Mechanistic-empirical method of pavement design extending unsaturated soil mechanics

Pavement system that typically constitutes of different soil and material layers is located within the vadose zone that is above the groundwater table, which is in an unsaturated condition. Due to this reason, suction is a crucial stress state variable for interpreting the behavior of pavements in the vadose zone. The Mechanistic-Empirical Pavement Design Guide (MEPDG) serves as a comprehensive design tool that accounts for both the resilient response and environmental influences on pavement material properties. In this study, a series of California Bearing Ratio (CBR) tests were conducted on both saturated and unsaturated compacted soils that are commonly used as pavement subgrade materials in Toronto, Ontario. A modified CBR apparatus was utilized, incorporating orifices drilled into the CBR mold to monitor matric suction, ψ and water content using MPS-6 (or TEROS-21) and EC-5 sensors, respectively. The measured CBR and ψ values along with resilient moduli were then used to develop correlations to estimate resilient modulus, M_R of compacted soils required for Level 2 design in the MEPDG. The modified CBR testing procedures used in this study are anticipated to be applicable to other soils for estimating M_R, aiding in the design of pavement subgrade materials.