Low-carbon construction optimization method for cement-soil mixing pile

Abstract

The invention discloses a low-carbon construction optimization method for a cement-soil mixing pile, and belongs to the technical field of geotechnical engineering foundation treatment.The low-carbon construction optimization method for the cement-soil mixing pile comprises the following steps that corn straw biochar, cement and water are mixed to be uniform, corn straw biochar-cement mixture slurry is prepared, and the mixture slurry is mixed with the cement; and the corn straw biochar-cement mixture slurry is added into a foundation soil layer, and the corn straw biochar-cement soil mixing pile is prepared. The compressive strength of the corn straw biochar-cement soil mixing pile prepared from the corn straw is equivalent to that of a cement soil mixing pile, and the requirement for engineering mechanical properties is completely met. And by reducing the cement consumption, the engineering construction cost is reduced, the consumption of natural resources in cement production is relieved, and the economic benefit and sustainability are improved.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering foundation treatment technology, and in particular relates to a low-carbon construction optimization method for cement-soil mixing piles. Background Technology

[0002] Against the backdrop of accelerated infrastructure construction and urbanization, foundation treatment has become a crucial aspect of engineering projects. Currently, cement-soil mixing piles are the mainstream foundation treatment technology, which involves injecting silicate cement into weak soil layers for solidification to improve the bearing capacity of the foundation. However, cement materials are not only costly in engineering construction, but their energy-intensive production process also places enormous pressure on the ecological environment. Therefore, while meeting engineering mechanical performance requirements, it is urgent to break through the limitations of traditional technologies, reduce the demand for and dependence on cement in engineering construction, and explore new foundation treatment methods that are economical, environmentally friendly, and highly efficient. Summary of the Invention

[0003] To address the above problems, this invention provides a low-carbon construction optimization method for cement-soil mixing piles.

[0004] A low-carbon construction optimization method for cement-soil mixing piles includes the following steps: mixing corn stalk biochar, cement, and water to prepare a corn stalk biochar-cement mixture slurry; adding the corn stalk biochar-cement mixture slurry into the foundation soil layer to prepare a corn stalk biochar-cement-soil mixing pile.

[0005] Furthermore, the corn stalk biochar accounts for 1-7% of the cement mass; and the corn stalk biochar-cement mixture slurry accounts for 5-20% of the foundation soil mass based on dry soil mass.

[0006] Furthermore, the foundation soil layer is selected from silty soft soil layer or peat soft soil layer.

[0007] Furthermore, when the foundation soil layer is a silty soft soil layer, the corn straw biochar accounts for 1-7% of the cement mass.

[0008] Furthermore, when the foundation soil layer is a peat-rich soft soil layer, the corn straw biochar accounts for 1-7% of the cement mass.

[0009] After incorporating a certain proportion of corn stalk biochar, the compressive strength of the corn stalk biochar-cement-soil mixing pile prepared by this invention is basically the same as that of the cement-soil mixing pile. This technology breaks through the traditional cement mixing pile method for treating soft soil foundations. Under the premise of ensuring that the soil strength meets the engineering construction standards, corn stalk biochar is used to replace part of the cement in cement-soil mixing piles for foundation treatment. This can significantly reduce cement usage, effectively reduce the use of high-energy-consuming building materials and carbon emissions, which is in line with the concept of green and low-carbon development. At the same time, it can realize the resource utilization of corn stalk waste, greatly reduce the improvement cost, and has significant environmental benefits and economic value, providing a new path for the treatment of soft soil foundations.

[0010] Furthermore, the preparation method of the corn stalk biochar includes the following steps: after drying, the corn stalks are crushed, sieved, and then subjected to pyrolysis treatment to obtain corn stalk biochar.

[0011] Furthermore, the pyrolysis treatment is performed at a temperature of 500°C for 2 hours.

