Numerical investigation of crown pillar recovery beneath stabilized rockfill

Significant mining reserves at the Crusader Mine have been sterilized due to the placement of loose rockfill above crown pillars as mining progresses in a top-down extraction strategy. The application of selectively injecting specifically developed ettringite type cement grout into loose rockfill, enables an artificial crown pillar to stabilize the surrounding rockmass and prevent the caving of loose rockfill from the previously backfilled stopes during extraction of the underlying crown pillar. In order to represent the physical separation and caving of undermined stabilized rockfill, PFC^2D has been used to simulate the recovery of crown pillars beneath stabilized rockfill. The PFC^2D modeling approach is more representative of a stabilized rockfill matrix than continuum modeling approaches, as the initial stresses developed within the stabilized rockfill are modeled explicitly during placement of the loose rockfill. Calibration of the adopted PFC^2D modeling methodology has been conducted during the recovery of two remnant crown pillars beneath stabilized rockfill.