Microscopic observation of shear band in plane strain compression tests of sand

A new device was developed to carry out shear tests of sand in which the movement of sand grains can be monitored continuously by a digital microscope. Tests on dense sand revealed that shear band was formed when the peak strength was achieved. This is in contrast with the pre-peak behavior in which the granular movement was uniform all over the specimen. After the peak strength, a significant flow of grains concentrated within the sheer band which is of approximately 10 grain diameters in width. The rotation of grains was substantial and random within the shear band and a dilatancy was important in the band as well.