Super-fluid soil backfilling method for special-shaped narrow space

Abstract

The invention provides a superfluid soil backfilling method for a special-shaped narrow space, which comprises the following steps: step S1, constructing a three-dimensional cavity model of the special-shaped narrow space, the special-shaped narrow space comprising an underground karst cave group or an underground goaf group; s2, components of the superfluid soil are determined, the superfluid soil is composed of engineering residue soil, a composite curing agent, hydrophobic glass beads and water, and the composite curing agent comprises fly ash, Portland cement, a magnesium oxide expanding agent of a core-shell structure and calcium stearate; s3, all the components of the superfluid soil are mixed; s4, the special-shaped narrow space is filled with superfluid soil; and S5, the filled superfluid soil is maintained and solidified. The superfluid soil adopted by the invention shows a self-repairing characteristic when backfilling a narrow special-shaped space, and after the flow of the slurry is blocked due to the influence of a backfilling space structure, the slurry can recover to the initial fluidity of 90% or above within 1-2 minutes, and the final space backfilling rate can reach 95% or above.

Description

Technical Field

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

[0002] With the continuous acceleration of urbanization, the development of underground space has achieved unprecedented development. The construction of infrastructure such as foundations, underground transportation pipelines, underground shopping malls and underground pipelines is becoming more and more extensive, providing important support for urban development. However, in the backfilling process of narrow spaces such as foundation pit fertilizer troughs and underground integrated pipeline corridors, due to space limitations, large and medium-sized compaction machinery cannot enter the site for operation, and construction workers can only rely on manual compaction. This inefficient method not only leads to insufficient density of backfill soil, but may also cause serious engineering accidents such as ground subsidence and landslides, posing safety hazards to urban construction and citizens' lives.

[0003] As a new type of green building material, superfluid soil or fluidized solidified soil has attracted much attention due to its environmental friendliness and practicality. It usually uses on-site engineering slag as the base material, cement, fly ash, slag, etc. as the cementing material. It can be self-leveling and self-compacting during pouring, and after curing, it forms a solidified body with certain strength, low permeability and long-term stability. Therefore, it is used in narrow space backfill projects in engineering construction, which not only saves time and cost, but also improves construction efficiency.

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

[0005] (1) The existing fluidized solidified soil has certain limitations in terms of flow performance. 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, which in turn causes premature solidification. This not only limits the further filling capacity of the slurry, but also significantly reduces the spatial 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 soil. 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 soil in large-scale irregular and narrow space backfill projects, because these scenarios not only require a high backfill rate, but also place higher requirements on the structural strength after solidification;

[0007] (3) During the solidification process, fluidized solidified soil loses water, resulting in volume shrinkage and prone to cracking. In conventional spaces or small-volume backfill projects, this problem can be alleviated to a certain extent through post-maintenance and other means. However, in backfill projects of large-scale, irregular and narrow spaces, shrinkage cracks are not only more likely to form but also have a wider impact range due to structural complexity and construction conditions, which 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 superfluid soil in an irregularly shaped narrow space, comprising: step S1, constructing a three-dimensional cavity model of the irregularly shaped narrow space, wherein the irregularly shaped 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 magnesium oxide expansion agent with a core-shell structure and calcium stearate; step S3, mixing the various components of the superfluid soil; step S4, filling the superfluid soil into the irregularly shaped narrow space; and step S5, curing and curing the filled superfluid soil.

[0010] In some embodiments, constructing a three-dimensional void 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, obtaining preliminary information on the underground structure of the irregular and narrow space, and determining the location and range of the suspected void; injecting a tracer containing magnetic nanoparticles into the suspected void, and locating the seepage path through a magnetic gradiometer, wherein after the tracer containing magnetic nanoparticles is injected into the suspected void, it will move with the seepage liquid, and the magnetic gradiometer can measure the change in magnetic field gradient, thereby determining the location and migration path of the tracer, so as to determine the seepage conditions inside the void; based on the location and range of the suspected void and the seepage conditions inside the void, these data are fused, analyzed and processed through an artificial intelligence algorithm to construct a three-dimensional void model.

[0011] In some embodiments, the mass ratio of the construction waste soil, the composite curing agent, the hydrophobic glass microspheres 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 silicate 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 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%.

