Large Diameter Bored Piles

Further information:
Cementation Skanska
skanska.co.uk/cementation
cementation@skanska.co.uk
Application
Can be used in a wide range
of strata.
Where non-cohesive or
water bearing soils exist
temporary casings and/
or bentonite or polymer
suspension can be used to
progress the bores.
Diameters range from
600mm to 3000mm with
pile depths up to 72 metres
and maximum working loads
of 20,000kN for straightshafted piles or 30,000kN for
under-reamed piles.
Advantages
• High load capacity
• Can be used with
CEMLOC® to plunge
structural steel columns
• In stiff clays under-reamed
bases can be formed to
increase pile capacity
• Depending on ground
conditions, pile concrete
can be terminated below
piling platform level.
Patents
UK Serial No. 2138033 Class
7, 37
UK Patent No. 2373801
US Patent No. 6739412
UK Patent No. 2362665
Trade Mark
CEMLOC®
Large Diameter Bored Piles
Cementation Skanska has a wide range of piling
rigs within the plant fleet, including crane-based
units, and all-hydraulic purpose-built mast
machines. Both are suitable for the construction of
large diameter cast-in-situ piles.
Mast machines are self-erecting. Establishment
time on site is shorter than for crane-mounts and
for contracts with small sites and/or few piles, this
can be an advantage. The crane-mounts are more
suitable for the larger diameter and deeper pile
range.
All of the rigs are fitted with a rotary boring unit
which operates a kelly bar. The boring tools are
fitted to the kelly bar. This equipment has been
used to construct large diameter piles in a wide
range of strata, including very soft silty clays, noncohesive soils and weak rocks.
The rigs can impart a vertical load on to the kelly
bar to improve production in difficult strata.
In addition to installing vertical piles, rigs within
our fleet can install raking piles, up to 1:4 rake,
without modification.
Depths
Kelly bars can be of single or telescopic
construction. Standard triple telescopic kelly bars
allow for depths of up to 55m. Exceptionally, when
required, extended triple telescopic kelly bars can
reach to 72m below ground.
Boring Tools
Boring tools are available to cope with different
strata. The range includes general purpose augers,
rock augers, boring buckets and coring barrels
amongst others.
Standard sizes of boring tools range from 600mm
to 2400mm in increments of 150mm, and thereafter
in increments of 300mm up to 3000mm.
In suitable strata it is possible to construct a dry
bore; in water-bearing strata it is often necessary
to progress the bore under flooded conditions, i.e
water, bentonite or polymer.
08/03/10 Rev 8
Concrete
Concrete grades up to 40N/mm² are common, and
higher grades can be used where necessary.
Where the pile bore is dry, a hopper with a short
tube is used to direct the concrete down the centre
of the reinforcement. Under flooded conditions a
full-length tremmie pipe is used.
In both situations it is often practical to terminate
the concrete at a low level. This is typically used
for top-down construction of deep basements. In
this situation it is possible for a steel column to be
plunged into the head of the concrete. Our unique
CEMLOC® equipment can be used to position the
columns to structural steel tolerances.
Pile Load Bearing Capacity
Depending on ground conditions pile loads of
20,000kN or greater can be safely carried on
straight-shafted piles.
Special tools are available to form enlarged bases
or "under-reamed" piles in suitable strata, typically
stiff clays. Under-ream diameters are usually
specified in increments of 150mm, and diameters
of 5400mm or greater can be provided. Piles of
30,000kN capacity have been formed in London
clays using under-reamers.
08/03/10 Rev 8