Elastic deformation properties of geomaterials

Abstract

The stress-strain relationships of various kinds of geomaterials; i.e., a cement-treated sandy soil, a sedimentary soft rock, gravels, sands and reconstituted kaolin, were examined in tests using specimens subjected to both monotonic and cyclic shear in triaxial, plane strain compression and torsional simple shear. A particular attention was paid on their stiffness at small strains, for which the deformation of specimens in triaxial and plane strain compression was measured locally over the central part with an accuracy of the strain measurement of about 0.0001%. In a series of tests performed on normally consolidated specimens, the elastic shear modulus, Gmax, was defined for small strain ranges having their limits with the order of 0.001%, below which the response was found to be practically linear elastic. The Gmax-value was hardly influenced by the rate of shearing and the type of loadings (i.e., static monotonic, static cyclic and dynamic loadings) within the small strain range. It was also demonstrated that the Gmax-value of sands was scarcely affected by the stress and strain histories as examined in tests using specimens subjected to different degrees of initial shear applied during consolidation and of overconsolidation, and to cyclic prestraining at relatively large strain levels. The results suggest that, with a supply of high-quality undisturbed samples, the Gmax-value, together with the strain level-dependent stiffness and the strength, of natural ground can be evaluated by having the results of laboratory monotonic loading tests with necessary corrections for the effects of sample disturbance. Also, the elastic shear modulus from in-situ elastic shear wave velocity can be directly used for the analyses of monotonic and cyclic problems as the effects of some factors, such as the strain level-dependency of the stiffness, are properly evaluated.