Spatial variation of void ratio and shear band thickness in sand using X-ray computed tomography

Abstract

A detailed study of spatial variation of void ratio and shear band thickness measurements is presented in this paper. A prismatic sand specimen that initially measured 57 . 4 mm wide 3 120 . 5 mm long 3 182 . 1 mm high was sheared under plane-strain (biaxial) loading conditions. The specimen was prepared at a relative density of 79% using F-75 Ottawa sand. X-ray computed tomography was used to scan the specimen before shearing and after the onset of the shear band. The specimen failed through a single shear band with an inclination angle of 65 . 68 measured from the direction of the minor principal stress. Computer algorithms were developed to calibrate CT images and quantify void ratio (e) variation within the specimen. CT data analysis revealed cross-sectional spatial variation in void ratio where density is higher in regions close to the edges of the specimen due to membrane effects and confining pressure with no significant variation in void ratio in the axial direction (top to bottom) before shearing. The shear band was easily identified from the CT images, and analysis of void ratio showed a noticeable jump in void ratio profile across the shear band. A detailed statistical summary of the thickness of the shear band and variation of void ratio across the shear band is presented and discussed.

The bearing capacity of footings on sand with a weak layer

“…The thickness of the observed shear band ranges from 6·1 to 9·1 mm corresponding to (6·3-9·4)d 50 for footings on sand A and from 3·2 to 5·4 mm corresponding to (7·1-12)d 50 for footings on sand B. In both cases, it is well within the range of (6-25)d 50 reported in geotechnical literature (Alshibli and Hasan, 2008;Finno et al, 1997;Mühlhaus and Vardoulakis, 1987;Tatsuoka, 2001;Tatsuoka et al, 1991).…”

Shear band in sand with spatially varying density

“…Liang et al, 1997;. The main techniques used have been gamma-ray (Coumoulos, 1968;Desrues et al, 1985) and X-ray CT (Desrues et al, 1996;Alshibli and Hasan, 2008). These techniques derive quantitative measurements of local density through correlation with measured radiation attenuations.…”

Characterization of mesoscale instabilities in localized granular shear using digital image correlation

“…Shear bands in sands are of considerable thickness, with values reported on the scale of about 8-25 grain diameters, e.g., [2,3,14,21,30,34]. The displacement field within the shear band is of particular interest, as once the shear band forms, all significant material straining is confined only to within the shear band, e.g., [30]: subscale kinematics within this material zone then govern macroscopic stress evolution from softening to critical state.…”