Superfluid soil backfill method for special-shaped narrow spaces

Abstract

The present disclosure provides a method for backfilling a narrow space with superfluid soil, comprising: step S1, constructing a three-dimensional cavity model of the narrow space, wherein the narrow space comprises an underground cave group or an underground goaf group; step S2, determining the components of the superfluid soil, wherein the superfluid soil comprises the following components: engineering slag, a composite curing agent, hydrophobic glass microbeads, and water, wherein the composite curing agent comprises fly ash, silicate cement, a core-shell magnesium oxide expansion agent, and calcium stearate; step S3, mixing the various components of the superfluid soil; step S4, filling the narrow space with the superfluid soil; and step S5, curing and curing the filled superfluid soil. The superfluid soil used in the present disclosure exhibits self-repairing properties when backfilling a narrow space with a special shape. When the slurry is affected by the structure of the backfill space and its flow is obstructed, it can recover to more than 90% of its initial fluidity within 1-2 minutes, and the final space backfill rate can reach more than 95%.

Description

Technical Field

[0001] The present disclosure relates to the field of construction, and more particularly to a superfluid soil backfill method for special-shaped narrow spaces. Background Art

[0002] With the accelerating pace of urbanization, underground space development has experienced unprecedented growth. The construction of infrastructure such as foundations, underground transportation lines, underground shopping malls, and underground pipelines is becoming increasingly widespread, providing critical support for urban development. However, during the backfilling process in confined spaces like foundation pits, fertilizer troughs, and underground utility corridors, space constraints prevent the use of large and medium-sized compacting machinery, forcing construction workers to rely on manual compaction. This inefficient method not only results in insufficient backfill density but can also cause serious engineering accidents such as ground subsidence and landslides, posing safety risks to urban construction and public life.

[0003] Superfluid soil, or fluidized solidified soil, is a new green building material attracting significant attention for its environmental friendliness and practicality. It typically uses on-site construction waste as a base material, with cement, fly ash, slag, and other materials as binders. It exhibits self-leveling and self-compacting properties during pouring, and after curing, forms a solidified structure with a certain strength, low permeability, and long-term stability. Therefore, it is used in narrow space backfill projects in construction, saving time and costs while improving construction efficiency.

[0004] Although fluidized solidified soil has many advantages, it still faces the following challenges when faced with large, narrow, and irregular spaces such as underground goafs and underground caves:

[0005] (1) The existing fluidized solidification soil has certain limitations in terms of flow performance. It is affected by the spatial structure of the backfill area. Especially when encountering irregular and narrow areas, the slurry will be affected by the flow resistance, resulting in a decrease in fluidity and thus premature solidification. This not only limits the further filling capacity of the slurry, but also significantly reduces the space backfill rate, and cannot meet the high backfill rate requirements of large-scale irregular and narrow spaces.

[0006] (2) It is difficult to balance the strength and fluidity of existing fluidized solidified soils. Generally speaking, the better the fluidity of the slurry, the lower the strength of the solidified body formed later. This characteristic limits the application of fluidized solidified soils in large-scale backfill projects with irregular shapes and narrow spaces, because these scenarios not only require a high backfill rate, but also place higher demands on the structural strength after solidification.

[0007] (3) During the solidification process, fluidized solidified soil shrinks due to water loss, which easily leads to cracks. In conventional spaces or small-volume backfill projects, this problem can be alleviated to a certain extent through post-maintenance measures. However, in backfill projects with large, irregular, and narrow spaces, shrinkage cracks are more likely to form and have a wider impact due to structural complexity and construction conditions. This seriously affects the strength stability after solidification. At the same time, traditional maintenance methods are difficult to implement and costly.

[0008] The above problems limit its application in complex engineering projects, and further technical improvements are urgently needed to overcome these limitations. Summary of the Invention

[0009] The present disclosure provides a method for backfilling a special-shaped narrow space with superfluid soil, comprising: step S1, constructing a three-dimensional cavity model of the special-shaped narrow space, wherein the special-shaped narrow space includes an underground cave group or an underground goaf group; step S2, determining the components of the superfluid soil, wherein the superfluid soil is composed of the following components: engineering slag, a composite curing agent, hydrophobic glass microbeads and water, and the composite curing agent includes fly ash, silicate cement, a core-shell magnesium oxide expansion agent and calcium stearate; step S3, mixing the various components of the superfluid soil; step S4, filling the special-shaped narrow space with the superfluid soil; and step S5, curing and curing the filled superfluid soil.

