Reliable characterization of subsurface soil in urban areas is a major concern in geotechnical and geological engineering projects. In this regard, this research deals with development of a 3D geological engineering model for the subsurface soil of the city of Mashhad, Northeast Iran, using Sequential Gaussian Simulation (SGS) approach. Intense variability of soil in the study area has sometimes caused major problems in civil engineering projects of the city. Therefore, a better understanding of the soil-related problems is critical for current and future civil engineering work. The main objectives of this study were investigating the spatial variability of soil through variograms and then predicting the values of soil properties at un-sampled locations using SGS method. In this study, some geotechnical index parameters including percentage of fine-grained material, plasticity index, and liquid limit have been employed as input data. A database including the data of 1750 boreholes was built and the hard data were transformed into normal scores in order for them to be applicable as input data in SGS modeling. Maps related to the average of all realizations along with Coefficient of Variation (CV) were provided for each variable as well. Then the maps were interpreted according to the sedimentary environment of Mashhad.

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