| Summary: | 碩士 === 國立中興大學 === 水土保持學系所 === 101 === Gravel formations are widely distributed in Taiwan, and cause many problems in construction process. Gravel formations are a complex geology material with mechanical parameters usually obtained by laboratory experiments, in which the remodeled specimens would always be disturbed and the specimen size is limited. Only a few researchers conducted large in situ direct shear test or plate-load test due to time, expense, and hard work. In order to be more effective when discussing the problems of geologic materials on both engineering and environment, more and more researchers adopt numerical analysis instead of traditional experiments. In this study, PFC2D which is based on discrete element method was adopted to simulate biaxial tests, and establish the relationship between macro and micro parameters. Macro parameters are strength (A), elastic modulus (E), and poisson ratio (ν); micro parameters are normal stiffness (kn), ratio of shear to normal stiffness (ks/kn), and friction coefficient (f). Through Multiple Regression Model we could obtain three equations. When the value of A, E, υ are all known, the three equations can be solved and the micro parameters are obtained. The results show that the error of empirical equations is satisfactory. Next we compare the results of the models with and without matrix. The strength and elastic modulus of the model with matrix are higher than those of models without matrix, but poisson ratio was on the opposite. Then PB design is used to study the relative influences between macro and micro parameters. The strength (A) is highly influenced by the friction coefficient (f); the influences of individual micro parameters on elastic modulus (E) are not so different, whereas the influence of kn is a little bit higher; Poisson ratio (ν) is highly influenced by ratio of shear to normal stiffness (ks/kn). At last, we investigate the influence of the maximum size and the contents of gravel on macro parameters, and the results are consistent with the conclusions of former researchers. The bigger size or the more contents of gravel, the higher value of A, E, ν, and φ, but the lower value of c. As a result, the numerical models are feasible to simulate mechanical behavior of gravel formations.
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