Method for constructing bearing pressure and load distribution function on weakly cemented stratum subjected to mining

Abstract

The application discloses a kind of weakly cemented strata upper abutment pressure and load distribution function construction method, which is based on weakly cemented strata mineral composition, microstructure and physical and mechanical properties, uses laboratory test to obtain the response law of weakly cemented strata deterioration property with influencing factors, builds the mining overburden damage similar material physical model of "hard-soft-hard" overburden and obtains the distribution curve of upper abutment pressure and load with mining, based on the curve, the numerical simulation calculation parameters of mining overburden damage law conforming to laboratory test are calibrated, the upper support pressure and load distribution data under different influencing factors are obtained by numerical simulation calculation under different working conditions, and the upper hard rock abutment pressure and lower basic roof load distribution function expression of weakly cemented strata deterioration is obtained.The application can effectively depict the distribution characteristics of upper abutment pressure and load of deteriorated weakly cemented strata, and provide support for revealing the strong rock pressure appearance and dynamic sand burst disaster of weakly cemented roof stope.

Description

Technical Field

[0001] This invention belongs to the field of water hazard prevention technology in underground engineering such as mines, and relates to a method for constructing the distribution function of hard rock support pressure above and basic top load below deteriorated weakly cemented strata. Background Technology

[0002] The deterioration of weakly cemented strata upon exposure to water has always been a major concern for rock mechanics and coal science and technology workers. In major coal-rich areas, where coal formation is primarily from the Early to Middle Jurassic period, the formation is characterized by late formation and poor diagenesis. This results in coal-bearing strata typically exhibiting insufficient cementation, low strength, susceptibility to disintegration, and easy weathering—typical engineering mechanical properties. This leads to severe mining hazards such as strong mine pressure manifestations and dynamic sand collapses during coal mining, seriously impacting the safe and large-scale development of coal resources in western mining areas.

[0003] After mining, weakly cemented strata deteriorate and disintegrate due to groundwater immersion, resulting in a significant reduction in their physical and mechanical properties. This has a crucial impact on the bearing pressure of the overlying hard rock and the distribution of the underlying basic top load, which is key to the occurrence of strong mining pressure manifestations and dynamic sand erosion. Therefore, understanding how to express the distribution functions of the bearing pressure of the overlying hard rock and the underlying basic top load in deteriorated weakly cemented strata is the theoretical basis for developing targeted preventative measures. However, existing domestic and international literature on the distribution of bearing pressure and load during the fracture and instability of hard rock under softened foundations mainly focuses on finite element analysis and probability distribution function substitution. For example, Pan Yue et al. used the Weibull distribution function to simulate the incremental load of uplift and studied the fracture law of hard rock. They found that the peak bending moment of the roof and the distance between the peak bending moment and the coal wall under the softened foundation support were significantly increased. The strain energy storage area and storage capacity in front of the coal wall were greatly increased, and the roof deflection was significantly increased compared with that under a fully elastic foundation support. Qian Minggao et al. used finite element analysis to show that the effect of the upper rock strata of the key layer after mining is non-uniformly distributed, and the load distribution and bearing pressure distribution are related to the thickness and hardness of the weak interlayer. The peak position is far away from the coal wall, which causes the span of the hard rock overhang to increase, the deflection to increase, and the strain energy storage area and size to increase. A thorough study of the supporting effect of softened foundations and the distribution law of incremental loads from overlying uplifts in rock strata, and the development of a functional expression that can characterize the properties of softened foundations and the occurrence characteristics of rock strata, will clarify the impact of water-induced degradation of weakly cemented strata on the supporting pressure below the hard rock strata and the load distribution above the basic top layer. Some scholars have also disclosed relevant patents regarding stope supporting pressure, but none of them have addressed the method for constructing a functional expression of supporting pressure and load distribution curves. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for constructing the distribution functions of upper support pressure and lower load in mining-induced weakly cemented strata. This method can effectively characterize the distribution features of hard rock support pressure above and basic roof load below deteriorated weakly cemented strata, reflecting the mechanical characteristics of the impact of mining-induced weakly cemented roof deterioration on hard rock support pressure and basic constant load. This provides effective support for revealing the manifestation of strong mining pressure and dynamic sand collapse disasters in weakly cemented roof stopes in western mining areas.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A method for constructing the distribution function of bearing pressure and load on weakly cemented formations during mining includes the following steps:

