向上滲流水對順向節理岩體邊坡可滑動體形成之影響

The Influence of Upward Ground Water on Sliding Blocks Forming in Consequent Slope of Jointed Rock

陸安(An Lu)

指導教授 ： 林銘郎

國立臺灣大學/工學院/土木工程學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201803892

摘要

近年來，岩石邊坡中的向上滲流地下水對邊坡穩定性的影響逐漸受到重視與研究，與其相關的案例有國道三號3.1公里順向坡崩塌和烏來忠治順向坡崩塌，兩者崩塌之促崩因子之一皆為向上滲流地下水。此外，並非所有的順向坡滑動破壞均會導致大量岩塊從邊坡上滑落，岩石邊坡中高角度節理的分布會限制滑動岩塊的大小，形成順向坡跳階破壞（Step-path failure），如汐萬路二號橋邊坡崩塌和碧山巖邊坡崩塌，兩者皆為順向坡跳階破壞。本研究中之陽明大學崩塌案例即是以向上滲流地下水為促崩因子之順向坡跳階破壞。
民國107年2月13日凌晨，國立陽明大學校園中研究大樓與實驗動物中心前方邊坡發生崩塌，此崩塌之邊坡為砍腳順向坡，沿砂頁岩互層與砂岩層交界面滑動。發生崩塌前並無強烈降雨，唯2月6日花蓮外海發生規模6.4地震，此次邊坡崩塌在地震後7日發生，因此推測地震並非主要促崩因子。陽明大學校區分布於順向坡之上，透過現地調查可以得知校區內砂岩層中高角度節理密集分布，可形成地下水水脈，故研判陽明大學邊坡崩塌的促崩因子為地下水。而邊坡崩塌後坡面上之殘餘塊體呈現階梯狀，從階梯狀殘餘塊體推測該岩石邊坡似乎因受走向節理切割，在遭受地下水影響後形成順向坡跳階破壞。
由於目前較少文獻探討以地下水為促崩因子之順向坡跳階破壞，因此本研究將以三種研究方法，分別為現地調查、物理模型與應用離散元素法軟體進行現地案例數值模擬，探討地下水對順向坡跳階破壞之影響。
本研究透過現地調查，除了找出主控此次崩塌之滑動面於陽明大學校區的出露位置以提供後續校園邊坡安全性評估使用之外，也依據陽明大學校區地質背景建立地質概念模型，提出此次邊坡崩塌之破壞機制。
隨後透過滲流傾斜儀設置半定性之物理模型，滲流傾斜儀平台底部之出水孔供水模擬現地之向上滲出地下水，並用雙層石膏塊體模擬現地含走向節理之岩石邊坡，物理模型中會改變出水孔開啟位置、傾斜儀傾斜角度與石膏試體擺放位置，討論向上滲流地下水對可滑動塊體形成範圍之影響。物理模型結果顯示出水孔開啟位置會直接影響滑動塊體形成範圍；傾斜角度越大，滑動塊體會越集中於下邊坡；上下層石膏試體擺放位置差距越大，滑動塊體範圍會越集中於物理模型中之下邊坡。物理模型完成後，利用離散元素法軟體UDEC模擬物理模型，待UDEC數值模擬成果與物理模型成果校核完成後，即會使用UDEC模擬陽明大學邊坡崩塌現地案例。
透過UDEC現地案例之模擬，得知節理內寬大小與塊體尺寸大小會影響UDEC中塊體穩定性與可滑動塊體形成範圍。此外，節理內部之水壓數值變化也與塊體發生滑動相關，最後將會透過UDEC數值模擬，討論於節理岩石邊坡中打設排水管對邊坡穩定性之影響。

關鍵字

順向坡 ； 地下水 ； UDEC ； 滲流傾斜儀 ； 跳階破壞

並列摘要

In this research, field work, physical model and UDEC numerical simulation would be applied to study the influence of groundwater on step-failure of dip slope. In the results of field work, the sliding surface in dip slope failure occurring on February 12, 2018 are decided by drill log data and elevation of ground surface. Furthermore, drill log data from different period are integrated and processed by GIS to find the distance between ground surface and sliding surface which caused dip slope failure this time. Physical model is built by simplifying the results of field work. In the physical model, double layers of gypsum blocks are put on water flow inclinometer to simulate the condition of flowing upward groundwater in the jointed rock slope. The results of physical model show that the location of opened valve would significantly affect the range of sliding blocks. Besides, the larger angle of tilt test and gap of different gypsum layer would cause lower range of sliding blocks. In the UDEC numerical simulation, numerical model is calibrated by physical model to make sure UDEC can be used on the issue of hydraulic coupling in slope stability. After the calibration is done, full-scale numerical model is built to discuss the influence of different hydraulic aperture of shale and sandstone and block size on slope stability. The results show that the hydraulic aperture of high dip angle joints plays an important role in range of sliding blocks and slope stability.

並列關鍵字

Dip slope ； Groundwater ； UDEC ； Water flow inclinometer ； Step-path failure

參考文獻

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