INFLUENCE OF SOIL TYPE ON THE EFFECT OF STRAIN RATE ON SMALL-STRAIN CYCLIC SHEAR MODULUS

MLADEN VUVETIC and KENTARO TABATA

ABSTRACT: Sixteen different soils were tested in an NGI type simple shear device to examine the effect of strain rate, ƒÁ, on cyclic secant shear modulus, G_s, at very small to small cyclic shear strain amplitudes, ƒÁ_c » 0.0003-0.01%. The effect of ƒÁ on G_s was characterized by strain-rate shear modulus parameter, ƒ¿_G, and strain-rate shear modulus factor, N_ƒÁ-G. Parameter ƒ¿_G describes the slope of G_s-log ƒÁ  data for a given ƒÁ_c, while N_ƒÁ-G is ƒ¿_G normalized by reference G_s. For the clayey soils and their conditions tested ƒ¿_G » 1.0-6.5 MPa and N_ƒÁ-G » 2.0-6.0% were obtained. For the sandy soils ƒ¿_G » 0.3-1.2 MPa and N_ƒÁ-G » 0.5-3.0% were obtained. Data revealed that ƒ¿_G decreases with increasing ƒÁ_c, while N_ƒÁ-G either slightly decreases with increasing ƒÁ_c or stays about constant. The trends of N_ƒÁ-G with plasticity index, I_p, liquid limit, w_L, clay content, and activity were examined. It was found that at a given ƒÁ_c, N_ƒÁ-G generally increases with increasing all of these properties and indices. Most consistent and strongest correlations were obtained between N_ƒÁ-G and I_p and N_ƒÁ-G and w_L. These two correlations can be useful for the soil dynamics engineering practice and are presented in the paper.

Key words: clay, cyclic shear, sand, shear modulus, simple shear test, small strain, strain rate (IGC: D7)