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United States Department of Agriculture

Agricultural Research Service

Research Project: MANAGING BIOGEOCHEMICAL CYCLES AND RHIZOSPHERE ECOLOGY FOR SUSTAINABLE PRODUCTION OF APPALACHIAN PASTURE AND AMENITY GRASSES Title: Reducing compaction effort and incorporating air permeability in Proctor testing for design of urban green spaces on cohesive soils

Authors
item Ibrahim, A -
item Persaud, N -
item Zobel, Richard
item Hass, A -

Submitted to: Journal of Soil Science and Environmental Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 2, 2010
Publication Date: February 1, 2010
Citation: Ibrahim, A.M., Persaud, N., Zobel, R.W., Hass, A. 2010. Reducing compaction effort and incorporating air permeability in Proctor testing for design of urban green spaces on cohesive soils. Journal of Soil Science and Environmental Management. 1(1):021-029.

Interpretive Summary: Urban greenspaces (e.g. football and soccer fields) can become seriously compacted during construction or use, resulting in increased likelihood of injury to users. Serious compaction requires expensive remediation and/or management efforts to alleviate the danger to users, but is often difficult to quantify. This report discusses the first tests of a simplified method to determine the extent to which soils have been compacted. If this procedure is proven through additional testing in the laboratory and in the field, it will speedup and increase the accuracy of the assessment process. Greater accuracy will reduce necessary management and remediation costs.

Technical Abstract: It is well established that compaction negatively affects agronomic productivity, that air permeability is a sensitive measure of the degree of soil compaction and therefore a good indicator of soil productivity impairment from compaction. Cohesive soils in urban settings are often heavily compacted by the common engineering practice to compact sub-grades of urban construction sites to 95% or more of the optimum density obtained in standardized Proctor tests. The objective of this study was to determine to what extent reducing compaction effort would increase the air permeability of Proctor test specimens. Quantifying this relationship it would permit more appropriate Proctor test specifications for the design of urban green spaces on cohesive soils. We designed a portable transient flow apparatus for rapidly measuring air permeability, and used it to measure air permeability on Proctor test specimens of three cohesive sub-grade soil materials covering a range of USDA textures (loam, silt loam, and silty clay) and Proctor compaction characteristics. We compacted test specimens at their Proctor optimum water content using efforts ranging from 100 % to 25% (the lowest practicable value) of that used in the standardized Proctor test. Results confirmed that compaction severely reduces air permeability of the test specimens, and indicated that the common practice of compaction to 95 % or more of the optimum Proctor density is probably not appropriate for construction of urban green spaces. Reducing compaction effort from 100 % to 25 % of the standardized Proctor test value increased air permeability 30, 89, and 42 times respectively for the loam, silt loam, and silty clay test specimens. More extensive studies are needed to correlate measured air permeability of Proctor test specimens to agronomic productivity of urban green spaces.

Last Modified: 7/31/2014
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