Water-conducting Fractured Zone Research Articles

Safe feasibility of retaining sand-proof coal rock pillars in full-mechanized caving mining of extra-thick coal seam

To solve the problem of increasing the mining upper limit by reasonably setting sand-proof coal rock pillars in an extra-thick coal seam under a thick loose stratum and thin bedrock of Yangcun Coal Mine in Yanzhou Mining Area, the geological and hydrogeological conditions of working face were systematically analyzed by taking 325 Working Face in No. 3 coal mining area of the mine as the background and combining with the mining experience of its adjacent working faces. The mining grade under the water body was determined to be grade II, consistent with the conditions for retaining sand-proof coal rock pillars on the roof of coal seam. On this basis, to avoid the limitation of a single method, this paper adopts the key stratum theory, empirical formula analogy, and numerical simulation; the heights of the maximum caved zone (CZ) and the water-conducting fractured zone (WCFZ) were determined as 32.8 m and 82.0 m, respectively. The thickness of protective stratum is 16.4 m; the height of sand-proof coal rock pillars in 325 Working Face is 49.2 m; the minimum thickness of bedrock pillar in 325 Working Face is 53.1 m. Thus, full-mechanized caving mining can be carried out according to the reservation of sand-proof coal rock pillars. The comprehensive application of various methods can effectively improve the reliability and accuracy of the calculation results. The research results provide the main reference for this working face and similar working faces in Yanzhou Mining Area in the future to increase the mining upper limit and set up safe coal rock pillars according to roof sand control.

Multiple Influence Factor Sensitivity Analysis and Height Prediction of Water-Conducting Fracture Zone

To explore the influence law and sensitivity of various factors on the height of the water-conducting fracture zone, and further predict the development height of the water-conducting fracture zone, taking the field survey and collected actual measured data as the research foundation, establishing mathematical model, regression analysis, and field measurement were adopted comprehensively. Based on the Data Processing System (DPS), influence factors of the development height of the water-conducting fracture zone were analyzed. By introducing sensitivity coefficient, a sensitivity quantification mathematical model was established, and sensitivity ranking was obtained. The regression relationship between each factor and the height of the water-conducting fracture zone was obtained by single factor analysis. Based on this, the prediction formula was proposed and successfully used in the field practice. Results show that the sensitivity coefficient of mining thickness, ratio coefficient of hard rock lithology, mining depth, and length of working face was 0.75, 0.69, 0.66, and 0.58, respectively. The dispersion degree of working face length and mining depth was greater than that of ratio coefficient of hard rock lithology and mining thickness. To some extent, it also reflects that the sensitivity of working face length and mining depth to the height of the water-conducting fracture zone was the weakest, which was consistent with the previous conclusions. Using the multiple regression mathematical model, a nonlinear statistical relationship between the height of the water-conducting fracture zone and ratio coefficient of hard rock lithology, mining thickness, working face length, and mining depth was obtained. This research provides some scientific basis and guidance for safe and efficient underwater mining.

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.

Formation Mechanism and the Height of the Water‐Conducting Fractured Zone Induced by Middle Deep Coal Seam Mining in a Sandy Region: A Case Study from the Xiaobaodang Coal Mine

The height of the water‐conducting fractured zone (WCFZ) is a basic parameter related to water protection in coal mines and is also crucial for aquifer protection and mine safety. In order to accurately detect the height and shape and reveal the formation mechanism of the WCFZ, which is caused by middle‐deep coal seam mining in a sandy region, the 112201 coalface at the 1# coal mine of Xiaobaodang was taken as a case study. Filed measurements including fluid leakage, borehole TV, and similar simulation were adopted to analyze the regularity of the WCFZ in this area. The detection results of field measurements showed that the maximum height of the WCFZ was 177.07 m in a borehole near the open‐off cut, and the ratio of the height of the water‐conducting fractured zone divided by the mining thickness was 30.53. The WCFZ acquired an inward‐convergent saddle shape, which was inclined to the goaf. The saddle bridge was located at the boundary of the goaf, and the saddle ridge was located at the center of the goaf. Also, through analyzing the results of similar simulations, we found that, in the process of mining, separation cracks and the beam structure were the main forms of overburden disturbance transmitting upward and ahead of mining, respectively. The main cause of the increase in height of the WCFZ was the connection of the separation cracks and vertical cracks caused by fractures of beam structures. The development of the WCFZ was divided into five stages: incubation stage, development stage, rapidly increasing stage, slowly increasing stage, and stable stage. Moreover, the duration of each stage was related to the lithology and mining technology. This research can provide significant theoretical insights for the prediction of the WCFZ, enabling the prevention of water hazards on mine roofs and assisting with water resources protection.

