Mechanical Behavior of Asphalt Pavement Considering the Stress and Moisture Dependency of Unbound Granular Base

Unbound granular material (UGM) has been well acknowledged for its nonlinearity, specifically its stress and moisture-dependent resilient modulus (Mr). Yet, the linear-elastic-theory-based design process is still prevailing in practice, which highlights the dilemma between the linear pavement structure design methods and nonlinear pavement material properties. This research sets out to reveal the discrepancies between nonlinear pavement analysis using a moisture-adjusted Uzan model and linear pavement analysis following the current linear pavement design protocols, i.e., US-MEPDG and China-D50 methods. Field temperature moisture data were collected as environmental inputs. Pavement responses and long-term performances (asphalt layer cracking and subgrade deformation) were analyzed given multiple temperature–moisture combinations. The results demonstrate that significant differences exist between nonlinear and linear analyses. Compared to nonlinear analysis, the tensile strain and compressive strain deviations can reach up to 84% and 38%, respectively. Fatigue life predictions of asphalt layers differ by −33% to 50%, and subgrade permanent deformation differs by −47% to 30% in linear analyses. These findings confirm that ignoring the stress dependency and moisture sensitivity of UGM can lead to substantial errors in pavement performance predictions. This study recommends incorporating nonlinear material models into future pavement design practices.