A composite material for repairing urban ground collapse and a graded perfusion repair method

Abstract

This invention discloses a composite material for urban ground subsidence repair and its graded injection repair method. The composite material comprises porous carbon and cohesive soil, wherein the specific surface area of ​​the porous carbon is 300-900 cm². 2 / g, pore volume 0.15-0.38cm³ 3 / g, with a particle size of 5-30µm; in cohesive soil, the particle size of silt particles is larger than that of porous carbon particles, while the particle size of clay particles is smaller than that of porous carbon particles. The remediation method adopts a graded grouting process: first, a composite material with a mass ratio of 1:1 is grouted to 10%-20% of the void height, then a composite material with a mass ratio of 1:2 is grouted to 20%-40%, and finally a composite material with a mass ratio of 1:10 is grouted to 40%-70%. This invention alleviates the negative pressure effect by absorbing water through porous carbon, forms a stable skeleton through particle size matching, and achieves a stepped distribution of moisture through graded grouting, which can reduce the soil moisture content change rate to below 0.26% and increase the strength of the grouting layer by more than 54%.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, specifically relating to a composite material for urban ground subsidence repair and its graded injection repair method. Background Technology

[0002] Road collapses have become a dangerous problem hindering traffic safety in recent years, with various urban road collapse accidents of varying sizes occurring in many cities. The hidden, sudden, and often collective nature of road collapses has made them a fundamental and long-standing obstacle to current road construction and development. Therefore, preventing and controlling road collapses in urban areas is of paramount importance.

[0003] Research has revealed that when the groundwater level inside the underground cavity at the site of a ground collapse is relatively stable, and the overlying soil layer is cohesive with poor permeability and aeration, a relatively sealed space forms inside the cavity. During groundwater level changes, the rate of change exceeds the infiltration rate of water in the cavity's top slab, causing the cohesive soil at the cavity's top slab to experience negative pressure due to the pressure difference effect. This vacuum negative pressure generates a downward suction force on the soil particles, which is detrimental to the stability of the exposed surface at the bottom of the overlying layer. This suction force drastically increases the infiltration rate of groundwater in the soil, enhancing its permeability and erosion capacity, ultimately leading to the instability of the soil structure at the top of the underground cavity and resulting in road collapse.

[0004] Currently, the methods for repairing ground subsidence face the following technical challenges: First, the microstructure design of existing repair materials is unreasonable, making it difficult to effectively absorb water accumulated in underground cavities and alleviate the negative pressure effect. Traditional repair materials often involve direct injection of ordinary cohesive soil or cement-based materials, which lack a large specific surface area and abundant pore structure, resulting in limited water adsorption and drainage capacity. When the water level changes, they cannot absorb and drain accumulated water in time, causing the negative pressure effect to continue acting on the top slab soil, making it difficult to fundamentally eliminate the inducing factors of collapse. As shown in Comparative Example 1, when only cohesive soil was used for injection, the soil moisture content change rate was as high as 10.7%, indicating that the material could not effectively control moisture, and the risk of collapse still existed. In addition, even when porous materials are added in existing technologies, the particle size matching relationship between them and cohesive soil is often neglected, resulting in the inability to form an effective skeleton support and pore filling mechanism between particles, leading to poor overall stability of the repair body.

[0005] Secondly, existing repair methods mostly employ a single material for one-time injection, failing to achieve the synergistic effect of multiple functions such as water absorption, water blocking, and load-bearing within the same repair body. If high-strength materials are used, their water absorption capacity is insufficient, failing to eliminate the negative pressure effect; if highly absorbent materials are used, the structural strength decreases, failing to meet the road surface load-bearing requirements. This technical dilemma of addressing one aspect while neglecting another often leads to the repaired ground collapsing again in a short period. Furthermore, single-material injection cannot create a tiered distribution structure where moisture gradually decreases from the inside out; moisture easily accumulates on the surface, causing the road surface to soften and further exacerbating the risk of structural instability.

[0006] Third, existing technologies lack reasonable limitations on the key parameters of porous carbon, making it difficult to simultaneously optimize water absorption performance and structural strength. Some technical solutions unilaterally pursue high specific surface area or large pore volume of porous carbon, ignoring the negative impact of these parameters on material strength. As shown in Comparative Examples 4-5, when the specific surface area is greater than 900 cm²... 2 / g or pore volume greater than 0.38cm³ 3 At a density of / g, although the soil moisture content change rate was low (0.09%-0.10%), the strength of the composite material decreased significantly, with the strength improvement rate of the grouting layer being only 14.5%-16.7%. This indicates that the porous carbon parameters need to be optimized and screened. Although exceeding the reasonable range results in excellent water absorption performance, it will sacrifice structural strength and is not conducive to the stability and long-term use of the pavement.

