Evolution of fault-induced fold at Chushan excavation site, central Taiwan, derived from numerical analysis of PFC simulations
| Autor: | Chia-Hsiang Hsu, 徐家祥 |
|---|---|
| Rok vydání: | 2016 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 104 Exposures in the Chushan trench were 40 m long and 10 m deep, excavated across a 1999 earthquake-induced escarpment of 2 m high. There were two main structure profiles, called north wall and south wall. On south wall the fold was truncated through along the axial trace of its anticline by a fault branch with a dip angle of 32 degrees and a maximum separation of 4.2 m while on the north wall the steep limb of the fold was displaced up to 3.0 m along the axial trace of its syncline by another fault branch with a dip angle of 24 degrees. The distance between two walls was only 14 m. This study intends to explore the geometerail condition of the site when the site fromed the pure monocline which is before the heterogeneous structure and explore how this heterogeneous structure might form using distinct element simulation of basement faulting. This study uses Particle Flow Code (PFC) based on discrete element method, regarding material as assembled rigid particles. The rigid particles can be connected by two types of bond models. Because the PFC parameters are different from geomaterial mechanic properties, we cannot directly use the values of geomaterial mechanic properties. In order to attain the values of PFC parameters equailvent to the mechanic properties. PFC simulations of direct shear test and bilateral test are perfomed. All our models consist of two mechanical layers, including an upper clayey layer of 7 meters thick and a lower gravelly layer of 8-15 meters thick, as revealed by the excavation, a borehole nearby and soil tests. At the vertical displacement of 3.6 meters, Our results show that the monocline fold can be simulated by a low-angle reverse faulting similar to a subsurface dominant fault with a dip angle of 24 degrees derived from the trench site at the ground surface and in a borehole in the hanging wall, and the monocline structure can only generate when the cohesion of the clay layer is 11~12 kPa. Furthermore, the different structures on the two exposures were mainly controlled by the dip-angle variation of the upper part of the subsurface dominant fault. The simulation of reverse faulting with a dip angle of 24 degrees shows a monocline forms in the clayey layer, and then a gravelly wedge starts to protrude into the clayey layer and displace it along the axial trace of the syncline similar to the structure on the north wall, and the simulation of reverse faulting with a dip angle of 32 degrees shows a monocline forms in the clayey layer, and then this monoclinal clayey layer starts to be displaced along the axial trace of the anticline similar to the structure on the southern exposure. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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