Elastic properties of soils

A triaxial apparatus to measure small strains in the range between 10(-6) and 10(-2) has been set up to investigate the reversible behavior of various types of soils (sands, gravels, clays). Reversible behavior, along compression and extension triaxial paths, was demonstrated for strain amplitudes lower than 10(-5). Elasticity was found to be nonlinear, since the Young's modulus depended on the mean effective stress. We also studied the influence of such parameters as deviatoric stresses, void ratio, stress and strain history, and soil structure on the elastic coefficients of these soils. A general equation was proposed for determining the Young's modulus E in initially isotropic soils, which was modified by further loading. In granular materials, strain hardening increased the value of E, while in structured materials, a decrease of E was observed due to internal structure damage.