Abstract
This study proposes an earthen levee reinforcement method with a new biopolymer-based material to prevent levee scour and breach. It is an eco-friendly method that can efficiently protect the levee slope as it enhances soil strength, even at a very low concentration of biopolymer, and has high resistance to surface runoff in addition to promoting vegetation growth. The function and effectiveness of this method were demonstrated through an overflow-based semi-scale experiment in a previous study. In this study, we examined the effect of biopolymer-mixed soil layer on levee stability against an overflow-induced breach. In these experiments, biopolymer-mixed soils were sprayed on the crest and land-side levee surface. Two full-scale tests were conducted (2.5–2.7 m high and 14 m wide on bottom). Case 1 (control case) consisted of bare sand without any treatment, while Case 2 consisted of a 1.0% biopolymer-mixed soil sprayed on the crest and landside slope of the levee and turf put on it. By applying an image analysis technique, we analyzed the breach phenomenon and breach retardation effect of the levee treated with a biopolymer and covered with vegetation. In this experiment, the slope loss rate of Case 2 was retarded 1.5 to 2.3 times over time as compared to Case 1. During the experiment, we observed that soil erosion followed through the narrow water channel formed by the stripped turfs. This means that the grasses did not root firmly enough to protect the surface. In this regard, although the experimental results may seem unsatisfactory, the biopolymer was found to help improve erosion retardation. In 2020, we will conduct more experiments with different compositions and concentrations of the biopolymer regardless of levee vegetation. With this research, we expect to confirm that the new technology of using biopolymer-treated soils is promising for solving the levee overflow breach problem.
Highlights
Overflow, seepage, and piping due to abnormal flooding can damage levees alongside rivers.Levee breaching in inland areas damages the river structure, it threatens human life and property
Of the water level data points measured according to the experimental conditions, those within before and after the levee overflow onset were analyzed
Since the maximum water level and reduction rate varied according to levee height, comparisons were made after nondimensionalization water level reduction rate varied according to levee height, comparisons were made after with the water level reduction rate according to the levee height of each experimental condition
Summary
Seepage, and piping due to abnormal flooding can damage levees alongside rivers.Levee breaching in inland areas damages the river structure, it threatens human life and property. Korea (2018) include the reduction of the hydraulic gradient of the levee, the cross-sectional enlargement of the levee to increase the stability of its slope, and the layering of a slope coating to prevent the seepage of precipitates or river water into the levee. Water 2020, 12, 1070 seepage and breaching by installing a cut-off wall on the foundation ground and the reduction of seepage pressure by lining the riverside surface with an impermeable material. Vegetation reinforcement is another method to stabilize the soil levee slope by creating conditions conducive to vegetation growth using natural materials, such as coconut mat [1,2,3]. The drawbacks of vegetated levees, are that they are less durable than stone or other solid materials and remain vulnerable until the vegetation has fully bloomed [4]
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