Water-conducting Fractured Zone Research Articles

Study on the evolution of fractures in overlying strata during repeated mining of coal seams at extremely close distances

In particular, the secondary development of overlying strata fractures can easily lead to the upper goaf, resulting in gas and water gathered in the goaf entering the working face of the lower coal seam through the overlying strata fractures, threatening the safety of coal mine production. Security risks may arise. To further understand the caving and evolution law of overlying strata during repeated mining in extremely close distance coal seam down mining, 9# coal and 10# coal in the Nanyaotou Coal Industry were used as the engineering background. The caving characteristics and fracture evolution law of overlying strata during single and repeated mining were analyzed through similar material simulation tests. Based on fractal geometry theory, the relationship between the advancing distance of the working face and the fractal dimension of the overlying strata fracture is established to reflect the changing trend of fracture development. The calculation formula is derived from the tensile rate of rock strata to predict the development height of water-conducting fractures. The results show that the overlying strata failure structure is mainly a “hinged structure” and a “step structure,” which respectively promotes and inhibits the development of overlying strata fractures. Repeated mining causes mining-induced fractures in the lower coal seam to pass through the goaf of the upper coal seam and develop more vigorously in the upper coal seam, and the fractal dimension can effectively reflect the development of overlying strata fractures. The height of the water-conducting fracture zone increases in four stages: incubation, gradual increase, further gradual increase, and stability, eventually stopping development under the influence of the key layer (thick mudstone) bearing the load above. The development height of water-conducting fractures predicted by on-site water injection measurement is similar to that predicted by simulation experiments and theoretical calculations, verifying the feasibility of predicting the development height of water-conducting fractures through simulation tests and theoretical analysis. This study provides a reference for coal seam mining under similar conditions.

Mechanism of Instantaneous High-Strength Sand–Water Inrush in Steeply Inclined Mining of Soft Coal Seam under Disturbed Rock–Soil Overburden

Abstract Water and sand inrush pose significant threats to underground geotechnical engineering, including shallow buried resource extraction and tunnel construction. To understand the mechanisms behind these phenomena, a mud collapse accident in Chaider Coal Mine was comprehensively investigated through field exploration and laboratory-based testings. Using numerical simulation experiments, we analyzed the failure patterns and seepage characteristics of overlying strata in steeply inclined coal seam mining under various working conditions. We established a structural instability model for water and sand inrush and identified the critical conditions for sand collapse occurrence. Our research indicates that the backfill in the surface mining pit provided a substantial material source for the accident. The overall destabilization of the top coal, due to its insufficient thickness and strength, created a pathway for sand collapse. Furthermore, frequent rainfall during the flood season and the inadequate arrangement of pumping equipment acted as triggers for the sudden water collapse. Preventative measures, such as limiting the mining height, enhancing the shear strength of the top coal, and altering the working face layout, can effectively control the development height of the water-conducting fracture zone. Additionally, timely evacuation and lowering of the aquifer water level, weakening its seepage effect in the top coal area, reducing the moisture content of the bottom soil, and improving its shear strength can mitigate water and sand inrush accidents in the backfill areas of open-pit mines.

Comparative study of five machine learning algorithms on prediction of the height of the water-conducting fractured zone in undersea mining

Prediction of water-conducting fractured zone (WCFZ) of mine overburden is the premise for reducing or eliminating water inrush hazards in undersea mining. To obtain a more robust and precise prediction of WCFZ in undersea mining, a WCFZ prediction dataset with 122 cases of fractured zones was constructed. Five machine learning algorithms (linear regression, XGBRegressor, RandomForestRegressor, LineareSVR, and KNeighborsRegressor) were employed to develop five corresponding predictive models, taking multiple factors into account.The optimal parameters for each model are obtained through ten-fold cross-validation (10CV). The model's predictive performance was validated and assessed using two metrics, namely the coefficient of determination (R2) and mean squared error (MSE). A comparison was made with the regression performance of commonly used empirical formulas. The results indicate that the constructed model outperforms reliance solely on theoretical criteria, showing a high R2 value of up to 0.925 and a low MSE value of 3.61. The proposed model was validated in a recently established mining area on Sanshan Island, China. It shows low absolute and relative errors of 0.71 m and 2.01%, respectively, between the predicted value from the model and observation result from the field, demonstrating a high level of consistency with on-site conditions. This paves a path to leveraging machine learning algorithms for predicting the height of WCFZ.

