BITUMEN COATING FOR DOWNDRAG MITIGATION IN COHESIONLESS SOILS

Effectiveness of bitumen coating in mitigating downdrag in cohesionless soils was investigated using direct shear apparatus and a rod shear test. Tests on soft and stiff bitumen sheared with sand and crushed limestone showed that changes in temperature, shear-strain rate, and normal stress significantly affected the shearing characteristics of bitumen coating. Increasing the normal stresses caused an increase in the soil-particle penetration layer into the bitumen and altered the viscous behavior of the material. High friction resistance was recorded when crushed limestone was used to shear the bitumen layers. Stiff bitumen coating provided better protection against soil penetration than soft bitumen. However, at high temperatures, both bitumens lost their protective capabilities, resulting in a significant soil penetration into the bitumen coating. Bitumen-coated samples tested with sand exhibited the lowest friction. The effectiveness of bitumen coating in this case was 98%; it dropped to 54% when crushed limestone was used.