[0012] The solid (biochar), liquid (bio-oil), and gaseous mixture generated from the pyrolysis of corn stalks in a roasting furnace are separated. First, the density difference between solid biochar particles and the gas / liquid mixture is used to separate the solid biochar from the gas-liquid mixture. Under the centrifugal force of a cyclone separator, the biochar particles are thrown against the side wall of the roasting furnace and settle to the bottom. After being cooled to 50°C by an air-cooling system, they are stored in a sealed silo. Second, the liquid bio-oil is separated from the gas by utilizing the boiling point differences of the different components. The condensable components are liquefied through temperature-controlled condensation, while the non-condensable gases remain in a gaseous state. After separation by a gravity gas-liquid separator, the liquid, due to its higher density, settles to the bottom and is collected through a pipeline. The uncondensed gas is discharged from the top. Finally, the gas is purified and used as fuel for the roasting furnace (replacing natural gas or coal), achieving energy self-sufficiency and reducing energy consumption.

[0013] Biochar, a typical product of agricultural and forestry waste resource utilization, is prepared through an oxygen-limited high-temperature pyrolysis process. It possesses a well-developed porous structure, excellent cation exchange capacity, and good chemical stability, demonstrating great potential in soil improvement. Corn stalks are one of the main agricultural wastes, produced in huge quantities. Converting them into biochar for foundation treatment not only achieves solid waste resource utilization and reduces environmental pollution but also effectively reduces cement usage, significantly saving engineering costs.

[0014] Furthermore, the specific operation of pumping the corn stalk biochar-cement mixture slurry into the foundation soil layer includes the following steps: the corn stalk biochar-cement mixture slurry is pressurized and transported to the grouting pipe of the deep mixing pile machine; the mixing pile machine continuously sprays the slurry to the designed depth of the foundation soil layer to be treated, with the spraying rate controlled at 30-50 L / min; while spraying the corn stalk biochar-cement mixture slurry, the mixing pile machine is continuously lifted upwards until the top of the pile, with a lifting rate not exceeding 0.5 m / min, and the dwell time at the top of the pile not exceeding 1 minute; subsequently, the mixing pile machine continuously stirs and sinks to the bottom of the pile, and the corn stalk biochar-cement mixture slurry is sprayed again and continuously stirred, lifted upwards until the top of the pile, with the spraying rate controlled at 25-40 L / min and the lifting rate not exceeding 0.8 m / min, thus preparing the corn stalk biochar-cement soil mixing pile.

[0015] Compared with the prior art, the present invention has the following advantages and technical effects:

[0016] (1) This invention uses corn stalks, agricultural waste, as biochar raw material, realizing the resource utilization of solid waste and effectively reducing environmental pollution and carbon emissions caused by incineration; at the same time, corn stalks are widely available and inexpensive, which greatly reduces the cost of engineering materials.

[0017] (2) The compressive strength of the corn stalk biochar-cement-soil mixing pile prepared by this invention is comparable to that of the cement-soil mixing pile, fully meeting the requirements of engineering mechanical performance. By reducing the amount of cement used, not only is the construction cost reduced, but the consumption of natural resources by cement production is also alleviated, thereby improving economic efficiency and sustainability.

[0018] (3) The corn stalk biochar-cement soil mixing pile provided by the present invention has a simple process operation and low technical threshold. It does not require complex equipment and special processes and can be directly applied to existing engineering construction scenarios. Moreover, it has high production efficiency and strong controllability, and has the potential for large-scale industrial production. It can be widely used in various engineering fields such as roads and foundations. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 The compressive strength of corn stalk biochar-cement silty soft soil mixing piles (7 days after pile formation);

[0021] Figure 2The compressive strength of corn straw biochar-cement silty soft soil mixing piles (14 days after pile formation);

[0022] Figure 3 The compressive strength of corn straw biochar-cement silty soft soil mixing piles (28 days after pile formation);

[0023] Figure 4 The compressive strength of corn stalk biochar-cement peat soft soil mixing piles (7 days after pile formation);

[0024] Figure 5 The compressive strength of corn stalk biochar-cement peat soft soil mixing piles (14 days after pile formation);

[0025] Figure 6 The compressive strength of corn stalk biochar-cement peat soft soil mixing piles (28 days after pile formation). Detailed Implementation

