Methods used to determine maximum and minimum dry unit weights of sand: Is there a need for a new standard?

Abstract

Known challenges exist with maximum (γ dmax ) and minimum (γ dmin ) dry unit weight measurements; the respective dry unit weight results depend very much on the method or standard used. A laboratory testing programme was completed to systematically determine and compare γ dmax and γ dmin values derived for six different sand types by using different methods. The tested sands contained a wide variety of mineralogical and fines contents. The γ dmax and γ dmin determinations were performed according to the following methods: British Standards Institution (BS) standards; American Society for Testing and Materials (ASTM) standards; Deutsches Institut für Normung (DIN) standards; Dansk Geoteknisk Forening (DGF) guidelines; Norwegian Geotechnical Institute (NGI), Geolabs, and Fugro proprietary methods. Differences in testing procedures, material requirements for testing, and the effects of soil degradation during testing introduce challenges and large differences in γ dmax and γ dmin values for each of the six sand types were observed. Therefore, it is concluded that there is a need for the development of new standards for a robust determination of γ dmax and γ dmin values. Specifically, a standard for determining γ dmax is required to consistently obtain results at the upper bound of dry unit weight values for the likely range of sands — without crushing the sand grains.