Law Of Overburden Fracture Evolution In Shallow Buried Close Distance Coal Seam Under Repeated Mining

Based on the Shigetai coal aquifer, aquifuge and overburden geological features，mechanism and control technique of water flowing fractured evolution of shallowburied close distance coal seam under repeated mining is put forward in this paper,solving the contradiction between the large scale mining of shallow buried closedistance coal seam and water resources protection. Numerical simulation andtheoretical analysis are conducted to analyze the mechanical properties of aquifuge,the laws of overburden movement and fracture development, the factors that impacton the water flowing fractured development of overburden between the upper and thelower and between the main key stratum and aquifuge, the main key stratum stabilitytheory, and technical measures of water conservation mining of shallow buried closedistance coal seam are proposed. The main research results are as follows:(1) The damage of aquifuge is in the form of tensile failure that breaks with thesudden by the test of mechanical properties, and aquifuge can remain integrity andhave a strong ability of water-resisting property as long as the level of tensiledeformation ε does not exceed0.20%~0.24%.(2) Simulation of12105working face draws the characters of overburden stratamovement, water flowing fracture evolution law and water resisting layer horizontaldeformation features. On the basis of Shigetai mine, Simulation makes a analysis tothe overburden geological conditions that affect the evolution of water flowingfractured and draws that can realize the water conservation mining the minimum D/Mand its corresponding development characteristics. The thickness relationship of stratabetween aquifuge and main key stratum which can contain aquifuge stability isobtained and draws best lithology combination for control water flowing fracturedafter main key stratum breaking.(3) Meanwhile, simulation analyzes the influence of different mining factors onwater flowing fractured, including mining height, working face layout, miningmethods and different mining speed of working face, and obtains water flowingfractured development characteristics under different mining conditions.(4) Criteria of the height of water flowing fractured is obtained by the analysis ofelastic thin plate theory and reasonable mining height is determined according to themain key stratum which does not damage instability. Combining with numericalsimulation and theoretical analysis results, some suggestions about water conservation mining are proposed in shallow buried close distance coal seam under repeatedmining and water conservation mining measures are given based on the stability of themain key stratum.