Abstract
Backfilling is commonly used in underground mine operations around the world. The main objective of backfilling is to improve the stability of openings and workers safety, while reducing the amount of mine waste stored on the surface. The environmental and economic benefits of returning part of the tailings or waste rock underground are also part of the rationale behind backfilling. Mine backfill can also serve to limit convergence of the walls and maintain the integrity of pillars by adding lateral support. A good understanding of the complex behavior of the fill material and its interaction with the surrounding rock mass is a key step in assessing ground stability issues. Stress distribution analyses inside backfill stopes are necessary for the initial assessment of filling capacity and deposition options. To date, most analyses conducted for the stress distribution and related arching effect in backfilled openings, including two and three-dimensional analytical solutions, have been performed for hard rock mines with little deformation of the walls after backfill placement. The analysis can however become more complex when the rock is subjected to time-dependent (creep) behavior as is the cases in many low porosity soft rocks and in deep excavations in relatively weak rock masses. To date, little work has been done on the time-dependent stress in backfill.
This investigation will present recent numerical and analytical solutions that help improve our understanding of the response of backfilled stope interaction with creeping rocks in underground mines. A series of numerical simulations are used to describe the evolving stress-strain conditions around backfilled stopes with conventional geometries. The simulations are performed with FLAC in which the time-dependent ISV-SH model (i.e. Internal State Variable model with Strain-Hardening) has recently been implemented. The numerical results show how the stress distribution in the fill material and surrounding rock mass evolve progressively when the rock exhibits a significant time-dependent response. This is also seen from field monitoring of the time-dependent stress state in the backfill. The numerical implementation and associated calibration of the model will be discussed for practical considerations towards site-specific applications.