2004 construction accident in Singapore
The Nicoll Highway collapse occurred in Singapore on 20 April 2004 at 3:30pm local time when a Mass Rapid Transit (MRT) tunnel construction site caved in, leading to the collapse of the Nicoll Highway near the Merdeka Bridge. Four workers were killed and three were injured, delaying the construction of the Circle Line (CCL).
The collapse was caused by a poorly designed strut-waler support system, a lack of monitoring and proper management of data caused by human error, and organisational failures of the Land Transport Authority (LTA) and construction contractors Nishimatsu and Lum Chang. The Singapore Civil Defence Force extracted three bodies from the site but were unable to retrieve the last due to unstable soil. An inquiry was conducted by Singapore's Manpower Ministry from August 2004 to May 2005, after which three Nishimatsu engineers and an LTA officer were charged under the Factories Act and Building Control Act respectively, and all four defendants were fined. The contractors gave S$ (US$) each to the families of the victims as unconditional compensation.
Following the incident, the collapsed site was refilled, and Nicoll Highway was rebuilt and reopened to traffic on 4 December 2004. Heng Yeow Pheow, an LTA foreman whose body was never recovered, was posthumously awarded the Pingat Keberanian (Medal of Valour) for helping his colleagues to safety ahead of himself. In response to inquiry reports, the LTA and the Building and Construction Authority (BCA) revised their construction safety measures so they were above industry standards. The CCL tunnels were realigned, with Nicoll Highway station rebuilt to the south of the original site underneath Republic Avenue. The station and tunnels opened on 17 April 2010, three years later than planned.
Background.
Nicoll Highway and Merdeka Bridge.
The Singapore Improvement Trust first planned Nicoll Highway in the late 1940s to relieve the heavy rush-hour traffic along Kallang Road and provide an alternative route from Singapore's city centre to Katong and Changi. These plans were finalised in July 1953; they included construction of a bridge spanning the Kallang and Rochor rivers. The construction contract for Kallang Bridge was awarded to Paul Y. Construction Company in association with Messrs Hume Industries and Messrs Sime Darby for $4.485 million (US$million in 2021) in December 1954. On 22 June 1956, Kallang Bridge was renamed Merdeka Bridge to reflect "the confidence and aspiration of the people of Singapore". Merdeka Bridge and Nicoll Highway opened on 17 August that year; crowds gathered on both ends of the bridge to witness the opening ceremony. By August 1967, the highway and the bridge had been widened to accommodate seven lanes.
Nicoll Highway station.
Nicoll Highway station was first announced in November 1999 as part of the Mass Rapid Transit's (MRT) Marina Line (MRL), which consisted of six stations from Dhoby Ghaut to Stadium. In 2001, Nicoll Highway station became part of Circle Line (CCL) Stage 1 when the MRL was incorporated into the CCL. The contract for the construction of Nicoll Highway station and tunnels was awarded to a joint venture between Nishimatsu Construction Co Ltd and Lum Chang Building Contractors Pte Ltd at S$270 million (US$ million) on 31 May 2001. In 1996, the joint venture was investigated for breaching safety rules in a previous project; infringements included loose planks on its scaffolding. In 1997, the companies damaged underground telecommunications cables in another underpass construction project.
The site was on land reclaimed during the 1970s and consisted of silty old alluvium and a layer of marine clay resulting from sea-level changes of the Kallang Basin. The station and tunnels were constructed from the "bottom-up": cut-and-cover excavation was supported by a network of steel king posts, walers, and struts to keep the site open.
Incident.
At about 3:30pm local time on 20 April 2004, tunnels linking to Nicoll Highway station caved in along with a stretch of Nicoll Highway near the abutment of Merdeka Bridge. The incident happened when most of the workers were on a tea break. The collapse of a tunnel's retaining wall created a hole 100 m long, 130 m wide, and 30 m deep (330 by 430 by100 ft). One person was found dead and three others, who were working on driving machinery at the bottom of the site, were initially reported missing. They included a foreman who had helped evacuate his workers to safety when the site collapsed but did not escape in time because a flight of exit stairs collapsed. Three injured workers were taken to hospital for treatment; two of them were discharged the same day. No motorists were driving along the stretch of road when it collapsed and others stopped in time.
Three power cables were severed, resulting in a 15-minute blackout in the Esplanade, Suntec City, and Marina Square regions. The collapse of the highway damaged a gas service line. From initial reports, eyewitnesses heard explosions and saw flames flashing across the highway; the Land Transport Authority (LTA), Singapore's transport agency, said it had no evidence of an explosion and that the witnesses might have mistaken the loud sound of the collapse for an explosion. As a precautionary measure, gas supply to the damaged pipe was shut off.
Rescue and safety measures.
The Singapore Civil Defence Force (SCDF) arrived at the site at 3:42pm. After rescuing the three injured people, specialist SCDF units, such as the Disaster Assistance and Rescue Team and Search Platoon, arrived as reinforcements to search for the missing workers. The first dead victim was found at 6:07pm. All machinery was turned off as the SCDF used a life-detector device in the collapse site but nothing was detected and sniffer dogs were brought into the search. The second body was recovered at 11:42pm on 21 April.
Prime Minister Goh Chok Tong visited the site on 21 April; he praised the coordination between the SCDF and the Public Utilities Board (PUB) for the ongoing rescue efforts and expressed relief at the small number of fatalities. Goh extended his condolences to the families of the victims and said the rescue efforts should be the priority rather than apportioning blame. He added the government would convene a public inquiry. President S R Nathan visited the site on 22 April to pay tribute to the rescue workers.