[0007] In summary, existing technologies lack a ground subsidence repair solution that can simultaneously address the negative pressure effect, achieve functional zoning, and optimize the matching of porous carbon parameters. Therefore, developing a composite material and repair method with excellent water absorption capacity, good structural strength, and the ability to form a tiered distribution of moisture is of significant practical importance and engineering application value. Summary of the Invention

[0008] This invention relates to a composite material for urban ground subsidence repair and its graded injection repair method, aiming to solve the soil instability problem caused by negative pressure effect in existing technologies. The composite material comprises porous carbon and cohesive soil. The porous carbon absorbs accumulated water and accelerates seepage through its large specific surface area and abundant pores. A stable particle skeleton is formed through particle size matching. Graded injection achieves a stepped distribution of water from the inside out, improving water absorption capacity and structural strength while ensuring road surface stability. To achieve the above objectives, this invention provides the following technical solution: A composite material for urban ground subsidence repair, the composite material comprising porous carbon and cohesive soil in a specific mass ratio, wherein the porous carbon has a specific surface area of ​​300-900 cm². 2 / g, pore volume 0.15-0.38cm³ 3 / g, with a particle size of 5-30µm; the cohesive soil includes silt and clay particles, wherein the particle size of the silt is larger than that of the porous carbon, and the particle size of the clay particles is smaller than that of the porous carbon.

[0009] As a preferred technical solution, the mass ratio of porous carbon to clay is 1:1, 1:2 or 1:10.

[0010] As a preferred technical solution, the mass ratio of silt to clay in the cohesive soil is 2:1.

[0011] As a preferred technical solution, the porous carbon has a specific surface area of ​​786.3 cm². 2 / g, pore volume is 0.38cm³ 3 / g, with a particle size of 10µm, the silt particle size of the clay is 28µm, and the clay particle size is 4µm.

[0012] As a preferred technical solution, the porous carbon has a specific surface area of ​​578.3 cm². 2 / g, pore volume is 0.28cm³ 3 / g, with a particle size of 10µm; the silt particle size of the clay is 28µm, and the clay particle size is 4µm.

[0013] As a preferred technical solution, the specific surface area of ​​the porous carbon is 456.9 cm². 2 / g, pore volume is 0.22cm³ 3 / g, with a particle size of 10µm; the silt particle size of the clay is 28µm, and the clay particle size is 4µm.

[0014] As a preferred technical solution, the porous carbon has a specific surface area of ​​786.3 cm². 2 / g, pore volume is 0.38cm³ 3 / g, with a particle size of 10µm; the silt particle size of the clay is 28µm, and the clay particle size is 4µm.

[0015] As a preferred technical solution, the porous carbon has a specific surface area of ​​786.3 cm². 2 / g, pore volume is 0.38cm³ 3 / g, with a particle size of 8µm; the silt particle size of the clay is 15µm, and the clay particle size is 2µm.

[0016] This invention also provides a graded injection repair method based on composite materials for urban ground subsidence repair, which uses the composite materials described in any of the preceding claims and specifically includes the following steps: S1: Mix porous carbon with clay at a first mass ratio to form a first mixture; S2: After adding an appropriate amount of water to the first mixture and stirring for a period of time, pour the resulting slurry into the collapsed area of ​​the ground. The pouring thickness is the first percentage of the height of the cavity to be repaired. S3: Mix porous carbon with clay at a second mass ratio to form a second mixture; S4: After adding an appropriate amount of water to the second mixture and stirring for a period of time, pour the resulting slurry onto the top of the first mixture at the ground subsidence point. The pouring thickness is a second percentage of the height of the cavity to be repaired. S5: Mix porous carbon with clay at the third mass ratio to obtain a third mixture; S6: After adding an appropriate amount of water to the third mixture and stirring for a period of time, pour the resulting slurry over the second mixture at the site of ground subsidence.

[0017] As a preferred technical solution, the stirring time in S2, S4 and S6 is 2 hours.

[0018] As a preferred technical solution, the first percentage is 10%-20%, the second percentage is 20%-40%, and the third percentage is 40%-70%.

[0019] As a preferred technical solution, the first mass ratio is 1:1, the second mass ratio is 1:2, and the third mass ratio is 1:10.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention achieves a synergistic improvement in the water absorption capacity and structural strength of composite materials through the optimized design of porous carbon microstructure and the particle size matching and control with cohesive soil, effectively solving the problem of soil instability caused by negative pressure effect in underground cavities.

[0021] First, regarding the microstructure of porous carbon, this invention employs a specific surface area of ​​300–900 cm². 2 / g, pore volume 0.15–0.38 cm³ 3The porous carbon, with its large specific surface area, provides ample adsorption sites, enabling the composite material to rapidly absorb water from underground cavities. Its abundant pore structure forms interconnected seepage channels, accelerating the lateral diffusion and vertical discharge of water. Through capillary adsorption, the porous carbon can buffer negative pressure effects during water level changes, delaying soil instability. Secondly, regarding particle size matching, this invention specifies that the particle size of silt particles in the cohesive soil is larger than that of porous carbon particles, while the particle size of clay particles is smaller than that of porous carbon particles, forming a "coarse-fine-coarse" particle size distribution structure. Larger silt particles form a skeletal support, ensuring the overall stability of the grouting layer; smaller clay particles fill the gaps between the porous carbon and silt particles, forming a dense microstructure; and porous carbon, as an intermediate-sized particle, forms both an intercalary structure with the silt particles and an adsorption interface with the clay particles. This synergistic matching of the three particle sizes effectively blocks the vertical migration channels of water.

