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#BACKCALCULATION SOFTWARE FOR PAVEMENT FULL#

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.

#BACKCALCULATION SOFTWARE FOR PAVEMENT FULL#

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.

EVERCALC uses RMSE.This topic will be oriented toward techniques which can be used to interpret nondestructive testing, NDT, data from the Falling Weight Deflectometer, FWD. In backcalculating layer moduli, the measure of how well the calculated deflection basin matches (or converges to) the measured deflection basin was previously described as the “error check.” This is also referred to as the “goodness of fit” or “convergence error.” The primary measure of convergence is typically Root Mean Square (RMS) or Root Mean Square Error (RMSE). Backcalculation Flowchart Measure of Convergence In some backcalculation programs, a range (minimum and maximum) of moduli are selected or calculated to prevent program convergence to unreasonable moduli levels (either high or low).įigure 1. Various methods have been employed within the various backcalculation programs to converge on a set of layer moduli which produces an acceptable error between the measured and calculated deflection basins. There are various error measures which can be used to make such comparisons (more on this in a subsequent paragraph in this section). This element simply compares the measured and calculated basins. Layered elastic computer programs are generally used to calculate a deflection basin. These moduli are usually estimated from user experience or various equations. The seed moduli are the initial moduli used in the computer program to calculate surface deflections. Includes all layer thicknesses and load levels for a specific test location. Includes the measured pavement surface deflections and associated distances from the load.