Method for simulating the control effect of grouting reinforcement on residual deformation of old goaf

Abstract

The application discloses a method for simulating the control effect of grouting reinforcement on residual deformation of an old goaf, which comprises the following steps: step (1), preparing equipment; step (2), installing a protective plate; step (3), mixing and stirring; step (4), molding; step (5), curing; step (6), model painting, monitoring point and speckle production; step (7), excavation and deformation observation; step (8), grouting; step (9), slurry consolidation; step (10), simulating residual deformation of the goaf; and step (11), water injection. The method has reliable performance, needs less testing materials, avoids the manpower and material resources required by field tests, is good in economy, and can efficiently, conveniently and intuitively study the influence of grouting reinforcement on deformation of the old goaf, thereby providing guidance for production and work such as goaf treatment.

Description

Technical Field

[0001] This invention relates to the field of goaf grouting treatment technology, specifically a method for simulating the control effect of grouting reinforcement on residual deformation in old goaf areas. By using similarity physical tests to simulate the control or influence of grouting reinforcement on residual deformation in "residual goaf areas", this method guides the design of the optimal range for goaf grouting treatment, providing an effective technical means for goaf grouting treatment and improving treatment effectiveness and economy. Background Technology

[0002] Coal has always been a major source of primary energy production and consumption in China, supporting approximately 9.5% of GDP growth. While providing a reliable energy guarantee for national economic and social development, coal has also created a large number of mined-out areas. In 2008, the area of ​​mined-out areas nationwide due to mining activities exceeded 809,600 hectares. Since engineering construction often cannot avoid mined-out areas, systematic remediation is necessary. However, current research mainly focuses on the failure patterns during the main deformation stages of mined-out areas, with insufficient understanding of the residual deformation of "residual mined-out areas" surrounding grouting reinforcement zones, or the supporting and deformation control role of grouting reinforcement zones on the overlying strata of mined-out areas.

[0003] Similarity material simulation is an experimental method that uses a scaled-down or enlarged model to simulate and study the motion and mechanical characteristics of the prototype. Similarity physical experiments can clearly observe the deformation patterns of the overlying strata in mining subsidence areas. Generally, the main deformation stage of the goaf in longwall mining occurs within three years of mining, accounting for 90-95% of the total deformation; the patterns of this stage have been extensively studied. However, after three years, old goaf areas will still experience 5-10% residual deformation; the patterns of this stage are still lacking in research, but it directly affects the safety of structures above the goaf.

[0004] Traditional similarity physical tests mainly study the deformation and failure patterns of rock strata and the surface within the original goaf area. There is limited research on the residual deformation of "residual goaf areas" formed after grouting reinforcement of some goaf areas. However, studies on the residual deformation of these "residual goaf areas" or the supporting and deformation control effects of grouting reinforcement on the overlying rock strata can provide more precise guidance on the treatment scope of goaf areas under buildings. This invention mainly analyzes the residual deformation of old goaf areas and provides treatment schemes for goaf areas, especially old goaf areas, allowing for direct observation and study of the impact of grouting reinforcement on the residual deformation of goaf areas. Summary of the Invention

[0005] The purpose of this invention is to provide a method for simulating the control effect of grouting reinforcement on residual deformation in old goaf areas. This method is used to simulate and study the residual deformation, overlying rock deformation and failure patterns of "residual goaf areas" after grouting reinforcement in some goaf areas, and to provide a theoretical basis for goaf area management.

[0006] This invention is achieved using the following technical solution: A method for simulating the effect of grouting reinforcement on controlling residual deformation in old goaf areas includes the following steps: (1) Equipment preparation: including model frame as test bench, marked side guards, transparent baffles on both sides, steel plate for compaction, steel plate and roller for leveling, mixer, electronic scale, measuring cylinder, acrylic small plate to simulate residual deformation, grouting bucket, grouting pump, grouting pipe and water injection pipe.

[0007] (2) Install protective plates: After cleaning and painting the model frame and the protective plates on both sides, draw the stratum lines and apply lubricating oil to the inside of the protective plates to prevent them from sticking to similar materials. Install protective plates on the front and back sides of the model frame to form a simulation space between the model frame and the protective plates on both sides for making the model.

[0008] (3) Ingredients and mixing: The model to be made consists of six types of strata, from bottom to top: mudstone layer, coal seam, sandy mudstone layer, mudstone layer, conglomerate layer, and topsoil layer; According to the requirements of each type, weigh out the sand, gypsum, and calcium carbonate needed for that layer, measure out an appropriate amount of water, mix the required materials with water and stir evenly, and use mica to simulate the layer.

[0009] (4) Model making: The model is made from bottom to top. The mixed material is poured into the simulation space and spread out. The material is leveled with a steel plate and compacted with a roller. Mica powder is sprinkled every 2cm to simulate the layer. A water-proof layer is made under the coal seam using sand, paraffin wax and hydraulic oil. Its function is to fit more tightly with the front and rear baffles to prevent the slurry from spreading downward. In the simulation space, a hose is buried every 15cm from the right side, for a total of 16 hoses. The four hoses on the right side are used for later grouting and serve as grouting pipes. The twelve hoses on the left side are used for later water injection and serve as water injection pipes. At this time, the model is divided into two parts. The area where the four grouting pipes are located is called the simulated deformation area, i.e. the treatment area. The area where the twelve water injection pipes are located is called the induced deformation area, i.e. the untreated area.

