This paper investigates the permeability characteristics of compacted loess by focusing on the anisotropy parallel and perpendicular to the compaction. Three tests are conducted on compacted loess: triaxial permeability test under confining pressure consolidation, triaxial permeability test under K0 consolidation, and SEM test. Samples are maintained and tested at different dry densities under saturated conditions. The test results show that the saturated permeability coefficient of compacted loess is exponentially related to the initial dry density under both confining pressure consolidation and K0 consolidation. The fitting equation can estimate the saturated permeability coefficient of compacted loess at different depths. The horizontal saturated permeability coefficient of compacted loess is larger than that in the vertical direction, showing obvious anisotropy. The saturated permeability anisotropy ratio is linearly related to the initial dry density. Comparing and analysing the saturated permeability coefficient, the saturated permeability coefficient of compacted loess under the K0 consolidation condition is smaller than that under the confining pressure consolidation condition. Under the condition of K0 consolidation, the connectivity of vertical and horizontal pores of compacted loess is weakened, the tortuosity is strengthened, and the void ratio is decreased. K0 consolidation makes the flake-, plate-, and needle-like particles in compacted loess rotate continuously parallel to the compaction surface, which enhances the orientation of particles and leads to the saturated permeability anisotropy increase. The research results provide the basis for water field analysis in loess filling engineering.

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The failure process in brittle rocks is an important topic in rock mechanics, whose good understanding assists in predicting the strength and deformation characteristics of rocks. Because it is difficult to directly observe microcracks in laboratory tests, a numerical model is a useful tool for investigating microcracking behaviors. However, the mechanism of microcrack evolution is still unclear at the grain scale considering the microscopic heterogeneities. This paper proposes a polygonal universal distinct element code grain‐based model to solve this problem. Compared with other grain‐based models, this model is different in that mineral grains are subdivided into polygon blocks. The grain size, composition, and bond types of the contacts are incorporated, and both inter‐ and intra‐grain cracks are mimicked. Subsequently, micro‐parameters of the blocks and contacts are carefully calibrated according to the laboratory results. Following this, the calibrated model is employed to study the microcracking behaviors of granite in unconfined compression, confined compression, and Brazilian splitting tests. Both the cumulative numbers and locations of microcracks in different grains are recorded, and the types of macroscopic fractures are identified. The modeling results show that tensile cracks dominate the generated microcracks in the low confined compression tests, and the macroscopic fracture pattern is axial splitting. Shear cracks are dominant in the high confined compression tests, and the macroscopic failure pattern is X‐type shear failure. The simulated results are consistent with those observed in the laboratory tests, and thus, may assist in improving rock acoustic emission monitoring and understanding the damage process of rock.

This paper investigates the dynamic properties of compacted loess under wetting and drying (W-D) cycles. A series of tests were conducted on compacted loess samples, namely, the soil dynamic triaxial test and the scanning electron microscopy (SEM) test. The test results showed that the dynamic stress-strain relationship of the compacted loess under the action of W-D cycles accords with the Hardin–Drnevich model. The initial dynamic shear modulus (G0) and the maximum dynamic shear stress (τy) of the compacted loess first decreased and then increased with the number of W-D cycles (n) increasing. The damping ratio (λ) increased linearly with the dynamic strain (εd) increasing in the semilogarithmic coordinate. The defined change rate of the damping ratio (η) first increased and then decreased with the n increasing. The macrostructure and microstructure characteristics of samples in the process of W-D cycles indicate that the increasing number of pores in the humidifying process and the cracks on the surface and inside of samples during dehumidification lead to the structural damage and dynamic properties reduction of compacted loess. The main reasons for structure strengthening and dynamic properties increasing are that soil particle structure develops to mosaic structure, pore structure develops to uniform small pore, and matrix suction makes soil sample tend to be dense.

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