Planning and support estimation of underground powerhouse in the Himalayas

Abstract

Underground structures like tunnels and caverns have major advantages in hydropower pro­jects. Tunnels are used for transporting the water from the intake to the tailrace outlet through the turbines whereas caverns primarily serve the purpose of powerhouse, transformer caverns, and settling basins. The site selection of the underground cavern is an important task to be considered to optimize the rock support and cost. Design aspects regarding stability and functionality are governed by the location, orientation, shape, and size of the caverns. Similarly, the choice of support for a particular geological condition and type and quality of rock mass needs to be carefully assessed during planning and implemented during the construction. This article discusses the location design and rock support requirement of the underground powerhouse cavern of the Super Dordi Hydropower Project in Nepal. The project lies in the lower boundary of the Higher Hima­layan rock formation. The powerhouse cavern has a length of 39 m and has width (span) and height of 14.5 m x 28 m, respectively. The rock support measures predicted during planning are modelled using 2D numerical modelling tools. The study on monitored data and numerically modelled data are compared and discussed.