Evan Dressel completes MASc

Congratulations to Evan Dressel for successfully defending his MASc thesis titled “Improving rock pillar stability guidelines through detailed numerical investigation“! Evan completed his MASc under the supervision of Prof. Mark Diederichs.

Shortly after completing his MASc, Evan began doctoral studies with QGGG under the supervision of Prof. Mark Diederichs and is being co-supervised by Dr. Kathy Kalenchuk from RockEng Inc. Evan’s PhD research will address delineation of seismic hazards based on incremental stress-strain response in seismogenic volumes.

Evan’s MASc thesis is available to download on QSpace via this link, and the abstract is as follows:

Pillar stability guidelines, for underground construction in rock, have been presented by various authors in the past, based on a combination of empirical (mostly visual) observations from mining applications and simple numerical elastic stress indices or data from continuum plasticity analysis. There have been numerous developments in the past several decades in mechanistic classification (brittle spalling, effective continuum rockmass, structural control) and mechanism-appropriate modelling and design metrics. The design of pillar dimensions and spacing is a key factor in construction projects beyond mining including the engineering for deep geological repositories, hydroelectric power cavern complexes, underground storage, quarrying and other applications. These applications are situated in a variety of rockmass environments and at stress regimes from shallow to deep. In such applications, the geometry of the pillars and surrounding excavations deviates from the classic mine pillar scenario where the traditional pillar stability charts may not be able to accurately capture the behaviour of hard rock pillars. To assess the viability of pillar stability charts, a similar (to historical experiments), more detailed experiment was conducted simulating 3D Hoek-Brown, finite element method (FEM) pillars, with varying rockmass material parameters. From these model simulations, a five-phase pillar failure classification was developed. Using the classification charts developed, refine pillar stability charts. The refined pillar charts indicate that the material parameters used in the modelling can significantly change a pillar’s behaviour and that a single pillar stability chart is likely inadequate for describing the behaviour of mine pillars. The residual behaviour of pillars was also assessed using a correlation developed for determining an estimated residual GSI (and the associated residual strength after yield). The data for the residual pillar data agrees with previous findings that a single chart is inadequate for describing pillar behaviour. Modifying the residual GSI for a pillar can significantly impact the resulting strength predictions for the pillar. Post-yield dilation increases the effective area of the pillar core, increasing pillar stability. Dilation does not have as large of an effect on more slender pillars (< 0.7 W:H ratio) as confinement is lesser on more slender pillars.

Dressel E. 2022. Improving rock pillar stability guidelines through detailed numerical investigation. MASc Thesis, Department of Geological Sciences and Geological Engineering, Queen’s University, Kingston, Ontario, Canada.