[0007] Step 1: Obtain the clay mineral composition and content, microstructure and porosity of the weakly cemented strata under natural conditions, as well as the physical and mechanical properties of the weakly cemented strata and its upper and lower strata under natural conditions; determine the microstructure and water absorption of the weakly cemented strata samples deteriorated by water under different water absorption times, rock strength and deformation parameters under different water absorption, rock strength and deformation parameters and disintegration under different loads, and water absorption under different porosities and clay mineral contents.

[0008] Step 2: Based on the parameters and physical and mechanical properties obtained in Step 1, build an indoor physical model test platform for similar materials of mining-induced weak cemented strata with a "hard-soft-hard" overburden structure, and collect data on the distribution of hard rock bearing pressure and lower basic top load on the deteriorated weak cemented strata during the simulation test to obtain the distribution curves of hard rock bearing pressure and lower basic top load on the similar material physical model with mining.

[0009] Step 3: Based on the distribution curve obtained in Step 2, calibrate the numerical simulation calculation parameters for the mining-induced weakly cemented strata, and conduct numerical simulation calculations under different influencing factors to obtain the distribution data of the bearing pressure of the upper hard rock layer and the lower basic top load of the mining-induced weakly cemented strata under different influencing factors:

[0010] Step 4: Constructing the distribution functions of bearing pressure and underlying basic top load of the upper hard rock layer after the deterioration of the weakly cemented strata: Based on the distribution data obtained in Step 3, the bearing pressure and load distribution curves are analyzed using basic statistical principles to determine the basic form of the curve function:

[0011]

[0012] In the formula, when x < 0, it is the function expression for the peak value of the support pressure and load distribution curve, where n = 1; when x < 0, it is the function expression for the peak value of the support pressure and load distribution curve. The expression for the peak value of the support pressure and load distribution curve is given, where n=2, and L is half the length of the goaf. A , BThe coefficient of determination for the trend of the influencing factor function; x It is a function variable, namely the recovery footage; x cn This represents the variable value at the peak.

[0013] The present invention also includes the following technical features:

[0014] Specifically, the physical and mechanical properties obtained in step 1 include compressive strength, tensile strength, Poisson's ratio, elastic modulus, internal friction angle, and cohesion.

[0015] Specifically, in step 2, the topsoil layer above the "hard-soft-hard" overburden structure is laid with a mixture of loess and water, and the "hard-soft-hard" overburden structure is laid with a mixture of sand, gypsum and water. The "soft" weak cemented strata are mixed with clay for laying.

[0016] By measuring the physical and mechanical properties of the paving material for the "hard-soft-hard" overburden structure strata under different proportions, the paving material proportion that conforms to the physical and mechanical properties of the weakly cemented strata and its upper and lower strata in step 1 is determined.

[0017] Specifically, in step 2, based on the clay mineral composition and content, microstructure and porosity of the weakly cemented strata obtained in step 1, as well as the microstructure and water absorption at different water absorption times, rock strength and deformation parameters at different water absorption rates, rock strength and deformation parameters and disintegration under different loads, and water absorption at different porosities and clay mineral contents, water is injected into a physical model of similar materials to simulate the test process.

[0018] Specifically, in step 3, the numerical simulation calculation of the weakly cemented strata is carried out by constructing a coal seam mining model using discrete element numerical simulation software, wherein the overburden structure and its physical and mechanical properties are consistent with the physical model of similar materials in step 2; the numerical simulation calculation parameters are calibrated by the test results of the physical model of similar materials in step 2, so that the numerical simulation calculation results are consistent with the test results of the physical model of similar materials.

[0019] Specifically, the different influencing factors in step 3 include the clay mineral content, porosity, thickness, and bedrock thickness of the weakly cemented strata.

