Floor Water Inrush Risk Research Articles

Investigation on Mining-Induced Floor Water Inrush from Column and Its Control Based on Microseismic Monitoring

Water inrush is the biggest threat for safe mining in the Ruifeng coalmine, located in North China. In the study mining area, the floor water inrush is mainly caused by mining activities and collapse column. In this article, the mechanical criteria of floor water inrush are obtained based on cusp catastrophe theory, which is used to assess floor water inrush risk in the Ruifeng coalmine. Theoretical analysis shows that floor water inrush is very likely to occur during coal mining without the influence of geological structures. Additionally, FLAC3D was used to simulate the damage of floor strata during the mining face advances. Numerical results show that the water inrush channel occurs in front of the mining face due to the influence of stress concentration. Therefore, a microseismic monitoring system was applied to monitor the formation of water inrush pathway. Field monitoring results show that two water inrush pathways were accurately predicted and positioned. Based on the microseismic monitoring results, target grouting was adopted to prevent water inrush. This study provides significant guidance for the prevention of floor water inrush.

Rule Study on the Risk of Floor Water Inrush Based on the Plate Model Theory

In order to mitigate the potential issue of abrupt water inrush in coal mining operations, the elastic-plastic mechanics theory was employed to simplify the water barrier of the floor strata into a thin rectangular plate. Subsequently, a fluid-solid coupling damage model was designed through the utilization of COMSOL Multiphysics software to investigate the coupled seepage and damage effects of the rock mass in an equivalent continuous medium. The results indicate that (1) the analysis of the theoretical equation of elastic mechanics shows that the fracture position of the four-sided clamped thin plate is in the center of the four sides, and the theoretical limit span and the theoretical limit water pressure formula are derived. (2) The damage factor is used to characterize the damaging effect of different mining distances and different pore water pressures on the rock mass of the floor aquiclude in the numerical simulation. It is found that the damage tends to the open-off cut and stop-mining line of the floor waterproof layer and the center position on both sides of the coal wall, and the stress is the most concentrated. (3) The results obtained by the two research methods are highly consistent, which provides a theoretical basis for the prevention and control of water in ground mining mines, so as to realize safe mining above the confined aquifer.

Failure Characteristics of Coal Seam Floor and Risk Assessment of Water Inrush Caused by Underground Coal Mining

Failure characteristics of the coal seam floor above-confined aquifer are key to evaluating the water inrush risk from the floor in the deep mining. At present, based on the analysis of water inrush impact indicators, mathematical evaluation methods are often used to evaluate the water inrush risk of a mining floor. This study proposes a theoretical risk assessment method for water inrush from the floor considering the failure characteristics of the coal seam floor above-confined aquifer. The 11301# coalface in the Wanglou colliery, Shandong Province, is considered as a case study. The mechanical model of the mining floor stress along the coalface inclination direction was established, and the analytical solutions of the vertical, horizontal, and shear stress and floor failure depth were derived. The floor failure mode along the coalface inclination direction is similar to the letter “lying flat-B” and the maximum and minimum failure depth is around 13 and 6 m. Furthermore, the dynamic failure characteristics of the floor during coal mining were simulated. Subsequently, the thickness of the floor key aquiclude was determined and the water inrush coefficient exhibits a certain trend from increasing to becoming stable in the mining process, that is, from 0.05 to 0.08 MPa/m. The analytical solution of the critical water pressure for floor aquiclude failure was derived based on the limit equilibrium theory. That is, the ultimate water pressure 3.9 MPa is greater than the actual water pressure 2 MPa, and there is no floor water inrush risk. Taking these into account, the water inrush risk of the mining floor above-confined aquifer was comprehensively analyzed and evaluated. The findings were deemed to be consistent with the actual mining case.

