Very-small to large strain dynamic behaviour of unsaturated sand in a wide range of suction

¹ Dept. of Civil and Environmental Engineering, Hong Kong Univ. of Science and Technology, Kowloon, Hong Kong
² Dept. of Civil and Environmental Engineering, Sharif Univ. of Technology, Tehran, Iran

^* Corresponding author: aakarimzadeh@connect.ust.hk

Abstract

Shear modulus (G_max at very small strain and G at large strain) and constraint modulus at very small strain (M) are important soil parameters for static and dynamic analysis in geotechnical applications. However, these dynamic properties of unsaturated soil are rarely reported. In this study, a cyclic simple shear apparatus was newly-modified for allowing both the shear and constrained moduli at both very small and large strains to be measured. Benders or ultrasonic sensors were embedded in an unsaturated soil sample for transmitting/receiving shear- and pressure-wave, respectively. Two very-small-strain tests were conducted to determine the G_max, M and soil damping ratio of a sand for a wide range of suction covering from the boundary-effect, transition and residual zone of the water retention curve of the sand. In addition, six large-strain cyclic simple shear tests were carried out to investigate G. The test results showed that G_max and M were approximately constant before reaching the air-entry value, but there was a significant increase in G_max as the sand dried further. Yet, M dropped within the transition zone, and interestingly when the suction was beyond the residual value, M increased. M along the wetting path was higher than that along the drying path. The damping ratio, on the other hand, first reduced before reaching the air-entry value, but it increased at the transition zone and then decreased within the residual zone. At large strain, G/G_max also increased as suction increased until reaching the residual zone, beyond which the normalised value show substantial decreased.