Predicting The Distribution Of Ground Fissures And Water-conducted Fissures Induced By Underground Coal Mining

The use of Top Coal Caving for exploiting the thick coal seam with shallow buried depth most likely has a strong negative impact on the stability. Top coal caving mining is one of the most widely used method of thick coal seam mining in China, when using this method, the depth of mining large thickness of coal seam, most likely failure of overlying rock subsidence caused by serious, violent, induce surface cracks and water flowing fractured abnormalities, leading to the goaf air leakage, Water Leakage accident, will seriously endanger the safety in production of coal mine. Therefore, when the top coal caving mining in shallow coal seam, large thickness, it is necessary to cause surface cracks and water conducted fracture distribution prediction.An Jialing No.1 Underground Mine and An Taibao Underground Mine are located in Shuozhou City, Shanxi Province. The coal seams of these coal mines are the thick coal seam with shallow buried depth. This paper focuses on predicting the distribution of ground fissures and water-conducted fissures induced by the exploiting of the coal seams. We first create a 3D computational model, and then use FLAC3D4.0 software to simulate the mining of coal seam. We calculate the displacements and tensile strain of the ground surface and strata, and predict the distribution of the ground fissures and water-conducted fissures. Finally, we further analyze the possibility of the perviousness and air leakage of the coal mine on the basis of the predicted distribution of fissures.The prediction results indicate that:(1) It can be learnt from the distribution of the ground fissures that: in the beginning of the mining process, the impact of underground mining on the deformation of ground surface is quite little, and cannot lead to the forming of ground fissures; then the ground fissures begin to occur; and in the subsequent steps of mining, the ground fissures periodically expand along both the two directions that are parallel to and perpendicular to the direction of mining; finally the opening fissures are oval-shaped distributed around the boundary of the mining area, while the dynamic fissures are mainly distributed above the mined-out area.(2) According to the distribution of the water-conducted fissures, the water-conducted fissures are formed in the process when the overlying strata crack and collapse, and alter periodically from being open to being closed. After the completion of mining, the distribution of the water-conducted fissures are saddle-shaped, which is quite consistent with the theoretical distribution form.(3) The water-conducted fissures are strongly developed and go through the aquifuge in some region; thus it may lead to potential perviousness of coal mines; part of the water-conducted fissures distributed in the north side of the panel connect with the ground fissures; and this behavior may cause the risk of air leakage.Moreover, the numerical results obtained by using the proposed method are well accidence with the analyzed theoretical results and those observed practical results. This definitely indicates that the prediction method proposed in this thesis is effective in practice.