A Prediction Method for Floor Water Inrush Based on Chaotic Fruit Fly Optimization Algorithm–Generalized Regression Neural Network

The research was aimed at predicting floor water-inrush risk in coal mines and forewarn of such accidents to guide safe production of coal mines in practice. To this end, a prediction method for floor water inrush combining the chaotic fruit fly optimization algorithm (CFOA) and the generalized regression neural network (GRNN) is proposed. Floor water inrush is predicted by virtue of the robust nonlinear mapping capability of the GRNN. However, because the prediction effect of the GRNN is influenced by the smoothing factor, the CFOA is adopted to optimize this factor. In this way, influences of human factors during parameter determination of the GRNN prediction model are decreased, and the prediction accuracy and applicability of the model are improved. Results show that the CFOA–GRNN prediction model has an accuracy of 93.2% for whether floor water inrush will occur or not. Compared with the BPNN, RNN, and GRU network prediction model, the CFOA–GRNN model is superior in the prediction accuracy and generalization, and it can more accurately predict floor water inrush.

Analytical stress analysis method of interbedded coal and rock floor over confined water: a study on mining failure depth

Deep mining commonly causes redistribution of the stress-strain field for coal seam floor strata. The study of this distribution law was of great significance to analyzing the characteristics of floor deformation and failure and predicting the risk of floor water inrush. In this paper, the damage of a coal seam floor with strong water pressure in the Junggar Basin in western China was examined, and the stress analytical formula for every point of floor confined aquifer was constructed using a stress model in the direction of coal seam strike. Combined with Mohr-Coulomb failure criterion, the maximum depth of floor failure was 17.5 m. According to geological and stratigraphic data of the stope floor, a 3D numerical model of fluid-structure coupling was built. Simulation results showed that under a 1.5 MPa water pressure, the maximum floor failure depth was 18 m. The internal stress of the coal-rock interface and soft rock increases significantly, and the weak coal seam intensifies the transfer of stress and strain at depth to some extent. Water pressure had a certain influence on floor deformation and failure. The joint simulation results of stress-seepage-fracture were closer to the real stope measurements. In the boreholes, two types of sensors, distributed fiber and electrodes were arranged. When the coal floor broke, the compressive strain increased with a peak of 4152 με. Meanwhile, the apparent resistivity of the rock seam reached 500–700 Ω•m. The comprehensive analysis showed that: the floor failure depth in the monitoring area of the 61,303 working face was −18 m, and the floor failure disturbance depth was −35 m. The results presented in this contribution can provide reference for future examinations of coal and rock interbedded floor failure over deep confined water.

Mine Water Inrush Risk Assessment Evaluation Based on the GIS and Combination Weight-Cloud Model: A Case Study.

With the increase in mining depth, the hydrogeological conditions of mines become more complex, which leads to higher possibility and harmfulness of water inrush accidents and brings great challenges to mine safety. It is particularly important to accurately evaluate the risk of mine water inrush. In order to study and prevent the floor water disaster of coal mines, it is necessary to correctly evaluate the risk of water inrush according to the limited borehole data. Based on the six main factors affecting water inrush, such as the seam dip angle, fault fractal dimension, key-strata thickness, water pressure, mining depth, and dip length, a comprehensive evaluation index system of floor water inrush risk is established in this paper. In the first step, we combine the combination weight method based on game theory with the cloud model to calculate the risk level of water inrush at each borehole location. In the second step, the risk level is displayed in a geographic information system, and the single index and comprehensive zoning map of water inrush risk in the study area are established to provide scientific guidance for mine water disaster prevention and control in this area. Through the case study of the Yangcheng Coal Mine, the whole process is further expounded. The results show that the five actual water inrush points in the Yangcheng Coal Mine are located in the dangerous area (grade IV) and the relatively dangerous area (grade III), which verifies the effectiveness of this method. At the same time, the evaluation results show that water pressure has great influence on floor water inrush.

