Experimental and numerical modelling studies for rockburst assessment
Sponsor: Alamos Gold Inc., MITACS, Agnico Eagle Ltd, NSERC
MSC Thesis, Carlos Rojas Perez (2025)
Rockburst control in underground mines is a challenging problem, especially in deep metal mines with high ore extraction ratio. The increased likelihood of rockburst occurrence can be a cause for safety concerns to the mine operators. The parameters associated with rockbursts are generally related to geological features such as dykes and faults, mechanical rock properties, seismic activities, and production rates. Mining aspects such as stope sequence, mining direction, stope geometry, backfill material, and the mining method all contribute to the occurrence of rockburst. This thesis investigates rockburst potential at two underground mines in northern Ontario, namely Macassa Mine of Agnico Eagle Mines Ltd and Young Davidson (YD) Mine of Alamos Gold Inc. The thesis begins with a comprehensive literature review of rockburst assessment methods.
The first case study of Macassa Mine is of a sill pillar situated 5,600 feet (1,700 m) below surface. It is 360 feet (110 m) long and 50 feet (15.5 m) in height, with a varying thickness averaging 3 m. The sill pillar is planned for extraction with longhole stoping in retreat. Past mining activities employed cut-and-fill methods. The levels above and below the sill pillar are tight filled with pastefill. To assess the stress condition in the pillar, a 3D mine wide numerical model was created with FLAC3D finite difference code. The numerical model employs the Macassa geomechanical database and in-situ stress regime. Pillar burst conditions are assessed using the deviatoric stress ratio, also known as the brittle shear ratio (BSR), to estimate potential brittle shear failure, and the burst potential index (BPI) based on energy considerations to examine strainburst potential. Model calibration relied on microseismic monitoring activities in the sill pillar over the past year. Rockburst mitigation and control methods with dynamic support in the sill drives are discussed.
The second case study of the YD Mine focused on the lower mine in the depth range of 900 m to 1200 m below surface where strong seismic events were recorded. The study first required laboratory testing for the determination of mechanical rock properties and rock burstability. Rock core samples were acquired from different lithologies namely syenite, porphyry syenite, basalt, diabase, sheared sediments and sediments. The experimental program involved uniaxial compressive strength (UCS), Brazilian tensile strength (BTS) tests, and uniaxial load-unload (LUN) tests to help determine rock burstability by loading the rock sample to 70-85% of its UCS then unloading it. A FLAC3D numerical model was then updated with the new geomechanical properties and used for stress analysis. The numerical model simulates mining-induced stress distribution while following the history of stope extraction. Assessment is conducted using the BSR. The study revealed that strong seismic activities are attributed mainly to high pre-mining differential stress (𝜎10−𝜎30) with 𝜎10 running in the NE direction at an oblique angle to the orebody.