Experimental study on the effect of passive interface resistance on the multiphysics process in cemented paste backfill

Abstract

As a novel technology, cemented paste backfill (CPB, a mixture of hydraulic binder, tailings and water) has been widely adopted in underground mines for ground support, particularly in Canada. After placement into underground excavation spaces (termed stopes), a narrow interfacial transition zone is formed along CPB-rock interface and affects the mechanical stability of bulk CPB at the macroscale. Moreover, CPB is simultaneously subjected to coupled thermal (T), hydraulic (H), mechanical (M) and chemical (C) loadings from early to advanced ages. Therefore, to assess the behaviour of CPB, the interface behaviours and associated multiphysics problems must be fully considered and assessed. In this study, a new large-scale THMC column model is developed to experimentally study the effect of interface behaviour on the CPB at the macroscale and its effect on the multiphysics processes. It has been found that the interface interaction significantly reduces the settlement and vertical stress and thus results in a large porosity in CPB matrix. Consequently, the porosity-dependent hydraulic conductivity is sensitive to the interface interaction, which in turn influences the evolution of matric suction. Similar indirect effects of interface interaction on the evolution of temperature and binder hydration were observed in this study. Moreover, it has been confirmed that the interface interaction can weaken mechanical behaviour and properties including elastic modulus, shear stiffness, cohesion, and UCS of CPB by its effect on the multiphysics processes. Therefore, the obtained results can further improve the strength-based design approach for CPB used in underground construction and thus contributes to its successful and safe implementation in practice.