In this study, a series of rainfall-induced seepage and slope stability analyses was performed using the strength reduction method of two-dimensional finite element technique to inspect the efficiency of remediation
measures for the down slope of the T16-tower pier (or T16-Slope), which is located on the hillside of Taipei City
Maokong tramway. The compound stabilization work of the T16-Slope comprises four types of engineering methods,
namely up-slope, up-middle-slope, middle-slope, and down-slope engineering methods. The numerical model and input
parameters were calibrated by inspecting the coincidence between numerical results and field observations for the triggering mechanism and occurrence time of landslide in T16-Slope during Typhoon Jangmi in 2008. After the aforementioned landslide in 2008, the potential sliding surfaces of the T16-Slope with and without remediation measures were both developed at the up-middle-slope, where a RC-grid-beam (RC-grillage) and anchorage had been constructed for remediation. Under 48-hour rainfall over a 50-year return period, the minimum time-dependent factors of safety FS(t)with and without remediation measures were FSwith(t)=1.191 and FSwithout(t)=1.004 respectively. The remediation measures prevented the up-middle-slope from reaching a critical state (FS = 1.0) during torrential rainfall. In this study,the relative factor of safety (RFS; RFS =FS(t)with/FS(t)without) was used to evaluate the efficiency of the remediation measures to protect slope stability. The RFS was highest (RFS=1.279) under the initial dry condition and lowest(RFS=1.145) during rainfall duration t=30 hours under design rainfall. The RFS values indicated that the stabilization effects of the remediation measures were significantly lower after prolonged heavy rainfall because of severe rainwater infiltration.
Key Words: Finite element technique, strength reduction method, compound stabilization work, rainfall-induced
seepage, stability analyses, Relative Factor of Safety.