Mastavault Megatree – Welsford Street Redevelopment

Project Overview: Welsford Street Redevelopment Stage 4 
Asset Owner: Greater Shepperton Council
Client: Apex Earthworks

The Challenge

Greater Shepparton City Council is undertaking design and upgrade works to Welsford Street, one of the major north-south travel corridors, to improve the traffic flow and safety. The new design incorporated new trees to be planted in Welsford and Fryers street. The new design also included a full depth reconstructed road pavement designed to cater for the increased vehicle traffic volumes. Because trees are especially sensitive to both compaction and low soil oxygen levels, planting trees in small pits or adjacent to roads further impacts soil drainage and reduces the ability of plants to acquire sufficient water and nutrients needed to withstand drought.

Therefore, with the increased traffic load it was imperative to provide a  structural soil cell system which could support the increased traffic loading and a full depth pavement while providing an uncompacted fertile soil for the tree roots to grow and flourish.

Our Solution

Polyfabrics MastaVAULT Megatree structural soil cells were used in this instance to support the traffic load and to provide uncompacted growing media (soil) for the tree roots to grow and flourish. Megatree modules offer an unconfined vertical load bearing capacity of 65 tons / sqm and an unconfined lateral load carrying capacity of >7.5tons/sqm. The selected species for tree for the street scape, Spotted Gum ( Orymbia Maculata), to deliver high and immediate impact on the street, required approx. 48-50 cm3 of un-confined soil for a healthy root system. Therefore, Megatree Quad modules (1350mm deep) were chosen to limit the foot print of 36 sqm per tree, due to site space constraints. As part of this development, 300 cubic meter of Megatree Structural Soil cells were installed to prevent soil compaction over time around the trafficked areas and to promote healthy tree root growth. 

The structural cell design also incorporated a 150mm concrete slab, on a Mastagrid 3030GT geogrid placed over the Megatree modules, extending 500mm beyond the Megatree structural soil cell excavation to overcome the differential settlement, of the backfill, if any, during the 100 year design life of the project. A 410mm Type 1 Deep strength pavement was then placed directly over the top of the concrete slab.

MastaVault Megatree soil cell systems retain the soil structure and volume which in turns retains the porosity resulting in continuous moisture replenishment, retention, and supply; excellent aeration; and a reduced resistance to the root penetration.  All of these factors, especially in an urban environment, are very critical for the trees’ long-term success.