East Arm Wharf Tie Rod Remediation
East Arm Port Stage 1 (EAP1) was designed and constructed by a consortium of Barclay Mowlem, Thiess and Westham Dredging and handed over to Darwin Port Corporation in December 1999.
The EAP1 structure consists of a sheet piled wall tied back to concrete deadmen with 201 pairs of lower level tie bars. The lower tie bars are in the tidal zone 5 metres below the wharf deck.
Since June 2005, sixteen of these lower bars have been discovered to have failed.
The ship mooring bollards are anchored by 78 upper level tie bars which also maintain the crane rail gauge. The upper tie bars are just over one metre below the wharf deck. One of these upper bars has failed.
The bar failures have occurred behind the concrete capping beam where the bars have bent due to settlement of the fill over time.
Remediation Agreement
The Barclay Mowlem/Thiess Joint Venture (the Joint Venture) and the Territory Government finalised an agreement on 10 November 2010 to replace the seaward end of all lower and upper tie bars to ensure the ongoing safety and structural stability of EAP1.
Description of the remedial works
The remedial works will be undertaken in 3 fenced Work Zones at the same time. Two of these Zones will be 60m long, and the third will be 43.6m long. The third zone is at the eastern end of the wharf and is shorter to cause less disruption to the oil rig tenders.
The work involves excavation down to the level of the lower tie bars, which are installed in pairs, cutting one bar, drilling a new hole through the concrete capping beam and inserting a new length of bar which is then welded to the landward end of the existing bar. The bar is locked off with a nut on the wharf face, and the procedure is repeated with the 2nd bar.
Because the upper bars are closer to the surface, they will be excavated by trenching back to a central coupler, and a new section of bar will be attached to the coupler rather than welding.
The excavations will be backfilled and sealed, and the Work Zones will move progressively along the wharf until all bars have been remediated.
On completion of the works, new stormwater drains will be installed to collect water from the whole of the EAP1 pavement, and a new asphalt pavement will be laid over the whole area that has been excavated.
The work is expected to take 18 months with final completion January 2013.
Associated works
Before commencing the main remedial works, the Joint Venture has two other tasks to complete:
- the relocation of the fuel and water lines which are buried behind the capping beam. The current services are in the way of the excavation for the remedial works and will be replaced with new services attached to the back of the capping beam within a grated concrete duct for ease of access; and
- an engineering trial to prove the efficacy of the proposed excavation method to access the tie bars for remedial works.
These two tasks will take approximately 6 months to complete, prior to the main works commencing. Work is expected to commence on site in January 2011.
Access to EAP1 during the Remedial Works
The wharf will operate in a “business as usual” mode during the remedial works.
A detailed Access Plan has been developed between the Joint Venture, Darwin Port Corporation and Department of Construction and Infrastructure who will be supervising the works.
The aim of the Access Plan is to ensure all parties are able to get on with their respective jobs with as little disruption as possible to the other parties and Port Users.
As part of the Access Plan, the three parties will meet on a weekly basis to coordinate the works and shipping movements and to mitigate potential delays and disruption.
Arrangements have been made to enable the works to proceed safely whilst the bulk ore ship loader is in operation, and to accommodate the needs of cattle ships and rig tenders which are the most common users of EAP1.
The Joint Venture will work 10 days on and 4 days off to make best use of the tides, with 24 hour work days.
Safety Management
Safety is of paramount importance to all parties during the remedial works. The Joint Venture has developed a detailed Safety Management Plan which has been approved by Darwin Port Corporation.
The Joint Venture will comply with the additional site safety requirements of Darwin Port Corporation including cyclone preparedness and the Wharf Operating Program, and will liaise with the Corporation’s OHS Manager.
All communication from Port Users or the media should be through the normal channels with Darwin Port Corporation, who will be happy to respond to any queries or concerns.
In addition a Frequently Asked Questions sheet is available for download.
Port Operations Contact: Terry O’Connor
General Manager Landside Operations
matthew.phillips@nt.gov.au
Mobile: 0438 505 227
Media Contact: Melissa Reiter
Corporate Services Manager
melissa.reiter@nt.gov.au
Mobile: 0401 117 076
