Construction method for reinforcing collapsible loess foundation based on grouting carbonization-vibration densification cooperation

Abstract

The invention discloses a construction method for reinforcing a collapsible loess foundation based on grouting carbonization-vibration densification cooperation, which is realized through a stirring grouting-resonance densification cooperation reinforcing device, and comprises the following construction steps: S1, site pretreatment; s2, preparing slurry; s3, paying off and positioning; s4, slurry spraying, stirring and sinking; s5, stirring and air injection are stopped; s6, vibration, air injection and lifting; s7, a next pile position is replaced; and S8, pile hole backfilling. The collapsible loess reinforcement construction method is efficient, low-carbon and low-disturbance, during construction, powerful crushing of a loess structure, efficient mixing and permeation of slurry, soil and gas and full excitation of low-carbon reaction can be achieved, immediate compaction is achieved through vibration, the bearing capacity of a foundation is remarkably improved, collapsibility is eliminated, and the collapsible loess reinforcement construction method has the advantages of being simple in structure and convenient to use. The grouting carbonization-vibration densification synergistic reinforcement device used in the method is flexible to move, convenient to operate and wide in application range, can meet the application requirements of large-scale engineering, and has remarkable advantages in the aspects of resource recycling and carbon emission reduction.

Description

Technical Field

[0001] This invention relates to the field of foundation treatment technology, and in particular to a construction method for reinforcing collapsible loess foundations based on grouting carbonization-vibration compaction synergistic reinforcement. Background Technology

[0002] Collapsible loess is widely distributed in Northwest my country, North China, and the middle reaches of the Yellow River, covering a total area of ​​over 630,000 square kilometers. It possesses unique engineering properties characterized by "large porosity, weak cementation, and high water sensitivity." In its natural state, it exhibits low compressibility and high strength, but upon contact with water, the soluble salts in its cementation dissolve, resulting in a high collapsibility coefficient. This leads to the instantaneous collapse of its porous structure, triggering sudden, localized, and uneven settlement, posing a fatal threat to settlement-sensitive projects such as railways, subways, and large factories. Therefore, appropriate reinforcement treatment is necessary before engineering applications to meet the bearing capacity and stability requirements of the overlying structures.

[0003] Existing treatment methods are broadly categorized into two types: conventional physical methods and chemical reinforcement methods. The former includes methods such as dynamic compaction, replacement, and compaction piles, while the latter includes silicification and alkaline solutions, all of which have certain drawbacks. Dynamic compaction offers relatively fast treatment speed but generates significant construction vibration, which has a substantial impact on the surrounding environment. Replacement methods suffer from high costs, long cycles, and significant soil disturbance, and their effectiveness in treating deep foundations is limited. Compaction piles can provide higher foundation bearing capacity, but their cost is typically high. Silicification involves injecting chemical solvents into the soil, expelling moisture and air, and forming a unified soil structure through cementation. It has many branches, with representative methods including pressure-based two-liquid, pressure-based single-liquid, pressure-mixed, and electro-silicification. The difference between two-liquid and single-liquid methods lies in the chemical solvents used: two-liquid methods typically use both water glass (sodium silicate) and calcium chloride solutions; single-liquid methods often use only water glass solution. These solutions react with calcium salts in the foundation soil, significantly improving the foundation strength. There are many types of silicification methods with a wide range of applications, which can be flexibly selected according to engineering needs. However, it is important to note that if the foundation contains organic matter such as asphalt or grease, it will hinder the penetration and contact of chemical solvents, so silicification methods are not suitable in such cases. The alkaline solution method involves allowing a heated alkaline solution (such as sodium hydroxide solution) to flow into the deep layers of the foundation by gravity, reacting with soil components to form water-insoluble and high-strength calcium aluminate complexes, thereby reinforcing the soil. However, this method is only suitable for specific soil types and carries the risks of groundwater contamination and sudden alkalization.

[0004] In recent years, emerging low-carbon soil improvement technologies have become a research hotspot, mainly focusing on MgO carbonization and solidification technology and microbial induced carbonate precipitation (MICP) technology. For example, Chinese patents ZL201210097042.2 "A method for carbonization and solidification of soil" and ZL201010604013.1 "A method and apparatus for carbonization and solidification of soil" both use active MgO as a soil solidification agent, carbonizing it under high concentration CO2 and high pressure conditions, which can improve soil strength in a short time. Compared with traditional cement-stabilized soil, it has advantages such as fast solidification speed, high strength, and good environmental benefits. However, when treating fine-grained soil with high moisture content, it can easily affect CO2 infiltration and carbonization uniformity. MIP technology, on the other hand, utilizes microorganisms (such as Bacillus pasteurellii or urease) to catalyze the decomposition of urea to produce CO3. 2 ⁻, and with Ca in CaCl2 2 ⁺ The formation of calcium carbonate through microbial induction cements soil particles and improves soil mechanical properties. It is mainly used in loose sandy soils, but its treatment effect is limited in clay with poor permeability. For example, Chinese patent ZL 201811304804.5, "A method for reinforcing coarse-grained soil based on microbial induced calcium carbonate deposition," fixes coarse-grained soil by adding a viscous bacterial solution and then cements the coarse-grained soil with urea and calcium ion treatment solution; ZL 201910325596.5, "An apparatus and method for simultaneously achieving MIP grouting to reinforce soil and remove its byproducts."

