Abstract
This paper presents a field monitoring study with emphasis on the design and construction of a subsurface drainage system and evaluation of its stabilization efficiency on the slope of You-Ye-Lin landslide using a three-dimensional finite element method program (Plaxis 3D) for the groundwater flow and slope stability analyses. The subsurface drainage system consists of two 4-m diameter drainage wells with multi-level horizontal drains and was installed to draw down the groundwater level and stabilize the unstable slope of the landslide. Results demonstrate that the subsurface drainage system is functional and capable of accelerating the drainage of the infiltrated rainwater during torrential rainfalls during the typhoon season. The large groundwater drawdown by the subsurface drainage system protects the slopes from further deterioration and maintains the slope stability at an acceptable and satisfactory level.
Highlights
The You-Ye-Lin landslide, a large scale landslide in a mountainous area of Taiwan, has a long history of intermittent large downslope ground movements during rainfall periods since TyphoonMorakot in 2008
The main remediation work for the You-Ye-Lin landslide is to lower the groundwater level through a deep subsurface drainage system composed of two drainage wells
After 20 days of the subsurface drainage, the groundwater level drops from the initial groundwater level at the end of horizontal drains of Drainage Well-1 (50 m away from Drainage Well-1) to the elevation of 4th level horizontal drains at approximately 32 m
Summary
The You-Ye-Lin landslide, a large scale landslide in a mountainous area of Taiwan, has a long history of intermittent large downslope ground movements during rainfall periods since TyphoonMorakot in 2008. The main remediation work for the You-Ye-Lin landslide is to lower the groundwater level through a deep subsurface drainage system composed of two drainage wells (a well shaft equipped with multi-level horizontal drains). The effectiveness of horizontal drains on lowering the groundwater level and improving the slope stability is closely related to the drainage length, spacing, number, and installation location [1,2,3,4,5]. The function and the effect of horizontal drains on the groundwater drawdown and the slope stabilization mechanism have been investigated by several researchers using numerical methods [6,7,8,9,10,11,12]. Cai et al concluded that lengthening a group of horizontal drains is more effective than shortening the spacing and increasing the number of a group of horizontal drains [6]
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