An approach to compensate for the influence of the system normal stiffness in CNS direct shear tests

Larsson, J., Flansbjer, M. An approach to compensate for the influence of the system normal stiffness in CNS direct shear tests. Rock Mechanics and Rock Engineering (external link) .

Applying accurate normal load to a specimen in direct shear tests under constant normal stiffness (CNS) is of importance for the quality of the resulting data, which in turn influences the conclusions. This paper presents the effective normal stiffness approach applicable to closed-loop control systems. Validation through direct shear tests indicates a clear influence of the system normal stiffness on the applied normal load (13% for the test system used in this work). The ability of the approach to compensate for this influence is confirmed herein. The approach is shown to effectively reduce the deviations between intended normal loads and the actual applied normal loads.