AASHTO Drainage Coefficients for Flexible Pavements


A method for determining American Association of State Highway and Transportation Officials (AASHTO) drainage (m) coefficients for flexible pavements is presented. In essence, m coefficients were developed as ratios of the layer coefficients of the AASHO road test granular base material under any given drainage and climate condition to the layer coefficient of the road test base material under road test site conditions. The layer coefficients were calculated from resilient moduli determined for various conditions by use of elastic layered analysis. The moduli were varied by changing subgrade and base moisture conditions for any given time of year. The base material moisture sensitivity (effect on θ model constants k1 and k2) was determined, in part, by the resilient modulus laboratory testing of granular materials. The result of the preceding analysis was the creation of a set of tables that guide the designer to a choice of m coefficients. The new m values can be used to provide a rational measure of the influence of pavement drainage on pavement performance.


Civil, Architectural and Environmental Engineering

Keywords and Phrases

Base Course (Pavements); Drainage Coefficient (Pavements); Flexible Pavements; Granular Materials; Laboratory Tests; Layer Coefficient (Pavements); Modulus of Resilience; Pavement Performance; Subgrade (Pavements); Tables (Data)

Document Type

Article - Journal

Document Version


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© 2001 Transportation Research Board, All rights reserved.

Publication Date

01 Jan 2001