Damping ratio of unsaturated silts from resilient modulus testing

Abstract

The dynamic response of soils under cyclic loading is strongly influenced by its ability to dissipate energy, commonly expressed through the damping ratio. Extensive research on saturated and dry conditions has established well-defined correlations between the damping ratio and various design parameters. In contrast, there has been limited research dedicated to the damping ratio of unsaturated soils. The importance of studying unsaturated conditions is reinforced through the fact that some in situ soils exist in a partially saturated state. Current studies on the damping ratio for unsaturated soils focus on clays and sands, leaving the behavior of silts relatively unknown. Furthermore, the damping ratio has been shown to be sensitive to the testing method, and no unified method has been established. In this thesis, correlations of the damping ratio from resilient modulus or cyclic triaxial compression testing of four samples of unsaturated silts with the plasticity index, and molding gravimetric water content, degree of saturation, relative compaction (void ratio), and effective stress were studied. Throughout this thesis, the mention of water content, degree of saturation, effective stress, and relative compaction refer to the values at the time of molding. Samples were prepared at six different physical states (three water contents at two relative compactions) and tested under fifteen distinct stress states. Three out of the four samples were prepared from dry to wet conditions. The results show that the damping ratio is very sensitive to sample preparation. The samples tested from dry to wet conditions showed a clear increase in damping ratio with water content and lower void ratios, and a clear decrease with lower effective stress. The influence of saturation was not fully clear. In contrast, the samples prepared from wet to dry exhibited a clear increase in damping ratio with increasing void ratio. Samples at intermediate saturation values showed a decrease in damping ratio with increasing saturation. The influence of effective stress and water content were not clearly defined. Common trends observed across all soils are a decrease in damping ratio with increasing plasticity index and an increase with increasing shear strain.