Centrifuge modelling of pipe piles in sand under axial loads

A series of model pile tests have been performed in the geotechnical centrifuge at the University of Western Australia to study the behaviour of driven piles in homogeneous sand. Open, sleeved and closed-ended piles have been driven by a miniature pile driving actuator into silica flour of varying densities. The model pile was fully instrumented, allowing strain gauge data to be monitored during dynamic and static testing. Analysis of the load tests revealed that the shaft friction increased approximately linearly with depth at a low rate, but with a marked increase close to the pile tip. The average shaft friction for the closed-ended tests was shown to be greater than for the open-ended tests. For all tests, the average values of shaft friction were greater than those suggested by current guidelines for design of offshore piles (API RP2A), and the ratio of tensile to compressive shaft capacity was always below unity. The end-bearing resistance normalized by the cone tip resistance was shown to reduce with depth for a given base displacement. Furthermore, tests conducted at similar depths in samples of different densities revealed that this form of normalization allows the end-bearing response to be reduced to a single curve. On the basis of these results, hyperbolic end-bearing mobilization curves have been developed for design and are compared with similar curves proposed by other researchers.