[0020] Compared with the prior art, the present invention has the following technical effects:

[0021] This invention provides a method for constructing the distribution functions of the upper hard rock bearing pressure and the lower basic top load of a deteriorated weakly cemented stratum. Based on the macroscopic and microscopic physical and mechanical properties of the weakly cemented stratum and the typical overburden structure of the weakly cemented stratum in the western mining area, this method obtains functional expressions of the distribution of the upper hard rock bearing pressure and the lower basic top load that reflect the actual influencing factors through indoor experiments and numerical calculations. This allows the distribution of the upper hard rock bearing pressure and the lower basic top load to change with mining and the deterioration properties of the weakly cemented stratum. Attached Figure Description

[0022] Figure 1 This is a technical roadmap of the method of this invention;

[0023] Figure 2 This is a schematic diagram of the support pressure curves of different rock strata on the roof during coal seam mining;

[0024] Figure 3 It is a stress-time curve based on earth pressure stress cell monitoring;

[0025] Figure 4 It is the curve of stress variation in the y-direction at the measuring point in model measuring line 1 as the working face is pushed and mined;

[0026] Figure 5 It is the stress variation curve of the measuring point in the y-direction as the working face is pushed and mined in model measuring line 2;

[0027] Figure 6 It is the stress variation curve of the measuring point in model measuring line 3 as the working face pushes and mines in the y direction;

[0028] The meanings of the labels in the diagram are as follows:

[0029] 1. Goaf; 2. Support pressure curves of roof strata at different heights. Detailed Implementation

[0030] This invention provides a method for constructing the distribution functions of upper support pressure and lower load in mining-induced weakly cemented strata. This method is based on the macroscopic and microscopic physical and mechanical properties of weakly cemented strata after water exposure and the typical "hard-soft-hard" overburden structure in western mining areas ("hard" representing the upper hard rock layer and the lower basic roof, and "soft" representing the weakly cemented strata). It utilizes laboratory experiments to obtain the response law of the water-induced deterioration properties of weakly cemented strata to influencing factors, constructs a similar material physical model test for mining-induced overburden failure, and reflects the "hard-soft-hard" overburden structure. The distribution curves of upper hard rock support pressure and basic roof load with mining are obtained. Based on these curves, a numerical calculation model for mining is calibrated, obtaining numerical simulation calculation parameters that conform to the mining-induced overburden failure law observed in laboratory experiments. By changing different influencing factors, the distribution of upper hard rock support pressure and basic roof load under different influencing factors is obtained, thus obtaining a functional expression that can effectively characterize the influence of the water-induced softening properties of weakly cemented strata on the distribution of upper hard rock support pressure and lower basic roof load.

[0031] This invention employs a method for constructing the distribution function of bearing pressure and load on weakly cemented strata, comprising the following steps:

[0032] Step 1: Obtain the clay mineral composition and content, microstructure and porosity of the weakly cemented strata under natural conditions, as well as the physical and mechanical properties of the weakly cemented strata and its upper and lower strata under natural conditions; determine the microstructure and water absorption of water-degraded weakly cemented strata samples under different water absorption times, rock strength and deformation parameters under different water absorption, rock strength and deformation parameters and disintegration under different loads, and water absorption under different porosities and clay mineral contents to obtain the effect of water on the deterioration of weakly cemented strata.

[0033] Step 1.1: Obtaining the mineral composition and content of weakly cemented strata in their natural state: First, analysis was conducted from the perspective of microscopic laboratory tests: X-ray diffraction and X-ray fluorescence spectrometry were used to perform qualitative and quantitative analysis of the clay mineral composition and content in the screened weakly cemented strata samples in their natural state. Then, analysis was conducted from the perspective of macroscopic stratigraphy: Since strata with high clay mineral content typically exhibit high natural gamma ray logging response values ​​and low resistivity logging response values, geophysical logging data was used to indicate the clay mineral content of weakly cemented strata using natural gamma ray logging response curves and resistivity logging response curves. The clay mineral content of the weakly cemented strata was calculated using empirical formulas relating natural gamma ray, resistivity, and clay mineral content. In summary, based on the results of microscopic laboratory tests and macroscopic stratigraphic analysis of the clay mineral composition and content of weakly cemented strata in their natural state, the magnitude and range of the clay mineral composition and content in these strata were determined.

