An Innovative Method of Assessing the Capacity of Existing Wharf Piles

North Queensland Bulk Ports (NQBP) is upgrading the Mackay Outer Harbour wharves. The work involves a fender replacement and bollard upgrading programme. As a result of the proposed upgrade, the axial capacity of the fender piles at Wharves 1, 4 and 5 is increased from the original design requirements.

The existing piles beneath the wharf deck are driven steel tubular piles and they range in diameter from 0.457 m for Wharves 1 and 4, to 1.0 m for Wharf 5. Unfortunately, no construction records could be found in relation to as-constructed pile toe levels, final driving energy and sets or pile load testing. Therefore, the as-installed pile capacities could not be readily assessed. Using conventional theoretical assessment methods, the design consultant concluded the existing piles would not have adequate capacity to support the increased axial loads. The challenge was to investigate and assess whether the existing fender piles can support the increased axial loads associated with the wharf upgrade, and if not, what are the options for remediation.

This paper describes the investigation and assessment of the axial capacity of the existing piles using a combination of innovative downhole magnetic testing adjacent to the existing piles to assess the as-constructed pile toe levels, conventional coring to assess the founding materials, and dynamic pile load tests on new prototype piles driven close to the existing piles. Using the innovative investigation and assessment technique, the existing piles were assessed to have adequate capacity and successfully avoided the costly option of remedial works for the client.