Risk evaluation of mine-water inrush based on principal component logistic regression analysis and an improved analytic hierarchy process

A method of evaluating the risk of floor water inrush using principal component logistic regression analysis (PCLRA) and an improved analytic hierarchy process (IAHP) is presented. The approach was validated by a case study at the Yangcheng coal mine in Shandong Province, China. First, the risk assessment index of floor water inrush was determined based on geological and hydrogeological conditions of the study area. Then, a comprehensive evaluation model (CEM), combining PCLRA with IAHP, was constructed to determine the comprehensive weight of each water-inrush evaluation index. Finally, water-inrush risk zoning was determined with GIS. The results show that the CEM, compared with the water-inrush coefficient method (WICM) traditionally and commonly used in China, has higher fitting accuracy and more detailed division of water-inrush risk areas. This method not only follows the observations in reality, but also fully considers the relative importance of water-inrush evaluation indices. The results can provide a theoretical basis for the safe mining of coal seams above confined groundwater.

Analysis and control of water inrush under high-pressure and complex karstic water-filling conditions

Karstic water damage is one of the main disasters that threatens safe production in coal mines. As coal mining in China moves toward deeper strata, deep karst water disasters caused by mining are increasingly common. This paper studies the Jiyang coal mine in Shandong Province, China; conducts an in-depth analysis of the water charging conditions of the Ordovician limestone karst aquifer; determines four evaluation indices of the Ordovician limestone water inrush risk (water yield, water pressure, geological structure complexity and effective aquifuge thickness); and establishes a multifactor model to evaluate the water inrush risk of the Ordovician limestone using multisource information fusion, the water resistance coefficient and the equivalent coefficient. In addition, the floor water inrush risk of the Ordovician limestone during caving mining, strip mining and backfilling mining of the No. 13 coal seam is evaluated in the study area, which is then divided into different zones: a safe zone, a relatively safe zone and a danger zone. According to the evaluation results, the full backfilling mining method with the minimum risk range of water inrush is selected for future mining. Using this method, most of the research area is classified as a safe zone or relatively safe zone, and only a very small area in the south is classified as a danger zone. The threat of Ordovician limestone inrush caused by coal mining is low. The evaluation results of the water inrush risk and optimization of the mining method provide a reference for the prevention and control of mine water damage and can provide guidance for safe coal mining.

Application of a new evaluation method for floor water inrush risk from the Ordovician fissure confined aquifer in Xiayukou coal mine, Shanxi, China

As the mining depth of North China-type coal fields increases year by year, the threat of Ordovician limestone karst water damage to coal seam mining is increasing, and the risk of floor water inrush increases gradually. To ensure safe production in coal mines and avoid casualties and economic losses, it is essential to accurately predict the risk of coal floor water inrush. The traditional approach to determine whether there is risk during the mining process is the water inrush coefficient method, which has certain limitations because it does not fully consider the water yield of the aquifer and the actual hydraulic resistance of the aquitard. Therefore, in this paper, a new method was put forward and applied for predicting the floor water inrush risk attributed to the Ordovician karst fissure confined aquifer from the Permian-age coal deposits in the Xiayukou coal field, Hancheng mining area, Shanxi, China. The influence of floor water inrush is comprehensively considered from the three aspects of the aquifer’s water yield, the hydraulic resistance characteristics of the aquitard and the tectonic development of the study area. Based on the new analytic hierarchy process-linear weighted average (AHP-LWA) method, a water abundance structure index (WASI) was created using the burial depth of the Ordovician aquifer (Dp), water abundance layer (Ly) and morphological features of the aquifer (Mf). Similarly, a hydraulic resistance structure index (HRSI) model was established using aquitard thickness (Tk), number of aquifers and aquitards (Num), sand–mud ratio (SMr) and core recovery rate (CRr); additionally, fractal dimension values were used to characterize the degree of structural development. Finally, a water inrush risk evaluation model was constructed, and a contour map was drawn using the risk index method of floor water inrush (RIWI) values and revealed three water inrush risk zones: normal mining area (0.18–0.32), medium-risk area (0.32–0.38) and high-risk area (0.38–0.52). Model verification was accomplished by the actual exposed water inrush points during the No. 3 coal seam mining work, which are all located in the high-risk area zoned by the RIWI method, and the water sources are all from the third section of the Upper Majiagou strong aquifer. The results show that the new evaluation model has high prediction accuracy, small error and wide applicability, and the model meets the basic requirements of mine production safety, provides favourable technical support for floor water inrush prediction during the Carboniferous–Permian lower coal group mining above the confined aquifer and is of great significance to ensure safe and efficient production of the coal mine.

