Sihong Liu

A yield function for granular materials based on microstructures

Purpose – The purpose of this paper is to propose a new yield function for granular materials based on microstructures. Design/methodology/approach – A biaxial compression test on granular materials under different stress paths is numerically simulated by distinct element method. A microstructure parameter S that considers both the arrangement of granular particles and the inter-particle contact forces is proposed. The evolution of the microstructure parameter S under the simulated stress paths is analyzed, from which a yield function for granular materials is derived. The way of determining the two parameters involved in the yield function is proposed. Findings – The new yield function is calibrated using the test data of one sand and two rockfill materials. The shape of the new yield surface is similar to that of the Cam-clay model. Originality/value – The paper proposes a microstructure parameter S, which considers both the arrangement of granular particles and the inter-particle contact forces. From t...

A New Method for the Generation of Polydisperse DEM Specimens

The mechanical properties of granular materials are closely related to their gradations. In the DEM simulation of granular materials, it is very important to generate a specimen with a reasonable gradation. In this study, a DEM specimen generation method that can take a predefined gradation into account is proposed. The proposed method is based on the probability density function (PDF) and can be easily programmed. The principle and the numerical procedures of the method are firstly presented. Then, it is used to generate a DEM specimen with the gradation of a real coarse material, which is compared with the one generated by a conventional method. The local polydispersity of the DEM specimens generated by the two different methods and their conformity with the real gradation are discussed. The results demonstrate that the grading curve of the specimen generated with the proposed method is more continuous and smooth, and will converge to the target gradation curve when the number of the generated particles increases.

Numerical Model for Electro-Osmotic Drainage in Unsaturated Soils

A numerical model coupling of water flow and electrical transport in a deformable porous medium is developed to simulate the electroosmosis drainage in the unsaturated soil. This model is in accounting for unsaturated-induced nonlinear changes in the physical and geoelectrical properties that take place on the soil, with the additions of two-dimensional consolidation, and an external hydraulic gradient. The exponential relation is used to represent nonlinear changes in the hydraulic and electro-osmotic conductivities, and soil-water retention curve. The algorithm of this model is conducted using finite-element method. The pore water pressure, settlement, moisture content, drainage, and electric potential and current density as a function of time and position within the soil can be obtained. Finally, the proposed numerical solution is verified to be accurate compared with the experimental measurement.