A third body was recovered from the site on 22 April at 12:15am. The SCDF had to vertically excavate through a pile of rubble and debris located within three cavities, two of which were flooded and blocked by twisted steel beams and struts. The operation presented significant difficulty due to the limited space for manoeuvring within the cavities and the lack of visibility in flooded areas. The LTA detected stability problems on 23 April at 1:05am and grouting was implemented to stabilise the soil while water was pumped out from cavities, allowing rescuers to further investigate. Heavy rain in the afternoon caused soil erosion and halted the search. Because of the instability of the collapsed area that could bury rescue workers and cause more damage to the surrounding area, the search for the foreman, Heng Yeow Pheow, was called off at 3:30pm.
The Nicoll Highway collapse led to the deaths of four people:
Safety measures were implemented after the collapse to minimise further damage to the collapsed area. A damaged canal had to be blocked up to prevent water from the Kallang River from entering the site, and canvas sheets were laid on slopes in the site to protect the soil. While the surrounding buildings were assessed to be safe, they were later monitored for stability with additional settlement markers and electro-level beams that were installed at the nearby Golden Mile Complex. The LTA halted work at 16 of the 24 CCL excavation sites so these could be reviewed.
Near the incident site, the approach slab before the abutment of Merdeka Bridge had collapsed. To prevent displacement of the first span triggering the collapse of the bridge, the first and second spans of the bridge were cut to isolate the first span. This also allowed Crawford Underpass beneath the bridge to be reopened. This project began on 23 April and was completed on 28 April. Eight prism points and five tiltmeters were installed to monitor any bridge movements.
The collapsed site was quickly stabilised through the injection of concrete into areas that were vulnerable to movement or further collapse. Several vehicles, equipment and construction materials were retrieved using a specialised crane. The remaining equipment and materials at the site were buried under infill to avoid further collapse. Access to the collapsed site via the completed parts of the tunnel and the shaft was sealed off.
Committee of Inquiry.
Singaporean authorities dismissed terrorism and sabotage as causes of the incident. On 22 April, Singapore's Ministry of Manpower established a Committee of Inquiry (COI) to investigate the cause of the incident. Senior District Judge Richard Magnus was appointed Chairman; he was assisted by assessors Teh Cee Ing from the Nanyang Technological University (NTU) and Lau Joo Ming from the Housing and Development Board. The COI called for 143 witnesses to provide evidence, including 14 experts. The COI visited the site on 23 April and the inquiry was originally scheduled for 1 June. Because all parties involved would need two-and-a-half months to prepare due to complex technical content, the inquiry was postponed to 2 August.
Inquiry.
At the first hearing of the inquiry, the inquiry panel established that there were "fundamental" design flaws in the worksite due to incorrect analysis of soil conditions by the contractors, leading to more pressure on the retaining walls. In April, the LTA had said the collapse happened without warning but the LTA had already found flaws in Nishimatsu–Lum Chang's design in October 2001: the contractor used a design-software simulator with incorrect parameters. An alternative design had been proposed in consultation with an NTU professor but the contractor had rejected the design. The LTA technical advisor for design management had advised against excavation of the site due to incorrect data.
In the two months before the cave-in, the tunnel's retaining walls had moved more than the maximum allowed. The contractors had petitioned the LTA to increase the agreed maximum threshold of movement. The contractors had miscalculated the amount of stress on the retaining walls but gave the LTA repeated assurances that their calculations were in order. Nishimatsu's senior on-site supervisor Teng Fong Sin claimed ignorance of the significance of the trigger values taken from the retaining wall. Teng said even if he had been aware of the significance, he lacked the authority to halt the ongoing work.
No readings were taken in the two days leading up to the collapse. This was because soil-monitoring instruments, which were placed roughly in the centre of the collapsed area, had been buried and the site supervisor Chakkarapani Balasubramani did not take the readings, although he raised the issue with the main contractor and was told the instruments would be dug out. Nishimatsu engineer Arumaithurai Ahilan said he saw "nothing alarming" in the soil-movement readings and accused Balasubramani of lying in testimony. While he was also alerted to other ground movements, Nishimatsu addressed these cracks by applying cement patches, and no further corrective actions were taken because the buildings did not suffer any structural damage. According to a system analyst from Monosys, the project's subcontractor, the strain-detecting sensors recorded readings that were still below trigger values at 3 pm. These readings were the last obtained before the collapse at 3:30pm.
The steel beams to hold up the walls had not been constructed when workers dug further into the site. LTA supervisor Phang Kok Pin, whose duty was to confirm the correct installation of support beams, said he visited the pit typically once or twice a day. He conducted only sporadic inspections and heavily relied on reports from Nishimatsu contractors to confirm the accurate installation of the beams.
Nishimatsu supervisors were warned about failing support structures on the day of the collapse but instructed the subcontracting site supervisor Nallusamy Ramadoss to continue installing struts and pouring cement on the buckled struts to strengthen the wall. The struts continued to bend further before the collapse; Ramadoss warned his workers of the danger and evacuated them to safety. Some workers said they were not warned of any danger or given any safety briefings but escaped in time. Other workers also reported hearing "thungs" of bent walers before the cable bridge swayed, and everything around them trembled and collapsed.
Resumption and conclusion.
The inquiry was