No abstract

Liquefaction can be considered to occur in saturated sand widely under seismic load, which will cause serious disaster, including road damage, ground subsidence, cracking of houses. Thus, it is quite necessary to study the liquefaction characteristics of saturated sand. For this aim, the undrained simple shear test on saturated sand under cyclic loading were simulated by three-dimensional distinct element method (DEM), where the stress-strain relationship, excess pore pressure ratio, mechanical coordination number and contact normal direction were analyzed. The results show that the liquefaction of saturated sand is manifested by the accumulation of excess pore pressure ratio. In addition, the mechanical coordination number gradually reduces and the sample anisotropy slightly fluctuates before the saturated sand reaches initial liquefaction. When the specimen approaches initial liquefaction, the mechanical coordination number drops abruptly and the sample anisotropy obviously increases.

Three-dimensional DEM (discrete element method) simulations of the true triaxial and wetting tests were conducted to study the macroscopic and microscopic mechanical properties of unsaturated structural loess under complex stress state. The simulation results were analyzed in terms of stress-strain relationships, void ratio responses and bond breakage number with water content. It is shown that collapsing failure occurs when the deviatoric stress approaches or exceeds the peak shear strength of the corresponding saturated structural loess sample. There is little difference in the axial strain between the quick wetting (QW) method and gradual wetting (GW) method, and the volumetric strain of the samples wetted by QW are larger than that by GW specimen. The bond breakage number of the sample wetted by QW is slightly higher than that by GW. However, the bond breakage number of the sample wetted by the two wetting methods is slightly higher than that of the saturated structural loess sample subjected to the same stress state.

This study investigates the shear behaviors of unsaturated structured loess in direct shear test by the discrete element method (DEM). A bond contact model characterized by the consideration of inter-particle attraction and van der Waals force was used. The direct shear tests were simulated under different suctions and vertical pressures. The simulation results were analyzed in terms of stress-strain relationships, volumetric responses, bond breakages and contact fabric. It is shown that: 1) The shear strength of structural loess samples can be enhanced by decreasing water content and increasing vertical pressure; the strain softening and dilatancy behaviors of structural loess enhance with the decrease of water content and vertical stress, respectively. 2) The bond breakage rate in shear band is related to the macroscopic mechanical response. 3) The anisotropy of the contact fabric changes more significantly in the shear band during shearing, it is of great significance to study the microcosmic properties of particles in shear band.

PurposeThe paper aims to find the correlation between the microparameters and the macroparameters of the soil. The study aims to calibrate the macroscale and microscale parameters of rolling resistance contact models to successfully apply the discrete element method to do some research of the geotechnical problem.Design/methodology/approachThe paper opted for an exploratory study using the PFC3D to simulate the triaxial tests that include more than 50 cases and the coupling analysis method, which considering several effect of various factors.FindingsThe paper provides a quantitative relationship between the macroparameters and microparameters of the rolling resistance linear model and a method for fast calibration of macroscopic parameters is proposed and verified by a triaxial test example.Originality/valueThis paper provides the quantitative relationship of micro and macroparameters in the rolling resistance linear model by studying a single factor and considering the coupling effect of various factors and a fast method for the calibration of microparameters based on the rolling resistance linear model is proposed.