Application of cross‐hole seismic measurements in site investigation surveys

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Abstract
Application of the cross‐hole seismic method to site investigation surveys for civil engineering developments is illustrated by case histories from the United Kingdom using the borehole sparker probe developed in McCann et al. (1975) as the seismic source. At Newborough, Anglesey, it is shown that this source generates both a compressional‐wave and a vertically polarized shear‐wave in the borehole; the measured velocity values are used to determine the dynamic elastic moduli of the saturated sand deposit at this site. At Cocking, Sussex and East Fleet, Dorset, the presence of an air‐filled void between two boreholes is shown to have a significant effect on the velocity of propagation and amplitude of the transmitted seismic signals. This work is extended at Maidstone, Kent, where the technique is used to confirm the presence of a cavity below the foundation of a house. In the Hot Dry Rock Geothermal Project at Rosemanowes, Cornwall, increased fracturing of the granitic rock mass following explosive stimulation in one of the exploration boreholes is shown to result in a significant reduction in the compressional‐wave velocity.

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