Height Of Water-conducting Fractured Zone Research Articles

Height Prediction of Water-Conducting Fracture Zone in Jurassic Coalfield of Ordos Basin Based on Improved Radial Movement Optimization Algorithm Back-Propagation Neural Network

The development height of the water-conducting fracture zone (WCFZ) is crucial for the safe production of coal mines. The back-propagation neural network (BP-NN) can be utilized to forecast the WCFZ height, aiding coal mines in water hazard prevention and control efforts. However, the stochastic generation of initial weights and thresholds in BP-NN usually leads to local optima, which might reduce the prediction accuracy. This study thus invokes the excellent global optimization capability of the Improved Radial Movement Optimization (IRMO) algorithm to optimize BP-NN. The influences of mining thickness, coal seam depth, working width, and hard rock lithology proportion coefficient on the height of WCFZ are investigated through 75 groups of in situ data of WCFZ heights measured in the Jurassic coalfield of the Ordos Basin. Consequently, an IRMO-BP-NN model for predicting WCFZ height in the Jurassic coalfield of the Ordos Basin was constructed. The proposed IRMO-BP-NN model was validated through monitoring data from the 4−2216 working faces of Jianbei Coal Mine, followed by a comparative analysis with empirical formulas and conventional BP-NN models. The relative error of the IRMO-BP-NN prediction model is 4.93%, outperforming both the BP-NN prediction model, the SVR prediction model, and empirical formulas. The results demonstrate that the IRMO-BP-NN model enhances the accuracy of predicting WCFZ height, providing an application foundation for predicting such heights in the Jurassic coalfield of the Ordos Basin and protecting the ecological environment of Ordos Basin mining areas.

Elastic wave prospecting of water-conducting fractured zones in coal mining

In order to understand the development law of water-conducting fractures in overlying strata during the mining process of coal seam, an elastic wave exploration method based on key stratum theory is proposed to predict the height of water-conducting fracture zone. Taking Yushen mining area as the background, the development and evolution of fractures and the three-dimensional distribution characteristics of water-conducting fracture zone are studied by combining well-ground microseismic monitoring, high-density three-dimensional seismic exploration, borehole investigation, FLAC3D numerical simulation and similar physical simulation tests. The results indicate that the trial mining face's fracture-to-coal ratio ranges from 25.86 to 30.76, with the maximum fracture-to-coal ratio near the cutting eye at 30.76 and the minimum in the central portion of the trial mining face at 25.86. The primary characteristics of rock mass fracture distribution in the mined area are the development of fractures predominantly along high-angle and even vertical bedding planes. Within the fracture zone, fractures increase from top to bottom, with high-angle fractures developing in the lower section and high-angle and horizontal fractures developing simultaneously in the upper section. The water-conducting fracture zone undergoes a developmental process from inception to development, reaching its maximum height, and eventually stabilizing as coal seam mining progresses, overlying rock subsides, strata separation, and damage formation. The three-dimensional shape of the water-conducting fracture zone in the roof of the Yushen mining area exhibits a morphological pattern where the height of the fracture zone gradually decreases from the cutting eye towards the goaf. It also transitions from high to low along both sides and from the periphery towards the interior of the working face. In the trend and strike directions, it exhibits saddle-like characteristics. By comparing the monitoring results, the rationality of the elastic wave prospecting method for predicting the height of water-conducting fracture zones based on critical layer theory was verified. This research holds significant reference value for coal mining under similar geological conditions, especially in terms of water preservation during mining operations.

