Physical modelling of the hydro-mechanical properties of backfilled mine stopes

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In most mining with cemented paste backfill (CPB) operations, the open stopes are usually backfilled in two sequences: the plug fill and the residual fill. In addition, backfill systems and waste rock barricades (WRB) have been designed by trial and error over time or based on assumptions and models that tend to overestimate the stress regime that governs the overall stability of filled stopes. The originality of this research program is the fact that this will be the first time that a physical modeling of both a backfilled stope and WRB is done. Thus, the work that will be carried out as part of this research program will provide knowledge on key design parameters and answer crucial and recurring questions posed by engineers (mining companies and engineering consulting firms). In terms of experimental devices, we will use a brand new-built physical model of a mine stope at 1/15 scale (P2MS) and a new designed K0-Consolidation and Hardening (K0-CH) cell. In addition, we will perform 1D consolidation, uniaxial and triaxial compressions, direct shear testing, and non-destructive testing (NDT), and in situ measurements. Three research themes are proposed: Theme 1 (T1): Hydromechanical characterization of backfilled stopes This theme will be divided into three parts: Part T1.1 (Assessement and prediction of horizontal pressure on WRB) will lift the scientific and technical locks in order to develop a methodology for accurate and reliable measurements of the horizontal pressures on the WRB during filling. We will used in situ stope measurements and P2MS device for this investigation. Part T1.2 (Evaluation of the need for a plug during backfilling) will investigate the real need of a plug during backfilling using the P2MS device. Part T1.3 (Scaling of in situ backfill mechanical strength from lab specimens testing) will scale the in situ strength of CPB from laboratory tests using the K0-CH cell. Previous work has shown that the strength of in situ CPB is sometime significantly different from the one obtained at the lab scale. Theme 2 (T2): Dimensioning of waste rock barricades as paste backfill-retaining structures For this theme, we will use the instrumented P2MS device to investigate the instability mechanisms and the failure strength of a WRB as well as the development of a guide for rational WRB design and construction. Theme 3 (T3): Development of design assistance tools of underground backfill systems For this theme, we will perform a probabilistic analysis of the required CPB strength, in conjunction with the development of a generalized analytical model, for predicting the CPB strength, and a free design software package for CPB systems. A total of 2 PhD and 3 MASc projects will be supported by the research program. Students will interact with their colleagues at UQAT, as well as with mining partners. In doing so, they will also become part of the technology transfer process so that Canada benefits from the results of this reserach.