[0026] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0027] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0028] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0029] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0030] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0031] This invention provides a low-carbon construction optimization method for cement-soil mixing piles: (1) Dry and crush corn stalks, place them in a pyrolysis furnace, and pyrolyze them at a constant temperature for a certain time under oxygen-limited conditions to obtain corn stalk biochar; (2) Mix cement, corn stalk biochar and water thoroughly according to a set ratio to obtain a corn stalk biochar-cement mixture slurry; (3) Pump the thoroughly mixed corn stalk biochar-cement mixture slurry into the foundation soil layer to obtain a corn stalk biochar-cement-soil mixing pile; (4) Drill core samples of corn stalk biochar-cement-soil mixing piles with different pile formation times for subsequent performance testing and analysis.

[0032] In some preferred embodiments of the present invention, waste corn stalks are used as raw materials. They are placed under the sun to dry until the internal residual moisture content is less than 10%. Then, they are crushed by a pulverizer and passed through a 0.075mm sieve to prepare corn stalk biochar with a finer particle size.

[0033] The pyrolysis process of corn stalks is the core link in the industrial production of corn stalk biochar. Dry, fine-particle corn stalks are loaded into a closed, continuous rotary roasting furnace. To prevent the corn stalks from decomposing violently and to ensure a more stable biochar structure, the rotary roasting furnace containing the corn stalks is slowly heated at a rate of 20°C / min until it reaches 500°C. The pyrolysis process takes 2 hours in the furnace to ensure complete carbonization.

[0034] The aforementioned corn stalk pyrolysis process produces solids (corn stalk biochar), liquids (bio-oil), and gases, which are collected separately by a separation system for use. Solid corn stalk biochar is discharged from the bottom of the roasting furnace. To prevent secondary combustion, it is cooled to 50°C by an air-cooling system and then stored in a sealed silo to prevent moisture absorption. The liquid bio-oil is a brownish-black viscous liquid that can be further processed as fuel or a chemical raw material. The gas, after purification (removal of tar and dust), can be used as fuel for the roasting furnace (replacing natural gas or coal), achieving energy self-sufficiency and reducing energy consumption.

[0035] The corn stalk biochar generated by pyrolysis is mixed with cement in a dry state, with the biochar accounting for 1-7% of the cement mass. The mixing process is carried out in a mixer at a speed controlled at 200-300 r / min for 30 min to ensure uniform mixing of the dry mixture of biochar and cement. Subsequently, the amount of water added is determined according to the optimum moisture content of the soil layer and added to the mixer. After contact with the dry mixture, it is first mixed at a low speed of 100-200 r / min for 15 min to allow initial water infiltration. Then, it is mixed at a high speed of 300-500 r / min for 30 min to promote cement hydration and dispersion of corn stalk biochar. Finally, it is mixed at a low speed of 100 r / min for 15 min to eliminate air bubbles and stabilize the slurry, thus preparing a corn stalk biochar-cement mixture slurry.

[0036] In some preferred embodiments of the present invention, corn straw biochar accounts for 1-7% of the cement mass; and the corn straw biochar-cement mixture slurry accounts for 5-20% of the foundation soil mass based on dry soil mass.

[0037] In some preferred embodiments of the present invention, the foundation soil layer is selected from silty soft soil layer or peat soft soil layer: when the foundation soil layer is silty soft soil layer, the corn straw biochar accounts for 1-7% of the cement mass; when the foundation soil layer is peat soft soil layer, the corn straw biochar accounts for 1-7% of the cement mass.

[0038] In some preferred embodiments of the present invention, the specific operation of pumping the corn stalk biochar-cement mixture slurry into the foundation soil layer includes the following steps: the corn stalk biochar-cement mixture slurry is pressurized and transported to the grouting pipe of a deep mixing pile machine; the mixing pile machine continuously sprays the slurry to the designed depth of the foundation soil layer to be treated, with the spraying rate controlled at 30-50 L / min. Simultaneously, while spraying the corn stalk biochar-cement mixture slurry, the mixing pile machine continuously rises until the top of the pile, with a rising rate not exceeding 0.5 m / min, and the dwell time at the top of the pile not exceeding 1 minute. Subsequently, the mixing pile machine continuously stirs and sinks to the bottom of the pile, and again sprays the corn stalk biochar-cement mixture slurry while continuously stirring, rising upwards until the top of the pile, with the spraying rate controlled at 25-40 L / min and the rising rate not exceeding 0.8 m / min, thus preparing a corn stalk biochar-cement soil mixing pile.

