An Investigation Of Structural Responses Of Inverted Pavements By Numerical Approaches Considering Nonlinear Stress-Dependent Properties Of Unbound Aggregate Layer

Inverted pavement has a unique structure that consists of an unbound aggregate base (UAB) layer sandwiched between a thin bituminous surface and a stiff cement-treated base (CTB). The stiffness of the successive pavement layers decreases with the depth, which is different from the conventional flexible pavement. The nonlinear stress dependent property of the UAB layer plays a critical role in the structural response of the inverted pavement, which contributes to its service performance and durability. This paper presents simulations of 3-D finite element models verified by GTPAVE data to investigate the effect of the UAB layer on the pavement structures. The linear elastic and nonlinear elastic models were applied to both inverted and conventional pavements. The results show that the inverted pavement was more sensitive to the nonlinear stress-dependent property of the UAB layer due to the compaction effect from two stiffer layers of an upper thin AC layer and a lower CTB layer. The stress distribution along the load centerline, deflection along the asphalt concrete (AC) layer, and the stiffness distribution contours within the UAB layer were also investigated to make a comparison of the structural response between the inverted pavements and conventional pavements under the effect of the UAB layer. The comparison study presents that the inverted pavement had better performance and saved more asphalt under the same loading condition: (1) the bottom of the AC layer in the inverted pavement experienced lower tension; (2) the deflection along the AC surface was also much smaller than that of the conventional pavement. In addition, the inverted pavements with different thickness of the UAB layers were compared, which showed that a thicker UAB layer could increase the tensile stress at the bottom of the AC layer but relieve the tension transferred from the bottom of the CTB layer.