Design of the power caverns for Pergau hydroelectric project, Malaysia

A power-generation cavern of 30-m span has been built in hydrothermally altered granite rock at the Pergau hydroelectric project in northern Malaysia. One implication of the fast-track design-and-build nature of the project was that the additional site investigation that was needed to provide specific data for the design had to be undertaken during the early part of the construction work. This execution of the design and construction work in tandem had a major influence on the way in which the design developed and on the design decisions that had to be made. The development of the design is described, from the initial analyses, in which relatively simple numerical programs and limited geotechnical data were employed, to the detailed analyses, in which, principally, the computer program UDEC was used together with discontinuity data acquired during the early construction phases of the project. The intersection of large fissures containing hot water and hydrothermally altered rock had not been predicted from the site investigation undertaken for the project and the solutions that were engineered for these unanticipated ground conditions are explained.