Search

Recent research found that stress state and relative density could influence internal instability significantly, however, current internal stability criteria were material-specific, and the effect of stress and density were not accounted for. Furthermore, current criteria were drawn from the dense soils, which could lead to unconservative assessments of loose soils. Because of this, this paper proposes a theoretical internal stability classification chart with considerations of soil density and applied stress. Based on soil fabric and force transmission, a texture triangle chart for three-component mixtures made up of coarse grains, fine grains, and voids was proposed through theoretical analysis of the void filling mechanism in coarse grains. The proposed chart demarcated the boundary between internally stable and unstable granular soils and the boundary between suffusion and suffosion phenomena for internally unstable granular soils. The classification chart relied on identifications of maximum and minimum porosities that coarse grains, fine grains, and coarse–fine mixtures may attain. The internal stability of coarse–fine mixtures with various densification levels could be evaluated by plotting their position in the proposed texture triangle chart. The influence of applied stress on internal stability could also be evaluated in this proposed chart by assessing the changes in volumetric strain. [ABSTRACT FROM AUTHOR]

Catalytic oxidation of toluene over noble metal catalysts is a representative reaction for elimination of volatile organic compounds (VOCs). However, to fully understand the activation of molecular oxygen and the role of active oxygen species generated in this reaction is still a challenging target. Herein, MgO nanosheets and single-atom Pt loaded MgO (Pt SA/MgO) nanosheets were synthesized and used as catalysts in toluene oxidation. The activation process of molecular oxygen and oxidation performance on the two catalysts were contrastively investigated. The Pt SA/MgO exhibited significantly enhanced catalytic activity compared to MgO. The oxygen vacancies can be easily generated on the Pt SA/MgO surface, which facilitate the activation of molecular oxygen and the formation of active oxygen species. Based on the experimental data and theoretical calculations, an active oxygen species promoted oxidation mechanism for toluene was proposed. In the presence of H2O, the molecular oxygen is more favorable to be dissociated to generate •OH on the oxygen vacancies of the Pt SA/MgO surface, which is the dominant active oxygen species. We anticipate that this work may shed light on further investigation of the oxidation mechanism of toluene and other VOCs over noble metal catalysts. [ABSTRACT FROM AUTHOR]

Failure frequency of a dam varies greatly with reservoir water level and time. It is important but difficult to dynamically estimate failure frequency of high concrete faced rockfill dams (CFRDs) merely based on the probabilistic approach due to limited failure cases of high CFRDs. In this study, a new method is developed for dynamically estimating the long-term revolution of seepage failure frequency of high CFRDs by combining an analogical approach with the Bayesian approach. A simple and precise seepage generalized method and a parameter named defect parameter are introduced to provide the basis of comparison between the dam of interest and the accumulated database of high CFRDs. Using the cumulative probability distribution from the database, the correlation between annual seepage failure frequency and defect parameter is established. A high CFRD case in China with an operation history of slab breakage and reinforcement is selected as an example to illustrate the applicability of the new method. It is verified that the variation tendency of safety level of high CFRD is well simulated through the annual seepage failure frequency calculated by the newly proposed method. [ABSTRACT FROM AUTHOR]

The recognition of stress-strain characteristics of soil under stress path of cyclic spherical stress and constant deviator stress is not sufficient, which can enhance understanding of structural behavior during cyclic variation of pore water pressure. Triaxial tests with cyclic spherical stress were carried out on Fujian sand. The influence of consolidation deviator stress on the stress-strain relationships was discussed. The results showed that the cyclic loading of spherical stress led to significant volumetric strain and shear strain in soil. The volumetric strain increased/decreased with the increase/decrease in spherical stress in each cyclic process. The relationships between volumetric strain and the logarithm of spherical stress could be approximately described as linear. The shear strain progressively increased with the increase in spherical stress in each cycle, but the growth was all less than 0.1%, and could be neglected. When spherical stress decreased, the shear strain featured diverse trend under different deviator stress, but the variation was on the same line with the increase in stress ratio, so the stress ratio was the key factor affecting the shear strain. The influence of consolidation deviator stress on the volumetric strain was little during the initial loading stage and became obvious during the subsequent reloading and unloading stage. The accumulative volumetric strain under different deviator stress was almost uniform. The consolidation deviator stress had great influence on the accumulative rate of shear strain, and the conspicuous initial deviator stress usually determined the development direction of accumulative shear strain. [ABSTRACT FROM AUTHOR]