Experimental study on dynamic properties of sand with emphasis on the degree of saturation

Cyclic drained and undrained tests were performed in a modified simple shear device in order to specifically investigate the effect of saturation ratio on shear modulus and damping parameters of sand. In addition to the degree of saturation, the effects of number of cycles, vertical consolidation stress, shear strain amplitude and relative density on dynamic properties of sand were investigated. Dynamic stiffness and damping characteristic were found to be substantially independent of saturation ratio in the range of 25−75%. However, by approaching the full saturation state, the values of modulus fall sharply and damping of loose samples increases dramatically from corresponding values of unsaturated levels. Results of drained tests revealed that most of increase in shear modulus and decrease in damping take place in the first 30 cycles. It was found that vertical consolidation stress is the most important parameter which affects shear modulus and damping ratio of sand. Similarly, relative density or void ratio significantly affects dynamic stiffness and damping under undrained conditions. Moreover, the influence of shear strain amplitude should be considered for both drained and undrained tests.

► G and D variations are independent of saturation ratio in the range of 25−75%.
► G of drained tests increases with the number of cycles in a logarithmic pattern.
► Shear modulus of undrained tests exponentially descends with the number of cycles.
► Power equations predict D variations with the number of cycles in drained tests.
► σv′ is the most important factor that affects G and D of drained and undrained tests.