Some large community water infrastructure projects are built just for the recreational fun of it. Based on HEB Construction’s winning entry in the 2016 CCNZ awards in Category 3 (projects with a value between $10m and $50m). By ALAN TITCHALL.
THE $25 MILLION VECTOR WERO Whitewater Park is the country’s first purpose-built artificial white water facility for recreation, sports, emergency services training, school programmes and youth development. It will host its first international event next year – the World Masters Games.
Construction of the water sports park started in September 2014 and the project was completed early April 2016, two working days ahead of schedule, thanks to some very diligent planning and contracting.
The park was built by HEB Construction for Second Nature Trust (formerly known as Counties Manukau Pacific Trust) and cost $25 million.
The project build had multiple work-fronts on a difficult and tightly constrained site and involved 100,000 cubic metres of earthworks, 7500 cubic metres of concrete (more than 1200 truckloads), utilities, ground improvements, bridges, roading, mechanical and electrical building works, and the installation of services, including water, storm water and sewer pipelines.
The earthworks and concrete works were very complicated, with organic shapes forming the water course channels and a large reservoir/pond. There were also numerous interfaces between the mechanical and electrical works – all requiring a tremendous amount of planning and programming, says HEB.
A big central pond
The main components of the park centre around a very large, 22 million litre, pond (reservoir) which feeds two courses (one short and one long) via a large pump station.
The Pump station construction, says HEB, was complex due to the precise shape and tight tolerances that had to be achieved to meet the design criteria.
The pump station houses seven pumps of which the four larger pumps have the ability to pump four cubic metres per second, and the three smaller pumps 3.5 cubic metres per second.
The station is capable of delivering simultaneous water flows of 14m3/s to the grade four course, and 10m3/s to the grade two course with an additional 2m3/s to operate a raft-able 3.5 metre high waterfall. The system can be run with one or both courses in operation at the same time.
The Formed Suction Intake (FSI) (intakes to the seven pumps) shape was determined by ‘Computational Fluid Dynamics’ (CFD) modeling performed by the pump manufacture and supplier, says HEB
“Any deviation from the confirmed FSI shape could possibly be detrimental to the performance of the pumps. It was therefore critical to complete the FSI construction within the required tolerances.
“We developed a formwork system that could be jacked up into position and after each pour be jacked down and pulled out again without dismantling it.
“This method ensured the shape remained the same. We then replaced the form ply and placed it in position again to construct the next FSI. This method ensured that all seven bays for each FSI were exactly the same and within the required tolerance.”
The concrete lined reservoir is fed from an on-site bore and harvested rainwater. This water is treated from an onsite treatment plant using filtration and ultra-violet (UV) disinfection.
The water courses are made from cement stabilised earth and lined with shotcrete. Grades, drops, groynes and obstacles were used to generate the rapids in the channels. Each rapid can also be ‘tuned’ to provide optimum rapids by moving the re-locatable obstacles on the channel floor.
HEB concedes that the project build required a “tremendous amount of collaborative planning and programming” involving site foremen, supervisors, and engineers.
“Each week a construction meeting was held to review the programme, monitor progress and make decisions to advance the works.
“Detailed work method statements were constructed to communicate the difficult aspects of construction.
“Each month, senior HEB staff who were involved in the pricing of the works were invited to site, and each engineer presented the construction methodology that they were planning. This was a good check to ensure that the work was following the proposed methodology developed during the ECI phase and helped to identify any improvements and potential changes.”
Temporary works were a big component of the project with significant works involved in constructing the in-situ concrete walls, organic shapes and transitions inside the pump station and conveyor structures.
There were also a number of tricky suspended in-situ slabs for the waterfall, pump station and conveyor structures, as well as propping of precast retaining wall panels. A number of diversions had to be put in place to construct the twin 1800 diameter stormwater pipe and the trunk sewer diversion.
Once the floor was poured in each area, a specialist team then worked on the structural elements. There were some precast retaining walls, with a considerable number of elements cast in-situ and they also used a pro-forma Doka box forming system.
“No two elements were alike, so the Doka system, which can be assembled like a jigsaw to accommodate unusual shapes, worked well,” says HEB.
The majority of all the vertical retaining walls within the facility were constructed mostly by using Doka shutters, due to the speed of this system.
The construction of the channels for the two courses was particularly difficult, says HEB, as they are made up of two-metre-thick stabilised (two percent lime and two percent cement) clay batters, which were then shotcrete lined with a 125mm thick concrete layer.
“The control required to ensure we got the correct stabilisation, compaction and excavation profile while placing the concrete on the batters, was particularly challenging.”
Once the concrete was shotcreted onto the banks it was steel trowelled to get the required finish.
“This was a challenge due to the requirement to complete 10 metre sections at a time which required us to pour continuously, up to a construction joint.”
HEB developed a mobile profile system that could be moved with the pour to ensure that the concrete was screeded and finished to the design angle.
The late award of the park contract meant that much of the earthworks had to be carried out over winter and this presented its own risk.
“We applied extra resource (working double shifts if necessary) when the weather was fine and suitable for earthworks and concrete pouring to catch up on time lost through unsuitable weather.
“Ground conditions were the biggest risk factor to the earthworks as they were so variable and the water table very high.
“Drainage was a significant risk with large diameter pipes, some buried quite deeply. The ground conditions mean that the ground was often wet, swampy, black and sticky. We managed the risk through slide rails and trench shields and de-watering. We had to work in conjunction with earthmovers as some pipes had to be put in before filling.”
A confined site
Although it appeared to be a huge site it was, in fact, restricted and a lot of juggling was necessary to manage the multiple work fronts.
“The site looked big, but in fact every part of the site was to be built on, there were no other ‘stages’ where materials could be stockpiled or dried etc. The site was hemmed in by SH1 motorway, the Great South Road, Vodafone Event Centre.”
The site was also situated in a greenfield swampy area with clay soils, which made working during the wet season difficult. The ground water table was also very high which made working in deep structures and trenching challenging with potential excavation collapses. Most of the site had also been ‘worked’ in the past, including pre-loading for the pump station and heavy structural elements.
“The geotech was an unknown quantity and we worked closely with Gaia Engineering regarding the geotechnical status of the site. We had to shift all pre-load and cut down until we encountered virgin ground. This was then surveyed and then filled with controlled fill. There was a lot of cutting, pre- loading and drying. Lime and cement were added to condition the material. We re-used as much of the cut down material as possible and a large portion went to fill the Northern Car Park.”
HEB admits it has never constructed anything like this project before and, as it is the first facility of its type in the country, the company had little design/build precedents to go on. Because the geometry of the concrete course structures is made up of a series of complicated shapes, everything had to be constructed as unique in its own way – there were no benefits or efficiencies from structural repetition.
“The integration of the Design and Build packages within the client supplied design also added complexity to the project,” HEB adds.
- The finished project is an achievement recognised in the 2016 CCNZ awards where it was the winner of the Category 3 (projects with a value between $10m and $50m).