Engineering - hydrogeological model of land subsidence area in the southwest of Tehran (Tehran – Shahriyar plain)

Land subsidence is an important geological hazard closely related with the development of urban areas. Intensive groundwater extraction attributed to economic development, and population growth has been identified as the main cause of land subsidence in many cities worldwide, especially those in densely populated and economically developed urban areas. The first step in fundamental studies of this phenomenon is the preparation of the engineering - hydrogeological model. This model is a pictorial representation of the hydrogeological units and their boundaries, physical and mechanical characteristics.
For separation and correlation of soil layers is used the geological logs data and their geotechnical characteristics (atterberg limits, unified soil classification and shear wave velocity). Elastic constants of soil layers (shear modulus, young,s modulus, bulk modulus and passion,s ratio) based on the estimated density and conventional empirical formulas are obtained. Then, the layers that have similar characteristics in an engineering geological unit are defined. Based on this model, a multi-layered aquifer system in southwest plain of Tehran includes three aquifer units and three aquitard units. This study shows that the heterogeneity of soil layers is high. This feature will change from one region to another (Shahriyar-Tehran plain, Shahriyar to Eslamshahr).