Specialists: Piling | Features

Types of piling
Bored piling
Type	Shaft Diameter (mm)	Max depth (m)	Remarks
Tripod	400-600	30	Installed using simple, lightweight rigs. Ideal for confined spaces
Continuous flight auger (CFA)	300-900	27.5	Quiet, quick and economical method of boring. Only suitable for soft ground conditions
Rotary/bored	300-3000	65	Hydraulic rigs for load-bearing and walling solutions. Ideal for tougher ground conditions and obstructions
Driven piling
Type	Typical shaft size (mm2)	Max depth (m)	Remarks
Precast concrete	230 and 270	Unlimited	Installed by hydraulic hammers. Piles are cast in 5-15 m lengths. Greater depth achieved by joining piles
Driven steel section	130-450	Unlimited with splicing connections	Available in high strength or corrosion-resistant steel. Advantage of being able to penetrate bedrock. Steel lugs can be welded to the pile to give it a higher friction load capacity
Sheet piling	N/A	18 m in cohesive soil. 12 m in granular soil	Sheet piling can be used as a cost-effective method of soil retention in temporary and permanent applications.
Diaphragm walling
Type	Typical wall thickness	Max depth (m)	Remarks
Diaphragm walling	600-1500	50	Ideal for constructing basement boxes, underpasses etc. Frequently used with bored piles and plunged columns in “top-down” construction.
Ground engineering
Type	Typical shaft diameter (mm)	Max depth (m)	Remarks
Mini	100-300	35	Ideal in confined areas
Anchors	100-300	35	Permanent and temporary applications
Soil nails	100-300	25	Ideal for stabilising slopes
Bored-pile retaining walls
Used for the construction of temporary or permanent retaining walls and for the provision of deep basements, underground structures and motorway cuttings. Bored-pile retaining walls are either “contiguous” or “secant”, the choice determined by soil type, ground water profile, maximum retained heights, programme, propping requirements, cost and life span.
Type	Shaft diameter (mm)	Centres	Max depth (m)
Contiguous	Up to 1200 for CFA. Up to 2400 for rotary	Generally 150 mm greater than diameter of the piles, thereby leaving gaps.	20 (can be extended with larger pile spacing)
Secant	CFA/ rotary - generally 500-900	Less than the diameter, creating interlocking	20 (30 can be achieved but difficulties may be encountered)

Case studies
Location	Pile type	Average length (m)	Diameter (mm)	No. of piles		Approximate cost (£)
					Per metre	Average per pile	Setup per pile
London	Cast in-situ reinforced concrete, lined, auger bored	28.5	750	99	50	1437	75
	Cast in-situ RC, CFA bored	17.5	350	178	17	300	0
		17.5	450	14	30	530	40
Cleveland	Cast in-situ RC, CFA bored	13	450	153	30	390	25
London	Cast in-situ, temporary casing, rotary bored	15	320	172	46	687	30
Bristol	Mini piles	19	300	156	67	1265	36
	Driven RC square section	13	285 x 285	333	21	275	36
Manchester	RC secant pile wall, CFA/rotary bored	18 hard	880	348	137	1717	included
		7 soft	750
London	RC secant pile wall, CFA/rotary bored	17 hard	600	525	107	1496	included
		11 soft	600
London	Cast in-situ RC, rotary bored	35	600-1050	127	198	6944	55
Costs exclude general preliminaries. Costs current at fourth quarter 2004