Elastic cross-anisotropy of chicago glacial clays from field and laboratory data

The initial anisotropy of natural clays can be characterized by the elastic shear moduli measured by wave propagation techniques both in situ and in the laboratory. This paper summarizes results of studies of the initial anisotropy of fresh water glacial clays from two sites in the Chicago area. Advanced cross-hole seismic tests which measure both horizontally propagating and vertically- and horizontallypolarized shear wave velocities and seismic cone penetration tests (sCPT) were performed in situ. Bender elements were used to measure propagation velocities on laboratory specimens cut from high quality block samples of soft to medium clays obtained from the excavation for the Ford Design Center project. These clays are lightly overconsolidated, supraglacial tills. Laboratory specimens of hard clay from the One Museum Park West site were obtained with a Pitcher barrel sampler; these clays are overconsolidated, basal tills. Both in situ and laboratory results for the soft to medium clays indicate that the magnitude of the shear moduli are the same in each polarized direction. These clays are slightly cross anisotropic. For the harder clays, the in situ shear moduli are larger than those measured in the laboratory, presumably as a result of the sample disturbance arising from Pitcher barrel sampling.