavation and filling interface.

[0050] Comparative Example 1

[0051] The difference from Example 1 is that the bentonite loaded with Bacillus pasteurellii in Example 1 is replaced with ordinary bentonite. The preparation method is the same as in Example 1, and will not be repeated here.

[0052] Comparative Example 2

[0053] The difference from Example 1 is that no surfactants and antioxidants are used, but the preparation method is the same as in Example 1, and will not be repeated here.

[0054] Experimental Example 1

[0055] The slurry prepared in Example 1 and Comparative Example 1 has a fixing effect on the loess excavation and filling interface.

[0056] Experimental methods:

[0057] sampling:

[0058] Loess soil was taken from the Baota area of ​​Yan'an, at a depth of 4m, with a density of 1.58g / cm³. 3 The moisture content was 13.68%; multiple undisturbed soil samples were taken using a ring cutter with a diameter of 10cm and a height of 20cm, and sealed and stored at room temperature (25℃); 100cm samples were also taken. 3 The loess was crushed and stored in a sealed container as a raw material for remolded soil.

[0059] Constructing experimental samples:

[0060] The original soil inside the ring cutter was removed, and a cylindrical soil sample was cut at a 45° angle from the top of the cylinder. The oblique section was used as the excavation interface. The soil sample with the excavation interface was placed in a mold with the same shape as the ring cutter. Then, the moisture content of the remolded soil was controlled to be the same as that of the original soil, and the mold was filled with soil to control the shape and density of the filled soil to be the same as that of the original soil, thus obtaining an experimental sample with an excavation-filling interface.

[0061] Conduct a comparative experiment:

[0062] Blank group: Uncirculated soil sampled by a ring sampler, with a moisture content of 12.36%.

[0063] Control group: The experimental samples with the excavation-fill interface were not subjected to grouting treatment.

[0064] Experimental Group 1: The experimental sample with the cut-fill interface was grouted at the cut-fill interface using a grouting device. The grouting standard was: 0.5 mL / cm² of the grout obtained in Example 1. 2 .

[0065] Experimental Group 2: The experimental sample with the cut-fill interface was grouted at the cut-fill interface using a grouting device. The grouting standard was 0.5 mL / cm² of the grout obtained in Example 2. 2 .

[0066] Experimental Group 3: The experimental sample with the cut-fill interface was grouted at the cut-fill interface using a grouting device. The grouting standard was 0.5 mL / cm² of the grout obtained in Example 3. 2 .

[0067] Experimental Group 4: The experimental sample with the cut-fill interface was grouted at the cut-fill interface using a grouting device. The grouting standard was: 0.5 mL / cm² of the grout obtained in Comparative Example 1. 2 .

[0068] Experimental Group 5: The experimental sample with the cut-fill interface was grouted at the cut-fill interface using a grouting device. The grouting standard was: 0.5 mL / cm² of the grout obtained in Comparative Example 2. 2 .

[0069] The control group, blank group, and experimental group were repeated 4 times each to explore the effects at different curing times (7d, 15d, 28d). After curing, shear and unconfined compressive strength tests were conducted, and the results are shown in Table 1.

[0070] Table 1. Performance Testing of Loess at Grouting-Cover Interface

[0071]

[0072]

[0073] As shown in the table above, the grout in this invention has a significantly higher reinforcement effect on the loess excavation and filling interface than the grout without grouting and the grouting in experimental groups 4 and 5. This indicates that the Bacillus subtilis in the grout obtained in Examples 1-3 of this invention has a high survival rate and activity in the soil. The effect gradually becomes more obvious over time, indicating that the calcium carbonate precipitate gradually penetrates to both sides of the interface.

[0074] Experimental Example 2

[0075] The preparation methods for the blank group, control group, and experimental group are the same as in Experiment Example 1. The purpose of this experiment is to test the permeability coefficient and collapsibility coefficient of each group. The measurement method is based on the building standard for collapsible loess areas (GB50025-2018). The formula for calculating the collapsibility coefficient is:

[0076]

[0077] Where: δ s h is the collapsibility coefficient. p h represents the height of the specimen after deformation stabilizes under a certain pressure level. ′ p h0 represents the height of the sample after it has stabilized following water immersion and deformation under a pressure of 200 kPa; h0 represents the initial height of the sample.