[0034] Step 1.2, obtain the microstructure of the weakly cemented strata in the natural state: use scanning electron microscopy to observe the weakly cemented strata samples in the natural state at different magnifications, and analyze the microstructure characteristics of the weakly cemented strata in the natural state.

[0035] Step 1.3: Obtaining the porosity of weakly cemented formations in their natural state: First, analysis from the perspective of indoor microscopic experiments: Scanning data of samples from weakly cemented formations in their natural state were obtained using a 3D micro-CT device. The data was then reconstructed using the 3D visualization software AVIZO to construct a refined 3D visualization model characterizing the rock and mineral crystals and porosity structure. Porosity structure and geometric parameters were extracted using threshold segmentation and porosity sieving principles, and the porosity of the weakly cemented formation samples was calculated. The permeability of the weakly cemented formation samples was calculated using the seepage simulation module in AVIZO FIRE software. Next, analysis from the perspective of macroscopic formations: Based on the sonic transit time logging curves and density logging curves from macroscopic formation drilling data, the porosity was calculated using the Raymer-Hunt-Gardner relationship and the Wyllie time-averaging formula in the velocity-porosity model, respectively. In summary, combining the porosity obtained from indoor microscopic experiments and macroscopic formation analysis, the magnitude and range of porosity in weakly cemented formations in their natural state were determined.

[0036] Step 1.4: Obtain the physical and mechanical properties of the weakly cemented strata and its overlying strata under natural conditions: The physical and mechanical properties of the weakly cemented strata and its overlying strata under natural conditions are determined using the GCTS rock mechanics testing system. These physical and mechanical properties include compressive strength, tensile strength, Poisson's ratio, elastic modulus, internal friction angle, and cohesion.

[0037] Step 1.5: Using scanning electron microscopy, the microstructure of weakly cemented strata samples deteriorated by water was observed at different water absorption times, and the changes in microstructure and water absorption over time were analyzed.

[0038] Step 1.6: Based on the GCTS rock mechanics testing system, the rock strength and deformation parameters under different water absorption and different loads are measured to obtain the relationship between rock strength and deformation parameters and water absorption and load.

[0039] Step 1.7: Conduct disintegration tests on water-absorbing rocks under different loads to determine the relationship between disintegration and load;

[0040] Step 1.8: The saturation water absorption of rock samples with different porosities and clay mineral contents was tested using a rock vacuum saturation device and a high-precision digital electronic balance, and the relationship between rock water absorption and porosity and clay mineral content was analyzed.

[0041] In summary, the relationships between clay mineral content, porosity, water absorption, time, load, and rock strength, deformation, and disintegration were obtained, as well as the relationships between porosity, clay mineral content, water absorption, and time. Specific experimental procedures are shown in Table 1.

[0042] Table 1. Experimental scheme for the effects of water absorption time, water absorption amount, load, porosity, and clay mineral content on rock mechanical behavior.

[0043]

[0044] Step 2: Construct an indoor physical model test platform for similar materials in mining-induced weakly cemented strata with a "hard-soft-hard" overburden structure, and collect data on the distribution of hard rock bearing pressure and lower basic top load in the deteriorated weakly cemented strata during the simulation test to obtain the distribution curves of hard rock bearing pressure and lower basic top load in the physical model of similar materials as mining occurs.

[0045] Step 2.1: Construct a physical model test platform for similar materials in "hard-soft-hard" overburden structures:

[0046] Step 2.1.1, determine the model size and the thickness of each layer: Taking the western mining area as the background, a similarity simulation test was carried out using a physical similarity material simulation test system for integrated mechanized mining. The model size is 2.8m × 1.4m × 0.2m (length × height × width), equipped with a small-scale hydraulic support with a support height of 5~15cm. The hydraulic control system of the support was improved to realize real-time monitoring of the hydraulic pressure. Based on the comprehensive columnar and physical and mechanical properties of the overlying rock of the working face and the principle of similar model test, the thickness of the strata to be laid in the model was determined.

