Nondestructive Sample Quality Assessment of a Soft Clay Using Shear Wave Velocity

While improvements in equipment and sampling methods have enabled collection of better quality samples of soft clays for more reliable engineering design and performance prediction, current sample quality assessment methods typically require destructive laboratory testing performed long after samples are taken. This paper describes a nondestructive technique for sample quality assessment of soft clays using shear wave velocity. A portable bender element device was used to measure shear wave velocity (Vvh) in the field immediately following collection of Sherbrooke block, tube, and split spoon samples of Boston blue clay. Vvh values were compared to in situ values from seismic piezocone (VSCPTU) tests. The ratio Vvh∕VSCPTU was compared with results from a conventional, laboratory-based assessment method. Results indicate a consistent correlation between laboratory-based methods and the Vvh∕VSCPTU ratio, which ranges from Vvh∕VSCPTU=0.77 for the block samples to 0.28 for split spoon samples. The portable bender element device and nondestructive assessment technique offer the potential for field quality assessment and allow for real time adjustments to sampling techniques and/or more effective selection of samples for laboratory testing.