Four face jail following Nicoll collapse enquiry

Singapore: Criminal prosecutions could follow publication of a report into the cause of last year's Nicoll Highway Station collapse in Singapore, which killed four construction workers (see iC's May 2004 news pages). The Committee of Inquiry's (COI) report recommended that legal action be taken against contractor Nishimatsu Construction, three of its officials and one from the Land Transport Authority of Singapore.

The collapse of the cut and cover excavation for the Nicoll Highway station box on Contract C824 of the Circle Line Metro project occurred at 3.30 pm on 20 April 2004.

The COI states that the collapse could have been prevented and that blame for the incident lies with the contractor, a joint venture of Nisihimatsu and Lum Chang.

As a result of the findings the COI has recommended that Nishimatsu should be prosecuted under the Factories Act and could face a US$ 120000 fine. The report also found that NishWF matsu's project director, project coordinator and design manager, along with the LTA project manager, are also liable for prosecution. If found guilty, the four will face either fines of up to US$ 120000 or a maximum of 12 months in jail.

The excavation was being carried out using ‘bottom-up’construction methods with diaphragm walls supported by a system of king posts, walers and struts. The excavation had reached the ninth of 10 levels, 30 m below ground level, when the cave-in occurred. This led to severe subsidence to a 13000 m² area, and caused a 100 m section of the Nicoll Highway to collapse.

According the COI's investigation, the collapse did not happen suddenly but was caused by a chain of technical and administrative factors. The COI also stated that warnings of the impending collapse were not taken seriously.

The three main causes outlined in the report were under design of the diaphragm wall through use of an inappropriate soil simulation model, under-design of the waler connection in the strutting system and deviations in the actual construction.

Excessive wall deflections, surging inclinometer readings, buckled waler beams and stiffener plates, ground settlement and plunging strain gauge readings were observed before the collapse.

“Monitoring of instrumentation was not carried out on a daily basis and the opportunity to detect adverse trends was lost,” said the report.

The COI's interim report also raised questions about safety on the scheme itself and the safety culture in Singapore.

“The Nicoll Highway collapse was rooted, among others, in failures in defensive systems that did not adequately deal with hazard identification, risk avoidance and reduction or control of the remaining residual risks,”it said.

Singapore's Ministry of Manpower is now in the process of introducing the Workplace Safety and Health Act to address the issues raised by the report. The LTA is also re-examining its project management process and has established a risk register to cover safety, design and construction on all sites.