Nicoll Highway Collapse Singapore 2004 – Causes, Lessons & Safety Review

The Nicoll Highway collapse in Singapore on 20 April 2004 was a major accident that occurred during the construction of the Circle Line Mass Rapid Transit (MRT). A section of the retaining wall supporting deep excavation works failed, causing the highway above to cave in. The collapse created a huge hole, killed four workers, injured three, and delayed the Circle Line project. Beyond the loss of lives, the accident damaged public confidence in construction safety and raised questions about engineering design, site supervision, and safety culture.

The purpose of this investigation is to review what happened, identify the main causes, and draw lessons that can prevent similar events in the future. The professional experts at Assignment Help Singapore makes use of Human Factors Analysis and Classification System (HFACS, 2014) to analyse the case, and also examines organizational, supervisory, and human factors that contributed to the collapse. It also reviews the emergency response and communication at the site.

The report is structured into factual information, analysis, conclusions, safety actions, recommendations, and broader applications to other industries. It highlights the importance of strong project management, clear safety procedures, and accountability. The findings are not only relevant to Singapore but also to global construction projects where deep excavation and public safety are involved.

Fig 1: Nicoll Highway Collapse. Source: Wikipedia.

Factual Information Detailing the Time and Events

Table 1: Timeline of Events

Date/Time	Event
Early 2004	Excavation and bracing works began at the Circle Line Nicoll Highway site.
April 20, 2004, 3:30 pm	The retaining wall failed; a large section of Nicoll Highway collapsed, creating a 150 m long, 100 m wide, and 30 m deep hole.
Immediately after	Workers nearby evacuated; some trapped due to collapsed exit stairs.
Around 5:00 pm	Emergency services arrived; rescue and recovery began.
Same day	Three injured workers were taken to hospital; two discharged later.
Following weeks	Search and recovery operations for missing workers; project halted.
Later months	Formal inquiry by the Ministry of Manpower (MOM) and engineering experts launched.

Fig 2: Factual Information of Nicoll Highway Collapse. Source: SG101.

Workers were not expecting it; the sudden collapse happened.. A rescue effort took place straight away, but their work was hindered by the unstable structure. Besides, support for survival went on for many days, and inquiries followed shortly (Endicott, 2013).

Injuries to People

The collapse cost the lives of four workers. One of the foremen was killed after assisting others to evacuate the building but was caught in a staircase that collapsed. Three employees were taken to hospital and injured, and two were discharged on the same day (Endicott, 2015). In addition to physical damage, colleagues and survivors suffered psychological damage because of seeing the collapse and losing a colleague.

Families of the victims were put under long term emotional and monetary pressure too. The crash showed that there was a high degree of danger even though many of the employees were on a break. The moral effects indicated that the more significant the safety culture in the construction process (Zou & Sunindijo, 2013).

Damages

The collapse demolished part of the Nicoll Highway at Merdeka Bridge and severely damaged the works of the MRT Circle Line tunnel excavation. Construction equipment that is buried or too damaged to be repurposed is covered with an excavation pit (Ghosh, 2018). The accident also stopped the Circle line project by an estimate of 2 years and millions of dollars of redesign, legal settlement and compensation. Direct costs were estimated to be in the hundreds of millions of dollars. It was in a truer sense that the population no longer believed in the security of the ideas, and it introduced cost exposures both to the contracting firms and to the authorities, at least indirectly, (Haycock, 2024).

Personnel Information

Engineers, supervisors, and construction workers of different qualifications were involved in the project. The majority of workers were possessing the corresponding technical skills and practical experience of the work in the excavation field. However, it was discovered that the scale of the project was more than that of supervision and monitoring (Endicott, 2015). The site foreman acted as a leader who tried to carry out an evacuation and ended up losing his life. Safety of excavations was under the authority of the supervisors, but the weaknesses of design of the retaining system were not taken into consideration.

The audit conducted by MOM demonstrated the flaws in the separation of duties between the contractors, consultants and the engineers (Hee, 2025). Hours of work and room breaks were not a significant problem; however, the lack of responsibility and control was a significant concern. The case identified a benefit to the supervisor who takes a proactive role in safety management along with the development of technical skill (Zou & Sunindijo, 2013).

