The Civil Engineering Contractor June 2019 | Page 30

FEATURE
Geotechnical investigations are currently underway in Lesotho for the Lesotho Highlands Water Project.
risks and methods suitable for the
project. For certain conditions you
will have certain methods of drilling,
and this has to be determined prior
to going to site.” It also enables the
contractor to give the client a price
which is not ‘qualified’. Nell says
that in most cases he sees there is
a substandard geotechnical report,
even for large developments. This
means the piling contractor has to
qualify his bid price, which can get
‘unpleasant’ he says, when conditions
underground prove to be different
to what was expected based on
information available.
In eight cases out of 10, there may
be no problem – but in the other two
cases out of 10 the blowout on costs
makes it worthwhile to have done
reports on all 10, he says.
“The law today requires a client to
have a certain level of geotechnical
report done, but the client typically
does the minimum – to try to keep
the building cost to an absolute
minimum. The saying in the industry
is that you pay for a proper report
either way – at the beginning of the
project or during construction.
“If a developer does the minimum
report, then the projects will have
a higher risk profile and the bidding
contractor will take cognisance of
that risk. We all have a good general
28 | CEC June 2019
idea of what is where – we know that
Sandton is on granite; Rosebank is the
same but a bit deeper; Centurion is on
dolomite; Pretoria is shale and some
other andesites – what we don’t know
is what the specific conditions of the
project are, as there can be significant
variability. Therefore, we qualify our
quotes. We put in a qualified design,
a re-measurable bill of quantities and
a method qualification. We would
say things like ‘we did not allow for
sidewall collapse’, or we priced CFA
piles taking cognisance of water and
so on. We do the best we can with
what we’ve got, and qualify it.
“If it goes well and the qualifications
were not required, then the client
is happy because he’s saved a bit
of money. If the site has conditions
different to what we assumed, we
may have to bring on additional
equipment and that causes cost
escalations, contractual claims and
time delays,” explains Nell. When
the client has to pay extra money, it
becomes quite unpleasant and often
evolves into a blame game.
“The client will argue that we’re the
experts and ‘should have known’. We
will argue that we ideally would have
been provided with a comprehensive
geotechnical investigation. It builds
up bad blood, and such disputes
can give our industry a bad name
– undeservedly.” It does help that
geotechnical consulting firms such
as Jones & Wagner have considerable
institutional memory around the
country with its more than 50-year
history and in the event of their
design, will bring the possible risks
to the fore.
However, in tough times like now,
contractors will try present the
most economical possible proposal
based on a pricing according to
the most optimistic interpretation
of site conditions provided in the
geotechnical report. “The likelihood
of things going wrong on site
therefore becomes bigger.”
A common problem is to
unexpectedly find a high water table
or soil that collapses during drilling
– so that when the drill is removed
the walls fall in, which in some cases
requires the CFA method, and in
other cases the use of temporary
sleeves, says Nell. “These are not
issues that undermine the integrity
of the structure, but they add to the
cost and time of installation,” he adds.
Types of geotechnical
investigations
The choice of tools and equipment for
a geotechnical investigation primarily
depends on the type of access to the
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