[0039] This invention involves drilling core samples from corn stalk biochar-cement-soil mixing piles at 7, 14, and 28 days after pile formation, and then conducting compressive strength tests using a universal testing machine to compare and analyze the strength of corn stalk biochar-cement-soil mixing piles and cement-soil mixing piles.

[0040] In some preferred embodiments of the present invention, the low-carbon construction optimization method for cement-soil mixing piles can further include the addition of microbial mineralizers and urea, specifically comprising the following steps: mixing corn stalk biochar, cement, microbial mineralizers, urea, and water to prepare a corn stalk biochar-cement mixture slurry; pumping the corn stalk biochar-cement mixture slurry into the foundation soil layer to prepare a corn stalk biochar-cement-soil mixing pile. The microbial mineralizer accounts for 3% of the cement mass, and urea accounts for 0.5% of the cement mass. The preparation method of the microbial mineralizer includes the following steps: preparing a spore suspension from a mixture of *Bacillus pasteurellii* and *Pseudomonas aeruginosa* spores, adding nutrients (yeast extract, ammonium nitrate, and inosine) and porous materials, then using a vacuum impregnation method to allow the bacteria and nutrients to enter the interconnected pores of the porous material, and drying to constant weight to prepare the microbial mineralizer. The concentration of the spore suspension is 8 × 10⁻⁶. 8 The concentration ratio of *Bacillus pasteurellii* to *Pseudomonas aeruginosa* is 10:1; the mass ratio of spore suspension to porous material is 1:10, the porous material is zeolite, and the nutrients include yeast extract, ammonium nitrate, and inosine, wherein the concentration of yeast extract in the spore suspension is 20 g / L, the concentration of ammonium nitrate in the spore suspension is 10 g / L, and the concentration of inosine in the spore suspension is 1 g / L.

[0041] In the above-mentioned preferred technical solution, the microbial mineralizer based on Bacillus pasteurellii and Pseudomonas aeruginosa works synergistically with corn straw biochar and cement to enhance the strength of the mixing pile through multiple pathways such as biomineralization, pore regulation, and cementation strengthening. The specific mechanism of action is as follows: Bacillus pasteurellii secretes urease, which catalyzes the hydrolysis of urea to generate CO3. 2- and NH4 + , with Ca in the environment 2+ (From cement hydration products) combine to form CaCO3, filling soil pores and cementing particles. *Pseudomonas aeruginosa* secretes extracellular polymers, aiding in the directional growth of CaCO3 crystals and enhancing the cohesiveness of the precipitate. Yeast extract, ammonium nitrate, and inosine provide the carbon, nitrogen, and energy sources necessary for microbial growth, extending the activity cycle of the microbial community and ensuring continuous mineralization. Zeolite, as a porous carrier, protects the microbial cells and slowly releases nutrients, preventing microbial inactivation due to the high alkalinity of cement (pH>12). Biochar, with its large specific surface area, can serve as a microreactor for microbial colonization, expanding the mineralization reaction interface while simultaneously adsorbing Ca. 2+ and CO3 2- This promotes the precipitation of CaCO3 in areas of high local concentration. The alkaline environment of biochar (pH 9-11) is compatible with the weakly alkaline conditions (pH 8-9) required for microbial mineralization, avoiding strong alkalinity that inhibits bacterial activity. From a microscopic perspective, the biochar-cement-microbial mineralization products form a three-dimensional network structure, enhancing interparticle bonding, which macroscopically manifests as an increase in compressive strength.

[0042] Example 1: Preparation method of corn stalk biochar-cement silty soft soil mixing pile

[0043] S1. Place the waste corn stalks under the sun until the internal residual moisture is less than 10%, then crush them with a pulverizer and pass them through a 0.075mm sieve. Put the sieved corn stalks into a continuous rotary roasting furnace, seal it, and heat it to 500℃ at a heating rate of 20℃ / min. Pyrolyze it in the roasting furnace for 2 hours, and separate the biochar, bio-oil and gas mixture generated by pyrolysis to obtain corn stalk biochar.

