Characterization of pressure arching effect of arch shell surrounding rock considering deviation of principal stress axis

The arching effect is the comprehensive performance of pressure transferr and redistribution of rock and soil mass around the excavated area, which widely exists in the self-bearing surrounding rock of underground mining projects. Aiming at the actual characteristics of the far-field arch shell structure outside the fractured arch of overlying strata in the mining area, the deviation response characteristics of the principal stress vector of the rock strata under the action of mining unloading are analyzed based on the principle of Terzaghi's soil arching effect, and by discussing the active released state of vertical pressure and the vertical stress distribution characteristics of overlying strata under the influence of deviation of the principal stress axis, the arching index of compressive stress of key part of the pressure arch in far-field surrounding rock is proposed. The numerical software FLAC^3D is used to simulate and calculate the arching law of deviated principle stress of overlying strata in the mining area, and the results show that the deviation angle of the principal stress in the far-field surrounding rock is controlled by the initial major principal stress, lateral pressure coefficient, shear stress increment and changing rate of principal stress difference after mining; the deviation angle of the principal stress of rock strata decreases from the midspan to both sides of the goaf boundary at the same horizontal position; the vertical stress of the exposed rock strata decreases with the increasing deviation angle of the principal stress; the deviation angle of the principal stress, active pressure coefficient and peak value of arching index at the arch top are greater than those in the arch foot region; and the rising vertical stress in the arch foot and arch waist behaves as the bearing pressure. According to the derived mechanical criterion for releasing state of the vertical pressure in rock strata and the arching index of compressive stress, the loading and unloading states of the far-field surrounding rock and the evolution characteristics of pressure arching effect under the influence of deviation of the principal stress axis are characterized.