PASTEFILL PRESSURE MONITORING AT INMET'S CAYELI UNDERGROUND COPPER AND ZINC MINE

摘要

Backfill is a critical component of ground control for many underground mines. Cemented Paste Backfill (CPB), a mixture of mine tailings, water and cement is becoming a widely used backfill material. Mine backfill is of great importance for Qayeli mine's ground control program and provides a number of environmental, technical and economic advantages for overall mine opertions.CPB is an engineered mixture that consist mainly of 70-85wt% of total filtered tailings, 5-8.5 wt% of Portland composite cement and sufficient water (15-30wt%) for transporting underground stope. CPB offers significant advantages over other backfill methods including rapid speed of emplacement, strength parameters designed for specific situations, and diversion of tailings to underground storage. CPB is also critical at Cayeli for tight-filling blind stopes where there is no overcut access. In order to improve backfilling safety and efficiency, Cayeli and the University of Toronto have conducted an in-situ instrumentation fieldwork campaign as part of a larger international project. Most mines do not measure CPB pressures on containment barricades and must use conservative backfilling strategies to avoid over-pressuring barricades. In-situ backfill measurements can provide critical data on how backfill behaves and so presents opportunities to better manage backfilling strategies. Using total earth pressure and pore pressure measurements, five stopes have been comprehensively instrumented to show fundamental controls on backfill pressure at Cayeli. Cement content, backfill pouring rates and tailings characteristics and chemistry are shown to affect the rate of CPB strength gain, and so in-situ pressures at containment barricades. At Cayeli, complex ore geology translates into variations in tailings chemistry and so appears to significantly affect the rate of cement hydration. This paper demonstrates how instrumentation was deployed at Cayeli, and used to accelerate the mining cycle through a 40% reduction in backfilling time while maintaining optimal safety.