Evaluation of water inrush from underlying aquifers by using a modified water-inrush coefficient model and water-inrush index model: a case study in Feicheng coalfield, China

Water inrush from underlying aquifers seriously threatens mining of Permo-Carboniferous coal seams in many North China coalfields. To evaluate the risk of water inrush from underlying aquifers, a modified water-inrush coefficient method—using the water inrush coefficient (T) and geological structure index (G)—and a water-inrush index model (WII model) were proposed. The T_G model improved the traditional water-inrush coefficient method by quantifying the degree of geological structure development, considering three main controlling factors: G, aquifer water pressure (P) and aquitard thickness (M). The WII model was constructed to assess the risk of floor water inrush by the entropy weight method, which integrated six factors: G, P, M, the depth at which ground pressure creates a broken-rock zone (Cp), aquifer water yield property (Y), and percentage of brittle rock within the aquitard (B). Results from the engineering practice data analysis validated the T_G and WII models as operational tools to evaluate the risk of water inrush from an underlying aquifer. The comparative analysis of the predictions by these two models shows that the prediction accuracy of the WII model is 13% higher than that of the T_G model, and approximately 21% of the two model predictions are not in agreement. A more reasonable prediction was obtained with application of the T_G and WII models to Feicheng coalfield in Shandong Province to evaluate water inrush risk from the underlying aquifer, and the prediction offers guidance on different preventive measures against water hazards in the underlying Ordovician limestone in the different zones.

Risk Assessment of Floor Water Inrush Using Entropy Weight and Variation Coefficient Model

In order to solve the problem of variation degree of water inrush factors in floor, the geological data of No. 315 mining area in Huatai Coal Mine were taken as engineering background. Entropy weight method (EWM) was combined with variation coefficient method (VCM) to construct the comprehensive weighting vulnerability index model to determine the weight of each factor. At the same time, the weighted value was combined with the geographic information system to draw the risk zoning map of floor water inrush to predict the risk of floor water inrush. The results show: (1) fault fractal dimension is used to increase the accuracy of prediction of floor water inrush and easy to calculate. (2) The combination of EWM and VCM can weaken the influence of abnormal indexes and make the weighting results more real and reasonable. (3) Compared with the method of water inrush coefficient, the prediction result of the vulnerability index model with comprehensive weight is more accurate, which beneficial for Huatai coal mine safety production.

An Improved Fuzzy Comprehensive Evaluation System and Application for Risk Assessment of Floor Water Inrush in Deep Mining

In view of the characteristics of outburst, hysteresis and strong disaster caused by floor water bursting in deep mining, scientific and reasonable water inrush risk evaluation in advance is an important means to prevent water inrush in deep mining. In this study, an improved fuzzy comprehensive evaluation system for the risk assessment of floor water inrush in deep mining was established, and an veracious and feasible system method was proposed to evaluate the water inrush risk of floor water in deep mining. The evaluation indices were divided into continuous variable indices, which were quantitatively graded according to floor water inrush risk and discrete variable indices, which were qualitatively graded by expert opinion. According to the characteristics of continuous variables and discrete variables, the triangular fuzzy function and Delphi method were used to calculate the membership degree, respectively, and the analytic hierarchy process was applied to analyze the weights. In order to test the accuracy of the evaluation system, Evaluation of six engineering practices were carried through with hydrogeological data of six mining faces in China. The results are consistent with the field-observed results, which shows that the approach is reasonable and feasible, providing a powerful tool for the risk assessment of floor water inrush in deep mining.

