Abstract
Soft soil deposits commonly found in the eastern coastal area of Langsa City, Aceh Province, are characterized by low bearing capacity, high compressibility, and shallow groundwater levels, which may cause excessive settlement under conventional embankment loading. One alternative solution is the application of Expanded Polystyrene (EPS) geofoam as a lightweight embankment material. This study aimed to evaluate the effects of EPS geofoam on settlement reduction and groundwater table behavior in soft subgrade soils in the eastern coastal area of Langsa City. The research was conducted through a literature review, geotechnical data collection, laboratory parameter evaluation, and numerical modeling using the Finite Element Method (FEM) implemented in PLAXIS 2D. Two embankment scenarios were analyzed: a conventional soil embankment and an EPS geofoam embankment. The evaluated parameters included vertical deformation, stress distribution, excess pore water pressure, slope safety factor, and groundwater table changes associated with soil consolidation. The results indicated that EPS geofoam reduced embankment loading by more than 95% compared with conventional fill, resulting in substantially lower settlement. In addition, excess pore water pressure generated during loading was significantly reduced, leading to a slower consolidation process. EPS geofoam did not directly alter the groundwater table elevation; however, it minimized relative groundwater level changes by reducing surface settlement. Therefore, EPS geofoam was considered an effective lightweight embankment solution for road infrastructure constructed on soft coastal soils in the eastern coastal region of Langsa City.