A unified framework for evaluating in situ state of sand with varying fines content

In the design and construction of large-scale earth structures such as hydraulic fills for artificial islands or tailings dams, a major concern is the susceptibility of sand fills to flow failure or liquefaction. The big challenge in liquefaction evaluation is to evaluate the in situ state of sand, because it is extremely difficult to obtain high-quality undisturbed samples for that purpose. Here an attractive framework is presented, which allows a direct evaluation of in situ states of sands with varying quantity of fines through shear wave velocity measurements. The framework is built upon a specifically designed experimental programme comprising small-strain shear wave measurements and large-strain undrained shear tests over a wide range of post-consolidation states. A marked feature of the framework is the unified characterisation of shear wave velocity for both clean and silty sands through a state parameter that properly combines the effects of void ratio and confining stress in a sound theoretical context. As the shear wave velocity can be reliably measured both in the laboratory and in the field, and since the state parameter is a meaningful index for characterising various aspects of sand behaviour, the proposed framework is highly promising in a range of geotechnical applications.