崩積地層的組成及形成機制-以梨山地區為例

Abstract

梨山崩積地層主要由破碎板岩及其風化形成的土壤所組成，後經侵蝕作用造成凹凸之緩起伏地形，存在著再滑動之地形條件與地質條件。本研究之主要目的為利用優質的地質鑽探、現地試驗及地形分析結果，探討梨山地區崩積地層的組成以及形成原因。現地試驗包括用孔內造影及懸垂式P-S波量測，地形分析則使用5m x 5m 數值地形模型(DTM)分析崩積地區之地形指標。 本研究使用旋鑽法搭配鋼索式岩心取樣，並以超泥漿□高分子穩定液作為鑽探循迴水，對於軟弱黏土層以及膠結黏土之風化板岩層，其岩心取樣率甚高且品質優良。考慮力學行為及形成條件，以鑽探所得岩心為基礎，本研究將梨山崩積層崩積材料重新分為五類，第一類灰色板岩夾黃色黏土(SY)；第二類灰色板岩夾灰色黏土(SG)；第三類灰色板岩(S)；第四類灰色黏土夾灰色板岩碎屑(C)；第五類回填土(BF)。 根據過去地質資料以及孔內造影之不連續面位態資料統計結果推論，梨山崩積地區可能為早期大規模山坡潛移破壞所造成。研究場址之B-9滑動體存在上下兩層軟弱層，推測其上層軟弱層可能因地下水位上下變動加速風化所形成；而下層軟弱層推測可能因大規模山坡潛移破壞，上下岩體剪動所形成。

Li-shan colluvial deposits are composed by the broken slate and its weathered soils. The surface of the ground exhibits the concave-convex landforms which are formed by weathering and erosion . Thus, the terrain and geology reflect that landslide is easy to triggered in the area. This thesis aims to investigate the compositions and the origins of Li-Shan colluvial deposits by the results of geological boring, in-situ testing, terrain analyzing. In situ tests includes discontinuty measurement used by the Borehole Televiewer (including Acoustic and Optical) and P, S wave velocity measurement used by the suspension PS Log system. The 5m x 5m Digital Terrain Model (DTM) analyzes the topographer indexes of the colluvial deposits. To obtain the excellent quality core samples, this study used wireline coring method and Neat Vis□ as the drilling medium. The high quality cores are used to establish the colluvial deposit classification and study the origins of colluvial deposits. According to the existed geological data and the results of the discontinuty measurement by Borehole televiewer, Li-shan colluvial deposits may be formed by large-scale hillslope creep. Research field, B-9 lanslide exists two weak layers which composed by silts, clays, and slate gravels, the upper formation originates possibly the ground water level changing frequently to accelerate the weathering speed; the lower formation may be the weathered product of a shear zone caused by the large-scale hillslope creep, which made the rock formation rub each other.