Influence Analysis of Mining’s Effect on Failure Characteristics of a Coal Seam Floor with Faults: A Numerical Simulation Case Study in the Zhaolou Coal Mine

A fluid–solid coupled numerical simulation was carried out for the Zhaolou coal mine using Flac3D software. The results showed that: (1) when the failure depth of the floor exceeded the extension depth of the floor rock mass and the hydrostatic seepage pressure of the fractured structure surface exceeded the stress state of the fractured element, floor water inrush will occur. (2) With other factors being equal, if the footwall is mined first, the pore pressure concentration near the fault is more obvious, and the floor-confined water is lifted 10–25 m higher than when the hanging-wall is mined first. Mining the floor adversely affects its plastic zone, and the failure depth is ≈ 10 m greater than when the hanging wall is mined first. (3) When advancing against the fault dip, the pore pressure concentration near the fault is more obvious, and the floor confined water is lifted 5–20 m higher than when the mine advances along the fault dip. Again, mining the floor first disrupts the floor plastic zone, and the failure depth is approximately 5 m greater than when the mine is advanced along the fault dip. (4) The risk of floor-water inrush is minimized when the hanging-wall is mined first and the mine advances along the fault dip; the risk is greatest when the footwall is mined first and is advanced against the fault dip. These results provide a theoretical basis for preventing mine water inrush.

Application on Floor Water Inrush Evaluation Based on AHP Variation Coefficient Method with GIS

The prediction and prevention of floor water inrush is directly related to the safety of the coal mine production. The previous evaluation method of floor water inrush was more one-sided and lacked main control factors related to mining conditions. In order to evaluate the floor water inrush more accurately, under the project background of geological data of Wanglou coal mine, stope width, mining depth, fault scale index, water pressure, water abundance and thickness of aquifer were selected as main controlling factors of floor water inrush. Combined with the subjective weight analytical hierarchy process and the objective weight variation coefficient method, the weight coefficients corresponding to the main controlling factors were obtained respectively. The thematic map of the risk assessment of coal seam floor water inrush was drawn by combining the constructed comprehensive weight vulnerability index model and geographic information system. The results show that: ① according to the actual geological data of mine, two fault related factors were removed. And stope width and mining depth were increased as the main controlling factors to evaluate floor water inrush. It is easier to compare and calculate the weight of evaluation factors. ② The constructed comprehensive weight vulnerability index model can comprehensively evaluate the risk of floor water inrush. And the results of the evaluation are more accurate. ③ The related thematic maps can directly reflect the risk of floor water inrush, which is of guiding significance for the prediction and prevention of coal seam floor water inrush.

Analytical Model of Stress Field and Failure Depth in Multilayered Rock Masses of Mining Floor Based on the Transfer Matrix Method

Accurate calculation of stress distribution and failure depth of coal seam floor is the key to the floor water inrush risk evaluation. In consideration of the fact that the floor rock masses are multilayered distribution due to deposition, this paper presents a mathematical model for calculating stress field and failure zones in the floor strata caused by coal mining. By the application of the Fourier transform, the transfer matrix describing the relationship between the abutment pressure of stope and the stresses in arbitrary depth of multilayered rock masses is derived in the transformed domain. Then, the actual solution in the physical domain can be obtained by the inversion of Fourier transform through a MATLAB program. Finally, numerical examples are presents to verify the model and study the influence of the layered rock mass properties on the stress distribution and failure depth of mining floor.

An Improved Vulnerability Assessment Model for Floor Water Bursting from a Confined Aquifer Based on the Water Inrush Coefficient Method

