State of the Art: Laboratory Strength Testing of Soils

A review and evaluation of the advantages and limitations of laboratory equipment for measuring the shear strength of soils are presented. Equipment evaluated include direct shear, torsional shear, simple shear, triaxial, multiaxial (true triaxial), plane strain, hollow cylinder triaxial, and directional shear devices. The evaluation indicates that the impetus to obtain parameters for constitutive equations and modeling has resulted in the development of improved equipment and testing techniques; specifically, the development of multiaxial (true triaxial) and hollow cylinder triaxial test equipment. Although these devices are more versatile, the conventional solid cylinder triaxial test is still the most popular. The evaluation suggests that direct shear and simple shear devices are best utilized by designers who have gained experience applying the results from such tests to structures that have behaved satisfactorily. Proper consideration must be given to the effects of membrane penetration, end restrain saturation and consolidation procedures, and rates of loading in any testing program.