Study of the development patterns of water-conducting fracture zones under karst aquifers and the mechanism of water inrush

The hydrogeological conditions of the Qianbei coalfield are complex, and karst water in the roof rock frequently disrupts mining operations, leading to frequent water inrush incidents. Taking the representative Longfeng Coal Mine as a case study, research was conducted on the development pattern of the water-conducting fracture zone and the water inrush mechanisms beneath karst aquifers. On the basis of key stratum theory and calculations of the stratum stretching rate, the karst aquifer in the Changxing Formation was identified as the primary key stratum. It was deduced that the water-conducting fracture zone would develop into the karst aquifer, indicating a risk of roof water inrush at the working face. Numerical simulations were used to study the stress field, displacement field, and plastic zone distribution patterns in the overlying roof strata. Combined with similar simulation tests and digital speckle experiments, the spatiotemporal evolution characteristics of the water-conducting fracture zone were investigated. During the coal mining process, the water-conducting fracture zone will exhibit a "step-type" development characteristic, with the fracture morphology evolving from vertical to horizontal. Near the goaf boundary, the strain gradually decreases, and the instability of the primary key stratum significantly impacts the mining space below, leading to the closure of interlayer voids or the redistribution of water-conducting fissure patterns. Field measurements of the water-conducting fracture zone reveal that postmining roof fractures can be classified into tensile-shear, throughgoing, and discrete types, with decreasing water-conducting capacity in that order, the measured development height of the water-conducting fracture zone (51 m) aligns closely with the theoretical height (51.37 m) and the numerical simulation height (49.17 m). Finally, from the perspective of key stratum instability, the disaster mechanisms of dynamic water inrush and hydrostatic pressure water inrush beneath the karst aquifers in the northern Guizhou coalfield were revealed. The findings provide valuable insights for water prevention and control efforts in the Qianbei coalfield mining area.

Research on the Development Height Prediction Model of Water-Conduction Fracture Zones under Conditions of Extremely Thin Coal Seam Mining

Addressing the difficult problem of predicting the height of water-conducting fracture zones in shallow and thin coal seams, a prediction model of water-conduction fracture zones based on a backpropagation (BP) neural network was developed by integrating theoretical analysis, field measurements, and algorithmic advancements. Firstly, through overburden migration analysis and correlation tests, the height index system of the water-conducting fracture zone was determined. This system includes mining height, buried depth, dip angle, working face width, and overburden rock lithology, with five groups of characteristic parameters. Then, 35 pairs of minefield-measured data were collected to establish the measured height data set of the water-conducting fracture zone. Secondly, a BP neural network prediction model and a traditional support vector regression (SVR) prediction model were constructed based on a Pytorch framework, and the models were trained and tested by selecting data sets. Thirdly, the optimal prediction model was determined by comparing the model with the empirical model and multiple regression model of mining regulations for coal pillar maintenance and pressure in buildings, water bodies, railways, and main shafts. Finally, a typical mine was selected for application to verify the suitability of the optimal model. The results show that: (1) the predicted value of the neural network model is consistent with the change trend of the measured value, which accords with the theoretical law; (2) compared with traditional forecasting methods, the error of the BP neural network prediction model is stable and the prediction effect is the best; (3) dropout can effectively mitigate mitigation training overfitting, achieve regularization, and improve prediction accuracy; (4) the field application further verified that the BP neural network model is the best for predicting the height of water-conducting fracture zones of extremely thin coal seams, and the research results can provide technical guidance for similar fragile coal seams.