Water-richness evaluation method and application of clastic rock aquifer in mining seam roof

Clastic rock aquifer of the coal seam roof often constitutes the direct water-filling aquifer of the coal seam and its water-richness is closely related to the risk of roof water inrush. Therefore, the evaluation of the water-richness of clastic rock aquifer is the basic work of coal seam roof water disaster prevention. This article took the 4th coal seam in Huafeng mine field as an example. It combined the empirical formula method and generalized regression neural network (GRNN) to calculate the development height of water-conducting fracture zone, determined the vertical spatial range of water-richness evaluation. Depth of the sandstone floor, brittle rock ratio, lithological structure index, fault strength index, and fault intersections and endpoints density were selected as the main controlling factors. A combination weighting method based on the analytic hierarchy process (AHP), rough set theory (RS), and minimum deviation method (MD) was proposed to determine the weight of the main controlling factors. Introduced the theory of unascertained measures and confidence recognition criteria to construct an evaluation model for the water-richness of clastic rock aquifers, the study area was divided into three zones: relatively weak water-richness zones, medium water-richness zones, and relatively strong water-richness zones. By comparing with the water inrush points and the water inflow of workfaces, the evaluation model's water yield zoning was consistent with the actual situation, and the prediction effect was good. This provided a new idea for the evaluation of the water-richness of the clastic rock aquifer on the roof of the mining coal seam.

Prediction and Application of the Height of Water-Conducting Fracture Zone in the Composite Roof: A Case Study of Jinxinda Coal Mine

The water inrush from the roof of the coal mine is closely related to the movement failure of overburdened rock and the height of the water-conducting fracture zone. In this work, based on the research background of water disaster prevention and control of the No. 2 coal seam roofs in Jinxinda Coal Mine, the stability characteristics of overlying rock in the working face are analyzed through combining theoretical analysis and numerical simulation. According to the theory of key strata, the fracture conditions of hard rock and soft rock are analyzed, and the maximum height of the water-conducting fracture zone in the 201 working face is calculated to be 35.72 m. The crack evolution law of composite roofs was simulated and analyzed using discrete element software. It was found that the basic roof (4.50 m thick) and the fine sandstone (7.64 m thick) are the two inferior key strata, and the maximum development height of the water-conducting crack is 36 m, which is basically consistent with the field measured results. Transient electromagnetic exploration technology was used to detect the working face, and nine abnormal areas were found. In order to prevent the influence of water disasters in abnormal areas during mining, drilling verification is carried out in abnormal areas. According to the analysis of drilling verification, there are no water disasters in the geophysical anomaly area, but the management of the roof after mining should be strengthened during mining. The expected research results not only enrich the rock formation control theory and roof water inrush mechanism; they also have important practical significance in guiding the safety production of a coal mine.

Study on the failure characteristics of overburden and the evolution law of seepage field in deep buried thick coal seam under aquifers

Water inrush at roof area seriously affects the safety of coal mines. The characteristics of aquifer and aquiclude at Wutongzhuang Mine are analyzed. Considering the effect of seepage field, a formula for calculating the height of water-conducting fractured zone (HWCFZ) in deep buried thick coal seam mining is derived. A damage-seepage coupling model with rock porosity and damage factor as independent variables is established. FLAC3D is re-developed by using FISH language, and the fluid–solid coupling calculation model of deep buried thick coal seam mining is established. The evolution law of the plastic zone, seepage field and water-conducting fractured zone (WCFZ)of the overburden in the gob with the advancement of the working face is analyzed, the main conclusions are as follows: With the continuous advancement of the working face, the distribution shape of the plastic zone and seepage field has changed from a trapezoidal to a saddle shape; when the working face reaches full mining, the maximum heights of the caving zone, fractured zone and HWCFZ are 24 m, 113 m, and 123 m, respectively; The 50 m-thick sandy shale aquifer is penetrated by the WCFZ, and the WCFZ on the side of the working face above the gob is the main water channel when the working face is advanced to 220 m. The on-site monitoring results showed that mine water inflow is not affected by surface rainfall and the 50 m-thick sandy shale is successively connected by the WCFZ. The results of comprehensive research showed that the HWCFZ cannot be calculated by traditional formulas when mining deep buried thick coal seams.

