Geology Reference
In-Depth Information
marginally lower than the load that was predicted would be applied to it.
'
Perhaps if a higher overall FoS (say 1.4) had been adopted for the design
of the walls, it might have compensated for the error in structural design
detail, but if it had done so it would have been essentially by chance.
Blockley (2011), in his paper on engineering safety, discusses a Swiss
cheese model (Reason, 1990) where the components controlling safety
are expressed as a series of layers such as management, design and
ground model, each with defects (holes) in them, including unsafe acts.
These are dynamic
some of the holes move around during construction
or generally with time. Failure occurs where the holes line up. The Nicoll
Highway collapse is an example where there were several such layers
with defects and it just happens that perhaps three out of
-
ve or so
linedupatthisparticularlocation and these were enough to initiate
failure. The fact that others lined up elsewhere on site (including diffe-
ring ground conditions and incorrect analysis) contributed to the scale of
the failure. The FoS or partial factor approaches of Eurocode 7 cannot be
expected routinely to cope with structural design faults nor errors in
ground models and analytical mistakes. At the BGA meeting, the
site was described as unforgiving, but this seems outside the sense of
thetermasusedin
Chapter4
whereitistakentodescribeparticularly
adverse geological
cult to
anticipate or to investigate using routine approaches which was not the
case here.
conditions
that would be very dif
As a general point, when things do go wrong and a detailed examina-
tion is made of the ground model assumptions vs. what caused the
failure, it is often found that the ground model was inadequate or
incorrect. Sometimes this can be because the GI was poorly designed or
conducted, but also because practice was poor. Some of the common
errors and poor practices are set out in
Table 7.1
.
Environmental factors include hydrogeological conditions,
in situ
stresses and earthquake shaking. Such factors should be considered
in preparing the ground model for a site. The environmental factors to
be accounted for depend largely on the nature, sensitivity and design
life of structures and the consequence of failure.
inattention to detail: landfill site in the UK
A quarry in Gloucestershire, UK, was used for disposing domestic
refuse. The quarry had been developed to extract moderately
