Assessment and Characterization of Road Embankment Failure Along Bako-Shanbu Road Project

Abstract

Road embankment failure is a serious natural disaster that can cause a damage on both human and animal lives, disrupt traffic, and even cause land to slide into rivers. Recently, a significant embankment failure along the Bako-Shambu road project in the Oromia region, specifically in the western Wellega zone have been occured. This study is focused on assessing and understanding the embankment failures happening along this road. During a visual inspection, we identified that the main concern in the Bako-Shambu road project is indeed the embankment failures, which have had a notable economic impact on local communities and have led to serious accidents along the route from Bako to Shambu. To gather data, we conducted site investigations at various points along the Bako-Shambu road project, particularly at Sites 1, 3, 5, 6, 7, 9, and the seven sections where embankments have failed. Both disturbed and undisturbed soil samples for laboratory testing have been collected, which included Atterberg limits, moisture content, specific gravity, unit weight, soil classification, and direct shear tests to analyze soil parameters. The lab results showed that the soil is clayey and highly plastic, with a significant swelling potential and sensitivity to moisture, which can lead to sliding. The grain size analysis indicated that more than 71% of the soil consists of fine-grained materials, primarily high plastic clay that becomes unstable when wet. Furthermore, the specific gravity measurements suggest that the soil within the range for clay and silty clay, which has multiple planes of weakness that can contribute to slope instability. The stability analysis of the slope was conducted using Geostudio/SlopW 2024 software, exploring various scenarios. The first scenario involves a fully saturated water table, which represents the worst-case situation, typically occurring during heavy rainfall or flooding. In this case, the factor of safety (FS) decreases across different methods. In the second scenario, where the water table is at the toe of the embankment, the FS value starts to increase.