POAL Maintenance Dredging and Fy/Fz Deepening

In 2011 this complex capital dredging project to deepen the Fergusson Fy and Fz berth involved the stabilisation of the armour rock batter slope under the wharf prior to any dredging in the berth pocket. This was achieved by divers high water blasting and air lifting sediment from between the armour rock and then pumping concrete grout into those voids to create a rock mattress. Once the mattress was complete, the toe of the batter slope was removed and replaced with high strength (UCS > 800Kpa) cement stabilised sediment (mudcrete).

The removal of the batter toe was not a continuous operation; the maximum length of toe that could be removed in one area was six metres - this involved continuously dredging six metres, and missing six metres, all while working around ships arriving, departing and laying in the berth. Once the complete toe had been replaced the complete 350 metre long berth pocket was dredged from 12.2 metres to 13.5 metres. All work was completed by the backhoe dredge Kimahia and tug Pacific Way.

The maintenance dredging involved the dredging of thirteen berth pockets within the Ports of Auckland precinct including the dredging of contaminated marine sediments from one berth; this was successfully completed utilising environmental grabs and sealed hopper barges.

The dredged marine sediment was loaded into hopper barges and transported to the Port of Auckland Fergusson Reclamation where it was stabilised with cement using a pugmill on Heron’s spudded construction barge Mesenge. The stabilised sediment (mudcrete) was placed to create land by way of reclamation to enable the Port of Auckland to expand their Fergusson Container Terminal operations and to build the revetment for the future Fergusson North wharf.