Analysis of soil subsidence due to change in groundwater level in unsaturated soils

Abstract

Land subsidence is one of the growing, crucial challenges faced in many great cities located in areas containing fine grained deposits. This phenomenon causes problems such as damaging buildings, roads and underground sewerage system. Recently, many areas affected by land subsidence have been observed in some arid regions in Iran including Tehran, Rafsanjan and the Khorasan plains. The main cause leading to this phenomenon is the excessive extraction of groundwater, which leads to drop in groundwater head. The process of land subsidence due to change in groundwater level can be analyzed using the theory of consolidation. This means that a drop in the groundwater level
results in an increase in the vertical effective stresses which, in turn, causes land subsidence. Moreover, changing groundwater level and increase in effective stress causes changes in some soil properties. In some soil layers, saturated soils turn into unsaturated soils and exhibit different behavior. In this study, the behavior of unsaturated soils is used to study and analyze land subsidence. Observations and measurements on land subsidence in the plains west of the city of Tehran are first studied and then compared with results of numerical modeling using the PLAXIS 3D software. These comparisons show reasonable agreement of predicted and measured subsidence. The calibrated numerical model is then used to predict future land subsidence in the same areas.