Study on Height Development Characteristics of Water-Conducting Fracture Zone in Fully Mechanized Mining of Shallow Thick Coal Seam under Water

The height of water-conducting fracture zone (HWCFZ) is one of the important technical parameters for water-preserved coal mining. The purpose of this paper is to acquire information about the height development characteristics of water-conducting fracture zone (WCFZ) in fully mechanized mining of shallow thick coal seam under water body in western mining area of China. The 91,105 fully mechanized mining face of Daheng coal mine under composite water body was taken as the research object, the development height, morphological characteristics, development and evolution process of WCFZ in working face mining were studied through underground up-hole water injection method by intervals, borehole TV and numerical simulation. The results show that the HWCFZ in 91,105 fully mechanized mining face is 52.7~53.6 m, and the fracture mining ratio is 12.55~12.76. The final development form is saddle-shaped with “large at both ends and small in the middle”. It is accurate and reliable to determine the development characteristics of overburden fractures and the HWCFZ by the field measurement of the combination of underground upward hole segmented water injection method and borehole TV. The development height of the water-conducting fracture zone obtained by numerical simulation is consistent with the field measured results. The development and evolution of the height of WCFZ presents four stages: “development–slow increase–sudden increase–stability”. When the WCFZ develops to a certain layer, the cracks generated by the weak strata in the fracture zone of overlying strata on the working face will automatically close with the advancement of the working face, resulting in “bridging phenomenon”, which inhibits the further development of the WCFZ. That is, the existence of soft rock with a certain thickness in overburden will become the key inhibiting layer for the development of WCFZ, effectively blocking the communication between water-conducting fracture and overlying aquifer. The research results are intended to provide guidance for the implementation of water preserving mining and ecological environment protection in ecologically fragile areas in western China.

Determination of the Height of Overburden Water-Conducting Fracture Zone in 215102 Working Face of Yue Nan Coal Mine

In order to extract gas accurately in Yue Nan coal mine and prevent gas over limit and gas accidents, a combination of theoretical analysis and numerical simulation was used to investigate the height of the overburden caving zone and fracture zone in the working face, using 215102 working face as the engineering background. The results show three key strata in the 215102 working face, namely siltstone, sandy mudstone, and sandy mudstone. The empirical formula’s calculation results are in good accord with the findings of the theoretical analysis, which indicates that the height of the water-conducting fracture zone created by mining in 215102’s working face is 87.35 m. The plastic zone, stress distribution and displacement variation of the model overburden of the working face were analyzed separately in the numerical simulation. The results of the plastic zone simulation show that the caving zone’s maximum height is about 15.96 m, and the fracture zone’s maximum height is approximately 82.39 m. The stress distribution shows that the caving zone’s greatest height is around 13.65 m, while the fracture zone’s maximum height is roughly 77.24 m. The amount of overburden subsidence proves that the caving zone’s maximum height of about 10.08 m, and the fracture zone’s maximum height of approximately 82.69 m. The height of the overburden caving zone and fracture zone of 215102 working face are ultimately found to be 14.02 m and 76.42 m, respectively, based on theoretical analysis, empirical formula calculation, and numerical simulation findings.

Research on the Development Law of Water-Conducting Fracture Zone in the Combined Mining of Jurassic and Carboniferous Coal Seams

The accurate prediction of the height of the water-conducting fracture zone is essential for the prevention of roof damage by water disasters in coal mines. The development law of water-conducting fracture zone in combined mining of Jurassic and Carboniferous coal seams is different from that of previous research results. This study constructed an engineering geomechanics model to carry out material simulation and numerical simulation. The changes of stress, displacement, and fracture propagation were analyzed and compared with the results of formula calculation and field measurement, revealing the combined action of Jurassic and Carboniferous coal seams on the development law of water-conducting fracture zone. The results show that: (1) stress concentration is formed in the middle of the goaf in Jurassic coal seam, resulting in the high height of water-conducting fracture zone and the fracture “closed”; (2) the mining of Carboniferous coal seams caused the second subsidence of Jurassic goaf, and closed fracture “activated”; (3) the height of the water-conducting fracture zone obtained by the empirical formula is small, which is quite different from the actual situation. These research results are of significance for determining the height of the water-conducting fracture zone in Jurassic and Carboniferous coal seams during combined mining and the prevention of coal roof water hazards.

