Influence of multiple mining damage on the stability of water-resisting control strata

The stability of sandwiched water-resisting strata plays a significant role in the closed multiple-seam mining.The upper accumulated water in the upper gobs can seeped and flow into the lower mining space once the stability of sandwiched water-resisting strata is destroyed. In some situations,a sudden release of upper accumulated water is oc-curred,which brings serious threats for the safe mining of lower coal seam. The basic concept of water-resisting control strata under the influence of multiple mining was proposed in this paper. The damage parameter (D) calculation model of interburden was established based on theories of damage mechanics. The relationships between the damage parame-ters (D) and the compressive strength / the damage range of interburden were analyzed,respectively. Then,the influ-ence of multiple mining damage on the stability of water-resisting control strata was investigated. The results showed that ① The water-resisting control strata referred to the strata which did not broken under the multiple mining influ-ences and played a significant role in preventing the downward seepage and expansion of accumulated water in the up-per gobs. ② The damage parameter ( D) could be used to measure the damage range of interburden under multiple mining influences. ③ The relationship between the compressive strength (RD ) of the interburden and the damage pa-rameter (D) was: RD of the interburden showed a linear decreasing trend with the increasing of D. The reduction fac-tor was 1-D. ④ The maximum failure depth / height (Hmax ) and the maximum distance to the working face (Lmax ) in-creased with the increase of damage parameter (D). The larger the damage parameter (D),the greater the increase of Hmax and Lmax . ⑤ The stability of water-resisting control strata was closely related with the superimposed damage in-duced by the multiple mining. It was necessary to comprehensively evaluate the damage range of interburden under the multiple mining of upper and lower coal seams. The stability of water-resisting control strata under six different condi-tions were determined and the reasonable control measures were then complemented to ensure the safety of lower coal seam mining. The study on the influence of multiple mining damage on the stability of water-resisting control strata can provide a theoretical guidance for the safe mining of lower coal seam under the water accumulation area.