State-of-the-art design guidelines in the use of unlined pressure tunnels / shafts for hydropower scheme

Technical soundness, cost effectiveness and long-term sustainability are the major issues that one should achieve while planning, designing, constructing and operating the hydropower schemes. With the changing world of competitiveness with other sources of renewable energies such as wind and solar, it is important that the hydro-energy still is able to compete in the renewable energy market. One of the possible solutions that helps to achieve the cost effectiveness, technically soundness and timely completion of the hydropower scheme is the use of unlined / shotcrete lined pressure tunnels. Such approach may help replace the traditionally used concrete and steel lined pressure tunnel systems, which are both cost intensive and long construction time taking. Nevertheless, there are several technical, geological and geo-tectonic challenges associated to this solution, which limits the use of this innovative concept. This manuscript will review the history of the use of unlined pressure tunnels / shafts in the world and presents prevailing design approaches in the use with the aid of the use of some very important cases of failures and successes where unlined / shotcrete lined pressure tunnels and shafts were used in the past. The detail evaluation and analysis on the geological and geo-tectonic environment are carried out. As an outcome, the state-of-the-art upgraded design criteria as well as guidelines for the use of unlined / shotcrete lined pressure tunnels are suggested with the belief that the vast hydropower resources still untapped in the Asian region will be even more cost effective, technically sound and long-term sustainable solution.