Pressurized confined water below coal seams are serious threats to mining. The conventional water inrush coefficient method fails to accurately assess the risk of floor water inrush under some specific conditions, such as high water pressure and low water yield in the source aquifers. Large amounts of water inrush data including water inrush flow rate, water inrush coefficient (T s ), floor aquiclude thickness (M), and water abundance, were collected and statistically analyzed. The results indicated that inrushes mostly occurred when M was less than 30 m and that the critical T s increased linearly with M. The occurrence of a water inrush and water inrush yield amount (Q in L/s) were related to both the values of T s and the unit water inflow (q in L/(s m)). In addition, 97.7% of the large- and medium-sized inrush events occurred when q > 2 L/(s m) and only a small proportion (3.2%) of the small-sized inrushes happened when q < 0.1 L (s m). T s , M and q were comprehensively analyzed and used to evaluate vulnerability to floor water inrush. By analyzing the distribution of water inrush points and the scale of water inrush events, the vulnerability was divided into four levels (safe, moderately safe, potentially dangerous, and highly risky) based on T s –M and T s –q models. Successful application of these models in the Huaibei mining area proved that they are feasible in practice. The T s –M and T s –q charts can be used independently or jointly. These new methods should improve the accuracy of predictions and evaluations during deep exploitation where the aquifers are often characterized with high pressure but low water abundance. The results could also help reduce the amount spent on mine water prevention and control.

Risk Evaluation of Water Inrush from Coal Floor Based on BP Neural Network

According to the nonlinear dynamic characteristic of coal seam floor water inrush, coal seam floor water inrush risk evaluation which includes 4 first level indicators,14 level two indexes was built based BP neural network. According to the test collection of engineering data, coal seam floor water inrush risk evaluation system based VB and MATLAB is reliable. Application to a mine coal seam No.2 working face was verified. The results show that, the evaluation method in water inrush is feasible, reasonable.

An Attribute Synthetic Evaluation System for Risk Assessment of Floor Water Inrush in Coal Mines

An attribute synthetic evaluation system was combined with attribute mathematical theory and the analytic hierarchy process (AHP) to evaluate the risk of floor water inrush in coal mines. The evaluation indices of floor water inrush were divided into continuous variable indices, which were quantitatively graded according to floor water inrush risk and discrete variable indices, which were qualitatively graded by expert opinion. Single index attribute measurement functions were constructed to calculate the membership degree of the continuous variable indices. The membership degree of the discrete variable indices were evaluated using expert opinion eliciting techniques, such as the Delphi method. The contribution weighting of the evaluation indices were rationally distributed by the AHP. A confidence criterion was applied to discern the risk of floor water inrush. These results were compared with those from a secondary fuzzy comprehensive evaluation; the results from the present method agrees well with field-observed results. This approach provides a referential methodology for engineers to systematically assess and manage risk of floor water inrush in coal mines.

Characterizing the hydraulic conductivity of rock formations between deep coal and aquifers using injection tests

The hydraulic behavior of the rock formations under coal floor is an important factor to evaluate the risk of floor water inrush, which is difficultly obtained exactly by laboratory hydraulic tests. For the purpose of obtaining the hydraulic conductivity of the rock formations between deep coal and aquifers and further evaluating the risk of floor water inrush, water injection tests are carried out at Baodian coal mine. Through drilling four boreholes, three water injection tests of three rock formations are carried out and the hydraulic conductivity of the rock formations is calculated. Experimental results analysis shows that the three test rock formations are low-permeability. The hydraulic conductivity propagation with injection pressure can be divided into two phases that include stable change phase and increase phase due to hydraulic fracturing. In addition, the crack connections and propagations model can be used to analyze the change process of hydraulic conductivity of rock formations under water pressure. It is a useful approach for obtaining the hydraulic conductivity of deep rock formation, evaluating the risk of floor water inrush, preventing water inrush and raising the coal mining efficiency in colliery.

Application of Kriging Method to Evaluation of the Water Inrush Risk

The water disaster of floor in coal mine is a difficult problem of production and scientific research. Coal mine workers and scientific-technological workers are very concerned about this problem.The pressure-bearing karst water of 5# limestone poses a threat to production of 8# coal seam. Combining with the method of water inrush coefficient and Kriging interpolation method analyze the possibility of water inrush. The water inrush coefficient contour map has good convexity, verisimilitude and smoothness. Results accord with actual situation and intuitively reflect the 8# coal seam floor water inrush risk .The water inrush coefficient in the actual mining area is not more than 0.1 MPa/m, but in the future and in mining regional the water inrush coefficient could be very big, so we need to take the necessary precautions.