A new torsional shear device.

Reliable small-strain measurements of deformational characteristics of soils have been one of the challenging aims in geotechnical engineering laboratories over the past decade, in particular when the mechanical behaviour of stiff clays and soft rocks has to be analysed under working conditions. A new torsional shear apparatus has been developed at the University of Naples “Federico II”, Italy, suited for accurate and continuous measurement of deformational characteristics at both small strain levels and high stress levels . In order to accomplish these requirements, the new device incorporates a special electro-magnetic loading system, designed to apply a maximum torque of more than 5 Nm, and a high resolution monitoring system, which allows accurate measurements at strain levels below 10-3%. In this paper the design criteria are described in detail and the efficiency of the new device is shown by several experimental results, using a prototype device