Customer: Port Nelson Ltd Contract: Design & Construct Location: Nelson, New Zealand

Fast Facts Deconstruction of existing 100m section of operational wharf Removal of 148 x 100-year-old timber piles 18,5000 m3 of seabed dredged 100 m long x 17 m deep driven sheet pile retaining wall 4,000 m3 of ground improvements 12m deep 48 x 762mm diameter tubular piles The placement of 7,000T of rock underlayer and armour Construction of new wharf deck and adjacent land slabs requiring 2,340m3 of concrete and 907T of reinforcing steel Eight 50T fender support panels were pre-cast on site Installation of pre-cast fender support panels under deck edge and post-tensioning of anchor bolts Installation of Trelleborg fender units and mooring bollard hardware Denso Seashield corrosion protection system for wharf support piles Installation of Cathodic protection for wharf deck reinforcement and steel piles Sprayed concrete cladding to sheet pile retaining wall Installation of two 300 m2 grout mattress protection

Port Nelson Limited awarded McConnell Dowell the contract to design and construct a 100m wharf replacement and associated works at Main Wharf North, Port Nelson in April 2019.

The existing wharf was nearly 100-year-old and needed to be demolished and rebuilt to ensure that the Port could meet the demands of larger container and cruise vessels in the future. The upgrade design was also required to improve the resilience of the facility in the event of seismic activity.

The work initially involved the design of the new wharf structure and building consent requirements. The construction phase commenced with the demolition and removal of the old timber and concrete structure, together with its associated fendering, concrete retaining wall, and two piled bollards, before the construction of the new structure could begin.

The challenge

The 100m wharf replacement and associated works at Main Wharf North needed to be undertaken without impacting the shipping operations and the ability of container vessels to continue to moor alongside the Main Wharf.  A methodology was developed by the team to minimise the interface between construction activities and Port operations in the confined site area. The work activities were also scheduled around ship movements wherever possible. Another major challenge was working over water while minimising disturbance to marine life and working around the 4m tidal.

The solution

Innovative design options and delivery methods were developed by the team to overcome the challenges. A detailed programme of parallel activities was established to manage work in the confined construction area so wharf operations weren’t impacted.

The team used local resources which provided more flexibility when the timing of critical activities was affected by unplanned shipping movements.

Ensuring mooring lines could be always secured to temporary or permanent bollards across operational areas of the site was also key.

Shotcrete was applied to the face of the sheet pile retaining wall in lieu of in-situ concrete to eliminate the need for temporary formwork in inter tidal zones. Equipment was also adapted for the marine environment, using floatation devices to minimise the need for lifting operations under the completed deck. These innovations helped protect the marine environment, ensured consent conditions were met and made completing the work much easier.

Key to success

The deployment of an integrated and experienced team, detailed programming, good communication and collaboration with the Port Nelson team, ensured the delivery of a high-quality infrastructure asset that will help unlock the region’s future growth.