Evolution of shear bands in sand

Abstract

Localisation of deformation in narrow shear bands is a fundamental phenomenon of granular material behaviour. When modelling granular materials, shear localisation has therefore to be considered. The model must include an adequate constitutive law with an intrinsic length determining the thickness of the localised shear zones, and a representation of microscopic inhomogeneities triggering shear localisation. In the framework of a Cosserat continuum the behaviour of non-cemented granular material can be described by a hypoplastic law including the evolution of non-symmetric stresses and couple stresses. Void ratio fluctuations are introduced by a physically justified probability density function. The assumption is that fluctuations are minimal in the densest state, and maximal in the critical state. It is shown that shear bands can evolve spontaneously in the interior of a granular body even under homogeneous stress or displacement boundary conditions. Experimental verifications are given. Numerical results are compared with laboratory tests performed with a Cornforth and a Hamblytype biaxial apparatus. Shear localisation in the experiment is visualised by means of an optical method called particle image velocimetry. Further numerical results are compared with experimental results taken from publications.

Vortex formation and dissolution in sheared sands

“…The base of the specimen rests on a one-way ball-bearing "sled", which allows for free lateral translation of the lower part of the specimen. For dilative sands (sands of high bulk density and tested under relatively low confining stress), while several conjugate shear bands typically form at peak stress, subtle material irregularities tend to favor the domination of one band [19,20]. If lateral translation between the regions above and below the dominant shear band is allowed, a single, persistent, minimally constrained and quasi-linear shear band will dominate; otherwise, the shear band may be biased by boundary constraints, e.g.…”

Continuum Modeling of Granular Media

“…The literature abounds with many interesting experimental observations (e.g., Ref. [43]) and numerical simulations of shear bands, with numerous striking examples presented in a sustained body of work by Tejchman [11,14] and Widuli nski et al [44]. Following the pioneering studies of J. Desrues, recent developments in X-ray computer tomography have led to grain-level visualization that reveal such bands via density contrasts arising from granular dilatancy [45].…”

Experimental Validation of a Numerical Model: Reverse Fault Rupture Propagation Through Sand

“…The standard finite element solution of strain localization in a rate-dependent material results in solutions that is strongly mesh-sensitive. Higher order constitutive models can solve this problem: viscoplastic model 12) , non local theory 13) , gradient elasto-plastic model 14) , otherwise, Gudehus & Nubel 15) , showed the size of elements has to be in the order of 3D 50 . Such fine mesh size prohibits the rigorous application of FE method to real-scaled problems.…”