Geotechnical Evaluation of soil at selected sites to build up Shatt Al-Arab Spillway in Basra City/ Southern Iraq

Abstract

The physical, chemical and engineering properties of soil had been carried out to evaluate the characteristics of Sehan and Al-bhar soil sites and their suitability for setting up Shatt Al-Arab spillway. Four boreholes drilled by Al-Ma'awal Company for soil investigation with depths ranging between (1- 40) m. The laboratory tests results for soil samples had been obtained from drilled boreholes showed that the soil in two sites divided in to several layers : 1st layer is a soft sandy silty clay soil (CH) with fill material from (0.0-1m) which should removal through building. 2nd layer is a very stiff sandy silty clay soil (CH) high density (1.78-1.81) gm/cm3 with bearing capacity (qa) ranged between (11- 41 T/m2) in two study sites at depths (1 to 5, 6.5 m) this layer is suitable for light loads of Shallow foundation. 3rd layer is a soft to medium stiff silty sandy clay soil (CH, CL) medium to high density (1.77-1.87) gm/cm3 with qa ranged between (2-9T/m2) at (6, 7 to 18m) depths which unsubtle for foundation because of high water content (28-30%) and high range of clay that led to settlement with time. Fourth layer is a very stiff [silty sandy clay soil (CL, CH)] to hard [silty sand soil (SW, SP)] with qa ranged between (12-40 T/m2) at (20 to 40 m) depths because increase the bulk density (1.84-2.12) gm/cm3 with depth as a result to compaction or a static load with appears dense silty sand strata this layer is suitable for heavy loads of deep foundation such as spillway structure. The results of chemical tests shows fluctuation in behavior through depths where the values of (SO3, T.S.S, CaCO3) shows increasing with depth and exceeded on permitted limits that need improvement, while the values of (Gyp, CL, O.M, pH) shows changing between increasing and reducing under normal levels with depths.