褶皺的曲滑作用模式數值模擬初探

Flexural Slip Model of Buckling Folds －Numerical Simulation & Analysis

鄭添耀(Tian-Yao Jeng)

指導教授 ： 鄭富書 ； 林銘郎

國立臺灣大學/工學院/土木工程學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.00503

摘要

本研究採用數值方法針對褶皺構造在曲滑作用下的力學行為進行分析。在前人的研究中，已成功推導出單層與複層褶皺的彈性理論解，惟理論背景有相當的簡化，無法全然的反應出自然界所見褶皺軸部產生破碎空洞、層面間相互滑動產生擦痕之地質構造，故本研究以前人提出之彈性理論解為基礎，使用彈塑性材料進行模擬比對，並探討曲滑作用對褶皺構造之影響，最後以分離元素法進行褶皺大變形行為之模擬，期望能更近似的模擬自然界所見之褶皺構造。
研究結果顯示：彈塑性褶皺生成後繼續壓縮，則褶皺軸的位置會產生變動而造成波數的增加，波長的減短。對振幅衰減波型之褶皺構造而言，受到岩層彈塑性行為的影響，提早產生挫屈形成雙頻褶皺，波數增加，波長有減短的趨勢。
褶皺軸部空洞(cavity)的產生和界面摩擦性質有助於岩層挫屈時，褶皺振幅的增長。褶皺軸部空洞的產生，使得介質反力下降，褶皺生成時低頻波長因而有增長的趨勢，但界面摩擦性質有助於彌補介質反力的損失。
曲滑作用在複層褶皺的模擬，成功的印證Currie et al. (1962)所提出以能量法推導得複層褶皺之理論公式，界面摩擦性質有助於增加所對應的單層等效層厚，促使褶皺生成時高頻波長增長，低頻波長減短。
由分離元素法模擬褶皺之發育，可成功的將褶皺的發育階段分成四個時期：(1)預壓縮階段。(2)岩層挫屈生成圓弧褶皺，褶皺軸部為了調適空間而產生空洞。(3)圓弧褶皺變形為尖頂褶皺，軸部產生塑性鉸。(4)褶皺軸部的破裂造成強度的喪失，褶皺開始壓扁變形，軸部的空洞閉合。

關鍵字

尖頂褶皺 ； 曲滑作用 ； 挫屈 ； 彈塑性 ； 界面性質 ； 數值模擬

並列摘要

The flexural slip folding of buckling folds is studied based on numerical analyses. In previous studies, the elastic theoretical solutions of single layer and multilayer folds have been formulated. However these analytical solutions are based on simplifications. Some of the geological structures in the field, such as the hinge cavity of folds and the slickenside formed by flexural slip folding are still awaiting for further exploration regarding the mechanism. In this research, elasto-plastic material was adopted in numerical simulation and compared with the elastic theoretical solution. The influence of flexural slip folding on folds is then discussed as well. In the end, simulation of the large deformation behavior of folds was conducted by using bonded particle model.
The results of study show that: For an unconstrained elasto-plastic layer under compression, the wavelength can be shortened in post-buckling stage. As to folds with decaying amplitude, the elasto-plastic behavior leads to an early buckle folding and shortens the wavelength.
The appearance of cavity results in reduction of the reactive force exerted by the matrix and increases the low-frequency wavelength; on the other hand, the interface friction can counteract the effect.
The flexural slip model of multilayer folds compares well with the theoretical solution by Currie et al. (1962). For multilayer folds, the interface friction tends to increase the high-frequency wavelength and shorten the low-frequency wavelength. Cavity and interface friction tend to increase the amplitude of fold.
From the simulation of fold growth by bonded particle model, it can be divided into four stages：1. Initial compression stage; 2. Circular fold yielded and cavity was formed; 3. The plastic hinge was formed, then circular fold turned into chevron folds; and 4. The folds were flattened and the cavity was filled with matrix.

並列關鍵字

chevron fold ； flexural slip ； buckle ； elasto-plastic ； interface properties ； numerical simulation

參考文獻

黃國品（2006）：單層岩層褶皺力學機制探討，國立台灣大學土木工程研究所博士論文，台北。

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Jeng, F. S., Lu, C. Y. and Chang, N. G., 2001. Buckle folding of elastic strata. Proceedings of 10th International Conference on Computer Methods and Advances in Geomechanics, Tucson, USA, 1309-1312.