[0010] In some embodiments, constructing a three-dimensional cavity model of an irregular and narrow space includes: using a six-rotor drone equipped with a ground-penetrating radar to scan a designated area along a preset route to obtain preliminary information on the underground structure of the irregular and narrow space, and determine the location and range of the suspected cavity; injecting a tracer containing magnetic nanoparticles into the suspected cavity, and locating the seepage path through a magnetic gradiometer, wherein the tracer containing magnetic nanoparticles will move with the seepage liquid after being injected into the suspected cavity, and the magnetic gradiometer can measure the change in magnetic field gradient, thereby determining the position and migration path of the tracer, so as to determine the seepage conditions inside the cavity; based on the location and range of the suspected cavity and the seepage conditions inside the cavity, these data are integrated, analyzed and processed through an artificial intelligence algorithm to construct a three-dimensional cavity model.

[0011] In some embodiments, the mass ratio of the construction waste soil, the composite curing agent, the hydrophobic glass microbeads and the water is 5:1.5-2.5:0.5-1.5:3.5-4.5, the particle size of the construction waste soil does not exceed 5 mm, and the moisture content does not exceed 20%.

[0012] In some embodiments, the mass ratio of the fly ash, the Portland cement, the core-shell structured magnesium oxide expansion agent, and the calcium stearate is 150:38-42:4-6:2-4, and the fly ash particles are spherical.

[0013] In some embodiments, the core-shell structured magnesium oxide expander comprises, from the inside out, a magnesium oxide core, a magnesium phosphate passivation layer with a thickness of 200-300 nm, and a nano-silicon dioxide layer with a thickness of 50-80 nm and a porosity of less than 5%.

[0014] In some embodiments, the nano-silicon dioxide layer has an amorphous structure, cracks exist on the surface, and the crack density is 10 6 / m 2 In an alkaline environment with a pH value exceeding 12, the nano-silica layer undergoes hydrolysis, and the MgO contained therein hydrates to form Mg(OH)2 precipitates, causing a primary expansion in volume. The primary expansion occurs within 3-6 hours of the solidification stage of the superfluid soil. The magnesium phosphate passivation layer is amorphous magnesium phosphate. When the pH value of the superfluid soil slurry rises to above 12 due to cement hydration, step-by-step dissolution occurs. The step-by-step dissolution process is as follows: the magnesium phosphate passivation layer and OH - The reaction generates soluble phosphate radicals, which combine with calcium ions in the slurry to generate hydroxyapatite precipitation, causing a secondary expansion in volume. The secondary expansion occurs within 6-48 hours of the solidification stage of the superfluid soil.

[0015] In some embodiments, the hydrophobic glass microspheres are spherical and have a particle density of 2.35-2.75 g / cm 3 , compressive strength of 115-125MPa, and a median particle size of 30±5μm; the hydrophobic glass microbeads are prepared by the following steps: adding glass microbeads, calcium stearate and alumina balls to a ball mill for mechanical dry grinding for 5-8 hours; the diameter of the alumina balls is 3mm, which serves as ball milling media to reduce mechanical damage to the glass microbeads caused by the dry grinding process; the mass ratio of the alumina balls to the glass microbeads is 4:1, and the mass ratio of calcium stearate to the glass microbeads is 1:20. After grinding, a sieve is used to separate the modified hydrophobic glass microbeads, grinding media and remaining calcium stearate; the thickness of the hydrophobic layer of the hydrophobic glass microbeads is 50-150nm.

[0016] In some embodiments, mixing the various components of the superfluid soil includes: first, adding the construction waste soil and hydrophobic glass microbeads into a mixer, and dry mixing them at a speed of 120-150 r / min for 3-5 minutes to ensure that the hydrophobic glass microbeads and the construction waste soil are fully mixed; secondly, adding water to the dry mixture of the construction waste soil and the hydrophobic glass microbeads, and wet mixing them at a speed of 80-100 r / min for 6-8 minutes to improve the uniformity of the mixture; finally, adding a composite curing agent to the wet material, and stirring at a speed of 60-80 r / min for 2-3 minutes to ensure that the composite curing agent is evenly dispersed in the mixture to obtain superfluid soil.

[0017] In some embodiments, filling the superfluid soil into the irregular and narrow space includes: filling the superfluid soil from the bottom of the filling area upward; synchronously applying 20-60 Hz axial vibration at a grouting pressure of 0.5-2.0 MPa to assist grouting; the front end of the grouting pipe is equipped with a night vision camera and an electromagnetic wave transmitter to observe and detect the filling effect in real time; high-frequency electromagnetic waves are emitted to the filling area by a ground-penetrating radar, and the internal structure and density of the superfluid soil in the filling space are analyzed and verified based on the propagation and reflection of the electromagnetic waves in the soil; the grouting process is non-stratified and non-interrupted, and the filling is completed in one go.

