Stratacells help transplant mature trees in Forrest Place Australia

By Kristyn Levis

The Citygreen modular Stratacell system has provided a much needed solution to the transplanting of trees for the Forrest Place project in Perth Western Australia.

The project’s aim was to link Forrest Place with the Perth Station Forecourt in order to create a “grand space” for the city’s primary urban area within the CBD.

Andrew Baranowski, director of Plan E, collaborated with Woodhead Architects and the City of Perth in the planning and design of the Forrest Place and Perth Station Forecourt.

Baranowski said the space was to be “contemporary but evocative of a traditional formal city square, cohesive in design and highly flexible to function with both a day and night culture”.

Plan E started designing the project in 2006. Construction was completed in 2013 with an overall budget of approximately $21 million. The project team was fully multidisciplinary and Plan E worked successfully with the architect, the construction engineers and electrical, structural, civil, hydraulic and irrigation consultants.

“The design establishes a seamless visual and physical connection between Forrest Place and the station forecourt by the removal of the pedestrian bridge and the stairs to Wellington Street, and extending consistent treatments across Wellington Street into the station forecourt,” Baranowski said.

He added that in order to improve the flexibility of Forrest Place as a venue for major performances and events, the stage area was repositioned and a new overhead canopy was provided.

“The space incorporates new seating areas, transplant trees, an interactive water feature and a controversial sculpture, combining to create a more dynamic and interesting space,” he said.

One particular issue with the project was the transplanting of trees in the area. Baranowski said nine mature Chinese Elms from the Perth Station Forecourt on Roe Street had to be relocated into the space, “which presented logistical problems in terms of transport and access, as well as soil depth and space (due to construction over car park slab)”. They had limited soil depths in which to plant the proposed mature Chinese Elms on the site.

Using Stratacells as the structural soil cell easily solved this issue. Baranowski said the Stratacells “offered the perfect system to ensure an adequate volume of soils to sustain the trees into the future”.

He said that providing adequate soil volumes to tree wells is the “single most important factor in the success of tree planting in urban spaces such as Forrest Place, particularly where the trees are semi-mature transplants and planted over a car park structure with limited soil depths ranging from 0.70 to 1.2 metres”.

That is why they wanted to ensure that the contractors installed the Stratacells correctly in the initial stage of the project. This was made easy by the site presence of a Citygreen representative during the installation process. Once the contractors knew how to install the Stratacells, every thing else fell into place. The system worked very well for the intended design of the project.

“The system is better due to its flexibility, modular design and speed of installation, in comparison to other systems we have used. The system is comparable in materials cost. However due its speed of installation, we believe that it is more cost effective overall,” he added.

He said that the trickiest issue they faced was getting the drainage to the tree wells working correctly. It resulted in a number of the trees failing. During replacement of the trees, further drainage was installed which resolved the problem.

Other challenges that the project faced include the lighting design, water delivery and the selection of robust materials. Lighting is a significant feature of the Forrest Place project. It has been designed so that “there is a high degree of control to act as theatre lighting for events”. The lighting will also change with the seasons, with a cooler light in summer and warmer lighting in winter.

Water harvesting design was also included in the project where all rainwater from paving is collected in a large underground tank and then used for irrigation.

The project also required the selection of “durable and robust materials and construction methods, including the granite paving (utilizing WA granite) and the precast concrete walls and seats”.

The Stratacell system fits well with what the project needed given the module’s extremely high compressive strength. It can sustain the weight of an ASV PT-50 multi terrain loader and has a 550kPA vertical load. Aside from having a very high strength capacity, the Stratacell modules are also recyclable and are manufactured from 100 per cent recycled polymer. As there are no steel components, the modules are corrosion free.

Plan E was quite happy with the system that it has been specified in other projects, including the Cambridge Streetscape, Perth City Link, and more.

“After the initial problem with drainage, and establishment of proper monitoring procedures, the trees are performing very well,” Baranowski said.