[0022] Furthermore, regarding the gradient design of mass ratios, this invention employs three mass ratios for the bottom, middle, and top layers of grouting, respectively, forming a performance gradient of water absorption, water resistance, and load bearing. The bottom composite material with a mass ratio of 1:1 has a high porous carbon content, fully utilizing its strong water absorption characteristics to quickly absorb water from cavities. The middle composite material with a mass ratio of 1:2 has an increased proportion of cohesive soil, forming a dense structure that prevents water from migrating upwards from the bottom layer. The top composite material with a mass ratio of 1:10 has cohesive soil as the dominant component, providing sufficient mechanical strength to bear the road load. In Example 1, the bottom layer has strong water absorption capacity, the middle layer has a dense structure, and the top layer has high strength, resulting in a final soil moisture content change rate of only 0.12% and a grouting layer strength improvement rate of 56.7%. Comparative Example 1, using only cohesive soil without porous carbon, showed a soil moisture content change rate as high as 10.7%, indicating that without porous carbon, moisture cannot be controlled, leading to a high risk of collapse.

[0023] 2. This invention, by layering composite materials with different mass ratios and optimizing the design of the grouting thickness ratio, forms a tiered distribution structure with gradually decreasing moisture from the inside out, thereby improving the overall water absorption capacity while ensuring road surface stability.

[0024] On the one hand, the layered grouting process achieves a tiered distribution of moisture. This invention uses steps S2, S4, and S6 to grout composite materials with different mass ratios, forming a three-layer functional structure. The bottom layer is grouted with a highly absorbent 1:1 composite material, which can quickly absorb water accumulated in cavities, eliminating the negative pressure effect on the water source foundation. The middle layer is grouted with a dense 1:2 composite material, forming a physical barrier layer to prevent moisture from migrating upwards from the bottom layer. The surface layer is grouted with a high-strength 1:10 composite material, providing sufficient load-bearing capacity to support the road surface load. The three layers work synergistically, resulting in a tiered distribution of moisture within the repair body, gradually decreasing from the inside out, preventing moisture accumulation on the surface and causing road softening. On the other hand, the optimization of the grouting thickness ratio further improves the overall performance. This invention preferably uses a first percentage of 10%–20%, a second percentage of 20%–40%, and a third percentage of 40%–70%. The bottom layer has a moderate thickness, absorbing enough moisture without becoming excessively soft; the middle layer is sufficiently thick to form an effective moisture barrier; and the top layer is the thickest, ensuring sufficient structural strength to withstand road loads and traffic pressure. The synergistic optimization of the thickness ratio of the three layers achieves the best balance between water absorption capacity and structural strength in the repair.

[0025] Furthermore, controlling the mixing time ensures the uniformity of the slurry. In all embodiments, the mixing time is 2 hours. Thorough mixing ensures that the porous carbon and clay are evenly dispersed, avoiding uneven performance caused by local agglomeration. At the same time, it allows water to fully wet the surface of the particles, forming a slurry with good fluidity, which is convenient for grouting operations. After grouting, the slurry can evenly fill the voids, forming a dense and uniform repair, avoiding weak points caused by local voids or poor delamination.

[0026] 3. This invention achieves simultaneous improvement in water absorption performance and structural strength by synergistically optimizing key parameters such as the specific surface area, pore volume, particle size of porous carbon, and particle size of clay, thus avoiding the disadvantages caused by optimizing only one performance.

[0027] When the specific surface area, pore volume, and particle size of porous carbon, as well as the particle sizes of silt and clay in cohesive soil, are all within the numerical ranges specified in this invention, and the preferred staged grouting process is adopted, as in Examples 1-10, the water content change rate of the grouting layer is less than 0.40%, reaching as low as 0.10%, while the strength improvement rate of the grouting layer is over 54%, achieving simultaneous optimization of low water content change rate and high structural strength. When the specific surface area, pore volume, and particle size of porous carbon, as well as the particle sizes of silt and clay in cohesive soil, are not within the ranges specified in this invention, or when other soils such as sand, loess, or gravelly soil are used, the water content change rate measured after grouting is over 7%, and the strength improvement rate is significantly reduced, indicating that the synergistic combination of various technical features is the key to achieving excellent performance. When the specific surface area is greater than 900 cm², 2 / g or pore volume greater than 0.38 cm³ 3At a density of / g, although the soil moisture content change rate is low, reaching 0.09%-0.10%, the strength of the composite material decreases significantly, and the strength improvement rate of the grouting layer is only 14.5%-16.7%. This indicates that the porous carbon parameter range defined in this invention has been optimized and screened. Although the water absorption performance can still be maintained outside this range, it will sacrifice structural strength, which is not conducive to the stability and long-term use of the pavement.

[0028] In summary, this invention, through the optimization of porous carbon microstructure, particle size matching and control with cohesive soil, gradient design of different mass ratios, and the synergistic effect of staged grouting process, significantly reduces the soil moisture content change rate while ensuring the strength of the grouting layer, effectively solving the problem of ground subsidence caused by negative pressure effect.