[0044] S2. Weigh the corn stalk biochar prepared in S1 and mix it with cement in a dry state, so that the corn stalk biochar accounts for 0% (control group, used to prepare cement-soil mixing piles), 1%, 3%, and 7% of the cement mass, respectively, to obtain corn stalk biochar cement mixtures; based on the moisture content and natural density of the silty soft soil layer, and the mass ratio θ of the corn stalk biochar cement mixture to dry soil (5%, 10%, and 20%), calculate the mass of corn stalk biochar and cement required to prepare corn stalk biochar-cement-soil mixing piles, and put the corn stalk biochar cement mixture into a mixer and stir. The mixture was stirred at a speed of 300 r / min for 30 min. The amount of water added was determined based on the moisture content of the silty soft soil layer. Water was added to the corn straw biochar cement mixture. The mixture was first stirred at a low speed of 200 r / min for 15 min to allow the water to initially wet the soil. Then, it was stirred at a high speed of 500 r / min for 30 min to promote cement hydration and dispersion of corn straw biochar. Finally, it was stirred at a low speed of 100 r / min for 15 min to eliminate air bubbles and stabilize the slurry, thus preparing the corn straw biochar-cement mixture slurry.

[0045] S3. The corn stalk biochar-cement mixture slurry prepared in S2 is pressurized and transported to the grouting pipe of the deep mixing pile machine. The slurry is continuously sprayed into the designed depth of the silty soft soil layer by the mixing pile machine, and the spraying rate is controlled at 40L / min. At the same time, while spraying the corn stalk biochar-cement mixture slurry, the mixing pile machine is continuously lifted upwards until the top of the pile, with a lifting rate not exceeding 0.5m / min and a dwell time at the top of the pile not exceeding 1min. Subsequently, the mixing pile machine continuously stirs and sinks to the bottom of the pile, and the corn stalk biochar-cement mixture slurry is sprayed again and continuously stirred, and lifted upwards until the top of the pile, with the spraying rate controlled at 40L / min and the lifting rate not exceeding 0.8m / min, to obtain corn stalk biochar-cement silty soft soil mixing piles and cement silty soft soil mixing piles.

[0046] Example 2: Preparation method of corn stalk biochar-cement peat soft soil mixing pile

[0047] S1. Same as Example 1;

[0048] S2. Weigh the corn stalk biochar prepared in S1 and mix it with cement in a dry state, making the corn stalk biochar account for 0% (control group, used to prepare cement-soil mixing piles), 1%, 3%, and 7% of the cement mass, respectively, to obtain corn stalk biochar cement mixtures; based on the water content and natural density of the peat soft soil layer, and the mass ratio θ of the corn stalk biochar cement mixture to dry soil (5%, 10%, and 20%), calculate the mass of corn stalk biochar and cement required to prepare corn stalk biochar-cement-soil mixing piles, and put the corn stalk biochar cement mixture into... The mixture was stirred in a mixer at a speed of 200 r / min for 30 min. The amount of water added was determined based on the moisture content of the peat soft soil layer. Water was added to the corn straw biochar cement mixture. The mixture was first stirred at a low speed of 150 r / min for 15 min to allow the water to initially wet the soil. Then, it was stirred at a high speed of 400 r / min for 30 min to promote cement hydration and dispersion of corn straw biochar. Finally, it was stirred at a low speed of 100 r / min for 15 min to prepare the corn straw biochar-cement mixture slurry.