[0010] (5) Curing: After laying the six types of strata in the simulation space in sequence, cure for 14 days to allow the model to dry and solidify.

[0011] (6) Model painting and monitoring point and speckle production: After the model dries, brush a layer of white light calcium carbonate on the model surface to produce a white background; wait 3 days for the white calcium carbonate to solidify before drawing monitoring lines, installing reflectors and drawing speckles; the monitoring lines are drawn using an ink line, the reflectors are made by creating a guide grid with cotton thread and then inserting pins into the model, and when drawing speckles, first use a hole punch to randomly punch holes in the plastic card and then use spray paint to spray them.

[0012] (7) Excavation and Deformation Observation: Leave 10cm coal pillars on both sides of the simulated coal seam in the model, and excavate the rest; the excavation length is 10cm at a time, and excavate once per hour. After the excavation is completed at the excavation location, immediately insert two layers of acrylic small plates to simulate residual deformation and observe the formation process of the three zones; after the excavation is completed and the deformation is stable, start the next step of the work. The stability condition is that the deformation is not obvious (<1mm) or the maximum subsidence coefficient of the central basin is 1.

[0013] (8) Grouting: After the deformation stabilizes, use baffles to seal the front and back sides of the model to prevent the grout from spreading; grout along the four reserved grouting pipes in the treatment area, and raise the grouting pipes above the obvious deformation position before grouting.

[0014] Grouting pipes are used to inject grout into goaf areas formed by similar materials. The grout spreads widely, effectively simulating the residual deformation characteristics of the goaf. The front and rear baffles are transparent polycarbonate plates, allowing for direct observation of the grout diffusion pattern and the solidification process of the rock mass during grouting. Steel beams can be fixed to the outside of the front and rear baffles, closely fitting the similar material to control the grout diffusion within the goaf.

[0015] (9) Slurry consolidation: After the cement slurry has solidified, observe the morphology and distribution pattern of the cement slurry.

[0016] (10) Simulated residual deformation in the goaf: baffles were installed above the acrylic panels simulating residual deformation to prevent the loose material in the collapse zone from sliding due to panel removal; in the untreated area, a layer of acrylic panels was removed at once to activate residual deformation. Digital speckle was used to capture the relative displacement across the entire field, and a total station was used for accuracy correction. By comprehensively analyzing the relative displacement data of the entire field and the displacement data of individual points, the influence of residual deformation in the untreated area on the treated area was better observed; the results showed that due to the presence of grout, the deformation within the grouting range of the treated area was small, while the untreated area bore the main deformation, indicating that the grout can effectively reduce the overburden deformation in the treated area.

[0017] (11) Water injection: In order to observe the deformation difference between the treated area and the untreated area, baffles were used to seal the front and back sides of the model, and water was injected into the untreated area using pre-embedded water injection pipes; gypsum was used as a cementing material in the similar material. Since its strength is significantly reduced in the wet and saturated state, water injection made the model reach the limit deformation state, which is beneficial to the analysis of the effect of grouting reinforcement on deformation; after injecting a large amount of water into the similar material, significant deformation occurred in the difficult-to-close delamination, pores and coal pillar support area; by comparing the deformation difference between the treated area and the untreated area, it is shown that the grouting body played an effective reinforcement role in the treated area, making the deformation in the treated area smaller; at the same time, the larger the amount of grout injected, the smaller the deformation, while the smaller the amount of grout injected, the slower the deformation.

[0018] In specific implementation, in step (4), the model from bottom to top is as follows: mudstone layer thickness 29cm, coal seam thickness 3cm, sand and mudstone layer thickness 37.4cm, mudstone layer thickness 20.4cm, conglomerate layer thickness 16.7cm, topsoil layer thickness 62.5cm.

[0019] In order to observe the stress variation pattern of the strata in the mining area, stress detection boxes were buried in the sandstone-mudstone layer, the mudstone layer (located above the sandstone-mudstone layer), and the topsoil layer. Seven stress detection boxes were arranged in each layer, for a total of 21 boxes in three layers.

[0020] To observe the displacement of the overlying rock strata, displacement observation points were set in the rock strata on the model surface at distances of 38.2 cm, 48.2 cm, 54.2 cm, 64.2 cm, 69.6 cm, 79.6 cm, 90 cm, 99 cm, 106.7 cm, 122 cm, 137.7 cm, and 147.7 cm from the bottom. Each monitoring line was spaced 10 cm apart and 5 cm from the boundary, for a total of 12 lines.

[0021] The method for controlling residual deformation in old goaf areas using simulated grouting reinforcement described in this invention is based on the principle of "equivalent mining thickness" in simulating the activation process. After excavation, a residual deformation induction plate of a certain thickness is rapidly inserted to simulate the residual deformation of the goaf. Considering the softening effect of groundwater on loose deposits, sudden and intense water filling of the goaf is often a significant factor inducing the "activation" of old goaf areas. The deformation characteristics of the model are observed by injecting water into the untreated area to soften similar materials. In specific implementation, the experimental similarity ratio and laying schemes for different strata are designed according to the site conditions. The geometric similarity ratio of this invention is 100, the kinematic similarity ratio is 10, the bulk density similarity is 1.5, and the stress similarity ratio is 150. Gypsum, calcium carbonate, and sand are used to simulate real strata, including mudstone, coal seams, sandy mudstone, mudstone, and conglomerate. The mix proportions of sand, gypsum, and calcium carbonate for different strata are calculated based on the stress similarity ratio. The experimental destructive process of this invention is intuitive, and it can effectively observe the deformation patterns of the goaf throughout its entire life cycle, including mining deformation, slurry diffusion, grouting reinforcement, and residual deformation. Unlike traditional similarity tests that only focus on the deformation patterns of the overlying rock in the goaf caused by mining, the experimental scheme of this invention can comprehensively simulate a series of complex deformation processes, such as grouting and induced re-deformation in the goaf.