[0029] Compared with existing technologies, the present invention has the following comprehensive advantages: First, it has strong water absorption capacity, and the soil moisture content change rate can be controlled below 0.26%; second, it has high structural strength, and the strength improvement rate of the grouting layer is more than 54%; third, it has stable and reliable performance, and the water is distributed in a stepped manner through layered grouting, avoiding water accumulation on the surface; fourth, the parameter range is optimized and reasonable, avoiding the technical misconception of sacrificing structural strength for excessive pursuit of water absorption performance.

[0030] Therefore, the composite material and repair method provided by this invention can effectively prevent urban ground subsidence, extend the service life of roads, and reduce maintenance costs, and have excellent engineering application prospects and promotion value. Detailed Implementation

[0031] To better understand the technical solution of this invention, the content of this invention includes, but is not limited to, the specific embodiments described below. Similar technologies and methods should be considered within the scope of protection of this invention. To make the technical problem to be solved, the technical solution, and the advantages of this invention clearer, a detailed description will be provided below in conjunction with specific embodiments.

[0032] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0033] The following specific examples illustrate this.

[0034] Example 1 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and clay are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 786.3 cm². 2 / g, pore volume 0.38 cm³ 3 / g, with a particle size of 10 µm; the silt particle size of the clay is 28 µm, and the clay particle size is 4 µm; S2: Add an appropriate amount of water to the mixture obtained in S1 and stir for 2 hours until it is evenly mixed. Then, pour the resulting slurry into the collapsed area of ​​the ground, with a pouring thickness of 15% of the height of the cavity to be repaired. S3: Mix porous carbon of the same specification from S1 with clay at a mass ratio of 1:2 to form a second mixture; S4: Add an appropriate amount of water to the mixture obtained in S3 and stir for 2 hours until it is evenly mixed. Then, pour the resulting slurry over the S2 layer, with a pouring thickness of 30% of the height of the cavity to be repaired. S5: Mix porous carbon of the same specification from S1 with clay at a mass ratio of 1:10 to form a third mixture; S6: Add an appropriate amount of water to the mixture obtained in S5 and stir for 2 hours to make it evenly mixed. Then, pour the resulting slurry above the S4 layer, with a pouring thickness of 55% of the height of the cavity to be repaired.

[0035] Example 2 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and clay are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 578.3 cm². 2 / g, pore volume 0.28 cm³ 3 / g, with a particle size of 10 µm; the silt particle size of the clay is 28 µm, and the clay particle size is 4 µm; S2-S6: Same as steps S2-S6 in Example 1.

[0036] Example 3 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and clay are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 456.9 cm². 2 / g, pore volume 0.22 cm³ 3 / g, with a particle size of 10 µm; the silt particle size of the clay is 28 µm, and the clay particle size is 4 µm; S2-S6: Same as steps S2-S6 in Example 1.

[0037] Example 4 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and clay are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 328.7 cm². 2 / g, pore volume 0.15 cm³ 3 / g, with a particle size of 10 µm; the silt particle size of the clay is 28 µm, and the clay particle size is 4 µm; S2-S6: Same as steps S2-S6 in Example 1.

[0038] Example 5 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and clay are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 786.3 cm². 2 / g, pore volume 0.38 cm³ 3 / g, with a particle size of 8 µm; the silt particle size of the clay is 15 µm, and the clay particle size is 2 µm; S2-S6: Same as steps S2-S6 in Example 1.

[0039] Example 6 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and clay are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 786.3 cm². 2 / g, pore volume 0.38 cm³ 3 / g, with a particle size of 15 µm; the silt particle size of the clay is 26 µm, and the clay particle size is 3 µm; S2-S6: Same as steps S2-S6 in Example 1.

[0040] Example 7 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and clay are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 786.3 cm². 2 / g, pore volume 0.38 cm³ 3 / g, with a particle size of 21 µm; the silt particle size of the clay is 28 µm, and the clay particle size is 4 µm; S2-S6: Same as steps S2-S6 in Example 1.

[0041] Example 8 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and clay are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 786.3 cm². 2 / g, pore volume 0.38 cm³ 3 / g, with a particle size of 10µm; the silt particle size of the clay is 28µm, and the clay particle size is 4µm; S2: Add an appropriate amount of water to the mixture obtained in S1 and stir for 2 hours until it is evenly mixed. Then, pour the resulting slurry into the collapsed area of ​​the ground, with a pouring thickness of 10% of the height of the cavity to be repaired. S3: Mix porous carbon of the same specification from S1 with clay at a mass ratio of 1:2 to form a second mixture; S4: Add an appropriate amount of water to the mixture obtained in S3 and stir for 2 hours until it is evenly mixed. Then, pour the resulting slurry over the S2 layer, with a pouring thickness of 40% of the height of the cavity to be repaired. S5: Mix porous carbon of the same specification from S1 with clay at a mass ratio of 1:10 to form a third mixture; S6: Add an appropriate amount of water to the mixture obtained in S5 and stir for 2 hours to make it evenly mixed. Then, pour the resulting slurry above the S4 layer, with a pouring thickness of 50% of the height of the cavity to be repaired.

