Bitumen Coating versus Plastic Sheeting for Reducing Negative Skin Friction

Abstract

The plastic sheeting approach for negative skin friction reduction in end-bent piles behind proprietary mechanically stabilized earth walls was investigated along with the conventional bitumen coating method. A number of concrete blocks were prepared and furnished with different arrangements of polyethylene sheets and bitumen materials, and tested in the laboratory using a direct-shear apparatus. Shearing resistance of the concrete-bitumen-soil samples was influenced by temperature, shear rate, and normal stresses. Bitumen-coated samples tested with crushed limestone exhibited the highest shearing resistance. Test results showed that wrapping concrete piles with polyethylene sheets reduced the skin friction by 78%. Additional reduction was achieved by lubricating the polyethylene sheets with oil. The effectiveness of oil-lubricated polyethylene sheets in reducing skin friction was about 94%. Factors that affect the shearing behavior of bitumen coating did not influence the friction characteristics of the polyethylene sheeting. Based on the results of this study, two formulas were suggested for estimating the shearing resistance of the bitumen-soil matrix and lubricated sheets.