[0022] Compared with the prior art, the technical solution provided by this invention has the following advantages: First, the present invention can perform conventional similarity simulation tests, and the similarity test bench is made of high-strength steel, so that almost no deformation occurs during the test.

[0023] Secondly, the present invention can grout goaf formed by similar materials through grouting pipes, and the grout diffusion range is good, which can better simulate the residual deformation characteristics of goaf.

[0024] Third, the front and rear baffles are made of transparent endurance plates, which allows for direct observation of the diffusion pattern of grout in the goaf and the solidification process of the stone body during the grouting process.

[0025] Fourth, the waterproof layer is made of sand, paraffin wax, and hydraulic oil, which can effectively prevent the slurry from spreading to the sidewalls.

[0026] Fifth, the side guards can be used to fix the front and rear baffles, so that they fit tightly with similar materials and control the spread of slurry.

[0027] Sixth, by inducing deformation in the goaf through "equivalent mining" and water injection softening methods, the deformation patterns of similar materials at each stage can be observed intuitively.

[0028] Seventh, this invention can comprehensively simulate the entire deformation process of goaf formation, grouting, and activation.

[0029] This invention is reasonably designed, has reliable experimental performance, requires few materials for testing, avoids the manpower and material resources required for on-site testing, and is economical. The experimental method can efficiently, conveniently and intuitively study the impact of grouting reinforcement on deformation in old goaf areas, and can provide guidance for production and work such as goaf management, and has great practical application value. Attached Figure Description

[0030] Figure 1 This is a schematic diagram illustrating the method flow of the present invention.

[0031] Figure 2 A schematic diagram showing the structure of a similarity test model.

[0032] Figure 3 This diagram illustrates the preparation process for model deformation monitoring.

[0033] Figure 4 This diagram shows the arrangement of pressure cells within the model.

[0034] Figure 5 This diagram shows the total station displacement detection lines on the model surface.

[0035] Figure 6 This represents the digital speckle plot showing the deformation of the model during mining.

[0036] Figure 7 This represents the deformation diagram of the model under initial pressure.

[0037] Figure 8 This shows a deformation diagram simulating mining to 130cm.

[0038] Figure 9 The total station displacement curve at 130cm is shown in the model.

[0039] Figure 10 This indicates that the model has completed all deformation diagrams.

[0040] Figure 11 This represents the total station displacement curves of the entire model.

[0041] Figure 12 This represents a map showing the three zones.

[0042] Figure 13 This indicates the grouting diffusion process.

[0043] Figure 14 This represents the speckle displacement contour map of the model during its first residual deformation failure.

[0044] Figure 15 The total station displacement curve represents the residual deformation of the model.

[0045] Figure 16 This represents a comparison of the displacement in the Y direction between mining deformation and residual deformation. Detailed Implementation

[0046] The specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0047] For the remediation of highway mining subsidence areas, surface deformation is mainly caused by residual deformation and "reactivation" deformation in unremediated subsidence areas. Current research lacks understanding of the deformation and failure patterns during the residual deformation stage of mining subsidence areas, and also lacks research on the supporting effect of grout filling in the remediation area. Similarity material simulation is an experimental method that uses an enlarged or reduced model to simulate and study the motion and mechanical characteristics of the prototype. Through similarity physical experiments, the displacement and variation patterns of overlying rock in mining subsidence areas can be observed more clearly. The design concept of this invention is to simulate, through similarity experiments, the impact of grouting and rock formations in the caving and fracture zones of mining subsidence areas on the residual deformation of unremediated areas and their protective effect on the grouting overlying areas.

[0048] The purpose of the similarity physical test is to: (1) study the release law of residual deformation in the goaf and observe the influence of grouting stone body on the deformation law; (2) observe the movement of the surface residual deformation basin after deformation occurs in the untreated area; (3) observe the morphology of grouting stone body and analyze its stress condition.

[0049] 1. Prototype of similarity physical experiment The Fenyang-Shilou Expressway is an important section of the "Three Vertical, Twelve Horizontal, and Twelve Ring" network in the "Shanxi Provincial Expressway Network Planning Adjustment Scheme." The section from K9+320 to K11+360 is located in the goaf area of ​​the No. 2 coal seam of the Gaoyang Coal Mine. Mining in this goaf area took place from 2001 to 2007, with the mining area ranging from 37°05′41″ to 37°11′28″ north latitude and 111°35′47″ to 111°42′18″ east longitude. The mining method was longwall mining, with a thickness of 2-4 meters, a recovery rate of 85%, and a mining depth of 120-180 meters. This section of the goaf has caused large-scale ground subsidence, and undulating collapse traces and residual surface deformation are still visible. In this embodiment of the invention, the location for the similarity physical test is selected perpendicular to the highway and passing through the right abutment of the No. 0 bridge of the No. 1 bridge. This location was chosen because of the availability of abundant monitoring data and the relatively shallow coal seam depth, which is beneficial for simulation and research. The main simulation study focused on the impact of the untreated area in the southwest of the research zone on the deformation caused by treatment. Ensuring that the distance from the treatment boundary to the coal face is greater than 128m can guarantee that the deformation in the untreated area will reach the level required for full mining.

