崩積層的地形特徵及崩積層的形成-以梨山崩塌地為例

Abstract

梨山崩積層主要由破碎板岩及其風化物質組成，經侵蝕產生凹凸緩起伏地形，具再次滑動之地質與地形條件。本研究旨在探討其滑動機制與軟弱層成因以及崩積層的地形特徵。本文研究內容及目的，包括進行地質鑽探取得品質良好之岩心；施作孔內造影獲取劈理位態以釐清滑動機制；孔內震波量測可輔助岩心判釋分層；以地電阻探查地層岩性改變；埋設TDR監測滑動深度以作為比對；航照判釋則可了解地形演變；數值地形模型(DTM)分析地形參數，以建立梨山崩塌區地形特徵參數範圍。 本研究採旋鑽法並搭配鋼索式取樣，輔以超泥漿□高分子穩定液為循迴水，提高夾大量黏土之破碎板岩岩心提取率，而崩積材料分類依據黃玉麟(2006)建議並加以修正。依孔內造影之劈理位態變化及過去資料推測，梨山崩積區研究場址B1、B4及B9滑動體深層之破壞方式為山崩潛移，而軟弱層成因則為潛移使岩體相互摩擦而成，與黃玉麟(2006)分析結果相同，但B4滑動體淺層存在一剪裂帶，其存在仍待釐清。而由破壞機制與軟弱層成因之結果，可推論梨山崩塌地之演變過程。地電阻與震波量測結果，對崩積層內之不同岩性產生不同反應:淺層黃色黏土夾板岩之電阻值及波速較低，表此層屬膠結不緊密，故縫隙大且含水多，反之，灰色黏土夾板岩數值皆較高，表此層較緊密，可推測黃色黏土其成因為堆積入滲，而灰色黏土則為風化之產物。 地形參數包含：坡度、坡向、曲率及粗糙度之分析，則可顯現地質與地形上之相關性，且經坡度、曲率及粗糙度三參數分析歸納後，可呈現一典型崩塌地，由崩落(凹陷陡峭)至堆積處(隆起平緩)之地形變化，與建立之地形剖面分析結果相似，而利用曲率及粗糙度更可推測崩積層積厚帶，其地形面起伏程度與崩塌次數的確存在正比關係，最後整合三參數結果並提出崩塌區地形特徵參數範圍，利用此範圍約略具有可區分出崩塌地不同之部位(頭部、趾部..等)之功用，若再加以詳細分析則單純以地形觀點即可定義出崩塌地特徵。

The Li-shan colluvial deposits are composed by the broken slate and its weathered soils. The ground surface exhibits concave-convex landforms which were formed by weathering and erosion. Thus, the terrain and geology exlpicit that landslide is easy to be triggered by rainfall or earthquake in the area. This thesis aims to investigate the origin of colluvial deposits and the weak layers in the deposits. Then, geological boring, in-situ tests, geophysical investigations, terrain analyzing were carried carried out. In-situ tests includes discontinuity measurement by a Borehole Televiewer (including Acoustic and Optical) and PS wave velocity measurement by a borehole suspension PS Logging system. Geophysical investigation includes electrical resistivity exploring and TDR monitoring. The 5mx5m Digital Terrain Model (DTM) was adopted for analyzing the topographic feature of the colluvial deposits. To obtain high quality core samples, this study used wireline coring method with the Neat Vis□ as the drilling medium. Based on the results of geological drilling and televiwer measurements, the materials of the colluvial deposits were classified according to Yu-Lin Huang(2006) and the origin of colluvial deposits was infered. The existed geological data and the results of the discontinuity measurement by televiewer reveal that the Li-shan colluvial deposits may be formed by a large-scale hillslope creep. The weak layer between the fresh slate and the colluvial deposits was caused by the rock formation rub each other. However, the weak layers in the colluvial deposits may be formed by weathering induced by groung water fluctuation. The inference of the origin of colluvial deposits and the weak layers in the deposits are agreed with Yu-Lin Huang(2006). The results of electric resistivity and wave velocity measurement show that the values of electric resistivity and wave velocity vary with material types. The values of resistivity and velocity value for shallow deposit of yellow clay with slate detritus (YS) are lower than those of grey clay with slate detritus (GS), which indicates that the GS is denser than the YS. We infer that the formation of YS was formed by infiltration and sedimentation, and the GS is the product of weathering induced by ground water. The parameters of terrain analysis include inclination, curvature and roughness, which can reveal the relationship between geology and terrain. The results of terrain analysis show that the range of the values of inclination, curvature and roughness varies with the locations of a landslide area, such as depletion zone and accumulation zone. It means that the accumulation zone of a landslide can be deduced from the results of terrain analysis. Associated with the mechanism of landslide, it can be found that the stronger of degree of roughness is the more of frequency of slope failure. Finally, a set of topographic parameters was presented to identify the characteristics of colluvial slopes.