Seismic cross-hole method as a useful tool for estimation of inherent stiffness anisotropy of overconsolidated clay

Abstract

We investigated the degree of overconsolidated Brno clay inherent stiffness anisotropy αG' in very small strain range [3] by means of seismic cross-hole measurements [1]. αG' stands for the ratio of square of shear wave velocities in-situ VppI and VptI and its value lies in the interval 1,20 - 1,30. A comparative triaxial laboratory testing of shear wave velocities VppL and Vtp L using bender elements was carried out [4] (condition Vtp = Vpt is valid only for homogenous soils [2]).

The obtained ratio of αG = (VppL)2/(VtpL)2 yields 1,45. Despite the aspects influencing the laboratory testing (scale effect, sample disturbance, possible presence of stiffer intrusions, different unit weight) and field testing (subjective evaluation of the output signal) the difference between αG' and αG is acceptable.