Geotechnical site investigations are vital for any construction project in brownfield re-development and/or greenfield sites. Many non-invasive, near-surface geophysical techniques are used for site characterisation, with electrical resistivity and seismic methods being two of the most popular techniques.
Although electrical resistivity has been used to detect buried foundations in brownfield sites, there is still research needed to identify optimal survey parameters and electrode configurations. In this study, four of the most common resistivity arrays (Wenner, dipole-dipole, pole-dipole and pole-pole) were utilized, on profiles (0.25 m electrode spacing and 64 electrodes) at different orientations and distances from a scaled-model of a buried foundation wall (wall dimensions are 1.5 m long × 0.36 m wide × 0.48 m height). The Wenner and dipole-dipole arrays, with surveys oriented parallel to the foundation wall, were found to be optimal.
Integration of geophysical (seismic (using 24 geophones and 1 m geophone spacing), electrical resistivity (2, 3 and 4 m electrode spacing and 64 electrodes) and gravity) with conventional in situ CPT tests surveys allowed good site characterisation of a geologically heterogeneous site.
Seismic surveys are routinely conducted for shear wave velocity-depth profile site determinations. Train-induced vibrations have been shown to be used as passive seismic sources for site characterisation studies. In a Midlands glaciated valley site, passing train vibrations were collected using three-component seismic stations and 1D/2D array configurations. Linear arrays (115 m total length and 5 m geophone spacing), oriented parallel to the railway, were found to be optimal. Analysis of three (i.e. vertical and horizontal) components revealed different shear wave velocities; however, it cannot be the case for the same site. Observing apparent wave velocities was the main interpretation for the differences in wave velocity. In addition, time-frequency analysis showed that potential Doppler shift was not noticeable on the observed train-induced vibrations.