[0018] In some embodiments, curing and solidifying the filled superfluid soil includes: for deep dry filling areas, spray curing is used; for deep moist filling areas, the humidity conditions of the underground space itself are used to naturally moisturize the filled superfluid soil; for exposed areas on the surface, plastic film or geotextile is used for covering and curing.

[0019] The core-shell structure magnesium oxide expansion agent used in the present invention can delay the expansion of the magnesium oxide expansion agent and compensate for the cracking caused by volume shrinkage during the solidification stage of superfluid soil; calcium stearate has a long-chain alkyl structure and will be arranged in a direction on the surface of soil particles to form a continuous hydrophobic film, separating the soil particles from external water and improving the fluidity of superfluid soil.

[0020] In addition, the hydrophobic glass microspheres used in the present invention have a rolling ball effect. The good hydrophobicity of the calcium stearate modified layer on its surface can allow more water in the superfluid soil slurry to be used for curing agent hydration, thereby enhancing the fluidity of the hydration product. At the same time, it can delay the contact time between some curing agent particles and water, slow down the heat release rate, prevent early cracking, and ensure strength. In addition, the hydrophobic glass microspheres have a viscosity-reducing effect. During the superfluid soil mixing stage and the backfill stage, the hydrophobic layer allows the glass microspheres to migrate freely in the slurry. The kinetic energy generated can prevent the clay particles in the engineering debris from agglomerating, thereby enhancing the fluidity of the slurry. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A schematic flow chart of a method for backfilling irregularly shaped narrow spaces with superfluid soil according to some embodiments is shown. DETAILED DESCRIPTION

[0022] The following embodiments may enable those skilled in the art to more fully understand the present disclosure, but are not intended to limit the present disclosure in any way.

[0023] Unless otherwise noted, the materials and reagents used in the following examples are commercially available. In this disclosure, construction waste refers to construction waste primarily composed of soil, generated during civil engineering activities such as construction, roads, subways, tunnels, and water conservancy projects. It has the following characteristics: 1) It originates from human activities related to civil engineering, specifically the construction, repair, and demolition of buildings, roads, railways, tunnels, pipeline corridors, bridges, ports, canals, and other structures, as well as the dredging of rivers and waterways; 2) It primarily consists of soil.

[0024] Figure 1 A schematic flow chart of a method for backfilling a narrow space with superfluid soil according to some embodiments is shown. Figure 1 The disclosed method for backfilling a special-shaped narrow space with superfluid soil includes: step S1, intelligent survey and modeling of the backfill area; step S2, designing the mix ratio of the superfluid soil for backfilling; step S3, mixing the raw materials of the superfluid soil; step S4, filling the superfluid soil; step S5, curing and solidifying; and step S6, quality inspection.

[0025] In some embodiments, in step S1, a three-source fusion exploration modeling technology of drone, ground penetrating radar and nano-tracer is used to determine the three-dimensional space and volume of the backfill area, specifically including: step S11, drone equipped with ground penetrating radar to perform regional scanning: first, a six-rotor drone equipped with a micro ground penetrating radar (frequency 1GHz) (Wuhan Jie Tan Technology GT-GPR wireless integrated geological radar) is used to scan the designated area according to a preset route to obtain preliminary information on the underground structure and determine the approximate location and range of the suspected cavity; step S12, tracer and magnetic gradiometer are used to locate the seepage path: inject into the suspected cavity (first drill a grouting hole on the ground, and then insert The slurry is injected into the cavity through a grouting pipe) containing a tracer containing magnetic nanoparticles (Fe3O4@SiO2) (mass content 5% to 20%. In addition to the magnetic nanoparticles, the tracer specifically includes a sodium polyacrylate dispersant with a mass content of 10% to 20%, and the remaining carbon quantum dots (CQDs). The carbon quantum dots are used for fluorescent tracing assistance, with an excitation wavelength of 365nm and an emission wavelength of 450nm, which facilitates more intuitive observation of the distribution of the tracer and makes the tracer emit fluorescence under light of a specific wavelength). The seepage path is located by a magnetic gradiometer (Bartington's Grad-13 digital three-axis gradient magnetometer). After the tracer containing Fe3O4@SiO2 is injected into the suspected cavity, it will move with the seepage liquid. The magnetic gradiometer can measure the change of the magnetic field gradient with high precision, thereby determining the position and migration path of the tracer, and helping to understand the seepage situation inside the cavity; Step S13, the building information model (BIM) and the geological radar data are combined with artificial intelligence (AI) to generate a three-dimensional cavity model: combining BIM and geological radar data, a high-precision three-dimensional cavity model is automatically generated through the AI ​​algorithm. Specifically, the AI ​​algorithm adopts the super-resolution convolutional neural network (SRCNN) algorithm + simultaneous localization and mapping (SLAM) algorithm. First, the super-resolution convolutional neural network (SRCNN) algorithm is used to process the multi-source heterogeneous data obtained by various survey methods, perform data fusion and optimization, improve the accuracy of low-resolution data, or use a generative model to fill in the missing parts in the data and improve the details; then the above data is processed end-to-end through the simultaneous localization and mapping (SLAM) algorithm to automatically generate a three-dimensional model of the goaf group / cavern group. The BIM model can provide a three-dimensional spatial framework for the project, geological radar data can provide detailed information on underground structures, and AI algorithms can fuse, analyze, and process these data to build a high-precision three-dimensional cavity model through a data-driven approach.By constructing a three-dimensional pore model, we can understand the spatial distribution and structural overview of the goaf group / cavern group and clarify the scale of treatment, such as calculating the volume of the goaf group / cavern group to be treated, and reversely inferring the amount of superfluid soil based on the treatment volume, and further reversely inferring the amount of raw materials for each part based on the mix ratio; in addition, through a detailed analysis of the three-dimensional model, we can clarify the difficulties in the treatment of the goaf group / cavern group, such as the occurrence form of the goaf group / cavern group: independent closed cavity structure, multiple cavity structures that penetrate each other, etc. According to the occurrence of the goaf group / cavern group, we can optimize the grouting method and improve the filling effect.

