The renovation commissioned by Auckland City includes a concrete overlay that covers the western and eastern ends of The Landing site, a three-hectare triangle of land overlooking a stretch of water at Okahu Bay in Tamaki Drive and home to a number of boating clubs. The new overlay will ensure the ramp remains useable and safe. Stevenson Precast and Stevenson Concrete were two of the sub contractors selected by main contractor NZ Strong to supply product and expertise to the project. The site required over 3000m2 of poured concrete together with 900m2 of precast concrete panels in the lower tidal area.
‘The existing ramp was old and slippery and so there were potential safety issues for the public and boaties using it,” says Stevenson Concrete Product Manager Brent Atkinson. “Stage one of the project has gone very smoothly. We had to use our ingenuity to address some of the practical and technical challenges involved in resurfacing the ramp. These included adjusting our working hours to accommodate the changing tide and managing the comings and goings involved in operating in a live boat yard/ramp environment.
Stevenson Concrete designed a range of different concrete mixes for the job. ‘These included a 50 MPa Microsilica mix to provide durability, because the ramp was covered in water. We also developed a sand and slurry mix that was injected into the rip-rap rocks wrapped in geotechnical filter fabric. At one stage we were pouring three different concrete mixes at a time to take advantage of the low tide. One morning we were grouting panels, injecting concrete mix or grout under the precast panels, while in the water, another team was laying the 50MPa marine concrete. We also supplied a blinding mix between the existing ramp and the marine concrete – all at the same time.Another of Stevenson Concrete’s technical innovations involved incorporating Rheomac GF 300, an antiwash, into the grouting mix. This prevented the concrete from washing out.
Stevenson Concrete was not alone in contending with the technical challenges presented by the project. As specified by the engineers, Stevenson Precast supplied four toe beam panels and four flat panels to NZ Strong. However, production was put on hold when the team realised that the logistics of installing the original design on site would prove very difficult. NZ Strong, Stevenson Precast and Stevenson Concrete came up with an alternative option of reducing the number of panels per bay from four to two and altering the orientation. This made installation of the precast relatively straight forward and allowed the team to make up the time lost during the redesign and to maintain programme.
“Originally, almost the entire job was specified in precast. Now the ramp has been re-surfaced with a combination of precast panels and in situ concrete – poured and placed on site at Okahu Bay,” explains Stevenson Precast Project Manager Jared Dickson. “Some of the installation was completed underwater and this was only possible at extreme low tide. So timing the delivery of our precast panels had to be very exact to accommodate the tides.”
The scale of the panels, the widest panels ever produced by Stevenson Precast, were 7.5m long by 3.75m wide and had to be delivered on site by special low loader trailers.
“This high profile community project required a proactive, cohesive team approach,” says Shane Brealey, Managing Director, NZ Strong. “A project of this nature presents many challenges and our team worked together to develop solutions and keep the works moving forward. As an example, concrete and grout mix designs were developed and fine-tuned by Stevenson Concrete to suit the unique conditions of the project. This greatly contributed to the positive outcome.”
“We had to contend with two tsunami warnings during the project, both of which resulted in an immediate site clearance. Protection of the harbour environment required the use of silt nets and we had to take great care to avoid any concrete discharge into the water. The site team received very good feedback from the ARC about the procedures implemented to meet the strict environmental requirements set by ARC and Auckland City Council.”