Document Type : Research Paper
Authors
Abstract
In some natural events such as soil failure the deformations are localized in narrow restrictions, which are called shear bands. This event which is a fundamental phenomenon in granular material, has been widely investigated during recent decades within expensive experimental tests and also some numerical simulations. Most of previously used numerical methods are based on continuum theories describing shear bands as interfaces along which solid masses move like rigid blocks. In this interpretation many physical events such as changes of the soil structure around failure line are neglected. In this paper the discrete element method is used to simulate the shear bands. Since in this method some of the problems of experiments and simulations are solved,
It would be an ideal method to obtain the stresses and strains, and also to investigate the behavior of shear bands in a granular media, while exposing to external forces. In this research by the use of DEM and conducting series of biaxial tests on assemblies of two-dimensional ellipse shaped particles, the effect of different factors such as average grain size, particle shape and confining pressure on the shear bands are studied and the results show that some investigated factors like average grain size and confining pressure have considerable effect on the shear bands characteristics.
The main results can be summarized as follows:
• The amount of rotation is a very sensitive characteristic and it changes considerably by all of the factors measured in this research.
• The most affecting factors on the displacement of the particles across the shear bands are the loading rate and confining pressure. Moreover by increasing the particle size the displacements increase with a great amount but if these values are divided by the particle radius, no significant changes in the particle displacement will be observed. Other factors do not seem to have any effects on this issue.
• 6-13d50 seems to be the best estimation for the shear band thickness, and other controlled factors affect this value within this restriction. The width of the shear bands seems to increase by the loading rate and confining pressure increase.
• The inclination of this localization is mostly affected by confining pressure (which increase leads to angle decrease), porosity (which increase leads to angle decrease), grading (its uniformity causes smaller shear band angles), and size (greater sizes of grains would result in failure with lower angles of sear band). Among these factors grain size has the least effect.
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