[0049] S3. The corn stalk biochar-cement mixture slurry prepared in S2 is pressurized and transported to the grouting pipe of the deep mixing pile machine. The slurry is continuously sprayed into the designed depth of the peat soft soil layer by the mixing pile machine, and the spraying rate is controlled at 40L / min. At the same time, while spraying the corn stalk biochar-cement mixture slurry, the mixing pile machine is continuously lifted upwards until the top of the pile, with a lifting rate not exceeding 0.5m / min and a dwell time at the top of the pile not exceeding 1min. Subsequently, the mixing pile machine continuously mixes and sinks to the bottom of the pile, and the corn stalk biochar-cement mixture slurry is sprayed again and continuously mixed, and lifted upwards until the top of the pile, with the spraying rate controlled at 40L / min and the lifting rate not exceeding 0.8m / min, to obtain corn stalk biochar-cement peat soft soil mixing piles and cement peat soft soil mixing piles.

[0050] Performance Test 1

[0051] After 7, 14, and 28 days of pile formation, the corn stalk biochar-cement silty soil mixing piles prepared in Example 1 and the corn stalk biochar-cement peat soft soil mixing piles prepared in Example 2 were drilled using a core drilling rig to prepare cylindrical specimens with a diameter of 39.1 mm and a height of 80 mm. Compressive strength tests were conducted using a universal testing machine with a loading rate set to 2 mm / min. The strengths of the corn stalk biochar-cement silty soil mixing piles, the corn stalk biochar-cement peat soft soil mixing piles, the cement silty soil mixing piles, and the cement peat soft soil mixing piles were compared and analyzed to obtain the compressive strength of the corn stalk biochar-cement soil mixing piles at different pile formation times. The results are shown in Table 1 and [Table data missing]. Figure 1-6 .

[0052] Figure 1-Figure 3 The compressive strength of corn straw biochar-cement silty soft soil mixing piles after 7 days, 14 days, and 28 days of pile formation are as follows: Figure 4-Figure 6 The compressive strength of corn straw biochar-cement peat soft soil mixing piles was measured in order at 7 days, 14 days, and 28 days after pile formation.

[0053] Table 1

[0054]

[0055]

[0056] Through Table 1 and Figure 1-6 It can be seen that, compared to pure cement-soil mixing piles, the compressive strength of corn stalk biochar-cement silty soft soil mixing piles and corn stalk biochar-cement peat soft soil mixing piles is similar to or even higher. At 7 days after pile formation, the compressive strength of corn stalk biochar-cement silty soft soil mixing piles and corn stalk biochar-cement peat soft soil mixing piles is basically the same as that of pure cement silty soft soil and cement peat soft soil mixing piles. As the pile formation time increases (greater than or equal to 14 days), the cement gradually hardens, and the strength of the mixing pile continuously increases, with the compressive strength of corn stalk biochar-cement soil mixing piles being slightly greater than that of pure cement-soil mixing piles.

[0057] The aforementioned compressive strength test confirms that corn stalk biochar can effectively replace part of the cement in cement-soil mixing pile foundation treatment. Its mechanism of action includes: firstly, the porous structure of biochar can fill the micropores inside the cement-soil mixture, optimizing the soil's microstructure; secondly, biochar slows down the cement hydration process by adsorbing free water, promoting a more complete hydration reaction and increasing the amount of cementitious products generated. Therefore, using corn stalk biochar to partially replace cement in the preparation of mixing piles can reduce cement usage and carbon emissions while maintaining or improving the overall strength of the mixing piles, aligning with the low-carbon development concept. Simultaneously, utilizing agricultural waste to prepare biochar achieves resource recycling, resulting in significant environmental benefits.

[0058] Example 3

[0059] S1. Same as Example 1;

[0060] S2. A concentration of 8 × 10⁸ CFU / mL was prepared by mixing the sporosomes of *Bacillus pasteurellii* and *Pseudomonas aeruginosa* at a concentration ratio of 10:1. 8 A spore suspension with cells / mL was prepared by adding yeast extract (20 g / L), ammonium nitrate (10 g / L), inosine (1 g / L), and zeolite (mass ratio of spore suspension to zeolite was 1:10) to the obtained spore suspension. The bacteria and nutrients were then impregnated into the interconnecting channels of the zeolite using a vacuum impregnation method. The mixture was then dried (50°C) to constant weight to prepare a microbial mineralizer.

