SMALL STRAIN BEHAVIOR OF GEOMATERIALS : MODELLING OF STRAIN RATE EFFECTS

ABSTRACT Experimental results for sand, gravel, sedimentary soft rock and stiff clay are presented which show that even at small strain levels (less than about 0.001%), these geomaterials exhibit nearly linear elastic behavior, but creep deformation and stress relaxation are not negligible. In cyclic loading tests, at these small strain levels, damping values are not negligible, and with a decrease in the loading frequency from a certain limit, the peak-to-peak secant modulus decreases and the damping values are not constant. These test results for the small strain domain, which show the existence of viscous effects, are successfully simulated by a rheological model called the Simple Asymptotic Body. It consists of a linear spring connected to a set of another linear spring parallel with a linear dashpot. According to this model, the peak-to-peak secant modulus has maximum and minimum values at very high and low loading frequencies where the damping value is zero, while the damping has the maximum value at an intermediate loading frequency. Some keys to answer the questions concerning i) the existence of difference in dynamic and static moduli and ii) “qua-si-linear domain” for geomaterials are also given.