Soil Characterization and Land Subsidence Prediction for the First MRT Line in HCM City

Abstract

The Mass Rapid Transit (MRT) system is being constructed in HCM city to meet the transportation needs of a fast growing population and rapid urbanization. Being located in the Sai Gon-Dong Nai delta HCM city area has low elevations and is underlain by a sequence of clayey, silty and sandy soil layers. Land subsidence due to groundwater extraction had been suspected and observed in HCM city. With the increasing groundwater pumping, land subsidence is unavoidable and its effect on infrastructure development of the city has to be seriously considered and controlled at certain degree. The presence of the underlying thick and soft clay layer is another important factor to contribute to land subsidence of the city. In this study, geotechnical characterization of the subsoil along the first MRT line was carried out. Prediction of land subsidence along this MRT line was conducted using a FEM consolidation code. As a result, a subsoil profile of 9 soil layers was characterized, including a soft and compressible clay layer located on top of the soil profile from surface to the depth of more than 20 m. The land subsidence analysis results found that the soft clay layers are vulnerable to drawdown caused by groundwater extraction.With a drawdown of 5.5 m in the second aquifer for a period from 1999 to 2009 a total subsidence of 0.35m can be reached after 20 years at Km. 2.0, the junction zone between the underground metro segment and the elevated train segment, while a maximum subsidence of 0.45 m could be found after 20 years at Km 3.0 where the very soft and soft clay layer is thickest.