Geology of Tehran Alluvium and Evaluation of Rieben Classification for Geotechnical Studies

City of Tehran is founded on Quaternary alluvium. During the last years, several researchers have studied characteristics of this alluvium. Amongst them, Rieben classification has been the most widely used classification rather than others. Rieben (1955) divided Tehran alluvium to four categories, A, B, C and D which are ranged from old to young, respectively, in terms of geologic age. In Rieben study, age and general characteristics of alluviums are considered rather than geotechnical and engineering applications. Study of alluvium based on age can give useful information about history of basin sedimentation and relevant change's trends and even it may help geotechnical engineers for preparing study plan and making sound conclusions over undertaken studies. For doing so, it is required to evaluate alluvium classifications with respect to sedimentation types. In order to evaluate Rieben classification capabilities for geotechnical studies of Tehran alluvium, following subjects are studied in this research: (A) Description of Rieben and other classifications that are presented based on age and specification of geology. (B) Discussing advantages and disadvantages of existing classifications in geotechnical studies. (C) Analysis of Tehran geological maps with consideration of alluvium formation and making comparison of these maps with some boreholes, test pits and site visit results. (D) Discussing geological factors affecting on geotechnical specifications of Tehran alluvium.