Small-Strain Stiffness of Natural Pumiceous Sand

This paper focuses on the small-strain shear modulus ($G_{\max }$) of natural pumiceous (NP) sands, a type of crushable volcanic soil commonly found in the North Island of New Zealand. These sands are also compressible and lightweight, resulting in difficulty to accurately evaluate their geotechnical properties. To better understand the $G_{\max }$ dependency of these NP sands on effective confining pressure (${\sigma }_c^{\prime }$) and void ratio ($e$), bender element tests are performed on three types of locally sourced NP sands and, for comparison purposes, similar tests are conducted on hard-grained Toyoura sand. The results illustrate that the $G_{\max }$ of NP sands are considerably lower than that of Toyoura sand over a wide range of $e$ and ${\sigma }_c^{\prime }$. Furthermore, materials with higher pumice content show higher dependency on ${\sigma }_c^{\prime }$ and lower dependency on $e$ compared with those with lower pumice content as well as Toyoura sand. Particle characteristics (e.g., particle shape, particle-size distribution, particle crushing, pumice content, compressibility, and fines content) are taken into consideration to explain the different response of the tested materials.