[0078] The permeability coefficient was calculated using a variable head permeability test.

[0079] The measurement data are shown in Table 2.

[0080] Table 2 Permeability and Collapse Coefficient of Loess at the Cut-Fill Interface for Reinforcement

[0081]

[0082]

[0083] As shown in the table above, the slurry obtained by this invention has a good reinforcing effect on the loess excavation and filling interface, and at the same time, it can prevent water subsidence and seepage to a certain extent after immersion in water, and can be applied to loess excavation and filling projects.

[0084] Experiments in groups 4 and 5 revealed the significant effect of *Bacillus pasteurellii*. Group 4, without the addition of *Bacillus pasteurellii*, remained classified as moderately collapsible loess. Group 5, lacking surfactants and antioxidants, showed relatively poorer efficacy and shorter survival time for *Bacillus pasteurellii*. Therefore, the activity of *Bacillus pasteurellii* has a certain impact on the reinforcing and sealing effect of the interface. Thus, increasing the survival time of *Bacillus pasteurellii* has a certain effect. (Loess should be defined as collapsible loess when the collapsibility coefficient is ≥0.015; slightly collapsible when the collapsibility coefficient is 0.015-0.03; moderately collapsible when the collapsibility coefficient is 0.03-0.07; and severely collapsible when the collapsibility coefficient is >0.07.)

[0085] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A grout for reinforcing the interface between excavation and filling of loess, characterized in that, Including the following parts by weight of raw materials: 225-300 parts silicate cement, 900-1350 parts standard sand, 500-800 parts fly ash, 50-100 parts bentonite loaded with Bacillus pasteurella, 20-30 parts urea, 30-50 parts calcium chloride, 1-5 parts surfactant, 1-5 parts antioxidant, 1-10 parts pH adjuster, 300-500 parts water, 30-50 parts methylcellulose, and 10-30 parts polycarboxylate superplasticizer. The surfactant is Tween 80 or Span 80; The antioxidant is 2,6-di-tert-butyl-p-cresol or diethylhydroxylamine; The method for preparing the bentonite loaded with Bacillus pasteurellium is as follows: 1×10 5 A CFU / mL solution of Bacillus pasteurellii was mixed with bentonite in a ratio of 2 mL: 1 g, allowed to stand for 2 hours, and then filtered and naturally dried to obtain bentonite loaded with Bacillus pasteurellii.

2. The grout for reinforcing the excavation and filling interface of loess according to claim 1, characterized in that, The raw materials are in the following weight proportions: 250-280 parts silicate cement, 1150-1200 parts standard sand, 600-700 parts fly ash, 75-80 parts bentonite loaded with Bacillus pasteurellii, 25-30 parts urea, 35-45 parts calcium chloride, 3-4 parts surfactant, 3-4 parts antioxidant, 1-10 parts pH adjuster, 350-450 parts water, 35-45 parts methylcellulose, and 15-25 parts polycarboxylate superplasticizer.

3. The grout for reinforcing the loess excavation and filling interface according to claim 2, characterized in that, The standard sand has a mesh size of 50-80.

4. The grout for reinforcing the loess excavation and filling interface according to claim 2, characterized in that, The fly ash is Class II fly ash, and its density is 2.8-3.2 g / cm³. 3 .

5. The method for preparing the slurry for reinforcing the loess excavation-fill interface according to any one of claims 1-4, characterized in that, Includes the following steps: Step 1) Weigh the raw materials according to the stated weight proportions; Step 2) Mix the bentonite loaded with Bacillus pasteurization, urea, calcium chloride, surfactant, antioxidant, methylcellulose and 20% water and let stand to obtain component A; Step 3) Mix the silicate cement, standard sand, fly ash, polycarboxylate superplasticizer and the remaining water to obtain component B; Step 4) After mixing components A and B, adjust the pH of the system to 7.0-8.0 using a pH adjuster to obtain a slurry for reinforcing the loess excavation and filling interface.

6. The preparation method according to claim 5, characterized in that, The settling temperature in step 2) is 30-35℃, and the settling time is 30-120 min.

7. The preparation method according to claim 5, characterized in that, The mixing rate in step 4) is 30-40 r / min, and the mixing time is 5-10 min.

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