Determining G-γ decay curves in sand from a Seismic Dilatometer Test (SDMT)

This paper investigates the use of the Seismic Dilatometer Test (SDMT) for the determination of in situ decay curves of sand stiffness with strain level (G-γ curves or similar). In situ, laboratory and field data (including footing and self-boring pressuremeter tests) obtained at a silica sand site and a calcareous sand site in Western Australia are used for this investigation. The approach adopted relies on the ability of SDMT to provide a small strain modulus (G0 from Vs), a “working strain” modulus (GDMT from MDMT) and an “operational strain” modulus (GDV from MDV). Thus, in situ G-γ decay curves are tentatively constructed by fitting curves through these three points. The approach is based on the premise that MDMT is a reasonable estimate of the working strain modulus (e.g. Monaco et al. 2006 and Marchetti et al. 2008), while MDV is a modulus operating at the settlement ratio s/B of 1.8%, applied by the flat dilatometer, derived using Lehane & Fahey (2004). The paper illustrates the potential of using the SDMT to obtain in situ G-γ decay curves, but also indicates that additional research is required to improve the reliability of the proposed approach.