A micro-mechanical simulation of sand liquefaction behavior by DEM
- Authors: Shi, Danda , Zhou, J. , Xue, Jianfeng , Zhang, Jiao
- Date: 2010
- Type: Text , Conference paper
- Relation: Soil Behavior and Geo-Micromechanics: Proceedings of the GeoShanghai 2010 International Conference p. 204-211
- Full Text: false
- Reviewed:
- Description: A two-dimensional Particle Flow Code (PFC2D) was applied to simulate sand liquefaction behavior induced by cyclic loading. The numerical sample was prepared with 4061 discs with its particle size distribution similar to Fujian Standard sand. Based on the theory of strain-controlled undrained cyclic triaxial test, a constant volume numerical test was carried out under cyclic loading with uniform strain amplitude. The macroscopic responses of the sample were obtained and the variation of average coordination number under cyclic loading was analyzed. The effects of cyclic strain amplitude and confining pressure on liquefaction resistance were further analyzed in numerical simulations. It was found that the numerical tests reproduced the general characteristics of liquefaction behavior of saturated sand under cyclic loading. The effects of cyclic strain amplitude and confining pressure on the liquefaction resistance of the numerical sample were comparable with reported experimental results.
DEM modeling of particle breakage in silica sands under one-dimensional compression
- Authors: Shi, Danda , Zheng, Lin , Xue, Jianfeng , Sun, Jing
- Date: 2016
- Type: Text , Journal article
- Relation: Acta Mechanica Solida Sinica Vol. 29, no. 1 (2016), p. 78-94
- Full Text: false
- Reviewed:
- Description: A Discrete Element Method (DEM) model is developed to study the particle breakage effect on the one-dimensional compression behavior of silica sands. The 'maximum tensile stress' breakage criterion considering multiple contacts is adopted to simulate the crushing of circular particles in the DEM. The model is compared with published experimental results. Comparison between the compression curves obtained from the numerical and experimental results shows that the proposed method is very effective in studying the compression behavior of silica sands considering particle breakage. The evolution of compression curves at different stress levels is extensively studied using contact force distribution, variation of contact number and particle size distribution curve with loading. It is found that particle breakage has great impact on compression behavior of sand, particularly after the yield stress is reached and particle breakage starts. The crushing probability of particles is found to be macroscopically affected by stress level and particle size distribution curve, and microscopically related to the evolutions of contact force and coordination number. Once the soil becomes well-graded and the average coordination number is greater than 4 in two-dimension, the crushing probability of parent particles can reduce by up to 5/6. It is found that the average contact force does not always increase with loading, but increases to a peak value then decreases once the soil becomes more well-graded. It is found through the loading rate sensitivity analysis that the compression behavior of sand samples in the DEM is also affected by the loading rate. Higher yield stresses are obtained at higher loading rates. © 2016 The Chinese Society of Theoretical and Applied Mechanics.
A DEM investigation on simple shear behavior of dense granular assemblies
- Authors: Shi, Danda , Xue, Jianfeng , Zhao, Zhenying , Shi, Jiyu
- Date: 2015
- Type: Text , Journal article
- Relation: Journal of Central South University Vol. 22, no. 12 (2015), p. 4844-4855
- Full Text: false
- Reviewed:
- Description: A micromechanical investigation on simple shear behavior of dense granular assemblies was carried out by discrete element method. Three series of numerical tests were performed to examine the effects of initial porosity, vertical stress and particle shape on simple shear behavior of the samples, respectively. It was found that during simple shear the directions of principal stress and principal strain increment rotate differently with shear strain level. The non-coaxiality between the two directions decreases with strain level and may greatly affect the shear behavior of the assemblies, especially their peak friction angles. The numerical modelling also reveals that the rotation of the principal direction of fabric anisotropy lags behind that of the major principal stress direction during simple shear, which is described as fabric hyteresis effect. The degrees of fabric and interparticle contact force anisotropies increase as particle angularity increases, whereas the orientations of these anisotropies have not been significantly influenced by particle shape. An extended stress-dilatancy relationship based on ROWE-DAVIS framework was proposed to consider the non-coaxiality effect under principal stress rotation. The model was validated by present numerical results as well as some published physical test and numerical modelled data. © 2015, Central South University Press and Springer-Verlag Berlin Heidelberg.
Three-dimensional DEM simulation of cone penetration test by using circumferential periodic boundary
- Authors: Yang, Yangchen , Deng, Yibing , Shi, Danda , Xue, Jianfeng
- Date: 2016
- Type: Text , Journal article
- Relation: Yanshilixue Yu Gongcheng Xuebao/Chinese Journal of Rock Mechanics and Engineering Vol. 35, no. (2016), p. 3372-3384
- Full Text: false
- Reviewed:
- Description: In order to explore the micro-mechanism of CPT, a new circumferential periodic boundary was developed to consider the three-dimensional axisymmetric problem with 1/4 of the cylinder. To validate the method, a drained triaxial test was modeled with the proposed method and the traditional full model. The results are comparable and the proposed method is very effective. The method was further used to simulate a cone penetration test in dry Fontainebleau sand. It was found that, the variation of cone radial stress and tip resistance during penetration from the model are in good agreement with the reported test results. The micromechanical responses, such as the distributions of particle displacement, internal stress and local porosity to cone penetration are extensively studied. The evolutions of fabric anisotropy during penetration are also discussed. The relationship between stress and fabric is quantitatively described using fabric tensor, which reveals the mechanism of cone penetration capacity microscopically. The results of the work not only improve the efficiency of three-dimensional discrete element method(DEM) simulation, but also promote better understanding of CPT mechanism. © 2016, Science Press. All right reserved.