Calculation of the Height of the Water-Conducting Fracture Zone Based on the Analysis of Critical Fracturing of Overlying Strata

Accurate division of the water-conducting fracturing zone (WCFZ) in the mining overburden serves as an important basis to evaluate the stability of coal mining under water bodies. Research on the WCFZ is conducive to controlling surface subsidence and realizing safe coal mining under water. Traditionally, the WCFZ is generally determined by field observation (liquid leakage method, borehole television, etc.) or empirical formula. Although these methods boast high accuracy, they are time-consuming and laborious and have some problems such as weak pertinence and a large value range. In this study, a mechanical model under the critical breakage condition of hard and soft strata was established on the basis of the specific geological and mining information of a mine. Besides, the stability condition for the broken strata to form the “masonry beam” structure and the deflection-based bending deformation formula of hard and soft strata were deduced, and the method of calculating the height of WCFZ based on the analysis of critical fracturing of soft and hard strata (hereafter referred to as the CFSHS-based height calculation method) was proposed. Furthermore, with reference to the results of specific engineering tests, the height of the WCFZ in the working face 15,101 of coal mine XJ was analyzed by means of theoretical analysis, numerical simulation and engineering verification, which verifies the rationality and practicability of the CFSHS-based height calculation method.