Waiting. Collapse site has been stabilized and prepared for resumption of construction. (Photo courtesy of Land Transport Authority)

Eight months after a Singapore mass-transit tunnel collapsed, the commission of inquiry has yet to determine why. Now in recess, it is expected to take a couple of months after it reconvenes in January to reach a verdict. The delay is prolonging confusion surrounding the project. Officials of the owner, Land Transport Authority, now say that recovering from the collapse will add two years to the schedule.

The commission on Aug. 2 began to investigate the April 20 collapse of the excavation for the Nicoll Highway Station on the Circle Line subway in which four workers were killed (ENR 5/17 p. 12). It was being built under a $158-million contract by a joint venture of Nishimatsu Construction Co., Tokyo, and Singapore-based Lum Chang Building Contractors.

"We were expecting the inquiry to be over by July," says Guy Taylor, senior project manager for Circle Line Stage 1. But the commission is struggling with a mass of documents and statements from some 120 witnesses. And the findings in the commission’s interim report, released in September, are prompting the government to re-examine its construction procedures, including the approach to both safety and contracting.

A failure to make the instrumentation contractor independent from the main contractor, for example, drew criticism. "The main contractor usually hires instrumentation contractors who set up equipment and take readings to assist its work," says Taylor. From now on, LTA will contract directly with the instrument contractor and separately from the main contractor. "The purpose is to ensure that there is no commercial dependence on the main contactor," he says.

The report also called for a stronger safety culture, noting that "specialist subcontractors must be told to go beyond mere contractual compliance and alert the employer of any deficiency in design, drawing and methods of construction which impacts safety."

The accident involved the collapse of temporary works, but has raised questions about design of the project’s permanent structures. At one time LTA separately designed the temporary and permanent works to make sure that they did not influence each other. The practice was allowed to lapse, and the design-build contractor now handles both tasks, says a senior engineer close to LTA.

Questions have been raised about whether the Nishimatsu/Lum Chang joint venture cut corners in the collapsed temporary structure and did the same with the permanent structure as well. "I cannot comment...because this issue about temporary and permanent works is being examined by the COI," says Taylor.

The commission’s interim report warned that the government should look closely at the design of temporary structures, and that this could be a problem in the engineering industry in the country as a whole. A government statement in response says, "As an immediate measure, LTA is engaging independent consulting engineers to carry out checks on the design of temporary works on all their projects." The Building Construction Authority is taking similar steps, it adds.

How and when to resume construction now is under study, says Tien Sio Low, LTA’s deputy chief. "The main contractor has gone very far in terms of recovery work. We are also looking at the possibility of opting for a new alignment altogether."

Taylor says it will be for COI to recommend the best option. "We cannot say what will be the increase in the project cost. It really would depend on the outcome of the inquiry, and on what direction we get from it," Taylor says.

There are strong indications that LTA might continue with the existing alignment, although it could involve removing obstructions like structural steel from the accident site before rebuilding on it. "Under the contract, the main contractor is expected to complete the work he has undertaken," Low says.