Instruments and methods for studying the rheological properties of clay soils

Abstract

1. The instruments now being used to study the rheological properties of disperse systems with a low concentration of disperse phase are not suitable for investigating the rheological properties of soils, principally because they do not permit the determination of the dependence of the rheological characteristics on the state of stress. 2. The ordinary shear boxes and stabilometers widely used in soil mechanics are not satisfactory for studying the rheological properties of soils owing to the nonuniformity of the stress and strain field in the sample during testing. 3. The plane-parallel shear apparatus and Roskoe's apparatus are quite suitable for rheological research. However, the boundary conditions in these apparatuses do not correspond to the scheme of simple shear, since there are no tangential stresses on two sides of the sample. 4. From the theoretical viewpoint the best possibilities are afforded by an instrument in which a hollow cylindrical sample is tested in torsion. However, since a uniform stress and strain field in the sample is achieved only in testing a thin-walled cylinder, the advantages of the apparatus are much reduced by the conditions of experimental error, associated with the important role of boundary surface effects and the possibility of concentration of deformation in a narrow zone (which is attributable to the specific properties of soils), as well as by difficulties in preparing and testing the samples. This limits the area of usefulness of the apparatus to special types of investigation. 5. In any test system the properties of the sample vary during the process of plastic deformation. To a considerable extent, the open system simulates the changes that take place in foundation soils. 6. It is recommended that studies of soils and other materials whose rheological properties depend not only on the tangential but also on the normal stresses be carried out on a simple shear apparatus.