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Land.Tiles: erosion Control tile System
from Living Systems
by TD Garden
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Products and Technologies // 157
Launch Stratify Fluid Grooming Digestive Translate struCtural soils //
Volatile
A major impediment to the success of tree growth in urban conditions is the lack of soil volume. Without sufficient soil volume to expand their root systems, the plants and trees are impacted in a number of ways, including their total growth, susceptibility to disease and drought, and long-term survival. Structural soils address this problem by creating an engineered medium that can both meet loadbearing requirements and serve as a medium for root growth. They use a combination of organic material and structural materials to create a medium that can be used as a subgrade underneath paved surfaces or surface for traffic and still maintain sufficient aeration, drainage, and flexibility for root growth. By allowing the growth of roots underneath paved surfaces, structural soils allow for a greater integration of trees in constructed environments, and reduce the likelihood of sidewalks heaving from restricted root growth. There are two types of structural soils: Cornell University Structural Soil™ and Amsterdam Tree Sand.
Cornell University Structural Soil (U.S. Patent # 5,849,069) employs a lattice of crushed stone as the structural basis of the medium. The soil is “gap-graded” such that intermediately-sized soil particles are excluded, preventing them from filling in the space within the lattice that enables proper aeration and drainage. Heavy clay loam and organic matter are mixed with the crushed stones to provide water, nutrient-holding, and cation exchange capacity. The complete soil recipe calls for crushed stone (granite or limestone) graded from ¾ – 1½in (1.3 –1.9cm), clay loam conforming to USDA soil classification system with < 30% gravel, 25 – 30% sand, 20 – 40% silt, 25 – 40% clay, and a small amount of Gelscape® hydrogel stabilizing agent, which acts as a tackifier.
Heicom’s Amsterdam Tree Sand was developed in Holland and is now manufactured world-wide under the brand name Amsterdam Tree Sand or Soil. With over 20 years of application, it has proven to be an effective medium for urban trees. It generally consists of 60 – 70% graded silica sand and 30 – 40% organic matter produced from composting landscape trimmings. The quality of silica granules allows the soil to achieve 85% – 90% compaction, thus supporting paving and resisting compaction from pedestrian and vehicular traffic. The silica’s texture also allows for oxygen and moisture to reach the root zone and support healthy tree growth. Added organic matter increases the soil’s aeration, water retention, and available nutrients.
Sources: Urban Horticulture Institute, Department of Horticulture, Cornell University; Heicom, UK
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