Investigating engineering properties of Neogene Marls of Siahkouh and Gatchab

This study is about the relation between erodibility rate and plasticity features of Neogene Marl deposits of Gatchab and Gitcha in southeast of Garmsar. The erosions al feature of Neogene sediments are rill، gully and waterway shapes. The depth of soil sampling for rill and waterway types is from surface to 30-centimeter thickness and for gully one is from head cut and all outcrop of gully bank. The engineering analyses for sediments include liquid limit، plastic limit and plastic index and engineering granulometry. On the basis of engineering classification of soil، the sediment of Gatchab and Siahkoh mountains are fine grained soils with low to very low degree cohesive، consequently low plastic limit and low internal consistency. The comparison of the results between marl units of Gatchab and Gitcha area have shown the M2 unit has low plasticity and high sensitive to erosion to other units M1 and M2. By the way، the M1 unit is high resistance to water erosion in comparison to M3 unit. From all aspect، Abundance of the lime and clay particle amounts is positive effects on decreasing of sensitivity rate to erosion of Neogene deposits. The above mentioned results base on plasticity features of Neogene deposits confirmed by field witness.