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Bachy Soletanche
is cleaning up
the River Ribble
Specialist geotechnical
contractor, Bachy
Soletanche, is working with
main contractor KMI water,
a joint venture between Kier
Construction, J Murphy and
Sons and Interserve Project
Services, on a project for
United Utilities to treat
the water that goes into
the River Ribble using a
storm water shaft solution
involving deep diaphragm
wall shafts and Cased
Secant Piling (CSP).
The project, which started in May of this
year, is due to run until October and is
worth an estimated £4.5m for Bachy
Soletanche, and £70m in total for KMI
Water. A 27m diameter shaft, adjoining
22m deep 50x20m screening chamber
and a 17m diameter shaft constructed
by diaphragm walling will connect
with nine additional cased CFA shafts
on the north side via a 3.5km tunnel
constructed 30m below the ground by
KMI Water and will pave the way for a
cleaner river.
One of the south diaphragm wall shafts
is formed by 14 interlocking panels
1m thick by 20m deep. Between each
panel a CWS waterbar is being installed
to stop water leaking through the joint
and ensure maximum water tightness
between adjoining panels. Panels are
dug under a bentonite suspension, then
reinforcement cages are placed and
concrete is tremied into the trench. All
trenches are going to be approximately
20m deep.
The screening chamber will only be used in
the case of extreme flood conditions when
the shafts can’t manage the load of the
storm water in need of treatment. The 12m
deep shafts on the north side of the River
Ribble will take up the dirty water, feed it
back under the river and into the treatment
works on the south side.
The cased CFA, CSP technique forms a
closed structure to act as a barrier in water
bearing soils and is ideal for a city centre
project, such as the Preston Shafts, due
to its flexible and compact operation. It
has the advantages of better tolerance,
better ultimate appearance and reduced
overbreak than an uncased CFA secant
wall and it is a speedier operation than the
more traditional ‘kelly / casing’ rotary bored
pile method. As it is a cased system it also
reduces the risk of distress to adjacent
structures in certain soils such as sands or
gravels
Steve Mallinson, Contract Manager for
Bachy Soletanche Limited, said:
“The large southside shafts are more than
20m deep, hence the use of the diaphragm
walls which involve less construction joints
than bored pile walls. On the northside
verticality has also been key throughout
this project due to the nature of the
interlocking between the male and female
piles to ensure a watertight solution is
created. Water companies are heavily
investing in waste water treatments at the
moment so the Preston Shaft project has
been a great one to work on and one we’re
sure will make a difference to the quality of
water going into the River Ribble.”
August 2010
NEwS
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