Modulus backcalculation program

Alternatively, elastic modulus correlations to field or laboratory derived CBR or the program default may be used. Wetter or more highly plastic materials warrant higher Poisson ratios. In many cases, spot repairs base and surface may be the only preparation before the existing structure is simply overlaid with new HMA. The Table below offers some guidance for selecting FPS values for this type of construction. Use for untreated materials, or select another layer with higher credit.

This procedure is used to determine modulus values for in situ pavement materials when these materials are used as is unmodified in FPS design. TxDOT currently uses version 7. Version 7. The software v 7. Also, basic operation and discussion of inputs, cautions, and example problems is presented in the Flexible Pavement Rehabilitation Strategies training course and Flexible Pavement Design workshop.

The raw deflection file, pavement layer thicknesses, layer Poisson ratios, probable layer moduli ranges, and asphalt temperatures at the time of testing are all required inputs to perform backcalculation. The backcalculation process works on the assumption that the pavement structure can be modeled as a linear-elastic layered system. If the parameters of layer thickness, deflection, and Poisson ratio are known, the modulus can be approximated.

Once a reasonable match is made, the moduli that allow this match are reported as the individual layer moduli. In addition, the program reports a depth to stiff layer or bedrock. There are precautions and limitations to the backcalculation procedure that the user must consider. In the end, engineering judgment will be needed to decide on the veracity of solutions generated. In addition to adjustments made to backcalculated average modulus values for outliers in the deflection data set, correction factors must be applied to the backcalculated HMA values.

This is particularly important for HMA surfaces greater than 4 inches in thickness. Where backcalculation of the HMA surface is possible, modulus adjustments are made using one of the following methods.

Search for the word or phrase:. Help Advanced. Damage Claim Procedure. Anchor: i 4. Search for the word or phrase: Help Advanced. Search in: this manual only. Limestone Rock Asphalt Pavement. Emulsified Asphalt Treatment Base. Foamed Asphalt Treatment Base. Lime or Cement Treated Subgrade. Emulsified Asphalt Treatment Subgrade. Item , various special specs.

Existing Pavement - Scarified, Reshaped and Compacted. Gr 70 ksi Gr 5: 50 ksi. MODULUS is a microcomputer-based backcalculation system that can be used on 2-, 3-, or 4-layer pavement systems with or without rigid bedrock layers.

It uses a linear elastic program to generate a data base of deflection bowls. Once generated, a pattern search routine is used to fit measured and calculated bowls; error minimization is rapid, less than 5 sec per bowl on a type microcomputer.

The system is general purpose and can process data from any nondestructive testing device. The user has several options when performing backcalculations, including specifying the depth to bedrock or using existing default data bases for common pavement structures.