The Klang Valley Mass Rail Transit (MRT) project consisted of three new MRT lines, which combined with previously existing rail networks to form the backbone of a comprehensive integrated public transport system for Kuala Lumpur and its conurbation. There will be two new radial lines, the 51km long Red Line and the 50km long Green Line; these new lines are linked to the existing lines by a 40km long Circle Line. The project design envisaged a total of some 45km of the lines being in tunnel. The largest length, of 21.5km, was in the Kenny Hill clay formation; some 17km was in Kuala Lumpur Limestone, and the remainder in granite. The limestone potentially provided the greatest challenges, with buried karstic features such as solution cavities, sinkholes, and rock pinnacles. Both earth-pressure-balance and slurry shield tunnelling machines were proposed, the former in the soft ground and the latter in the rock formations.
GCG were required to provide advice on various tunnelling issues, including the effects of the geological conditions, selection of tunnel boring machines, settlement analyses, construction of tunnel boxes, shafts and cross passages, use of ground treatment, and tunnel lining design. GCG reviewed all the documentation provided by the project’s Joint Venture in support of their proposal, identifying issues and areas where further information was required, along with potential ‘show stopper’ issues that required resolution before the scheme could be allowed to proceed. The most important of the last of these involved the advance identification of voids and cavities and the ground treatment needed to deal with these ahead of tunnelling.