Anisotropic small-strain stiffness of lightly biocemented sand considering grain morphology

Small-strain stiffness and stiffness anisotropy of a sand are sensitive to the sand fabric, which can be significantly affected by particle shape and cementation. In this study, multidirectional bender element and isotropic compression tests were performed on glass sands with different particle shapes and biocementation levels. The small-strain stiffness and stiffness anisotropy of the untreated and biotreated sands were systematically investigated. A natural cementation process is used to investigate the small-strain stiffness of cemented sand; this might be a potential way to replicate the mechanical behaviour of undisturbed sand with weak cementation. Test results showed that the small-strain stiffness increases with increasing sand angularity. It is proposed that shear wave velocity has different sensitivities to particle shape parameters for uncemented sands. The stiffness anisotropy increases with the increase in sand angularity and decreases with increasing stress levels at an identical void ratio state. For the lightly biocemented sands, the small-strain stiffness can be improved significantly after the biotreatment reaction with the calcite bonds among grains. The development of small-strain stiffness with stress is different for specimens with different cementation levels. The stiffness anisotropy ratio first increases and then decreases with the increase of the biocementation level, which cannot be changed even with normalisation using the parameter A in the Hardin equation.