Regional Division and Its Criteria of Mining Fractures Based on Overburden Critical Failure

Abstract

Mining fracture is the key factor in realizing water-conservation mining, stability evaluation of coal mining subsidence areas, and accurate restoration of the surface eco-environment. To clarify, the evolution and distribution of mining fractures, based on the key strata theory and the mining degree of overburden failure, the contact state of rock stratum after overburden critical failure was analyzed, the formation mechanism of “saddle shaped” water conducting fracture zone was revealed, and the permanent mining fractures were determined to be primarily concentrated in the overburden structure at the boundary of the working face. According to the shear test of sandstone in the fracture zone, the damage degree of the rock sample was positively correlated with shear stress, and the overburden structure exhibited no instability. Based on the distribution of mining fractures, the fracture zone was divided into the original fracture, tensile fracture, structural void, and void compaction areas in the horizontal direction. The structural void area had the largest residual deformation in the goaf. A regional division method based on overburden critical failure was proposed and applied in engineering by using surface movement monitoring. The results showed that the surface subsidence near the boundary of working face was greater than that in the middle, and the residual surface deformation in the goaf was closely related to the mining time, which has long-term characteristics. The rationality of the regional division method of mining fractures was also verified.

Characteristics and Formation Mechanism of Surface Residual Deformation above Longwall Abandoned Goaf

“…The formation of surface residual deformation mainly lies in the overburden gaps, and the distribution of overburden gaps mainly lies in the overburden failure and its structure [35]. Thus, the influencing factors of surface residual deformation are equivalent to that of overburden structure and caved zone, which also is the influence factors of overburden failure height.…”

Green coal mining under buildings by overburden grout injection for coalmine sustainable development of central China

“…Meanwhile, with the panel continuous advances, the subsidence and separation occur only in the middle of bending zone. The contact state of the rock stratum interface will go through the process of point-to-surface, line-to-surface from the non-contact state to the surface-to-surface contact, and the separation will gradually reduce to the compaction state until the mining subsidence is transferred to the surface [ 39 ]. For ensuring the effectiveness of overburden grout injection and safe mining under buildings, backfilling slurry needs to be injected before the maximum development of separation space, and there must be a key stratum in the bending zone.…”

Stability-Level Evaluation of the Construction Site above the Goaf Based on Combination Weighting and Cloud Model

“…Many scholars have carried out research around this topic using to different theories. By analyzing the overburden failure and structure formation conditions, Bai et al (2022) proposed a regional division method and concluded that the residual surface deformation of a goaf was closely related to the mining time [14]. Xu et al (2023) evaluated the stability of a goaf through numerical simulations, and then classified the suitability of the site based on the simulation results and proposed different ecological restoration schemes [15].…”