Trans-Koolau Hawaii : Critchfield, J W World TunnlgV4, N4, June 1991, PN37–N39

Abstract

This article describes the construction of the Trans-Koolau tunnels, carrying the Hawaii Interstate H-3 highway under a range of mountains on the island of Oahu. The twin tunnels will each be about a mile long, with a two-lane carriageway 38ft wide. Because of access difficulties, they are being built from both sides of the range under separate contracts. The contracts include: (1) mining and lining; (2) ventilation buildings at each of the four portals; (3) a control building; (4) major civil works near the portals. Three more speciality contracts are required for: (1) ventilation fans; (2) systems components; (3) architectural finish. The types of matrials encountered underground have so far been very much as expected, and ground behaviour has been favourable. The tunnels are being driven through an interbedded sequence of Pahoehoe and aa/clinker. (Pahoehoe is a basaltic lava flow. Aa is a basaltic lava). These are moderately weathered to unweathered. Work started with the construction of an exploratory tunnel, and then with the main tunnels, which are being excavated with horseshoe section, with excavated width about 48ft at the invert and height 38ft. Because of their large size, the tunnels must be excavated in stages, using a centre top heading 18ft wide and 20ft high as pilot. There are also ten 8ft wide and 10ft high cross- passages, at intervals of 485ft to 500ft.