Subsurface characterization and prediction of land subsidence for HCM City, Vietnam

•A new and comprehensive computer-aided subsurface database with data collected from more than 3000 boreholes for HCM City•A detailed characterization of the HCM City aquifer system up to 360 m deep (hydrogeological model)•A detailed characterization of the HCM City subsoil profile up to 140 m deep (geotechnical model)•A useful approach to predict land subsidence of HCM City in the conditions of lacking of pore pressure and settlement monitoring data

The demands of domestic and industrial water supply in Ho Chi Minh City (HCM City) have surged rapidly since 1990s with the opening up of Vietnam's economy. In the same time groundwater extraction has continuously increased and is suspected to have caused land subsidence, which in turn would affect the growing infrastructure of the city. By now only a few monitoring stations have been installed, and both pore pressure and settlement observation data are not yet available. As an alternative, we proposed an approach to estimate land subsidence based on the available data of groundwater drawdown in the pumped aquifer and geotechnical properties of the adjacent clay layers. In this study, a large amount of borehole data was collected to construct a computer-based subsoil database. As a result a complete characterization of a six-aquifer system up to 360 m deep and that of the shallower subsoil profile up to 140 m deep was done based on data from more than 3000 boreholes. Examples of land subsidence prediction were done for three cases, i.e.: (i) at a borehole location that has sign of well protrusion; (ii) along the new MRT line no. 1; and (iii) over a profile crossing the city from NW to SE. The first two cases were to show the procedure of land subsidence prediction, while the third case was to compare the FEM analysis results with those estimated by satellite image analysis. The results of this study showed that the subsoil in HCM City with thick soft clay layers is vulnerable to the groundwater extraction. It is expected that the maps of drawdown and the subsoil database developed by this study in combination with a 1D FEM consolidation program will provide a useful tool to estimate land subsidence of HCM City while the pore pressure and settlement data are not yet available.