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Effect of Fabric Anisotropy on Bifurcation and Shear Band Evolution in Granular Geomaterials
Jiangfang Chang,Wei Wang,Qinghe Niu,Lei Wen,Wei Yuan 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.8
Strain localization, usually manifesting as shear bands, is frequently observed in geomaterials and is of the essential reason inducing the failure of geostructures. Anisotropic characteristics of soils has an important effect on the shear band behavior. This paper is devoted to study the effect of the fabric anisotropy on the initiation and evolution of the shear bands. In particular, the anisotropy is introduced to the strength parameter of the yield criterion by incorporating the material principal direction and the joint invariant of the stress tensor and the microstructure tensor. Furtherly, an elasto-plastic constitutive model considering the fabric anisotropy is established in the micropolar theory framework, and is then applied to simulate the shear bands in transversely geomaterials via three numerical examples, including the plane strain compression test, slope stability and the shallow foundation problems. Moreover, the mesh independency of the proposed model is discussed. Results show that the bifurcation, the shear bands pattern, and the bearing capacity highly depend on the material principal orientation and the anisotropic degree. Comparison with existing study indicates that the proposed model has a good performance in simulating the typical pre and post strain localization behaviors of transversely isotropic geomaterials.
Wang Wei,Liang Xuanyu,Niu Qinghe,Wang Qizhi,Zhuo Jinyi,Su Xuebin,Zhou Genmao,Zhao Lixin,Yuan Wei,Chang Jiangfang,Zheng Yongxiang,Pan Jienan,Wang Zhenzhi,Ji Zhongmin 한국원자력학회 2023 Nuclear Engineering and Technology Vol.55 No.8
It is essential to evaluate the blasting-enhanced permeability (BEP) feasibility of a low-permeability sandstone-type uranium deposit. In this work, the mineral composition, reservoir physical properties and rock mechanical properties of samples from sandstone-type uranium deposits were first measured. Then, the reformability evaluation method was established by the analytic hierarchy process-entropy weight method (AHP-EWM) and the fuzzy mathematics method. Finally, evaluation results were verified by the split Hopkinson Pressure Bar (SHPB) experiment and permeability test. Results show that medium sandstone, argillaceous sandstone and siltstone exhibit excellent reformability, followed by coarse sandstone and fine sandstone, while the reformability of sandy mudstone is poor and is not able to accept BEP reservoir stimulation. The permeability improvement and the distribution of damage fractures before and after the SHPB experiment confirm the correctness of evaluation results. This research provides a reformability evaluation method for the BEP of the low-permeability sandstone-type uranium deposit, which contributes to the selection of the appropriate regional and stratigraphic horizon of the BEP and the enhanced ISL of the low-permeability sandstone-type uranium deposit.
Relationship of fractures in coal with lithotype and thickness of coal lithotype
Pan, Jienan,Wang, Haichao,Wang, Kai,Niu, Qinghe Techno-Press 2014 Geomechanics & engineering Vol.6 No.6
The fractures in coal are the main migration and output channels of coalbed methane, directly influencing the permeability of the coal seams. It is of great significance to study the effect of fracture distribution in coals on the permeability of coal seam. The development rules of endogenetic and exogenetic fractures are different among various coal lithotypes. There is also difference in the fracture density for the same lithotype with different thicknesses. Through the observation and description of the macroscopic fractures in coal and the origin of fractures in coal, the effect of the coal lithotype and its thickness on fracture development in coal was discussed. It was found through the study that the density of fractures in vitrain band was the maximum for the same coal rank and thickness, followed by clarain band. There were few fractures developed in the durain band. However, the changes of fracture density in three types of bands presented different declining trends for low, medium and high coal rank. There were no fractures developed in the fusain. There were three variation patterns for the fracture densities at the same coal rank and coal lithotype: linear decrease, nonlinear decrease, and first decrease then remaining unchanged. However, the overall trend was that the fracture density decreased with the increase of thickness of coal band for the same coal rank and coal lithotype.