| With the great development of highway construction in the China, pavement investment has occupied a big part of road and highway investment since the reform and open-up, at the same time, pavement quality affects the total quality of highway, and pavement usage life span directly has an effect on the investment benefit and the quality of highway. The original testing method of project quality, which is obtained by taking pavement core samples, is a slow, low-efficient, poor-representative and destructive task, thus it is necessary to develop a quick, simple, efficient and nondestructive testing method of pavement quality. In road structure surveys, GPR has been used to measure layer thickness, to detect voids under concrete slabs, to evaluate the density and water content of subsurface layers of the pavement. In fact, GPR, which is a quick, high-precision, non-touching and nondestructive testing tool, and which directly gains subsurface section images and carries on real-time imaging disposal of testing data, has a wide application foreground. GPR has been caught the attention of a lot of countries; many universities and research institutions have introduced into the foreign GPR equipments, carried out some work and gained some fruits.In this paper, a systematical study was done for the engineering problem using GPR to evaluate pavement structure. The results are as follows:!) A detailed narration is concerned about GPR's makeup and exploration theory; 2) There is a qualitative analysis and a summarization about subterranean reflected signals according to the basic theories of electromagnetic, based on the dielectric characteristics of common subterranean medias;3) Two kinds of pavement models of reflected signals have been founded, including one-layer pavement model and multi-layers pavement model. At the same time relative programs have been compiled on the basis of electromagnetic wave theories and pavement models, some examples are also given to prove that the programs are valid and feasible; 4) GPR has a wide range of applications on roads and highways, attentions have focused on measuring the thickness of the asphalt surfacing layer on flexible pavements with air-launched horn antennas and void identificationwith detailed cases; and 5) A back-calculation method is described in connection with volumetric concentrations of pavement materials of the different layers within a multiplayer pavement system, based on the results of forward modeling by employing a wave propagation model of the pavement system, and relative back-calculating computer program is implemented according to System Identification Method.1. GPR theoryGPR sytems are a set of equipments with the detail information of subsurface medium by electromagnetic techniques. GPR systems use discrete pulses of radar energy to generate a single pulse of a high frequency. When the pulse, during the course of diffuse, meet the subsurface objects with different dielectric, such as voids and interface, it will reflect into the ground and be captured by an antenna. GPR is a non-ground, continuous, quick and nondestructive testing tool, it also can directly represent the object. GPR techniques have become the most important surveying methods in the physical geography fields, it has been widely used in many fields including subterranean pipes exploration, structures nondestructive testing, rock and soil survey, subsurface caves, and so on.GPR systems typically have the following three components: 1) an antenna which transmits the pulse into the medium to be measured, 2) a pulse generator which generates a single pulse of a given frequency and power, and 3) a sampler/recorder which captures and stores the reflected signals from the medium. Once the return waveform is captured another input pulse is generated and transmitted into the medium.2. Forward modelingGPR works according to a pulse-echo principle. A narrow electromagnetic pulse, generated by the transmitter, is radiated towards the pavement's surface through an antenna, the transm... |
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