Rock mechanical engineering to the design of underground tunnelling works of Bakun River diversion project in Sarawak, Malaysia

摘要

The Bakun Hydropower project is including the construction of a Hydroelectric power plant with an installed capacity of 2520 MW and a power transmission system connecting to the existing transmission networks in Sarawak and Western Malaysia. In a state of readiness to allow the Balui river will have to be detoured through three Diversion tunnels with a length of some 1400 m each prior to dam construction. The geology of the Bakun area belongs to the several thousand meters thick Belaga Formation deposited from the late Cretaceous to the early Tertiary in the Norhwest Borneo Geosyncline. The orientations of the strata strike at N55 deg E to N 70 deg E and dip at 50 deg SE to 70 deg SE at the construction site. This description deals with the construction design of the underground structures in view of Rock Mechanics. For underground structures stability calculations have been performed b numerical method and the required rock support has been evaluated to provide sufficient structural analysis during river diversions. It was necessary to carry out further numerical analysis for stability during the excavation progress to adjust the rock support according to the actual geological conditions. The geotechnical parameters applied in the stability calculations have been taken over from the geotechnical investigation as the relevant data from the construction design. However, it was realized that the geological conditions of this area did not coincide with the original assumptions and expectations of the Tender Design prior to construction. Additional geotechnical investigation was performed and the slope inclination and supporting methods of tunnels were modified.