Coupled thermo-hydro-mechanical-chemical processes in cemented paste backfill and implications for backfill design – experimental results

Abstract

In the field, a cemented paste backfill (CPB) structure is simultaneously subjected to mechanical (M), hydraulic (H), chemical (C), and thermal (T) loads from early to advanced ages once it has been built. Field studies have shown that the in situ properties and performance of CPB differ from those obtained in laboratory. This is mainly due to effects of the aforementioned coupled THMC processes. Thus, understanding and assessing the response of CPB to the aforementioned coupled THMC loads or processes are crucial to reliably determine the performance and optimal design of CPB structures. However, despite the tremendous progress that has been made in understanding the behaviour and assessment of the performance of CPB during the past few years, the THMC response of CPB is not yet fully understood, and to date, there is no study that addresses these issues. The deficiency of consideration given to these coupled THMC processes has long been defended on the basis that it is difficult to do so. However, it does not mean that these issues are not essential. A thorough understanding of the coupled THMC processes that occur in CPB are needed for economic reasons, mine-worker safety and the development of economically and environmentally sustainable mining strategies. This research program has been conducted during the past years in response to the limited knowledge about coupled THMC processes in CPB. The objectives of the present paper are firstly; to present and describe the developed THMC experimental setup that allows us to cure CPB under coupled THMC conditions, i.e. close to field conditions. The setup is capable to cure the CPB specimens under controlled curing under stress, curing temperature and various coupled THMC conditions, while continuously monitoring the evolution of total stress, pore pressure, suction, temperature, water drainage, chemical composition of the pore water and vertical deformation. Once the required curing time is achieved the specimen can be extracted and then subjected to various experimental mechanical, hydraulic and thermal tests; and secondly to present and discuss some samples of results with regards to the THMC response of CPB and their implications for the cost-effective design of backfill structures. The results of this paper will provide a better understanding of the field behaviour of CPB and thus contribute to the better design of CPB structures.