Establishing andmanaging trees under urban conditions provide a lesson in opposing needs within limited spaces. In the same soil volume, there are competing requirements for pavement support versus biological carrying capacity. Media to support both pavements and tree growth have been used for decades. However, with several media designs being advanced and discussed, there is limited research testing to inform mix design when new component sources are considered, or when comparing different components and mixtures. Designed media need to perform an engineering function immediately, but trees require time for growth to reach the designed service size. Therefore, there is a need to understand fundamental trends prior to waiting decades for tree performance evaluation. A common evaluation rubric needs to be developed in order to compare successful and unsuccessful systems and to better target mix designs of locally available materials. The media discussed in this article is a group that establishes an aggregate skeletal matrix for load bearing with an added horticultural component for tree root growth within the matrix. To understand both matrix development for load bearing and the critical soil component for tree biotic capacity, one convenient media evaluation method would be a voids analysis based on a four-component system of air, water, soil, and aggregate. A further adaptation from a similar method to define the critical amount of bitumen in asphalt concrete design seems contextually appropriate. This approach would use a voids analysis on a four-component system, akin to historic Marshall Testing Protocols. The term "percentage of apparent voids filled" is used as one component in a voids analysis approach.An initial voids analysis output series is suggested using peak compacted density, California bearing ratio, hydraulic conductivity, plant-available moisture/percent air voids at field capacity, percent voids in compacted mineralmatrix, and percentage of apparent voids filled as measured across increasing soil-stone ratios within defined aggregate and soil pairings. Using archived data from a series of past experiments, a voids analysis example is used to illustrate a common format to reconcile the varied soil design systems into a commonmatrix for better comparison, understanding, and refinement.
All Science Journal Classification (ASJC) codes
- Soil Science
- Tree growth matrix
- Urban soil design
- Voids analysis