| 摘要: | 地電阻影像剖面法可以獲得地下連續性之電性地層剖面資料，具有技術成熟與資料穩定之優點，且對於含水與含泥質地層有較敏銳之反應。在崩塌地之探測應用上，常因崩積層與岩盤之電阻率對比明顯而有良好之成果，配合電井測方法獲得之地下水流動層次、地質及水位監測資料，可進一步獲得測區之崩滑機制與水文地質模式。 本研究應用於台灣中部之梨山地滑東南區與石岡岡仙巷地滑區進行崩滑區之機制研究。可獲得下列成果： 1.根據電阻率之差異與鑽孔岩心之對比，可將梨山地滑東南區之地層區分為崩積層、剪裂帶與板岩。其中剪裂帶具低透水性，在地下形成地下水流之自然障礙，在來自福壽山農場源源不斷之地下水供應下，使得剪裂帶上方之地下水位維持動態平衡。電阻率剖面顯示崩積層之形貌呈一連串之凹弧狀，顯示為由下至上之向源侵蝕及反覆崩塌後所形成，此應與構造運動抬升造成地形之加速侵蝕有關。 2.岡仙巷地滑區之等電阻率曲線與岩層層面位態相當符合，顯示電阻率主要受控於岩性，係因岩層透水性低、節理與裂隙發育不良。可進一步推估岩層中之地下水對邊坡穩定之負面影響甚低，惟當大量雨水入滲聚集在崩積層內，無法及時排除，增加重量與降低抗剪強度，形成崩滑並可能影響至淺部岩層。靠近火燒坪台地側岩坡之解壓節理開口現象明顯，風化程度亦高，岩體易崩落，顯然與來自於台地具高水力坡降之地下水滲入有關。 Resistivity Image Profiling (RIP), a mature technique and that provides stable quality data, can acquire a continuous subsurface image. Moreover, it is sensitive to water and fine content. In general, the significant results can be produced at landslide due to high contrast of resistivity between colluvium and bedrock. Combining RIP, groundwater mobility obtained from E-Logging, geological and groundwater level data, the mechanism and hydrogeological model of landslide can be further determined. The southeastern part of Lishan and Gangxianxiang landslide areas of central Taiwan were chosen as study sites. The following conclusions can be drawn: 1. The southeastern part of Lishan landslide area: Based on RIP and rock samples collected from boreholes results, three electrical strata are recognized; colluvium, the shear zone composed of shear gouges and shattered slate, and the undisturbed slate formation. The steep shear zone serves as aquitard, it forms a natural barrier which blocks and retains groundwater flowing down the slope. Groundwater will brim over the barrier when the water level is high. Sufficient supply of groundwater from Fushoushan Farm creates a dynamic balance of groundwater with a stable water level where is higher than shear zone. A series of curved basal surface of the colluvium associated with the main slope failure shown from resistivity variation indicated that the slope migrated upwards, this may be caused by the uplift of the tectonic movement. 2. Gangxianxiang landslide area: The trend of iso-resistivity line in bedrock is similar to the bedding plane, it indicates that lithological characters dominate resistivity. The low permeable bedrock with poor developed joint and fracture can be further inferred. The groundwater within the bedrock lowers the negative effect on slope stability. When a large quantity of groundwater accumulates in the colluvium; this increases the downward force of the slope and decreases the resistance of surface between colluvium and bedrock. The sliding surface occurred from colluvium down to shallower bedrock. The open release joint of rock slope, highly weathered, near upslope Huoshaoping Terrace is well developed. The rock body, cut by joints, collapse easily, it must be related to groundwater flow with higher gradient from Huoshaoping Terrace. |
