Height Of Water-flowing Fractured Zone Research Articles

Physical Modeling of the Controlled Water-Flowing Fracture Development during Short-Wall Block Backfill Mining

Abstract Short-wall block backfill mining (SBBM) technology is an effective method to solve the environmental problems in the mining process. Based on the technical characteristics of SBBM technology and the physical similarity criterion, the physical similarity models for comparing the control effects of water-flowing fracture (WFF) development using short-wall block cave mining (SBCM) and SBBM were established, and the deformation and the WFF development of overlying strata above gob were monitored. The test results determined that the composite materials of 5 mm thick pearl sponge+5 mm thick sponge+10 mm thick paper+6 mm thick board were adopted as the similar backfill materials by comparing the stress-strain curves between the similar backfill materials and the original gangue sample. When the backfilling body was filled into the gob, it would be the permanent bearing body, which bore the load of the overlying strata accompanied with the protective coal pillar. At the same time, the backfilling body also filled the collapse space of overlying strata, which was equivalent to reduce the mining height, and effectively reduced the subsidence and failure height of the overlying strata. Compared with SBCM, the test results showed that the maximum vertical deformation, the height of water-flowing fractured zone, and activity range of overlying strata using SBBM were reduced by 91.4%, 82.5%, and 64.9%, respectively. SBBM had a significant control effect on strata damage and WFF development, which could realize the purpose of water resource protection in coal mines.

A DOFS-Based Approach to Calculate the Height of Water-Flowing Fractured Zone in Overlying Strata under Mining

The distributed optical fiber sensing (DOFS) is a technique that can obtain full spatial and temporal information concerning the behavior of a large range of measurand fields along a fiber path and realize the distributed monitoring of the overburden section under mining. To calculate the height of water-flowing fractured zone caused by the exploitation of coal, this study employed distributed optical fiber sensors with OSI-C-S optical frequency domain reflectometry (OFDR) technology and designed a similar-material model test based on the engineering geological conditions of Daliuta Coal Mine. Through the test, deformation characteristics of overlying strata were studied, the linear relationship was summarized between the strain gradient and the shear stress measured by fiber sensors when the rock layer cracks, and a method was proposed of using the measured strain to measure the height of the water-flowing fractured zone in overlying strata. The test results show that there are several locations where the sign of the shear stress changes (positive to negative or vice versa) in the overlying strata during the initial stage of coal seam mining. As the working face advanced, the change locations gradually concentrated at the place where the rock cracks. By identifying the breakpoints of the rock and the locations where the sign of the shear stress measured by fiber sensors changes, this paper calculated the height of the water-flowing fractured zone in Daliuta Coal Mine. After comparing the height with the abscission layer position in the model test and the predicted height by the empirical formulas in the specification, it has been found that the three results are basically consistent, which in turn verifies the accuracy of this method.

Neural network–based prediction methods for height of water-flowing fractured zone caused by underground coal mining

The accurate calculation of the height of water-flowing fractured zone (WFFZ) in coal mine is a critical factor in ensuring mine safety and protecting surficial eco-environment. In view of inapplicability of traditional empirical formula for predicting the height of WFFZ, the correlation of the height of WFFZ and influence factors was analyzed firstly based on 82 collected groups of coalfield measured data in China. Results show that the mining thickness and mining depth have a significant effect on the height of WFFZ. Subsequently, the measured data were divided into two parts: 80% for training models and the remaining 20% for validation. Two prediction models, i.e., the multiple regression (MR) model and BP neural network (BPNN) model, were established and trained. A new merging model, multiple regression-BP neural network (MR-BPNN) model, was proposed by combining the multiple regression and BP neural network model. The prediction accuracy and generalization ability of the three models were verified by the recorded testing samples. Results of comparison suggest that three models all had better applicability for predicting the height of WFFZ in the coalmine, compared with the existing empirical prediction methods. More importantly, the MR-BPNN merging model combined the nonlinear mapping ability of neural network and empiric of multiple regression model, which could provide high-accurate, strong-generalized, and practical application for predicting the height of WFFZ of coalfield. In addition, the reason for the inapplicability of traditional empirical formula and the practicability of the proposed neural network-based prediction models were discussed.

