NUMERICAL ANALYSIS OF EMBANKMENT BEHAVIOR ON SOFT GROUND IMPROVED BY PVD AND SOIL-CEMENT COLUMNS

Abstract

Soft soil improvement is always a very challenging problem in the design and building for infrastructure construction on soft and thick clay deposits. Recently, there are a number of embankment constructions around the world using the improvement method by combination of prefabricated vertical drains and soil cement columns to reduce settlement and speed up consolidation rate in the soft soils. Although the advantages of this method have been mentioned in the previous studies, the analysis method of this method for applying in the practice has not received much attention in the geotechnical engineering field. This paper presents an equivalent plane strain model in numerical analysis of embankment on soft ground reinforced simultaneously by prefabricated vertical drains and soil cement columns, in which the permeability coefficient of the ground soil and other parameters of soil cement columns (i.e., stiffness, width in plane strain model) are converted from the in-situ condition into the equivalent 2-D model. The conversion formulas in the current model are based on the previous studies for the cases of soft soil reinforced by prefabricated vertical drains only or reinforced by soil cement columns only. However, this combination creates a new solution that can be used in the equivalent plane strain model to predict the behavior of the soft ground improved by combining the prefabricated vertical drains and soil cement columns. The role of the prefabricated vertical drains in the composite foundation is also investigated and analyzed through the horizontal displacement behavior of the subsoil. The analysis results show that the settlement obtained from the presented model is in good agreement with the field data. The prefabricated vertical drains used in the combined method can significantly reduce the lateral displacement of soft ground. By this study, the combined method is recommended to apply in Vietnam, especially for the embankment construction on soft thick clay deposits.