[0005] Furthermore, Chinese patent ZL202510090965.2, "Magnesium Oxide Carbonized Foundation Solidified Soil and Its Preparation Method and Application," uses in-situ soil as raw material and active magnesium oxide as a cementing material. It adds Bacillus subtilis, which produces carbonic anhydrase, to improve carbon fixation capacity and adds reinforcing agents to enhance the carbonization bonding strength and CO2 absorption capacity of the raw material interface. However, the preparation process involves mixing and granulation of various raw materials, including amine solutions, making the process complex and requiring strict control over the physical properties of the raw materials, such as particle size, which limits its large-scale application. Chinese patent ZL202310242854.X, "An Inorganic Solid Waste-Microbial Composite Solidifying Agent and Its Preparation Method and Application," adds a composite of carbonic anhydrase and Bacillus subtilis to materials such as active magnesium oxide, then introduces CO2. It achieves sludge solidification through inorganic solid waste carbonization and microbial mineralization. However, the material preparation process is complex, involving porous material preparation and microbial microencapsulation, resulting in high costs and hindering widespread application. Chinese patent ZL202310003073.5, "Method, Materials and Application of Bio-carbonized Magnesium Oxide Solidification of Geological Materials Based on Urea Pre-hydrolysis," mixes urea and commercial bacterial solution for pre-hydrolysis, then mixes it with a solid mixture of geological materials and active magnesium oxide. While this improves the utilization rate of urea and active magnesium oxide and the performance of solidified soil, it requires more bacterial solution to produce a fluid slurry, necessitates the addition of a hydration agent for MgO pre-hydrolysis, and has limitations on raw materials (such as geological materials with a pH value less than 9.5), thus limiting its applicability. Chinese patent ZL202211271891.5, "A Method for Solidifying Dredged Silt Using Bio-carbonized Active Magnesium Oxide Technology," first prepares a pre-hydrolyzed urea solution using urease-producing bacteria, then separately mixes the pre-hydrolyzed urea solution and active magnesium oxide into the dredged silt, stirs it into a slurry, and fills it into a designated site for curing. However, it requires separate addition of the pre-hydrolyzed urea solution and active MgO, and the pre-hydrolysis conditions are harsh, limiting its applicability.

[0006] Clearly, the above methods all have shortcomings in the actual construction of reinforcing collapsible loess foundations. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a construction method for reinforcing collapsible loess foundations based on grouting carbonation and vibration compaction synergistic reinforcement. This method achieves a strengthening effect on loess foundations through the synergistic effect of internal and external sources. Specifically, it utilizes the carbonate ions generated by urea hydrolysis induced by microorganisms for internal carbonation reinforcement, while simultaneously injecting CO2 for external carbonation.

[0008] The following technical solutions can be adopted: The construction method for reinforcing collapsible loess foundations based on grouting carbonization-vibration compaction synergistic reinforcement described in this invention is achieved through a mixing grouting-resonance compaction synergistic reinforcement device, and includes the following construction steps: S1. Site Pretreatment: Level the site and remove debris such as grass roots, branches, and stones. Combine the survey results and on-site supplementary measurements to determine the basic physical and mechanical parameters of the collapsible loess soil layer, and then determine the construction parameters. The basic physical and mechanical parameters include soil layer thickness, water content, void ratio, and collapsibility coefficient. The construction parameters include the dosage of low-carbon solidification grout, water-grout ratio, and resonance compaction. S2. Slurry preparation: Microbial inoculum, urea solution, magnesium oxide, carbide slag, slag and added enzymes are mixed evenly according to the design ratio to prepare low-carbon solidification slurry. Before use, the temperature of the low-carbon solidification slurry is kept at 25-35℃. S3. Layout and positioning: Mark the mixing pile positions on the pretreatment site, control the center distance between adjacent mixing pile positions to be 1.5-2.0 times the effective influence radius of resonance, then move the chassis of the mixing grouting-resonance compaction co-reinforcement device, adjust the posture of its guide frame, and ensure that the mixing rod remains vertical and the central axis of the mixing rod is aligned with the center of the mixing pile position. S4. Grouting and Sinking: Rotate the mixing rod clockwise, and the auger bit and fixed blades on it will gradually rotate and cut the soil and sink. The telescopic blades will simultaneously expand to their maximum diameter. At the same time, the low-carbon solidified grout will be sprayed into the stratum through the grout delivery pipe and grouting hole. The fixed blades and telescopic blades will evenly mix the low-carbon solidified grout with the soil. While mixing, sinking and grouting are carried out, the auger bit will reach the predetermined depth to form a mixed material pile. S5. Stop mixing and spraying: After stopping the spraying, the mixing rod continues to rotate clockwise for 1 minute; then switch the mixing rod to rotate counterclockwise, and the telescopic blades gradually retract; then inject CO2 gas into the soil through the gas supply pipe and the jet hole, and control the injection time within 1 minute. S6. Vibration-Jet-Lifting: Start the vibrator and pause CO2 injection to make the resonance wing resonate with the mixed soil of the stratum, and keep vibrating for 1-3 minutes; after pausing the vibrator, resume CO2 injection, lift the vibrator at a predetermined speed of 0.4-1.5 m / min, and keep the mixing rod rotating counterclockwise. S7. Move to the next pile location: Move the mixing and grouting-resonance compaction co-reinforcement device to the next mixing pile location. The next mixing pile location is adjacent to or alternates with the previous mixing pile location. Repeat steps S3-S6 to construct the next pile. S8. Pile Hole Backfilling: For the upper pile holes formed after construction, low-carbon mixture shall be used for layered backfilling, with each layer not exceeding 40cm in thickness. After backfilling, compaction shall be carried out with a small tamping hammer or rolling with a light roller, and the surface shall be leveled and covered for curing for no less than 7 days.

