(1200 mm) from the center of the plate load. Several researchers have developed regression equations to predict the subgrade modulus, E SG, from plate load and deflections measured at distances from about 24 in. There is a clear consensus, however, that the deflections measured beyond the primary effects of the load stress bulb relate quite well to the resilient modulus of the subgrade. In general, the success of these regression equations to predict the resilient modulus of the surfacing layers has been limited.
The subsequent parameters to be presented were developed to provide a means of obtaining the resilient modulus values of the surfacing layers more easily or quickly than full backcalculation. Deflections in this region relate quite well to the stiffness of the subgrade below the pavement surfacing. The deflections toward the end of the basin.
These parameters tend to reflect the relative stiffness of the base or lower regions of the pavement section. The slope or deflection differences in the middle of the basin about 11.8 in.These parameters tend to reflect the relative stiffness of the bound or upper regions of the pavement section. The slope or deflection differences close to the load such as Radius of Curvature (R), Shape Factor (F 1), and Surface Curvature Index (SCI).It has been used for many years as the primary input for several overlay design procedures. This was obviously the first deflection parameter which came with the Benkelman Beam. Plate or center load deflection which represents the total defection of the pavement.A fairly complete summary of deflection basin parameters was provided by Horak at the Sixth International Conference Structural Design of Asphalt Pavement ] and is shown in Table 1.īenkelman Beam, Lacroux deflectometer, FWD Over the years numerous techniques have been developed to analyze deflection data from various kinds of pavement deflection equipment. These basics do not rely on specific software but do largely involve layered elastic analysis. The last theme focuses on the basics associated with backcalculation of layer moduli. The second theme will cover basic parameters which can be quite useful in analyzing existing pavement structures. A short discussion on AASHTO developed models follows along with some of the work done in South Africa and companies such as the Shell Oil Co. This is followed by a discussion of some easy to use models to predict layer moduli that were developed by the University of Washington for the Washington State DOT (WSDOT). The introduction will start with an overview of some of the deflection basic parameters that have been used in the past although, some of the NDT equipment noted is rarely used today (such as the Dynaflect). This article is separated into three broad themes: (1) an introduction, (2) indices for project analysis, and (3) fundamentals of backcalculation.
There are all kinds of NDT data which can be collected on or about pavements but concentration is placed on measured surface deflections. It can also be used to perform loss of support analysis and load transfer efficiency (LTE) calculations.This topic will be oriented toward techniques which can be used to interpret nondestructive testing, NDT, data from the Falling Weight Deflectometer, FWD. The tool is capable of analyzing raw deflection data files obtained from Falling Weight Deflectometer (FWD) testing devices, backcalculating in-place elastic layer moduli for flexible and rigid pavements and generating inputs for performing rehabilitation design using Pavement ME.
The Pavement ME Deflection Data Analysis and Backcalculation Tools is a standalone software program that can be used to generate backcalculation inputs to the AASHTO Pavement ME Design software for rehabilitation design. ME Design is a production-ready software tool to support the day-to-day pavement design functions of public and private pavement engineers.
ME Design supports AASHTO"s Mechanistic-Empirical Pavement Design Guide, Interim Edition: A Manual of Practice. ***ĪASHTOWare Pavement ME Design is the next generation of AASHTOWare® pavement design software, which builds upon the mechanistic-empirical pavement design guide, and expands and improves the features in the accompanying prototype computational software. ***AASHTOWare Pavement ME Design v2.6 is now available. ***AASHTOWare Backcalculation Tools v1.1.5 is now available.