Stress evolution in stope roof with roof-contacted filling by expansive backfill under lateral confinement release during second-step mining

Abstract

In order to investigate the stress evolution of the roof of roof-contacted filling with expansive backfill during the state of lateral confinement release following the second-step of mining, this paper employs both theoretical analysis and numerical simulation methods to examine the variations in roof stress under three distinct roof-contact modes: roof-contacted unfilling (RCU), roof-contacted filling with ordinary backfill (RCO), and roof-contacted filling with expansive backfill (RCE). The results indicate that: (1) During the second-step extraction, upward expansion of the expansive backfill is constrained. Following self-expansion, it exerts pressure on both the roof and the underlying filled pillar, generating expansive stress. This expansive stress actively counterbalances the vertical load on the roof while extending the distribution range of compressive stress upward, leading to a shift in tensile stress concentration towards the center of the stope during this step. (2) The distribution shape of compressive stress within the roof adopts an arch form, extending from points of contact with both sides toward adjacent stopes in this second-step. The roofs of those stopes situated near pillars receive significant support from expansive backfill. (3) The downward pressure exerted by expansive backfill on conventional backfill increases vertical stress at their contact surface between pillars and roofs, thereby enhancing restraint against lateral slippage of pillars.