Reducing Negative Friction with Bitumen Slip Layers

Negative friction exerted by settling soil layers on foundation elements such as bearing piles can be considerably reduced by providing the elements with a 0.4-in.- (10-mm)-thick layer slip made of a special grade of bitumen. Theoretical studies at the Koninklijke/Shell-Laboratorium, Amsterdam, have defined the properties the bitumen should have in order to stand up to the conditions of application, storage, driving, and reduction of negative friction. Full-scale trials, including test loadings, have demonstrated these slip layers to be very effective. Depending on the type of foundation and the structure of the soil it is possible to reduce the number of foundation piles by 15-50% or even more, at an additional cost of 10-20% of the cost of the piles driven. About 10,000 piles with bitumen slip layers were used for the foundations of plants of Shell Nederland Chemie in the Netherlands.