Height Development Characteristics of Water-Conducting Fracture Zone in a Fully Mechanized Longwall Face with a Large Panel Width

Height Development Characteristics of Water-Conducting Fracture Zone in a Fully Mechanized Longwall Face with a Large Panel Width

Hydrogeology and groundwater control at Chambishi mine, Zambia

The hydrogeological conditions in the Chambishi mine area in Zambia. were investigated. Chambishi is a very wet mine and groundwater discharge costs are high. The research goal was to identify methods to reduce the discharge costs without greatly affecting the mining process. Hydrogeological data was obtained from measurements in drill-holes and from drill cores. The differences in structural deformation in different areas determine whether a layer of rock is an aquifer. In the mine region, the Lower Roan Group ore shale and quartz-sandstone unconformably lie on the basal schist and granite aquifuge. The Upper Roan Group dolomite is continuously distributed over a large area around the orebody. This dolomite is the main target of groundwater control efforts, and its water yield is also influenced by the deformation intensity. Based on the observations, backfilling was gradually adopted to appropriately safeguard the integrity of the aquifuge above the orebody. The overlapping relationship between the aquifer and aquifuge has been utilized to increase mine drainage efficiency. This measure has not only greatly reduced the costs of mine drainage, but also improced protection of the groundwater environment. The old drill-holes that were not sealed after exploration drilling were grouted. Further, possible water-conducting fracture zones were investigated. Cover drilling towards the suspected zone was conducted to prevent the high-pressure groundwater from shallower aquifers from entering stopes in deep areas of the mine.

Study on Fracture Evolution and Water-Conducting Fracture Zone Height beneath the Sandstone Fissure Confined Aquifer

Studying the evolution law of overlying rock fissures and predicting the development height of water-conducting fissure zones is the key to preventing roof water damage, protecting mine water resources, and realizing the safe and sustainable development of the mine. To study the overburden fracture evolution law of coal mining under aquifer conditions, the 1402 working face of Longwangzhuang Mine in Shaanmian Coalfield serves as the engineering background based on the Fractal Theory and similar simulation technology; this paper analyzes the fracture evolution of overburden rock and the development law of Water-Conducting Fracture Zone (WCFZ) during the advancing of working face, and further puts forward a model for the location discrimination of overburden fracture based on plate theory. The results indicate that post-mining, overburden rock failure assumes a trapezoidal shape, and fractures around the cutting hole and the side of the working face fully develop, while those in the middle of the goaf tend to compact. The distribution of the fracture network of mining strata at different advancing distances has good self-similarity, and the fractal dimension of the fracture network of overlying rock can be divided into three stages: ascending dimension, decreasing dimension, and stable phase. The II 1 coal seam fracture does not spread to the Sandstone Fissure Confined Aquifer. These findings provide strategic guidance for protecting mine aquifer water resources, preventing and controlling roof water inrush, and ensuring safe and sustainable production within the study area.

Extension Mechanism of Water-Conducting Cracks in the Thick and Hard Overlying Strata of Coal Mining Face

It is of great significance for coal safety production and water resource protection in the Yuheng mining area to master the evolution law of water-conducting fractures under the condition of thick and hard overburden. This research focuses on the 2102 fully mechanized mining face in the Balasu Coal Mine as the research background. The fracture evolution and strata movement characteristics in thick and hard overlying strata are simulated and analyzed by combining numerical simulation with physical simulation, and the formation mechanism of a water-conducting fracture in the overlying strata is revealed and verified by field measurements of the development height of “two zones”. The results show that the anisotropy of fracture propagation in low-position overlying strata is high, and the fracture propagation in high-position overlying strata is mainly vertical, which indicates characteristics of leapfrog development. The number and development height of fractures undergo the change–growth process of “slow–rapid–uniform”. Multiple rock strata together form a complex force chain network with multiple strong chain arches. The local stress concentration leads to the initiation of micro-cracks in contact fractures, and the cracks gradually penetrate from bottom to top and then the strong chain arches are broken. The water-conducting cracks in overlying strata show a dynamic expansion process of “local micro-cracks–jumping cracks–through cracks–water-conducting cracks”. The fracture between the caving zone and fracture zone presents obvious layered characteristics, the overall shape of the water-conducting fracture zone is “saddle-shaped”, and the maximum development height lags behind the coal mining face by about 180 m. Through the observation of water injection leakage and borehole TV observation of three boreholes under underground construction, combined with the results of water pressure tests, it is comprehensively determined that the height of the water-conducting fracture zone is 103.68~107.58, and the fracture–production ratio is 31.42~32.60, which is basically consistent with the results of numerical simulation and physical simulation. This research provides theoretical guidance and a scientific basis for coal mine water disaster prevention under similar geological conditions.