[0050] The main mining area in Gaoyang is the No. 2 coal seam. Using one geological survey borehole and three bridge survey boreholes in the study area, and considering the experimental objectives and conditions, the local rock strata were integrated and simplified. The study area consists of, from top to bottom, loess overburden, Upper Tertiary Baode Formation conglomerate, Lower Permian Shihezi Formation mudstone, Lower Permian Shanxi Formation sandstone and mudstone interbedded layers, No. 2 coal seam, and Lower Permian Shanxi Formation mudstone. Rock mechanical parameters and lithology are shown in Table 1 below.

[0051] Table 1 Rock mechanics determination in goaf areas

[0052] 2. Physical similarity simulation experiment design 2.1 Determination of test parameters for the example Based on the research objectives, the maximum dimensions of the model in this embodiment of the invention are 2500mm*300mm*2000mm (length*width*height). The main focus is on studying the process of overlying rock strata collapse and fracture caused by mining, and the effect of grouting reinforcement on controlling residual deformation. The geometric similarity ratio of this model is 100, the kinematic similarity ratio is 10, the unit weight similarity is 1.5, and the stress similarity ratio is 150.

[0053] 2.2 Specific test steps of the embodiments of the present invention In the process of preparing similar material models, the geometric, mechanical, and other parameters of the model should be made as similar as possible to the prototype. Different types of materials composed of different proportions of aggregates and binders often have different mechanical properties. Based on the basic data of the prototype coal and rock strata, sand was used as the aggregate, gypsum as the binder, and calcium carbonate as the auxiliary binder. Sand is the most common aggregate in similarity physical tests, with a gravel diameter <2mm. Gypsum is a commonly used main binder, characterized by rapid setting and hardening, a stable strength of around 5 MPa, and a tensile strength to compressive strength ratio of approximately 1:4. Calcium carbonate is a conventional auxiliary binder with extremely low strength, used to reduce material strength and increase material plasticity. Furthermore, humidity has a significant softening effect on gypsum binders, providing the possibility for softening with water leading to "activation" and deformation of the goaf.

[0054] Table 2 Similarity physical test parameters

[0055] Based on the basic data of the prototype coal and rock strata, a model was laid using sand as aggregate and gypsum and calcium carbonate as binders. The mix ratio was selected according to the compressive strength of the rock strata, and the amounts of sand, gypsum, calcium carbonate, and water were calculated based on the size of the model and the thickness of the rock strata. The amount of materials used in each layer of the model can be calculated using the following formula.

[0056] Q= l × b × m × ρ m × k In the formula, l The length of a planar model, in meters (m). b The width of a model, in meters; m The layer thickness of a model, in meters; ρ m Mass density of similar materials, kg / m³ ３ ; k —Material loss coefficient, taken as 1.1.

[0057] Table 3 Material proportions for each layer within the model

[0058] 2.3 Model Making Process This invention simulates the activation process primarily based on the principle of "equivalent mining thickness." After excavation, acrylic panels of a certain thickness are rapidly inserted to simulate residual deformation in the goaf. Based on the softening effect of groundwater on loose deposits, sudden and forceful water injection into the goaf is a significant inducing factor for the "activation" of old goaf areas. The deformation characteristics of the model are observed by injecting water into the untreated area to soften similar materials. The experimental equipment mainly includes a similar simulation test bench (model frame), steel tape measure, total station, digital speckle display, camera, acrylic transparent protective plate, pressure testing box, etc. The model frame is made of high-strength steel, and almost no deformation occurs during the experiment. After preparing the necessary tools and materials for model laying, the model laying can begin. The specific steps are as follows: (1) Equipment preparation: including model frame as test bench, marked side guards, transparent baffles on both sides, steel plate for compaction, steel plate and roller for leveling, mixer, electronic scale, measuring cylinder, acrylic small plate to simulate residual deformation, grouting bucket, grouting pump, grouting pipe, water injection pipe, etc.

[0059] (2) Install protective plates: After cleaning and painting the model frame and protective plates, draw the stratum lines and apply lubricating oil to the inside of the protective plates to prevent them from sticking to similar materials. Install protective plates on the front and back sides of the model frame (that is, form a simulation space between the model frame and the protective plates on both sides for making the model).

[0060] (3) Ingredients and mixing: The model to be made consists of six types of strata, from bottom to top: bottom mudstone, No. 2 coal seam, P1 s Sandstone and mudstone, P1 x Mudstone, N2 d Conglomerate, Q3 topsoil.

[0061] According to the requirements of each type, weigh out the sand, gypsum, and calcium carbonate needed for that layer, measure out an appropriate amount of water, mix the required materials with water and stir evenly, and use mica to simulate the layer.