Equipment Operation

The support wall-line used in the deep cut-off of the loose clay soils was a contributory cause of the collapse. What made the wall and bracing not stable were the lateral earth pressure and flaws in its design (Luo et al., 2022). Some machines such as hydraulic grabs and cranes used in excavation which were already in operation did not directly cause failure. Rather, an emphasis was placed on engineering planning and construction techniques. Insufficient safety margins in the support system resulted in inconclusive working conditions which demonstrate that the right equipment is not sufficient to provide safety in the presence of the wrong design (Endicott, 2013).

Meteorological Information

The collapse was not brought about by weather. The condition on April 20, 2004 was common to the tropical weather conditions in Singapore and no abnormal weather or severe events were reported. That validated structural and geotechnical rather than environmental failure (SgWiki, 2020).

Communication

There was normal reporting of activities between management, supervisors and workers at the site. But, warning signals of the movement of retaining walls were not effectively reported to decision-makers (SgWiki, 2020). Workers were also screaming warnings during the collapse, and some supervisors assisted others in evacuating the building. Emergency contact procedures were mobilized and within a short time, police, fire and medical teams rushed to the site.

All this observation notwithstanding, preventive action was abridged without the high degree of observation and in-house communications. In their results published by MOM, it was defined that in the situation of safety in large-scale construction, it is impossible to reach safety without effective communication, including elaborate risk and warning reporting (Garrett and Teizer, 2009).

Emergency Responses

Some workers became stuck in the stairways; nevertheless, evacuation of the building was undertaken after its collapse. Barricades were placed to ensure that people did not move around the unstable location. Minutes later fire and rescue units arrived, yet the ground was unstable, so they could not search. Such a collapse would not happen soon and, therefore, heavy equipment could not be run in panic (Hee, 2025).

Emergency measures were taken but the disaster exposed gaps in excavation preparation on a very big scale. It might also put their safety at considerable risk, and it turns out that in the field of safety in construction, a progressive plan to counter a course of an accident that does not occur frequently but has a high frequency (frequency) is more appropriate (Haycock, 2024).

Tests and Research

Design review and soil-stability studies were considered as post-incident investigations. It was proven by special studies that the retaining wall and support system lacked enough safety margin when the condition of soft clay is encountered (Jalali et al., 2023). The findings were relevant to both revising the construction standards in Singapore and to educating new engineers (Tang et al., 2021).

Analysis

Examination Using HFACS

The Human Factors Analysis and Classification System (HFACS) helps to understand the different layers of causes that led to the Nicoll Highway collapse.

Organisational Influences

The collapse reflected weaknesses in project management and regulatory oversight. Budget and schedule pressures meant that cost-saving measures were prioritized over safety margins (Endicott, 2015). The retaining wall system used was not designed with a wide enough safety factor for Singapore’s soft clays (Shappell & Wiegmann , 2000). Regulatory reviews were present, but monitoring was not strict enough to catch flaws in the design and construction approach.

Unsafe Supervision

Supervision at the worksite was not sufficient. Warning signs of wall movement and soil instability were reported but not acted on quickly enough (Endicott, 2013). Risk assessments were carried out but were too general, and site conditions were not fully reflected. Supervisors did not escalate concerns strongly, and management accepted progress over caution.

Preconditions for Unsafe Acts

The excavation was carried out in weak marine clay, which has poor stability. This made the site more vulnerable to collapse (Jalali et al., 2023). Human factors such as worker fatigue were less critical, but there were gaps in training on how to identify soil instability. The construction culture emphasized getting the job done rather than carefully checking safety margins.

Unsafe Acts

At the sharp end, unsafe acts included ignoring small signs of wall deflection and not reinforcing the bracing adequately (Shappell & Wiegmann , 2000). Workers followed instructions but lacked authority to stop unsafe activities. Some warning cracks and ground movement were overlooked. These unsafe acts did not directly cause the collapse but allowed deeper organizational failures to turn into disaster (Small, 2020).

