Structural Zone is a mixture of 40-60 mm clean stones and ScapeSpec Tree Pit media (TP120) which meets engineering requirements for a load-bearing paving base, while allowing tree pits to be extended beneath hard surfacing.
An organic hydrogel prevents the soil and stone from separating during the mixing and installation process. The compacted stone and soil mix has 20-30% void space for the storage and dispersal of air and water.
Tree Pit media (TP120)
TP120is an engineered soil that supports tree maturity in urban environments. It is blended from quality sands, premium Waikato topsoil and rich compost. Working alongside Structural Zone, it has excellent workability. Slow releasing fertiliser can be added to give a good dose of nutrients and minerals to help tree root growth.
Importance of Design Criteria
A uniformly-graded stone with the proper stone-to-soil ratio creates a rich medium for healthy root growth, which can also be compacted to meet engineers' load-bearing requirements.
In the correct ratio, each stone touches another, forming a rigid lattice or skeleton, while soil almost fills the spaces between them. Aeration and bearing capacity are compromised if the voids are overfilled with soil.
As part of the mixing process, hydrogel is added as an adhesive gel to stabilise the mix. Stones and TP120 mix uniformly when the gel is applied, minimising separation caused by vibration in transit, dumping, and working the material during installation.
Read more about Structural Soil.
