Constant volume cyclic shear (DSS) tests were performed on Brusselian sand using the new NGI simple shear apparatus and a special control system for cyclic strain controlled testing. Test results are compared with those from cyclic triaxial (TXS) tests. The tests investigated the degradation of the cyclic shear modulus for different relative densities (from 60% to 90%), different consolidation pressures (from 5OkPa to 200kPa) and different shear strain amplitudes (from 0.1% to 9%). The comparison of the soil specimen behavior in the two different test types shows that soil degradation is mainly function of (1) the dilative or contractive behavior of the soil and of (2) the extreme state reached during the previous cycles. The test results show that there exists an unique relationship between the secant shear modulus of a given cycle and the energy dissipated during that cycle. A model is presented that predicts the hysteresis loops induced on a dilative soil during a cyclic strain controlled direct simple shear test
