On April 20, 2004, a stretch of Nicoll Highway collapsed in Singapore, killing four men and leaving a 30-meter (98 ft) deep ravine. The incident occurred due to the collapse of a temporary retaining wall of a tunnel at the nearby Mass Rapid Transit (MRT) station. As a result, the collapsed section was unpassable for more than seven months.
Nicoll Highway spans 759 meters (2,490 ft) long and was officially opened on August 17, 1956. It was built by the British for $8 million (or US$61.2 million today), serving as a connector between Kallang and the Central Business District. The road was named after the former governor of Singapore, John Nicoll.
In 2004, the Circle Line of the Mass Rapid Transit system was being built in an underground tunnel. One of the stations in the line was situated at Nicoll Highway. However, the construction had to be delayed and moved to a new site after the collapse.
Cave-in at the Construction Site
On 20 April, 2004, at 9:00 AM, Kori Construction site workers heard strange noises from the steel supports at the excavation pit. The workers evacuated the pit for safety measures. However, later at 2:00 PM, some workers went into the pit and attempted to stabilize the structure using cement.
At about 3:30 PM, the construction workers at the station construction site were having their tea break when the steel supports over the tunnel began to fall over, collapsing into the deep tunnel. The surrounding area caved in as well, forming a crater of twisted steel beams, cranes and rubble.
Crisis management was activated immediately. A rescue team arrived at the scene 10 minutes later, made up of 75 personnel and their rescue dogs, which found three workers injured and four others unaccounted for. The first body of the missing was uncovered at 6:15 PM. Two others would be found in the subsequent three days, but the search was called off on the fourth day before the last missing person could be found because the rescue mission was deemed to be too risky, and there was a low survival chance by that point.
The collapse of the highway caused water, gas and electricity cables to snap, resulting in a 20-minute power outage for approximately 15,000 people and 700 businesses. Tremors were felt in the nearby residential and commercial Golden Mile Complex, and everyone inside was evacuated.
Measures were immediately taken by the police, who cordoned off the adjoining Merdeka Bridge and closed all the roads leading to Nicoll Highway. The closure affected thousands of commuters, including those taking public transport along the route, since Nicoll Highway was a key connector to and from the Central Business District.
It was decided that the Nicoll Highway subway station would still be built, but shifted 100m (330 ft) from its original proposed location. Island-wide excavation works at all the Circle Line construction sites were temporarily suspended, delaying the expected completion of the subway line by about a year.
In total, the estimated cost of damages from the collapse was said to go into the millions. The main contractor in charge of the construction site, Nishimatsu-Lum Chang, unconditionally offered an ex gratia payment of S$30,000 (US$21,637) to the family of each of the four victims.
Nicoll Highway was reopened for use more than seven months later on December 4, 2004.
How Did It Happen?
An official three-man committee was formed to investigate the cause of the collapse and to suggest recommendations to prevent such a disaster from happening in the future. The official report concluded that the collapse happened due to critical design and construction errors, causing the strut and beam earth retaining wall system to fail.
For one, an inappropriate soil simulation model had been used. The model overestimated the soil strength at the construction site and underestimated the forces on the retaining walls where the tunnel was being excavated. In reality, the surrounding soil was weaker and the retaining walls were not able to support it fully.
There was also an error in the design of the strut-waler support system, with its connections being under-designed. Additionally, it was found that the construction of props to spread the load from struts to walers had been omitted. These errors altogether resulted in the strut-waler system being half as strong as it should have been, resulting in the steel supports giving way and causing the collapse of the structure.
In the wake of the Nicoll Highway disaster, some civil engineering protocol has been changed. MRT stations in Singapore were conventionally built from the “bottom up”, making use of propping provided by steel supports (struts) affixed to king posts at mid-span, and bearing on to waling beams installed across the diaphragm walls of the tunnels. These walers were meant to distribute the forces exerted by the struts along a larger surface of wall. Following the incident, the steel supports were changed to be installed at every 3-meter interval in depth.
Some newer stations were also constructed from the top down, using a permanent reinforced concrete roof slab as a giant support, thus eliminating the need for steel struts entirely. This greatly saves time and increases safety at the construction site.
Four individuals were faced with criminal charges as a result of the Nicoll Highway collapse. One was Ng Seng Yoong, a project director of the Circle Line MRT and in charge of monitoring the excavation and design work. It is alleged that there were readings of instruments on site that suggested some faults within the construction, but the warnings were not heeded. Furthermore, it was found that the regulator of building works had written to Ng regarding the absence of 26 reports of instrument readings that should have been received over the past six months. To date, Ng is the only person who has been prosecuted for the collapse, having been fined S$8,000 (US$5,770) by the court.
The contractor company, Nishimatsu-Lum Chang, ended up spending S$11.7 million (US$8.4) on rescue operations, reconstruction and checks on nearby buildings. The company was also barred from further contracts for five years.
The fourth victim, Mr Heng Yeow Peow – whose body was never uncovered – was hailed as a hero in the aftermath of the disaster. Heng was a 40-year-old foreman at the construction site. According to survivors’ accounts, Heng had selflessly helped his workers to safety at the expense of his own life. He became trapped and was never found after the collapse. To support his wife and two young children, a trust fund was set up that raised money from public donations alone, initially paying the family the equivalent of Heng’s salary with overtime on a monthly basis. The monthly payout was eventually increased to double the original to accommodate the children’s higher education.
Construction of the Circle Line and Nicoll Highway station at its new location continued after the suspension on the construction sites was lifted. Nicoll Highway station started operation earlier than expected, on 17 April 2010.