Laboratory Investigation on Bitumen Coating and Polyethylene Sheeting for Downdrag Reduction in Piles: A Comparative Study
In this study, the polyethylene sheeting method for downdrag mitigation in piles has been investigated along with the conventional bitumen coating method. A large number of concrete blocks were prepared with different arrangements of bitumens and polyethylene sheets and tested in the laboratory using direct shear apparatus. The shear resistance of the concrete-bitumen-soil specimens was susceptible to changes in temperature, strain rate, and normal stresses. Bitumen-coated specimens tested with crushed limestone exhibited the highest friction. Soil particle penetration into bitumen doubled the shear resistance of the bitumen coating. Factors that govern the shear behavior of bitumen coating were found to slightly affect the friction characteristics of the concrete-polyethylenesoil specimens. According to the laboratory results, furnishing the concrete blocks with two 6-mil (0.15-mm) polyethylene layers reduced the shear resistance by 78%. More reduction could be achieved from the two oil-lubricated polyethylene sheets. This layering arrangement provided the most effective performance (95% efficiency) for the polyethylene sheeting method.