[0062] (4) Model making: The model is made from bottom to top. The mixed material is poured into the simulation space and spread out. It is leveled with a steel plate and compacted with a roller. A 2cm layer of mica powder is laid to simulate the surface. A water-proof layer is made below the coal seam using sand, paraffin wax, and hydraulic oil. Its function is to fit more tightly with the front and rear baffles to prevent the slurry from spreading downwards. In the simulation space, a flexible tube is buried every 15cm from the right side, for a total of 16 flexible tubes. The four flexible tubes on the right side are used for later grouting and serve as grouting pipes. The twelve flexible tubes on the left side are used for later water injection and serve as water injection pipes. At this time, the model is divided into two parts. The area where the four grouting pipes are located is called the simulated deformation area, i.e., the treatment area. The area where the twelve water injection pipes are located is called the induced deformation area, i.e., the untreated area.

[0063] (5) Curing: After laying the six types of strata in the simulation space, the model is cured for 14 days to allow it to dry basically.

[0064] (6) Model painting and monitoring point and speckle creation: After the model is basically dry, brush a layer of white light calcium carbonate on the model surface to create a white background. After waiting for 3 days for the white calcium carbonate to basically solidify, draw the monitoring lines, install the reflectors, and draw the speckles. The monitoring lines are drawn using an ink line, and the reflectors are made by creating a guide grid with cotton thread and then inserting pins into the model. When drawing the speckles, first use a hole punch to randomly punch holes in the plastic cardstock, and then use spray paint to spray them.

[0065] Figure 2 The diagram shows the structure of the similarity test model. Figure 3 The deformation monitoring preparation process of the model shown.

[0066] (7) Excavation and Deformation Observation: Leave 10cm coal pillars on both sides of the simulated coal seam in the model, and excavate the rest. The excavation length is 10cm at a time, and excavation is carried out once per hour. After the excavation is completed at the excavation location, immediately insert two layers of acrylic small plates (the thickness of the two layers is 1cm) to observe the formation process of the three zones (collapse zone, fracture zone, and bending deformation zone). The acrylic small plates are used as residual deformation induction plates, and their dimensions are 30cm long, 5cm wide, and 0.5cm thick. After the excavation is completed and the deformation stabilizes, the next step of the work can begin. The stabilization condition is that the deformation is not obvious (<1mm) or the maximum subsidence coefficient of the central basin is 1.

[0067] (8) Grouting: After the deformation stabilizes, use transparent acrylic sheets to seal the front and back sides of the model (to prevent grout diffusion). Grout along the four pre-reserved plastic grouting pipes in the treatment area. Before grouting, raise the grouting pipes above the obviously deformed position. After grouting one layer, raise the grouting pipes again for grouting. The grouting material is a mixture of cement, fly ash, and water (add 5% water glass by mass to the grouting liquid in the grouting liquid of the right edge grouting pipe to limit grout diffusion). Cement:fly ash = 3:7, water-cement ratio = 1:1. The grouting is completed using an air pump and grouting bucket. The grouting bucket can detect the grouting pressure and stir in real time to prevent cement from solidifying.

[0068] (9) Slurry consolidation: After the cement slurry has basically solidified for about 7 days, observe the morphology and distribution of the cement slurry before starting the next test.

[0069] (10) Simulating residual deformation in the goaf: A baffle support was installed above the acrylic panels (as residual deformation induction panels) to prevent the removal of the panels from causing the loose material in the collapse zone to slide. In the untreated area, a layer of acrylic panels was removed at once to activate residual deformation. Displacement at the entire field and at individual points was measured using a combination of digital speckle (DIC) and a total station with reflectors. By comprehensively analyzing the displacement data at the entire field and individual points, the impact of residual deformation in the untreated area on the treated area can be better observed.

[0070] The experimental results show that the deformation within the grouting area is relatively small due to the presence of the grout, while the untreated area bears the majority of the deformation. To expand the experimental phenomenon and observe the resistance of grouting reinforcement to deformation, a single layer of acrylic sheet was extracted twice during the experiment. The small thickness of the single-layer sheet suggests that the smaller deformation in the grouting area may be due to incomplete deformation release. After the two extractions, the deformation patterns were basically the same, indicating that the grout can effectively reduce the deformation of the overburden in the treated area.

[0071] (11) Water Injection: To observe the deformation difference between the treated and untreated areas, baffles were used to seal the front and back sides of the model, and water was injected into the untreated area using pre-embedded water injection pipes. Gypsum was used as a cementing material in the similar material. Since its strength is significantly reduced in a wet and saturated state, water injection can bring the model to its limit deformation state and is beneficial for analyzing the effect of grouting reinforcement on deformation. In the experiment, after injecting a large amount of water into the similar material, some difficult-to-close delaminations, pores, and coal pillar support areas underwent significant deformation. By comparing the deformation difference between the treated and untreated areas, it can be clearly seen that the grouting body played an effective reinforcement role in the treated area, resulting in smaller deformation in the treated area. The experiment also found that the larger the amount of grout injected (such as the collapse zone and fracture zone), the smaller the deformation; while the deformation of the area with a smaller amount of grout injected was also slowed down.

