A New Urban Tree Soil to Safely Increase Rooting Volumes Under Sidewalks    (View PDF)

Jason Grabosky and Nina Bassuk

Abstract: Soil compaction, which is necessary to safely support sidewalks and pavement, conflicts with urban trees' need for usable rooting space to support healthy tree growth. We have defined a rigid soil medium that will safely bear loads required by engineering standards yet still allow for rapid root exploration and growth. This was accomplished by forming a stone matrix and suspending soil within the matrix pores with the assistance of a hydrogel gluing agent. Initial studies using three stone types and various stone to soil ratios showed that the compacted stone-soil test medium (dry densities > 1700 kg/m3) increased root growth by a minimum of 320% over the compacted clay loam control (dry density of 1378 kg/m3). The proposed system can safely bear load demonstrated by California Bearing Ratios consistently exceeding 40. Discussion of a critical mixing ratio is presented as an approach for developing a specification for field installation.

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https://doi.org/10.48044/jauf.1995.030