應用地電阻法探測地下橫向排水工法之施工效益

向陽國家森林遊樂區遊客中心位於地下水豐富之邊坡上，致此區地下水位觀測井觀測長期有湧水現象，為避免孔隙水壓力之作用影響邊坡不穩定導致地層滑動，故進行建置地下橫向排水工法，以降低土體中孔隙水壓或減小破碎岩體不連續面上之靜水壓力，以提高土體或不連續面之抗剪強度，進而改善邊坡之穩定性。而本研究欲探討其施工效益，故利用地電阻法探測於地下橫向排水工法施工前、後之向陽國家森林遊樂區之遊客中心地下水變化，應用電位差推測地層電性構造進而瞭解地下水之狀況，並配合地質鑽探、地下水位觀測及地下排水流量觀測等綜合評估，同時探討邊坡安全係數是否達到水土保持技術規範所定之要求。本研究成果顯示遊客中心所設置之BH-1、BH-2、BH-7及BH-8觀測井為同一邊坡縱斷面，於地下水檢層試驗結果研判為拘限含水層；由降雨量、地下水位及地下排水流量資料綜合分析，排水流量則與雨量相互影響不大，地下橫向排水管A、B流量均達3~4 CMH，平均地下水位皆於地下橫向排水工法施工後明顯降低約1 m，但 BH-1及BH-7豐水時期依然有滿水位狀態，建議平均地下水位需下降2~4 m較為適宜，使邊坡安全係數可達到1.5，故建議增設4~8支地下橫向排水管，以確保邊坡之穩定性。

關鍵字

地電阻法；地下水；地下橫向排水工法；邊坡穩定

並列摘要

The Siangyang National Forest Recreation Area brought a lot of heavy rains in the typhoon Morakot in 2009, causing serious damage to the recreation area and the possibility of becoming a Geological Sensitive Area of landslide. However, the visitor center is located on the slope with groundwater rich area, making the groundwater level in this area The observation well has long-term water inrush. In order to avoid the pore water pressure inducing the soil be unstable and the strata slide. Therefore, the Subsurface Horizontal Drainage should be built to reduce the pore water pressure in the soil or reduce the discontinuity of the broken rock mass. The hydrostatic pressure on the surface can improve the shear strength of the soil or discontinuous surface, thereby improving the stability of the slope. However, this study wants to explore the Construction Benefits. Therefore, the underground water change of the visitor center in the Siangyang National Forest Recreation Area before and after the construction of the Subsurface Horizontal Drainage is detected by the Electrical Resistivity Survey. The resistivity difference is used to estimate the ground electrical structure to understand the groundwater condition. Cooperate with geological drilling, underground water level observation and Subsurface Drainage flow observation to assess whether the safety factor of slide slope meets the threshold set by the standard. The results of this study show that the BH-1, BH-2, BH-7 and BH-8 observation wells set up in the visitor center are the same slope longitudinal section, and the Groundwater Logging Analysis results are judged as a Confined Aquifer; Comprehensive analysis of rainfall, groundwater level and Subsurface Drainage flow data, the drainage flow has little effect on the rainfall, and the Subsurface Horizontal Drains A and B flow are discharged by 3~4 CMH, and the average groundwater level is obviously reduced after the Subsurface Horizontal Drainage. About 1 m, but BH-1 and BH-7 are still prone to full water level during the flood period. It is recommended that the groundwater level should be reduced by 2~4 m, so that the safety factor of slide slope can reach 1.5, so it is recommended to add 4~8 Subsurface Horizontal Drains to ensure the safety and stability of the slope.