Numerical analysis on influence of principal parameters of topography on hillslope instability in a small catchment

Abstract

This study was conducted to identify the influence of three principal parameters constituting topography (slope inclination, soil depth, and slope length) on hillslope instability in a small catchment, known as Higashifukubegawa of Shikoku Island, western Japan. The typhoon rainfall of 19-20 October 2004 was significant in causing a total of seven slope failures in the catchment, though other rainfall events of various intensities in the same year did not cause failure. To understand the influence of the three principal parameters, numerical modeling of seepage and slope stability was performed in slope profiles constructed by varying the three parameters across their permissible range prepared from the seven slope failures of Higashifukubegawa in GeoStudio (GeoStudio Tutorials includes student edition lessons, Geo-Slope International Ltd., Calgary, 2005 v.4). The change in porewater pressure and slope mass weight due to variation in values of principal parameters was used to interpret the change in factor of safety or instability. The results showed that (1) instability increases with increase in the values of all three selected parameters across their range in Higashifukubegawa with remarkable decreasing trend in factors of safety, (2) slope inclination and soil depth were observed to affect instability through change in both unsaturated zone moisture content and mobilizing force of slope mass, (3) but with slope length, the unsaturated zone moisture content was not found to change considerably which implies that the instability due to slope length is mainly governed by change in slope mass weight. Overall, this study has dealt in great detail with how hillslope instability changes with principal parameters of topography under the same simulating conditions of hydrological and geo-mechanical parameters.

Numerical Analyses of Slope Stability Considering Grading and Seepage Prevention

“…Most slope instability is caused by pore water pressure (PWP) change. Due to the periodic changes in reservoir water levels and rainfall, bank slope soil is influenced by the following processes: (1) water content variation [3], (2) the wet and dry cycle [4], (3) groundwater seepage [5,6], and (4) the hydrochemistry process [7,8]. Traditionally, bank slope stability is evaluated at a single time, which cannot reflect the real situation of the slope.…”

Numerical Analysis of Slope Stability Considering Grading and Seepage Prevention

“…Increasing evidence suggests that approximately 90% of slope instability is related to some extent by pore water pressure (PWP). Due to the periodic changes in reservoir water levels and rainfall, the landslide soil undergoes periodic soil-water effects, namely: (1) changes in water content (Acharya et al 2015); (2) alternating wet and dry effects (Reid and Parkinson, 1984); (3) groundwater seepage (Take et al 2015;Pender et al 2016); and (4) hydrochemistry (Wei et al 2012;Wen and He 2012). At present, the stability evaluation of the bank slope mainly shows a steady state, i.e., a single event corresponds to a single safety factor.…”