[0042] Example 9 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and clay are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 786.3 cm². 2 / g, pore volume 0.38 cm³ 3 / g, with a particle size of 10 µm; the silt particle size of the clay is 28 µm, and the clay particle size is 4 µm; S2: Add an appropriate amount of water to the mixture obtained in S1 and stir for 2 hours until it is evenly mixed. Then, pour the resulting slurry into the collapsed area of ​​the ground, with a pouring thickness of 10% of the height of the cavity to be repaired. S3: Mix porous carbon of the same specification from S1 with clay at a mass ratio of 1:2 to form a second mixture; S4: Add an appropriate amount of water to the mixture obtained in S3 and stir for 2 hours until it is evenly mixed. Then, pour the resulting slurry over the S2 layer, with a pouring thickness of 30% of the height of the cavity to be repaired. S5: Mix porous carbon of the same specification from S1 with clay at a mass ratio of 1:10 to form a third mixture; S6: Add an appropriate amount of water to the mixture obtained in S5 and stir for 2 hours to make it evenly mixed. Then, pour the resulting slurry above the S4 layer, with a pouring thickness of 60% of the height of the cavity to be repaired.

[0043] Example 10 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and clay are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 786.3 cm². 2 / g, pore volume 0.38 cm³ 3 / g, with a particle size of 10 µm; the silt particle size of the clay is 28 µm, and the clay particle size is 4 µm; S2: Add an appropriate amount of water to the mixture obtained in S1 and stir for 2 hours until it is evenly mixed. Then, pour the resulting slurry into the collapsed area of ​​the ground, with a pouring thickness of 20% of the height of the cavity to be repaired. S3: Mix porous carbon of the same specification from S1 with clay at a mass ratio of 1:2 to form a second mixture; S4: Add an appropriate amount of water to the mixture obtained in S3 and stir for 2 hours until it is evenly mixed. Then, pour the resulting slurry over the S2 layer, with a pouring thickness of 30% of the height of the cavity to be repaired. S5: Mix porous carbon of the same specification from S1 with clay at a mass ratio of 1:10 to form a third mixture; S6: Add an appropriate amount of water to the mixture obtained in S5 and stir for 2 hours to make it evenly mixed. Then, pour the resulting slurry above the S4 layer, with a pouring thickness of 50% of the height of the cavity to be repaired.

[0044] Comparative Example 1 A method for repairing urban ground subsidence includes the following steps: Add an appropriate amount of water to the cohesive soil and stir for 2 hours to make it evenly mixed. Then, pour the resulting slurry directly into the collapsed area of ​​the ground, with the pouring thickness being 100% of the height of the cavity to be repaired. The cohesive soil has a silt particle size of 28 µm and a clay particle size of 4 µm.

[0045] Comparative Example 2 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and clay are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 155.3 cm². 2 / g, pore volume 0.05 cm³ 3 / g, with a particle size of 10 µm; the silt particle size of the clay is 28 µm, and the clay particle size is 4 µm; S2: Add an appropriate amount of water to the mixture obtained in S1 and stir for 2 hours until it is evenly mixed. Then, pour the resulting slurry into the collapsed area of ​​the ground, with a pouring thickness of 15% of the height of the cavity to be repaired. S3: Mix porous carbon of the same specification from S1 with clay at a mass ratio of 1:2 to form a second mixture; S4: Add an appropriate amount of water to the mixture obtained in S3 and stir for 2 hours until it is evenly mixed. Then, pour the resulting slurry over the S2 layer, with a pouring thickness of 30% of the height of the cavity to be repaired. S5: Mix porous carbon of the same specification from S1 with clay at a mass ratio of 1:10 to form a third mixture; S6: Add an appropriate amount of water to the mixture obtained in S5 and stir for 2 hours to make it evenly mixed. Then, pour the resulting slurry above the S4 layer, with a pouring thickness of 55% of the height of the cavity to be repaired.

[0046] Comparative Example 3 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and clay are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 289.1 cm². 2 / g, pore volume 0.12 cm³ 3 / g, with a particle size of 10 µm; the silt particle size of the clay is 28 µm, and the clay particle size is 4 µm; S2: Add an appropriate amount of water to the mixture obtained in S1 and stir for 2 hours until it is evenly mixed. Then, pour the resulting slurry into the collapsed area of ​​the ground, with a pouring thickness of 15% of the height of the cavity to be repaired. S3: Mix porous carbon of the same specification from S1 with clay at a mass ratio of 1:2 to form a second mixture; S4: Add an appropriate amount of water to the mixture obtained in S3 and stir for 2 hours until it is evenly mixed. Then, pour the resulting slurry over the S2 layer, with a pouring thickness of 30% of the height of the cavity to be repaired. S5: Mix porous carbon of the same specification from S1 with clay at a mass ratio of 1:10 to form a third mixture; S6: Add an appropriate amount of water to the mixture obtained in S5 and stir for 2 hours to make it evenly mixed. Then, pour the resulting slurry above the S4 layer, with a pouring thickness of 55% of the height of the cavity to be repaired.

[0047] Comparative Example 4 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and clay are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 1178.3 cm². 2 / g, pore volume is 0.61 cm³ 3 / g, with a particle size of 10 µm; the silt particle size of the clay is 28 µm, and the clay particle size is 4 µm; S2-S6: Same as steps S2-S6 in Comparative Example 2.