[0026] Compared with the traditional "geophysical exploration + drilling mutual verification method", the "drone + ground penetrating radar + nanotracer three-source fusion modeling method" in step S1 can increase efficiency by 5 times, reduce costs by 40%, and identify cracks as small as 5 cm.

[0027] Specifically, in some embodiments, efficiency improvement can be achieved through the following aspects: 1) Rapid positioning and large-scale detection by UAVs: UAVs have fast maneuverability and flexible flight capabilities, can quickly reach the target area for large-scale preliminary surveys, quickly obtain macroscopic information such as topography, determine areas where anomalies may exist, and provide precise positioning guidance for the subsequent application of ground-penetrating radar and nano-tracers, avoiding the inefficient working method of blindly arranging exploration points over a large area in traditional methods; 2) Efficient detection by ground-penetrating radar: Ground-penetrating radar uses the propagation characteristics of high-frequency electromagnetic waves in underground media to quickly and continuously scan geological structures within a certain depth range underground. Compared with traditional geophysical exploration + drilling, A large amount of underground structure information can be obtained in a short period of time, greatly improving the detection efficiency; 3) Precise indication of nanotracers: Nanotracers have unique physical and chemical properties, can migrate quickly and accurately in the underground environment, and can quickly identify their position and distribution through specific detection methods, thereby quickly determining the location and scope of underground void areas, without the need for a large amount of drilling sampling and analysis work like traditional drilling; 4) Three-source data fusion and modeling: The terrain data obtained by drones, the underground structure data of ground-penetrating radar, and the distribution data of nanotracers are integrated and modeled, which can quickly and comprehensively present the underground geological conditions, reduce the time for data processing and analysis, and improve overall work efficiency.

[0028] In some embodiments, cost reduction can be achieved through the following: 1) Reducing drilling workload: The traditional "geophysical exploration + drilling mutual verification method" requires a large amount of drilling work to obtain underground geological information, and the rental, transportation, operation, and consumables of drilling equipment all require significant investment. The "UAV + GPR + Nanotracer Three-Source Fusion Modeling Method" uses drones and GPR for early, large-scale exploration, and nanotracers for precise positioning to accurately determine the location and size of underground goaf / cavern clusters, significantly reducing the drilling workload and the number of holes drilled, thereby lowering drilling costs. 2) Improving equipment utilization: Drones, GPR, and other equipment can be quickly transferred and reused across different projects and regions, resulting in relatively short idle times, improving equipment utilization and reducing unit costs. 3) Reducing labor costs: Due to the reduced drilling workload and complexity of on-site operations, the number of workers and working hours required are also reduced, thereby reducing labor costs. Furthermore, data fusion modeling and other tasks can be performed indoors using computer software and professional technicians, reducing the manpower required for field operations.