[0009] The mixing grouting-resonance compaction co-reinforcement device includes a traveling chassis with hydraulic outriggers at the bottom. A control box, grout tank, CO2 gas tank, winch, and hydraulic rod are mounted on top of the chassis. A guide frame connected to the hydraulic rod is mounted on one side of the chassis, and when vertically positioned, it forms surface contact with a buffer block at the end of the chassis. A lifting frame connected to the winch is slidably mounted on the side of the guide frame, with an upper mixing rod support frame and a lower vibrator mounted on the lifting frame. The vibrator is connected to a hollow resonant column, which has resonant wings on its outer side. A mixing rod is mounted on the mixing rod support frame, and the mixing rod includes... An outer stirring rod driven by a first motor and an inner stirring rod driven by a second motor are both hollow structures. The outer stirring rod is sleeved inside the resonant column, and the inner stirring rod is sleeved inside the outer stirring rod. The outer and inner stirring rods are connected by a rotating bearing. The inner stirring rod is equipped with a slurry delivery pipe connected to the slurry tank and a gas delivery pipe connected to the CO2 gas tank. The outer stirring rod extends downward beyond the resonant column, and its end sidewall is equipped with telescopic blades. The inner stirring rod extends downward beyond the outer stirring rod, and its end sidewall is equipped with fixed blades, a slurry spray hole connected to the slurry delivery pipe, and a jet nozzle connected to the gas delivery pipe. A spiral drill bit is installed at the bottom of the inner stirring rod.

[0010] Preferably, the low-carbon curing slurry in step S2 is composed of the following raw materials in parts by weight: Microbial inoculum solution: 10-25 parts; Urea: 5-20 parts; Magnesium oxide: 10-30 parts; Carbide slag: 20-50 parts; Slag: 30-70 parts; Add enzyme: 0.1-0.5 parts; Water: 80-100 parts; The microbial culture was composed of urease-producing bacteria, selected from commercially available Bacillus pasteurellii, with a bacterial concentration of OD0. 600 =0.8-1.2, effective viable bacteria count greater than 10 8 CFU / mL; the magnesium oxide is lightly calcined MgO or active MgO, with an activity greater than 40 according to the iodine adsorption method; the slag is fine powder of grade S95 or above; the added enzyme is carbonic anhydrase; the water is deionized water, distilled water or groundwater. The low-carbon curing slurry needs to be continuously stirred during storage, transportation and spraying, and the spraying into the formation must be completed within 6 hours after preparation.

[0011] Preferably, the effective radius of influence of resonance in step S3 is determined by on-site micro-motion testing or numerical simulation, and is the radial distance corresponding to the decay of vibration energy or ground vibration acceleration to 15-30% of peak energy.

[0012] Preferably, in step S4, the rotation speed of the stirring rod is 30-60 rpm, the sinking speed of the stirring rod is 0.8-1.5 m / min, and the spraying pressure of the low-carbon curing grout is 0.5-2.0 MPa; the spraying volume per unit pile length is determined according to the soil parameters and design requirements, and is jointly controlled by the sinking speed of the stirring rod and the spraying pressure.

[0013] Preferably, in step S5, the purity of the CO2 gas is not less than 60%, the temperature is controlled at 15-30℃, and the CO2 injection pressure is controlled at 0.2-0.4MPa.

[0014] Preferably, in step S6, the vibration frequency of the vibrator is controlled at 20-40 Hz, and the excitation force is adjusted according to the soil type and depth; the lifting speed of the vibrator is controlled at 0.5-0.8 m / min.

[0015] Preferably, the low-carbon mixture in step S8 is prepared by one of the following two methods: mixing the low-carbon solidification slurry obtained in step S2 with the site soil, wherein the amount of low-carbon solidification slurry is 5-15% of the weight of the site soil; or mixing the alkaline slag solidifying agent with the excavated soil, wherein the amount of alkaline slag solidifying agent is 10-25% of the weight of the site soil, wherein the alkaline slag solidifying agent is composed of carbide slag or magnesium oxide and slag, and the amount of carbide slag or magnesium oxide is 20-30% of the mass of slag.

[0016] Preferably, the collapsibility coefficient of the collapsible loess foundation before reinforcement is not less than 0.015 and the natural moisture content is not more than 15%, and the collapsibility coefficient after reinforcement is reduced to below 0.01.

