Reviewing Compost Use In Construction and Modeling The Hydrologic Response of Vegetated Compost Blankets

Written by Corey Poland – August 2018

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Abstract
The objective of this independent study is to evaluate the use of compost in large scale earthwork projects such as those conducted by Departments of Transportation. A literature review outlining how compost can be used for soil stabilization, runoff reduction, and vegetation establishment in construction sites shows that compost is viable for these purposes. Important design parameters related to compost were taken from scientific literature, as well as from recommendations by the American Association of State Highway and Transportation Officials and the U.S. Composting council, the authority on composting in the U.S.

Then each state’s latest DOT design specification document was assessed for if/how compost use is prescribed. Most states had some mention of compost, but specifications varied widely in scope. The particle size distribution requirements differed from state to state significantly. Many of the requirements outlined by the U.S. Composting Council and the American Association of State Highway and Transportation Officials were not incorporated design specifications for each state.

Modeling of the hydrology of vegetated compost blankets explored different vegetation scenarios, depths of compost, and types of compost in the one-dimensional domain. Fully established vegetation represents a significant sink of soil water from the root zone as transpiration or root water uptake. Since fully established vegetation covers exposed soil, it limited evaporation as well. Varying the depth of the compost layer had less of an effect on the change in soil water storage, evaporation and transpiration than changing the vegetation or type of compost. Different depths of compost did, however, affect the runoff depth more than changing the vegetation. Changing the hydraulic properties of the surface layer, based on hydraulic testing of various composts, had the greatest effect on runoff. While modeling different types of compost, we found the evaporation from the surface is not necessarily an indicator of the hydrologic effectiveness of a surface compost layer, as more water can infiltrate but is subject to evaporation, leading to similar cumulative evaporation.

Overall, the positive effects of compost have been demonstrated while DOTs and other construction companies would benefit from expanded understanding of how to use compost effectively on site. A way to model vegetated compost blankets is presented, which can help engineers determine how to best incorporate compost into design.