ABSTRACT:A spatial data management and analysis frame is required for global problem application. Global Discrete Grid (GDG) has seamless, excellent hierarchy characteristics. GDG has been used for spatial data management, indexing and cartographic generalization. However, most GDGs are unequal-area. To extend GDG application ranges in spatial modelling and statistical analysis, the method for constructing hierarchical and equal-area GDG is discussed in this paper. The detail steps to build GDG based on inscribe polyhedron is presented. The method of transferring polyhedron surface grids onto sphere surface is described. The ratio of max, min length of grid edges and grid angle is acquired. Length ratio converges to1.7 and angle ratio converges to 3.0. The result indicates that there exists difference in length and grid angle and the ratios of them are convergent.
Due to the extensive excavation of open-pit coal mines in northwest of China, the rock slopes formed by special environments are subjected to freeze-thaw (F-T) action, which has a certain impact on their stabilities. In order to evaluate the mechanical properties and micro damage characteristics of coal under different freeze-thaw cycles, uniaxial compression experiments combining acoustic emission tests were conducted. The results suggest that as the number of freeze-thaw cycles increased, elastic modulus of coal samples decreased, the samples showed ductile damage characteristics and initial compaction stage gradually increased. Compared with unfrozen-thawed coal sample, the compressive strength of the coal samples decreased by 23.27% after 10 F-T cycles, 31.06% after 15 F-T cycles, and 36.01% after 20 F-T cycles. The internal fissures in the coal samples transitioned from tensile fissures to shearing fissures, and the samples gradually showed tensile-shear combined failure. The final cumulative energy of the coal sample became lower, the cumulative energy duration increased and the time point of the energy surge was delayed with the increase of cyclic freeze-thaw times. A damage model based on the evolution law of the cumulative energy was established to bridge the gap between macro-micro damage mechanics.
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