An Approach to Assess the Stability of Unsaturated Multilayered Coastal-Embankment Slope during Rainfall Infiltration

Jian-Feng Zhu,Chang-Fu Chen,Hong-Yi Zhao

doi:10.3390/jmse7060165

Abstract

This study aims to develop a simple but effective approach to investigate the stability of an unsaturated and multilayered coastal-embankment slope during the rainfall, in which a Random Search Algorithm (RSA) based on the random sampling idea of the Monte Carlo method was employed to obtain the most dangerous circular sliding surface, whereas the safety factor of the unsaturated slope was calculated by the modified Morgenstern–Price method. Firstly, two typical distributions of matric suction were illustrated and the associated methods for determining the strength parameters of unsaturated soil were developed. Based on this, the Morgenstern–Price method was further modified to calculate the safety factor, and RSA was adopted to locate the most dangerous sliding surface of the unsaturated multilayered coastal-embankment slope. Finally, the slope breaking process under rainfall infiltration was simulated through continuously searching the critical slip surfaces under different groundwater levels by RSA. The results indicated that the stability of the unsaturated embankment slope was gradually deteriorated with the increase of rainfall infiltration. It was also found that both of the distributions of the matrix suction (ua-uw) and the suction angle (φb) had significant effects on the safety factor of the embankment slope. Basically, linear distribution of (ua-uw) along the depth and linear relationship between φb and (ua-uw) should be adopted in assessing the stability of the unsaturated multilayered coastal-embankment slope.

Highlights

As one of the effective defensing coastal structures, embankment slope or breakwater is widely used to protect ashore human life and property from severe environment
Most of the above literature has mainly focused on wave-induced seabed instability, in which the soil was considered as saturated material [4,6,9,10,11,12,13]
It becomes more and more urgent to develop a simple but effective method to assess the stability of the unsaturated-soil slope during rainfall infiltration

Summary

Introduction

As one of the effective defensing coastal structures, embankment slope or breakwater is widely used to protect ashore human life and property from severe environment (storm, rainfall, long-term wave loading, etc.). After determining the safety factor of a given slip surface, another work to investigate the stability of an unsaturated multilayered coastal-embankment slope is to adopt an effect global optimization algorithm to locate the most dangerous slip surface. It should be noted that the stability of coastal-embankment slope with the unsaturated and multilayered feature during rainfall were greatly different from those of dry or saturated soils and should be investigated by a simple and effective approach in consideration of effect of matric suction distributions and underground water levels. In the framework of this research (shown in Figure 2), the influence of rainfall infiltration on unsaturated-soil slope was simulated by the gradual rise of the groundwater level and strength parameters under different distributions of matric suction were determined. The influence of the determined method of suction angle on the safety factor is discussed in detail

A Simple Approach to Simulate Rainfall Infiltration

Failure Criterion of Unsaturated-Soil

Distributions of Matric Suction