[0029] In some embodiments, the ability to identify 5 cm cracks is achieved through the following aspects: 1) High resolution of ground penetrating radar: Modern ground penetrating radar technology continues to develop, and the performance of its transmitting and receiving antennas continues to improve, capable of transmitting and receiving electromagnetic waves with shorter wavelengths, thereby having higher resolution; for cracks of about 5 cm, the electromagnetic waves of the ground penetrating radar can produce obvious reflection, scattering and other signal changes at the cracks. Through the precise analysis and processing of these signals, the existence and location of the cracks can be identified; 2) Sensitivity of nanotracers: Nanotracers have very small particle sizes and strong permeability and diffusivity, and can enter tiny cracks and form a unique distribution in the cracks. pattern; through precise detection of the distribution of nanotracers, such as using magnetic detection, fluorescence detection and other technologies, the enrichment or abnormal distribution of nanotracers in 5 cm cracks can be found, thereby indirectly identifying the existence of cracks; 3) Three-source data complementation and enhancement: The topographic data obtained by the drone can provide macro-environmental information on the possible existence of cracks, the ground penetrating radar provides overall information on the underground structure, and the nanotracer has a unique indicative effect on tiny cracks; the fusion analysis of these three types of data can complement and enhance each other, characterizing the underground geological conditions from different angles and scales, so that 5 cm cracks that were originally difficult to identify by a single method can be accurately identified and located.

[0030] In some embodiments, in step S2, the raw materials for the superfluid soil are composed of the following components: construction waste soil, a composite curing agent, hydrophobic glass microspheres, and water. In some embodiments, the construction waste soil is generally locally sourced, with a particle size not exceeding 5 mm and a moisture content not exceeding 20%. In some embodiments, the mass ratio of construction waste soil, composite curing agent, hydrophobic glass microspheres, and water is 5:1.5-2.5:0.5-1.5:3.5-4.5. In some embodiments, the optimal mass ratio of construction waste soil, composite curing agent, hydrophobic glass microspheres, and water is 5:2:1:4. In some embodiments, construction waste soil is the primary raw material, accounting for 5 parts by weight. The amount used must ensure a certain skeleton structure, providing basic strength and stability for the overall material, while also achieving resource utilization and reducing costs. Excessive construction waste soil will result in a relatively insufficient composite curing agent, which will not fully react with the soil, making it difficult to increase the material's strength. Excessive construction waste soil may also reduce fluidity, making molding difficult and affecting construction quality. If there is too little construction waste, the material cost will increase, and it will not be able to form a sufficient skeleton structure, the overall strength and stability will be affected, and the material may become too soft and unable to meet the requirements of use. In some embodiments, the composite curing agent can chemically react with the components in the construction waste to improve the strength and durability of the material. The mass proportion of the composite curing agent is 2 parts, which can ensure that there is enough curing agent to fully react with the waste so that the material performance meets the requirements. If there is too much composite curing agent, the reaction will be too violent, and excessive internal stress will be generated inside the material, which will easily cause problems such as cracking; at the same time, the material cost will increase, and the excess curing agent will not be able to play a role, resulting in waste. If there is too little composite curing agent, it will not be able to fully react with the construction waste, and the strength and durability of the material will not meet the design requirements.

[0031] In some embodiments, hydrophobic glass microbeads accounting for 1 part by mass can improve the hydrophobicity of superfluid solidified soil while reducing the weight of the material; an appropriate amount of hydrophobic glass microbeads can exert its unique physical properties without affecting the strength of the material. If there are too many hydrophobic glass microbeads, the strength of the superfluid soil will be reduced and the stability of the particle suspension will decrease; if there are too few hydrophobic glass microbeads, the hydrophobicity will not be effectively improved and the fluidity of the superfluid soil will decrease. In some embodiments, the mass proportion of water is 4 parts, and its main function is to participate in the curing reaction and adjust the working properties of the material, such as fluidity. The right amount of water can ensure that the curing reaction proceeds fully, so that the material has good formability and density. If the water content is too much, the material will be too fluid and difficult to solidify and form, and the evaporation of water during the curing process may form pores inside the material, reducing the strength and density of the material. If the water content is too little, the curing reaction cannot proceed fully, the material strength cannot reach the expected level, and it is easy to cause a decrease in fluidity.

[0032] In some embodiments, the composite curing agent comprises the following raw materials: fly ash (providing a silico-alumina active ingredient), Portland cement (used to alkali-activate the gelling activity of the fly ash), core-shell magnesium oxide (expansive agent), and calcium stearate (hydrophobic agent), in a mass ratio of 150:38-42:4-6:2-4, with a preferred mass ratio of 150:40:5:3. In some embodiments, the fly ash particles are spherical, creating a rolling effect that reduces friction and resistance between particles during slurry flow, thereby improving fluidity. The core-shell structure delays the expansion of the magnesium oxide expansive agent, compensating for cracking caused by volume shrinkage during the curing stage of the superfluid soil. Calcium stearate, with its long-chain alkyl structure, aligns itself on the surface of soil particles, forming a continuous hydrophobic film that separates the soil particles from external water and enhances the fluidity of the superfluid soil.

