Minnesota Department of Transportation
Poor drainage of roadway base materials can lead to increased pore water pressure, reduction of strength and stiffness, and freeze-thaw damage. Drainability is dependent on soil/aggregate physical properties that affect water flow and retention in the porous matrix, notably including particle-size distribution, particle shape, fines content, and density or porosity. The objective of this project was to quantitatively assess permeability and water retention characteristics of soil and aggregates applicable to pavement applications and to evaluate and derive predictive equations for indirect estimation of these properties. Samples of 16 materials used in transportation geosystems were obtained and laboratory tests were conducted to determine grain size distribution, index properties, saturated hydraulic conductivity, and soil-water characteristic curves. Results were analyzed to examine applicability of estimation equations available in the literature and to develop dataset-specific equations for the specific suite of materials. Procedures were provided to qualitatively assess base course drainability as "excellent," "marginal," and "poor" from grain size properties, thereby offering rationale to reduce pavement life- cycle costs, improve safety, realize material cost savings, and reduce environmental impacts.
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