Development of a large-size cyclic direct simple shear device for characterization of ground materials with oversized particles

Direct simple shear (DSS) testing, despite its limitations, is one of the most common laboratory element tests in geotechnical engineering practice. The development and validation of a 300-mm diameter DSS device as well as test data generated for two materials with oversized particles, specifically pea gravel and municipal solid waste, are presented. The device has the capability to execute shear wave velocity measurements using both bender elements and accelerometers, as well as monotonic and cyclic testing under constant load or constant volume conditions. Validation testing using Ottawa sand C109 confirmed that the monotonic and cyclic constant volume response of the sand using the large-diameter device was similar to the results presented using conventional-sized DSS test devices. The shear wave velocity measurements using bender elements and accelerometers were found to be practically identical for the tested sand and pea gravel and were also consistent with data reported in the literature. The importance of axial (or vertical) displacement control during constant volume shearing is emphasized. It was found that tests that meet the ASTM D6528-07, Standard Test Method for Consolidated Undrained Direct Simple Shear Testing of Cohesive Soils, threshold of 0.05 % maximum axial strain during shearing may still result in different constant volume response, and it is recommended that (a) the threshold is changed to a maximum of 0.025 % and (b) the evolution of axial strain during constant volume shearing is always reported.