Design criteria for caverns under high stress rock conditions for Snowy 2.0 Power Station Complex

Snowy 2.0 is a major hydro power project currently under construction in Australia. This new development aims to increase the capacity of the existing Snowy Mountains hydro power scheme by 2000 MW, making it the largest source of renewable energy in Australia and one of the largest pumped-storage projects in the world. The exceptional size of the Power Station Complex, situated at about 720m depth under significant in-situ stresses, in sedimentary rocks of fair to good resistance represented a major design challenge. This article presents the main features of the Snowy 2.0 Power Station Complex (PSC) project, in particular the geological context and the general layout of the PSC. It focuses on the methodology adopted for the definition of the design criteria, with the absence of relevant code or standard for the design of large deep underground caverns under high stress conditions. These criteria concern mainly (i) the stability analysis of the rockmass surrounding the excavation, including the stability of the rock pillars at the centre of the Power Station Complex; and (ii) the design of the rock support composed of fully grouted rockbolts, shotcrete and wiremesh.