Tight sites in Singapore

Standing on the stairs of a high building near Singapore’s Little India district and looking north you can see a long line of cranes and earthmovers, strutted excavations and reinstated ground, heading roughly north. Just below are the huge steel struts for the Little India station excavation, like giant red Meccano pieces. This is the new North-East Line – the NEL.

If you have ever driven a car around Singapore, you will appreciate its need for efficient public transport.

Singapore announced plans for the railway line in 1996, just before the 1997 Asia currency falls, and construction work began just when the region needed a public spending boost. A prestigious new spur line to the airport is also under construction with two more stations in addition to the 16 stations now taking shape for the NEL running 20km from Marina Bay.

New towns will be integrated into the route and linked to the city centre. Light rapid elevated train loops, like the one already completed at Bukit Panjang, are planned to integrate with the main line which also has interchanges with the two existing lines.

There will also be links to at least another two full scale lines planned for the near future.

Chew Tai Chong, project and engineering director for the Land Transport Authority (LTA), the new government client that incorporates the old Mass Rapid Transit organisation, says that the plan is for public transport use to rise as the population grows over the next decades. There simply is no room for uncontrolled car use.

But the NEL has meant activity enough with its dozen contracts using a variety of civil engineering techniques. LTA took a design and build path for the work letting it out in one or two station sections, with the tunnel links between.

Tunnelling is largely complete and the cut and cover work for stations are now the main civils activity, merging into building and fitting out. For the majority a conventional strutted bottom-up method is used.

Large numbers of cranes supply materials to the busy interiors beneath, working through the open tops.

Little India station, an otherwise typical station, has provision for a 16 storey development over the top. According to LTA senior project engineer Lim Kim Kwang, this meant simply integrating the future load requirements into piles and barettes for the station.

Contractor Hyundai Engineering & Construction of Korea, working with Germany’s Ed Zublin which is doing the tunnel work, has a busy site underway with concreting now well advanced inside the 225m by 30m diaphragm walls formed down to 20m in relatively good ground. Hydromills were used for the work, particularly for accuracy. Diaphragms are 800mm thick and because stations will also be used as civil defence shelters another 1.15m of concrete inner wall is added later.

The site is littered with lifting equipment, mostly Tadano and Kato truck cranes from Japan. They lift in almost everything from reinforcement steel to final finishes. The heaviest lifts have been for massive steel blast doors, which are required for civil defence purposes. These weigh 31t each and have meant bringing in cranes with capacities up to 500t.

Though work has gone well, the civil defence requirements make the interiors much more complicated than usual, says Lim. There are numerous extra room dividers to add for special ventilation equipment, decontamination rooms, water tanks, standby power systems and so on. This all means complicated lifting work.

Chinatown station is another bottom-up construction but one of the more difficult, being formed in the middle of the road through a bustling and long developed area of Singapore. Buildings, some dating back to the 1920s and of historical significance, sit within just 1.5m of construction. There are three bridges across the road to support and a large tropical rain drainage channel to divert.

John Teo, LTA project manager on this section, says that craneage has been particularly awkward with just “two little mole holes for the deliveries”. It has meant careful planning of logistics and a ‘just-in-time’ system for deliveries because there is not much space to lay materials down.

Crane access has been greatly eased at Boon Keng and Putong Pasir stations despite the choice of a top-down construction method. The heavy, 2m thick, concrete station ‘lids’ required for civil defence had seemed to rule out top-down construction but the contractor worked with British engineer Robert Benaim to devise a system that avoids forming the whole slab at first. Large square sections are left as voids, with the 5m wide concreted sections in between forming ‘struts’. This not only reduces the weight and allows the advantage of working downward, but also means site access is very open for cranes.

“The uncluttered site means work can proceed very quickly,” says engineering manger Roger Mitchell, “even though the reinforcement can sometimes be fiendishly complicated.”