The full potential of geophysics in engineering investigations is shown on a daily basis. With investigative capabilities ranging from the detail of GPR to the long traverses of studies of geological structure, the many available techniques can provide important information about the ground, its mass properties, its small-scale variations, and its anomalies of structure or content. The advantage of a geophysical survey is that it enables information to be obtained for large volumes of ground that cannot be investigated by direct methods because of the costs involved. The multiple applications of geophysics in the analysis of concrete structures (foundations, walls, dams, tunnels) has proven its value long time ago. However, many of these tools are still insufficiently or inappropriately used in engineering and their newer capabilities are not yet fully appreciated by the engineering community. There is a need for up-to-date guidance about how to apply geophysical investigations.
A constant effort must be applied from the geophysics practitioner to guide civil and geotechnical engineers on:
- The integration of geophysical investigations into the design and construction process.
- The use of geophysics for determining engineering parameters.
- The capabilities of geophysics for investigating ground parameters.
These are some (of many more) geophysical applications in civil engineering:
- Bridge decks
A geophysical investigation is an indirect approach to the investigation of the ground or a built structure. Geophysical techniques can be used, for example, to measure the variation of the physical properties of subsurface materials, eg compressional and shear wave velocities, electrical conductivity and resistivity. Interpretation of geophysical survey data usually requires some prior knowledge of the underlying geological structure. For an optimum interpretation of geophysical survey data it is important to have ground-truth information, which can be provided by boreholes or trial pits.
Geophysical surveys can offer considerable time and financial savings compared with borehole investigations. At an early stage of site investigation, it may be beneficial to undertake a reconnaissance geophysical survey to identify areas of the site which should be investigated by drilling, ie those where anomalous results are obtained. On sites where contamination is suspected, a geophysical survey may form part of a preliminary risk assessment, prior to drilling or sampling. During the on-site drilling programme geophysical surveys may be used to check the interpretation of the geological structure between the boreholes. Further geophysical surveys, both within and between the boreholes and on the ground surface, can be used to determine the geological, hydrogeological and geotechnical properties of the ground mass in which the engineering construction is taking place.