An entropy based spatial–temporal cube with its application to assess stress of overburden due to mining

Underground coal seam mining significantly alters the stress and energy distribution within the overlying rock, leading to eventual structural degradation. Therefore, it is imperative to quantitatively identify the temporal and spatial characteristics of stress evolution of overlying rock caused by mining. This paper introduces a novel rock stress model integrating entropy and a spatial–temporal cube. Similar material model tests are used to identify the abrupt entropy changes within the mining rock, and the trend analysis is carried out to describe the spatial–temporal evolution law of stress during mining. Experimental findings indicate elevated stress levels in the unmined rock preceding and following the panel, as well as within specific rock strata above it. Definitively, dynamic stress arches within the surrounding rock of the stope predominantly bear and distribute the load and pressure from the overlying rock, and each stress mutation is accompanied by a sudden stress entropy change. Over time, z-score shows that the noticeable reduction in mining-induced overburden stress becomes increasingly pronounced, especially in the water-conducting fracture zone. The model's bifurcation set serves as the comprehensive criterion for the entropy-induced sudden changes in the rock system, signifying overall failure.

An Improved Back Propagation Neural Network Based on Differential Evolution and Grey Wolf Optimizer and Its Application in the Height Prediction of Water-Conducting Fracture Zone

Given that the conventional back propagation neural network (BPNN) easily falls into the local optimal solutions, resulting in poor prediction accuracy, an improved BPNN based on the differential evolution and grey wolf optimizer (DEGWO) is proposed, the so-called DEGWO-BPNN. The prediction of the water-conducting fracture zone (WCFZ) height is significant for mine safety operations. A total of 104 sample data are trained and 25 sample data are tested to identify the optimal prediction model. Five evaluation indexes are selected to assess the prediction performance of the models quantitatively. Finally, the DEGWO-BPNN model is applied to a specific engineering case. The main conclusions are as follows: (1) Mining height, mining depth, coal seam dip, panel width, and ratio of hard rock as the main factors affecting the WCFZ height are selected. The topology structure of the model is defined as ‘5-12-1’; (2) the bias between the predicted value and the actual value of the training samples is smaller with an average error of 2.39. Test samples further validate the prediction precision through evaluation indexes. The values of MAE, RMSE, MAPE, and R2 are 2.3952, 3.4674, 5.3148%, and 0.99077, respectively. The prediction accuracy is 94.6852%; (3) ‘Mining Code’, MLR, BPNN, and GWO-BPNN models are treated as the comparison groups. The comparative analysis shows that the prediction performance of ‘Mining Code’ is the worst, while that of DEGWO-BPNN is the best, and it outperforms other algorithms and statistical approaches; (4) the prediction of WCFZ height in the 11601 panel is in line with the actual value. The prediction error of the DEGWO-BPNN model is lower than that of the comparison models. As such, the DEGWO-BPNN model can be well applied to the prediction of WCFZ height and is suitable for coal mines with different regional geological conditions. It can provide a valuable reference for mine safety operations.

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.

