![backcalculation fwd on subgrade backcalculation fwd on subgrade](https://www.researchgate.net/profile/Der-Wen-Chang/publication/267919084/figure/fig4/AS:392041591787538@1470481407699/Comparative-subgrade-layer-backcalculation-results-for-FWD-measurements-on-case-study_Q320.jpg)
More accurate estimation of modulus can save maintenance cost in the future.
![backcalculation fwd on subgrade backcalculation fwd on subgrade](http://www.aashtoresource.org/images/default-source/default-album/newsletters/fwd-measurement-error.jpg)
Moduli of back-calculation using LEM and VEM methods were used to perform flexible pavement analysis, which showed that with an 8% reduction of modulus, the pavement service life reduced by 25%. However, for stiffer soil, the average error of back-calculation using the LEM and VEM method was 12.4% and 4.3%, respectively. In the case of low stiffness soil, the average error of back-calculation using the LEM and VEM was 53.1% and 14.8%, respectively. The back-calculated modulus using the LEM and VEM was higher than that using the PLT. In situ test results showed that a time lag existed between the peaks of deflection and load, and load-deflection curves were nonlinear, which indicated the viscoelastic nature of the soil.
![backcalculation fwd on subgrade backcalculation fwd on subgrade](https://slidetodoc.com/presentation_image_h/cde54bee7d267676c8d80903ddc2ecce/image-2.jpg)
The effectiveness of the proposed method was verified with the in situ plate load test (PLT) conducted on a highway embankment. The back-calculation program was compiled with MATLAB. A quasi-static dynamic analysis technique of Laplace transformation and a modified Gauss–Newton optimization algorithm were adopted in the proposed method.
#Backcalculation fwd on subgrade portable
To improve the accuracy of back-calculation of soil modulus using the portable falling weight deflectometer (PFWD), a viscoelastic method (VEM) overcoming the limitations of the conventional linear elastic method (LEM) was proposed.