In Structural Soil—Part 1, the many problems confronting urban trees were outlined and the need for a specially designed growing medium for such trees was amply demonstrated. In Part 2, the authors describe their development of CU-Structural Soil™ and share lessons learned after using this load-bearing soil for 15 years.
Why was CU-Structural Soil™ developed?
Soils under pavement need to be compacted to meet load-bearing requirements so that sidewalks and other pavements won’t subside and fail. Soils are often compacted to 95% peak (Proctor or modified Proctor) density before pavements are laid. When trees are planted into these soils, root growth is severely reduced or eliminated beyond the tree-planting hole. When root growth is restricted, tree growth suffers as water, nutrients and oxygen are limited. The need for a load-bearing soil under pavement gave rise to the development of CU-Structural Soil™, a blended soil that can be compacted to 100% peak density to bear the load of a pavement while allowing tree roots to grow through it.