Study on water inrush risk of overlying old goaf water in fully mechanized caving mining of lower coal group

This paper focuses on the risk of water inrush from the old goaf water of the upper coal group to the first mining face of the lower coal group under the condition of fully mechanized caving mining. Data from the 2101 working face of the No. 15 coal seam in the Wulihou Coal Mine were used to calculate the height of the water-conducting fracture zone on the first mining working face and the floor failure depth in the overlying No. 5 coal seam. An engineering geological model was developed, considering the lithological combination of the upper and lower coal groups, as well as the geological and hydrogeological conditions. Numerical simulations were conducted to analyse the deformation and failure characteristics of the roof and floor after dual-seam mining. The results revealed a floor damage depth of 12 m and a water-conducting fracture zone height of 109 m. Field monitoring data confirmed that after mining the 2101 working face, there was no water inrush risk from the overlying old goaf water into the No. 15 coal seam through the water-conducting fracture zone. The research results provide a reference for preventing water inrush accidents in similar fully mechanized top coal caving mining under the old goaf water.

Non-invasive geophysical methods for monitoring the shallow aquifer based on time-lapse electrical resistivity tomography, magnetic resonance sounding, and spontaneous potential methods

The Ningdong coalfield has played a pivotal role in advancing local economic development and meeting national energy. Nevertheless, mining operations have engendered ecological challenges encompassing subterranean water depletion, land desertification, and ground subsidence, primarily stemming from the disruption of coal seam roof strata. Consequently, the local ecosystem has incurred substantial harm. Water-preserved coal mining presently constitutes the pivotal technology in mitigating this problem. The primary challenge of this technique lies in identifying critical aquifer layers and understanding the heights of water-conducting fracture zones. To obtain a precise comprehension of the seepage patterns within the upper coal seam aquifer during mining, delineate the extent of water-conducting fracture zones, non-invasive geophysical techniques such as time-lapse electrical resistivity tomography (TL-ERT), magnetic resonance sounding (MRS), and spontaneous potential (SP) have been employed to monitor alterations within the shallow coalfield’s aquifer throughout the mining process in the Ningdong coalfield. By conducting meticulous examinations of fluctuations in resistivity, moisture content, and self-potential within the superjacent strata during coal seam extraction, the predominant underground water infiltration strata were ascertained, concurrently enabling the estimation of the development elevation of water-conducting fracture zones. This outcome furnishes a geophysical underpinning for endeavors concerning local water-preserved coal mining and ecological rehabilitation.

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.

Research on height prediction of water-conducting fracture zone in coal mining based on intelligent algorithm combined with extreme boosting machine

The development of water-conducting fracture zones (WCFZ) caused by coal mining is a destructive phenomenon of mining damage. The development height of the WCFZ is an important reference index for the prevention and control of safety hazards such as water infiltration or sand intrusion in mines and for program optimization. In this work, a combinatorial optimization model for height prediction of WCFZ is established by combining the extreme gradient boosting machine and several commonly used intelligent algorithms: genetic algorithm, particle swarm optimization, jaya algorithm, sparrow search algorithm. Accordingly, 142 sets of WCFZ composed of 4 main parameters were selected as the input independent variables, and the maximum height (H) was selected as the output dependent variable. In addition, to demonstrate the validity of the proposed combinatorial optimization models, this study used the following four models (Random Forest, Bagging, XGBoost and AdaBoost) for comparison. Model performance evaluation criteria including the coefficient of determination, root mean square error, mean absolute error, and variance accounted for are used to evaluate the model. In this work, 142 sets of cases to the WCFZ analyzed and the method of Shapley Additive Explanations was used to explain the importance and contribution of features to maximum height prediction. The research results show that, compared with other machine learning models, the combinatorial optimization model put forward in this work can improve the predicted accuracy and reliability of height prediction of WCFZ. The research in this work may help researchers use machine learning models to predict and research the height development of WCFZ.

Water-inrush mechanism from the head-on working face roof in a Jurassic coal seam in the Ordos Basin.