Limitations in Evidence

One limitation in this investigation is that most of the detailed evidence comes from the official Committee of Inquiry and engineering case studies. Contractors involved may not have fully disclosed internal communications or cost pressures that influenced decisions. This means the true scale of management oversight problems may be larger than reported (Small, 2020).

Another limitation is that one will rely on publicly available reports and academic studies rather than raw site data. Independent access to soil monitoring records, inspection logs, and real-time measurements could have provided stronger insight. Finally, since the accident happened in 2004, memories of survivors and witnesses may not fully capture what happened on the ground. Despite these gaps, the available evidence is still strong enough to identify the main engineering and organizational causes (Abdi & Ou, 2023; Hee, 2025).

Scientific Verification

Engineering studies confirm that the Nicoll Highway collapse was mainly caused by failure of the retaining wall and bracing system in soft clay soils. Research by Abdi and Ou (2023) used soil-structure interaction models to show that the wall did not have enough strength and stiffness. This scientific evidence matches the findings of the Committee of Inquiry, which identified under-designed bracing as the main cause.

Other case studies (Endicott, 2013, 2015) confirm that the bracing system failed to handle earth pressure during excavation. Soil tests showed the marine clay had very low shear strength, which meant that any small movement in the retaining wall could quickly worsen into collapse. This scientific evidence gives confidence that the cause was structural and geotechnical, not due to weather or random chance.

Scientific verification also comes from comparisons with other excavation failures worldwide, which show the same patterns of weak bracing and insufficient safety margins leading to collapse. These studies confirm that the Nicoll Highway collapse fits into a known category of engineering failure (Tang et al., 2021).

Unknowns, Uncertainties, and Controversies

There are still debates about how responsibility should be shared between designers, contractors, and regulators. Some argue that the design engineers should have done more detailed soil analysis, while others say the contractors failed to follow safe construction methods (Hee, 2025). The role of MOM is also debated: critics argue that regulatory checks should have been stricter, but MOM notes that contractors and consultants carry the primary responsibility.

Another uncertainty is whether early warning signs could have been detected with better technology. Some reports suggest ground movement was visible, but it remains unclear if advanced monitoring would have given enough time to act. Finally, there is controversy over whether cost-cutting directly influenced design choices. While no evidence of deliberate neglect was proven, many believe that budget and schedule pressures indirectly led to reduced safety margins (Haycock, 2024). These controversies continue to influence construction safety policy in Singapore and abroad.

Conclusion

This highway crash of Nicoll Highway was not caused by one mistake but by multiple mistakes in design, supervision, and organization. The real cause was that the retaining wall and its bracing were poorly-designed and could not withstand soil pressure in the Singaporean marine clay (Abdi and Ou, 2023). This was aggravated by poor responses to warning signals and poor surveillance.

Project management pressures at the organizational level resulted in safety margins that were either too low or underestimated risks were underestimated. Contractors and consultants were using optimistic design considerations, and the regulators failed to exert strong enough influence to insist on better safety standards. As per the case, there exist top-down malfunctions in safety culture. When warning signs were involved, it was considered as petty and not a serious issue, and supervisors did not have power to halt unsafe work. There was regulatory oversight which was more reactive than preventive.

Concisely, the failure was caused by a combination of engineering defects that were influenced by the organizational and regulatory failures. It demonstrated that the culture of safety and risk management should be incorporated in all phases of design and construction and supervision.

Safety Actions

The Ministry of Manpower (MOM) of Singapore launched an Inquiry Committee (COI) to investigate the causation of the collapse. The COI traced critical design, oversight and project management failures. This resulted in fines to the companies and professionals detected and the withdrawal of their license in some cases (Hee, 2025). Shortly after this came regulatory changes.

The Building and Construction Authority (BCA) and MOM enhanced the deep excavation Code of Practice. There were new conditions requiring additional safety considerations during retaining wall design, increased scrutiny of engineering calculation by peers, and increased site monitoring. On worksites, changes were implemented on the spot.

Compulsory risk tests were increased and more specifications were made in terms of excavation safety. Safety officers became a bit more empowered to halt work when risks were detected. The evacuation operations, along with the passing of the emergency response preparedness as obligatory, helped to achieve better emergency response preparedness and other positive results.