[0014] In some embodiments, the nano-silicon dioxide layer has an amorphous structure, and cracks exist on the surface, with a crack density of 10 6 / m 2 ; In an alkaline environment with a pH value exceeding 12, the nano-silicon dioxide layer is hydrolyzed, and the MgO contained inside is hydrated to generate Mg(OH)2 precipitation, causing the volume to expand in a first order, and the first order expansion occurs within 3-6 hours of the solidification stage of the superfluid soil; the magnesium phosphate passivation layer is amorphous magnesium phosphate, and 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 secondary expansion of the 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, median particle size of 30±5μm; the hydrophobic glass microspheres are prepared by the following steps: adding glass microspheres, calcium stearate and alumina balls into a ball mill for mechanical dry grinding for 5-8 hours; the diameter of the alumina balls is 3mm, which are used as ball milling media to reduce the mechanical damage to the glass microspheres caused by the dry grinding process; the mass ratio of the alumina balls to the glass microspheres is 4:1, and the mass ratio of calcium stearate to the glass microspheres is 1:20. After grinding, a sieve is used to separate the modified hydrophobic glass microspheres, grinding media and remaining calcium stearate; the thickness of the hydrophobic layer of the hydrophobic glass microspheres is 50-150nm.

[0016] In some embodiments, mixing the various components of the superfluid soil includes: first, adding the construction waste soil and the hydrophobic glass beads into a mixer, and dry mixing 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, adding water to the dry mixture of the construction waste soil and the hydrophobic glass beads, and wet mixing them at a speed of 80-100r / 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 60-80r / 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 narrow space includes: filling the superfluid soil from the bottom of the filling area upward: synchronously applying 20-60Hz axial vibration 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 by 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 time.

[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 perform natural moisturizing curing on 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 the 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 make more water in the superfluid soil slurry used for curing agent hydration, thereby enhancing the fluidity of the hydration product and delaying the contact time between some curing agent particles and water, thereby slowing down the heat release rate, preventing early cracking, and ensuring strength. In addition, the hydrophobic glass microspheres have a viscosity-reducing effect. During the superfluid soil mixing stage and the backfilling 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 slag 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 a special-shaped narrow space 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 do not limit the present disclosure in any way.

[0023] Unless otherwise specified, the materials, reagents, etc. used in the following embodiments can be obtained from commercial sources. In this disclosure, construction waste refers to construction waste generated in civil engineering activities such as construction, roads, subways, tunnels, water conservancy, etc., and its main component is soil, with the following characteristics: 1) The source is human activities in civil engineering, specifically covering the construction, repair, and demolition of buildings and structures such as buildings, roads, tracks, tunnels, pipelines, bridges, ports, canals, and dredging of rivers and waterways; 2) The main component is 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 superfluid soil backfilling method for special-shaped narrow spaces disclosed in the present invention includes: step S1, intelligent investigation and modeling of the backfilling area; step S2, design of the superfluid soil mix ratio for backfilling; step S3, mixing of raw materials of the superfluid soil; step S4, filling of the superfluid soil; step S5, curing and solidification; step S6, quality inspection.

[0025] In some embodiments, in step S1, a three-source fusion exploration modeling technology of unmanned aerial vehicle, ground penetrating radar and nano-tracer is used to determine the three-dimensional space and volume of the backfill area, specifically including: step S11, unmanned aerial vehicle equipped with ground penetrating radar to scan the area: first, a six-rotor unmanned aerial vehicle 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 locate the seepage path: inject into the suspected cavity (first drill a grouting hole on the ground, and then insert A grouting pipe is used to inject the slurry into the cavity) containing a tracer of magnetic nanoparticles (Fe3O4@SiO2) (mass content is 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 / emission wavelength of 450nm, which facilitates a more intuitive observation of the distribution of the tracer and makes the tracer fluoresce under light of a specific wavelength), and 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 magnetic field gradient with high precision, so as to determine the position and migration path of the tracer, and help 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: Combine BIM and geological radar data to automatically generate a high-precision three-dimensional cavity model 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 multi-source heterogeneous data obtained by various survey methods are processed by the super-resolution convolutional neural network (SRCNN) algorithm, and data fusion and optimization are performed to improve the accuracy of low-resolution data, or a generative model is used 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, the geological radar data can provide detailed information on the underground structure, and the AI ​​algorithm 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 hole 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, the difficulties in the treatment of the goaf group / cavern group can be clarified, such as the occurrence form of the goaf group / cavern group: independent closed cavity structure, multiple cavity structures that are interconnected, etc. According to the occurrence of the goaf group / cavern group, the grouting method can be optimized to 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 can identify cracks as small as 5 cm.

