Assessment of expansion and strength properties of sulfidic cemented paste backfill cored from deep underground stopes

Abstract

The expansion and strength of cemented paste backfill (CPB), especially when prepared from sulfide mill tailings, are valuable properties for the estimation of design parameters for underground stope filling. These properties are particularly important for deep mining. In this paper, the free expansion ratio of CPB specimens containing sulfides was investigated using an invented apparatus called the free expansion measuring instrument. Moreover, the unconfined compressive strength (UCS) of backfill materials cored from the deep stope was studied. In the laboratory, the filling specimens continued to expand, and substantial cracks were observed at 28 days. Moisture and other reactants entered the samples through the cracks, and the specimens continuously expanded until collapse. In the deep mining stope, the strength of the backfill body in the same horizontal plane presents a wave-type change along the flow direction of the paste (or y-direction) and a hammock-shaped change along the x-direction (or crossing the y-direction). In the deep mining stope, due to the wall convergence effect of the deep surrounding rock and the expansion effect of the filling body, the filling material underwent a consolidation process. The backfill material after consolidation had a finer pore mechanism and a more compact microstructure based on the results of scanning electron microscopy. Therefore, the strength of the backfill near the surrounding rock was higher than that in the central area. The mechanical properties of the CPB mass differ at different locations along the same height in the stope, and the expansion of the sulfidic cemented paste and the convergence of the rock wall play reinforcing roles.