Sand Shear Band Thickness Measurements by Digital Imaging Techniques

Abstract

Digital imaging analysis was used to study localized deformations in granular materials tested under plane strain condition. Two independent techniques were applied and compared. In the first technique, the digitized optical images of a grid printed on the latex membrane were used to measure the shear band orientation angle and thickness, and were found to be 54.5° and 3.01 mm, respectively. The second technique involved introducing an ultra-low viscosity resin into the specimen in preparation for thin-sectioning and microscopic study of the internal fabric. A total of 24 microscopic images obtained from four thin sections were analyzed and void ratio variation was measured. The shear band thickness measurements from images located along the shear band axis (at two locations) were equal to 3.19 and 3.29 mm, which are very close to the average value obtained from surface analysis. The study was then extended to investigate the effects of sand grain-size, specimen density, and confining pressure on shear band thickness. It was found that the normalized shear band thickness decreases as grain-size increases and as density decreases. Finally, shear band thickness is dependent on the specimen dilatancy angle.