This was done to seal off the loopholes brought about by the collapse of the Nicoll Highway. They represented the direction towards active guarantee of safety, rather than passive regulation in the Singapore construction sector.

Safety Recommendations

Possible recommendations to prevent the aforementioned accidents can be organized in the hierarchy of Controls:

Elimination

• Deep excavation should be avoided, in particular, by using some other construction methods (e.g., tunnel boring machines).
• Feasibility: Low but good when choice of design is available.

Substitution

• Substitute high-risk retaining systems with more solid methods, including a diaphragm wall rather than a sheet pile wall.
• Effect: High, since the diaphragm walls provide greater stability in the loose clay.

Engineering Controls

• Demand increased safety of design and building bracing systems and soil-retention.
• Monitor in real time (inclinometers, piezometers) to send alerts when limits are surpassed.
• Impact: highly effective and becoming relatively cheaper with digital sensors.

Administrative Controls

• Carry out independent third party design testing prior to the commencement of excavation.
• Enforce safety training and scenario-based training on all deep excavation projects.
• Effects: medium to high, according to enforcement.

PPE or Personal Protective Equipment

• Verify all workers on the excavation sheets to ensure that they have helmets, safety harnesses, and communication devices.
• Impact: Can only soften the blow when accidents happen, and not avert the collapse.
• Weight of priority: Engineering controls and administrative measures are to be prioritised due to the direct impact on reducing risks of collapse. The initial design stage should allow elimination and substitution, but PPE still needs to be a final defence measure.

These recommendations combined provide a series of protection levels, allowing any organizational and engineering vulnerabilities not to develop into disasters.

Expansion

The Nicoll Highway lessons go beyond Singapore. Another issue with underground transport systems in soft soil conditions is rapidly growing cities like Jakarta, Manila and India. Stricter codes of design and independent peer review and computer based monitoring systems should be established in such areas at the start.

This is no exception in other types of jobs, such as tunnelling, mining or offshore oil and gas, which require ground or structural stability. Another important factor in these industries is strong bracing, monitoring and emergency planning. The communication chain may turn into a disaster by driving the safety drill. The results are also applicable in large organizations that handle high-risk transportation, utility, and mega structural construction projects (Luo et al., 2022).

Hydroelectric dams, underground pipelines and nuclear facilities are just a few examples that require a strong culture of safety, good design, and regulatory openness. Overall, the lesson of the Nicoll Highway collapse is that safety needs to be approached as a system-wide issue. The design engineers, regulators, and workers on-site must all become part of creating resilience. When implemented around the world, such lessons can save lives and expensive setbacks in future infrastructure endeavours.

The Nicoll Highway collapse is a disaster that goes beyond just the site of the accident, in fact, it has become a lesson for organizations in highly sensitive areas that have to deal with integrating resilience engineering and systems thinking into their safety management.

A similar set of principles as those used by aviation and nuclear industries that rely on redundancies, multiple checks, and fail-safe devices to eliminate the possibility of catastrophic risks, can be implemented in civil engineering projects (Jalali et al., 2023). In particular, these should be projects in rapidly urbanized areas where there is a boom of underground infrastructure development at unprecedented rates. Besides, the incident at Nicoll Highway also points to the importance of a thoroughly open regulatory oversight and sharing of knowledge beyond borders.

The countries that are executing megaprojects like the Belt and Road Initiative (China) or metro expansions (India) will, possibly, get the most advantages if they embed stricter international standards into their procurement and project governance. The global dimension of these lessons, as this case shows, is that well-established safety practices are not merely local necessities but also the main instruments for assuring the public trust in the provision of critical infrastructure anywhere in the world.

Assignments based on civil engineering are technical as they require the application of mathematical and scientific principles to real world problems. The given case analysis of Nicoll Highway collapse also required the application of problem solving skills to recommend ways in such incidents can be stopped from occurence. If you need assistance with similar types of civil engineering case studies or any other subject, get in touch with our trusted assignment writing experts in Singapore to assist you with all types of case studies and assignments.