Embankment failure at gravel compaction pile improved ground : case study

Abstract

The rapid development and population growth in a country raise the demand for extensive infrastructure, leading to a scarcity of available land. This scarcity prompts the utilization of areas marked by weak soil deposits, often deemed marginal or inappropriate for construction. Weak soil deposits have challenging properties such as high moisture content, compressibility, and very low shear strength. To address these challenges, various ground improvement techniques are employed, with Gravel Compaction Pile (GCP) emerging as a soft ground improvement method. GCP aims to increase load-bearing capacity, accelerate consolidation, and reduce settlement by densifying subsoil. While successfully applied in the Outer Circular Highway and Colombo-Kattunayake Expressway projects in Sri Lanka for soft soil improvement (5-10m thickness), the GCP technique failed in Section 1 of the Southern Expressway Extension Project (Matara to Beliatta), where the soft soil layer varied from 6-18m in thickness. This research study aims to identify the causes of GCP failure in the trial embankment section. The study includes an analysis of geotechnical parameters in subsurface soil and an assessment of slope stability during construction using Matsuo and Kawamura's method based on field monitoring data. Additionally, the stability of the embankment is numerically analyzed using GEOSLOPE SLOPE/W software. The study highlights improper site investigation, inadequate field monitoring, and insufficient precautions for the high-thickness soft soil layer as the main causes of failure. To prevent similar failures in the future, the research discusses possible stabilizing techniques and recommendations based on its findings.