Strain-Rate Effect on Soil Secant Shear Modulus at Small Cyclic Strains

Abstract

The effects of the shear strain rate γ˙=dγ/dt on the secant shear modulus Gs of three clays and three sands at small cyclic shear strain amplitudes γc under simple shear loading conditions are described. The amplitude γc varied between 0.0003 and 0.02% and γ˙ between 0.0002 and 0.04 %/s. For all six soils Gs increases with γ˙, such that the Gs versus log γ˙ data plot approximately along a straight line. The slope of this line is αG=strain-rate shear modulus parameter, while its normalized value αG/Gs=Nγ˙-G=shear strain-rate modulus factor. For the clays tested αG ranges between 2.5 and 7.5 MPa and Nγ˙-G between 2.0 and 11.5%. For the sandy soils αG ranges between 0.2 and 3.0 MPa and Nγ˙-G between 0.2 and 6.0%. Both αG and Nγ˙-G decrease moderately with increasing γc, i.e., the largest αG and Nγ˙-G were obtained at the smallest γc. For five soils the families of the normalized modulus reduction curves (Gs/Gmax)-log γc were constructed, such that each curve pertains to a constant γ˙. It was found that γ˙ has essenlially no effect on the shape of the constant-γ˙ (Gs/Gmax)-log γc curve. A brief review of previous experimental studies is included.