Geotechnical
Specialists
Leading geotechnical
specialist, Bachy Soletanche Limited (BSL) has
recently completed work on a
circular secant shaft near Ammanford, South Wales.
The shaft will assist in the construction works
of the Felindre to Tirley natural gas pipeline,
transporting natural gas from Tirley to the two new
terminals under construction at Milford Haven in
Pembrokeshire.
Barhale Construction plc awarded BSL the circular
shaft contract on the 90kilometre stretch from
Felindre to Brecon. However, the essential pipeline
works - in its entirety - will run from Felindre to
Tirley, covering a total of 196kilometres. The two
sections are to be built by two separate
contractors.
National Grid has estimated that more than 20
percent of UK gas requirements will run through the
natural gas pipeline, helping to meet the UK’s
growing demands and address the decline in North
Sea reserves*.
The shaft is vital in the preparation works for the
project, as a tunnel-boring machine (TBM) will be
lowered 22metres below ground to begin the
tunnelling works for a section of the pipeline.
Steve
Mallinson, contract manager for Bachy Soletanche
commented:
“BSL designed the shaft around the ground conditions
and the required depth. Our design was for a
hard/hard secant circular shaft using large diameter
auger (LDA) piles.”
“The original design was for a traditional Caisson
Shaft, but due to large boulders found in the
ground we came up with a piled solution as an
alternative.”
The hard/hard secant piling method requires the use
of reinforced concrete piles for permanent
retention. Secant walls are constructed in two
stages with the primary, female piles installed
first.
Secondary, male piles are then cut into the primary
piles.
BSL’s design was to create a circular shaft using
the secant piling method that would provide a shaft
large enough to accommodate the TBM.
In order to create the circular shaft, 32 rotary
piles of 1200mm diameters are bored to a depth of
24metres. The piles are bored through a ground
profile including one metre of soft clay, dense
gravel with large boulders to 15.5 metres, and weak
to strong mudstone down to 25metres.
A Bauer BG 24 was utilised as the ground conditions
required heavy-duty drilling equipment.
However, even this powerful rig still required
additional torque, and a torque multiplier was
employed to increase the rig’s torque from 24Tm to
48Tm. Steve Mallinson continued:
“Our rig needed enough power to drill through the
large boulders and screw the casing down to
24.0m”
The piles are reinforced with steel, yet carbon
fibre bars are used for piles in the area of the
tunnel drive. This creates a “soft eye” at the start
of the tunnel - allowing the tunnelling to begin
with ease.”
Bachy Soletanche began work on site in late March
and completed the project at the end of May. Further
works on the project will continue throughout the
year.
Email:
fiona@manifestcomms.co.uk
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Editor's Note: Bachy Soletanche provide:-
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Bachy Soletanche Ltd-digs deep at the Felindre to Tirley pipeline
Arundel Jones Associates Ltd Registered in England
and Wales No. 07334149 News Categories : Geotechnical Specialists |