Study on optimization of expansion material ratio and filling effect of end slope mining tunnel

In order to solve the problem that the backfill body can not be connected to the roof in the process of end slope filling mining in open pit coal mine and to investigate the influence of filling rate on the deformation and failure characteristics of mining tunnel, the effects of different contents of red mud, cement and mineral powder on different properties of the expansive filling materials and the deformation and failure of the mining tunnel under different filling rates were studied by means of laboratory test and numerical simulation. The results indicate that when the mass ratio of red mud, cement, and mine powder is 4:2:3, the performance of the expansive filling material is optimal; the extreme values of roof subsidence and compression of supporting coal pillars exhibit a quadratic decreasing relationship with the filling rate; when the filling rate is in the range of 80%-90% and 90%-100%, the compression extremum of the supporting coal pillar decreases by about 3.5 mm and 6.5 mm, respectively, and the compression deceleration speed of the supporting coal pillar shows an increasing trend with the increase of the filling rate; under different filling rate conditions, the vertical stress variation of supporting coal pillars demonstrates a superimposed “saddle-shaped” distribution pattern; in the filling rate range of 80% to 100%, the development height of the plastic zone in the overlying strata decreases with the increase in filling rate, and the overall decrease rate of height accelerates with the rise in filling rate; increasing the filling rate with expansive materials significantly reduces the deformation of the roof and supporting coal pillars, narrows the plastic zone range.