| The Ground Penetrating Radar (GPR), which is an effective, speedy, continuous and non-destructive testing equipment, its application in pavement has been the international active subject since 1980s. At present, most of the achievements mainly focus on the measurement of pavement thickness. The current GPR data analyzing method for pavement thickness can only give the acceptable results for new asphalt concrete pavement, but for aged asphalt concrete pavement and cement concrete pavement, the accuracy is not satisfactory because of the theoretic modeling and data acquisition difficulties. The study on pavement compaction, moisture content and asphalt content is under exploration and the program for processing GPR data based on rigorous theoretic model can not be found in literature.The backcalculation of the dielectric property and thickness of pavement structures is studied in this paper in order to solve the above problems of GPR applied technology. The forward model for GPR electromagnetic wave propagation in pavement system is established based on the basic theory of electromagnetic through analyzing the propagation characteristics of electromagnetic wave propagation in pavement, then the reflected signals of GPR wave propagation in different pavement structures are simulated. Applying this forward model, the system identification theory is firstly introduced to GPR signal analyzing field, and the SIDTHK program is developed for backcalculating dielectric property and thickness of pavement structures.The main achievements and conclusions of this paper are summarized below:1. The forward model of GPR electromagnetic wave propagation in pavement system is developed based on Maxwell Equation in electromagnetic theory. This forward model is more precise in theory and more close to the engineering condition since the imaginary part of material dielectric is taken into account. So it can be applied not only to asphalt concrete pavement with lower absorption of electromagnetic energy but also to cement concrete pavement structure with higher absorption of electromagnetic energy.2. The influences of the real part and imaginary part of dielectric on reflected GPR waveform are examined. The conclusions from this research include: (1) The real part mainly effects the delay time between two peaks of GPR signal, the larger the real part, the longer the delay time. (2) The imaginary part mainly affects the peakamplitude of GPR waveform except that from pavement surface, the higher the imaginary part, the lower the peak amplitude. (3) The neglect of imaginary part of dielectric will increase the analyzing error obviously when it is higher.3. The system identification method is presented for backcalculating the dielectric property and thickness of pavement structures. The method of singular value decomposition is put forward to diagnose the ill-conditioned governing equation and the problem of finding solution to ill-conditioned governing equation is successfully resolved. The parameter adjustment arithmetic with high accuracy, which is based on precise theory and can be converged rapidly, is established. The SIDTHK program that first successfully combines the rational GPR waveform forward model and the effective, stable parameter backcalculation method is developed for backcalculating dielectric property and thickness of pavement structures. Therefore, the present status that the current GPR data processing method mainly relied on experience or adjusting parameter manually is totally changed by this successful combination.4. The evaluation for SIDTHK program shows that its backcalculation procedure is stable and its accuracy is higher, furthermore, the backcalculated results are not effected by the selection of seed value at a very wide range. The accuracy of SIDTHK program is much better than that of current GPR data analyzing method no matter for new or aged asphalt concrete pavement and cement concrete structure. In addition, the pavement thickness backcalculation results f...
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