[0047] Step 2.1.2: Determine the similarity ratio and materials for the model test: Based on the similarity principle of the model test, the length and width, and the physical and mechanical properties of the strata, a model similarity ratio of 1:150 is selected. The topsoil layer above the "hard-soft-hard" overburden structure of the coal seam is laid using a mixture of loess and water, while the "hard-soft-hard" overburden structure is laid using a mixture of sand, gypsum, and water. The "soft" weakly cemented strata are laid with appropriate types of clay mixed in a specific ratio. The compressive strength, tensile strength, Poisson's ratio, cohesion, internal friction angle, and elastic modulus under different material ratios are calibrated through indoor physical and mechanical property tests. Combined with the physical and mechanical properties of the overburden strata and weakly cemented strata obtained in Step 1, a similar material ratio is determined that matches the compressive strength, tensile strength, Poisson's ratio, cohesion, internal friction angle, and elastic modulus of the weakly cemented strata and its upper and lower overburden strata.

[0048] Step 2.1.3, simulation of the deterioration of weakly cemented strata: Based on the clay mineral content, porosity, water absorption and the relationship between porosity, clay mineral content and water absorption, time and other factors obtained in Step 1, the simulation of the deterioration process of weakly cemented strata when exposed to water in actual process is achieved by injecting a quantitative amount of water into the weakly cemented strata in proportion.

[0049] Step 2.2: Data collection on the distribution of bearing pressure and underlying load of the hard rock layer above the deteriorated weakly cemented strata during mining:

[0050] The model employs an optical photogrammetric digital strain-displacement measurement system to record overburden deformation and overburden failure characteristics throughout the mining process, and analyzes information such as displacement field changes. Fiber optic strain sensors are used to monitor strain characteristics between the weakly cemented strata and the upper hard rock layer, between the upper hard rock and the loaded strata, and between the weakly cemented strata and the base roof during mining. Earth pressure stress cells are combined to monitor vertical stress changes between the upper hard rock, weakly cemented strata, and base roof during mining, obtaining the support pressure distribution curves of the deteriorated weakly cemented strata and the rock load distribution curves. The hydraulic pressure of a small-scale hydraulic support column is monitored to obtain the magnitude of the incremental load on the base roof caused by overburden deformation and failure and water absorption by the weakly cemented strata.

[0051] Step 3: Based on the distribution curve obtained in Step 2, calibrate the numerical simulation calculation parameters for the mining-induced weakly cemented strata, and conduct numerical simulation calculations under different influencing factors to obtain the distribution data of the bearing pressure of the upper hard rock layer and the lower basic top load of the mining-induced weakly cemented strata under different influencing factors:

[0052] Step 3.1, Numerical simulation parameter calibration:

[0053] Step 3.1.1, Model Construction: Based on a certain mining area, a coal seam mining model is constructed using discrete element numerical simulation software, wherein the overburden structure characteristics and its physical and mechanical properties are consistent with the physical model test of similar materials in Step 2;

[0054] Step 3.1.2, Boundary conditions: The model joint adopts the Mohr-Coulomb surface contact slip model, the left and right boundaries are deformation constraint boundaries, and the displacement in the X direction is defined as 0; the lower boundary is a fixed boundary, and the displacement in both the X and Y directions is 0; the excavation settings and step distance are consistent with the physical model test of similar materials.

[0055] Step 3.1.3, setting up survey lines: set up stress, strain and displacement monitoring lines at the upper and lower interfaces of hard rock and basic top, as well as the interface below the weakly cemented strata, to record stress, strain and displacement data of hard rock and basic top, as well as the strata below the weakly cemented strata at different mining depths in real time.

[0056] Step 3.1.4, Comparison and calibration of numerical simulation calculation data with test data of similar material physical model: The numerical simulation calculation parameters are calibrated by the test results of similar material physical model, and the numerical calculation parameters such as the physical and mechanical properties of the strata that are consistent with the characteristics of mining-induced overburden failure, rock load distribution and bearing pressure distribution in the test of similar material physical model are obtained.

