Engineering Seismic Geophysics at Bothkennar.

This thesis covers a seismic geophysical investigation at the soft clay test bed site, Bothkennar. The principle geophysical methods that have been used to characterise the site are the standard crosshole and the continuous surface wave techniques. One new geophysical technique has been developed as part of this research, the surface source to crosshole technique. The surface source to crosshole technique allows the measurement of the propagation velocity of horizontally polarised, horizontally propagating shear waves at depth, without the use of a specialised borehole source or the installation of a third borehole. The surface source technique uses a surface based impulse source and relies on the ray path curvature of a geomaterial where stiffness increases with depth to produce horizontally propagating shear waves at the crosshole section. A critical comparison has been carried out between the seismic geophysical methods of crosshole (standard and surface source), the continuous surface wave technique and geophysical testing carried out by other researchers. Comparison between horizontally and vertically polarised crosshole indicates that the Carse clays at Bothkennar should be considered to be slightly cross anisotropic, with the stiffness in the vertical planes being typically greater than the horizontal plane. It has been shown that at Bothkennar the crosshole technique yields very similar results to the seismic cone penetration technique (Powell and Butcher (1991)). Two continuous surface wave surveys have been conducted, the results of which delineate the stiff superficial layer known to exist at Bothkennar and correlate well with the standard crosshole surveys. Comparison has been drawn with very small strain, high quality triaxial testing (Heymann (1998). Stiffnesses determined in the triaxial cell and geophysically have been found to be analogous but in general, the latter are slightly greater