as geophysical surveys, piezocone (CPTu), pressuremeter,
dilatometer, direct shear, triaxial testing, consolidation testing,
among others, all of which supplement a conventional
investigation that is based on SPT. Dependent on the unique
circumstances of a project, one or more of these methods
should be included in the scope of the geotechnical investigation
for a truly reliable design that mitigates underground
and structural risk.
An important way to control the cost of a geotechnical
investigation while reducing risk is to undertake staged or
phased geotechnical investigations, by which a smaller scope
initial investigation provides clarity on the second phase of
an investigation that may incorporate more advanced testing
techniques targeting issues highlighted in the first phase.
Phase II perhaps incorporates more than one investigation
technique to further drill down on items of interest identified
in Phase I. Often early geotechnical investigations do
not encapsulate the full intention of the project scope as it
may still be in development. A Phase II investigation later in
the project cycle can help to capture the importance of any
design development that may have happened and can help
instruct further investigation (i.e. bigger structures with
more basements may require deeper geotechnical borings in
Phase II).
As positive as managing geotechnical risk can be to an
owner’s bottom line, excess conservatism in design can
negatively affect the bottom line. Unlike geotechnical risk,
excessive conservatism usually goes unidentified, and
owners often don’t have any idea how much money is wasted.
When the scale and/or quality of geotechnical investigation
is low, contractors can easily over or underestimate the
cost by as much as 30 per cent! If there is not enough data
to properly manage risk or accurately estimate the project’s
construction, don’t expect a cutting-edge design to lower
costs. Unfortunately, unlike geotechnical risk, there is no reliable
study to determine how much money is lost on overly
conservative designs.
There are examples of projects where owners ended up
paying much more than what was needed due to an overtly
conservative design. On the other hand, there are other projects
where the thorough geotechnical investigation lowered
the perceived risk and allowed the owner/designer to allocate
funds more effectively. A good quality investigation can
lead to cost-effective solutions such as ground improvement.
Solutions like this need a quality engineering assessment, and
a proper engineering assessment needs reliable information.
Allocation of the geotechnical risk is another tool in risk
management. However, some owners do not have a realistic
expectation of the concept. Increasingly owners are
attempting to download all of the risks onto the contractors
without truly understanding the consequences and reliability
of this approach.
TECHNICAL
ANELA47/123RF
Increasingly owners are
attempting to download all of
the risks onto the contractors
without truly understanding the
consequences and reliability of
this approach.
PILING CANADA 69
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/Consolidation_(soil)
/profile_anela47
