The Committee of Inquiry (COI) into last year’s fatal collapse at Nicoll Highway in Singapore (T&TI, May, p6) has lambasted both design and site procedures on the contract saying warnings of the approaching collapse were not taken seriously and the safety culture on the project fell short, concluding: “The Nicoll Highway collapse could have been prevented.” The final report obtained by T&TI into last April’s collapse on Circle Line project C824 described a series of events that led to the tragedy. Under design of both the diaphragm wall and the waling led to the failure of the waler strutting and the inability of the overall retaining wall system to meet the redistributed loads as the strutting failied. This led to the catastrophic collapse of a section of the wall. The COI said: “The collapse did not develop suddenly. A chain of events preceded the collapse.” The COI report described “failures to demonstrate the necessary level of care” from the early stages of the project, blaming technical and administrative functions for the failure to deal with the “insidious warning signs”. It said two significant contributory factors were the abuse of back analyses for the conditions where the collapse took place and the failure to set up a “regular, close and effective monitoring regime”.
In the run up to the collapse, indicators such as excessive wall deflections, surging inclinometer readings, water beam buckling, stiffener plates buckling, ground settlement, trespass of water and soils into the excavation through cracks in the diaphragm walls, failure of concrete corbels, failing support brackets, plunging strain gauge readings and “thung” sounds from the heart of the strutting system were all deemed insufficient to halt the works. The COI simply stated, “time took its toll” and said the blame falls squarely on the contractor, the Nishimatsu-Lum Chang JV.
The failure to monitor inclinometers at key locations on a daily basis during critical periods led to a lost opportunity to detect adverse trends said the COI. Further, the interpretation of the instrumentation data was said to be perfunctory and past experience gave a confidence that was misplaced as it was not adapted to local incidences on the project. The report also said the overall corporate competency of the contractor was insufficient.
Responding to the report, the Singaporean government accepted the COI findings through statements issued by the Ministry of Manpower, the Ministry of National Development and the Ministry of Transport. Mah Bow Tan, minister for national development said he agreed with the findings and the COI’s recommendations, but added that he wished to reassure the public about the safety of existing deep excavation sites. He said a Singapore Code on Deep Excavation was hoped to be ready soon that features input from statutory bodies, tunnelling professionals and academics. Pending this, an advisory had been issued to the industry to set preliminary standards for the design and construction of temporary earth retaining structures.
A Joint Review Committee (JRC) was set up by the Ministry for Manpower and the Ministry of National Development to review the regulatory framework and practices of the construction industry. Mah Bow Tan said this and the COI investigation complemented each other as one considered a specific incident and the other, the industry as a whole and how the specific findings could be addressed industry-wide. Reminding people of the seriousness of their actions, he urged: “Let’s work together, because precious lives are at stake.” Full details of the COI investigation and recommendations can be found on the Ministry for Manpower’s website at www.mom.gov.sg
