||Design Resilient Modulus for Coarse-Grained Subgrade Soils
M. Shabbir Hossain
In 2018, the Virginia Department of Transportation (VDOT) implemented AASHTO Mechanistic Empirical Pavement Design Guide (MEPDG) for new, reconstruction, and lane widening projects in primary and interstate roadways. To facilitate the pavement design, MEPDG recommends the resilient modulus (MR) to characterize the subgrade soils. As part of the VDOT MEPDG implementation efforts, Materials Division Soils Lab collected both fine- and coarse-grained soil samples from around the state and performed MR tests on them. For fine-grained soils (A-4, A-5, A-6, and A-7), with a sufficient amount of the test results statewide, average MR values were able to be determined. These average values have been currently used in the design of low volume (AADT <10,000) roadways. In addition, the correlations with the results of Unconfined Compression Strength (UCS) test that were developed from a VTRC study (2014)are currently being used to estimate design MR for high volume (AADT >10,000) projects as an alternative to actual MR testing. However, no statewide average MR values or correlations are currently available for coarse-grained soils (A-1, A-2 and A-3). Although some actual measured values are available, it has also been noted from the data that MR of coarse-grained soil is measured significantly lower than AASHTO recommended MR values (MEPDG default) which needs to be further investigated. The objectives of the proposed project are to develop recommended MR values for local coarse-grained subgrade soils and to establish correlations (if available) with other simple conventional soil tests to estimate MR values for coarse-grained subgrade soils that can be used when necessary. The findings from this study are expected to facilitate proper pavement design for Virginia roadways and help in VDOT’s efforts in implementing MEPDG.