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Publication Number: FHWA-HRT-13-007
Date: October 2012
Printable Version (.pdf, 1.1 mb)
Step-by-step instructions for interpreting and evaluating pavement deflection data for network-level pavement management system (PMS) applications are available in a new guide released by the Federal Highway Administration’s (FHWA) Long-Term Pavement Performance (LTPP) program.
Simplified Techniques for Evaluation and Interpretation of Pavement Deflections for Network-Level Analysis: Guide for Assessment of Pavement Structural Performance for PMS Applications (Pub. No. FHWA-HRT-12-025) spotlights how to assess a pavement’s structural characteristics using falling weight deflectometers (FWDs) or heavy weight deflectometers (HWDs), combined with other readily available pavement performance data.
While there are many viable techniques available for evaluating the structural capacity of pavements that use FWDs for project-level analysis, many of these techniques are time consuming and require an experienced analyst. As a result, using pavement deflection testing for network-level analysis has been limited. The new guide presents a simpler approach.
The guide examines required input data, including pavement age, average daily volume of 18-wheel truck traffic, average annual daily truck traffic, average annual precipitation in the geographical area, the base type for asphalt pavements, and subgrade type for concrete pavements. Data on rutting and surface cracking should be included for asphalt pavements, while joint faulting and transverse slab cracking should be examined for jointed concrete pavements. Roughness data should be included for both types of pavements. Also featured in the guide are recommended sensor positions for network-level FWD or HWD testing.
Selecting appropriate analysis techniques is covered. The appropriate technique depends on the pavement type and the type of distress an agency wants to use to characterize structural condition. At a minimum, the guide recommends that the typical distresses observed on the local road network be used. As system-wide load deflection data is not available for most agencies, it is recommended that global models and threshold values be used until local calibration of the FWD or HWD can take place.
Local calibration will significantly improve the accuracy of the models. Guidelines are provided for local calibration, taking agencies through the necessary steps. The guidelines encompass data preparation, logistic model calibration, verification of accuracy, and analysis of the sensitivity of the logistic models to a given set of site characteristic variables. These variables could range from high truck volume to a cold climate. Two examples of sensitivity analysis are provided.
Analysis techniques highlighted for asphalt pavements include the structurally based roughness performance model and fatigue cracking performance model. For concrete pavements, featured analysis techniques are structurally based roughness performance models, joint faulting models, and the transverse slab cracking performance model. Also examined are optimum spacing and timing for FWD measurements. Deflection testing should be avoided when pavements are frozen and during the spring thaw. Asphalt pavements should be tested on a 5-year cycle, while concrete pavements can be tested every 10 years.
To download a copy of the guide, visit www.fhwa.dot.gov/publications/research/infrastructure/pavements/ltpp/12025/index.cfm. For more information, contact Larry Wiser at FHWA, 202-493-3079 (email: firstname.lastname@example.org).
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