Microscopic Study of Shear Mechanisms in Soils

A general microscopic mechanism has been clarified using both rate process theory and the adhesion theory of friction. Physical evidence for the existence of solid-to-solid contact between clay particles in the form of microphotographs from the scanning electron microscope and acoustic emissions is presented. A generalized concept for the normal force acting at contact points between particles and intergranular stress during shear is also developed. Theoretical considerations for a microscopic model of shear resistance and the microscopic meaning of soil strength parameters are developed based on these generalized concepts. As a result the proportionality coefficient which relates the shear resistance of soils to normal forces acting at the contact points between particles is given a physical basis on the microscopic scale, and the meanings of the true angle of friction and conventional strength parameters in effective stress representations are clarified.