Abstract

Many physical properties of rocks and engineering soils may be determined from geophysical measurements, eg bulk density, porosity and permeability. The most important geophysical parameters, for measuring physical properties, are electrical resistivity (Section 5.1) and seismic wave velocity (Section 5.4). Others, such as thermal conductivity (Section 5.7) are used more directly in engineering studies. Some derived properties need to be modified, usually according to semi-empirical constitutive relationships. For example, the modification of elastic moduli determined by elastic wave propagation methods takes account of larger strains, different mean effective stress and duration. Other geophysical measurements can be translated by empiricism into useful engineering indices (eg rippability from seismic velocity and corrosivity from electrical resistivity).

With the improvements in imaging by seismic, electrical and radar methods (Section 5.5), the ground may be more readily characterised in terms of the distribution of a geophysical or derived physical property, and this may lead to particular engineering design choices.

At the initial stage of site investigation planning, it is often more appropriate to consider the use of geophysical methods in the context of the overall engineering project, rather than in the identification of specific targets or engineering parameters. The main areas of engineering practice, and the associated subject of construction materials, are covered separately in this chapter, but there is a measure of overlap between some areas. For example, the geophysical assessment of bearing capacity is appropriate to bridges, power stations, dams and off shore structures, and geophysical assessment of construction materials is appropriate to