EVALUATION OF STATIC AND DYNAMIC BACKCALCULATION OF LAYERS MODULI, USING THE PROGRAMS: MODULUS6., ELMOD5.0, EVERCAL5.0 AND DBSID

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AMERI MAHMOUD; YAVARI N.

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Journal: JOURNAL OF TRANSPORTATION RESEARCH Year:2009 | Volume:6 | Issue:2 (19) Page(s): 125-147

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Title

EVALUATION OF STATIC AND DYNAMIC BACKCALCULATION OF LAYERS MODULI, USING THE PROGRAMS: MODULUS6., ELMOD5.0, EVERCAL5.0 AND DBSID

Author(s)

AMERI MAHMOUD | YAVARI N. | Issue Writer Certificate

Keywords

BACKCALCULATIONQ3

DEFLECTION BASINQ3

ELASTO-STATICQ3

DYNAMICQ3

FWDQ2

VISCOELASTICQ2

MODULUS OF ELASTICITYQ2

Abstract

Backcalculating layer moduli, using the deflections measured by the FWD (Falling Weight Deflectometer) device, is the basis for structurally evaluating pavements when considering maintenance and rehabilitation options. Many algorithms have been developed to perform the BACKCALCULATION.Classical pavement- subgrade system analyzes is based on multi- layer linear elastic analysis, infinite pavement layer dimensions and a semi-infinite subgrade. Linear elastic response assumptions are valid when there is no discontinuity, for example at joints in rigid pavements, or cracks. The assumed static loading conditions are also a simplification of reality.The duration of loading runs from 20 ms to 65 ms depending on the type of FWD device. The FWD provides excellent structural information if it is fully utilized. From a review of the sensor peak values for each measurement location, it becomes clear that points farther from the center of load plate attain their peak values later than locations closer to the plate. This time differences are known as phase difference of deflections and are measures of the velocity of propagation of the shockwaves. These types of time history data contain useful information that if well utilized would contribute to improved accuracy of the structural pavement evaluation. The use of only peak values discards this potentially very useful information. Most of the common BACKCALCULATION programs with ELASTO-STATIC basis use an elastic layer program for forward analysis and an error optimization algorithm. In this study, the programs MODULUS6.0, ELMOD5.0, and EVERCALC5.0 have been used to perform traditional back analysis.The DBSID program, which is based on the system identification methods, was also employed for the DYNAMIC BACKCALCULATION. System identification methods were developed by electrical engineers who were interested in determining the characteristics of a filter by using the input and output signals of the filter and an assumed model of the filter. The characteristics of the filter are changed systematically using a search technique until the model produces an output that is acceptably close to that of the filter. The procedure is in fact exactly analogous to what is being done in backcalculating the moduli of pavements. An impulse load is applied to the pavement at a remote distance; and the surface motion is sensed as signals received by two sensors, which are separated by a distance, x. the pavement between the two sensors is regarded as the filter, the characteristics of which are to be determined. The unknowns in each layer are its modulus, percent damping, thickness, and unit weight.In this study, the results of soil mechanic tests for subgrade layers have been used as a “ground-truth” to compare with the moduli values derived from the FWD data and the ones suggested by the laboratory tests. The ELASTO-STATIC programs terminate when the convergence condition between deflections is satisfied. The Root Mean Squared Errors (RMSE’s) higher than 5% were not accepted. Reviewing the results is always necessary because every predicted modulus may not be acceptable. For example, the moduli which are equal to the lower or upper limit of the acceptable range are difficult to justify given the known quality of the materials.In EVERCALC program, it was found that moduli convergence usually happened earlier than deflection convergence. So the program was rerun by changing the moduli range to achieve the best deflection fit.The DBSID program tries to create the best fit between measured and computed deflection time histories. The surface moduli are most dependent on the deflection measured at the sensor in the middle of the load plate (W1 at 0 inches), so in the final evaluation, not only the RMSE have been considered, but also the peak error at the W1 sensor.In most of the DBSID output files from the different sections on the Zanjan-Tabriz highway both RMS and peak errors were high. The time histories of the measured deflections also had irregular shapes. These output files were excluded from the final conclusion.The results were classified in scatter and bar charts. Lastly, the results (the predicted moduli) of all the four programs were compared with each other and with the expected values which were extracted from the soil mechanic tests.In the end, by considering all the defined criteria, MODULUS6.0 is suggested as the most appropriate program for the cases under study.

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APA: Copy

AMERI, MAHMOUD, & YAVARI, N.. (2009). EVALUATION OF STATIC AND DYNAMIC BACKCALCULATION OF LAYERS MODULI, USING THE PROGRAMS: MODULUS6., ELMOD5.0, EVERCAL5.0 AND DBSID. JOURNAL OF TRANSPORTATION RESEARCH, 6(2 (19)), 125-147. SID. https://sid.ir/paper/83771/en

Vancouver: Copy

AMERI MAHMOUD, YAVARI N.. EVALUATION OF STATIC AND DYNAMIC BACKCALCULATION OF LAYERS MODULI, USING THE PROGRAMS: MODULUS6., ELMOD5.0, EVERCAL5.0 AND DBSID. JOURNAL OF TRANSPORTATION RESEARCH[Internet]. 2009;6(2 (19)):125-147. Available from: https://sid.ir/paper/83771/en

IEEE: Copy

MAHMOUD AMERI, and N. YAVARI, “EVALUATION OF STATIC AND DYNAMIC BACKCALCULATION OF LAYERS MODULI, USING THE PROGRAMS: MODULUS6., ELMOD5.0, EVERCAL5.0 AND DBSID,” JOURNAL OF TRANSPORTATION RESEARCH, vol. 6, no. 2 (19), pp. 125–147, 2009, [Online]. Available: https://sid.ir/paper/83771/en

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