BHP Mitsubishi Alliance (BMA) appointed Central Queensland business, Walz Group, for a $31m project to remove decommissioned marine infrastructure from the Hay Point Coal Terminal, south of Mackay.
Walz Group deconstructed and removed the original trestle and conveyor that transported coal from the terminal to waiting bulk carriers for more than 40 years from when the facility opened in 1971.
The Hay Point Coal Terminal exports 55 million tonnes of metallurgical coal per annum.
The project included the removal of seven old conveyor galleries from the wharf of the terminal. The gallery spans weighed up to 155 tonnes and were heavily corroded and structurally compromised.
The conveyor gantry sections had formed the link between Berths 1 and 2 at Hay Point Coal Terminal and roadway removal lifts were performed 123 times from within the aged gantry to reduce weight.
Twelve heavy lifts were conducted by a Manitowoc 16000 Series 3, with a 30m mast and 72m boom and the crane working from Jack-Up-Barge (JUB) D377 Sep Desley Anne.
It was imperative for the project not to disturb shipping schedules.
Gantry removal rigging included a range of 30t-50t soft slings, 35t-85t safety bow shackles, a 150t spreader bar, 22mm-32mm single leg chains (various configurations) and a 100t Oblong Ring
FIELD Engineers designed lifting beam and lifting toggle for the project.
Roadway (123 deck units) were stripped out of the structure to reduce weight. The process was designed with 30-minute cycle time. Gantry sections were supported and cut in half to allow for a smaller crane and barge to fit inside the wharf structure, away from coal ships.
There were a number of lifting innovations within the project including a “Marine Forklift” used for gantry removal where cantilevered support beams were fixed to front of Jack-Up Barge (JUB) and used as a “Marine Forklift”.
This allowed the galleries to be removed in halves, reducing the size of the heavy lift crane.
The jacking system also used for the gantry removal counteracted deflection of the structure during cutting and removal and prevented disturbance to surrounding structures.
The beam and toggle system allowed roadways sections to be rigged from top side only which led to efficient and fast lifts. 123 lifts performed with 30-minute cycle time and engineering analyses was performed to certify the system.
Lift Plans were developed for every lift and all lifts were executed as per the plan.
Risk assessment and OH&S factors were also covered with Safe Work Management Statements (SWMS) and Job Safety Analysis (JSA) documents completed by the deconstruction work crews.
Designed Lift Risk Assessment included engineering-specific risk assessment which gave the crane crew input into the lift planning, design and analysis processes. The results of risk assessments were used to set the scope of engineering analysis.
Engineering controls were based on the analysis of the aged structures which took the levels of corrosion into account. This was required to allow crew access for strip out of parts and roadway, as well as for the major lifts.
Calculation of effects of wave action, windspeed, and JUB spud settlement were also critical and detailed mass and centre of gravity calculations were taken from drawing take-off and then verified by site measurement. This ensured no surprises during lifts.
To ensure the project remained on schedule work was tracked and updated daily with lifting windows taking into account shipping schedules, tides and weather. Progress reporting discipline meant problems were quickly dealt with in a team approach.
A number of environmental factors were considered for the project, which occurred offshore immediately adjacent to the Great Barrier Reef Marine Park. This meant no spillage or dropped material was allowed, and required that work areas were encapsulated.
All work was carried out from either the working barge, or the structure that was being deconstructed. Clearances were very tight and every crane motion was modelled in 3D to ensure no clashes occurred.
There was no space for repositioning or set-down if things went wrong, everything had to go exactly as planned, every time.
There were also logistical challenges to the project.
Access to site was by barge, or through the operating coal port with full maritime security, both required forward planning and approval.
All equipment and materials greater than 6 meters in length could not be transported by road through the port. The use of drones for remote inspection or spotting was not allowed by port security and lifting and logistics operation for each load lasted until it was unloaded onshore at the waste processing area.
Thorough planning for climatic and ground conditions was also necessary and project scheduling had to be set around cyclone season. Tide and swell affected rated crane capacity due to Dynamic Amplification Factors (DAF) and load-specific windspeed limits were calculated and wind speeds monitored constantly
Seabed survey was conducted in areas where spuds would be deployed but spud settlement was difficult to predict. Barge level state were monitored constantly due to risk of stability effect on crane.
Almost all of the lift parameters addressed by AS2550.1 had the potential to become the limiting factor for these lifts (mass, COG, crane capacity, crane position, rigging capacity, headroom, barge capacity, gantry structural capacity, windspeed limits and sea state limits).
Adding to the complication of the project, many of the parameters were interrelated: changing one affected the others. This often required a balance of the risks associated with high utilisation of different factors e.g, trading crane radius for deck capacity utilisation.
Communication of critical factors and their utilisation values was vital for every lift to ensure the team was focused on where highest risk lay.
An extensive dilapidation survey and structural analysis was required to ensure that the gantries would be able to withstand the stresses generated during removal.
Structural analysis was completed on every element of the falsework required. This included the temporary steel, crane beams, hold-down frames and jacking frames.
Detailed process planning of the roadway removal was required to ensure it was possible, then make it safe and efficient. Structural analysis was completed on JUB barge deck, by ASO Marine Consultants.
“Offshore lifting projects such as this are especially challenging. Given that the structures being lifted were 40-plus years old, it added another layer of engineering and construction consideration and complexity. I was very impressed by the innovation that the project team bought to the job to make it both safe and efficient,” said a BMA Hay Point spokesperson.