Development and applications of rock fracture mechanics modelling with FRACOD: a general review

Rock failure is often controlled by fracture initiation, propagation and coalescence, especially in hard rocks where explicit fracturing rather than plasticity is the dominant mechanism of failure. Prediction of the explicit fracturing process is therefore necessary when the rock mass stability is investigated for engineering purposes. However, the fracture mechanics approach is rarely used in practical rock engineering design partly due to the inadequate understanding of complex fracturing processes in jointed rock mass and partly due to the lack of tools which can realistically predict the complex fracturing phenomenon in rock mass. Since 1990s, a new approach to simulating rock mass failure problems has been developed using a numerical code namely FRACOD. FRACOD is a code that predicts the explicit fracturing process in rocks using fracture mechanics principles. Over the past three decades, significant progress has been made in developing this approach to a level that it can predict actual rock mass stability at an engineering scale. The code includes complex coupling processes between the rock mechanical response and thermal process and hydraulic flow, making it possible to handle coupled problems often encountered in geothermal, hydraulic fracturing, nuclear waste disposal and underground Liquefied Natural Gas (LNG) storage. During this period, numerous application cases have been conducted using FRACOD, which includes: borehole stability in deep geothermal reservoir, pillar spalling under mechanical and thermal loading; prediction of tunnel and shaft stability and excavation disturbed zone, etc. This paper summarises the theoretical fundamentals of the fracture mechanics approach with FRACOD and the most recent developments. Several selected application cases are also discussed briefly in this paper to demonstrate the effectiveness of this approach.