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Permeability of Base Material for Maine Roads

Cutting the cost of road maintenance and reducing life-cycle costs are the main reasons the FHWA has increased its emphasis on drainage in the pavement structural section. Good drainage requires that the base and subbase drain freely and relatively quickly. Poor drainage is thought to cause the Maine Department of Transportation (MaineDOT) to spend millions of extra dollars each year maintaining its state highways. Improved specifications and design policies for subbase material were developed by investigating the gradation and permeability of the subbase currently used by MaineDOT. Eight field projects were selected to investigate the permeability and gradation of subbase material for Maine roads. Results indicate that typical MaineDOT subbase gradations have excess fines and sand-size fraction compared with FHWA recommendations. The standard subbase currently used by MaineDOT has an average coefficient of permeability of 5.9 × 10−4 cm/s (1.7 ft/day) whereas the FHWA recommends a minimum coefficient of permeability of 0.35 cm/s (1,000 ft/day) for permeable base material. With multivariable regression analysis, an equation was determined to estimate subbase permeability from percent fines and coefficient of uniformity. Life-cycle cost savings of up to $244,000/km ($406,000/mi) of road can be achieved in Maine with the use of permeable base.