Shear wave velocity as a geotechnical parameter: an overview

Shear wave velocity, V-s, is a soil mechanical property that can be advantageously measured in both the field and laboratory under real and controlled conditions. The measured V-s values are customarily used in conjunction with other in situ (e.g., standard penetration test blow count, N-SPT, and cone penetration resistance, q(c)-CPT) and laboratory (e.g., effective confining pressure, sigma(m)', and void ratio, e) measurements to establish an abundant number of V-s-based correlations that could later be utilized to augment (in some cases, replace) designated testing. An attempt is made here to present the salient features of some existing widely used correlations to provide the reader with a comprehensive understanding about the nature of these correlations and their applicability in geotechnical engineering practices. It is recognized that the reliability of some of these empirical formulations, still in general use today, has been questioned, as they are characterized by their lack of dependence on stress state and particle characteristics. A new V-s1-(N-1)(60) (where V-s1 is the stress-normalized shear wave velocity, and (N-1)(60) is the stress-normalized penetration blow count) correlation that accounts for grain sizes is highlighted by combining a recently published V-s1-q(c1) (where q(c1) is the stress-normalized cone tip resistance) formulation and available (N-1)(60)-q(c1) relationships. The new formulation is applicable to uncemented relatively young Holocene-age soil deposits. The estimated V-s1 values based on the proposed correlation are compared with reliable laboratory and field measurements, and the comparison shows that accounting for grain size of granular soils yields more realistic results regarding the V-s values than when particle size is not considered. The prime effect of grain size was to change the range of possible void ratios, which in turn had a substantial impact on V-s values. Moreover, a new V-s1-(N-1)(60) chart has been proposed, allowing the practitioner to estimate V-s1 values based on a combination of data including N-SPT, e, grain size, and relative density.