Development of Tehran alluvium classification based on geological characteristics and geotechnical parameters

The proposed classification based on the combination of geological variables and geotechnical parameters provides the possibility of using geological knowledge in estimating the geotechnical parameters. The city of Tehran is one of the metropolises that founded on Quaternary alluvium. The alluvium is divided into four groups, A, B, C, and D, based on age and formation conditions. Some researchers have proposed a new classification using the combination of geological variables and geotechnical parameters for A and C Tehran's alluvia. The aim of this study is to sub-classification of unit B of Tehran alluvia based on combination of geological variables and geotechnical parameters. In this research, based on geological findings in 66 locations of Tehran's alluvia, the geological variables affecting the geotechnical parameters of the coarse-grained B alluvia including grain size, grain form, grain contact, cement between grain, homogeneity and layering were identified and based on these variables, unit B was divided into four units of Bn1, Bn2, Bn3 and Bn4. Using the results of 27 performed direct shear test and 70 plate loading tests in specified units, the geotechnical parameters of these four units, including the internal friction angle, cohesion, and modulus of deformability were determined. With combination of geological variables and geotechnical parameters, new classification of unite B was proposed that make it is possible to estimate the geotechnical parameters based on the geological variables for this alluvium.