Pile Design and Construction Practice, Fifth edition

Chapter 10
The durability of piled foundations
10.1 General
In all situations consideration must be given to the possibility of the deterioration of piled
foundations due to aggressive substances in soils, in rocks, in ground waters, in the sea and
in river waters. Piles in river or marine structures are also exposed to potentially aggressive
conditions in the atmosphere, and they may be subjected to abrasion from shifting sand or
shingle, or damage from floating ice or driftwood.
In considering schemes for protecting piles against deterioration due to these influences,
the main requirement is for detailed information at the site investigation stage on the
environmental conditions. In particular, adequate information is required on the range of
fluctuation of river or sea levels and of the groundwater table. In the latter case, the highest
levels are required when considering the likely severity of sulphate attack on concrete
piles or the corrosion of steel piles, and the lowest possible levels are of considerable
importance in relation to the decay of timber piles. The possibility of major changes in
groundwater levels due to, say, drainage schemes, irrigation, or the impoundment of water
must be considered.
In normal soil conditions it is usually sufficient to limit chemical analyses of soil or
groundwater samples to the determination of pH-values, water-soluble sulphate content (mg
per litre) and chloride content. Where the sulphate content exceeds 0.24% in soils it is
advisable to determine the water-soluble sulphate content, expressing this in mg of SO 4 per
litre of water extracted. For brownfield sites, full chemical analyses are required to identify
potentially aggressive substances (2.6) . Methods of investigating and assessing brownfield
sites are given by Harris et al. (10.1) , drawing attention to the health and safety precautions
necessary, the need to employ specialist personnel, and care in selecting representative
samples.
Bacterial action can be an influence in the corrosion of steel piles. Samples of soil
and groundwater should be obtained in sterilized containers, which are then sealed for
transportation to the bacteriological laboratory for later analyses. Where steel piles are used
for foundations in disturbed soils or fill material on land, an electrical resistivity survey
is helpful in assessing the risk of corrosion and in the design of schemes for cathodic
protection (see Section 10.4.2).
Investigations for marine or river structures should include a survey of possible sources
of pollution which might encourage bacteriological corrosion, such as contaminated tidal
mud flats, discharges of untreated sewage or industrial effluents, dumping grounds for