Abstract

Once placed in the underground mine excavations (stopes), cemented paste backfill (CPB) structures have to satisfy certain mechanical resistance requirements to ensure a safe underground working environment for all mining personnel. Moreover, mine backfill failures have considerable financial ramifications and can result in fatalities or injuries. One of the key parameters for assessment of the mechanical resistance of CPB structure and often used in the practice is its strength; namely, unconfined compressive strength (UCS). Knowing the time at which the CPB reaches its reasonable strength is very important for reducing the mining cycle and ensuring the safety of mine workers. In this paper, a numerical model is developed (and implemented into FLAC software) for predicting the UCS development and distribution of undrained hydrating CPB structure, taking into account the coupled effects of temperature (thermal factor) and binder hydration (chemical factors). Data from field and laboratory studies are employed to validate the developed model. The validation results show a good consistency between the predicted and the field and laboratory results. The developed tool is then used to simulate the strength development within CPB structures in several practical cases. The developed tool can contribute to more cost-effective and safer design of CPB structures.

1. INTRODUCTION

Mining industries contribute strongly to the economy of Canada and many other countries [1-4]. Aside from significant economic contributions, mining activities also generate a large amount of solid waste, such as waste rock and tailings. In Canada, it is estimated that about 500-650 million tons of waste are generated annually [5-6]. This issue is also faced by mining industries worldwide because they follow the same mining principle for extracting valuable minerals and disposing waste [7-8]. In the not so-distant past, surface impoundments were the most widely used method of tailings disposal, and even the returning of tailings to underground mines has long been practiced for the purpose of assisting mining operations [9]. However, the surface disposal of such waste can create several environmental and geotechnical problems.

Public perception and strict government regulations with regards to the disposal of such waste compel the mining industry to develop new strategies which are environmentally sound and cost effective. In this scenario, the recycling of such waste into mining or civil engineering construction materials have become a great challenge for the mining and civil engineering community [10]. In recent decades or years, there is an increasing trend to make the tailings a useful construction material [e.g., 11-12]. One of these materials is mine backfill. In mine backfilling, the tailings and/or waste rocks are returned to the underground to fill the voids left by ore extracting in the form of mine backfills (hydraulic backfill, rockfill, and cemented paste backfill). Cemented paste backfill (CPB, mixture of dewatered tailings, water and binders) is the most used method of mine backfilling in Canada and many other countries. As a relatively new technology, CPB has been increasingly and intensively used for the backfilling of previously mined-out underground voids (which are called stopes) in many mines around the world over the past three decades [13-14]. The application of CPB can produce substantial economic and environmental benefits as well as ensure a safe work environment in underground mines

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