Abstract: Due to the low bearing capacity of roadside backfill in the early stage of roadside backfilling, it is critical to maintain the stability of key block at the face end during roadside backfilling. In this paper, based on the criterions of slip instability and rotation instability, the formula of roadside support resistance is derived, through establishing the mechanical model of key block structure in the gob-side entry retaining. Taking headentry of No.512(5) mining face as project background, we have studied the effects of roadside coal support resistance, roadway-inside support resistance, roadside support resistance and width of roadside backfill on the stability of key block. The results show that it is beneficial to improve the stability of key block, when using high active supporting force in roadway-inside support, high pre-stressed, high-strength bolting in roadside coal support, and adopting the backfilling materials with high strength and quickly increased resistance at early stage in roadside support. Based on the study results mentioned above, the supporting parameters of gob-side entry retaining in the headentry of No.512(5) face are designed. The engineering practices show that, it is reasonable and feasible to adopt combined support with bolting, cable and wire mesh as the basic supporting in roadway-inside, use different strengthening supporting in different zones of roadway-inside, and choose backfilling process system of pumping quick-setting materials of high water in roadside supporting. The stability of key block during the gob-side entry retaining can be ensured when the support resistances of roadway-inside and roadside are not less than 0.15 MPa and 3.5 MPa, respectively, with the width of roadside backfill is 2.5 m.

Key words: the gob-side entry retaining , the stability of key block , roadside support resistance, the width of roadside backfill