[0017] This invention is a high-efficiency, low-carbon, and low-disturbance construction method for reinforcing collapsible loess. During construction, it can achieve strong crushing of the loess structure, efficient mixing and infiltration of grout and gas, full activation of low-carbon reaction, and instant compaction using vibration, significantly improving the bearing capacity of the foundation and eliminating collapsibility. The grouting carbonization-vibration compaction synergistic reinforcement device used is mobile, easy to operate, and has a wide range of applications, which can meet the application needs of large-scale projects. It has significant advantages in achieving resource recycling and carbon emission reduction.

[0018] The advantages and technical effects of this invention are as follows: 1) A three-stage composite process is adopted, which is "sinking grouting (clockwise opening blades) - stationary jetting (reverse blade retraction) - vibration jetting lifting". Combined with a specific low-carbon slurry formula and CO2 injection strategy, it creatively integrates multiple mechanisms such as mechanical crushing, biochemical reaction (microbial mineralization, enzyme catalysis), inorganic reaction (magnesium-based, slag cementation, carbonation) and physical densification (vibration), which significantly improves the collapsibility improvement and reinforcement effect, and is low-carbon and environmentally friendly. 2) Using commercially available or indigenous microbial inoculum to prepare microbial inoculum for hydrolyzing urea and replacing water in soil samples improved the carbonization degree of alkaline materials such as magnesium oxide in the mixed soil. 3) Active MgO, carbide slag, olivine powder and other solid wastes are added to the fill material, such as engineering waste soil and shield tunnel slag. These are all low-carbon and environmentally friendly materials with good CO2 carbon sequestration effect. The pH value of the solidified soil is low, which can realize resource recycling and carbon emission reduction. It has the advantages of low-carbon environmental protection and sustainable development. 4) A constant heater is specially installed on the gas pipeline to prevent condensation and water vapor accumulation in the gas pipeline caused by low-temperature compressed gas; 5) Utilize the carbonate ions generated by urea hydrolysis induced by microorganisms and external CO2 injection for dual carbonization to optimize gas diffusion uniformity and enhance carbonization effect; 6) The construction method of this invention is simple, and each step is carried out in sequence, which greatly improves the construction efficiency of roadbed paving and soil reinforcement. The strength of the filled roadbed is controllable, the cost is low, and the adaptability is strong, meeting the needs of large-scale engineering applications. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the structure of the grouting carbonization-vibration compaction synergistic reinforcement device described in this invention.

[0020] Figure 2 yes Figure 1 Cross-sectional view of the stirring rod support frame.

[0021] Figure 3 yes Figure 1 A schematic diagram of the structure at the ends of the inner and outer stirring rods.

[0022] Figure 4 yes Figure 3 A top view of the mixing rods.

[0023] Figure 5 This is a flowchart illustrating the construction process of the loess foundation reinforcement method described in this invention.

[0024] Figure 6 This is a line graph showing the effect of magnesium oxide content on the strength of microbial-MgO solidified soil under normal curing conditions.

[0025] Figure 7This is a line graph showing the effect of magnesium oxide content on the strength of microbial-MgO solidified soil under CO2 carbonization conditions in this invention.

[0026] Figure 8 This is a line graph showing the effect of bacterial solution content on the strength of microbial-MgO solidified soil under normal maintenance conditions.

[0027] Figure 9 This is a line graph showing the effect of bacterial solution content on the strength of microbial-MgO solidified soil under CO2 carbonization conditions in this invention.

[0028] Figure 10 This is a line graph showing the effect of urea concentration on the strength of microbial-MgO solidified soil under normal maintenance conditions.

[0029] Figure 11 This is a line graph showing the effect of urea concentration on the strength of microbial-MgO solidified soil under CO2 carbonization conditions in this invention. Detailed Implementation

[0030] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings. These embodiments are implemented based on the technical solution of the present invention, and detailed implementation methods and specific working processes are given. However, the scope of protection of the present invention is not limited to the following embodiments.

[0031] The construction method for reinforcing collapsible loess foundation based on grouting carbonization-vibration compaction synergistic reinforcement described in this invention is achieved through a grouting-vibration compaction synergistic reinforcement device.

[0032] like Figure 1-4 As shown, the above-mentioned mixing grouting-resonance compaction co-reinforcement device includes a walking chassis 1, which is a tracked walking chassis. The bottom of the walking chassis 1 is equipped with hydraulic outriggers 101. The top of the walking chassis 1 is equipped with a control box 102, a grout tank 103, a CO2 gas tank 104, a winch 105, and a hydraulic rod. The walking chassis 1 is also equipped with a laser ranging-positioning system for real-time acquisition of pile position coordinates and automatic centering in conjunction with the guide frame 2.

[0033] A guide frame 2 connected to hydraulic rods is provided on one side of the chassis 1. When the guide frame 2 is vertically positioned, it forms surface contact with the buffer block 106 at the end of the chassis 1. The hydraulic rods include an upper hydraulic rod 107 and a lower hydraulic rod 108, both coplanar with the guide frame 2. One end of each rod is positioned downwards on the guide frame 2, and the other end is positioned forwards on the chassis 1. The posture of the guide frame 2 can be adjusted by extending and retracting the upper hydraulic rod 107 and the lower hydraulic rod 108. During construction, the guide frame 2 must be vertically positioned. To better monitor the tilt angle of the guide frame 2, tilt sensors are installed on the chassis 1 to detect the rotation angle of the upper hydraulic rod 107 and the lower hydraulic rod 108.