[0072] 2.4 Model Observation 2.4.1 Measurement Method Similarity physics experiments have long been an important research method in scientific research, and their monitoring methods and signal acquisition techniques are crucial for obtaining effective data. In the area of ​​deformation monitoring of physical simulation test models, the quality of the monitoring equipment and technology is directly related to the quality of the test data. The most common monitoring method for similarity physical experiments is total station monitoring. Total station deformation monitoring is characterized by high accuracy, reaching 0.5″ (0.1 mm). Displacement monitoring using a total station has been proven accurate and reliable in practice. It utilizes the principle of laser ranging to accurately measure the spatial position of a single reflection point, resulting in high accuracy and reliability in absolute displacement measurement. However, total stations have drawbacks, including significant human error and the limitation to single-point measurement. Numerical speckle (DIC) is a recently emerging full-field displacement monitoring method that is effective in monitoring the overall relative deformation of the research object. Digital speckle is an image correlation analysis-based technique that treats a pattern composed of black and white pixels as a subset and calculates displacement by tracking the positional changes of this subset within the image. This method is highly sensitive to the relative positional changes of the subset within the entire image, but the estimated absolute displacement may have errors due to the influence of ambient light and the rigid body displacement of the imaging equipment. This invention utilizes digital speckle (DIC) to capture full-field relative displacement and a total station for accuracy correction, leveraging the advantages of both devices. By comprehensively analyzing full-field relative and single-point displacement data, the impact of residual deformation in the untreated area on the treated area can be better observed.

[0073] 2.4.2 Observation Points In order to observe the stress variation pattern of the formation in the mining area, such as Figure 4 As shown, stress test boxes are embedded in layers within the rock strata, starting from 50cm (sandstone / mudstone), 77cm (mudstone), and 134cm (topsoil). There are 7 stress test boxes per layer, with one box 15cm inside the boundary, one 20cm outside, and one 40cm from the boundary, for a total of 21 boxes. The maximum stress measurement range of each test box is 50 kPa.

[0074] In order to observe the displacement of the overlying strata, such as Figure 5The displacement observation points are set in the rock strata at the following distances from the bottom of the model: 147.7cm (line 1, top displacement layer), 137.7cm (line 2, stress detection box embedded at this height), 122cm (line 3, middle layer of topsoil), 106.7cm (line 4, conglomerate-topsoil interface), 99cm (line 5, middle layer of conglomerate), 90cm (line 6, mudstone-conglomerate interface), 79.6cm (line 7, stress detection box embedded at this height), 69.6cm (line 8, sandstone-mudstone interface), 64.2cm (line 9, predicted fracture zone height), 54.2cm (line 10, stress detection box embedded at this height), 48.2cm (line 11, predicted caving zone height), and 38.2cm (line 12, 3 times the sampling thickness). Each monitoring line is spaced 10cm apart and 5cm from the boundary.

[0075] Table 4 Deformation monitoring lines

[0076] 3. Analysis of test results during the mining phase This similarity physical test first creates a standard goaf, and the standard goaf is excavated according to the conventional similarity test to cause deformation and damage.

[0077] 3.1 Continuous Deformation Analysis in Mining Figure 6 The diagram shows the digital speckle pattern of mining deformation. The similarity model indicates initial collapse failure at 75cm. Figure 6 (a) Over time, the strata gradually bent and deformed, forming a more distinct coal pillar support zone and an equilateral trapezoidal coal pillar support zone. Subsequently, periodic pressure occurred approximately every 15 cm. As mining continued, the surface was affected at a depth of 130 cm, and a mining-induced basin began to form. Figure 6 (e)). The fully deformed maximum bending zone and the fully mined zone conform to the typical deformation laws of mining subsidence.

[0078] 3.2 First visit to the hospital Figure 7 The initial compression is shown. The initial collapse at 75cm demonstrates the model's gradual bending deformation, delamination development, and eventual overall collapse. This deformation and collapse resulted in a large number of delaminations. Figure 7 (b) The delamination gradually closes in the later stages. However, the coal pillar support zone is difficult to close, which is the main reason for the activation.

[0079] 3.3, Mining down to 130cm When the coal was mined to a depth of 130cm, deformation reached full extent, and displacement extended to the surface. Delamination continued to move upwards, but the scale of delamination was smaller than before, although the number of delaminations was greater. The coal pillar support area showed almost no deformation. Figure 8The mining process was completed at a depth of 130m, through which... Figure 8 It can be seen that the coal pillar support area does not undergo significant deformation. Figure 9 The curves showing settlement deformation at different elevations of 130cm are shown. Figure 9 It can be seen that the steeper the ground movement angle, the smaller the deformation as the survey line rises. The deformation gradually develops towards both sides.

[0080] 3.4. All mining completed After all mining was completed, the surface underwent significant deformation, forming distinct mining basins and mining compression zones. Figure 10 The deformation is completed as shown, through Figure 10 The deformation trends and patterns at different locations and the obvious mining basins can be observed. Figure 11 The figures show the settlement deformation curves at different elevations. Figure 11 This shows the subsidence of the mining basin and the specific displacement data of the basin.

[0081] 3.5 Three-zone distribution and periodic pressure pass Figure 12 It can be seen that as the mining progresses, the changes in the delamination layer exhibit four stages: The first stage (bending deformation stage) occurs between the opening of the cut and the first periodic pressure. During this stage, the overlying strata near the cut are relatively stable due to the support of the coal pillar, resulting in a small average amount of delamination. As the distance from the coal pillar increases, the overlying strata gradually deform and break under stress, leading to the formation of delamination. This stage primarily occurs in the area above the mining location where bending deformation and delamination are not yet developed.

[0082] In the second stage (the collapse and failure stage), as the distance between the mining location and the coal pillar increases, larger delaminations begin to form. Due to the supporting effect of the coal pillar, the pressure of the overlying strata is relatively low. In this stage, larger delaminations mainly form in areas closer to the mining location.