[0027] Specifically, in some embodiments, efficiency improvement can be achieved through the following aspects: 1) UAV rapid positioning and large-scale detection: UAVs have fast maneuverability and flexible flight capabilities, can quickly reach the target area for large-scale preliminary surveys, quickly obtain macro information such as topography, determine areas where abnormalities may exist, and provide accurate 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 of 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 time, greatly improving the detection efficiency; 3) Precise indication of nanotracers: Nanotracers have unique physical and chemical properties, can migrate quickly and accurately in underground environments, and can quickly identify their location 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 radars, 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 aspects: 1) Reducing drilling workload: The traditional "geophysical exploration + drilling mutual verification method" requires a lot of drilling work to obtain underground geological information, and the rental, transportation, operation of drilling equipment and consumables during drilling all require a lot of cost investment; while the "drone + ground penetrating radar + nano-tracer three-source fusion modeling method" can accurately determine the location and scale of underground goaf groups / karst cave groups through the early large-scale detection of drones and ground penetrating radars and the precise positioning of nano-tracers, greatly reducing the drilling workload and the number of holes, thereby reducing drilling costs; 2) Improving equipment utilization: drones, ground penetrating radars and other equipment can be quickly transferred and reused in different projects and regions, and the idle time of the equipment is relatively short, which improves the utilization of the equipment and reduces the unit cost; 3) Reducing labor costs: Due to the reduction of drilling workload and the complexity of on-site operations, the number of manpower and working time required are also reduced accordingly, thereby reducing labor costs. At the same time, data fusion modeling and other work can be carried out indoors through computer software and professional technicians, reducing the manpower investment in field operations.

[0029] In some embodiments, the following aspects are used to achieve the recognition of 5 cm cracks: 1) High resolution of ground penetrating radar: Modern ground penetrating radar technology is constantly developing, and the performance of its transmitting and receiving antennas is constantly improving, which can transmit and receive 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 have strong permeability and diffusivity. They 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 complementarity and enhancement: The topographic data obtained by the drone can provide macro-environmental information on possible 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, characterize the underground geological conditions from different angles and scales, and make it possible to accurately identify and locate 5 cm cracks that were difficult to identify with a single method.

[0030] In some embodiments, in step S2, the raw materials of superfluid soil are composed of the following parts: engineering slag, composite curing agent, hydrophobic glass microbeads, and water. In some embodiments, engineering slag 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 engineering slag, composite curing agent, hydrophobic glass microbeads and water is 5:1.5-2.5:0.5-1.5:3.5-4.5. In some embodiments, the optimal mass ratio of engineering slag, composite curing agent, hydrophobic glass microbeads and water is 5:2:1:4. In some embodiments, engineering slag is used as the main raw material, with a mass ratio of 5 parts, and its amount must be guaranteed to form a certain skeleton structure, provide basic strength and stability for the overall material, and realize resource utilization and reduce costs. If there is too much engineering slag, the composite curing agent will be relatively insufficient, unable to fully react with the slag, and the material strength will be difficult to improve; too much slag may also deteriorate fluidity, make molding difficult, and affect construction quality. If there is too little construction slag, 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 use requirements. In some embodiments, the composite curing agent can chemically react with the components in the construction slag 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 slag 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 slag, and the strength and durability of the material will not meet the design requirements.

