Piled cantilever retaining wall at Port Hedland – driveability and wall deflection

This paper describes the design, driveability and deflection monitoring results of a piled cantilever retaining wall at Port Hedland, Western Australia. The retaining wall was required to stabilise an existing access road and conveyor foundations to an existing wharf, prior to the dredging operations for a new export facility in the port. By designing the dredging profile (in front of the retaining wall) as an underwater batter, a cantilever retaining type structure made up of steel tubular piles was found to be feasible. The stability and deflection criteria requirements indicated that some of the retaining wall piles were required to be driven to a toe level of -30 mCD, penetrating through approximately 25 m thick very weak to medium strength rock. General experience of driving piles at Port Hedland area is that the piles are very likely to refuse on a 4 m thick medium strength Conglomerate rock layer starting at about -14 mCD. The piles equipped with external and internal shoe thickening were found to be easier to drive. Measured wall deflections were found to be lower than the initially predicted deflection due to difference in the as-built dredging profile and the assumed design dredging profile. The predicted wall deflection was found to be very similar to the measured deflection when a reanalysis was carried out considering the post dredging as-built batter slope profile. Data from static tension load test carried out on a 610 mm OD and a 1050 mm OD piles for wharfs near the retaining wall is also provided.