Quantitative evaluation and planning method of shallow surface water response in multi-face mining—Case study regarding Zhuanlongwan coal mine

Multi-area coal extraction can cause aquifer depressurisation and subsurface dewatering, in which the mechanism of overburden permeability and shallow water responding to underground gob keeping extending is the key. This paper focuses on the water resource protection in ecologically fragile mines in western China. With the equivalent permeability coefficient(EPC) and subsurface hydraulic responses as basis, the paper conducted mathematical statistics and theoretical analysis to construct a decision-making model for multi-panel longwalls and a longwall design methodology that considered subsurface water stability. Firstly, fitting the field measurement data produced an empirical equation regarding the height of water-conducting fracture zone (HWCFZ), and a model for quantifying the correlation between the damage values of effective soil units and effective bed rock units was established, by which the EPC was quantified. Secondly, the paper developed a subsurface water quantification model that considered infiltration recharge to study the subsurface piezometric evolution with varying geometry, range, and number of longwall units, further revealing the subsurface water responses to varying mining zones. Finally, a model for evaluating the subsurface water depressurisation was proposed and applied to study the subsurface water responses to multi panels in Zhuanlongwan Coal Mine. The longwall design obtained via the decision-making model agreed with the piezometric variation in the mine, suggesting that this research can provide theoretical and technical supports for green mining.

Comprehensive Water Inrush Risk Assessment Method for Coal Seam Roof

In order to prevent coal mine water inrush accidents, it is necessary to appropriately assess the water abundance of coal mines based on drilling and geophysical data. This paper studied a comprehensive risk assessment method of water inrush. First, a water inrush risk index was proposed based on the analytic hierarchy process-entropy method (AHP-EM) and the water-rich structure index was proposed based on the geological data coupled calculation, then weighted two indices above which established the comprehensive water inrush risk assessment method. Secondly, eight factors were chosen as risk control factors of water inrush: core recovery, aquifer thickness, distance from the indirect aquifer to the coal seam, aquiclude thickness, height of water-conducting fracture zone, sand-mud ratio, total layers of aquifer and aquiclude, and the equivalent thickness of sandstone. Finally, the No. 2 coal seam of Dahaize coal mine was taken as the research object, the factors were calculated, and a comprehensive water inrush assessment model was constructed. With site investigation and observation, the water inrush risk assessment model of the No.2 coal seam roof is consistent with the actual mining situation, which verifies the validity of the model. In addition, this method was used to evaluate the water-richness of the weathered bedrock fractured aquifer in the Zhangjiamao coal mine. The practical application of the two mines has verified the generality of the approach. The research could provide scientific assistance for mine water hazard mitigation and mining safety.

Numerical simulation of abnormal roof water-inrush mechanism in mining under unconsolidated aquifer based on overburden dynamic damage

Separation layer poses a potential threat to safety mining under an unconsolidated aquifer. A dynamic load will be generated when the upper stratum in the separation layer is broken, leading to an abnormal roof water-inrush. To explore this phenomenon, the 7130 coalface in Qidong coalmine is selected as an example, and the dynamic damage analysis is performed for overburden rock during mining by numerical simulation. A model is presented based on the continuum damage mechanics for simulating the failure of overburden rock under the dynamic load. A new dynamic damage variable is introduced into the model. Subsequently, a user-defined (U-D) model is implemented under the C++ language environment in FLAC-3D. The U-D model is applied to study the abnormal roof water-inrush of the 7130 coalface, compared with the Mohr-Coulomb (M−C) model in FLAC-3D. The research results show that a larger dynamic failed zone than the M−C model under the dynamic load exists. Additionally, the height of water-conducting fractured zone (WCFZ) by the U-D model is 68.6 m and conforms to the in-situ data of 56.9–80.2 m, while the height of WCFZ by the M−C model is only 35.6 m. It can be inferred that the effect of overburden dynamic damage can lead to the upward development of WCFZ, resulting in disasters of roof water-inrush. The study will be helpful to the prevention and control of roof water-inrush.

