Study on strata movement control in deep partial backfill mining with massive weakly-cemented overburden considering secondary compression behavior of multi-lithology gangue

Partial filling mining is an effective active subsidence control and loss reduction technology for controlling ground subsidence. However, in the complex environment of massive weakly-cemented overburden in the western region, under the coupled influence of high ground stress-water environment, the composite rock gangue filling body will undergo significant secondary compression deformation, making it impossible to precisely control geological disasters such as rock burst and surface subsidence. Therefore, by establishing the PFC-FLAC coupling model of partial filling mining, this paper explores the secondary compression deformation characteristics of multi-lithology gangue filling under the coupling action of high ground stress-water environment, and deeply discusses the influence law of partial real filling rate on rock movement control. The results show that the change of filling rate has a linear function relationship with overburden stress, roof subsidence and surface subsidence, which is a direct factor to reduce subsidence space and inhibit roof and surface settlement. Under the coupling effect of high ground stress and water environment, the secondary compression rate of the multi-lithology gangue backfill reaches 5%-8%, and the filling rate has a great influence on the synergistic mechanism of the composite carrier. When the real filling rate is close to 81%, the saddle-double triple arch-half mushroom arch stress field is formed by the synergistic interaction between the composite carrier and the triple arch on both sides, which makes the surface subsidence coefficient of the superfull mining state only 0.31. This study can provide data reference for the design of multi-lithology gangue filling, which has high practical value for the green mining of coal resources and environmental protection.