Possible correlation methods for clays between undrained shear strength and shear or compression wave velocity are explored. A correlation method between undrained shear strength, su, and shear wave velocity, vs, for normally consolidated clays is discussed:
su = Ψρa nc vs2anc exp(bnc),
where anc and bnc are parameters describing the soil¹s mean relationship between shear modulus and effective vertical stress, and Ψ is its c/p ratio. The uncertainty in this relationship is shown to be a function of two terms describing the scatter about the soil’s mean Gmax/σ’vand su/σ’v relationships. When employed in situ, this relationship is also affected by uncertainty due to spatial variability of shear waves. The potential for correlation’s between su and vs for overconsolidated clays is also investigated. For these soils it is determined that developing accurate su / vs relationships would be difficult, so that, for this purpose, high quality experimental data would be particularly important.
The accuracy with which the constant increase in strength with depth at a location could be determined based on geophysical data is also investigated. It is concluded that this type of analysis should be feasible, given geophysical information from sufficient depths and low uncertainty in the inferred values of shear strength. Measuring the magnitude of the changes in the strength/depth ratio, though, is shown to be more difficult.
It is shown that there should be no relationship between compression wave velocity and characteristics of a saturated clay above a void ratio of approximately one; and therefore, compression wave velocities should rarely be useful for determining the undrained shear strength of offshore clays.