Characteristics of Overburden Failure and Fracture Evolution in Shallow Buried Working Face with Large Mining Height

In order to solve the issues of uncertain overburden failure height and water loss at the Daliuta coal mine, the collapse characteristics of overburden and the development height of water-conducting fractured zone were studied by using physical modeling, FLAC 3D numerical simulation, and field observation, which were used to verify each other. In order to quantitatively analyze the distribution characteristics of fracture rate of overlying rock mass in goaf, the overburden collapse image was binarized. The results showed that: (1) the failure characteristics of overburden in goaf obtained by the three research methods were roughly consistent, and the reliability of the results was high. The overburden failure height of No. 5−2 coal with large mining height was 137.32–153 m, which was 20.8–23.2 times the mining height. (2) The repeated mining of No. 5−2 coal intensified the further failure of the disturbed rock mass in the No. 2−2 coal goaf. (3) In the horizontal direction of the goaf, the fracture rate of rock mass was distributed in the shape of “saddle”. In the longitudinal direction of the goaf, the rock mass fracture rate decreased in a logarithmic function with the increase of the height from the mining coal seam. Overall, the conclusions are of engineering significance for accurately adopting water resources protection mining technology and reducing mine water inrush disasters.

Multiscale Intelligent Inversion of Water-Conducting Fractured Zone in Coal Mine Based on Elastic Modulus Calibration Rate Response and Its Application: A Case Study of Ningdong Mining Area

Abstract Water-conducting fractured zone is the direct inducement of water inrush, water losing, and environmental deterioration in coal mines. How to predict the height of water-conducting fractured zone economically and accurately has always been the research difficulty of water-preserved mining. The paper selects the Meihuajing coal mine in Ningdong mining area as the engineering background. Firstly, transform the distribution law of the water-conducting fractured zone into a deterioration mechanism of coal-rock strength under the action of water-rock. Through laboratory tests, the water-rock coupling degradation law of rock mass under uniaxial action is revealed, and an intelligent statistical model of damage rate response under different water content is proposed. Secondly, based on the cross-scale elastic modulus calibration principle and the rate response intelligent statistical model proposed above, the borehole elastic modulus instrument is used to quantitatively characterize the strength characteristics of elastic modulus rate response law and field lithological parameters. Finally, based on the 18 samples of the water-conducting fractured zone, a height prediction model of a water-conducting fractured zone based on the measured value of elastic modulus is proposed by using the method of PSO-SVR. Taking R2 and RMSE as evaluation indexes, the error comparison between PSO-SVR and the empirical formula is carried out. Research indicates that, compared with the empirical formula, R2 of the PSO-SVR model increased by 18.3% and RMSE decreased by 92.7%. The predicted value of the PSO-SVR is consistent with the measured value, which significantly improves the prediction accuracy of the height of the water-conducting fractured zone. It provides a theoretical basis and technical support for the coordinated development of safe and efficient development of coal and ecological protection in Ningdong mining area.

Determination of Water-Proof Coal (Rock) Pillar Height in Mining Coal Seam Group under Water-Bearing Rock Stratum

In order to determine the reasonable height of water-proof coal (rock) pillar when mining multiple coal seams under aquifer, this paper analyzes the expansion height of water-conducting fracture zone when coal seams mining. Considering the expansion law of water-conducting fracture zone in coal seams mining, two schemes of coal seams mining in upper and lower groups and one-time mining of all coal seams are designed for comparative analysis, and the height of water-proof coal (rock) pillar is determined based on the expansion height of water-conducting fracture zone. The results show that the height of water-proof coal (rock) pillar is calculated as 91.08 m when mining upper and lower groups and 105.46 m when mining all coal seams at the same time. According to UDEC numerical simulation results, the height of water-proof coal (rock) pillar is 56.08 m when mining upper and lower groups and 86.36 m when mining all coal seams at the same time. Comparing the results of theoretical calculation and numerical analysis, the maximum value is selected as the final result, and the reasonable water-proof coal (rock) pillar height is determined to be 105.46 m.

