Sandstone is encountered in many hydropower projects in China, and its permeability evolution characteristics during the deformation process are one of the most important issues in engineering design. In this study, microstructure observation and mineral content analysis of a sandstone are performed, and triaxial flow experiments under different fluid pressures are carried out. The experiment results show that the permeability evolution with volumetric strain is associated with microcrack development in the process of rock deformation and failure. The volumetric strain is closely related to the permeability and fluid pressure, and it plays a role of linking the flow field and the stress field. A conceptual model is suggested to describe the permeability evolution of the rock. Scanning electron microscope analysis results on some failed specimen pieces illustrate that the fluid pressure plays a role in the development of microcracks. A high fluid pressure can accelerate crack propagation and rock f...

Purpose: This paper aims to present a digital image processing (DIP)-based discrete element method (DEM) for the analysis of heterogeneous geomaterials. Taking a soil and rock mixture as an example, the direct shear test is used to illustrate the application of this method. The numerical result is validated by the laboratory experiment and implies its feasibility in the analysis of heterogeneous geomaterials. Design/methodology/approach: This method has two major steps. Based on a modification of the connected-component labeling algorithm, a novel vectorization method, which can transform the digital photos to vectorized geometry automatically, is proposed first. Then, a simple yet effective method for the generation of heterogeneous DEM models is presented using the simulation of simplicity technique. Findings: DIP-DEM method is a feasible approach for the analysis of mechanical behavior of heterogeneous material. For soil and rock mixtures (SRM), the horizantal deformation at peak shear point becomes larger with the normal stress. Compared with pure soil, the rock aggregates mainly improve the friction angle of SRM. Originality/value: As a universal method taking advantage of both DIP and DEM, this method has broad application prospects in related fields.

A columnar joint network is a natural fracture pattern with high symmetry, which leads to the anisotropy mechanical property of columnar basalt. For a better understanding the mechanical behavior, a novel modeling method for columnar jointed rock mass through field investigation is proposed in this paper. Natural columnar jointed networks lies between random and centroidal Voronoi tessellations. This heterogeneity of columnar cells in shape and area can be represented using the coefficient of variation, which can be easily estimated. Using the bisection method, a modified Lloyd’s algorithm is proposed to generate a Voronoi diagram with a specified coefficient of variation. Modelling of the columnar jointed rock mass using six parameters is then presented. A case study of columnar basalt at Baihetan Dam is performed to demonstrate the feasibility of this method. The results show that this method is applicable in the modeling of columnar jointed rock mass as well as similar polycrystalline materials.