An Application of ERT on Investigation of Rupture Surfaces of Landslides

地電阻剖面影像探測法（Electrical Resistivity Tomography，ERT）運用於坡地調查，因其能獲取坡地二維與三維剖面地層特性，施作時間相對較短且較經濟，多年來已有廣泛應用與研究成果。藉由ERT可以重建邊坡與滑動體的形狀，判釋滑動面，推估滑動層厚度，求得滑動崩塌區內含水量較高的範圍。但ERT剖面資料為一相對性資料，藉之判釋坡地滑動特性時，仍需要參考鑽探與地質探勘成果印證之。 本研究針對嘉義、高雄二處存在明顯滑動現象坡地，蒐集ERT，地質鑽探與監測成果，探討以地電阻影像剖面判釋滑動面之可行性。此外，在嘉義研究坡地以固定電極方式，在某次降雨前、後分別進行地電阻探測；嘗試以時間推移影像剖面（time-lapse ERT, tl-ERT）探究滑動面電阻率可能之變化。 二處坡地地層為舊崩塌岩塊覆蓋於泥岩或頁岩之上，滑動面以上地層變位有兩種類型，一類為各深度位移相近的平行滑動，另一類為淺層變位大而略深層變位小的倒三角形滑動。在本次研究坡地上，邊坡發生平行滑動時，測得之電阻率約5~17Ω-m的帶狀區域，大致與監測所得滑動深度相近。但當滑動變位屬於倒三角形型態時，不易以電阻率分布情形判釋其滑動面位置。 在嘉義的邊坡上，降雨過後施測之ERT影像與乾季所得結果相近；滑動面上電阻率並無明顯差異，推測因該次降雨事件未在原有滑動面之外，造成其他滑動面，故滑動面上特性未產生明顯改變，測得之電阻率亦然。The electrical resistivity tomography (ERT) in landslide investigation could be used to get 2D or 3D profile in landslide area. For the ERT can be completed in relatively shorter time, and economical in cost. ERT has been widely used in landslide investigation these years. The ERT technique could be applied to reconstruct the area of landslide, to locate the potential rupture surface and estimate the thickness of sliding material. But the ERT data are not definite and unique. When interpreting information from ERT, geological boring and exploration results are necessary. This study collects ERT and monitoring data in two landslide sites located in ChiaYi and Kaohsiung, Taiwan. Try to study if the rupture surface could be defined directly from ERT by comparing with in-situ geological boring stratigraphy and inclinometer monitoring results. Besides, the time-lapse ERT method is used in ChiaYi site before and after rainy period to check possible electrical resistivity change along rupture surface. The strata distribution in these two sites was with alluvial deposit over mudstone or shale. Two types of inclinometer displacement can be classified: one is parallel sliding with nearly the same displacement above rupture surface. The other type is inverted triangular sliding that apparent displacement occurred near surface and decrease with depth to rupture surface. In the landslides with parallel sliding, the narrow zone with low resistivity 5~17 Ω-m seems consistent with rupture surfaces. But in the inverted triangular sliding, it can't be easily to define the rupture surfaces from ERT. ERT results along rupture surface after rainy period in ChiaYi site seems similar with that before rainy period. There may be no multiple rupture surface induced after that rain period, so there is no apparent change with the characteristics of sliding and resistivity distribution.摘 要 i Abstract ii 目 次 iii 表目次 iv 圖目次 v 第一章 緒 論 1 1.1 研究動機 1 1.2 研究內容 2 1.3 研究流程 3 第二章 文獻回顧 5 2.1 地層地電阻 5 2.2 地電阻探測方法 7 2.3 推移時間地電阻探測方法 10 2.4 應用ERT成果研判滑動面的問題 12 第三章 研究區位與試驗流程 16 3.1 研究區位一嘉義中埔基地背景資料 16 3.2 研究區位二高雄柴山基地背景資料 19 3.3 地電阻探測 23 3.4 地質鑽探與傾斜管量測 24 第四章 結果與討論 26 4.1 研究區位一地質與地層滑動情形 26 4.2 研究區位一ERT影像與滑動面 30 4.3 研究區位一tl-ERT影像與滑動面 37 4.4 研究區位二地質與地層滑動情形 43 4.5 研究區位二ERT影像與滑動面 47 第五章 結論與建議 53 5.1 結論 53 5.2 建議 54 參 考 文 獻 55 附 錄 岩心照片 5