- 學位論文
砂頁岩層面浸水引致強度弱化與警戒管理值之探討
Study on Strength Reduction of Sand-Shale Due to Soaking and Warning Management Values
摘要
山坡地約佔全台灣面積的四分之三，而西部麓山帶地質區為砂頁岩層面者佔相當大的比例。砂頁岩層面浸水，其強度易弱化進而改變其工程性質，每當降雨即易造成層面之剪力強度減低，許多地層之滑動面常發生在砂岩與頁岩之層面上。如何災前探求可能災變區域，並進行監控及整治，以減少傷亡損失，便成為災害防治的重要課題。 依據過去九份地區整體坡地滑動評估成果，發現降雨對現地之土壤強度的弱化影響顯著，地層皆沿著砂頁岩層面上滑動，可知水對砂頁岩層面有潤滑作用。因此，本研究以數值軟體PLAXIS進行邊坡穩定分析，由滑動點位移量之計算值與量測值進行比對，以平均絕對誤差率為評估標準，最後選用等比例剪力強度折減方式，建立降雨量與剪力強度之關係模式。藉由降雨量反算土壤強度的折減量，再由折減量推算現地位移量，同時以平均絕對誤差率為評估標準，與監測資料進行比對。經由模擬整體邊坡到破壞值時，以折減破壞值為管理值之制訂標準，提出一套適用於九份地區的警戒管理值。
並列摘要
Slopes account for 3 quarters of the entire Taiwan. Most of the western hills are geologically covered in sand-shale layers. When soaked in water, the strength of sand-shale layers tends to drop and their engineering properties become different. The shear strength of the layers reduces whenever there is rainfall. The sliding surface of many landslides occurs at sandstone and shale layers. It has become a critical issue for disaster prevent to investigate potential disaster areas before disasters happen, and start appropriate monitoring and remediation in order to minimize possible casualty. According to the results of overall landslide evaluation at Chioufen area in the past, it is found that rainfall has significant weakening effects on local soil strength, and the ground slides along the sand-shale layer. It is clear that water serves as lubricant between sand-shale layers. Therefore, the numeric software PLAXIS is introduced for slop stability analysis. The calculated and measured values of displacement at sliding point are compared with mean absolute percentage of error as criteria of evaluation. Finally, the shear strength reduction of equal proportion is chosen to establish the relationship between rainfall and shear strength. From rainfall, the reduction of soil strength is calculated, and in turn the on-site displacement, which is compared with monitoring data with mean absolute percentage of error as criteria of evaluation. A complete set of warning management values specifically for Chioufen is established with the reduction of failure as the criteria for management values when the overall simulation of slope stability reaches the failure threshold.