以三維個別元素法模擬卵礫石層的物理特性

Modeling of Physical Properties in Gravel Formation Using Three-Dimensional Distinct Element Method

徐薇(Wei Hsu)

指導教授 ： 徐松圻

朝陽科技大學/理工學院/營建工程系/碩士(2009年)

摘要

由於卵礫石之力學行為與卵礫石顆粒大小、形狀、排列方式、細料含量及性質等均有密切關係，卵礫石為大小不同之顆粒所組成，卵礫石層的性質主要控制於顆粒間之互鎖、相互滑動和滾動及粒徑大小分佈等，應視為不連續體來模擬分析，而且細顆粒土壤(如粉土及黏土)甚至砂土的含量在台灣中部卵礫石層中比例較少，粗顆粒土壤的含量在卵礫石層中的比例較多，對於卵礫石層的工程特性與行為也有較大之影響。
本研究內容主要分為兩大類，第一種主要是利用個別元素法為主數值分析軟體PFC2D與PFC3D，在不同摩擦角、不同邊界條件及不同粒徑之條件下模擬分析其孔隙率與側向土壓力係數K值。來比較PFC2D與PFC3D之差異性，並做卵礫石層相關物理性質之比較。第二種主要是以台灣西部麓山地帶之卵礫石層為研究對象，以PFC2D與PFC3D數值分析軟體進行現地直接剪力試驗之模擬。
由分析結果顯示，顆粒間摩擦角愈大孔隙率會逐漸上升而側向土壓力係數則會逐漸變小，多種粒徑之孔隙率會小於一種粒徑之孔隙率而多種粒徑之側向土壓力係數會比單一粒徑的K值大一些，而顆粒霣降時也會受到兩邊界影響。利用2D與3D模擬直接剪力試驗結果顯示，當大顆粒粒徑百分比增加時其迴歸出來的摩擦角越大，剪動速度及顆粒的旋轉性也會影響整體剪力強度。直剪上下盒開口之尺寸對於摩擦角也並無太大之影響。

關鍵字

PFC ； 個別元素法 ； 卵礫石

並列摘要

The mechanic behavior exhibited by gravels is closely related to gravel size, shape, distribution, fines content and property. Gravels comprise granular materials of various sizes. The properties of gravel layer are mainly determined by interlocking, slipping among gravels, rolling and diameter. Gravels should be regarded as a discontinuation for simulation and analysis. There is lower fines content (such as silt and clay) and sand, and higher percentage of coarse-grained soil existing in the gravel formation in central part of Taiwan. These coarse-grained materials cause greater effects on the engineering characteristics and behavior while working on a gravel layer.
The contents of this study are divided into two major sections. In the first section, distinct element method based numerical softwares, PFC2D and PFC3D, are applied to simulate and analyze the porosity and the coefficient of lateral earth pressure, K, under the conditions of different angles of friction, boundary conditions and gravel diameters. The comparisons in the differences between PFC2D and PFC3D as well as the comparisons in related physical properties of a gravel layer are made accordingly. The second section deals with the gravel layers located in the mountains in the west of Taiwan. These two and three dimensional softwares are used to simulate the direct shear test performed in situ.
The results obtained from the analysis showed that a bigger angle of friction between particles would lead to increasing porosity and decreasing coefficient of lateral earth pressure. Porosity formed by gravels of a variety of diameters was smaller than that formed by gravels of one granular diameter. Meanwhile, the coefficient of lateral earth pressure,K, formed by gravels of various diameters was bigger than that by gravels of a single diameter. The subside of granular material was influenced by the two lateral margins. The results obtained from the simulated 2D and 3D direct shear tests indicated that the material with higher percentage of bigger diameters is relative to have bigger angle of friction after regression of analyzed result. The size of opening gap between upper and lower direct shear boxes has no significant effect on the angle of friction.

並列關鍵字

distinct element method ； PFC ； gravel

參考文獻

3. 鄧屬予，「台灣卵礫石層的地質背景」，，地工技術，第55期，第7頁，1996。

18. 賴泊靖，「以分離元素法模擬卵礫石層中地錨拉拔行為」，朝陽科技大學，碩士論文，台中，2009

17. 黃任中，「平面應變試驗離散元素法數值模擬與土壤參數標定研究」，雲林科技大學，碩士論文，雲林，2008

4. Matheson, Gordon M., “Relationship between Compacted Rockfill Density and Gradation,” Journal of Geotechnical Engineering,ASCE, Vol.11,No 12, pp 1119-1124 (1986)。

8. Ting, J. M., Corkum, B. T., Kauffman, C. R., and Greco, C., “Discrete Numerical Model for Soil Mechanics,” Journal of Geotechnical Engineering, ASCE, Vol.115, pp. 379−398, 1989.