Effects of Straining on Shear Modulus of Clays

High strain amplitude resonant column tests were conducted on hollow cylindrical samples of five natural cohesive soils and one artificially prepared bentonite silica flour mixture to assess affects of shearing strain amplitude and repetitions of shearing strain on dynamic shear modulus. Results of these tests show that: (1)A threshold level for strain exists below which the modulus is virtually independent of strain or number of cycles of strain; (2)cycles of strain cause a progressive decrease in modulus when strain amplitude exceeds a threshold level; (3)cycling above a threshold level causes a decrease in low-amplitude modulus measured immediately after the end of the high-amplitude cycling; and (4)a time-dependent increase in low-amplitude modulus occurs if additional cycles of high-amplitude strain are not applied. Cycle and post-straining effects are then empirically related to strain amplitude, number of repetitions of strain, and time.