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Large Diameter Bored Piles

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					                                 Large Diameter Bored Piles
Further information:
Cementation Skanska
skanska.co.uk/cementation
cementation@skanska.co.uk




Application                      Cementation Skanska has a wide range of piling
Can be used in a wide range      rigs within the plant fleet, including crane-based
of strata.
                                 units, and all-hydraulic purpose-built mast
Where non-cohesive or            machines. Both are suitable for the construction of
water bearing soils exist
temporary casings and/           large diameter cast-in-situ piles.
or bentonite or polymer
suspension can be used to
progress the bores.
                                 Mast machines are self-erecting. Establishment
                                 time on site is shorter than for crane-mounts and
Diameters range from
600mm to 3000mm with
                                 for contracts with small sites and/or few piles, this
pile depths up to 72 metres      can be an advantage. The crane-mounts are more
and maximum working loads        suitable for the larger diameter and deeper pile
of 20,000kN for straight-
shafted piles or 30,000kN for    range.
under-reamed piles.
Advantages                       All of the rigs are fitted with a rotary boring unit
•	 High load capacity            which operates a kelly bar. The boring tools are
•	 Can be used with
   CEMLOC® to plunge
                                 fitted to the kelly bar. This equipment has been
   structural steel columns      used to construct large diameter piles in a wide
•	 In stiff clays under-reamed   range of strata, including very soft silty clays, non-
   bases can be formed to
   increase pile capacity        cohesive soils and weak rocks.
•	 Depending on ground
   conditions, pile concrete     The rigs can impart a vertical load on to the kelly
   can be terminated below
   piling platform level.        bar to improve production in difficult strata.
Patents
UK Serial No. 2138033 Class      In addition to installing vertical piles, rigs within
7, 37                            our fleet can install raking piles, up to 1:4 rake,
UK Patent No. 2373801
US Patent No. 6739412
                                 without modification.
UK Patent No. 2362665
Trade Mark
                                 Depths
CEMLOC®                          Kelly bars can be of single or telescopic
                                 construction. Standard triple telescopic kelly bars
                                 allow for depths of up to 55m. Exceptionally, when       Concrete
                                 required, extended triple telescopic kelly bars can      Concrete grades up to 40N/mm² are common, and
                                 reach to 72m below ground.                               higher grades can be used where necessary.

                                 Boring Tools                                             Where the pile bore is dry, a hopper with a short
                                 Boring tools are available to cope with different        tube is used to direct the concrete down the centre
                                 strata. The range includes general purpose augers,       of the reinforcement. Under flooded conditions a
                                 rock augers, boring buckets and coring barrels           full-length tremmie pipe is used.
                                 amongst others.
                                                                                          In both situations it is often practical to terminate
                                 Standard sizes of boring tools range from 600mm          the concrete at a low level. This is typically used
                                 to 2400mm in increments of 150mm, and thereafter         for top-down construction of deep basements. In
                                 in increments of 300mm up to 3000mm.                     this situation it is possible for a steel column to be
                                                                                          plunged into the head of the concrete. Our unique
                                 In suitable strata it is possible to construct a dry     CEMLOC® equipment can be used to position the
                                 bore; in water-bearing strata it is often necessary      columns to structural steel tolerances.
                                 to progress the bore under flooded conditions, i.e
                                 water, bentonite or polymer.
08/03/10 Rev 8
                 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

				
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