Experimental study to investigate the shear deformation of sand under constant normal stiffness conditions

Pile shaft friction is often modelled by performing interface shear tests in the laboratory under constant normal load (CNL) conditions. This boundary condition does not accurately model the shearing along a pile as the volumetric change in the shear band, immediately in contact with the pile, will cause change in the normal stress acting on a pile. The effects of soil contraction/ dilation on the normal stress at the interface between the soil and the piles can be controlled by conditions of constant normal stiffness (CNS). This paper reports an experimental study to investigate the shear deformation of sand samples using the GDS electromechanical dynamic cyclic simple shear (EMDCSS) device. The device is capable of performing both static and dynamic simple shear tests in CNS conditions. A series of cyclic direct simple shear tests were performed on Leighton Buzzard sand samples with varying densities. A comparison between CNL and CNS tests is made.