[0057] Step 3.2, Numerical simulation calculations under different influencing factors: Combining the feedback characteristics and response relationships of the water-induced degradation properties of the weakly cemented strata in Step 1 on the changes in clay mineral content, water absorption and time, load, porosity and other influencing factors, considering factors such as clay mineral content, porosity, thickness and bedrock thickness (greater than the predicted height of the water-conducting fracture zone) of the weakly cemented strata (Table 2), numerical simulation calculations under different influencing factors are carried out to obtain the corresponding hard rock, the top load distribution of the basement and the support pressure distribution of the deteriorated weakly cemented strata below the hard rock.

[0058] Table 2 Control Variables Calculated in Numerical Simulation

[0059]

[0060] (Note: The contents of clay minerals such as A1, A2, and A3, and the porosities of strata such as B1, B2, and B3 are all determined based on the experimental results mentioned above.)

[0061] Step 4: Construct the distribution functions of the bearing pressure of the upper hard rock layer and the lower basic top load after the deterioration of the weakly cemented strata:

[0062] Based on the distribution data obtained in step 3, the basic principles of statistics are used to analyze the support pressure and load distribution curves to determine the basic form of the curve function:

[0063]

[0064] In the formula, when x < 0, it is the function expression for the peak value of the support pressure and load distribution curve, where n = 1; when x < 0, it is the function expression for the peak value of the support pressure and load distribution curve. The expression for the peak value of the support pressure and load distribution curve is given, where n=2, and L is half the length of the goaf. A , B The coefficient of determination for the trend of the influencing factor function; x It is a function variable, namely the recovery footage; x cn This represents the variable value at the peak.

[0065] By using grey relational analysis and Pearson correlation coefficient, the influence of variable factors on each parameter in the function is quantitatively compared, the main controlling factors of the curve distribution pattern are explored, the range of the trend determination coefficients A and B of the influencing factor function are determined, the physical meaning of the parameters in the bearing pressure and load distribution curve function is explained from the perspective of rock mechanics and elastoplastic mechanics, and the bearing pressure and load distribution law function related to the deterioration properties and formation occurrence characteristics of weakly cemented strata is constructed.

[0066] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0067] Example:

[0068] This embodiment provides a method for constructing the distribution function of bearing pressure and load on a mining-induced weakly cemented stratum, including:

[0069] First, analyze the physical and mechanical properties of the weakly cemented strata before and after deterioration to determine the characteristics of the influence of moisture on the deterioration of the weakly cemented strata:

[0070] Samples of weakly cemented strata from the roof of a coalfield in the Huanglong coalfield of Shaanxi Province were collected. X-ray diffraction revealed that the contents of quartz, kaolinite, and illite in the samples were 64.7%, 14.4%, and 12.9%, respectively. The contents of other minerals, such as potassium feldspar, plagioclase, calcite, chlorite, montmorillonite, talc, hematite, anatase, goethite, and siderite, were all below 2.1%. The small particle size and strong hydrophilicity of minerals such as kaolinite and illite make the weakly cemented strata prone to deterioration when exposed to water. The physical and mechanical properties of the weakly cemented strata were obtained using micro-CT scanning and the GCTS rock mechanics behavior comprehensive testing platform. The sandy mudstone had a porosity of 3%, a water content of 1.78%, a compressive strength of 19.33 MPa in its natural state, a compressive strength of 9.47 MPa in its saturated state, a softening coefficient of 48.99%, a tensile strength of 0.81 MPa, an internal friction angle of 31.64°, a cohesion of 2.36 MPa, an elastic modulus of 11.93 GPa, and a Poisson's ratio of 0.2. The argillaceous siltstone had a porosity of 1.53%, a water content of 1.22%, a compressive strength of 16.35 MPa in its natural state, a compressive strength of 8.01 MPa in its saturated state, a softening coefficient of 48.99%, a tensile strength of 0.88 MPa, an internal friction angle of 33.16°, a cohesion of 1.61 MPa, an elastic modulus of 12.47 GPa, and a Poisson's ratio of 0.25.

