Micromechanical model for shear band formation in granular soils and its application to bearing capacity problems

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Soil engineers may admit that occurrence of shear bands is one of the most dramatic phenomena in soil bodies at failure. The purpose of the present study is to do some numerical and physical tests on granular soils, and also, based on these results, to suggest a new micromechanical model of shear band formation. The study has not been completed yet, but some interesting observations, which seem important in the dynamic interpretation of shear bands, have been done so far, as summarized below:1. Three shear bands, two from natural soils and the other from an artificial assembly of photoelastic rods, were studied with special interest in their micro-fabric induced by shearing deformation. Development of column-like load paths and their collapse by rotation are most important observations to be taken into account in micromechanics of granular soils. It is concluded from these findings that couple-stress can play an important part in the formation of shear bands.2. Numerical model tests using BALL developed by Cundall and Strack (1979) have been carried out to see if the fabric development observed in the physical tests can be reproduced in such numerical simulations. The result strongly suggests that the numerical simulation provides a very useful tool for studying shear band formation.