Mechanism and comprehensive control techniques for large deformation of floor heave in block filling gob-side entry retaining

In order to solve floor heave, a common problem in gob-side entry retention (GER), with block filling gob-side entry retaining in Faer Coal Mine as engineering background, deformation characteristics and mechanical mechanisms of floor heave were studied through theoretical analysis, numerical simulation, and filed tests, and comprehensive control technology was proposed. Results have shown that floor heave of GER mainly occurs during first mining period, and with the advance of working face, deformation of floor presents three stages: variable acceleration accelerated deformation, variable acceleration decelerated deformation, and constant acceleration decelerated deformation. During the process of retaining roadway, vertical concentrated stress of coal wall and block wall cause plastic slip of rock below to produce horizontal stress, which pushes roadway floor strata to produce triangular slip zone, thus causing floor heave. The maximum failure depth and effective driving force of plastic slip of floor are proportional to vertical concentrated stress of coal wall and block wall, therefore vertical concentrated stress on two sides of retaining roadway caused by mining is a fundamental reason for floor heave. Based on this feature, the comprehensive control technique for floor heave integrating "pressure relief by roof cutting, flexible yielding, controlling wall with double-direction-control anchor bolts, and controlling roof with reinforcing anchor cables" was proposed. An engineering test was carried out, and field monitoring results have shown that this technique can control floor heave well in GER. © 2022, Editorial Board of Journal of Mining & Safety Engineering. All right reserved.