[0033] In some embodiments, a core-shell MgO expander is prepared by pretreating light-calcined MgO in a magnesium phosphate solution (concentration: 0.5-1.5 mol / L) for 6-8 hours using an impregnation method to form a dense passivation layer 200-300 nm thick. The layer is then coated with a nano-SiO2 layer 50-80 nm thick and with a porosity of less than 5% using fluidized bed vapor deposition (deposition time is generally between 4-8 hours; deposition temperature is typically between 300-500°C; pressure is between 0.6-1 kPa; and gas flow rate is between 50-150 standard cubic centimeters per minute (sccm)). The core-shell structure of the MgO expander has a step-by-step expansion mechanism that can gradually offset shrinkage and cracking caused by water loss during the curing stage of superfluid soil.

[0034] In some embodiments, the nano-SiO2 layer formed by vapor deposition has an amorphous structure, microcracks exist on the surface, and the crack density is 10 6 / m 2 In an alkaline environment with a pH exceeding 12, the nano-SiO2 layer hydrolyzes, and the MgO contained within it hydrates to form Mg(OH)2 precipitation, causing the volume to expand (first-order expansion). The first-order expansion occurs during the initial setting stage of the superfluid soil (within 3-6 hours):

[0035]

[0036] MgO+H2O→MgO(OH)2

[0037] In some embodiments, the passivation layer is amorphous magnesium phosphate (molecular formula Mg3(PO4)2·xH2O). When the pH value of the superfluid soil slurry rises to 12 or above due to cement hydration, step-by-step dissolution occurs. The step-by-step dissolution process is as follows: the passivation layer and OH - The reaction generates soluble phosphate, PO4 3- With Ca in the slurry 2+Combined with the formation of hydroxyapatite precipitation, causing volume expansion (secondary expansion); secondary expansion occurs within 6-48 hours after the initial setting stage of superfluid soil:

[0038]

[0039]

[0040] In some embodiments, the hydrophobic glass microspheres are spherical, mainly composed of SiO2, and have a particle density of 2.35-2.75 g / cm 3 , compressive strength 115-125MPa, median particle size (d 50 ) is 30±5 μm. In some embodiments, the hydrophobic glass microspheres are prepared by ball milling, specifically: glass microspheres, calcium stearate, and high-density alumina balls are added to a ball mill for mechanical dry grinding for 5-8 hours; the high-density alumina balls have a diameter of 3 mm and are used as ball milling media to reduce mechanical damage to the glass microspheres caused by the dry grinding process; the mass ratio of alumina balls to glass microspheres is 4:1, and the mass ratio of calcium stearate to glass microspheres is 1:20. After grinding, a sieve is used to separate the modified glass microspheres, grinding media, and remaining calcium stearate; the thickness of the hydrophobic layer of the glass microspheres is 50-150 nm, and the water contact angle increases from 0° to 105-152° after modification.

[0041] In some embodiments, the hydrophobic glass microspheres exhibit a rolling ball effect. The excellent hydrophobicity of the calcium stearate modified layer on their surface allows more water in the superfluid soil slurry to be used for curing agent hydration, enhancing the fluidity of the hydration product. This also delays the contact time between some curing agent particles and water, slowing the rate of heat release, preventing premature cracking, and ensuring strength. In some embodiments, the hydrophobic glass microspheres exhibit a viscosity-reducing effect. During the superfluid soil mixing and backfilling stages, the hydrophobic layer allows the glass microspheres to migrate freely within the slurry. The kinetic energy generated prevents the agglomeration of clay particles in the construction waste soil, enhancing the slurry's fluidity.

[0042] In some embodiments, in step S3, a three-stage embedded mixing method is used to mix the raw materials on site to prepare superfluid solidified soil or superfluid soil, specifically including: step S31, first adding construction waste soil (construction waste soil generated by excavation at the construction site) and hydrophobic glass beads into a mixer, and dry mixing them at a speed of 120-150r / min for 3-5min to reduce the possibility of cohesive soil agglomeration and ensure that the hydrophobic glass beads and construction waste soil are fully mixed, laying a good foundation for subsequent wet mixing; step S32, adding water to the dry mixture of construction waste soil and hydrophobic glass beads, and wet mixing them at a speed of 80-100r / min for 6-8min to eliminate the cohesive soil agglomeration phenomenon and further improve the uniformity of the mixture; step S33, finally adding a composite curing agent to the wet material, stirring at a speed of 60-80r / min for 2-3min to ensure that the curing agent is evenly dispersed in the mixture, and finally obtaining superfluid soil. In some embodiments, the superfluid soil prepared in step S3 may have an initial fluidity of more than 300 mm, a 28-day unconfined compressive strength of more than 6.0 MPa, and a shrinkage rate after curing of no more than 0.3%.

