Contractors World - UK & Ireland Vol 3 No 5 - page 14

Page 14
Contractors World - UK & Ireland Vol 3 No 5
the rotary bored and cased piles
methods, was installing the 271
rotary bearing piles, 750 mm
diameter, typically 26.0 m long
with low level cut-offs.
Temporary single wall
casings were used through
some 3 m made ground and
river terrace deposits and
sealed into underlying London
Clay. Residue of pile length
was drilled with conventional
open auger techniques into
stable cohesive London Clays
to design toe level without
bore support.
Prefabricated steel pile cages up to 30.0 m long were installed, pri-
marily due to tension loadings induced by ground heave associated with basement excavation.
Because of the need to a continuous supply of concrete at times, the contractors used their
own Schwing Stetter 1250 model pumps using concrete supplied by Hanson from a nearby
batching plant.
Associated Works
The retaining walls and structural piles was the main part of the £1.05 million contract for
P J Edwards, but there were also other associated works.
These included a number of smaller diameter piles outside of the retaining wall and piling
foundations for two tower cranes.
There were 3 maintained load tests for bearing piles to validate design Factor of Safety
of 2.2 adopted for works (in accordance with current LDSA design guidance notes). The
geotechnical design was verified by the satisfactory static testing of three of the piles up to
5,000 kN.
All piles were integrity tested using NDT instrumentation. Sonic logging tubes were also
inserted in to the large 1,500 mm pile.
Job Done To Main Contractor Satisfaction
Despite challenging weather conditions at time, the 14 people on site successfully completed
the 10 week project, two weeks ahead of schedule. The company is currently negotiating for
other works associated with the massive development that will transform what had become
a brownfield wasteland to a all embracing community development.
The project required 265 tonnes of steel and 4,410 m³ of readymixed concrete. For cased
rotary bearing piles the materials quantities split is 192 t of steel / 2900 m³ concrete; for CFA
contiguous bored pile retaining wall materials is 70 t steel / 1400 m³ concrete; for single
large diameter 1500 mm rotary pile constructed under bentonite support fluid the material
used was 3 steel / 110 m concrete.
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