Numerical and theoretical study of large-scale failure of strata overlying sublevel caving mines with steeply dipping discontinuities

Abstract

The deformation and fracture evolution mechanisms of the strata overlying mines mined using sublevel caving were studied via numerical simulations. Moreover, an expression for the normal force acting on the side face of a steeply dipping superimposed cantilever beam in the surrounding rock was deduced based on limit equilibrium theory. The results show the following: (1) surface displacement above metal mines with steeply dipping discontinuities shows significant step characteristics, and (2) the behavior of the strata as they fail exhibits superimposition characteristics. Generally, failure first occurs in certain superimposed strata slightly far from the goaf. Subsequently, with the constant downward excavation of the orebody, the superimposed strata become damaged both upwards away from and downwards toward the goaf. This process continues until the deep part of the steeply dipping superimposed strata forms a large-scale deep fracture plane that connects with the goaf. The deep fracture plane generally makes an angle of 12°–20° with the normal to the steeply dipping discontinuities. The effect of the constant outward transfer of strata movement due to the constant outward failure of the superimposed strata in the metal mines with steeply dipping discontinuities causes the scope of the strata movement in these mines to be larger than expected. The strata in the metal mines with steeply dipping discontinuities mainly show flexural toppling failure. However, the steeply dipping structural strata near the goaf mainly exhibit shear slipping failure, in which case the mechanical model used to describe them can be simplified by treating them as steeply dipping superimposed cantilever beams. By taking the steeply dipping superimposed cantilever beam that first experiences failure as the key stratum, the failure scope of the strata (and criteria for the stability of metal mines with steeply dipping discontinuities mined using sublevel caving) can be obtained via iterative computations from the key stratum, moving downward toward and upwards away from the goaf.

Keywords

sublevel caving mines / universal distinct element code (UDEC) numerical approach / large-scale ground movement / steeply dipping superimposed cantilever beam / toppling failure

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