Laboratory and Numerical Studies of Rainfall Infiltration into Residual Soil Slope Improved by Biomediated Soil Cover

Min Lee Lee,Du Jia Chin,Siaw Yah Chong,Chai Hoon Koo

doi:10.3390/w14050744

Min Lee Lee, Du Jia Chin + Show 2 more

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https://doi.org/10.3390/w14050744

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Abstract

The capillary barrier system is a widely researched method used to control rainfall infiltration into soil slopes for mitigating rainfall-induced landslides. Conventional capillary barrier systems, however, are subjected to several weaknesses, such as the inability of the upper fine layer to function effectively under intense or prolonged rainfall, and sliding failure or erosion may occur in the fine layer as a result of excessive lateral seepage. This study aims to investigate the feasibility of using biomediated soil cover in a capillary barrier system to minimize rainfall infiltration into a residual soil slope. Firstly, the engineering properties of the original and biomediated residual soils were investigated. Secondly, an instrumented one-dimensional physical soil column was set up to investigate the infiltration behaviour of the tropical residual soil with and without biomediated soil cover. A numerical seepage model was simulated to compare the experimental and numerical results, as well as to verify the input parameters of the numerical simulation. Lastly, a two-dimensional slope model was simulated to investigate the effectiveness of the biomediated soil cover in minimizing infiltration under both intense (1-h, 4-h, 8-h, 24-h extreme rainfalls) and prolonged (72-h extreme rainfall) rainfall conditions. The results showed that the soil column with biomediated soil cover could effectively maintain the soil in an unsaturated state for a longer period of infiltration (i.e., 60 min) as compared with the original residual soil (i.e., 10 min only). The numerical simulation results agreed reasonably well with the experimental findings. The two-dimensional seepage analysis results indicated that the slopes with biomediated soil cover could reduce the infiltration of water into the underlying soil slope, and hence resulted in a shallower wetting front, particularly under short and intense extreme rainfall conditions.

Highlights

Rainfall-induced slope failure is a common geohazard in tropical countries, such as Malaysia
It should be noted that the initial conditions of the two soil columns were slightly different, at the middle of the columns, because of the difficulty in creating an initial suction condition identical to that of the original soil with the presence of the biomediated soil layer
The suction in the control original residual soil column was almost diminished after 14 min of infiltration, while a residual suction of 2.8 kPa still existed in the soil column encapsulated with biomediated cover even after 1 h of infiltration time

Summary

Introduction

Rainfall-induced slope failure is a common geohazard in tropical countries, such as Malaysia. The capillary barrier system (CBS) is a widely researched mitigation method for rainfall-induced slope failures. The CBS is normally formed by two or more layers of alternating fine and coarse layers. Each layer has different unsaturated hydraulic properties that can be described through hydraulic conductivity function and the soil water characteristic curve (SWCC). The upper fine layer may have a higher permeability than the underlying coarse layer [1]. Tapping on this unique unsaturated soil characteristic, the underlying coarse layer forms a hydraulic barrier and causes water to flow laterally in the fine layer, provided a breakthrough has not occurred

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