Abstract
A series of direct shear tests were carried out in order to characterize the pile–soil interface strength for various pile materials including steel, concrete, and grout and to investigate the influence of fiber-reinforced polymer (FRP) materials on the pile–soil interface strength in soft clay. The study investigated both pile–soil interface friction and interface adhesion by simulating drained and undrained conditions. The results among the traditional pile materials indicated the superior performance of grout and concrete relative to steel. FRP interfaces were shown to perform at a level the same as or higher than that of traditional steel piling under both drained and undrained conditions in clays. The FRP–clay interface friction angles were 5 % to 19 % greater than those in traditional steel–clay interfaces and 12 % to 23 % smaller than that of concrete. In addition, FRP interface adhesion was observed at between 86 % and 135 % of the interface adhesion of steel and between 65 % and 75 % of the interface adhesion of concrete.