Pore Fluid Composition Impact on the Geotechnical Behaviour of Foundations—A Mini-review

The composition of pore fluids influences the geotechnical properties and behaviour of soils. If the pore fluid composition is significantly different from that of distilled water, then care must be taken during geotechnical works. Pore fluids vary in composition for a number of reasons, for example, near the coast or in arid environments high levels of salinity mean that porewater densities are higher than those of pure water resulting in an increase in uplift pressures. The presence of saline water is predictable for a given site, and so can be accounted for. However, where sites are contaminated changes in geotechnical properties can also occur due to lubrication, density or viscosity effects for example. Given the increasing number of construction projects on brownfield sites, there will be an increasing need to assess the effects of different pore water compositions on the geotechnical behaviours of soils. The majority of groundwater contamination is caused by either heavy metals or hydrocarbons. Of these two, hydrocarbon contamination is dominant. However, as there are many different types of hydrocarbon, and these can be mixed in different types of soil the impact on soil behaviour is variable. In general, liquid limits decrease and plastic limits increase with hydrocarbon contamination. The maximum dry density and the optimum moisture content decrease. There is a reduction in the angle of friction and an increase in the value of cohesion for pure bentonite or kaolin soils, but for clayey and silty soils with mixed minerology there is an increase in the angle of friction and a decrease in the cohesion. The compression index increases, but the coefficient of volume compressibility decreases, and the permeability decreases. The extent of these effects is dependent both on the type and extent of contamination and the soil properties, it is therefore important that this is quantified during site investigation.