Quantitative Characterization of Overburden Rock Development Pattern in the Goaf at Different Key Stratum Locations Based on DEM

The overburden rock mining fissures are the main cause of coal spontaneous combustion, gas pooling, and mine water inrush caused by goaf air leakage. Rapid and accurate determination of the development and evolution law of mining fissures have great significance for the application of coal spontaneous combustion prevention and control, gas disaster prevention and control, and water damage prevention and control measures. In this paper, a preliminary judgment of the development height of the water‐conducting fracture zone is made based on the theoretical analysis, and the physical model size of the numerical simulation is determined according to its judgment result. It is judged that the development height of its water‐conducting fracture zone is between 49 and 64.2 m, which is in line with the actual results. Based on this, a three‐dimensional solid model was established in PFC (Particle Flow Code) software to analyze the fissure development pattern of the overburden rock and the development height of the water‐conducting fracture zone when the main key stratum of the rock seam is in different positions by simulating the excavation process of the coal seam. The results show that when the main key stratum is located in the “original crack belt boundary,” the development of water‐conducting fracture zone is significantly inhibited; when the main key stratum is located in the “original caving zone,” the water‐conducting fracture zone is fully developed, and the crack belt finally develops to the top of the model. In order to verify the accuracy of the numerical simulation, similar material simulation experiments were performed under the same scheme. The results are consistent with the numerical simulation conclusions, effectively verifying the accuracy of the numerical simulation. Finally, the extraction of porosity of the goaf was carried out based on numerical simulation, and the permeability zoning of the goaf was performed; the results show that the development of the water‐conducting fracture zone has a significant influence on the permeability of the mining area, and the more fully developed the fissure is, the greater is its permeability. In this paper, the fissure development law in the goaf under different key stratums is explored by various research stratums, and the results show a good consistency, which provides a scientific basis for the prevention and control of disasters such as water inrush and coal and gas outburst in mines, and provides theoretical guidance for safe mining.

Study of roof water inrush forecasting based on EM-FAHP two-factor model.

To solve the problem of predicting and evaluating coal mine roof water inrush accidents, based on the background of Hongliu coal mine, the relevant weight values of the main control factors of water inrush were determined based on the water-richness index method, combined with the entropy method and FAHP two-factor method. The grid processing function of GIS and the kriging interpolation method are used to draw thematic maps of the main controlling factors, and the weight values of the water permeability indicators are coupled into the GIS. The FLAC3D numerical simulation software is used to analyze the water-conducting fracture zone after the mining of the Hongliu Coal Seam numerical simulation of development and water pressure distribution changes. The results show that the permeability hazard zoning map obtained by the EM-FAHP two-factor model is in line with the results of the damage height and the increased water pressure zone obtained by the numerical simulation.

A Model to Estimate the Height of the Water-conducting Fracture Zone for Longwall Panels in Western China

Accurate prediction of the height of the water-conducting fracture zone (WCFZ) is very important for safe coal mining, water resource storage, and protecting the environment. The proportion coefficient of hard rock and the actual height of the top caving coal were defined to predict the height of the WCFZ more accurately. A multivariate regression analysis method was adopted to establish a nonlinear model for predicting the height of the WCFZ based on various factors, including mining height, panel width, proportion of hard rock, mining depth, and extraction rate. Investigations conducted using data from western China show that the ratio of the height of the WCFZ to the mining height obtained using the actual height of the top caving coal is ≈ 20, which is consistent with the distribution of the longwall full-seam mining technology. The values predicted by the multiple regression model in this study are closer to the measured values than those derived using traditional empirical equations, with a relative error < 10%. The ratio of the height of the WCFZ to mining height was generally higher in the western mining area than in the eastern mining area, due to the increase in panel dimensions and harder lithology. However, the influences of extraction rate and mining depth on the development of the WCFZ were found to be relatively weak. Finally, the model accurately predicted the height of the WCFZ in panel 12,511 of the Bulianta coal mine.

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.

