Shear Phenomena in Granular Random Packings

Abstract

This work was carried out on the background of Winterkorn's macrometric liquid theory which relates the performance of granular assemblies to the behavior of molecular liquids. For both substances the phase transition form the solid to the liquid state occurs for a distinct void ratio. This analogy induced Winterkorn to propose an equation correlating the shear strength of granular soils with their void ratios. The results of shear tests are greatly conditioned by the test method. As a well defined zone of shear failure is desirable for the comparison with the viscosity of liquids, the shear strength was determined by direct shear tests. Special investigations were performed on the effect of the sample dimensions and the mode of force application on the test results. The knowledge gained was utilzied for the design of a new testing machine which continuously records the shear strength of cohesionless material and its dilatancy during the test. The testing time is cut down considerably by this machine. The evaluation of data obtained for binary mixtures of ideal material turned out valuable information on the mechanism of shear failure. It was observed that shear failure occurs according to two mechanisms resulting in different value for all properties involved. By application of energy principles and statistical methods a correlation could be established between the coefficient of internal friction the void ratio of the specimen and the three soil values: ultimate shear strength critical void ratio and a newly defined minimum void ratio. It agrees with Winterkorn's formula derived from the analogy with the viscosity of liquids, if the constant C in this equation is expressed by these three soil values. The minimum void ratio appears to have the same importance for shear phenomena as the critical ratio. With the help of this equation and the discovery of the double mechanism, the dependence of shear strength on the normal pressure could be explained by the change of the critical void ratio upon application of different loads.