Geotechnical News • September 2015
37
GEO-INTEREST
Errors in geotechnical engineering - Case history 1
extract from Suit is a Four letter Word
(Hugh Nasmith, 1986)
Hugh Nasmith has put together an
excellent book on litigation which
is easy to read, covers the litigation
scene thoroughly, has subtle humour,
and most important of all, is umder-
standable. He remarks in the opening
paragraphs that experienced geotech-
nical engineers will find nothing new
in the book except comfort that their
situation is not unique. This is true but
experienced engineers should read it
anyway. (From a review by William A.
Trow).
An incorrectly
located borehole
is probably one of
the more common
errors in
geotechnical
engineering.
In most cases the error goes unde-
tected since site preparation will
destroy the evidence of the actual
location of the borehole, and for most
purposes a wrongly located borehole
is not critical unless it actually hap-
pens to be on the wrong property. The
following account describes a case
where a wrongly located borehole
was the basis of a complex dispute
though in this case it appears that the
losses suffered by the plaintiff arose
from other causes than the consultant’s
error.
The client was an industrial firm
which employed a firm of architects to
design and supervise the construction
of a building to house heavy machin-
ery. The foundation investigation was
carried out by a firm of geotechnical
engineers who were familiar with
local practice and conditions.
An incorrectly located borehole is
probably one of the more common
errors in geotechnical engineering.
The subsurface investigation was
conducted in two stages. In the first
stage the general site conditions were
identified and it was recognized that
the heavy machinery loads would
have to be carried on end-bearing
piles driven through soft clay to a very
hard bedrock. From local experience
it was known that the bedrock surface
was very irregular and that difficulty
in seating piles on steeply sloping
surfaces was often encountered.
In the second stage a further drilling
program was carried out to explore in
more detail the area to be occupied by
the building itself. Unfortunately three
borings were plotted approximately
fifty feet from their actual locations.
The drilling information from the two
programs and reference to the geo-
technical report was included on the
bid documents along with a disclaimer
which stated “This information is
presented for the foundation sub-
contractor. He shall satisfy himself as
to prevailing conditions, and no extras
will be allowed should conditions dif-
fer from those indicated.”
The contract for the building was let to
a local general contractor who called
for proposals for the installation of
end-bearing piles as shown on the
bid drawings. Contrary to the recom-
mendation of the local geotechnical
engineer the client insisted that the
contract for piles be on a lump sum
basis.
Proposals were received from several
contractors. The successful piling
contractor had not worked in this area
previously and proposed an alternative
to the type of pile shown in the bid
documents. Acceptance of the alterna-
tive required structural analysis and
some modifications of the piling sys-
tem to achieve the same results as the
system shown in the bid documents.
By the time all of
the facts of the
case had been
explored and the
only uncertainty
remaining was how
the judge would
interpret the facts.
During the negotiations prior to
the award of the contract the piling
contractor carried out some drilling
at his own expense and confirmed
that bedrock slopes steeper than 45
degrees would be encountered. After
the contract was signed but before any
work had started a further revision to
the pile system was proposed by the
piling contractor and was accepted on
the condition that there would be no
change in the lump sum price for the
piles.
The piling contractor was required by
the terms of the contract to employ the
geotechnical firm to provide inspec-
tion services. The geotechnical firm
was thus fortunate to have an inspector
on the site to obtain firsthand knowl-
edge of the pile driving records. How-
