Development of a new direct shear testing apparatus

Politecnico di Torino and G.D.S. Instruments Ltd, UK has developed an innovative servo controlled direct shear apparatus named High Pressure Back Pressure Shear Apparatus-HPBPSA. The apparatus allows direct shear tests to be performed under closely controlled conditions in terms of axial load and back pressure applied to the specimen. Two shear boxes, built in stainless steel, are available to host cylindrical specimens of 50 or 100 mm diameter and 50 mm height. If a test is to be performed on a joint, different gaps up to a maximum of may be set between the two halves of the shear box. The apparatus is equipped with a number of measuring transducers that allow for testing to be performed in closely controlled conditions. The axial load is applied to the specimen by a transverse steel bar joined both to the loading ram and to the two uprights. The acquisition and control system is based on a two-level hierarchical approach. The novel equipment allows direct shear tests to be performed on either soil or soft rock