[0048] Comparative Example 5 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and clay are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 1506.7 cm². 2 / g, pore volume 0.85 cm³ 3 / g, with a particle size of 10 µm; the silt particle size of the clay is 28 µm, and the clay particle size is 4 µm; S2-S6: Same as steps S2-S6 in Comparative Example 2.

[0049] Comparative Example 6 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and clay are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 786.3 cm². 2 / g, pore volume 0.38 cm³ 3 / g, with a particle size of 35 µm; the silt particle size of the clay is 23 µm, and the clay particle size is 4 µm; S2-S6: Same as steps S2-S6 in Comparative Example 2.

[0050] Comparative Example 7 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and clay are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 786.3 cm². 2 / g, pore volume 0.38 cm³ 3 / g, with a particle size of 2 µm; the silt particle size of the clay is 23 µm, and the clay particle size is 4 µm; S2-S6: Same as steps S2-S6 in Comparative Example 2.

[0051] Comparative Example 8 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and clay are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 786.3 cm². 2 / g, pore volume 0.38 cm³ 3 / g, with a particle size of 2 µm; the silt particles of the clay have a particle size of 3 µm, and the clay particles have a particle size of 4 µm; S2-S6: Same as steps S2-S6 in Comparative Example 2.

[0052] Comparative Example 9 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and sand are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 786.3 cm². 2 / g, pore volume 0.38 cm³ 3 / g, with a particle size of 10 µm; the sand has a particle size of 28 µm; S2-S6: Same as steps S2-S6 in Comparative Example 2.

[0053] Comparative Example 10 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and loess are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 786.3 cm². 2 / g, pore volume 0.38 cm³ 3 / g, with a particle size of 10 µm; the loess has a particle size of 28 µm; S2-S6: Same as steps S2-S6 in Comparative Example 2.

[0054] Comparative Example 11 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and gravelly soil are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 786.3 cm². 2 / g, pore volume 0.38 cm³ 3 / g, with a particle size of 10 µm; the gravelly soil has a particle size of 28 µm; S2-S6: Same as steps S2-S6 in Comparative Example 2.

[0055] Comparative Example 12 A method for repairing urban ground subsidence includes the following steps: Porous carbon was mixed with clay at mass ratios of 1:1, 1:2, and 1:10 respectively. Then, the three mixtures were combined at concentrations of 15%, 30%, and 55% of the collapse height, respectively, to form a final mixture. The specific surface area of ​​the porous carbon was 786.3 cm². 2 / g, pore volume is 0.38cm³ 3 / g, with a particle size of 10µm; the silt particle size of the clay is 28µm, and the clay particle size is 4µm; Add an appropriate amount of water to the total mixture and stir for 2 hours until it is evenly mixed. Then, pour the resulting slurry into the collapsed area of ​​the ground in one go, with the pouring thickness being 100% of the height of the cavity to be repaired.

[0056] Comparative Example 13 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and clay are mixed at a mass ratio of 1:10 to form a first mixture; the specific surface area of ​​the porous carbon is 786.3 cm². 2 / g, pore volume is 0.38cm³ 3 / g, with a particle size of 10µm; the silt particle size of the clay is 28µm, and the clay particle size is 4µm; S2: Add an appropriate amount of water to the mixture obtained in S1 and stir for 2 hours until it is evenly mixed. Then, pour the resulting slurry into the collapsed area of ​​the ground, with a pouring thickness of 15% of the height of the cavity to be repaired. S3: Mix porous carbon and clay at a mass ratio of 1:2 to form a second mixture; S4: Add an appropriate amount of water to the mixture obtained in S3 and stir for 2 hours until it is evenly mixed. Then, pour the resulting slurry over the S2 layer, with a pouring thickness of 30% of the height of the cavity to be repaired. S5: Mix porous carbon and clay at a mass ratio of 1:1 to form a third mixture; S6: Add an appropriate amount of water to the mixture obtained in S5 and stir for 2 hours to make it evenly mixed. Then, pour the resulting slurry above the S4 layer, with a pouring thickness of 55% of the height of the cavity to be repaired.

[0057] Comparative Example 14 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and clay are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 786.3 cm². 2 / g, pore volume is 0.38cm³ 3 / g, with a particle size of 10µm; the silt particle size of the clay is 28µm, and the clay particle size is 4µm; S2: Add an appropriate amount of water to the mixture obtained in S1 and stir for 2 hours until it is evenly mixed. Then, pour the resulting slurry into the collapsed area of ​​the ground, with a pouring thickness of 50% of the height of the cavity to be repaired. S3: Mix porous carbon and clay at a mass ratio of 1:2 to form a second mixture; S4: Add an appropriate amount of water to the mixture obtained in S3 and stir for 2 hours until it is evenly mixed. Then, pour the resulting slurry over the S2 layer, with a pouring thickness of 40% of the height of the cavity to be repaired. S5: Mix porous carbon and clay at a mass ratio of 1:10 to form a third mixture; S6: Add an appropriate amount of water to the mixture obtained in S5 and stir for 2 hours to make it evenly mixed. Then, pour the resulting slurry above the S4 layer, with a pouring thickness of 10% of the height of the void to be repaired.

