Cranbrook College
Natural turf oval redevelopment over a 50-metre swimming pool
New South Wales

Led by SPORTENG’s Senior Civil Engineer Cameron Nayar, the oval at Cranbrook College presented a unique challenge as the project had already begun when SPORTENG was engaged to produce design drawings within a tight timeframe.

“We had to produce a set of construction drawings in the space of about a month to allow them to continue construction without any delays, to reach the window for the grass growing season”, said Cameron.

Another challenge was that construction had already started on the other parts of the sporting facility, which meant that the Field of Play had to be designed within a fixed perimeter.

“Whatever we did, we couldn’t change the levels too much, and we had to try and make it work within the Field of Play area. It was a difficult challenge, as there were a lot of different parties involved in the project, and we constantly had to come up with solutions that would work in the already existing fixed perimeter”, added Cameron.

The third challenge was designing a solution for the oval profile, as half of it would sit over the school’s underground swimming pool, the other half on natural ground.

“It would be poor design to have water sitting directly on the concrete slab for long periods. If it did, it would create an extra surcharge on the slab, putting more weight and pressure on it. The best option here is to get the water away from the slab as quickly as possible; there is also the issue of two different subgrades, which can lead to differential settlement. This needed to be accounted for in the profile design”, explained Cameron.

With such a long train of command and a short timeframe, SPORTENG had to come up with smart solutions to be able to deliver the design on time.

Cameron started with on-site visits to understand the subgrade requirements: “The first thing I did was to check if any testing has been done on the existing ground”, said Cameron. “I went on-site and investigated this side of the natural turf and dug some holes to check the profile.”

He discovered that it was a sandy profile; therefore, no subgrade improvements were necessary, and we could safely lay gravel sand on sand without too much risk of settlement. Tests were also conducted on imported fill on-site to ensure it didn’t contaminate the sandy subgrade.

The next challenge was creating a homogeneous profile that could drain quickly over the two different subgrades. Cameron solved this by using a perched water table profile which consisted of a homogeneous layer of gravel and sand, with the addition of a drainage cell on top of the concrete slab to allow the runoff to drain more quickly. The level differences were corrected with different thicknesses of drainage gravel, and a constant depth sand layer was installed.

Also, a different process solution was needed for this project: “Rather than delivering a fully comprehensive design in one package, we adopted a staged method, where we worked the contractor enough lead time to order materials and bring it to the site, before moving on to the next stage”, Cameron said.

SPORTENG delivered the requested design on time while staying within the budget designated by our client Landscape Options.

The school is now using the oval for school practice and competition. The school also plans to open the sporting complex to the broader community through various activities.

When asked about the new sporting facility, School Council President Jon North said: “[Students] find it really inspirational. The school’s environment is important for learning and designed in line with Cranbrook’s educational philosophy, which is about inquiry and experience, and being creative. A lot of the facilities were built 50 years ago, and they were built for a smaller school and fundamentally we needed more teaching and learning spaces.”

Source: Cranbrook unveils $125m revamp as private schools compete in building boom