[0034] A support beam 201 is provided at the top of the guide frame 2. Guide wheels 202, connected to the wire rope of the winch 105, are located at both ends of the support beam 201. The wire rope is connected to a lifting frame 3 slidably mounted on the side of the guide frame 2. When the winch 105 is operating, the wire rope pulls the lifting frame 3 up or down along the guide frame 2. Therefore, a displacement sensor is installed on the support beam 201 to detect the distance the wire rope moves, thereby indicating the position of the lifting frame 3.

[0035] The aforementioned lifting frame 3 is connected to the mixing rod support frame 301 and the vibrator 302. The mixing rod support frame 301 is on top, and the vibrator 302 is below. The vibrator 302 is a variable frequency hydraulic or electric vibratory hammer with a vibration frequency range of 15-50Hz. Its output end is connected to a hollow resonant column 401. Resonant wings 402, arranged in a cross or X shape, are provided on the outer side of the resonant column 401. Due to the large size of the resonant column 401 and resonant wings 402, under the action of the vibrator 302, the resonant column 401 will drive the resonant wings 402 to produce vertical vibration and polarization. To achieve good resonance with the soil, the outer edge of the resonant wings 402 has a continuous or intermittent sawtooth structure. The sawtooth is triangular, trapezoidal, or wavy, with an inclination angle of 30°-60°. In addition, each vibrating wing 402 is provided with a circular hole 403 with a diameter of 0.2-0.5 times the radial width of the resonant wing 402. The circular holes 403 are evenly distributed in a matrix on the vibrating wing 402 or evenly spaced along the axis of the resonant column 401. In order to limit the amplitude of the vertical vibration of the resonant column 401, an upper vibration limiter 404 is installed at its top and a lower vibration limiter 405 is installed at its bottom.

[0036] A first motor 501 and a second motor 502 are mounted on the stirring rod support frame 301. The output end of the first motor 501 is connected to the outer stirring rod 503, and the output end of the second motor 502 is connected to the inner stirring rod 504. Both the outer stirring rod 503 and the inner stirring rod 504 are hollow structures, connected together and coaxially arranged with the resonance column 401. The outer stirring rod 503 and the inner stirring rod 504 extend downwards, pass through the housing of the vibrator 302, and then pass through the inner cavity of the resonance column 401, exiting from the end of the resonance column 401. The outer stirring rod 503 and the inner stirring rod 504 are connected by a rotating bearing, and the end of the inner stirring rod 504 extends beyond the outer stirring rod 503.

[0037] Telescopic blades 505 are provided on the end sidewall of the outer stirring rod 503. Each telescopic blade 505 includes a fixed section, a folding section, and a return spring. The fixed section is located on the outer stirring rod 503, the folding section is hinged to the fixed section, and the two ends of the return spring are connected to the fixed section and the folding section respectively. The telescopic blades 505 are arranged in two or three layers along the axial direction of the outer stirring rod 503. When a two-layer structure is adopted, each layer is provided with a pair of axisymmetric telescopic blades 505, and the horizontal projections of the upper and lower layers of telescopic blades 505 coincide with each other (see...). Figure 3 , 4 When a three-layer structure is used, each layer can be equipped with one telescopic blade 505, with the horizontal projection angle between adjacent telescopic blades 505 being 120°; or each layer can be equipped with a pair of axisymmetric telescopic blades 505, with the horizontal projection angle between adjacent telescopic blades 505 being 60°. Normally, the folding section remains in a contracted state under the action of the return spring. When the outer mixing rod 503 rotates clockwise, the folding section extends under the action of centrifugal force and soil resistance; when the outer mixing rod 503 rotates counterclockwise, the folding section retracts under the action of the return spring.

[0038] The inner cavity of the inner stirring rod 504 is provided with a slurry delivery pipe 506 connected to the slurry tank 103 and a gas delivery pipe 507 connected to the CO2 gas tank 104. The end side wall of the inner stirring rod 504 is provided with a fixed blade 508, a slurry spraying hole 509 connected to the slurry delivery pipe 506, and a jetting hole 510 connected to the gas delivery pipe 507. The bottom of the inner stirring rod 504 is provided with a spiral drill bit 511.

[0039] The aforementioned fixed blades 508 are arranged in two layers along the axial direction of the inner stirring rod 504, with a pair symmetrically arranged along the central axis of the inner stirring rod 504 in each layer, and the horizontal projections of the upper and lower layers of telescopic blades 508 coincide with each other. Spray holes 509 and air jet holes 510 are located between the two layers of fixed blades 508, and there are one or more spray holes 509 and air jet holes 510, which are staggered along the circumference of the inner stirring rod 504. A pressure pump set, a flow meter, and a pressure sensor are installed on the slurry tank 103, while a pressure reducing valve, a heater, and a pressure gauge are installed on the gas delivery pipe of the CO2 gas tank 104.