[0058] Comparative Example 15 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and clay are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 786.3 cm². 2 / g, pore volume 0.38 cm³ 3 / g, with a particle size of 10 µm; the silt particle size of the clay is 28 µm, and the clay particle size is 4 µm; S2: Add an appropriate amount of water to the mixture obtained in S1 and stir for 2 hours until it is evenly mixed. Then, pour the resulting slurry into the collapsed area of ​​the ground, with a pouring thickness of 15% of the height of the cavity to be repaired. S3: Mix porous carbon of the same specification from S1 with clay at a mass ratio of 1:2 to form a second mixture; S4: Add an appropriate amount of water to the mixture obtained in S3 and stir for 2 hours until it is evenly mixed. Then, pour the resulting slurry over the S2 layer, with a pouring thickness of 10% of the height of the cavity to be repaired. S5: Mix porous carbon of the same specification from S1 with clay at a mass ratio of 1:10 to form a third mixture; S6: Add an appropriate amount of water to the mixture obtained in S5 and stir for 2 hours to make it evenly mixed. Then, pour the resulting slurry above the S4 layer, with a pouring thickness of 75% of the height of the cavity to be repaired.

[0059] Comparative Example 16 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and clay are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 786.3 cm². 2 / g, pore volume 0.38 cm³ 3 / g, with a particle size of 10 µm; the silt particle size of the clay is 28 µm, and the clay particle size is 4 µm; S2: Add an appropriate amount of water to the mixture obtained in S1 and stir for 2 hours until it is evenly mixed. Then, pour the resulting slurry into the collapsed area of ​​the ground, with a pouring thickness of 15% of the height of the cavity to be repaired. S3: Mix porous carbon of the same specification from S1 with clay at a mass ratio of 1:2 to form a second mixture; S4: Add an appropriate amount of water to the mixture obtained in S3 and stir for 2 hours until it is evenly mixed. Then, pour the resulting slurry over the S2 layer, with a pouring thickness of 60% of the height of the cavity to be repaired. S5: Mix porous carbon of the same specification from S1 with clay at a mass ratio of 1:10 to form a third mixture; S6: Add an appropriate amount of water to the mixture obtained in S5 and stir for 2 hours to make it evenly mixed. Then, pour the resulting slurry above the S4 layer, with a pouring thickness of 25% of the height of the cavity to be repaired.

[0060] Comparative Example 17 A method for repairing urban ground subsidence includes the following steps: S1: Porous carbon and clay are mixed at a mass ratio of 1:1 to form a first mixture; the specific surface area of ​​the porous carbon is 786.3 cm². 2 / g, pore volume is 0.38cm³ 3 / g, with a particle size of 10µm; the silt particle size of the clay is 28µm, and the clay particle size is 4µm; S2: Add an appropriate amount of water to the mixture obtained in S1 and stir for 2 hours until it is evenly mixed. Then, pour the resulting slurry into the collapsed area of ​​the ground, with a pouring thickness of 50% of the height of the cavity to be repaired. S3: Mix porous carbon and clay at a mass ratio of 1:10 to form a second mixture; S4: Add an appropriate amount of water to the mixture obtained in S3 and stir for 2 hours to make it evenly mixed. Then, pour the resulting slurry above the S2 layer, with a pouring thickness of 50% of the height of the cavity to be repaired.

[0061] The strength improvement rate of the grouting layer and the change rate of soil moisture content after the tests in the examples and comparative examples are shown in Table 1 below: Table 1. Increment of grouting layer strength and change in soil moisture content in the examples and comparative examples

[0062] As can be seen from all the above embodiments, when the specific surface area, pore volume, and particle size of the porous carbon in the composite material, as well as the particle size of the silt and clay particles of the cohesive soil, work synergistically within the numerical range specified in this invention, it can not only ensure that the water content change rate of the grouting layer is relatively low (less than 0.26%, and can reach as low as 0.10%), but also ensure that it has high strength. In contrast, in the comparative examples, because the specific surface area, pore volume, and particle size of the porous carbon, as well as the particle size of the silt and clay particles of the cohesive soil, are not within the range specified in this invention, or other soils, such as sandy soil or loess, are used, the water content measured after grouting is relatively high, above 7%. In contrast, the specific surface area used in comparative examples 4 or 5 is greater than 900 cm². 2 / g or pore volume greater than 0.38 cm³ 3 Although the measured soil moisture content change rate is relatively low at 0.09%, this will significantly reduce the strength of the composite material, and consequently significantly reduce the strength of the grouting layer, which is detrimental to the stability and long-term use of the pavement.

[0063] As shown in Examples 1, 5, and 8, when the specific surface area reaches 786.3 cm²... 2 / g, pore volume 0.38 cm³ 3 At a specific surface area of ​​100 g / g, the composite material can effectively absorb moisture in underground cavities and accelerate water seepage, resulting in a soil moisture content change rate as low as 0.10%-0.16%, significantly reducing the risk of soil instability caused by negative pressure effects. In contrast, when the specific surface area is less than 300 cm²...2 / g or pore volume less than 0.15 cm³ 3 When the soil moisture content changes by 7.5%–8.6% at a rate of / g, it indicates insufficient water absorption capacity and poor water circulation, which cannot effectively mitigate the negative impact of groundwater level changes.

