Structural soils can be used as base material under pavement or can serve as the sub-base, 18” to 36” deep, for the entire pavement section. Geo-textile can be used to discourage root growth in undesirable areas; however, it should not interfere with water flow. Preferable plants choices are alkali-soil type and drought tolerant species. This is subject to climatic variations.
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Some construction concerns arise from the soils sensitivity to change. Batching, shipping and installation are critical to the success of the soils’ structural integrity, and should be monitored by soil experts throughout the process of acquiring and installing. The structural soil has to be mixed and placed consistently throughout the site.
During the placement, the soil must be damp, but protected from rain. The soils can be compacted to 95%. Some providers specify the use of certain equipment to achieve the perfect compaction and evenness. For example, CU-Soil requires using 6” lift for placing and compacting soils. The right balance of aggregate material and soil is necessary, and complications can arise if the ratio is inappropriate. If too much soil is added, the lattice structure is weakened, increasing the possibility of erosion. When installed properly, the system requires little maintenance, unless subsurface irrigation or aeration structures are used.
The installation of trees into structural soil is similar to the normal street tree installation procedure. This makes the system easier to replicate on a larger scale. While this process of properly installing structural soil is costly, the long-term benefits should outweigh the burden of initial costs. Fortunately, the high cost of this technology is temporary. As structural soil practices become more common and standardized, success rates are likely to increase. This will hopefully spur widespread use, standardization, and decreased overall costs.
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