Relation between liquefaction resistance and shear modulus of crushable volcanic soils

¹ Geotechnical Engineer, Jacobs Ltd, Auckland New Zealand
² Department of Civil & Environmental Engineering, University of Auckland, New Zealand

^* Corresponding author: r.orense@auckland.ac.nz

Abstract

Pumice-rich soils originating from volcanic eruptions are deposited in various parts of the world, such as in the central region of North Island, NZ. The pumice sand components of these natural pumiceous (NP) soils are known to be crushable and lightweight, resulting in a significant difference in their cyclic resistance ratio (CRR) and small-strain shear modulus (G_max) when compared to hard-grained (quartz) sands. In this paper, the results of a number of cyclic triaxial and bender element tests performed on reconstituted specimens of three types of NP sands having different pumice contents (PC), as well as on quartz-type Toyoura sand specimens, are discussed. Then, the concept of modified cyclic yield strain, ε_ay,m, which relates the CRR of the specimen to its G_max, is used. The results indicate that ε_ay,m appears to be dependent only on the soil type, and independent of the confining pressure applied and the relative density of the specimen. All NP sand specimens show higher ε_ay,m when compared to Toyoura sand because of their higher CRR and lower G_max, with values of ε_ay,m increasing as the PC of the specimen increases. Based on the results obtained, an empirical chart is developed to estimate the CRR of NP sands from their shear wave velocity (V_s) values under field conditions.