[0064] As shown in Examples 1, 5, and 6, when the porous carbon particle size is 8–21 µm, the powder particle size is 15–28 µm, and the clay particle size is 2–4 µm, the composite material forms a stable particle skeleton after infusion, and the strength improvement rate of the infused layer reaches 55.1%–56.7%. In Comparative Examples 6–8, when the particle size matching relationship is broken, such as the porous carbon particle size being too large or too small, or the clay particle size being larger than the porous carbon, the strength improvement rate of the infused layer drops to below 10%, and the soil moisture content change rate is still as high as 7.7%–9%, ​​indicating poor structural stability and poor water permeability, failing to form an effective water barrier layer and effectively alleviate the soil instability problem caused by the negative pressure effect. As shown in Examples 8–10, when the thickness ratio of each layer is within a reasonable range, such as 10% / 40% / 50%, 10% / 30% / 60%, or 20% / 30% / 50%, the soil moisture content change rate is less than 0.22%, and the strength improvement rate of the grouting layer is more than 54%, which fully verifies the effectiveness of the layered grouting process.

[0065] In comparison, Comparative Example 12, which uses a single, non-layered grouting method and employs the same materials, suffers from a significantly increased soil moisture content change rate (5.80%) and a decreased grouting layer strength enhancement rate (30.1%) due to the inability to form a functional gradient structure. Comparative Example 13 reverses the layering order, with a high-cohesion bottom layer and a highly porous carbon top layer, resulting in ineffective water barrier and a soil moisture content change rate of 6.20%. In Comparative Examples 14, 15, and 16, the grouting ratios deviate from the optimal range, which not only reduces the overall strength of the grouting layer but also disrupts the tiered distribution of water within it. Comparative Example 17 lacks a middle water-blocking layer, allowing direct upward infiltration of bottom-layer water, resulting in a soil moisture content change rate as high as 4.90%. These comparisons clearly demonstrate that the present invention significantly improves the overall performance of the restoration through the synergistic design of layered grouting, optimized sequence, and appropriate thickness ratios.

[0066] The foregoing description illustrates and describes several preferred embodiments of the present invention. However, as previously stated, it should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept described herein through the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A composite material for urban ground subsidence repair, characterized in that, The composite material comprises porous carbon and clay, wherein the porous carbon has a specific surface area of ​​300-900 cm². 2 / g, pore volume 0.15-0.38 cm³ 3 / g, with a particle size of 5-30 µm; the cohesive soil includes silt and clay particles, wherein the particle size of the silt is larger than that of the porous carbon, and the particle size of the clay particles is smaller than that of the porous carbon.

2. The composite material according to claim 1, characterized in that, The mass ratio of porous carbon to clay is 1:1, 1:2, or 1:

10.

3. The composite material according to claim 1, characterized in that, The mass ratio of silt to clay in the cohesive soil is 2:

1.

4. The composite material according to claim 1, characterized in that, The porous carbon has a specific surface area of ​​786.3 cm². 2 / g, pore volume 0.38 cm³ 3 / g, with a particle size of 10 µm; the silt particle size of the clay is 28 µm, and the clay particle size is 4 µm.

5. The composite material according to claim 1, characterized in that, The porous carbon has a specific surface area of ​​578.3 cm². 2 / g, pore volume 0.28 cm³ 3 / g, with a particle size of 10 µm; the silt particle size of the clay is 28 µm, and the clay particle size is 4 µm.

6. The composite material according to claim 1, characterized in that, The specific surface area of ​​the porous carbon is 456.9 cm². 2 / g, pore volume 0.22 cm³ 3 / g, with a particle size of 10 µm; the silt particle size of the clay is 28 µm, and the clay particle size is 4 µm.

7. The composite material according to claim 1, characterized in that, The porous carbon has a specific surface area of ​​328.7 cm². 2 / g, pore volume 0.15 cm³ 3 / g, with a particle size of 10 µm; the silt particle size of the clay is 28 µm, and the clay particle size is 4 µm.

8. The composite material according to claim 1, characterized in that, The porous carbon has a specific surface area of ​​786.3 cm². 2 / g, pore volume 0.38 cm³ 3 / g, with a particle size of 8 µm; the silt particle size of the clay is 15 µm, and the clay particle size is 2 µm.

9. A method for graded injection repair of urban ground subsidence, using the composite material described in any one of claims 1-8, characterized in that, Includes the following steps: S1: Mix porous carbon with clay at a first mass ratio to form a first mixture; S2: Add water to the first mixture and stir. Pour the mixture into the collapsed area of ​​the ground. The pouring thickness is a first percentage of the height of the cavity to be repaired. S3: Mix porous carbon with clay at a second mass ratio to form a second mixture; S4: After adding water to the second mixture and stirring, pour it over the first mixture, with the pouring thickness being a second percentage of the height of the cavity to be repaired; S5: Mix porous carbon with clay at a third mass ratio to form a third mixture; S6: Add water to the third mixture and stir, then pour it over the second mixture.

10. The method according to claim 9, characterized in that, The stirring time in S2, S4 and S6 is 2 hours; the first percentage is 10%-20%, the second percentage is 20%-40%, and the third percentage is 40%-70%; the first mass ratio is 1:1, the second mass ratio is 1:2, and the third mass ratio is 1:10.

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