A Case Study of the Water Abundance Evaluation of Roof Aquifer Based on the Development Height of Water-Conducting Fracture Zone

In the eastern mining area of Ningxia, China, multi-layered sandstone aquifers are widely distributed in the underground. However, the water abundance of these aquifers is not clear, which brings great challenges to the prevention and control of mine water disaster. In this paper, five mining areas in eastern Ningxia were taken as the study area, and the distribution characteristics of aquifer and the mine water filling source were analyzed through the analysis of geological data and numerical simulation. Finally, the lithology influencing index (LII) was constructed, and the water abundance of the aquifer was evaluated. The results show that the sandstone aquifer III in the lower part of the Jurassic Zhiluo formation is the main water-source aquifer of the #2 coal seam in the study area, while the middle aquifer II and the upper aquifer I are indirect water-source aquifers; the areas with extremely strong and strong water abundance are Maiduoshan, Hongliu, the south of Shicaocun, southeast and southwest of Meihuajing, and the central and southern areas of Shuangma mining areas; when the depth of water drainage boreholes in the roof reaches the development height of the water-conducting fracture zone, the pre-drainage measures can effectively control the mining inrush water of the working face and ensure the safety production. This research is of great significance to the prevention and control of mine water disaster.

A Novel Approach for Predicting the Height of Water-Conducting Fracture Zone under the High Overburden Caving Strength Based on Optimized Processes

The height of water-conducting fracture zones (WCFZs) is vital for the prevention of water, gas, and roof accidents in coal mines. However, its dynamic evolution law and maximum height are difficult to be obtained by traditional prediction methods, especially for conditions in which there is high overburden caving strength and a thick coal seam. Therefore, taking the 150,313 fully mechanized caving working face in Yingying Coal Mine as a background, according to the principle of optimized processes, a new predicting approach based on the Brillouin optical time-domain reflectometry (BOTDR) is proposed. Firstly, we estimated the height through empirical formula calculation, theoretical analysis, and similar model simulation tests. Secondly, we studied the optimized layout of optical cables in the overburden in detail for predicting the maximum height of the WCFZ and keeping the cables in good performance during field prediction. Thirdly, we researched and optimized the borehole parameters, optical fiber selection, and the special protection measures. Finally, we applied the aforementioned optimized outcomes in the field experiment to dynamically predict the height of the WCFZ. As a result of the field experiment, the distribution characteristics of optical fiber strain, the maximum height, and the evolution law of the WCFZ were obtained through the regular monitoring of fiber strain using BOTDR. The experiment demonstrated that its maximum height is consistent with the results studied indoors. The validation and feasibility of the approach proposed in this paper were verified via the aforementioned studies. The research in this paper has good reference value and important significance for predicting the height of the WCFZ using BOTDR in coal mines with similar geological and productive conditions.

Determination of caved and water-conducting fractured zones of “two soft and one hard” unstable coal seam

The height of the development of a caved zone (CZ) and a water-conducting fractured zone (WCFZ), hereinafter “CZ and WCFZ”, in mining of soft coal with a soft mine floor, hard mine roof and different thicknesses of the coal seam, hereinafter “two soft and one hard” unstable coal seam, is of interest in the long wall coal mining. An observation borehole was drilled above a coal seam with an average thickness of 4.0 m. By using borehole imagery technique and comparing the borehole images at different distances from the working face, the height of “CZ and WCFZ” at the working face is calculated under the condition of insufficient mining. Based on field observations, a 3D numerical model is developed under the condition of full mining, the height of CZ is calculated to be 14.4 m and the height of WCFZ calculated to be 67.0 m. The numerical model also shows changes in the vertical stresses in the overburden strata above the roof of the coal seams and it is related to the development of the “CZ and WCFZ”. At the same time, based on the key strata theory and multiple linear regression, the height of WCFZ in the working face of this case study is predicted to be 67.0 m and 64.8 m respectively, which is close to the numerical simulation results. At the same time, 30 groups of measured data are collected to analyze the main factors affecting the WCFZ, and the influence of different lithology characteristics of overburden strata on the WCFZ is mainly discussed. The results show that the height of WCFZ is hard–hard > hard–soft > soft–hard. The results provide important practical guidelines for the prevention and control of roof water hazards in coal mine thus improving the safety of mining.

