In 2006, Worley Parsons (WP) was commissioned by Fortescue Metals Group to undertake the EPCM activities for a large iron ore transfer facility at Anderson Point near Port Hedland. The work was undertaken by Team 45, formed jointly by FMG and WP. It included the infilling of a large area of mangrove swamp, after
initial construction of a circumferential bundwall, consisting of fine soil.
For long-term protection of the bundwall against erosion by waves and currents, WP considered various lining options. After thorough analysis it was concluded that a ‘Flexmat’ concrete block mattress lining would be preferable to a traditional rock lining in recognition of the fact that it would provide a durable and more economical solution, at a substantially faster rate of installation.
The outer surface of the bundwall was smoothed by means of tracked bobcats. This was followed by the placement of a layer of non-woven fabric, for the purpose of preventing the upward migration of fine soil particles during conditions of severe wave attack. After this layer had been secured by pins at the top of the embankment (against downward sliding) a second layer of polypropylene loopmatting was placed on top of the non-woven base layer.
This was followed by placement of six interconnected steel mould sections, five of which were placed on the slope with one section placed horizontally at the toe of the embankment. The block cavities in the mould sections were then filled by premix concrete grout with a relatively high slump.
This made it possible to adopt a novel filling procedure whereby the grout, deposited at the top the embankment was ‘cascaded’ down the slope of the bank, aided by the force of gravity. The process was speeded up by filling the toe mould and the moulds at the lower half of the embankment by pumping the grout into the mould cavities. Pencil vibrators were used to ensure that the base matting’s loops would penetrate adequately, in upward direction, into the base of the concrete grout in order to ensure excellent long-term bonding between the matting and cured concrete blocks.
The work, which commenced in November 2006 and was completed towards to the end of February 2007, was undertaken during daylight hours only, with Flexmats cast simultaneously at two locations.
The total number of workers engaged per location was in the order of 20. In line with the Contractor’s social, employment and training policy, the majority of the workers was recruited from the indigenous population. It is the intention to continue this policy in regard to future maintenance.
(which is unlikely to be substantial given the fact that - in contrast to the rock pieces in a traditional rock lining- the Flexmat blocks can not dislodge, held in place by their strong bonding to the loops of the base fabric)
The applied loopmatting is a woven, high strength, polypropylene fabric, supplied by Robusta Technical Fabrics, Netherlands. It contains special anti-leach additives in order to ensure an operational lifetime in seawater of at least 50 years.
In Australia the fabric was first applied as base matting for precast standard Flexmats supplied to Woodside Energy in 1986 for scour prevention around the footings of its Rankin-A offshore platform. (the original Flexmats are still in place, performing well, without any signs of deterioration)
In regard to the design principles and standards:
Manufacturing standards and controls:
These were established by the installation Contractor (Goodline) in close consultation with Marecon and subsequently approved by Team 45’s project manager, prior to commencement of the work.
Construction process and quality systems:
This was entirely the responsibility of the installation Contractor, operating in strict compliance with the installation specifications prepared by Marecon and the terms specified in the Technology Licence granted by Georgiou Group.
The work did not commence until the Contractor’s quality systems had been reviewed and approved by Team 45.
Project/contract management:
This was entirely the responsibility of Team 45. Regular inspections were performed by Marecon and reported to Team 45’s project manager on site. This occasionally led to minor remedial work, undertaken successfully by the Contractor to the satisfaction of the project manager.
Environmental implications
The amount of energy required for the in-situ casting of concrete block mattresses is substantially smaller than for an equivalent rock lining. (which has a high energy demand at each if its successive processing stages: quarrying (blasting), crushing, sieving, road transportation and placement) This implies that in the case of a rock lining the emission of greenhouse gasses is substantially higher than in the case of a concrete mattress lining.
The use of second generation biofuel for the powering of all equipment and machinery required during the installation of Flexmats™ on future projects is part of a deliberate strategy in regard to the sustainable development and preservation of the natural environment, to the maximum extent possible.
Maintenance efficiency and effectiveness
Due to high-strength bonding of the concrete blocks to the loopmat base layer there is no risk that individual blocks would be dislodged, even during extreme wave attack. Consequently the requirement for maintenance will be minimal (if any). By contrast, rock linings require recurrent maintenance to replace rock pieces moved or dislodged during severe wave action.
Finally, it is confirmed that all aspects of the work were performed in strict compliance with relevant international and Australian Standards, the most important of which are listed as follows:
ISO 9001 Quality management systems
AS 1012 Method of Testing of Concrete
AS 1379 The Specification and Manufacture of Concrete
AS 1478 Chemical Admixtures for Use in Concrete
AS 2350 Methods of Testing Portland and Blended Cements
AS 3600 Concrete Structures in marine environment
AS 3610 Formwork for Concrete
AS 3972 Portland and Blended Cements
AC1305R-91 Hot Weather concreting
The implementation of the project and its aftermath (in regard to recurrent inspection and maintenance) was beneficial to the local economy by improving the financial status and purchasing power of, especially, the indigenous workers and their dependants. In addition the early completion of the works has provided an economic benefit to FMG and, indirectly, to the national economy.
The potential for future application of Flexmat™ linings is huge, due to its environmental and cost saving advantages in comparison to traditional solutions such as rock linings.
This is especially the case in Australia considering the huge annual expenditure on foreshore protection, road shoulder stabilisation, bundwalls, river banks and groynes. (all of which would require a protective lining)