[0040] The length of the fixed blade 508 is greater than the retracted length of the telescopic blade 505 but less than the unfolded length of the telescopic blade 505. The unfolded length of the telescopic blade 505 is 250-500 mm. The radial width of each resonant wing 402 is not less than the length of the fixed blade 508 and not greater than the unfolded length of the telescopic blade 508. The lower surfaces of the fixed section and folding section of both the fixed blade 508 and the telescopic blade 505 are provided with carbide spikes 512 with a cone angle of 30°-60°. The pitch of the spiral blades of the aforementioned auger drill bit 511 gradually increases from bottom to top.

[0041] The construction method for reinforcing collapsible loess foundations based on grouting carbonization-vibration compaction synergistic reinforcement described in this invention, such as... Figure 5 As shown, the construction steps include the following: S1. Site pretreatment: Level the site and remove debris such as grass roots, branches, and stones. Combine the survey results and on-site supplementary measurements to determine the basic physical and mechanical parameters such as the thickness, water content, void ratio, and collapsibility coefficient of the collapsible loess layer. Then determine the construction parameters such as the dosage of low-carbon solidification slurry, water-slurry ratio, and resonance compaction. S2. Slurry preparation: Mix microbial inoculum, urea solution, magnesium oxide, carbide slag, slag and added enzymes evenly according to the design ratio to prepare low-carbon solidification slurry, and keep the temperature of low-carbon solidification slurry at 25-35℃ before use; The above-mentioned low-carbon curing slurry is composed of the following raw materials in parts by weight: Microbial inoculum solution: 10-25 parts; Urea: 5-20 parts; Magnesium oxide: 10-30 parts; Carbide slag: 20-50 parts; Slag: 30-70 parts; Add enzyme: 0.1-0.5 parts; Water: 80-100 parts; The microbial culture solution contained urease-producing bacteria, selected from commercially available Bacillus pasteurellii, with a bacterial concentration of OD0.05. 600 =0.8-1.2, effective viable bacteria count greater than 10 8The concentration of CFU / mL, or the microbial solution using indigenous urease-producing bacteria screened and cultured on-site; magnesium oxide, lightly calcined MgO or active MgO, with an activity greater than 40 according to the iodine adsorption method; slag, grade S95 or higher fine powder; added enzyme, carbonic anhydrase; water, deionized water, distilled water, or fresh groundwater. The above-mentioned low-carbon solidification slurry requires continuous stirring during storage, transportation, and spraying, and must be sprayed into the formation within 6 hours of preparation.

[0042] S3. Layout and positioning: Mark the mixing pile positions on the pretreatment site, control the center distance between adjacent mixing pile positions to be 1.5-2.0 times the effective influence radius of resonance, then move the chassis of the mixing grouting-resonance compaction co-reinforcement device, adjust the posture of its guide frame, and ensure that the mixing rod remains vertical and the central axis of the mixing rod is aligned with the center of the mixing pile position. The effective radius of influence of the above resonance was determined by field micro-motion tests or numerical simulations, and was defined as the radial distance corresponding to the decay of vibration energy or ground vibration acceleration to 15-30% of the peak energy.

[0043] S4. Grouting and Mixing for Sinking: Start the first and second motors to make the inner and outer mixing rods rotate clockwise. The auger bit 511 and the fixed blade 508 gradually rotate and cut the soil to sink. The telescopic blade 505 simultaneously expands to its maximum diameter. At the same time, start the pressure pump group to send the grout in the grout tank 103 into the grout delivery pipe 506 at a pressure of 0.5-2.0MPa, and spray it into the stratum through the grouting hole 509. The fixed blade 508 and the telescopic blade 505 uniformly mix the low-carbon solidified grout with the soil. While mixing, sinking and grouting are carried out, the auger bit 511 reaches the predetermined depth to form a mixed material pile body. During the above operation, the rotation speed of the inner and outer mixing rods is 30-60 rpm, and the sinking speed is 0.8-1.5 m / min; the amount of grout sprayed per unit pile length is determined according to the soil parameters and design requirements, and is jointly controlled by the sinking speed of the mixing rods and the grout spraying pressure.

[0044] S5. Stop mixing and spraying: Close the spraying valve to stop spraying, and keep the inner and outer mixing rods stirring clockwise for 1 minute; switch the inner and outer mixing rods to rotate counterclockwise, and the telescopic blades 505 gradually retract; then start the CO2 gas tank 104, adjust the CO2 injection pressure to 0.2-0.4MPa, and inject CO2 gas into the soil through the jet hole 510, with the injection time controlled within 1 minute; The purity of the CO2 gas is not less than 60%, and it can be obtained by capturing industrial exhaust gas. A heater is installed on the gas pipeline 507 to keep the CO2 gas temperature at 15-30℃.

[0045] S6. Vibration-Air-Lifting: Start vibrator 302 and pause CO2 injection. Control the vibration frequency of vibrator 302 at 20-40 Hz. Adjust the excitation force according to the soil type and depth to make the resonant wing 402 resonate with the mixed soil. Continue vibrating for 1-3 minutes. After pausing vibrator 302, resume CO2 injection. Control the CO2 injection pressure at 0.2-0.35 MPa. At the same time, control the wire rope to lift vibrator 302 at a predetermined speed of 0.5-0.8 m / min, and keep the inner and outer mixing rods rotating counterclockwise. Each lifting height is 2-4 m. Under the action of its own weight and the excitation force of vibrator 302, the resonant wing 402 transmits vertical vibration and polarization to the mixed soil, making the mixed soil compacted.