[0083] The third stage (the delamination closure and upward movement stage) involves the overlying strata gradually compacting the lower collapsed strata, resulting in the compaction of delamination fissures. This stage primarily involves the compaction of the lower strata while the upper strata begin to fracture. As the distance from the coal pillar increases, new collapses form after the coal seam is excavated, creating significant delamination in the upper part of the model. This leads to substantial damage in the coal pillar support area, the location of mining deformation, and the concentrated areas of upper delamination.

[0084] In the fourth stage (separation closure and ground subsidence stage), when the mining location is far enough away from the coal pillar, deformation and damage reach the surface. Under the action of stress, the overlying strata gradually close, and the ground begins to subside. The strain is more obvious at the boundary of the fully mined area.

[0085] 4. Grouting diffusion and reinforcement analysis Figure 13 The grouting diffusion process is shown. Figure 13 It mainly reflects the process of experimental grouting. Figure 13 (a) is a photograph of the experimental setup after it has been sealed. Figure 13 (b) is a photo of the grouting process. Grouting is mainly carried out by pressurizing with an air pump and transmitting the air pressure into the grouting tank to inject the grout into the model. Figure 13 (c), (d), (e), and (f) represent the gradual diffusion of the grout, which can effectively simulate the actual grouting process. Figure 13 (g) is a photograph of the grouting location. Figure 13 (h) and (i) show the appearance of the slurry-filled stone body after the model was disassembled, and it can be seen that the goaf was well filled.

[0086] Furthermore, it can be observed that the difference in diffusion between the caving zone and the fracture zone is that flower-shaped stone bodies first form near the grouting hole, and then gradually diffuse downwards along the grouting hole, forming larger stone bodies in the fracture zone and caving zone. It can also be seen that the grout diffuses well within the bedding plane.

[0087] 5. Residual Deformation Analysis 5.1 Residual Deformation Figure 14 The first residual deformation failure speckle displacement cloud map is shown. The deformation law of residual deformation is analyzed in this stage, and the deformation caused by mining is deducted. Figure 15 The curves show the subsidence deformation at different elevations.

[0088] Figure 14 These are DIC deformation monitoring data after induced residual deformation. DIC monitoring shows that the main subsidence occurred on the outer side of the grouting treatment area, and the overall deformation tilted to the left. This indicates that the grouting aggregate in the treatment area effectively protected the overlying strata. The higher purple position of the residual deformation indicates that the deformation release was relatively sufficient, with most of the deformation occurring in the untreated central area. Figure 15 The subsidence of the measuring line after deducting mining deformation shows that the deformation and damage are milder than before due to the influence of grouting rock bodies. The overall displacement deformation is inclined, which is different from mining deformation. Grouting rock bodies cause the deformation pattern of the overlying strata to differ from that of mining deformation. When studying the scope of goaf treatment, the supporting effect of grouting rock bodies can be taken into account.

[0089] 5.2 Comparative Study of Mining Deformation and Residual Deformation Figure 16The differences between mining deformation and residual deformation were compared and analyzed. First, the mining deformation, with its Y-axis displacement remaining largely symmetrical, contrasts sharply with the residual deformation, which clearly shows the influence of the grouting area and the concentrated deformation due to the larger remaining space in the coal pillar support zone. The overall deformation trend is from upper right to lower left; this asymmetrical deformation pattern reflects two key pieces of information: 1. Grouting treatment zones cause the deformation pattern of the overlying strata to differ from that of mining; 2. Areas with larger residual porosity are likely to experience greater deformation. Second, the grouting treatment zone influences deformation; an arc-shaped deformation curve exists near the treatment zone, indicating that the treatment zone can protect the stability of the overlying strata. The existence of the treatment zone affects the surface deformation diffusion pattern, and the treatment zone provides some protection to the overlying strata.

