Research On Portable Falling Weight Deflectometer Based On Embedded System

With great developments on transportation, the density and load of highways and railways are growwing quickly year by year in our country. More and more new requirements are set forth on the quality of the transportation construction projects. While constructing highways or railways, to evaluate and monitor the filling quality in scientific and effective ways is the most important guarantee to the subgrade quality assurance. In normal construction evaluation, a method is used to calculate the dynamic resilient modulus by means of measuring of the intensity and deformation. The dynamic resilent modulus is therefore taken as the criteria to judge the subgrade compactness. The method has become a trend of the technology development to evaluate the quality of subgrade construction. Traditionally, such characteristics as intensity and deformation of the subgrade are obtained through static plate load testing, i.e. through measuring the subgrade coefficient K30. But actually, the subgrade stands not only the static load but also the dynamic load caused by the heavy traffic. Especially while building the subgrades of highways or railways, the subgrade stability is mainly effected by the dynamic load, as well as the distortion problem is mainly caused by. Therefore, the dynamic stress and dynamic strain index caused by dynamic shock on the subgrade are used as the testing criteria to evaluate the subgrade construction quality.The thesis provides a method to design the Portable Falling Weight Deflectometer, trying to meet the engeneering practical application while emphasizing on such features as portability and non-destructiveness. At first, a falling weight is used to hit the subgrade, simulating the dynamic stress caused by the shock. Secondly, the vertical subsidence and pressure on the surface of the subgrade are measured. Finally, by making use of the measured data, the dynamic resilient modulus is estimated. And consequently, the construction quality of the subgrade is evaluated.The thesis analyses the operating principle of the Protable Falling Weight Deflectometer, emphasizing on the hardware and the software design. The design of hardware includes the selection of sensors, the sampling and amplifying of the small signals, and selecting the modes of data transmission. The power management is specially designed to make the PFWD portable. The design of software highlights the realization of digital signal processing on acquired data, withdrawing of the real signal and estimating of the dynamical resilient modulus.