[0071] II. Physical model calibration test for similar materials in the deterioration of weakly cemented strata in "hard-soft-hard" overburden structure strata:

[0072] Using a coal mine in western China as a case study, a similar material simulation study was conducted on a test rig with dimensions of 2800mm × 200mm × 1400mm (length × width × height). A plane strain model was employed, with metal counterweights used for loading. Data recording was achieved using optical speckle, a digital camera, and a pressure cell. Considering the influence of boundary effects and experimental conditions, the average coal seam thickness was set at 10m, with a dip angle of 0°. Since this experiment could not simulate the entire stratum thickness, counterweight loading was used. Because the thickness and strength of the base plate do not significantly affect the overall experiment during mining, the coal seam base plate was simplified during the actual model installation. The installation process strictly adhered to the actual dimensions of each coal and rock stratum. The maximum thickness of each layer was 3cm, ensuring smooth and uniform installation. Mica powder was added between each layer to clearly define the stratification of the model. The bedrock was laid using a mixture of sand, gypsum, and water. The weakly cemented strata were mixed with appropriate types of clay in proportion. The proportions of the similar materials used were determined experimentally based on the physical and mechanical properties and similarity ratios of the overburden and weakly cemented strata to establish a reasonable mixing ratio. Specific proportions are detailed in Table 3. The weakly cemented strata were mixed with 12.9%-14.4% bentonite according to their stratum mass to simulate weakly cemented strata.

[0073] Table 3. Similar Material Model Proportions

[0074]

[0075] The average height of the coal seam above the surface in the ZF202 working face of this coal mine is 489m. The simulation scheme is set at 1:150, with a model laying height of 1163mm. The simulated roof strata height is 156.5m, and the remaining 332.5m is pressured using simulated pressurization, with a vertical stress of 7.17MPa and an actual vertical loading force of 2731.23Kg. Two stress-strain measurement lines are arranged on the immediate roof and the old roof, respectively, with nine strain gauges on each line, spaced 25cm apart, located at the top of the coal seam and the top of the immediate roof (sandy mudstone). Pressure data is automatically collected using a data acquisition device. The earth pressure stress-cell load variation curve is obtained. Figure 2 ).

[0076] 3. Numerical simulation calculation of the deterioration of weakly cemented strata in the "hard-soft-hard" overburden structure under different influencing factors:

[0077] Based on the coal seam occurrence conditions, a numerical simulation model with a length of 600m and a height of 313m was established using numerical simulation software. Considering the boundary effects generated by coal seam mining, 115m coal pillars were left on both sides of the working face of the model, with a mining depth of 370m. The step-by-step mining depths were 50m, 50m, 20m, 20m, 20m, 20m, 20m, 50m, 50m, and 50m, respectively, and the cumulative mining depths were 50m, 100m, 120m, 140m, 160m, 180m, 200m, 220m, 270m, 320m, and 370m, respectively. The coal seam was nearly horizontal, and the dip angle of the strata was generalized to 0°. Based on the stratigraphic overburden structure, three survey lines were laid out on the model. Survey line 1 was located at the top interface of the coal seam, survey line 2 was located at the top interface of the mudstone 49m away from the top interface of the coal seam, and survey line 3 was located at the top interface of the medium-grained sandstone 99m away from the top interface of the coal seam. The three survey lines started 50m from the left and ended 550m from the right, with 40 measuring points spaced 12.82m apart, and the survey lines were 500m wide from left to right. The variation curves of the lower basic top load and the upper hard rock bearing pressure were obtained by collecting data. Figures 3-6 ).

[0078] Fourth, construct the distribution functions of the upper hard rock bearing pressure and the lower basic top load after the deterioration of the weakly cemented strata:

[0079] By analyzing the support action and load distribution curves using basic statistical principles, the basic form of the curve function is determined as follows:

[0080]

[0081] In the formula, E 0 is f The initial slope of (x).

[0082] By using grey relational analysis and Pearson correlation coefficient, the influence of variable factors on each parameter in the function is quantitatively compared, the main controlling factors of the curve distribution pattern are explored, the physical meaning of the parameters in the bearing pressure and load distribution curve function is explained from the perspective of rock mechanics and elastoplastic mechanics, and the bearing pressure and load distribution pattern function related to the deterioration properties and formation occurrence characteristics of weakly cemented strata is constructed.

