Assessing the Effects of Rainfall Intensity and Hydraulic Conductivity on Riverbank Stability

Toan Thi Duong,Kazuya Yasuhara,Duc Minh Do

doi:10.3390/w11040741

Toan Thi Duong, Kazuya Yasuhara + Show 1 more

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https://doi.org/10.3390/w11040741

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Abstract

Riverbank failure often occurs in the rainy season, with effects from some main processes such as rainfall infiltration, the fluctuation of the river water level and groundwater table, and the deformation of transient seepage. This paper has the objective of clarifying the effects of soil hydraulic conductivity and rainfall intensity on riverbank stability using numerical analysis with the GeoSlope program. The initial saturation condition is first indicated as the main factor affecting riverbank stability. Analyzing high-saturation conditions, the obtained result can be used to build an understanding of the mechanics of riverbank stability and the effect of both the rainfall intensity and soil hydraulic conductivity. Firstly, the rainfall intensity is lower than the soil hydraulic conductivity; the factor of safety (FOS) reduces with changes in the groundwater table, which is a result of rainwater infiltration and unsteady state flow through the unsaturated soil. Secondly, the rainfall intensity is slightly higher than the soil hydraulic conductivity, the groundwater table rises slowly, and the FOS decreases with both changes in the wetting front and groundwater table. Thirdly, the rainfall intensity is much higher than the soil hydraulic conductivity, and the FOS decreases dominantly by the wetting front and pond loading area. Finally, in cases with no pond, the FOS reduces when the rainfall intensity is lower than hydraulic conductivity. With low hydraulic conductivity, the wetting front is on a shallow surface and descends very slowly. The decreasing of FOS is only due to transient seepage changes of the unsaturated soil properties by losing soil suction and shear strength. These obtained results not only build a clearer understanding of the filtration mechanics but also provide a helpful reference for riverbank protection.

Highlights

Rainfall is one of the main factors causing slope failure in tropical areas
Those research works concluded that when the rainfall intensity is greater than the saturated hydraulic conductivity of the surface soils, a runoff occurs along the slope surface [8,22]. Those previous research works had unobvious objectives focusing on building the effects of hydraulic conductivity, the results clearly showed that the slope stability was significantly affected by the soil hydraulic conductivity and the rainfall intensity boundary
Setting the initial conditions leads to different mechanisms of infiltration, seepage, and changes of groundwater pressure

Summary

Introduction

Rainfall is one of the main factors causing slope failure in tropical areas. The effects of rainfall properties on slopes have been studied in large amounts of research that have analyzed slope stability by both investigation and simulated models. By the simulation of different conditions of slopes and rainfall boundaries, previous research has indicated the changes of soil unsaturated properties, such as the reduction of suction, shear strength, and the increasing of hydraulic conductivity and pore-water pressure [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20] The change of the area from unsaturated to saturated is caused by the advancement of the wetting front from the surface [4,5,9,13,21,22,23] and groundwater table from depth [6,7,8,10,11,12,13,14,15,16,17,18,19,20]

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