Using gangue backfilling in underground coal mining not only controls the roof deformation in the gob area but also reduces the amount of mining waste rock. However, due to the limitations of the complicated engineering conditions, backfilling mining in the steep coal seam is not widely applied. In this study, a long-distance backfilling technology with a scraper winch for a steep coal seam was proposed and applied in a flexible shield supporting working face in Datai Mine, Beijing. Aiming at the problem of the decreasing backfilling ratio in field practice, numerical simulation was carried out to research the moving law of gangue in the goaf. The gangue mainly experienced four stages: gangue landslide stage, small-scale subsidence stage, funnel-shaped subsidence stage, and large-scale subsidence stage. The moving area of the gangue could be divided into five areas including a motionless area, a landslide area, a subsidence area, a funnel-shaped subsidence area, and a to-be-backfilled area. With the increase of the inclined length of the working face, the moving time of the gangue increased gradually. Based on the simulation results, the scheme of backfilling and mining in Datai Mine was optimized, for which the inclined length of the working face was shortened, and a higher backfilling ratio was obtained.

Waste-rock material used in underground backfill mining has a granular texture and acquires non-linear deformation characteristics when compressed. The deformation modulus of waste-rock measured by a laboratory compression test is significantly different from the true deformation modulus in the field, due to the complete confining effect of the loading steel cylinder. In this study, we performed a series of laboratory-based compression tests on waste-rock samples. The results showed that lab-acquired deformation modulus variations of waste rock could be divided into three stages: slow increase, accelerated increase, and rapid increase. We also measured the true deformation modulus of backfill waste rock by conducting a field test in gob areas of the Tangshan coal mine, China. The hardening process of backfill waste rock during the field test was analyzed, and could be divided into four stages: roof contact, rapid compression, slow compression, and long-term stable. With the increase of axial strain, the lab- and field-measured deformation moduli of waste rock both increased exponentially. A correction parameter was proposed to investigate the relationship between the field-generated true deformation modulus and the lab-tested deformation modulus. The correction parameter k positively correlated with the axial strain, in the form of an exponential function. The magnitude of k was between 0.5616 and 0.6531.

The pressure relief with large‐diameter boreholes is one of the effective methods to prevent coal bumps in deep coal roadway. An unreasonable pressure relief design can cause the rockbolt support failure and aggravate the deformation of the surrounding rocks. In this paper, a coupling model of roadway sidewall considering borehole pressure relief and rockbolt support was established. The influence of the destressing borehole diameter on the rockbolt located in the plastic zone and the roadway deformation was studied by theoretical calculation and numerical simulation. The results show that there is a critical zone of the borehole diameter for the influence on the rockbolt normal stress and roadway convergence. When the destressing borehole diameter exceeds the critical zone, the rockbolt normal stress decreases sharply. Considering the existence of the broken zone in the surrounding rock, the bolehole diameters in the critical zone increase with the increase of the distance between the borehole and the rockbolt, the residual strength, and decrease with the increase of initial stress. In the engineering analysis, with the increase of the destressing borehole diameter, the ultimate pullout force of rockbolt decrease, and the plastic zone of surrounding rock, the roadway deformation, the maximum axial force, and slippage of the rockbolt all increase. Therefore, to better keep the stability of the surrounding rock in coal roadway, the borehole pressure relief needs to be coordinated with the rockbolt support. The destressing borehole diameter in the pressure relief design should not be greater than the critical zone.