Denis Thibodeau

Stochastic evaluation of haulage drift unsatisfactory performance using random Monte–Carlo simulation

Mine haulage drifts are the primary access to the mining blocks of an ore body in a multi–level mining system of a tabular ore deposit. Drift instability could lead to serious consequences such as injuries, production delays and higher operational cost. In this paper, the haulage drift stability is evaluated on the basis of the primary rock support system comprising 1.8m resin grouted rebars in the drift walls and 2.1m long in the drift back. Three failure criteria adopted and compared are Mohr–Coulomb yield zones, elasto–plastic and linear elastic brittle shear failure with respect to lower and same–level mining and filling steps in the vicinity of the haulage drift. The Random Monte–Carlo (RMC) is used in conjunction with finite–difference FLAC for random assignment of model input parameters in the FLAC grid. The results are presented in terms of probability of instability and categorised with respect to failure condition and mining step.

Geotechnical Risk Assessment of Mine Development Intersections with Respect to Mining Sequence

Abstract Mine developments such as haulage drifts and their intersections with cross-cuts are the only stope access in sub-level stoping mining system. Thus, they must remain stable during their service life. Haulage drift instability could lead to serious consequences such as: production delay, damage to equipment, loss of reserves and high operational cost. The goal of this paper is the stability of mine developments with respect to mining sequence with focus on the performance of haulage drift intersection during the production plan. A case study, the #1 Shear East orebody at Vale’s Garson Mine in Sudbury Ontario will be examined in this paper. A three-dimensional, elastoplastic, finite difference code (FLAC3D) is used for this study. The extent of strength-to-stress ratio corresponds to Mohr–Coulomb strength-to-stress ratio of 1.4 is used as failure evaluation criterion. The unsatisfactory performance is reached when the extent of strength-to-stress ratio exceeds the anchorage limit of the rockbolt. Stochastic analysis; adopting point-estimate method, is then employed with the numerical modelling to tackle the inherent uncertainty associated with rockmass properties. Then, the probability of instability at various mining steps is estimated for the roof and north wall of the studied intersection. The cost of consequence models is introduced to provide an economical solution if the intersection failed, blocked or damaged. Furthermore, the geotechnical risk associated with the instability of mine development intersection is estimated using risk-indexing tool. The results are presented and categorized in terms of probability, cost of consequence and risk-index at various mining stages.

Numerical modelling and in situ monitoring of drift support performance with respect to mining sequence

Haulage drifts in deep hard rock mines require special attention in ensuring their long-term stability and safety, as these drifts must remain functional during the life of a mine plan. The stability of a haulage drift is influenced by many factors, most notably nearby stoping activities and the distance between the drift and production stopes. Thus, the evaluation of drift support performance before and during nearby stope extraction is important. In this study, numerical modelling is performed to evaluate the support performance in the drift. In order to calibrate the numerical model, selected bolts were instrumented with load cells to measure the axial load acting on the bolts as mining progresses. The load distribution along the rockbolt is computed after each mining step. The peak load is found to be consistently at the bolt head in both the fully grouted rebar and the modified cone bolt. It is found that same-level mining of nearby stopes has a more severe effect on the drift support system than lower-level mining. The optimum timing for enhanced support system installation with respect to stope sequencing is also examined.

Estimating Probability of Instability of Haulage Drift with Respect to Mining Sequences

Haulage drifts play a vital role in providing personnel and equipment access to ore extraction areas for mine production. Thus, their stability is of crucial importance during the life of a mine plan. Many Canadian mines use longhole mining methods or one of its variants. These methods require access to the orebody through haulage drifts on multiple levels. This paper examines the stability of mine haulage drifts with respect to planned mining sequence. A case study of an underground mine is presented. The case study examines #1 Shear East of the Garson Mine in Sudbury, Ontario. A two-dimensional, elastoplastic, finite difference model (FLAC 2D) is developed for a haulage drift situated 1.5 km below surface in the footwall of the orebody. The stability of the haulage drift is evaluated in terms of the spread of yield zones into the rockmass due to nearby mining activities. The performance of the drift stability is evaluated at various mining stages, employing the RMC (Random Monte-Carlo) technique in conjunction with finite difference modeling to study the probability of unsatisfactory performance of the drift. The results are presented and categorized with respect to probability, instability and mining stage.