Effects of Two-Phase Flow of Water and Air on Shallow Slope Failures Induced by Rainfall: Insights from Slope Stability Assessment at a Regional Scale

Sinhang Kang,Byungmin Kim,Gyu-Hyun Go,Sung-Eun Cho

doi:10.3390/w12030812

Abstract

Over 160 shallow landslides resulted from heavy rainfall that occurred in 26–27 July 2011 at Umyeon Mountain, Seoul, South Korea. To accurately reflect the fluid flow mechanism in the void spaces of soils, we considered the two-phase flow of water and air for rainfall infiltration analysis using available historical rainfall data, topographic maps, and geotechnical/hydrological properties. Variations in pore water and air pressure from the infiltration analysis are used for slope stability assessment. By comparing the results from numerical models applying single- and two-phase flow models, we observed that air flow changes the rate of increase in pore water pressure, influencing the safety factor on slopes with a low infiltration capacity, where ponding is more likely to occur during heavy rainfall. Finally, several slope failure assessments were conducted to evaluate the usefulness of using the two-phase flow model in forecasting slope stability in conditions of increased rainfall sums. We observed that the two-phase flow model reduces the tendency of over-prediction compared to the single-phase model. The results from the two-phase flow model revealed good agreement with actual landslide events.

Highlights

Rainfall-induced landslides have caused many human casualties and severe property damage worldwide [1,2]
We evaluated the performance of the analysis for slope failure assessments applying the two-phase flow model
To validate the two-phase flow model utilized for infiltration simulations, we compared the matric suction measured by the Seoul Metropolitan Government [41] in the study area from 0:00 on

Summary

Introduction

Rainfall-induced landslides have caused many human casualties and severe property damage worldwide [1,2]. The initiation of rainfall-induced landslides is affected by various factors, such as the material properties of soil, topographic features, geological and hydrological characteristics, slope surface cover, and vegetation [3,4]. The increase in water content causes an increase in the unit weight of the soil [9,10], and the loss of matric suction as wetting bands progress into the slope decreases its shear strength and effective stress [11,12]. Numerous physically based studies have investigated infiltration behavior during rainfall using various approaches: (1) Adopting assumptions for simplification to solve the differential equation of Richards [14] by applying a single-phase fluid

Methods

Results

Conclusion