Characterization and Treatment of Expansive Subgrade Soils in Sudan By Omer Siddig Mustafa Hamza (B.Sc. Omdurman Islamic University 2005, M.Sc. University of Khartoum 2014) A Thesis Submitted to the University of Khartoum in Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Civil Engineering Supervisor: Dr. Magdi Mohamed Eltayeb Zumrawi Department of Civil Engineering Faculty of Engineering July 2019