Evaluating the Efficiency of Subsurface Drainages for Li-Shan Landslide in Taiwan
Der-Guey Lin1, Sheng-Hsiung Hung2, Cheng-Yu Ku3, and Hsun-Chuan Chan41Professor, Department of Soil and Water Conservation, National Chung-Hsing University 2Doctoral student, Department of Soil and Water Conservation, National Chung-Hsing University 3Professor, Department of Harbor and River Engineering, National Taiwan Ocean University 4Associate Professor, Department of Soil and Water Conservation, National Chung-Hsing University
Received: 09 Nov 2015 – Accepted for review: 28 Dec 2015 – Discussion started: 19 Jan 2016
Abstract. This study investigates the efficiency of subsurface drainage systems includes drainage wells (vertical shaft with drainage boreholes or horizontal drains) and drainage galleries (longitudinal tunnel with sub-vertical drainage boreholes) for the slope stabilization of Li-Shan landslide in central Taiwan. The efficiency of the subsurface drainages is verified through a series of two-dimensional (2-D) rainfall induced seepage and slope stability analyses without and with subsurface drainages remediation during two typhoon events. Numerical results and monitoring data both show that the groundwater level at B5 monitoring station with subsurface drainages remediation during Toraji Typhoon (2001) is about 40 m lower than that without remediation during Amber Typhoon (1997), and the factor of safety Fs of the first potential sliding surface (1st-PSS, the most critical potential sliding surface) is promoted simultaneously from 1.096 to 1.228 due to the function of subsurface drainage systems. In addition, the Fs values of the three potential sliding surfaces (1st- PSS, 2nd-PSS, and 3rd-PSS) stabilized by subsurface drainage systems are constantly maintained greater than unity (FS>1.0 or FS≥1.217) during rainfalls with return periods increases from 25 to 50 and 100 years. This demonstrates the subsurface drainage systems in Li-Shan landslide are functional and capable of accelerating the drainage of infiltration rainwater induced from high intensity and long duration rainfall and protect the slope of landslide from further deterioration.
Lin, D.-G., Hung, S.-H., Ku, C.-Y., and Chan, H.-C.: Evaluating the Efficiency of Subsurface Drainages for Li-Shan Landslide in Taiwan, Nat. Hazards Earth Syst. Sci. Discuss., doi:10.5194/nhess-2015-309, 2016.