Investigation of the short-term stress distribution in stopes and drifts backfilled with cemented paste backfill

Abstract

Cemented paste backfill (CPB) is largely used in underground mines worldwide. A key issue associated with application of CPB is to estimate the stresses in backfilled stopes and on barricades. Recent numerical and experimental results show that arching effect is absent shortly after the placement of CPB in stopes. However, stress decreases in barricade drift with increasing distance between the measurement points and drawpoint have also been observed, demonstrating arching effect shortly after the pouring of CPB. To explain these paradoxes, CPB is considered as Bingham fluid having a yield shear stress. Three dimensional analytical solutions are proposed to evaluate the short-term total stresses in backfilled stopes and on barricades, accounting for the CPB’s yield shear stress-induced arching effect. Stress diminution due to such arching effect in the backfilled stopes and on barricades is indeed obtained. But the reduction becomes insignificant using typical yield shear stress and stope geometry. More analyses indicate that the typical yield shear stress values do not fully correspond to field conditions where the yield shear stress would increase exponentially due to apparent consolidation (loss of water by drainage, a phenomenon similar to the desiccation of overly saturated fine-grained materials).