[0031] In some embodiments, a hydrophobic glass microsphere with a mass ratio of 1 part can improve the hydrophobicity of the superfluid solidified soil and reduce the weight of the material; an appropriate amount of hydrophobic glass microspheres can exert its unique physical properties without affecting the strength of the material. If there are too many hydrophobic glass microspheres, 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 microspheres, the hydrophobicity will not be effectively improved, and the fluidity of the superfluid soil will be reduced. In some embodiments, the mass ratio of water is 4 parts, and its main function is to participate in the curing reaction and adjust the working performance of the material, such as fluidity. The right amount of water can ensure that the curing reaction is fully carried out, so that the material has good formability and compactness. If the water content is too much, the material fluidity will be too large, and it will be difficult to solidify and form, and the evaporation of water during the curing process may form pores inside the material, reducing the strength and compactness of the material. If the water content is too little, the curing reaction cannot be fully carried out, 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 includes the following raw materials: fly ash (providing silica-alumina active ingredients), silicate cement (used for alkali-activated fly ash gelling activity), core-shell structured magnesium oxide (expansion agent), calcium stearate (hydrophobic agent), with a mass ratio of 150:38-42:4-6:2-4, and preferably 150:40:5:3. In some embodiments, the fly ash particles are spherical and have a ball effect, which can reduce the friction and resistance between particles when the slurry flows and improve the fluidity; the core-shell structure can delay the expansion of the magnesium oxide expansion agent and compensate for the cracking caused by volume shrinkage during the curing stage of superfluid soil; calcium stearate has a long-chain alkyl structure, which will be arranged in a directional manner on the surface of soil particles to form a continuous hydrophobic film, which separates the soil particles from external water and improves the fluidity of superfluid soil.

[0033] In some embodiments, the preparation method of the core-shell structure MgO expansion agent is: pre-treating light-burned MgO in a magnesium phosphate solution (concentration is 0.5-1.5 mol / L) for 6-8 hours by an impregnation method to form a dense passivation layer with a thickness of 200-300 nm, and then coating a nano-SiO2 layer with a thickness of 50-80 nm and a porosity of less than 5% by fluidized bed vapor deposition (the deposition time is generally between 4-8 hours; the deposition temperature is generally between 300-500°C; the pressure is between 0.6-1 kPa; the gas flow rate is between 50-150 standard cubic centimeters per minute (sccm)). The core-shell structure of the MgO expansion agent has a step-by-step expansion mechanism, which can gradually offset the shrinkage and cracking phenomenon 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, and microcracks exist on the surface, with a crack density of 10 6 / m 2 In an alkaline environment with a pH value of more than 12, the nano-SiO2 layer is hydrolyzed, and the MgO contained inside is hydrated to form Mg(OH)2 precipitation, which causes the volume to expand (first-order expansion). The first-order expansion occurs in the initial setting stage of 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), and 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 specifically as follows: the passivation layer and OH - The reaction generates soluble phosphate, PO4 3- Ca in the slurry 2+Combined, hydroxyapatite precipitation is generated, 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±5μm. In some embodiments, the hydrophobic glass microbeads are prepared by ball milling, specifically: glass microbeads, calcium stearate and high-density alumina balls are added to a ball mill for mechanical dry grinding, and the dry grinding time is 5-8 hours; the diameter of the high-density alumina balls is 3mm, which is used as a ball milling medium to reduce the mechanical damage to the glass microbeads caused by the dry grinding process; the mass ratio of alumina balls to glass microbeads is 4:1, and the mass ratio of calcium stearate to glass microbeads is 1:20. After grinding, a sieve is used to separate the modified glass microbeads, grinding media and remaining calcium stearate; the thickness of the hydrophobic layer of the glass microbeads is 50-150nm, and the water contact angle increases from 0° to 105-152° after modification.

[0041] In some embodiments, the hydrophobic glass microspheres have a rolling ball effect, and the good hydrophobicity of the calcium stearate modified layer on its surface can make more water in the superfluid soil slurry be used for curing agent hydration, enhance the fluidity of the hydration product, and at the same time delay the contact time between some curing agent particles and water, slow down the heat release rate, prevent early cracking, and ensure strength. In some embodiments, the hydrophobic glass microspheres have a viscosity reduction effect. During the superfluid soil mixing stage and the backfill stage, the hydrophobic layer allows the glass microspheres to migrate freely in the slurry, and the kinetic energy generated can prevent the clay particles in the engineering slag from agglomerating, thereby enhancing the fluidity of the slurry.

[0042] In some embodiments, in step S3, three-stage embedded mixing 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 for 3-5 minutes at a speed of 120-150r / min to reduce the possibility of cohesive soil agglomeration and ensure that the hydrophobic glass beads and construction waste soil are fully mixed, thereby 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 for 6-8 minutes at a speed of 80-100r / min 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 2-3 minutes 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 28d unconfined compressive strength of more than 6.0 MPa, and a shrinkage rate of no more than 0.3% after curing.