[0046] S7. Move to the next pile position: Move the tracked chassis 1 to the next pile position. The next pile position can be adjacent to or alternate with the previous pile position. Repeat steps S3-S6 to construct the next pile. S8. Pile Hole Backfilling: For the upper pile holes formed after construction, low-carbon mixture shall be used for layered backfilling, with each layer not exceeding 40cm in thickness. After backfilling, compaction shall be carried out with a small tamping hammer or rolling with a light roller, and the surface shall be leveled and covered for curing for no less than 7 days.

[0047] The aforementioned low-carbon mixture is prepared by one of the following two methods: mixing the low-carbon solidified slurry obtained in step S2 with the site soil, wherein the amount of low-carbon solidified slurry is 5-15% of the weight of the site soil; or mixing the alkaline slag solidifier with the excavated soil, wherein the amount of alkaline slag solidifier is 10-25% of the weight of the site soil, wherein the alkaline slag solidifier is composed of carbide slag or magnesium oxide and slag, and the amount of carbide slag or magnesium oxide is 20-30% of the mass of slag.

[0048] This invention is applicable to loess with a collapsibility coefficient of not less than 0.015 and a natural moisture content of not more than 15%. After reinforcement, the collapsibility coefficient is reduced to below 0.01. Figure 6-11 As can be seen, due to the presence of exogenous carbonization conditions protected by CO2 injection in the soil, this invention can significantly improve the solidification strength of the soil compared with conventional methods. Furthermore, the construction device used in this invention can achieve powerful crushing of loess structures, efficient mixing and infiltration of soil-gas mixtures, full activation of low-carbon reactions, and instant compaction through vibration. All these factors work synergistically, thus significantly improving the bearing capacity of the foundation and significantly eliminating the collapsibility of the foundation.

[0049] It should be noted that in the description of this invention, terms such as "front," "rear," "left," "right," "vertical," "horizontal," "inner," and "outer" indicating orientation or positional relationships are based on the orientation or positional relationships shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

Claims

1. A construction method for reinforcing collapsible loess foundations based on grouting carbonization-vibration compaction synergistic reinforcement, characterized in that, This is achieved through a combined reinforcement device of mixing grouting and resonant compaction, including the following construction steps: S1. Site Pretreatment: Level the site and remove debris such as grass roots, branches, and stones. Combine the survey results and on-site supplementary measurements to determine the basic physical and mechanical parameters of the collapsible loess soil layer, and then determine the construction parameters. The basic physical and mechanical parameters include soil layer thickness, water content, void ratio, and collapsibility coefficient. The construction parameters include the dosage of low-carbon solidification grout, water-grout ratio, and resonance compaction. S2. Slurry preparation: Microbial inoculum, urea solution, magnesium oxide, carbide slag, slag and added enzymes are mixed evenly according to the design ratio to prepare low-carbon solidification slurry. Before use, the temperature of the low-carbon solidification slurry is kept at 25-35℃. S3. Layout and positioning: Mark the mixing pile positions on the pretreatment site, control the center distance between adjacent mixing pile positions to be 1.5-2.0 times the effective influence radius of resonance, then move the chassis of the mixing grouting-resonance compaction co-reinforcement device, adjust the posture of its guide frame, and ensure that the mixing rod remains vertical and the central axis of the mixing rod is aligned with the center of the mixing pile position. S4. Grouting and Sinking: Rotate the mixing rod clockwise, and the auger bit and fixed blades on it will gradually rotate and cut the soil and sink. The telescopic blades will simultaneously expand to their maximum diameter. At the same time, the low-carbon solidified grout will be sprayed into the stratum through the grout delivery pipe and grouting hole. The fixed blades and telescopic blades will evenly mix the low-carbon solidified grout with the soil. While mixing, sinking and grouting are carried out, the auger bit will reach the predetermined depth to form a mixed material pile. S5. Stop mixing and spraying: After stopping the spraying, the mixing rod continues to rotate clockwise for 1 minute; then switch the mixing rod to rotate counterclockwise, and the telescopic blades gradually retract; then inject CO2 gas into the soil through the gas supply pipe and the jet hole, and control the injection time within 1 minute. S6. Vibration-Jet-Lift: Start the vibrator and stop the CO2 injection to make the resonance wing resonate with the mixed soil of the stratum, and leave the vibration for 1-3 minutes; After pausing the vibrator, resume CO2 injection, raise the vibrator at a predetermined speed of 0.4-1.5 m / min, and keep the stirring rod rotating counterclockwise; S7. Move to the next pile location: Move the mixing and grouting-resonance compaction co-reinforcement device to the next mixing pile location. The next mixing pile location is adjacent to or alternates with the previous mixing pile location. Repeat steps S3-S6 to construct the next pile. S8. Pile Hole Backfilling: For the upper pile holes formed after construction, low-carbon mixture shall be used for layered backfilling, with each layer not exceeding 40cm in thickness. After backfilling, compaction shall be carried out with a small tamping hammer or rolling with a light roller, and the surface shall be leveled and covered for curing for no less than 7 days.

