Relationship between Shear-Wave Velocity and Undrained Shear Strength of Peat: Fid-Bau Portal

Relationship between Shear-Wave Velocity and Undrained Shear Strength of Peat

Trafford, Andrew / Long, Michael

A significant challenge for engineers working with peat is the estimation of the undrained shear strength ( $s_{u}$ ). This is particularly the case for shallow, slightly overconsolidated peats found on natural hillsides and at the toe of embankments. Existing laboratory and in situ techniques may not be suitable due to issues such as access to remote areas, the resolution and accuracy of measuring equipment, sampling disturbance effects, and the influence of fibers on the measured results. It is logical to attempt to correlate $s_{u}$ with shear-wave velocity ( $V_{s}$ ) because both parameters depend on the same set of fundamental factors. A lightweight portable probe has been developed that can be used to resolve the low $V_{s}$ values in peat reliably and repeatably. It was not possible to determine $s_{u}$ directly from the $V_{s}$ measurements. However, a strong correlation was found between normalized $V_{s}$ (by water content, $w$ ) and $s_{u}$ (derived from direct simple shear tests). A single operator can collect a continuous profile of $V_{s}$ and $w$ simultaneously and therefore derive a one-dimensional (1D) $s_{u}$ profile for the full peat thickness. Some limitations in the use of the derived empirical equations are outlined.