Chapter 3 - Events leading up to the Collapse by FYP - The Collapse of Nicoll Highway

Parties Mention:

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Nishimatsu-Lum Chang Joint Venture (NLCJV), Builder

Paul Broome, responsible for temporary works design

Key Events leading up to Collapse:

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(problems since early March to the Final Collapse)

Incident at Launch Shaft 2 (LS2)
Incident at Type K
Incident at Type M2
Incident at Type M3

1. Incident at Launch Shaft 2

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Back Analysis was done due to the deflection and settlement of the diaphragm wall at LS2 that were still increasing slowly despite the implemented measures

Under-design of diaphragm wall using Method A

Paul Broome insisted in following the analysis he considered appropriate
NLCJV insisted that their design was sound and that LTA should not dictate what needs to be done
LTA had to aceept their assessment as the actual deflection at Type K showed that Method A was more representative

2. Incident at Type K

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major incident after incident at Launch Shaft 2

January 2004: Excavation stopped immediately and NLCJV was told to submit a design review due to the sudden strong surge in the wall deflection

2.1 Design Reviews, Type K

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Repeated breaches of the instrumentation review levels

2nd Back Analysis was done as the maximum deflection measured by I-63 have exceeded the revised design level of 422mm
2nd Analysis was severely criticized as LTA asserted that NLCJV's primary goal for submitting the analysis was just to gain permission from LTA to continue excavation
NLCJV and Paul Broome were hoping to pull it off regardless of what was being said

3. Incident at Type M2

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Part of this area, together with Type M3, constituted the collapse area

Repeated breaches of the instrumentation review levels

Back Analysis was done due to the deflection at Type M2 that has exceeded the design level measured by I-102

Back Analysis also includes:

Reducing the strength of JGP, marine clay and wall stiffness
Adding one more layer of struts by closer strut spacing below 5th level, increasing the total level of struts from 10 to 11

4. Incident at Type M3

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Collapse took place here

Abuse of Back Analysis/ Repeated breaches of the instrumentation review levels

Back Analysis was done as I-104 (south) repeatedly exceeded its revised design levels
Endorsed and issued by Paul Broome who maintained his belief that the BA2 method was working, the wall was capable of withstanding greater forces and that it was safe to continue

4.1 Contributing Factors at Type M3

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Failure to institute regular, close, effective monitoring system

Close monitoring was necessary throughout but no readings were taken for I-104 as Paul Broome explained that both I-65 (north) and I-104 south) were tracking very similar movements
Inclinometer was covered with 'a lot of soil', preventing workers from collecting data

Failure of the 9th level strut-waler connections

According to Paul Broome:

By the 9th/10th level of struts, there was 6m or so to the base of excavation
there would not be sufficient room for a small excavator required to carry out the final excavation
there would not be sufficient room to carry out the hacking down of bored piles at the final level