| Summary: | 碩士 === 臺灣大學 === 土木工程學研究所 === 98 === Engineers are accustomed to using finite element method (FEM) to simulate the failure problem in sand. In this way, however, they are unable to solve the case with rapture and rolling. In order to analyse the real stress and strain situation in soil, more and more researchers choose to use distinct element method (DEM) to simulate the physics experiment and field problem. Nevertheless, the shear zone localization is still a significant issue to be further studied.
In order to localize the shear zone, this research simulates the most basic soil experiment, direct shear test, by using a DEM software PFC2D, trying to propose a method which can point out the shear zone location. According to a structural geologic analysis method recommended by Ramsay and Huber (1983), this study defines the homogeneous strain in the soil by ellipticity R. R is a relative physical quantity to shear strain γ which is more familiar to engineers. Then this study set many grid points in the direct shear test simulation, separating the simulating soil into several squares with same area size. Every square is a shear strain calculating unit named grid square. The shear strain can be regarded as homogeneous if the grid square is small enough, and then the shear strain of the grid square can be represented by the ellipticity R. Combining two definition mentioned above, we can calculate the shear strain of every single grid square. Then, it is clear to localize the shear zone by giving every square different color related to its shear strain. Finally, this study also localize the shear zone in the fault sand box simulation and land slide simulation, and compare the result in the fault sand box in this study with the research studied by Chung (2007).
No program can calculate the ellipticity in PFC2D, so in this study matrix calculating software MatLab is used to develop a program that can solve this problem.
The simulation results indicate that the shear zone in the direct shear test is horizontal and its shape looks like lens. Also, particle rolling inside the shear zone can be observed. In the fault sand box simulation, the result demonstrates the development of the shear zone and the fault tip of tri-shear zone. In the land slide simulation, the result demonstrates the development of sliding surface and the appearance of tension crack.
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