geological and engineering geological characteristics of surface alluviums in the gorgan city

Engineering properties of soils and the 3d modeling of geological formations are widely used in site investigations and thepreparation of geological hazard maps. the present study was conducted to characterize the engineering geological properties of theyoung surface alluviums of the gorgan city (iran) to a depth of 25 m and 3d modeling of their geology using boreholes data. to thisend, after determining the location of the available boreholes on the aerial map of gorgan, four hypothetical cross-sections wereconsidered in the north-south and east-west directions. then, the borehole data were marked on each section and their 2dgeological cross-sections were manually drawn using correlation of the similar layers. in the next step, by expanding the informationof these sections, a 3d geological model of gorgan city was prepared using a conceptual-observational method. according to theevidence from the boreholes and field observations, the depositional environment of gorgan alluviums was an alluvial fan created bythe ziarat river. additionally, in terms of engineering characteristics of alluviums, the gorgan subsurface soils can be divided intofour engineering units, including upper clay unit (ucu), middle gravel unit (mgu), lower clay unit (lcu), and sandy unit (su),which share the same engineering characteristics. finally, the results of tests performed on samples from different depths wereemployed to calculate the engineering geological characteristics of each unit, including atterberg limits, compressibility, undrainedshear strength, and drained shear strength parameters.