The Ingenieur Vol 59 July-Sept 2014 The Ingenieur Vo. 59, July-Sept 2014 | Page 57

Nicoll Highway collapse
of around 33m. The bracing involved 10 levels
of conventional steel struts with waling beams,
and two additional jet grout struts (one of which
was sacrificial). The steel struts were supported
by piled king posts at mid span. The failure was
initiated at the strut/waler joint at level 9, located
just above the sacrificial jet grout strut which was
being excavated. Level 10 struts were not effective
at the time of failure.
Causes of failure
A Drained Soil Analysis had been used instead of
the more appropriate und-drained approach. The
consequence was to significantly under-estimate
the loads on the temporary works by a factor of
up to 2.
1. The load concentration at the strut/waler
junction was severely under-estimated
as the intended splay members which
would have distributed the load, were
omitted.
2. The stiff bearing lengths were grossly
over-estimated (misinterpreting BS5950)
3. The change to the stiffening arrangements
(by using C Channels) following buckling
of plate stiffeners, was critically flawed.

Key lessons from this event
Trends during critical periods must be
●●
capable of being monitored.
Those interpreting the outputs must
●●
be competent to do so. The dangers of
drawing conclusions from past behaviour,
without careful consideration of the
actual conditions, must be recognised.
The management of uncertainty must
●●
be robust. There must be approved and
tested contingency plans.
Those involved must be competent at
●●
both organisational level and individual
level
The project must operate within a safety
●●
culture conducive to safe working. This
means, inter alia, a ‘stop work’ procedure
to be in place, clearly understood by
all, and supported by management and
clarity in the chain of command and in
responsibilities. - Inforeach
Source:
www.internet-stg.mnd.gov.sg
www.eresources.nlb.gov.sg
www.cms.structural-safety.org
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