軟岩河床之沖刷機制、理論模型、與分析方法

Abstract

以往土木工程所關心的沖蝕問題多侷限於沖積層，常忽略岩石河床（以下簡稱『岩 床』）與岩石河岸（以下簡稱『岩岸』）也可能受顯著沖蝕之機會。近年來國內不少攔河 堰、橋樑等跨河構造物下游側一再發生之河床、河岸大幅沖蝕，不但危及河床、河岸本 身之穩定，亦嚴重威脅跨河構造物安全或危及公共用水來源。特別當岩床或岩岸之地質 屬於年代較為年輕之軟岩或弱面較為發達之破碎岩體時，此類問題常常更為嚴重。國內 西部麓山帶很多攔河堰與跨河構造所在區域之地質即是屬於年輕或較為破碎之岩層，因 此經常出現過度沖蝕之現象，嚴重危及跨河設施之永續利用。然而現階段仍缺乏合宜之 學理與分析方法足以定量地掌握問題的關鍵。 本子計畫因此擬結合整合性計畫中其他的子計畫，針對年輕岩層河床的沖蝕機制深 入探討，試圖深入瞭解各種條件下之主控機制、探討影響因素、進而嘗試以岩石力學、 土壤力學、損壞力學、與破裂力學等為基礎以建立理論模型，期能最後用於研發可行之 量化分析方法。本計畫書提出三年之研究計畫，擬探討內容包括：(1) 相關文獻收集整 理、案例探討；(2) 不同條件下岩床主控機制之探討；(3) 個別岩石沖蝕機制概念模型之 建構；(4) 個別沖蝕機制之理論模型發展；(5) 個別沖蝕機制之影響因子參數探討；(6) 分 析方法與數值模型之研發；(7) 案例運用。

Conventional civil engineering does not usually pay much attention to the potential erosion of rock bed in river channel. However, rock bed erosion can sometimes be a serious problem. Recently, intensive erosion cases have been found in front of checkdams or bridges; the extent of river incision and widening had resulted in serious threat to the stability of cross-river structure or to the secure of public water supply. The rock-bed erosion problem was most serious in cases of soft rock or heavily jointed rock mass. Many checkdams and cross-river structures in the west foot-hill of Taiwan, however, do sit on formation composed of soft rock or jointed rock mass. Serious rock-bed erosion is sometimes triggered after the completion of cross-river structures. Unfortunately, the existing theory and analytical methods are not necessarily appropriate to analyze these types of problems in engineering scope. Toward improving the understanding on this category of problems, the three-year project aims to study the erosive mechanisms of soft rock in engineering scale. This project will try to investigate the dominant erosive mechanism for various conditions of rock properties, loading types, flow conditions, and so on. Conceptual and theoretical models in terms of the framework of rock mechanics, soil mechanics, damage mechanics, and fracture mechanics will be developed and finally be adopted in approaches for quantitative analysis. The scopes of this project include (1) literature review and case study; (2) investigation of dominant erosive mechanisms under various conditions; (3) construction of conceptual model for individual erosion mechanisms; (4) formulations of theoretical models; (5) parametric study for important factors that controls rock erosion; (6) development of analytical methods and numerical models for rock-bed erosion problems; (7) practical application.