裂隙地下水滲流及排水穩定工法對岩體邊坡變形影響以光華崩塌地為例

經由過去光華崩塌地調查報告得知，邊坡最大變形量發生在無降雨期間。然而目前關於光華崩塌地之形成機制仍屬於未知，且較少有針對地中原始資料進行探討。因此為了解該變形塊體形成之演育與崩塌機制，本研究透過地表地質調查建立光華崩塌地之地質模式，並推演光華崩塌地的形成與演育，針對區域內露頭進行岩體評分與岩心判釋成果印證所提出之地盤模式的合理性。再以地盤模式為框架，利用離散元素法模擬分析軟體UDEC探討光華崩塌地之演育過程與排水穩定工法之量化評估。本研究藉由模擬結果之塊體旋轉量大小，將光華崩塌地區分為A、B、C三區，其中B區為旋轉量最高的區域，也是目前光華崩塌地最活躍範圍。由數值模擬分析結果顯示，B區內主要破壞機制為傾倒破壞，在靠近崖頂的岩層有垂直向張力裂縫形成，容易促使地下水沿節理網絡流動往坡面滲出，而較深的位置未來也有可能形成滑動面；C區岩體則受到B區傾覆岩層推擠的影響，主要發生滑動行為，但在變形過程因塊體間節理的開裂順序不同而有塊體倒轉的現象，反映了現地調查所觀察到的位態翻轉，而C區塊體的滑動變形與互鎖效應也說明過去持續在此範圍內發生的崩塌與滲水；A區為相對穩定的區域，比對遙測影像確認此處為目前光華崩塌地崖部以上的農墾地與植生茂密處，根據塊體水平位移監測點顯示，C區為最先發生的事件，導致B區趾部缺乏支撐力而向下邊坡傾倒，後期則是B區推擠影響C區坡體外滑動。本研究更進一步考量地下水之敏感度分析，了解不同水壓力對崩塌地之穩定性影響，擬合出當左側之定水頭高為1250公尺時，會使C區塊體之水平位移量增大，因此將加入不同排水穩定工法進行數值模擬分析，同時觀察節理岩體內裂隙水滲流之影響，並量化其對坡體內之地下水位的影響。未來面對活躍地下水之節理岩坡時，可提供相關整治工法的配置與評估地下水位監測之位置。

關鍵字

地質模式；地盤模式；離散元素法；地下水；排水穩定工法

並列摘要

Based on the previous investigation reports on the Guanghua landslide, the slope has the largest amount of deformation during no rainfall. However, the deformation mechanism remains unknown at present, and few studies researched the subsurface data. To understand the evolution and landslide mechanism of the deformed block, this study established a geological model of the Guanghua landslide through surface geological surveys and deduced the formation and evolution of the Guanghua landslide. The outcrop scoring and core interpretation results confirm the rationality of the proposed ground model. Using the ground model as the framework, we further analyzed the evolution process of the Guanghua landslide and the quantitative evaluation of the drainage stabilization with the Universal Distinct Element Code (UDEC), the analysis and simulation software implementing the discrete element method. The simulation results show that the Guanghua landslide can be divided into three areas: A, B, and C, according to the magnitude of the block rotation. Among them, area B is the one with the largest rotation amount and is currently the most active area of the Guanghua landslide. Numerical simulation analyses show that the main failure mechanism in area B is toppling failure, and the formation of vertical tension cracks in the rock strata near the top of the cliff makes it easy for groundwater to flow in the joint network in this area and seep out to the slope. Deeper positions may also form a sliding surface in the future. The rock mass in area C mainly exhibits a sliding behavior, affected by the toppling strata in area B. In the process of deformation, the cracking order of the joints across the blocks resulted in rock mass inversion, which reflects the positional inversion observed in the field investigation. The sliding deformation and interlocking effect in the area C also indicate the landslide and water seepage that have occurred in this range in the past. Area A is relatively stable, and the telemetry imagery confirms this area is the farmland and dense vegetation above the cliff of Guanghua landslide. According to the horizontal displacement monitoring station, area C first caused a lack of supporting force in the toe of area B. The toppling and pushing of area B later on incurred the sliding of the slope outside area C. This study further considers the sensitivity analysis of the groundwater to understand the impact of different water pressures on the stability of the landslide. The simulation shows when the fixed water head on the left side is 1250 meters in height, the horizontal displacement of the area C will increase. Therefore, we performed numerical simulation analysis on different drainage stabilization methods, observing the effect of cleft water in the jointed rock mass and quantifying its influence on the groundwater level in the slope. This can be a reference for both the configuration of remediation methods and the evaluation of the groundwater-level monitoring when facing the jointed rock mass with active groundwater in the future.