Back-Calculation of Soil Modulus from PFWD Based on a Viscoelastic Model

Rui Zhang,Md Ashrafuzzaman Khan,Tianzeng Ren,Jianlong Zheng,Yusheng Teng

doi:10.1155/2019/1316341

Rui Zhang, Md Ashrafuzzaman Khan + Show 3 more

Open Access

https://doi.org/10.1155/2019/1316341

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Abstract

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. A quasi-static dynamic analysis technique of Laplace transformation and a modified Gauss–Newton optimization algorithm were adopted in the proposed method. The back-calculation program was compiled with MATLAB. The effectiveness of the proposed method was verified with the in situ plate load test (PLT) conducted on a highway embankment. 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. The back-calculated modulus using the LEM and VEM was higher than that using the PLT. 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. However, for stiffer soil, the average error of back-calculation using the LEM and VEM method was 12.4% and 4.3%, respectively. 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%. More accurate estimation of modulus can save maintenance cost in the future.

Highlights

Research ArticleRui Zhang ,1,2 Tianzeng Ren, Md Ashrafuzzaman Khan, Yusheng Teng, and Jianlong Zheng
Introduction e Mechanistic-Empirical Pavement Design Guide and other existing pavement design guides use elastic modulus (E) as the primary input parameter for subgrades. e soil modulus is typically determined by different laboratory tests or in situ nondestructive tests. e falling weight deflectometer (FWD) and plate load test (PLT) can be used to determine the stiffness of pavement, but these devices have some limitations when they are used during the construction of pavement subgrade. e FWD is not always applicable to the project site
The PLT takes several hours so that it can slow down the construction process. ese limitations can be overcome by conducting a test with a portable falling weight deflectometer (PFWD), a nondestructive and costeffective tool used to determinate the soil modulus [1,2,3,4,5,6]. e soil modulus can be determined by the deflection profile and the back-calculation method

Summary

Research Article

Rui Zhang ,1,2 Tianzeng Ren, Md Ashrafuzzaman Khan, Yusheng Teng, and Jianlong Zheng. Based on a viscoelastic model, a back-calculation method which incorporated a quasi-static dynamic response analysis method with elastic half-space theory was proposed first. Erefore, it is necessary to establish a simple method for back-calculation modulus that can better reflect the nonlinear dynamic response characteristic of high plasticity soil embankments under an impact load. E deformation hysteresis effect of a high plasticity soil embankment under impact load is similar to the mechanical behavior of viscoelastic materials mentioned earlier. Erefore, based on the viscoelastic constitutive model, a high plasticity soil modulus back-calculation method was established in this research.

Peak deflection

Measured LEM VEM

LEM VEM

Findings

Conclusions