Measurements of Elastic Properties of Geomaterials in Laboratory Compression Tests
Two types of axial loading devices having high and low capacities of axial load, respectively, for use in displacement-controlled compression tests on geomaterials (i.e., natural soils and rocks, and treated soils) in the laboratory are described. They were designed so that the loading direction can be reversed without any noticeable time lag under a highly constant axial strain rate while using a gear system. Results of representative triaxial and plane strain compression tests on a sand, a sedimentary soft rock, and a clay are presented. These results were obtained from very slow monotonic (or one-way) loading tests with several unload/reload cycles measuring axial strains locally along the lateral surfaces of a specimen continuously for a strain range from the order of 0.0001% (10-6) to that at failure. It is demonstrated that initial stiffness at strains less than about 0.001% (10-5) during primary loading is the same as stiffness during small unload/reload cycles applied immediately after the start of loading. Initial deformation properties are rather linear and elastic.