Abstract: The shear mechanical properties and parameters of the interface between backfill and boundary medium are the basic data for studying the stress distribution of backfill stope and evaluating the stability of backfill exposure. Through the combination of indoor direct shear test and RFPA3D numerical simulation test,the backfill-boundary medium combination (backfill-surrounding rock,backfill-ore body,cemented backfill-unconsolidated backfill) with three cement-sand ratios (1 ∶4, 1∶8 and 1∶20) and four contact surface normal stresses (50 kPa,100 kPa,150 kPa and 200 kPa) is studied. The results show that:with the decrease of the ratio of lime to sand,the peak shear strength of the backfill-surrounding rock combination decreases, and the failure mode changes from brittleness to ductility,and the failure mode changes from particle adhesion and block adhesion to the tip of the convex body and is cut. When the cement-sand ratio is 1∶4,the shear stress decreases vertically,and the ringing count rate suddenly increases,while the ringing count rate is relatively small at other stages. From the crack compaction stage to the failure stage,the acoustic emission ringing count rate is dense,and there is obvious dilatancy deformation in the shearing process. The peak shear strength of the interface between filling body and boundary medium decreases with the decrease of normal stress and lime-sand ratio. The peak shear strength of cemented backfill-surrounding rock interface is slightly less than that of cemented backfill-ore body,and the peak strength of cemented-non-cemented backfill combination is far less than that of ore-rock combination,which is close to the strength of non-cemented backfill itself. The cohesion and internal friction angle of the interface between the filling body and the boundary medium combination decrease with the decrease of the ra-tio of lime and sand. The cohesion and internal friction angle of backfill-surrounding rock and backfill-ore body are close,but the parameters of cohesion and internal friction angle of cemented-unconsolidated backfill are much smaller than those of cemented- ore-rock combination. The research results expand the acquisition method of shear mechanical properties of backfillboundary medium combination,and provide basic data for stability analysis of backfill stope.

Key words: backfill mining,backfill-boundary medium combination,nonlinear interface,shear mechanical properties,numerical simulation