Study on “Two Zone” Development Height of Overburden Rock in Fully Mechanized Face with Large Mining Height

In terms of the problems of the development height of the “two zones” of overburden in the fully mechanized mining face was difficult to predict, taking the 31303 working face in Chahasu coal mine as an example, methods of empirical formula, leakage of drilling fluid and borehole colour TV were used for prediction and exploration. On the basis, the concept of empirical formula error was proposed, and the error rate predicted by slicing mining and fully mechanized caving mining in thick seam was analysed. The results showed that the fracture-mining ratio and caving-mining ratio of 31303 working face were 23.67 and 5.6 respectively, that is, the development height of water-conducting fracture zone and caving zone were 106.50 m and 25.20 m respectively. The “two zones” empirical formula of thick seam slicing mining and fully mechanized caving mining deviated greatly from the predicted results of fully mechanized mining face with large mining height. The formula for calculating the error rate of empirical formula was proposed. The error rates of the empirical formulas for layered mining and fully mechanized caving mining were quantitatively analysed, which were 50% and ± 28%, respectively, indicating that the traditional empirical formula was not universal in the prediction of “two zones” of fully mechanized mining with slicing mining.

The application of short-wall block backfill mining to preserve surface water resources in northwest China

As one of main directions of green mining, short-wall block backfill mining (SBBM) could provide active control of water-conducting fractures development and strata movement. Furthermore, it could solve the problem of gangue accumulation on surface. According to the physical similarity criterion and the characteristics of SBBM technology, the protection effect for surface water resources of SBBM was studied by physical similarity simulation tests. The results of tests had shown that SBBM decreased the water-conducting fractures development caused by strata movement after coal mining, and it has a significant effect in protecting surface water resources above the working face. Therefore, based on movement characteristics of overlying strata using SBBM, a mechanical analysis model was established under SBBM for a superimposed beams in elastic foundation with extended water-conducting fractures in overlying strata, furthermore, a method to calculate the height of water-conducting fractured zone (HWFZ) in SBBM was given, and the mechanical mechanism of water-conducting fractures development in overlying strata was revealed. The calculated HWFZ after SBM was only 2.0 m according to the mechanical model, whereas the measured HWFZ of the washing fluid loss and drilling TV imaging was 6.3 m in experimental SBBM working face. The field-measured data was closely consistent with the results of the tests (7.9 m) and the mechanical calculation (2.0 m), which verified the accuracy of physical similarity simulation tests and the mechanical model. The results of the study will enhance the recovery rate of coal resources, and they have a significant for protection of the ecological environment.

Height of water-conducting fractured zone in a coal seam overlain by thin bedrock and thick clay layer: a case study from the Sanyuan coal mine in North China

The accurate determination of the height of the water-conducting fractured zone (HWCFZ) in a coal seam covered by thin bedrock and thick clay layer is crucial for aquifer protection, mine safety, and eco-environmental conservation. Using the Sanyuan coal mine in North China as a case study, theoretical analysis, numerical simulation, and field measurements were used to analyze the regularity of the HWCFZ in this area. Per mechanical theory, a geometrical model for calculating rock bending and subsidence was established. Two arcs of equal curvature and lengths and opposite curvature direction were used to fit the curve section of intermediate rock layer after bending. The theoretical method for solving the HWCFZ was given by calculating the rock layer's tensile ratio. In addition, rock failure process analysis (RFPA) software was used to simulate the development of the water-conducting fractured zone (WCFZ) during the mining process, and the HWCFZ was measured by the drilling fluid loss measurement, both which verified the feasibility of the theoretical calculation. To determine the primary controlling factors affecting the HWCFZ, the seepage characteristics and plastic properties of the Quaternary clay layer were also analyzed using laboratory tests. Results show that the Quaternary clay with a depth greater than 130 m has a permeability coefficient of E−10 m/s, a liquidity index less than 0.25, and a plasticity index more than 17, indicating the clay layer is impermeable and of great importance to inhibiting the development of WCFZ. The research can provide significant theoretical insights for effectively preventing water hazards on mine roofs.