Scientific and Technological Research Institute, Xi'an Railway Administration，Xi' an , Shanxi 710054，China； 2.Xi'an Jiaotong University, Xi'an, Shanxi 710049，China
Abstract：Research purposes: The status of railway subgrade is of vital importance to the security of railway transportation. Nowadays China has railway lines with total length of over 70000 km, the diseases of railway subgrade are still inspected with manual inspection, but this general inspection cannot be done for the diseases of entire lines over the country and it is exigent to research the method of subgrade inspection.
Research methods: The railway subgrade inspection car is equipped with Ground Penetrating Radar System(GPR ) to inspect the status of railway subgrade. GPR system transmits short electromagnetic pulse into subsurface and receives the reflections from the interface underground. The collected reflections are displayed as a waveform. When the antenna is moving, a continuous profile is obtained and based on which the geometric shape of subgrade and water content of soil can be deduced to seek the subgrade diseases.
Research results: The subgrade inspection car, developed by Scientific and Technological Research Institute of Xi'an Railway Administration and Xi' an Jiaotong University, is equipped with GPR, with testing speed of 45 km/h and penetrating depth of about 3. 0 m. The three sets of antenna are located at the centre of track and on both sides of tie for inspecting three profiles at the same time. The car has been tested on Beijing-Kowloon, Yangpingguan-Ankang and Liangyungan-Lanzhou railways with good results.
Research conclusions：However the speed of 45 km/h is lower to use in main lines ， GPR system of higher scan speed should be developed.
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