Kuala Lumpur’s dual purpose tunnel is a world first

Kuala Lumpur’s Stormwater Management and Road Tunnel (SMART) is a unique solution to the Malaysian capital’s long-term traffic and stormwater management problems and the first tunnel of its kind in the world. The dual-purpose tunnel will divert floodwaters away from the confluence of the two major rivers running through the city centre while its central section will double up as a two-deck motorway to relieve traffic congestion at the main southern gateway into the city centre.

SMART was originally conceived as a flood relief tunnel to divert the 1 in 100 year flood away from the city centre. Then it was considered that the 11.8m internal diameter tunnel could be utilised in periods of low rainfall as a highway tunnel to alleviate Kuala Lumpur’s congested highway infrastructure. Mott MacDonald was approached by the MMC Engineering Group-Gamuda JV to carry out the feasibility study for this innovative dual purpose tunnel and then provide detailed design services to take the project from concept through to construction, working in association with SSP Consultants. The SMART project is now being implemented under the supervision of Mott MacDonald/SSP on behalf of the joint venture. The highway section is due for completion in 2005 and the bypass tunnel a year later.

The overall £335 million scheme comprises 9.5km of tunnel with the central 3km incorporating a double deck motorway. Major components include an upstream intake structure, holding pond and storage reservoir, diversion tunnel, twin box culvert and ingress/egress connectors to the motorway tunnel. Ventilation of the road tunnel requires construction of four 15m-high shaft structures.

Three mode tunnel operation
SMART will work on a three mode system. Mode one operates under normal conditions or when rainfall is low such that no water needs to be diverted into the tunnel. Moderate storms activate mode two. This will divert floodwater into a bypass tunnel in the lower section of the motorway tunnel which will remain open to traffic. During the once or twice yearly heavy storms a switch is made to mode three when the tunnel is closed to road traffic and the full tunnel section with a combined capacity of 3 million cubic metres becomes available to divert the dramatically increased flows. Extensive monitoring stations will ensure sufficient time is allocated to allow the last vehicle to exit before the automated watertight gates are opened. The motorway will then reopen to traffic after clearing of the tunnel within 48 hours of closure. We’re helping ensure that the change-over between modes from vehicle to flood use is practical and efficient.

TBM tunnelling
Ground conditions dictated construction by tunnel boring machine which is now under way with two slurry TBMs working in opposite directions from the middle of the tunnel alignment. We helped develop the TBM procurement strategy and produce contract documents to enable the contractor to purchase two 13.2m diameter machines – among the world’s largest in diameter. A ventilation shaft sited near central Kuala Lumpur served as the launch site for the TBMs. The ventilation facilities are located in Limestone rock, with the largest excavation being 150m in length, 20m wide and 28m deep.

The first TBM launching shaft was completed in January 2004 ready for assembly of the first TBM which commenced tunnel boring in June 2004. Shortly after this the second TBM arrived for assembly and commissioning and began tunnelling in August 2004.