Stress evolution with time in stopes with hydraulic backfill


Mr Constant Bienvenu Noutchogwe Tatchum ( - École Polytechnique Montréal), Mr Pengyu Yang ( - École Polytechnique Montréal), Prof Li Li (Professeur agrégé - École Polytechnique Montréal)

Hydraulic backfill is often used to fill large underground voids created during the mining operations. It is produced and distributed as a slurry at a pulp density P = 65-75% (solid content) which, therefore, contains a substantial amount of water that drains after placement. Inadequate drainage has been regarded as the main cause of barricade failure for stopes with hydraulic backfill. Therefore, a good understanding of the evolution of the total and effective stresses within such backfilled stopes is critical for improving the design of barricades. To date, most existing analytical solutions for assessing the stresses in backfilled stopes were developed based on Marston’s approach by considering a fully drained condition without pore water pressure or with a hydraulic equilibrium state. These two conditions are not always sufficient to represent the stress state behind the barricades. When a slurried hydraulic backfill is placed in a stope, the drainage and consolidation of the fill material is fairly rapid. For the case of conventional barricade having a limited capacity of drainage, upstream drainage can be slowed down and water accumulation can occur within and on top of the backfill. Efficient drainage at the base of the stope allows the local water table to descend, producing changes in the total and vertical stresses with time. In this paper, the authors present a simple analytical solution that can be used to estimate the total and effective stress evolution with time in stopes with hydraulic backfill. Sample calculation results are presented using typical backfill properties to analyze the key influencing factors. A discussion follows on some particular features and limitations of the proposed solution.