[0043] In some embodiments, in step S4, the superfluid soil is filled upward from the bottom of the area to be backfilled by using variable frequency vibration pumping + embedded sensor grouting pipe + ground penetrating radar; the variable frequency vibration pumping method is: 20-60Hz axial vibration is simultaneously applied under a grouting pressure of 0.5-2.0MPa to assist grouting; the front end of the grouting pipe is equipped with a miniature night vision camera and a miniature electromagnetic wave transmitter, which can observe and detect the filling effect in real time; the ground penetrating radar can emit high-frequency electromagnetic waves to the filling area, and further analyze and verify the internal structure and density of the superfluid solidified soil in the backfill space according to the propagation and reflection of the electromagnetic waves in the soil; the grouting process is non-stratified and non-interrupted, and the filling is completed in one time.

[0044] In some embodiments, in step S5, based on the internal survey of the space and the dry and wet conditions at different depths of the backfill area, an appropriate curing method is selected to cure the superfluid solidified soil. Specifically, (1) for the deep dry backfill area (a medium weathered area with a rock and soil permeability coefficient of less than 1×10 -7 cm / s, the rock mass is dense, impermeable, and the cavity environment is dry), spray curing is used; (2) For deep wet backfill areas (strong to fully weathered areas, rock and soil permeability coefficient> 1×10 -5cm / s, fault zones, fracture zones, etc. are visible, and the infiltration of bedrock fracture water causes the cavity environment to be moist), and the humidity conditions of the underground space itself are used to naturally moisturize and maintain the filled superfluid soil; (3) For the surface exposed areas (the surface exposed areas disclosed in this disclosure refer to the following two areas: disaster areas such as collapse and cracks on the surface due to the existence of underground goaf groups or cave groups; construction areas caused by drilling, excavation, etc. on the surface overlying the goaf groups or cave groups due to grouting needs. The areas outside the surface exposed areas are deep areas), plastic films, geotextiles and other materials are used for covering and maintenance.

[0045] In some embodiments, in step S6, after the superfluidized solidified soil is cured, engineering geological drilling can be performed on the backfill area, and the drilled core can be tested for compressive strength to detect the strength of the superfluidized solidified soil in the backfill space.

[0046] In some embodiments, large, narrow, irregularly shaped spaces include underground caves and mined-out areas. In some embodiments, superfluid soil exhibits self-healing properties when backfilling such large, narrow, irregularly shaped spaces. When the slurry is affected by the structure of the backfill space and its flow is obstructed, it can recover to over 90% of its initial fluidity within 1-2 minutes, ultimately achieving a space backfill rate exceeding 95%.

[0047] Those skilled in the art should understand that the above embodiments are merely exemplary embodiments and that various changes, substitutions, and alterations may be made without departing from the spirit and scope of the present disclosure.

Claims

1. A superfluid soil backfill method for special-shaped narrow spaces, characterized in that: include: Step S1, constructing a three-dimensional cavity model of an irregularly shaped narrow space, wherein the irregularly shaped narrow space includes an underground cave group or an underground goaf group; Step S2, determining the components of the superfluid soil, wherein the superfluid soil is composed of the following components: construction slag, a composite curing agent, hydrophobic glass microspheres, and water, wherein the composite curing agent includes fly ash, Portland cement, a core-shell structured magnesium oxide expansion agent, and calcium stearate, wherein the core-shell structured magnesium oxide expansion agent includes, from the inside to the outside, a magnesium oxide core, a magnesium phosphate passivation layer with a thickness of 200-300 nm, and a nano-silicon dioxide layer with a thickness of 50-80 nm and a porosity of less than 5%; Step S3, mixing the various components of the superfluid soil; Step S4, filling the superfluid soil into the special-shaped narrow space; Step S5: curing and solidifying the filled superfluid soil.

2. The superfluid soil backfilling method for special-shaped narrow spaces according to claim 1, characterized in that: Constructing a 3D cavity model for an irregular and narrow space includes: A six-rotor drone equipped with ground-penetrating radar is used to scan a designated area along a preset route to obtain preliminary information on the underground structure of unusually shaped and narrow spaces and determine the location and extent of suspected cavities. Injecting a tracer containing magnetic nanoparticles into the suspected void and locating the seepage path using a magnetic gradiometer. After being injected into the suspected void, the tracer containing magnetic nanoparticles moves with the seepage liquid. The magnetic gradiometer can measure the change in magnetic field gradient to determine the position and migration path of the tracer, thereby determining the seepage situation inside the void. Based on the location and scope of the suspected cavity and the seepage conditions inside the cavity, these data are fused, analyzed and processed through artificial intelligence algorithms to construct a three-dimensional cavity model.

