邊坡土壤中孔隙水壓的急劇變化通常為邊坡破壞發生的主要原因，因此藉由邊坡孔隙水壓的監測，將能提供邊坡災害的早期預警。相較於其它物理探測法而言，自然電位法便宜、便利、省力且為非侵入性探測法，本研究利用自然電位法對於邊坡破壞進行探測，嘗試找出自然電位在邊坡破壞時之變化。本研究目的為利用量測之電位變化，與模擬邊坡之孔隙水壓歷程，判斷邊坡破壞時之電位與孔隙水壓間之關係。本研究首先利用自然電位法監測二維砂箱試驗中的邊坡，並取得在不同的孔隙水壓下，砂箱中土體破壞時所量測到的自然電位分布，試驗完成後會得到試驗錄影、自然電位數據及壓力水頭分布；另外本研究利用Hydrus2D計算邊坡之壓力水頭分佈率定得知土體之水力傳導係數為0.013cm/s；接著以FLAC3D軟體模擬砂箱土體邊坡模型，進行水力參數率定及水流入滲情況驗證得知水力傳導係數為0.0125cm/s、孔隙率為0.3，此參數亦利用模擬邊坡破壞面與砂箱試驗破壞面位置關係獲得驗證。接著本研究分析電位資料，以影像擷取對應電位資料訊號，判斷邊坡破壞事件；最後將FLAC3D模擬結果將能求得非極化電極擺設位置每秒之孔隙水壓，與自然電位相互比較，即得電位與孔隙水壓間的關係圖。由試驗與數值模擬結果擬合分析發現，當邊坡開始濕潤後電位會有上升趨勢，此趨勢隨著孔隙水壓上升速度變慢，電位反而下降至較原本背景訊號低之位置，故得知孔隙水壓在邊坡逐漸濕潤時與電位關係為正相關，在邊坡破壞前夕此關係轉為逆相關。孔隙水壓在達至最大值前電位會有下降反應，且邊坡破壞後之電位變化依舊有明顯之震盪反應，由此得知邊坡破壞之電位前兆可能為下降趨勢。;The changes of pore pressure in slopes is recognized to be the main reason to trigger slope failure events. Pore pressure monitoring are the typical means in providing early warnings for such slope disasters. Comparing with other geophysical measuring methods, self-potential technique is an efficient, convenient, labor-saving and non-invasive method for site characterization. To assess the variations of self-potential signal induced by pore pressure variations and slope failure events, this study employed the technique of self-potential measurements for monitoring saturation process and the associated slope failure processes in a two-dimensional sandbox experiment. In the experiment, the distribution of self-potential were measured associated with monitoring of slope failure events and pore pressure variations in the sandbox. The study also employed numerical models to simulate the soil saturation and slope failure processes in the sandbox. The Hydrus2D numerical model was employed to estimate soil hydraulic conductivity based on the distribution of pressure head near and below the developed slope in the sandbox. This study then used FLAC3D software to simulate and calibrate the slope failure in the sandbox. The pore pressure variations and slope failure events from FLAC3D software are the basis to develop relationship between pore pressure and self-potential variations. Experiment results showed that the increase of soil saturation can lead to increase of self-potential voltage differences. However, significant drops of signals are obtained associated with the slope failure events. The pore pressure (or saturation) is positive correlated with the self-potential variations. However, the negative correlation was obtained right before a slope failure event (few seconds before the first slope failure event). Such behavior can be one of the precursor to predict slope failure evens for practical applications.