[0043] In some embodiments, in step S4, the superfluid soil is filled upward from the bottom of the area to be backfilled by 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 0.5-2.0MPa grouting pressure 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 dryness and moisture 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, fissure zones, etc. are visible, and the penetration of bedrock fissure water causes the cavity environment to be humid), 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 and other work on the overlying surface of 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 film coverage and maintenance.

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

[0046] In some embodiments, the large-scale narrow irregular spaces include underground caves, underground goafs, etc. In some embodiments, the superfluid soil exhibits self-repairing properties when backfilling the above-mentioned large-scale narrow irregular spaces. When the slurry is affected by the structure of the backfill space and the flow is blocked, it can recover to more than 90% of the initial fluidity in 1-2 minutes, and the final space backfill rate can reach more than 95%.

[0047] Those skilled in the art will appreciate 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 backfilling method for special-shaped narrow spaces, characterized in that: include: Step S1, constructing a three-dimensional cavity model of an irregular narrow space, wherein the irregular 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, and the composite curing agent includes fly ash, silicate cement, a core-shell structured magnesium oxide expansion agent and calcium stearate; 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 is characterized in that: The construction of a 3D cavity model for an irregular and narrow space includes: A six-rotor drone equipped with ground-penetrating radar is used to scan the designated area along a preset route to obtain preliminary information on the underground structure of the special-shaped narrow space and determine the location and scope of the suspected cavity; Injecting a tracer containing magnetic nanoparticles into the suspected void and locating the seepage path by using a magnetic gradiometer, wherein the tracer containing magnetic nanoparticles will move with the seepage liquid after being injected into the suspected void, and the magnetic gradiometer can measure the change in magnetic field gradient, thereby determining the position and migration path of the tracer, and determining the seepage situation inside the void; Based on the location and range 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 method for backfilling superfluid soil in special-shaped narrow spaces according to claim 1, characterized in that: The mass ratio of the construction waste soil, the composite curing agent, the hydrophobic glass microspheres 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%.

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

5. The method for backfilling superfluid soil in special-shaped narrow spaces according to claim 1, characterized in that: The core-shell structured magnesium oxide expansion agent comprises 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%.

6. The method for backfilling superfluid soil in special-shaped narrow spaces according to claim 5, 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 value exceeding 12, the nano-silicon dioxide layer is hydrolyzed, and the MgO contained inside is hydrated to form Mg(OH)2 precipitation, causing the volume to expand in the first order. The first order 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 secondary expansion of the volume. The secondary expansion occurs within 6-48 hours of the solidification stage of the superfluid soil.

7. The method for backfilling a special-shaped narrow space with superfluid soil 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, median particle size of 30±5μm; the hydrophobic glass microspheres are prepared by the following steps: adding glass microspheres, calcium stearate and alumina balls into a ball mill for mechanical dry grinding for 5-8 hours; the diameter of the alumina balls is 3mm, which are used as ball milling media to reduce the mechanical damage to the glass microspheres caused by the dry grinding process; the mass ratio of the alumina balls to the glass microspheres is 4:1, and the mass ratio of calcium stearate to the glass microspheres is 1:

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

8. The method for backfilling superfluid soil in 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 microbeads into the mixer and dry mix them at a speed of 120-150r / min for 3-5 minutes to ensure that the hydrophobic glass microbeads and the construction waste soil are fully mixed; Secondly, water is added to the dry mixture of construction waste soil and hydrophobic glass beads, and wet mixing is performed at a speed of 80-100r / min for 6-8min 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.

9. The method for backfilling superfluid soil in special-shaped narrow spaces according to claim 1, characterized in that: Filling the superfluid soil into the special-shaped narrow space comprises: Fill the superfluid soil from the bottom of the filling area upwards: apply 20-60Hz axial vibration 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 non-interrupted, and the filling is completed in one go.

10. The method for backfilling a special-shaped narrow space with superfluid soil according to claim 1, characterized in that: The method of curing and solidifying the filled superfluid soil comprises: For deep dry filling areas, spray curing is used; For deep wet filling areas, the humidity conditions of the underground space itself are used to naturally moisturize and maintain the superfluid soil in the filling area; For exposed surface areas, use plastic film or geotextile for covering and maintenance.

Images