Assessment of matric suction effect on dynamic parameters of saturated and unsaturated sand and silt

Abstract

This paper aims to present an experimental investigation on the unsaturated dynamic parameters of two types of soil i.e. sand and silt. These dynamic parameters are compared with emphasis on the influence of matric suction on the variations of small-strain shear modulus and damping ratio. Seven bender element and resonant column tests were performed on saturated and unsaturated specimens. The soils used in this study were Firoozkooh sand (No. 161) and non-plastic Firoozkooh silt. For this purpose, an unsaturated triaxial cell equipped with a set of bender elements and an unsaturated resonant column have been used. All specimens had an initial void ratio of 0.7 and were tested in various matric suctions under a mean net stress of 50 kPa. For applying and controlling of the matric suction, the axis translation technique and water head control (WHC) methods have been implemented. The obtained results from both bender element and resonant column tests, implied that there was a significant impact of matric suction on the shear modulus of the tested soils. The shear modulus of the tested sand started from the fully saturated state and increased to reach its maximum value around and between the Air-Entry value (AEV) and the Residual value (RV), then decreased and remained approximately constant with increase of matric suction; whereas, the shear modulus of the non-plastic silt continuously increased with increasing the matric suction. Also, the output data indicated that for the silt specimens, the damping ratio decreased with the increasing matric suction while in the sand specimens, noticeable variations of damping ratio with the matric suction occurred around and between the AEV and Residual value (RV). In addition, the values of shear modulus measured by the bender element tests were slightly higher than those obtained by resonant column tests.