Influence of Bitumen Addition on Sabkha Soil Shear Strength Characteristics under Dry and Soaked Conditions

High salt content in sabkha soils means they are significantly affected by changes in water content. Dissolution of salts within sabkha soil mass decreases their shear strength upon inundation with water, resulting from the destruction of cementation bonds between soil particles. Therefore, successful improvement for these soils must be based on reducing the dissolution of sabkha salts to minimize their unfavorable properties. This paper investigated the effect of bitumen addition as a stabilizing waterproofing agent on the shear strength properties of sabkha soil. 0%, 4%, 8% and 10% bitumen and sabkha soil were mixed thoroughly. The experimental program on the bitumen-mixed sabkha soils included physical and chemical soil characterization, modified compaction tests and direct shear strength tests. The results showed that bitumen addition modified the physical properties by up to 8%. Under dry conditions, the ultimate shear strength and the horizontal shear displacement increased with bitumen addition. Under soaked conditions, the improvement in shear strength properties was pronounced. The shear strength parameters for the natural sabkha soil fell upon soaking, while the bitumen-mixed sabkha soil samples maintained their integrity. The adsorbed bitumen layer on the cemented soil lumps acted as a waterproofing agent that reduced salt dissolution and alternatively, the shear strength.