3rd Specialty Conference on Material Engineering & Applied Mechanics 3e Conférence spécialisée sur le génie des matériaux et mécanique appliquée Montréal, Québec May 29 to June 1, 2013 / 29 mai au 1 juin 2013 MEC-016-1 EVALUATION OF PRE-OVERLAY RUT DEPTH FOR LOCAL CALIBRATION OF THE MEPDG RUTTING MODEL IN ONTARIO Afzal Waseem, Xian-Xun Yuan and Medhat Shehata Department of Civil Engineering, Ryerson University, Toronto, ON Abstract: Pre-overlay rut refers to the terminal rut depth at the end of previous life cycle of a rehabilitated flexible pavement section. Sensitivity analyses have shown that it is a very important input parameter for the rut depth prediction of rehabilitated sections in the mechanistic-empirical pavement design guide (MEPDG). However, due to limitations of historical pavement performance database, the pre-overlay rut is not always available. An uncertain pre-overlay rut would result in an inefficient local calibration, particularly when the pavement management system data are used for local calibration. This paper presents results from an investigation to estimate the pre-overlay rut depth and its effects on local calibration results based on data from Ontario’s long-term pavement management system. The study showed that 7mm, the average value of terminal rut depth, can be used for the pre-overlay rut when it is unavailable for local calibration. This result overturned the 4mm assumption that the ministry staff suggested before. 1 Introduction The need for a mechanistic approach was first recognized in 1986 when AASHTO Guide for Design of Pavement Structures was developed. In March 1996, the AASHTO Joint Task Force, NCHRP and FHWA decided to work on development of a mechanistic-empirical pavement design methodology. A decade later in 2004, the Mechanistic-Empirical Pavement Design Guide (MEPDG) was developed by NCHRP under project 1-37A [1]. In July 2008, the AASHTO released the interim edition of the Manual of Practice (MOP) of the MEPDG [2]. More recently a Guide for local calibration of the MEPDG based on the research under project 1-40D was published in 2011 [3]. Transfer functions or distress models in the MEPDG that link the structural responses and pavement distresses and performance were globally calibrated using the Long Term Pavement Performance (LTPP) data. These distress models may not represent locally utilized material, traffic, climate, subgrade soil, and construction and maintenance practices. Due to these various differences in local conditions, globally calibrated coefficients would not be the optimum choice. Although the LTPP data included pavement sections from Ontario, still globally calibrated calibration coefficients were found to be over predicting distresses, particularly the rut depth [4]. Therefore there is a strong need to conduct local calibration for pavement design in the province of Ontario. In response to this need, a research project was initiated by the Ministry of Transportation of Ontario (MTO) to develop a local calibration database by using the long-term pavement performance data that have been collected through the second-generation Pavement Management System (PMS-2) operated by the Ministry since 1980s. In Ontario, a vast majority of roads have flexible pavements, and a main