The maximum shear modulus (G_(max)) of soils is a fundamental input parameter in the nonlinear dynamic analyses of soil structures. This paper focuses on the G_(max) of natural pumiceous soils, which originated from a series of volcanic eruptions centred in the Taupo and Rotorua regions of New Zealand and were then mixed with other materials and distributed over the Waikato Region. They are highly crushable, compressible, and lightweight due to the presence of internal voids in the pumice particles, making them problematic from an engineering point of view. The test specimens for reconstituted testing were obtained from a site near Rangiriri, Waikato Region. The G_(max) of the pumiceous samples are measured using bender elements and the effects of effective confining pressure (σ_c') and void ratio (e) on the G_(max) of the soils are assessed. For comparison purposes, similar tests are also conducted on reconstituted hard-grained Toyoura sand. The test results indicate that the G_(max) of natural pumiceous soil is considerably lower than that of hard-grained Toyoura sand at all levels of σ_c' under a similar void ratio. Furthermore, the G_(max)-σ_c' dependency of natural pumiceous soil is more pronounced as compared to Toyoura sand; in contrast, the G_(max)-e relation shows a lower dependency for pumiceous soils. Such behavior can be explained in terms of particle shape characteristics and crushability.
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