Abstract
This paper presents experiences with design and construction process of the Tanju Tunnel, West Nusa Tenggara. The objective of this research was to characterize the volcanic and intrusive rock masses for designs of the tunnel excavation method and support system. Engineering geological investigations were carried out, upon which the tunnel stand-up time was estimated and the tunnel excavation method and support system were determined based on the rock mass classifications of RMR (Bieniawski, 1989). The investigation results showed that the tunnel construction area consisted of colluvium, andesite, and tuff breccia. The rock masses were dominated by the andesite, which had UCS of intact rock ranging from 200 to 300 MPa classified as strong intact rock. Based on the RMR value, the andesite was classified as a good quality rock mass. The tunnel had unsupported roof stand-up time approximately 20.000 hours for a 3 m tunnel span. The recommended tunnel excavation method was full face, 1.0-1.5 m advance, and complete support 20 m from face, while the support systems were locally bolt in crown 3 m long and 2.5 m spacing, with occasional wire mesh, 50 mm thick shotcrete in crown where required.
Highlights
This research is carried out at the construction site of Tanju Tunnel, which is administratively, located in the village of Bara, Woja, Dompu District, West Nusa Tenggara (Fig. 1)
The area of the Tanju Tunnel construction site consists of three rock units, namely colluvium, andesite, and tuff breccia
The tunnel construction area consisted of colluvium, andesite, and tuff breccia
Summary
This research is carried out at the construction site of Tanju Tunnel, which is administratively, located in the village of Bara, Woja, Dompu District, West Nusa Tenggara (Fig. 1). In order to cover the lack of inflow into the reservoir, a 3 m diameter and 1.6 km long drainage tunnel is needed to convey water from the Rababaka River to Tanju Dam. The most effective and safe excavation method needs to be determined. Several investigations were carried out in the tunnel construction design stage, including the rock mass characterizations for designs of the tunnel excavation method and support system. This paper presents results of engineering geological investigations to characterize the rock masses at the Tanju Tunnel construction site. Results of the rock mass characterization for designs of the tunnel excavation method and support system are described. It is expected that this paper provides a better understanding of drainage tunnel design and construction in tropical regions, in Indonesia
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