Flexible Pavement Design: Sensitivity of the NCHRP 1-37A Pavement Design Guide, A Global Approach

摘要

The design guide developed under National Cooperative Highway Research Program NCHRP 1-37A project is a very complex pavement analysis tool, with many input factors which characterize materials, climate, traffic and construction. Sensitivity analyses have been conducted recently to try and better understand the influential input parameters of the process. These sensitivity analyses have utilized the one-factor-at-a-time method, which is generally referred to as local sensitivity analysis. A global sensitivity analysis samples the entire input parameter space of selected input variables. These samples are used to create a matrix of design scenarios which were then be run through the NCHRP 1-37A design software, to predict pavement performance. This research effort, evaluated the following input parameters: AADTT, Truck Traffic Classification (TTC), HMA Thickness, Subgrade Strength (characterized by CBR), Nominal HMA Base Size, AC Binder Grade (standard grade and "bumped" grade for improved performance), Climate Zone, Construction Month and HMA base Gradation (coarse/fine). One hundred design sections were sampled from the input parameter space of these variables. Pearson's and Spearman's correlation coefficients were used to evaluate the relationship between the input parameters and predicted performance. This analysis indicated that several variables did not exhibit influence on the predicted performance, most notably, HMA base thickness, "bumping" of the PG binder grade, and HMA base gradation. This may indicate that further refinement and evaluation of the design guide models may be necessary, both in the prediction of HMA complex modulus and in the prediction of pavement distresses. To verify the potential reduction in variables, these variables were given default nominal values, while the remaining inputs were varied throughout their parameter space. Design scenarios were then run through the 1-37A design software and compared with scenarios which used the complete set of design inputs. This comparison indicated that satisfactory results could be obtained with the reduced set of input parameters. Findings of this study may be used to verity the link between Superpave and the NCHRP 1-37A Design Guide. Future research will expand the parameter space under investigation to include additional HMA mix design parameters.