Zoning method for mining-induced environmental engineering geological patterns considering the degree of influence of mining activities on phreatic aquifer

Environmental engineering geological patterns (EEGPs) are the generalized manifestation of environmental engineering geology with the protection of phreatic water resources as the core, especially in mining areas with fragile eco-geological environment. Based on the formation mechanism of mining-induced EEGPs, with the aim of win-win between protection of phreatic water resources and exploitation of coal resources, this study presents a zoning method for EEGPs. Taking the Yushenfu mining area in northern Shaanxi, China, as a case study, four types of EEGPs (basically unaffected model, gradually restored model after destruction, gradually deteriorated model, and disaster model) were defined separately. On the basis of the degree of influence of mining activities on phreatic aquifer, the zoning method for EEGPs was proposed. Firstly, the height of water-flowing fractured zone (WFFZ) and the residual aquifuge thickness were calculated using multivariate linear regression method. Secondly, according to the relationship among phreatic water leakage, groundwater recharge, and variation in groundwater level, the thickness of laterite, loess and bedrock as the thresholds between the EEGPs were separately determined. Thirdly, based on the thresholds between EEGPs and the linear variation of residual aquifuge thickness combination, the zoning criteria for EEGPs were formulated. Finally, the zoning results were obtained. Furthermore, the verification of the types of EEGPs in coalfaces and the comparison between the zoning results obtained using variable weight theory and those given in the present study indicated that the zoning results presented in the current study are more accurate and reasonable. The research results can provide theoretical basis for solving the contradiction between coal resource exploitation and eco-geological environmental protection.

A Mechanical Model of the Overlying Rock Masses in Undersea Coal Mining and a Stress-Seepage Coupling Numerical Simulation

The water inrush of a working face is the main hidden danger to the safe mining of underwater coal seams. It is known that the development of water-flowing fractured zones in overlying strata is the basic path which causes water inrushes in working faces. In the engineering background of the underwater mining in the Longkou Mining Area, the analysis model and judgment method of crack propagation were created on the basis of the Mohr–Coulomb criterion. Fish language was used to couple the extension model into the FLAC3d software, in order to simulate the mining process of the underwater coal seam, as well as to analyze the initiation evolutionary characteristics and seepage laws of the fractured zones in the overlying strata during the advancing processes of the working face. The results showed that, during the coal seam mining process, the mining fractured zones which had been caused by the compression-shear and tension-shear were mainly concentrated in the overlying strata of the working face. Also, the open-off cut and mining working face were the key sections of the water inrush in the rock mass. The condition of the water disaster was the formation of a water inrush channel. The possible water inrush channels in underwater coal mining are mainly composed of water-flowing fractured zones which are formed during the excavation processes. The numerical simulation results were validated through the practical engineering of field observations on the height of water-flowing fractured zone, which displayed a favorable adaptability.

Research on the Height of Water-Flowing Fractured Zone under the Weak Roof Strata and Fully Mechanized Caving Condition

The first working face production has suspend because of the great roof water inrush in Mindongyi coal mine, which has weak roof strata and mining use the fully mechanized caving method. In order to detect the height of water-flowing fractured zone, loses of drilling fluid observation method has carried on the flied test, the results showed that while the full-mechanized caving mining thickness is 7.7 m, the height of water-flowing fractured zone is 79.78 m, and the ratio of height to thickness is 10.36, meanwhile, the numerical simulation and similar material simulation have proved the test results are correct. The study enriched the domestic research fruits of the height of water flowing fractured zone, and provided technical references for Mindongyi coal mine mining.

Research on the Influence by Different Dip Angles Faults of the Damage Height of Superincumbent Stratum

For the issue of fault impact on the height of water-flowing fractured zone, the study worked out several damage heights of superincumbent stratum under the influence of different dip angles faults. The research shows that small angle fault influence area is apt to develop a wide range of the plastic zone,and the water-flowing fractured zone of high-angle fault influence area is apt to increase along the fault surface and breakover the aquifers of coal seam roof and floor.