Principle of using borehole electrode current method to monitor the overburden stratum failure after coal seam mining and its application

The overburden stratum of the working face mined using caving method will be damaged after mining. Mastering the development heights of the caving zone and the water-conducting fracture zone is of great significance for the safe mining. Theoretical analysis showed that the electrode current is inversely proportional to the stratum resistivity. Changes of the electrode current can reflect the changes of the stratum resistivity. In this study, we elaborated the principle of electrode current method and proposed the method and construction procedure of using the borehole electrode current method to monitor the overburden stratum damage. Before mining the coal seam of a certain working face, two boreholes with different elevation angles were drilled to the roof of the coal seam working face in the adjacent roadway, and the on-site experiment of overburden stratum deformation and failure caused by coal mining was carried out. Analysis of the measured data showed that the electrode current is very sensitive to the influence of the caving zone with amplitude dropping by more than 90%. The electrode current of the fracture zone changes more dramatically than the apparent resistivity. With the gradual advancement of the working face, the currents of the borehole electrodes in the caving zone and the fracture zone generally show a trend of gradual decrease with good stability. The on-site application of the method shows that the current or current ratio of the borehole electrodes can directly reflect the resistivity of stratum near each electrode, and the height of the caving zone and the water-conducting fracture zone can be determined. Overall, using the borehole electrode current method to monitor overburden stratum damage is effective, and the data changes are stable and easy to explain. The method does not require complex data inversion and has low requirement for data quality. Thus, it is suitable for working face with complex overburden stratum.

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.

Numerical simulation and experimental study on floor failure mechanism of typical working face in thick coal seam in Chenghe mining area of Weibei, China

The hydrogeological conditions of Weibei coalfield in China are complex; the main mining No. 5 coal seam is seriously threatened by Ordovician limestone karst water disaster at the bottom of coal measures. Chenghe No. 2 Mine is a typical example. With the increase of mining depth, confined water pressure increases year by year. To find out the law of floor deformation and failure caused by No. 5 coal seam mining in Chenghe No. 2 Coal Mine, this paper takes 24,508 working face of Chenghe No. 2 Coal Mine as engineering geological background, and carries out research by numerical simulation and field test methods. The stress field, displacement field distribution law and plastic zone evolution characteristics of No. 5 coal seam roof and floor varying with the advancing degree of mining face are obtained by simulation calculation. The progressive failure process of the whole floor stratum is reproduced dynamically, and the development height of the water conducting fracture zone of overburden is given. The maximum failure depth of the floor occurs at the mining distance of about 1.5 times the mining width, at which time “the saddle shape” supporting pressure arch reaches its maximum. At the same time, the multi-point separated layer displacement meter is used to carry out field measurements. The results show that the maximum failure depth of floor occurs in the goaf, and the maximum range of the relative displacement of the floor is 8.0–8.5 m, which is close to − 6.1 m from the coal mining surface, consistent with the results of the numerical simulation. Comprehensive analysis shows that the maximum failure depth of coal seam floor in Chenghe No. 2 Coal Mine is 8.3 m. The conclusion provides a favorable basis for the rational formulation of water disaster control countermeasures. It provides reference and experience for mining under safe water pressure of aquifuge for prevention and cure water of similar working face in Chenghe mining area in the future.

Predicting the Water-Conducting Fracture Zone (WCFZ) Height Using an MPGA-SVR Approach

Mine water that inrushes from coal-roof strata has always posed a substantial threat to mining activities every year. Therefore, an accurate prediction of the water-conducting fracture zone (WCFZ) height in the mining overburden strata is of great significance for the prevention and control of mine water accidents. The support vector regression (SVR) is proposed to predict the height of the WCFZ based on the mining depth, hard rock proportional coefficient, mining thickness and length of the working face. Simultaneously, the multi-population genetic algorithm (MPGA) is employed to search for the optimal SVR parameters. The MPGA-SVR model is trained and tested with a total of 69 collected data samples, and it is also applied to a field test. The accuracy and stability of the model were measured by the mean squared error and correlation coefficients. The obtained results show that the MPGA-SVR model achieves a higher accuracy and stability than the traditional empirical formula and genetic algorithm (GA)-SVR model. In terms of the process for optimizing the SVR parameters, the MPGA can find the optimal parameters more quickly and accurately, and it can effectively overcome the problem of premature and slow convergence of the genetic algorithm (GA). The proposed model improves the prediction accuracy and stability, which will help to avoid accidents caused by the inrush of water inrush in mining overburden strata and protect the ecological environment of the mining area.

