Effect of lubrication layers on small strain stiffness of dense Toyoura sand

Small strain stiffness of dense Toyoura sand was investigated by performing triaxial compression tests using large-scale apparatus. The specimens were rectangular prismatic with dimensions of 50 cm high and 23.5 cm times 23.5 cm in cross-section. The specimens were prepared by employing air pluviation method and keeping dry densities within the range of 1.62-1.63 g/cm(3). Dynamic and static Young's moduli were evaluated by wave velocity measurement and by conducting small unloading/reloading cycles, respectively. As a result of this study, following conclusions were made; (i)-no effect of lubrication layer was found on either dynamically or statically measured vertical Young's moduli; (ii)-quasi-elastic vertical Young's moduli obtained by static and dynamic methods were repeatable in all the four tests conducted at similar densities. The values of the dynamic vertical Young's moduli were by 15-25% larger than the static values, due possibly to the particulate nature of the specimen; (iii)-the test results on large specimens were consistent with those on small specimens after making due corrections for the effects of different void ratios.