Flexible Pavement Design Simulation Using Mechanistic-Empirical Pavement Design Guide

The KDOT （Kansas Department of Transportation） is currently adopting MEPDG （mechanistic-empirical pavement design guide） to replace the 1993 AASHTO （American Association of State Highway and Transportation Officials） design method. The main objective of this study was to compare flexible pavement design using 1993 AASHTO design guide and MEPDG. Five newly built Superior PERforming Asphalt PAVEments （Superpave）, designed using the 1993 AASHTO Design Guide, were selected as test sections for the design simulation study. Deflection data were collected approximately 8 to 10 weeks after construction using FWD （falling weight deflectometer）. The FWD deflection data were used to back-calculate the pavement layer moduli using three different back-calculation programs. The existing pavement structures were analyzed for a 10-year analysis period. The maximum numbers of years the existing pavement structures will be in a serviceable condition as well as the minimum thicknesses of different layers to serve for 10-years were also determined. Effects of changing subgrade modulus, target distress, and reliability were also investigated. The MEPDG design analysis shows that the 1993 AASHTO Guide-designed flexible pavements do not show the distresses currently observed in Kansas for the 10-year design period. The MEPDG design simulation shows that the thinner the pavement sections, the higher the permanent deformation. The existing pavement structures can serve for more than 20 years as per the MEPDG design analysis if the default failure criteria and nationally-calibrated models are used.

Can back-calculated lengths based on otoliths measurements provide reliable estimates of Atlantic halibut(Hippoglossus hippoglossus)growth in the Gulf of Maine (U.S.A.)?

Atlantic halibut(Hippoglossus hippoglossus,Linnaeus,1758)are a data-poor stock within the waters of the United States.This study evaluated the use of otolith measurements to back-calculate lengths of Atlantic halibut at previous ages.Back-calculations have proven useful for estimating length at age and growth rates of other species.To the best knowledge of the authors,this study is the first to document the use of this method for Atlantic halibut.Otolith back-calculations rely on a few key assumptions,such as proportionality of fish length and otolith length,which are not always met.This study shows that backcalculations using the Fraser-Lee method can provide reasonable estimates of Atlantic halibut length at previous ages,especially when samples from young halibut are included to improve estimates of the intercept of the linear regressions.Based on back-calculated estimates,female and male halibut in the Gulf of Maine showed different growth rates after age five.There was no evidence of changes in growth rates over an approximately 15 year time period.Halibut caught in the Gulf of Maine and on the neighboring Scotian Shelf showed some differences in growth rates;however,the results did not support strong conclusions about differences between the two regions as the direction of the differences was not consistent between the sexes and previous tagging studies have shown extensive movement between the two areas.The finding of reasonably accurate back-calculated lengths at previous ages is important for this data-poor species,as back-calculations increase the amount of information that can be obtained from otoliths.

Assessing artificial neural network performance for predicting interlayer conditions and layer modulus of multi-layered flexible pavement

The objective of this study is to evaluate the performance of the artificial neural network(ANN)approach for predicting interlayer conditions and layer modulus of a multi-layered flexible pavement structure.To achieve this goal,two ANN based back-calculation models were proposed to predict the interlayer conditions and layer modulus of the pavement structure.The corresponding database built with ANSYS based finite element method computations for four types of a structure subjected to flling weight deflectometer load.In addition,two proposed ANN models were verifed by comparing the results of ANN models with the results of PADAL and double multiple regression models.The measured pavement deflection basin data was used for the verifications.The comparing results concluded that there are no significant differences between the results estimated by ANN and double multiple regression models.PADAL modeling results were not accurate due to the inability to reflect the real pavement structure because pavement structure was not completely continuous.The prediction and verification results concluded that the proposed back-calculation model developed with ANN could be used to accurately predict layer modulus and interlayer conditions.In addition,the back-calculation model avoided the back-calculation errors by considering the interlayer condition,which was barely considered by former models reported in the published studies.