In 1999, the Ontario Ministry of Transportation awarded the Highway 407 ETR Concession a 99-year lease to operate, maintain, and expand Ontario Highway 407. Highway 407 consists of 69 km of 6-lane divided highway which extends to the east (14.7 km to Markham) and west (24.7 km to Hamilton). The initial designs for the Highway 407 pavement structures were completed using the 1993 AASHTO Guide for the Design of Pavement Structures and the associated DARWin pavement design software. After completing the AASHTO-based designs, a mechanistic analysis of each design section was completed using the Shell BISAR computerised elastic-layer pavement analysis program and an established asphalt concrete fatigue damage model. BISAR facilitates the mechanistic modelling of the pavement structure and calculates the stresses and strains caused by vehicle loading. The purpose of the mechanistic analysis was to predict when pavement structural deterioration (fatigue cracking) would reach a level that the pavement required structural enhancement (e.g. an HMA overlay). The critical pavement response is the horizontal (tensile) strain at the bottom of the asphalt layer. The tensile strain occurs when the pavement is loaded and is a function of the load magnitude, tire pressure, and pavement thickness and stiffness. Over time, repeated tensile strains at the bottom of the AC layer result in fatigue cracks that begin at the bottom of the HMA layer and propagate to the pavement surface. Each pavement section was modelled in BISAR using the pavement layer thickness and the material properties developed for the AASHTO designs. The structural characteristics of the subgrade and pavement layers vary from month to month, depending on moisture conditions and temperature. After completing the BISAR analysis, the monthly AC stiffness (modulus) values and associated tensile strains were used as inputs into a fatigue equation from the program PDMAP. The PDMAP equation is based on laboratory test data that has been calibrated to the levels of cracking observed at the AASHTO Road Test. This paper presents an outline of the analysis, calibration, and validation methodology for the mechanistic-empirical pavement design of the high-volume Highway 407. (Author/publisher)
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