[0061] S3. Weigh the corn stalk biochar prepared in S1, cement, microbial mineralizer prepared in S2, and urea, and mix them in a dry state so that the corn stalk biochar accounts for 1% and 3% of the cement mass, the microbial mineralizer accounts for 5% of the cement mass, and the urea accounts for 0.5% of the cement mass, thus obtaining a corn stalk biochar cement mixture. Based on the water content and natural density of the silty soft soil layer, and the mass ratio θ (20%) of the corn stalk biochar cement mixture to dry soil, calculate the mass of corn stalk biochar, cement, microbial mineralizer, and urea required to prepare corn stalk biochar-cement-soil mixing piles. The biochar-cement mixture was placed in a mixer and stirred at a speed of 200 r / min for 30 min. The amount of water to be added was determined based on the moisture content of the silty soft soil layer. Water was added to the corn straw biochar-cement mixture and stirred at a low speed for 15 min at a speed of 200 r / min to allow the water to initially wet the mixture. Then, it was stirred at a high speed for 30 min at a speed of 300 r / min to promote cement hydration and dispersion of corn straw biochar. Finally, it was stirred at a low speed for 15 min at a speed of 100 r / min to prepare a corn straw biochar-cement mixture slurry.

[0062] S4. The corn stalk biochar-cement mixture slurry prepared in S3 is pressurized and transported to the grouting pipe of the deep mixing pile machine. The slurry is continuously sprayed into the designed depth of the silty soft soil layer by the mixing pile machine, and the spraying rate is controlled at 40L / min. At the same time, while spraying the corn stalk biochar-cement mixture slurry, the mixing pile machine is continuously lifted upwards until the top of the pile, with a lifting rate not exceeding 0.5m / min and a dwell time at the top of the pile not exceeding 1min. Subsequently, the mixing pile machine continuously stirs and sinks to the bottom of the pile, and the corn stalk biochar-cement mixture slurry is sprayed again and continuously stirred, and lifted upwards until the top of the pile, with the spraying rate controlled at 40L / min and the lifting rate not exceeding 0.8m / min, to obtain the corn stalk biochar-cement silty soft soil mixing pile.

[0063] Example 4

[0064] S1. Same as Example 1;

[0065] S2. A concentration of 8 × 10⁸ CFU / mL was prepared by mixing the sporosomes of *Bacillus pasteurellii* and *Pseudomonas aeruginosa* at a concentration ratio of 10:1. 8 A spore suspension with cells / mL was prepared by adding yeast extract (20 g / L), ammonium nitrate (10 g / L), inosine (1 g / L), and zeolite (mass ratio of spore suspension to zeolite 1:10) to the obtained spore suspension. The bacteria and nutrients were then impregnated into the interconnecting channels of the zeolite using a vacuum impregnation method. The mixture was then dried (50°C) to constant weight to obtain a microbial mineralizing agent.

[0066] S3. Weigh the corn stalk biochar prepared in S1, and mix it with cement, the microbial mineralizer prepared in S2, and urea in a dry state, so that the corn stalk biochar accounts for 3% and 7% of the cement mass, the microbial mineralizer accounts for 5% of the cement mass, and the urea accounts for 0.5% of the cement mass, to obtain a corn stalk biochar cement mixture; based on the moisture content and natural density of the peat soft soil layer, and the mass ratio θ (20%) of the corn stalk biochar cement mixture to dry soil, calculate the mass of corn stalk biochar, cement, microbial mineralizer, and urea required to prepare corn stalk biochar-cement soil mixing piles. The corn straw biochar cement mixture was placed in a mixer and stirred at a speed of 200 r / min for 30 min. The amount of water to be added was determined according to the moisture content of the peat soft soil layer. Water was added to the corn straw biochar cement mixture and stirred at a low speed for 15 min at a speed of 200 r / min to allow the water to initially wet the mixture. Then, it was stirred at a high speed for 30 min at a speed of 300 r / min to promote cement hydration and dispersion of corn straw biochar. Finally, it was stirred at a low speed for 15 min at a speed of 100 r / min to prepare a corn straw biochar-cement mixture slurry.