[0090] The method of this invention provides technical guidance for designing the treatment scope of goaf and predicting the residual deformation of goaf, helping to obtain a safe and economical goaf treatment plan. It can effectively and intuitively analyze the protective effect of the grouting stone body on the above-ground structures when the residual deformation of the goaf occurs.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the embodiments of the present invention have been described in detail, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for simulating the effect of grouting reinforcement on controlling residual deformation in old goaf areas, characterized in that: Includes the following steps: (1) Equipment preparation: including model frame as test bench, marked side guards, transparent baffles on both sides, steel plate for compaction, steel plate and roller for leveling, mixer, electronic scale, measuring cylinder, acrylic small plate to simulate residual deformation, grouting bucket, grouting pump, grouting pipe, water injection pipe; (2) Install protective plates: After cleaning and painting the model frame and the protective plates on both sides, draw the stratum lines and apply lubricating oil to the inside of the protective plates to prevent them from sticking to similar materials. Install protective plates on the front and back sides of the model frame to form a simulation space between the model frame and the protective plates on both sides for making the model. (3) Ingredients and mixing: The model to be made consists of six types of strata, from bottom to top: mudstone layer, coal seam, sandy mudstone layer, mudstone layer, conglomerate layer, and topsoil layer; According to the requirements of each type, weigh out the sand, gypsum and calcium carbonate required for the layer, measure an appropriate amount of water, mix the required materials with water and stir evenly, and use mica to simulate the layer. (4) Model making: The model is made from bottom to top. The mixed material is poured into the simulation space and spread out. The material is leveled with a steel plate and compacted with a roller. Mica powder is sprinkled every 2cm to simulate the surface layer. A water-proof layer is made under the coal seam using sand, paraffin wax and hydraulic oil. In the simulation space, a hose is buried every 15cm from the right side, for a total of 16 hoses. The four hoses on the right side are used for grouting later and serve as grouting pipes. The twelve hoses on the left side are used for water injection later and serve as water injection pipes. At this time, the model is divided into two parts. The area where the four grouting pipes are located is called the simulated deformation area, i.e. the treatment area. The area where the twelve water injection pipes are located is called the induced deformation area, i.e. the untreated area. (5) Curing: After laying the six types of strata in the simulated space in sequence, cure for 14 days to allow the model to dry and solidify; (6) Model painting and monitoring point and speckle production: After the model dries, brush a layer of white light calcium carbonate on the model surface to produce a white background; after waiting 3 days for the white calcium carbonate to solidify, draw the monitoring lines, install the reflector and draw the speckle. Among them, the monitoring line is drawn using an ink fountain; the reflector is made by creating a guide grid with cotton thread and then inserting it into the model using pins; when drawing speckle, first use a hole punch to randomly punch holes in the plastic card, and then use spray paint to draw it. (7) Excavation and Deformation Observation: Leave 10cm coal pillars on both sides of the simulated coal seam in the model, and excavate the rest; the excavation length is 5cm at a time, and excavation is carried out once per hour. After the excavation is completed at the excavation location, immediately insert two layers of acrylic small plates to simulate residual deformation and observe the formation process of the three zones; after the excavation is completed and the deformation stabilizes, start the next step of the work. The stabilization condition is that the deformation is not obvious (<1mm) or the maximum subsidence coefficient of the central basin is 1. (8) Grouting: After the deformation stabilizes, use transparent baffles to seal the front and back sides of the model to prevent the grout from spreading; grout along the four reserved grouting pipes in the treatment area, and raise the grouting pipes above the obvious deformation position before grouting. (9) Grout consolidation: After the cement grout has solidified, observe the morphology and distribution pattern of the cement grout. (10) Simulate residual deformation in the goaf: baffle support is installed above the acrylic small plate simulating residual deformation to prevent the loose body in the collapse zone from sliding due to plate removal; in the untreated area, a layer of acrylic small plate is removed at once to activate residual deformation; digital speckle is used to capture the relative displacement of the whole field and a total station is used for accuracy correction. By comprehensively analyzing the relative displacement data of the whole field and the displacement data of a single point, the influence of residual deformation in the untreated area on the treated area can be better observed. The results show that due to the presence of the grout, the deformation within the grouting area of ​​the treated zone is small, while the untreated zone bears the main deformation, indicating that the grout can effectively reduce the deformation of the overburden in the treated zone. (11) Water injection: In order to observe the deformation difference between the treated area and the untreated area, baffles were used to seal the front and back sides of the model, and water was injected into the untreated area using pre-embedded water injection pipes; gypsum was used as a cementing material in the similar material. Since its strength is significantly reduced in the wet and saturated state, water injection made the model reach the limit deformation state, which is beneficial to the analysis of the effect of grouting reinforcement on deformation; after injecting a large amount of water into the similar material, significant deformation occurred in the difficult-to-close delamination, pores and coal pillar support area; by comparing the deformation difference between the treated area and the untreated area, it is shown that the grouting body played an effective reinforcement role in the treated area, making the deformation in the treated area smaller; at the same time, the larger the amount of grout injected, the smaller the deformation, while the smaller the amount of grout injected, the slower the deformation.

2. The method for controlling residual deformation in old goaf areas by simulating grouting reinforcement according to claim 1, characterized in that: In step (4), the model is constructed from bottom to top as follows: mudstone layer thickness 29cm, coal seam thickness 3cm, sandy mudstone layer thickness 37.4cm, mudstone layer thickness 20.4cm, conglomerate layer thickness 16.7cm, topsoil layer thickness 62.5cm.

3. The method for controlling residual deformation in old goaf areas by simulating grouting reinforcement according to claim 2, characterized in that: In step (4), in order to observe the stress change law of the strata in the mining area, stress detection boxes are buried in the sandstone, mudstone and topsoil layers. Seven stress detection boxes are set up in each layer, and a total of 21 boxes are set up in the three layers.

4. The method for controlling residual deformation in old goaf areas by simulating grouting reinforcement according to claim 3, characterized in that: In step (6), in order to observe the displacement of the overlying rock strata, displacement observation points are set in the rock strata on the surface of the model: 38.2cm, 48.2cm, 54.2cm, 64.2cm, 69.6cm, 79.6cm, 90cm, 99cm, 106.7cm, 122cm, 137.7cm, and 147.7cm from the bottom; each monitoring line is spaced 10cm apart and 5cm from the boundary, for a total of 12 lines.

5. The method for controlling residual deformation in old goaf areas by simulating grouting reinforcement according to claim 4, characterized in that: In step (8), the grouting material is a mixture of cement, fly ash and water, wherein the ratio of cement to fly ash is 3:7 and the water-cement ratio is 1:

1.

6. The method for controlling residual deformation in old goaf areas by simulating grouting reinforcement according to claim 5, characterized in that: In step (8), 5% water glass by mass is added to the grouting fluid of the grouting pipe on the right edge to limit the diffusion of the grout.

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