The Influence Of Particle Geometry And The Intermediate Stress Ratio On The Shear Behavior Of Granular Materials

Sandy soil is widely used in engineering constructions, for example, roads, railways,buildings, dams, et al. As typical granular materials, their mechanical behavior (e.g. stress strain, dilation, critical state behavior, liquefaction) is very complex in nature and can be affected by particle shape, stress path,fabric,density,particle size distribution,amongst others.But the classical approach is based on indirect phenomenological observations at the continuum level. For granular materials like sand, the particle geometry (e.g. aspect ratio,sphericity, convexity) can affect the behavior of sand. The open source code YADE was used to study the macroscopic and microscopic behavior of sand. The main research results are as follows:A series of conventional compression tests were conducted using the samples with different particle aspect ratios and a unique particle size distribution (PSD). Test results show that particle aspect ratio affect the macro- and micro-scale response. At the macro-scale, the shear strength decreases with an increase in particle aspect ratio values and the dilatancy is significant under lower particle aspect ratio. At the micro-scale,the particle aspect'ratio have influence on the fabric evolution of the sample. The critical state fabric norm decrease with an increase particle aspect ratio. The results from discrete element method analyses are qualitatively agree with available experiment data.Two types of true triaxial test (with intermediate stress ratio values specified) were performed: constant mean effective stress and constant minor principal stress. The results showthat the true numerical triaxial test can reflect the strength and deformation of sandunder three-dimensional unequal stress state. The stress path greatly affect the macro-response of the sample. The numerical results compare well with Lade-Duncan failure criterion.The influence of particle aspect ratio and the intermediate stress ratio on the critical state behavior of sand are discussed based on a number of conventional compression triaxial test and constant minor principal stress true triaxial test results. It is observed that the position of critical state loci in the compression (e-p') space is only slightly affected by particle aspect ratio. The critical state line is unique. It is independent of density, confining pressure, drainage conditions, shear model (intermediate stress ratio) and stress path. The critical state stress ratio decrease with an increase of the particle aspect ratio and intermediate stress ratio. It is demonstrated that the influence of the aspect ratio and the intermediate stress can be captured by micro-scale fabric evolutions that can be well understood within the framework of existing critical state theories. It is also found that for a given stress path, a unique critical state fabric norm is dependent on the particle shape but is independent of critical state void.