[0067] S4. The corn stalk biochar-cement mixture slurry prepared in S3 is pressurized and transported to the grouting pipe of the deep mixing pile machine. The slurry is continuously sprayed into the designed depth of the peat soft soil layer by the mixing pile machine, and the spraying rate is controlled at 40L / min. At the same time, while spraying the corn stalk biochar-cement mixture slurry, the mixing pile machine is continuously lifted upwards until the top of the pile, with a lifting rate not exceeding 0.5m / min and a dwell time at the top of the pile not exceeding 1min. Subsequently, the mixing pile machine continuously mixes and sinks to the bottom of the pile, and the corn stalk biochar-cement mixture slurry is sprayed again and continuously mixed, and lifted upwards until the top of the pile, with the spraying rate controlled at 50L / min and the lifting rate not exceeding 0.8m / min, to obtain the corn stalk biochar-cement peat soft soil mixing pile.

[0068] Performance Test 2

[0069] After 7, 14, and 28 days of pile formation, the corn straw biochar-cement silty soil mixing piles prepared in Example 3 and the corn straw biochar-cement peat soft soil mixing piles prepared in Example 4 were drilled using a core drilling rig to prepare cylindrical samples with a diameter of 39.1 mm and a height of 80 mm. The compressive strength was then tested using a universal testing machine with a loading rate set to 2 mm / min. The compressive strength of the corn straw biochar-cement soil mixing piles at different pile formation times was obtained, and the test results are shown in Table 2.

[0070] Table 2

[0071]

[0072] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A low-carbon construction optimization method for cement-soil mixing piles, characterized in that, Includes the following steps: Corn stalk biochar, cement, and water are mixed to prepare a corn stalk biochar-cement mixture slurry. The corn stalk biochar-cement mixture slurry is then pumped into the foundation soil layer to prepare a corn stalk biochar-cement soil mixing pile.

2. The low-carbon construction optimization method for cement-soil mixing piles according to claim 1, characterized in that, The corn stalk biochar accounts for 1-7% of the cement mass; and the corn stalk biochar-cement mixture slurry accounts for 5-20% of the foundation soil mass based on dry soil mass.

3. The low-carbon construction optimization method for cement-soil mixing piles according to claim 2, characterized in that, The foundation soil layer is selected from silty soft soil layer or peat soft soil layer.

4. The low-carbon construction optimization method for cement-soil mixing piles according to claim 3, characterized in that, When the foundation soil layer is a silty soft soil layer, the corn straw biochar accounts for 1-7% of the cement mass.

5. The low-carbon construction optimization method for cement-soil mixing piles according to claim 3, characterized in that, When the foundation soil layer is a peat-rich soft soil layer, the corn straw biochar accounts for 1-7% of the cement mass.

6. The low-carbon construction optimization method for cement-soil mixing piles according to claim 1, characterized in that, The preparation method of the corn stalk biochar includes the following steps: after drying, the corn stalks are crushed, sieved, and then subjected to pyrolysis treatment to obtain corn stalk biochar.

7. The low-carbon construction optimization method for cement-soil mixing piles according to claim 6, characterized in that, The pyrolysis treatment was carried out at a temperature of 500°C for 2 hours.

8. The low-carbon construction optimization method for cement-soil mixing piles according to claim 1, characterized in that, The specific operation of pumping corn stalk biochar-cement mixture slurry into the foundation soil layer includes the following steps: the corn stalk biochar-cement mixture slurry is pressurized and transported to the grouting pipe of the deep mixing pile machine; the mixing pile machine continuously sprays the slurry to the designed depth of the foundation soil layer to be treated, with the spraying rate controlled at 30-50 L / min; while spraying the corn stalk biochar-cement mixture slurry, the mixing pile machine is continuously lifted upwards until the top of the pile, with a lifting rate not exceeding 0.5 m / min, and the dwell time at the top of the pile not exceeding 1 minute; subsequently, the mixing pile machine continuously stirs and sinks to the bottom of the pile, and the corn stalk biochar-cement mixture slurry is sprayed again and continuously stirred, lifted upwards until the top of the pile, with the spraying rate controlled at 25-40 L / min and the lifting rate not exceeding 0.8 m / min, thus preparing the corn stalk biochar-cement soil mixing pile.

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