Evaluating the Efficiency of Subsurface Drainages for Li-Shan Landslide in Taiwan

Abstract

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.

Effectiveness of Horizontal Sub-drain to Increase Slope Stability with Vertical Cracks and Weathering Soil in Areas with High Rainfall Intensity

“…This is in line with the discoveries of (Kenney and K.C. Lau, 1982), (Kopeckr, Ondrasi and Antolova, 2013), (Ahmed et al, 2012b), (Lin et al, 2016), (Pfeiffer, 2014) and (Amatya and Mori, 2018).…”

“…An effective cohesion range in each layer, c′= 0-90 kPa, the effective angle of internal friction, ϕ'= 1-40°, and unit weight of soil, γ = 17-19 kN/m 3 , were used in the slope stability analyses. According to (Lin et al, 2016), shear strength parameters of soil were also kept constants for all cases. This was to ensure that the changes in the stability of the slope were only due to pore-water pressure (or matric suction) changes in the soil.…”

“…In this study, the boundary conditions were determined based on previous investigations conducted by (Rahimi, Rahardjo and Leong, 2010), (Rahimi, Rahardjo and Leong, 2011), (Suryo, 2013), (Lin et al, 2016), and many others. Meanwhile, the boundary conditions used for the transient seepage analysis are shown in Fig.…”

Stabilization of major soil masses using drainage tunnels

“…Main advantages of this drainage solution are: • Groundwater lowering through predominantly vertical flow, conceptually eliminating / reducing significantly destabilizing seepage forces; • Use of gravity flow, eliminating the necessity of energy supply and long-term maintenance of pumping systems; • No need of any activity, including construction, inside the unstable soil mass; • No impact on the surface and risk of damage to the stabilizing system through vandalism. Stabilization of unstable or failed soil masses through drainage tunnels has been used in several locations around the world, with case histories presented, from different locations, in Europe (for example, Bardanis & Cavounidis, 2016;Bertola & Beatrizzotti, 1997;Eberhardt et al, 2007;Marinos & Hoek, 2006;Futai et al, 2009), in the Americas (Rico & Castillo, 1974;Vargas, 1966;Wolle et al, 2004;Yassuda, 1988), Asia (JLS, 2002;Lin et al, 2016;Sun et al, 2009;Wang et al, 2013;Wei et al, 2019;Yan et al, 2019), and Oceania (Gillon & Saul, 1996).…”

Technical Efficiency of the Subsurface Drainage on Agricultural Lands in the Moldova River Meadow

“…Their harmful influences are reflected by the degradation of soil characteristics and functions, of soil bio-productive capacity, affecting yields and food safety, with consequences on human life quality [3][4][5]. These conditions are determined either by natural factors [6][7][8] or by agricultural and industrial activities that might have a negative synergic action [9,10]. Some of the main limiting factors of crop production in Suceava County are excess water, floods, low infiltration rate and soil compaction, soil erosion, and landslides.…”