2. The construction method for reinforcing collapsible loess foundations based on grouting carbonization-vibration compaction synergistic reinforcement according to claim 1, characterized in that: The mixing grouting-resonance compaction co-reinforcement device includes a traveling chassis with hydraulic outriggers at the bottom. A control box, grout tank, CO2 gas tank, winch, and hydraulic rod are mounted on top of the chassis. A guide frame connected to the hydraulic rod is mounted on one side of the chassis, and when vertically positioned, it forms surface contact with a buffer block at the end of the chassis. A lifting frame connected to the winch is slidably mounted on the side of the guide frame, with an upper mixing rod support frame and a lower vibrator mounted on the lifting frame. The vibrator is connected to a hollow resonant column, which has resonant wings on its outer side. A mixing rod is mounted on the mixing rod support frame, and the mixing rod includes... An outer stirring rod driven by a first motor and an inner stirring rod driven by a second motor are both hollow structures. The outer stirring rod is sleeved inside the resonant column, and the inner stirring rod is sleeved inside the outer stirring rod. The outer and inner stirring rods are connected by a rotating bearing. The inner stirring rod is equipped with a slurry delivery pipe connected to the slurry tank and a gas delivery pipe connected to the CO2 gas tank. The outer stirring rod extends downward beyond the resonant column, and its end sidewall is equipped with telescopic blades. The inner stirring rod extends downward beyond the outer stirring rod, and its end sidewall is equipped with fixed blades, a slurry spray hole connected to the slurry delivery pipe, and a jet nozzle connected to the gas delivery pipe. A spiral drill bit is installed at the bottom of the inner stirring rod.

3. The construction method for reinforcing collapsible loess foundations based on grouting carbonization-vibration compaction synergistic reinforcement according to claim 1, characterized in that: The low-carbon curing slurry in step S2 is composed of the following raw materials in parts by weight: Microbial inoculum solution: 10-25 parts; Urea: 5-20 parts; Magnesium oxide: 10-30 parts; Carbide slag: 20-50 parts; Slag: 30-70 parts; Add to Enzyme: 0.1-0.5 parts; Water: 80-100 parts; The microbial culture was composed of urease-producing bacteria, selected from commercially available Bacillus pasteurellii, with a bacterial concentration of OD0. 600 =0.8-1.2, effective viable bacteria count greater than 10 8 CFU / mL; the magnesium oxide is lightly calcined MgO or active MgO, with an activity greater than 40 according to the iodine adsorption method; the slag is fine powder of grade S95 or above; the added enzyme is carbonic anhydrase; the water is deionized water, distilled water or groundwater. The low-carbon curing slurry needs to be continuously stirred during storage, transportation and spraying, and the spraying into the formation must be completed within 6 hours after preparation.

4. The construction method for reinforcing collapsible loess foundations based on grouting carbonization-vibration compaction synergistic reinforcement according to claim 1, characterized in that: In step S3, the effective radius of influence of resonance is determined by on-site micro-motion testing or numerical simulation, and is the radial distance corresponding to when the vibration energy or ground vibration acceleration decays to 15-30% of the peak energy.

5. The construction method for reinforcing collapsible loess foundations based on grouting carbonization-vibration compaction synergistic reinforcement according to claim 1, characterized in that: In step S4, the rotation speed of the stirring rod is 30-60 rpm, the sinking speed of the stirring rod is 0.8-1.5 m / min, and the spraying pressure of the low-carbon curing grout is 0.5-2.0 MPa. The spraying volume per unit pile length is determined according to the soil parameters and design requirements, and is jointly controlled by the sinking speed of the stirring rod and the spraying pressure.

6. The construction method for reinforcing collapsible loess foundations based on grouting carbonization-vibration compaction synergistic reinforcement according to claim 1, characterized in that: In step S5, the purity of CO2 gas is not less than 60%, the temperature is controlled at 15-30℃, and the CO2 injection pressure is controlled at 0.2-0.4MPa.

7. The construction method for reinforcing collapsible loess foundations based on grouting carbonization-vibration compaction synergistic reinforcement according to claim 1, characterized in that: In step S6, the vibration frequency of the vibrator is controlled at 20-40 Hz, and the excitation force is adjusted according to the soil type and depth; the lifting speed of the vibrator is controlled at 0.5-0.8 m / min.

8. The construction method for reinforcing collapsible loess foundations based on grouting carbonization-vibration compaction synergistic reinforcement according to claim 1, characterized in that: The low-carbon mixture in step S8 is prepared by one of the following two methods: mixing the low-carbon solidification slurry obtained in step S2 with the site soil, wherein the amount of low-carbon solidification slurry is 5-15% of the weight of the site soil; or mixing the alkaline slag solidifier with the excavated soil, wherein the amount of alkaline slag solidifier is 10-25% of the weight of the site soil, wherein the alkaline slag solidifier is composed of carbide slag or magnesium oxide and slag, and the amount of carbide slag or magnesium oxide is 20-30% of the mass of slag.

9. The construction method for reinforcing collapsible loess foundations based on grouting carbonization-vibration compaction synergistic reinforcement according to claim 1, characterized in that: The collapsible loess foundation has a collapsibility coefficient of not less than 0.015 and a natural moisture content of not more than 15% before reinforcement, and the collapsibility coefficient drops to below 0.01 after reinforcement.

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