Height of water-conducting fractured zone in coal mining in the soil–rock composite structure overburdens

Large-scale mining of coal seams gives rise to the leakage of phreatic water and further deteriorates the ecological environment of arid and semiarid mining areas in Northern Shaanxi Province. The height of the water-conducting fractured zone (WCFZ) in coal mining is the key to evaluating the presence of phreatic water leakage. This paper adopts the running water quantity of boreholes monitoring and distributed optical fiber sensing (DOFS) technology to conduct in situ measurements of the WCFZ height in soil–rock composite structure overburdens. Twenty groups of data were used to analyze the factors which influence the development height of the WCFZ and several equations are proposed to estimate the WCFZ characteristics. As indicated by the study results, the DOFS technology effectively ascertains the height of water-conducting fractures in soil and the soil layer had an obvious inhibitory effect on the height of WCFZ, with an inhibiting factor of about 0.5. The maximum relative error between predicted values and measured values was 5.34% and the relative error between predicted values and numerical simulation results was within 1.5%, verifying the accuracy of the prediction equations. The study results will help avoid water inrush hazards in mining areas and protect mining areas against ecological damages.