Consolidation process of uncemented backfill slurry in a mine stope considering hydro-geotechnical properties of rockmass in adjacent stopes

Abstract

A reasonable assessment on pore water pressure (PWP) and effective stresses of backfill slurry during consolidation process is critical to ensure a secure and economic backfilling in mine stopes. This task can be accomplished by analytical or numerical simulations, but most of the previous simulations did not take into account the hydro-geotechnical properties of rockmass in adjacent stopes, which was mainly simplified to an impervious boundary. This treatment may not be representative of the field conditions in underground mine stopes because of the presence of geological joints and/or mining induced cracks in surrounding rockmass that serve as seepage paths for pore water discharged from the filled slurry. In this paper, numerical modeling was conducted with FLAC3D to investigate consolidation process of uncemented backfill slurry in a vertical stope considering the surrounding rockmass with different permeability, initial saturation, porosity, and the rockmass width. The results show that the PWP and effective stresses of backfill slurry in a mine stope considering adjacent rockmass can be very different with numerical outcomes by simplifying the rockmass as impermeable or permeable boundaries assumed in previous studies. For the same backfill slurry in mine stopes with different drainage conditions along side walls, the peaks of the PWP and effective stress differ by a factor of three to five for each consolidation process. This would make the evaluations on backfill slurry consolidation either too conservative, with impermeable side walls, or too aggressive, with free drainage side walls, ignoring the actual rockmass hydro-geotechnical parameters. Different hydro-geotechnical properties of the rockmass have different impacts on the evolutions of the PWP and effective stresses of the consolidating backfill slurry. However, when the hydraulic conductivity of the surrounding rockmass is lower than 10− 8 m/s, the simulated PWP and effective stresses for the backfill slurry will be comparable to the numerical models that simplify the rockmass to a watertight boundary. Furthermore, the influences of different hydro-geotechnical properties of adjacent rockmass on the lateral earth pressure coefficient of consolidated backfill were also discussed. In addition to the validations of simulated PWP and stresses against the analytical results with Gibson model and an arching model respectively, the numerical results were compared with the previous published in-situ monitoring benchmarks to validate the consolidation process simulated by FLAC3D here.