Alessandra Bianchini

Thin asphalt pavement performance equation through direct computation of falling weight deflectometer-derived strains

A fundamental aspect in a pavement management system is the evaluation of the pavement structural condition and its capability in supporting the designated traffic. The nondestructive technique of the falling weight deflectometer and the layered elastic model are commonly used to identify pavement structural condition. The approach in this article is mechanistic–empirical, with the intent to correlate the strain at the bottom of the asphalt layer with the number of coverages to failure. Strains were computed through mathematical approximation of the deflection basin measured at failure. The proposed asphalt criterion showed the same trend of the subgrade strain criterion developed in conjunction with the reformulation of the California bearing ratio (CBR)-Beta design criteria. The approach provided encouraging results when compared with the other analyses in the development of the CBR-Beta criteria. The database was from the full-scale flexible pavement testing at the US Army Engineer Research and Development Center in Vicksburg, MS, USA.

Correction for the asphalt overlay thickness of flexible pavements considering pavement conditions

Abstract Pavement overlays represent a common technique used for pavement rehabilitation and maintenance and to increase the structural support of the pavements. In the Department of Defense, the methodology for the design of flexible pavement overlays is contained in the Unified Facilities Criteria 03-260-02 criteria and involves the use of an empirically derived formulation. The overlay design of flexible pavements is based on the thicknesses of the existing asphalt, base and subbase layers and the required minimum thickness for the asphalt layer. However, this formulation does not take into account the quality or the structural condition of the existing surface layers. The current formulation considers the materials to have full structural strength and no deterioration. This study proposes an improved methodology for calculating the required flexible overlay thickness of a flexible pavement by taking into account the structural condition of the existing asphalt layer. An asphalt thickness correction factor is introduced to quantify the amount of the existing asphalt layer thickness that can still offer structural support, and therefore influence the overlay thickness. The asphalt correction factor is based on the existing load-related distresses affecting the asphalt surface. The implementation of this new approach showed that an asphalt layer in poor condition requires up to 60% more in thickness than an asphalt layer in good condition. The proposed methodology aims to standardise the design and evaluation of flexible pavements overlaid with asphalt layers and account for existing structural conditions. Moreover, allocation of maintenance funding can be optimised, thus limiting pavement overdesign.

Fuzzy cluster approach for area FWD representative basin from deflection measurement spatial variability

ABSTRACT Pavement evaluation surveys represent the key element for efficient pavement management and for assuring pavement mission capability. In the Department of Defense (DOD), the Unified Facilities Criteria (UFC) 3-260-03 Airfield Pavement Evaluation provides the current guidance for pavement structural evaluations. During structural surveys, FWD tests are executed at different locations within the same section, with the objective of obtaining a full assessment of the section’s structural capability. The availability of multiple deflection measurements for the same section raises the challenge of identifying the deflection basin best representing the entire section and its use in the backcalculation routine to determine the section’s structural strength. This manuscript proposes a fuzzy-based approach for the selection of a representative basin over multiple deflection basins collected for a specific section. The approach accounted for the spatial variability enclosed within the basin membership function obtained by fuzzy c-mean partitioning. The proposed methodology showed promising results for flexible pavements by offering more robust structural assessment that can account for spatial variability and thus minimise some aspects of mission risk that had a large effect on funding allocation and mission readiness.

Fröhlich Theory-Based Approach for Analysis of Stress Distribution in a Layered System: Case Study

The California bearing ratio (CBR) procedure for the design of airfield flexible pavements was originally developed in the 1940s for supporting new heavy bombers and reviewed in the 1970s to allow handling multiwheel tire groups. In view of an active debate at the International Civil Aviation Organization level on further adjustments to the design procedure, a U.S. Army Engineer Research and Development Center (ERDC) research team reformulated the original CBR procedure. The new CBR design procedure was redefined with the introduction of Fröhlichs theory for computing the pavement thickness and validated through full-scale testing. This study evaluated the influence of each layer in the stress distribution with the final objective of recommending specific values of the Fröhlich stress concentration factor. The data for this investigation were collected during full-scale testing at the ERDC in 2008. The analysis allowed identification of several influencing factors in the stress distribution for computing the stress acting at the top of the subgrade. Such factors included the subbase and subgrade CBR, the thickness of the subbase layer, and the stress distribution represented by the respective n factor of the layer group. The linear regression confirmed the statistical importance of these variables in assessing stress distribution above the subgrade. This case study provided encouraging results for additional investigations on the stress distribution within a layered system with the objective of quantifying more accurately the stress acting at the top of the subgrade.