When Chinese coal mines are mining Carboniferous Permian coal seams, the mechanism of water inrush from the roof of the working face usually conforms to the "Upper Three Zones" or "Upper Four Zones" theory. The water inrush passageway is water-conducting fracture zone, and the water inrush position is located in the goaf. However, when mining Jurassic coal seams in Chinese coal mines, the location of water inrush often appears at the head-on working face, above the coal mining machine. Due to the support of the fully mechanized mining support, the roof rock layer cannot collapse and therefore cannot form water-conducting fracture zone. Therefore, the water inrush mechanism cannot be explained by the above two theories. This paper is guided by the Practical Mine Pressure Control Theory, and based on the explanation of the motion forms of bending (pulling) failure movement and shearing (cutting) failure movement, and combined with on-site examples, it is revealed that the passageways leading to from the head-on working face roof in a Jurassic coal seam in the Ordos Basin are splitting zones type, fracture line type and structural fracture type, respectively. Taking the changes in water inflow during the mining process of the 3301 and 3302 working faces in Zhujiamao Coal Mine as examples, this paper reveals the mechanism of water inrush from the head-on working face roof caused by splitting zones type, and proves the existence of this passageway through on-site 3D high-density electrical detection and tracing experiments. Taking two catastrophic water inrush accidents that occurred head-on in the 1309 working face of Guojiahe Coal Industry Co., Ltd. as examples, the water inrush mechanism of the fracture line type and the water inrush mechanism of the structural fracture type were respectively revealed. Based on mechanism of water inrush from head-on roof of working face and the analysis of the on-site water inrush process, a method for distinguishing the type of water inrush passageway from the front roof of the working face is proposed. The results indicate that the Jurassic coal seam mining in the Ordos Basin is prone to shearing (cutting) failure movement, resulting in the frequent formation of the three types of water inrush passageways mentioned above.

Evolution mechanism of water-conducting fractures in overburden under the influence of water-rich fault in underground coal mining

Based on the 7618 working face in Yaoqiao coal mine of Datun mining area, the activation mechanism of water-rich faults and the development characteristics of water-conducting fractures in overlying strata under the influence of faults are studied by theoretical analysis, numerical simulation and field measurement in this paper. The research results show that Anderson model and Mohr–Coulomb strength criterion are combined to establish the fault failure mechanical model, and the fault activation criterion under the influence of mining is obtained. FLAC3D numerical simulation results show that with the advance of the working face, the fault begins to be affected by the mining effect of the working face at the distance of 20 ~ 30 m from the fault. Meanwhile, with the advance of the working face, the overburden shear failure range also expands, and the fault fracture gradually expands from top to bottom. The failure zone of the working face roof is connected with the fault fracture zone. Then the fault is "activated" and causes the fault to become a water gushing channel, and finally the water gushing disaster occurs. Through numerical simulation and comparative analysis, the development height of water-conducting fracture is 73.2 m in the absence of fault, and 73.7 m in the presence of fault, indicating that the fault has little influence on the maximum development height of water-conducting fracture. The actual development height of the water-conducting fracture zone in the 7618 working face is 73.97 m and the fracture production ratio is 13.7. The research results can provide theoretical reference for the safe mining of similar working faces across faults.

Research on the Stability and Water Isolation of Waterproof Coal Pillars between Adjacent Working Faces under the Influence of Water Ponding Goaf—A Case Study

Retaining a waterproof coal pillar is an important measure to defend against water inrush accidents in mining areas and guarantee the safe mining of the next working face. In this paper, the mechanical model of the coal pillar is established and the calculation formula of the waterproof coal pillar width is derived. Then, the development of the water-conducting fracture zone of the overlying rock layer under different coal pillar widths is analyzed using numerical simulation and finally, the integrity of the coal pillar is detected using the geophysical survey method. The main conclusions are as follows: (1) According to the mechanical failure characteristics of the coal pillar, it can be divided into the plastic zone, elastic zone, and water pressure damage zone. The mechanical calculation model for each zone was established, and the formula for calculating the width of the waterproof coal pillar was obtained. (2) Numerical simulation was employed to investigate the development condition of the water conducting fracture zone in the overlying rock strata under the actual width of the waterproof coal pillar; the simulation results indicated that the water conducting fracture zone of two working faces was not connected, which can effectively prevent the accumulation of water in the 2303 goaf. (3) On-site geophysical surveys determined that the influence of water-logged goaf on the coal pillar is between 5 to 15 m; the integrity of the waterproof coal pillar is good, which effectively prevents water accumulation in the previous working face goaf and ensures safe mining in the next working face.