Interface Shear Behavior of Cementing Underground Mine Backfill

This paper presents the findings from an experimental investigation that was conducted to assess the shear behavior and the changes in the shear behavior and strength parameters for cemented paste backfill (CPB)-CPB interface as well as the effects of key influential factors (normal stress, curing time, interface roughness, and tailings) on the shear characteristics at the CPB-CPB interface. An extensive program of direct shear tests and microstructural analysis will be conducted to gain insights into the shear behavior at the CPB-CPB interface and the fundamental processes that are responsible for the observed behavior. The results show that the shear characteristics at the CPB-CPB interface are a function of the curing time (degree of cementation), the surface roughness of the CPB, normal stress, and chemical composition of the tailings. The shear behavior of a rough CPB-CPB interface is different from that of a smooth interface. A stress hysteresis loop was observed, and the prepeak linear phase of the shear stress-shear displacement response was an elastoplastic process. The shear failure at the CPB-CPB interface follows Mohr-Coulomb failure criterion. In addition, it was found that the CPB-CPB interface was not necessarily a weak plane with respect to the shear failure of the CPB structure. The shear strength at the CPB-CPB interface could be higher than that of the control CPB material (backfill without an interface) and depends on the surface roughness of the CPB and the curing time. An index of the transition curing time for the CPB-CPB interface was proposed to evaluate when the backfill structure would fail first along the CPB-CPB interface. The results presented in this paper will contribute to a better understanding of the shear behavior and the changes in the shear strength parameters of the CPB-CPB interface and guide the development of a constitutive equation for backfill structures that have an interface as well as providing a more cost-effective design for CPB structures.