Evolution characteristics of water flowing fracture in shallow buried coal seam in water abundance gully valley area

The occurrence conditions of shallow buried coal seams under the water-rich gully region are special, and the development and evolution characteristics of water-conducting fractures in the overlying strata of the stope are complex. In order to reveal the evolution law of overlying rock fracture in shallow buried coal seam under mining disturbance in gully area, taking the mining stage of 1305-2 working face in Zhujiamao Coal Mine as the engineering background, the conceptual model of overlying rock fracture-seepage field was established by means of theoretical analysis, physical similarity simulation, numerical simulation and field effect verification. The development of overlying rock structure and the evolution of microseismic energy were studied, the distribution characteristics of overlying rock deformation and plastic failure were analyzed, and the prevention and control measures of water flowing fracture in shallow buried coal seam under gully area were put forward and applied to field engineering practice. The results show that the fracture-seepage field model under mining disturbance is a ‘terrace’ structure, which is divided into three regions: initial seepage region, stable seepage region and turbulent seepage region. Substituting the working condition data of the studied mine into the model structure, the range of each infiltration area is calculated, and the grouting measures are taken for the stable infiltration area of the mine according to the calculation results. When the working face is mined to the valley section, the shape of the overburden fracture domain presents the expansion and evolution characteristics of “arch-trapezoid-composite trapezoid”. The longitudinal development height of the fracture reaches 163 m and is connected with the surface of the valley area. With the advance of the working face, the surface cracks experience the process of “slip-extrusion-tearing” in turn. The displacement cloud map of the valley area shows a “high trapezoidal” fracture pattern of lagging mining, and the subsidence displacement value at the bottom of the ditch is the largest, reaching 3.47 m. In view of the large-scale expansion and penetration of cracks caused by mining, it is proposed to carry out grouting treatment of mining-induced cracks on the ground and grouting plugging in the overlying strata of the working face, so as to realize the joint prevention and control of “up-hole-down-hole” mining in the gully area and ensure safe mining. The results of this study can provide a new scientific basis for the mining of shallow coal seams in the valley area, the prevention and control of mining-induced cracks, and the “water-preserved coal mining” in water-rich areas.