Knowledge of Effects of Different Mississippi Soil Deposits on Pavement Performance

MDOT S.O.P. TMD-20-14-00-000, “Centerline Soil Profiles and Standard Design Procedures for Construction of Roadways Through High Volume Change Soils,” specifies use of the Mississippi Office of Geology’s Geologic Map of Mississippi to identify the boundaries/areal extent of geologic units of various soil types distributed across the state. This S.O.P. references eight geologic units that include active clays requiring either replacement or treatment with lime. The Mississippi Department of Transportation (MDOT) Assistant Chief Engineer – Operations advised that MDOT does not construct rigid pavements within the “Loess” geologic unit due to the erodibility of this type soil. These examples demonstrate that given soil deposits impact selection of pavement type or construction practice. Mississippi DOT is in the process of implementing the Mechanistic-Empirical Pavement Design procedure for designing rigid and flexible pavements. This effort includes providing the agency with a manual, “Mississippi DOT Pavement ME Design User Input Guide.” The current draft manual needs to be enhanced with the addition of a chapter focused on the various soil deposits located throughout the state. This chapter will capture available institutional knowledge on the general properties of each geological unit of soil deposit and their effects on the performance of pavements constructed thereon. Given geological units requiring special pavement design or pavement foundation considerations will be addressed. This chapter will also list the geologic units that preclude construction of rigid pavements. It is envisioned that the Mississippi Office of Geology’s Geologic Map of Mississippi will be used as the basis for this chapter with accompanying discussion of each geologic unit and corresponding impact on pavement performance.