Types of pile 69can withstand fairly hard driving and it is resistant to attack by aggressive substances in the
soil, or in sea water or groundwater. However, concrete in precast piles is liable to damage
(possibly unseen) in hard driving conditions. Concrete with good workability, using plasti-
cizers as appropriate, should be placed as soon as possible after boring cast-in-place piles.
Weak, honeycombed concrete in cast-in-place piles is liable to disintegration when aggres-
sive substances are present in soils or in groundwater.
Steelis more expensive than timber or concrete but this disadvantage may be outweighed
by the ease of handling steel piles, by their ability to withstand hard driving, by their
resilience and strength in bending, and their capability to carry heavy loads. Steel piles can
be driven in very long lengths and cause little ground displacement. They are liable to
corrosion above the soil line and in disturbed ground, and they require cathodic protection
if a long life is desired in marine structures. Long steel piles of slender section may suffer
damage by buckling if they deviate from their true alignment during driving.
2.8 Reuse of existing piled foundations
As the redevelopment of city sites continues, it is inevitable that many will be underlain with
deep and complex foundations from the previous buildings. A foundation system that has
already been tested and ‘proved’by supporting the existing load could provide considerable
economic advantage for a new structure on the same site. Clearly the foundations must be
investigated thoroughly and shown to have an adequate factor of safety against failure and
settlement for the new loads. Where an increase in load is to be applied or where new foun-
dations have to be compatible with the old, the observational method can be adopted to
ensure robustness of design and construction.
A comprehensive investigation into the problems that may be posed by the existence of
old foundations and the potential solutions has been completed recently by a research
consortium co-ordinated by the Building Research Establishment (the ‘RuFUS project’) and
a Handbookpublished(2.21)giving guidance on the following:
Why and when to consider reusing foundations
Decision models to manage risk when reuse is considered
Investigation, assessment, and performance of old foundations
Upgrading performance and combining old foundations with new; and
Measurement of performance.
2.9 References
2.1LOVE, J. P. The use of settlement reducing piles to support a flexible raft structure in West London,
Proceedings of the Institution of Civil Engineers, Geotechnical Engineering, Vol. 156, 2003,
pp. 177–81.
2.2RAISON, C. A. North Morcambe Terminal, Barrow: pile design for seismic conditions, Proceedings
of the Institution of Civil Engineers, Geotechnical Engineering, Vol. 137, 1999, pp. 149–63.
2.3MARSH, E. and CHAO, W. T. The durability of steel in fill soils and contaminated land, Corus
Research, Development & Technology, Swindon Technology Centre, Report No. STC/CPR
OCP/CKR/0964/2004/R, 2004.
2.4 A corrosion protection guide for steel bearing piles in temperate climates, Corus Construction
and Industrial, Scunthorpe, 2005.
2.5 The Institution of Civil Engineers, Specification for Piling and Embedded Retaining Walls,
Thomas Telford Ltd, London, 1996. (2nd edition in preparation 2006)