Study on strike failure characteristics of floor in a new type of pillarless gob-side entry retaining technology above confined water

Abstract

In deep mining, the traditional technology of gob-side entry retaining by backfilling (GERB) would result in an increased degree of floor damage due to high stress and existence of pillar filling bodies. Especially when the GERB is implemented above confined water, due to long continuous excavation distance and large range of mining disturbance, there is usually a higher risk of floor water inrush along strike direction. To reduce mining disturbance of floor and study failure characteristics along strike direction, this paper first introduces a new type of technology of roof-cutting and gob-side entry retaining without pillars (RGERP) above confined water. It includes its application principle, process flow, comprehensive prevention and control method of water inrush. Second, based on theory of additional stress and Mohr-Coulomb criterion, the theoretical model of the RGERP floor along strike direction is constructed, and the form, range of failure zone in 11005-working face are calculated by a typical engineering case. Then, to study lifting law of confined water in the RGERP, a similar simulation test system is designed, and inflow rate and cumulative volume at different positions are obtained. In addition, the coupled numerical model of FLAC-PFC^3D is established to verify the theoretical model and similar simulation results. Based on this, the floor damage zone of the RGERP is characterized by distribution characteristics of fractures between particles, and developmental characteristics of floor four zones of the RGERP are defined. Finally, the floor failure law is measured by using the drillhole direct current method. The maximum floor failure depth is determined by unfolding the apparent resistivity in space with different electrode distances. The results are compared to traditional empirical formula, which comprehensively verifies the effectiveness of the RGERP for floor failure reduction and the rationality of four zones division.