Claims

1. A method for constructing the distribution function of bearing pressure and load on weakly cemented strata, characterized in that, Includes the following steps: Step 1: Obtain the clay mineral composition and content, microstructure and porosity of the weakly cemented strata under natural conditions, as well as the physical and mechanical properties of the weakly cemented strata and its upper and lower strata under natural conditions; determine the microstructure and water absorption of the weakly cemented strata samples deteriorated by water under different water absorption times, rock strength and deformation parameters under different water absorption, rock strength and deformation parameters and disintegration under different loads, and water absorption under different porosities and clay mineral contents. Step 2: Based on the parameters and physical and mechanical properties obtained in Step 1, build an indoor physical model test platform for similar materials of mining-induced weak cemented strata with a "hard-soft-hard" overburden structure, and collect data on the distribution of hard rock bearing pressure and lower basic top load on the deteriorated weak cemented strata during the simulation test to obtain the distribution curves of hard rock bearing pressure and lower basic top load on the similar material physical model with mining. Step 3: Based on the distribution curve obtained in Step 2, calibrate the numerical simulation calculation parameters for the mining-induced weakly cemented strata, and conduct numerical simulation calculations under different influencing factors to obtain the distribution data of the bearing pressure of the upper hard rock layer and the lower basic top load of the mining-induced weakly cemented strata under different influencing factors: Step 4: Constructing the distribution functions of bearing pressure and underlying basic top load of the upper hard rock layer after the deterioration of the weakly cemented strata: Based on the distribution data obtained in Step 3, the bearing pressure and load distribution curves are analyzed using basic statistical principles to determine the basic form of the curve function: In the formula, when x < 0, it is the function expression for the peak value of the support pressure and load distribution curve, where n = 1; when x < 0, it is the function expression for the peak value of the support pressure and load distribution curve. The expression for the peak value of the support pressure and load distribution curve is given, where n=2, and L is half the length of the goaf. A , B The coefficient of determination for the trend of the influencing factor function; x It is a function variable, namely the recovery footage; x cn This represents the variable value at the peak.

2. The method for constructing the distribution function of bearing pressure and load on weakly cemented formations as described in claim 1, characterized in that, The physical and mechanical properties obtained in step 1 include compressive strength, tensile strength, Poisson's ratio, elastic modulus, internal friction angle, and cohesion.

3. The method for constructing the distribution function of bearing pressure and load on weakly cemented formations as described in claim 1, characterized in that, In step 2, the topsoil layer above the "hard-soft-hard" overburden structure is laid with a mixture of loess and water, and the "hard-soft-hard" overburden structure is laid with a mixture of sand, gypsum and water. The "soft" weak cemented strata are mixed with clay for laying. By measuring the physical and mechanical properties of the paving material for the "hard-soft-hard" overburden structure strata under different proportions, the paving material proportion that conforms to the physical and mechanical properties of the weakly cemented strata and its upper and lower strata in step 1 is determined.

4. The method for constructing the distribution function of bearing pressure and load on weakly cemented formations as described in claim 1, characterized in that, In step 2, based on the clay mineral composition and content, microstructure and porosity of the weakly cemented strata obtained in step 1, as well as the microstructure and water absorption at different water absorption times, rock strength and deformation parameters at different water absorption rates, rock strength and deformation parameters and disintegration under different loads, and water absorption at different porosities and clay mineral contents, water is injected into a physical model of similar materials to simulate the test process.

5. The method for constructing the distribution function of bearing pressure and load on weakly cemented formations as described in claim 1, characterized in that, In step 3, the numerical simulation calculation of the weakly cemented strata is carried out by constructing a coal seam mining model using discrete element numerical simulation software. The overburden structure and its physical and mechanical properties are consistent with the physical model of similar materials in step 2. The numerical simulation calculation parameters are calibrated by the test results of the physical model of similar materials in step 2, so that the numerical simulation calculation results are consistent with the test results of the physical model of similar materials.

6. The method for constructing the distribution function of bearing pressure and load on weakly cemented formations as described in claim 1, characterized in that, The different influencing factors in step 3 include the clay mineral content, porosity, thickness, and bedrock thickness of the weakly cemented strata.

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