3. The superfluid soil backfilling method for special-shaped narrow spaces according to claim 1, characterized in that: The mass ratio of the construction debris, the composite curing agent, the hydrophobic glass microbeads and the water is 5:1.5-2.5:0.5-1.5:3.5-4.

5. The particle size of the construction debris does not exceed 5 mm and the moisture content does not exceed 20%.

4. The superfluid soil backfilling method for special-shaped narrow spaces according to claim 1, characterized in that: The mass ratio of the fly ash, the Portland cement, the core-shell magnesium oxide expansion agent and the calcium stearate is 150:38-42:4-6:2-4, and the fly ash particles are spherical.

5. The superfluid soil backfilling method for special-shaped narrow spaces according to claim 1, characterized in that: The nano-silicon dioxide layer has an amorphous structure and cracks on the surface, with a crack density of 10 6 / m 2 In an alkaline environment with a pH exceeding 12, the nano-silica layer hydrolyzes, and the internally encapsulated MgO hydrates to form Mg(OH)2 precipitates, causing a primary expansion in volume. The primary expansion occurs within 3-6 hours of the curing stage of the superfluid soil. The magnesium phosphate passivation layer is amorphous magnesium phosphate. When the pH value of the superfluid soil slurry rises to above 12 due to cement hydration, step-by-step dissolution occurs. The step-by-step dissolution process is as follows: the magnesium phosphate passivation layer and OH - The reaction generates soluble phosphate radicals, which combine with calcium ions in the slurry to generate hydroxyapatite precipitation, causing a secondary expansion in volume. The secondary expansion occurs within 6-48 hours of the solidification stage of the superfluid soil.

6. The superfluid soil backfilling method for special-shaped narrow spaces according to claim 1, characterized in that: The hydrophobic glass microspheres are spherical and have a particle density of 2.35-2.75 g / cm 3 , compressive strength of 115-125MPa, and a median particle size of 30±5μm; the hydrophobic glass microbeads are prepared by the following steps: adding glass microbeads, calcium stearate and alumina balls to a ball mill for mechanical dry grinding for 5-8 hours; the diameter of the alumina balls is 3mm, which serves as ball milling media to reduce mechanical damage to the glass microbeads caused by the dry grinding process; the mass ratio of the alumina balls to the glass microbeads is 4:1, and the mass ratio of calcium stearate to the glass microbeads is 1:

20. After grinding, a sieve is used to separate the modified hydrophobic glass microbeads, grinding media and remaining calcium stearate; the thickness of the hydrophobic layer of the hydrophobic glass microbeads is 50-150nm.

7. The superfluid soil backfilling method for special-shaped narrow spaces according to claim 1, characterized in that: Mixing the various components of the superfluid soil includes: First, add the construction waste soil and hydrophobic glass beads into the mixer and dry mix them at a speed of 120-150r / min for 3-5 minutes to ensure that the hydrophobic glass beads and the construction waste soil are fully mixed; Secondly, add water to the dry mixture of construction waste soil and hydrophobic glass beads, and wet mix at a speed of 80-100 r / min for 6-8 minutes to improve the uniformity of the mixture; Finally, add the composite curing agent to the wet material and stir at a speed of 60-80r / min for 2-3 minutes to ensure that the composite curing agent is evenly dispersed in the mixture to obtain superfluid soil.

8. The superfluid soil backfilling method for special-shaped narrow spaces according to claim 1, characterized in that: Filling the superfluid soil into the special-shaped narrow space includes: The superfluid soil is filled from the bottom of the filling area upwards: 20-60Hz axial vibration is applied simultaneously at a grouting pressure of 0.5-2.0MPa to assist grouting; the front end of the grouting pipe is equipped with a night vision camera and an electromagnetic wave transmitter to observe and detect the filling effect in real time; high-frequency electromagnetic waves are emitted to the filling area through ground-penetrating radar, and the internal structure and density of the superfluid soil in the filling space are analyzed and verified based on the propagation and reflection of the electromagnetic waves in the soil; the grouting process is non-stratified and uninterrupted, and the filling is completed in one go.

9. The superfluid soil backfilling method for special-shaped narrow spaces according to claim 1, characterized in that: Curing and solidifying the filled superfluid soil includes: For deep dry filling areas, spray curing is used; For deep moist filling areas, the humidity conditions of the underground space itself are used to naturally maintain the moisture retention of the superfluid soil filled; For exposed surface areas, use plastic film or geotextile for covering and maintenance.

Images