北橫公路沿線岩坡傾倒破壞之研究

A study on the Toppling Failure of Rock slopes along the Northern Cross-Island Road

陳志豪(Chih-Hao Chen)

指導教授 ： 葛德治

中原大學/工學院/土木工程研究所/碩士(2001年)

https://doi.org/10.6840/cycu200100135

摘要

台灣地區位處西太平洋亞熱帶，年年豪雨颱風頻繁，長期性的風化致使原本陡峭山坡上之岩體多為破碎，山多平原少的特點造成山坡地的開發與日俱增，因此邊坡穩定的問題十分的重要。
根據塊體運動的不同機制，將山崩細分為落石、傾倒、滑動、土石流等四種形式。一般而言傾倒破壞發生在層狀岩層之逆向坡，只有極少數發生在高角度的順向坡。此類破壞主要始於坡趾處，屬於漸進式破壞，一但誘發即持續進行且其擾動範圍逐漸向坡內擴大 (即愈晚整治所需成本愈高)。
本文主要研究北橫公路復興至巴陵段逆向岩石邊坡，借由現地探勘及運動學分析挑選十個具有傾倒潛能之區域，做為傾倒破壞模擬之研究。根據現地資料使用TOP 程式建立基本岩坡幾何，並分析各岩坡之安全係數 (F.S)。另外以硬度鎚之值轉換得岩塊楊氏係數 (E) 配合DDA 程式模擬在提高安全係數的情況下，於坡趾處所需要之水平支撐力大小，並評估坡趾開挖對邊坡之穩定性影響。在文中也對TOP 和DDA 做驗證模擬。
TOP 分析結果顯示，10組案例安全係數介於 1~1.15 之間，皆屬於偏低，其中案例 2、5 者近似於一此與現地調查之落石遺跡和持續整治工程現況大至吻合。以 DDA 模擬在 FS=1.2 時於坡趾所需施加之水平支撐力，與 TOP 比較發現 DDA 較為保守，該範圍值可做為整治施工之參考依據。另外由岩坡坡趾開挖模擬結果得知，現地岩坡不容許任何的開挖動作。

關鍵字

TOP 程式 ； 安全係數 ； DDA 分析法 ； 逆向坡 ； 傾倒坡壞

並列摘要

Because of its inferior geological conditions and environmental factors, intense geological hazards like slope failure have been a serious issue in Taiwan. Among several modes of slope failure, toppling always happens in the anaclinal rock slopes composed of one single steeply-dipping discontinuity set. According to rock characteristics and discontinuity spacing, toppling failure can be classified further as block, flexural, and block-flexural types. Failure of this kind often initiates at the toe of a slope, and gradually propagates upslope, causing a progressive type of failure. The main objective of this thesis is to establish a comprehensive methodology of analyzing the stability of rock slopes mainly involving the block-toppling mode, by taking the cases along the Northern Cross-Island (NCI) Road for example.
Three different kinds of stability analyses are used in this thesis, i.e., kinematics analysis (KA), limit equilibrium method (LEM), discontinuous deformation analysis (DDA). KA is conducted merely based on the three-dimensional orientation data of rock slope and discontinuity, and it is a simple tool to identify the toppling potential spots over large areas. The LEM used is the TOP code, in which a rock slope is idealized as a system of rigid columnar blocks formed by one discontinuity set, and it can be utilized to quickly determine the safety factor (FS) of a slope as well as the support force at the toe (P0). DDA is otherwise a sophisticate discrete analysis which deals with the complex interactions of multiple deformable blocks, and it can yield more precise estimates of FS and P0 based on the computed displacement history of selected control points. According to the methodology proposed in this thesis, KA, TOP, and DDA are adopted to prescreen a number of sites of interest, to calculate the FS values of these prescreened sites, and to determine the P0 values and disturbed zone of some critical sites, respectively.
The NCI Road chosen for illustrative purpose is located in the northern part of Shen-Shan Geologic Region, and its route is mainly covered by inter-bedded sandstone and shale. By reviewing previous geological records and performing KA, ten sites were selected along the road, followed by field data collected including the corresponding idealized profiles of rock slopes. The analysis results of TOP code show that the FS values of these sites vary from 1.00 to 1.15, and three sites with the lowest FS values match their field observations, i.e., continuous toppled mass near their toes. DDA simulation results indicate that the P0 values of these sites for a FS of 1.20 are in the magnitude of 10ton/m, and no further horizontal excavation at the toe is allowed for every site under investigation.

並列關鍵字

DDA ； safety factor ； anaclinal slope ； toppling failure ； TOP code

參考文獻

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