Physical Simulation of the Water-Conducting Fracture Zone of Weak Roofs in Shallow Seam Mining Based on a Self-Designed Hydromechanical Coupling Experiment System

Due to inappropriate mining practices, water-conducting fracture zones can develop in an aquifer, not only destroying the surface-water environment but also causing water inrush, even hurting or killing workers. To avoid such disasters, investigating and simulating the evolution mechanism of water-conducting fractures are becoming a research focus in mining engineering, especially regarding the organisation and development of fractures. Our work mainly involved the design of low-strength analogous materials and the simulation of fracture evolution for weak-roof problems in shallow seam mining based on a self-built experimental hydromechanical coupling system. The experimental results show that the vertical stress in the roof increases first as the working face approaches and finally decreases to near its initial value as the working face passes. The relationship between fracture depth and coal-seam excavation distance is obviously nonlinear. The leakage velocity of surface water remains stable in the early stage of excavation and increases when the fracture develops through the main aquifuge. The maximum fracture depth is 76.18 m for the Yili coal mine with weak roofs and shallow coal seams. In addition, we numerically simulated and verified the evolution patterns with the FLAC3D platform. The simulated fracture depth of the Yili coal mine agreed with the in situ borehole observation very well and was more accurate than the output of the empirical formula. Our work provides new methods and relevant data for research on the evolution of water-conducting fractures in weak roofs during shallow seam mining.

Formation mechanism and height calculation of the caved zone and water-conducting fracture zone in solid backfill mining

To study the heights of the caved zone and water-conducting fracture zone in backfill mining, the failure mechanism of strata during backfill mining was analyzed, and a method for determining the heights of the two zones was proposed based on key strata theory. The movement and failure regularity of the strata above the backfilling panel were revealed through numerical simulation. Considering the geologic conditions of the CT101 backfilling panel, the height of the fracture zone was determined using the proposed method along with empirical calculation, numerical simulation, and borehole detection. The results of the new calculation method were similar to in situ measurements. The traditional empirical formula, which is based on the equivalent mining height model, resulted in large errors during calculation. The findings indicate the reliability of the new method and demonstrate its significance for creating reference data for related studies.

Study on the Height of the Mining-Induced Water-Conducting Fracture Zone Under the Q2l Loess Cover of the Jurassic Coal Seam in Northern Shaanxi, China

A method to calculate the height of a water-conducting fractured zone (HWCFZ) was developed based on the plate and shell theory, and the development of the HWCFZ in bedrock and Q2l loess strata is discussed in detail. First, the subsidence-deflection curve equation of the overlying stratum is theoretically derived, and then the ultimate deflection and free space height of rock strata are calculated. Moreover, the strata tensile strain is calculated by using integral calculus. In addition, the failure state of the rock is analyzed by comparing the theoretically calculated tensile strain with the experimentally measured yield tensile strain, allowing one to attain the maximum value of HWCFZ. This approach was tested at the Jinjitan coal mine; the theoretically predicted, experimentally measured, and numerically computed maximum HWCFZ values were 189.5, 187.3, and 188.5 m, respectively, demonstrating the accuracy of the proposed method. These results are highly significant for safe and environment-friendly coal mining in northwest Shaanxi, China.

Method to Predict the Height of the Water Conducting Fractured Zone Based on Bearing Structures in the Overlying Strata

Numerous mining-induced water inrush hazards have been recorded in northern and eastern China, wherein landforms comprise thick unconsolidated layers. To prevent such hazards, the height of the water conducting fractured zone (WCFZ) must be determined in advance. This study presents a method to predict the height of this zone by determining the location of the key strata (KS) and considering the overburden load transfer under an arch structure in the unconsolidated layers. When the distance between the primary key stratum (PKS) and coal seam is more than 7–10 × M, where M refers to the mining height, the WCFZ tends to extend up to the floor level of the first KS, approximately the same distance (7–10 × M) above the mining seam, thereby making the height of this zone equal to the distance between the KS and coal seam. When the vertical distance between the PKS and coal seam is less than 7–10 × M, the height of this zone tends to be equal to or greater than the thickness of the bedrock strata. The theoretical results were verified by field observations.