Design of Temporary Construction Adit and Tunnel Plug for Nenggiri Hydroelectric Project

Abstract

The Nenggiri Hydroelectric Power Plant Project, located in the state of Kelantan, Malaysia, is among the largest renewable energy initiatives in the country. The main dam structure is 88.1m in height and can hold 1.239 billion m3 of water. A twin main diversion tunnel (DT) is required to divert existing river flow to enable construction of the cofferdam and the main dam structures. The horseshoe-shaped temporary construction adit (TCA) with a 6m span and approximately 146m long, excavated using drill and blast method, aims to expedite construction progress by providing access at the middle of the proposed DT thus allowing additional excavation faces for the DTs. Key design approach involves NGI-Q System for initial tunnel support design, followed by the Convergence-Confinement Method to establish relationship between stress relaxation and advance length, forming the basis for subsequent temporary support design using finite element RS2 program. This paper presents an optimized design and construction approach for the TCA and the tunnel plug located at the TCA-DT junction. Innovative design was adopted that results in significant reduction of plug length compared to conventional design. Despite various major challenges the TCA and DTs were able to be completed one month ahead of schedule.