| High-speed railway in China has undergone massive growth over the past few years.The Beijing-Tianjin high-speed railway was China’s first high-speed railway line which went into operation in 2008.Today,China is home to more than 50 per cent of the world’s total constructed high-speed railway and by 2020,the total mileage of high-speed railway network is expected to reach approximately 21,000 km.Effective transportation is a critical component of economic development,nationally as well as globally.Moreover,high-speed rail transportation is of major significance in the Belt and Road Initiative as it promotes economic cooperation and enhances transnational connectivity through infrastructure and trade from China to Europe,Africa and beyond.However,although high-speed railway offered good solution for a sharing economy,an acute problem was the question of the future maintenance and repair techniques.In words,with the increase of operating hours,track slabs are facing performance degradation,natural disasters,etc.In the long-term operation,concrete cracks,steel corrosion,escape of CA mortar layer and other diseases will inevitably occur and seriously affect the safe operation of the train.Therefore,in response to these complex defects,sustainable track maintenance is of vital importance for ensuring the preservation of existing infrastructure assets in the long term.Firstly,according to visual inspections,typical CA mortar cracks and voiding were observed in a section of Shanghai-Hangzhou railway line.The internal condition of the defective structure is examined by penetration with non-specialized inspection tools such as metal strip,tape measure and steel rulers.These defects cause excessive impact loads on track when trains are passing.The characteristics of the defects were successfully reproduced through a numerical simulation in order to estimate the track-induced vibrations.Secondly,distributed optical fiber monitoring which is an emerging technology in recent years,is combined with the impact imaging detection method to inspect the faults in the CA mortar layer.The monitoring and analysis of the vibration data of the track plate before and after the CA mortar layer was repaired were studied.The vibration monitoring uses the DOVS fiber continuous distributed vibration monitoring system.DOVS is a distributed vibration monitoring system based on the principle of Φ-OTDR fiber interference.The system operates a real-time detection,location and alarm by using optical cable to determine the position of the vibration point after measuring the input light pulse and the received optical signal delay.Through numerical simulation,space-time monitoring and impact imaging detection method,the potential and effectiveness of Φ-OTDR vibration monitoring to diagnose faults in high-speed railway were completed and the following conclusions are obtained:The numerical simulation results show that in the elastic field,the track plate defects have a significant amplification effect on the vibration,and the magnification can be more than 2 times.The space-time monitoring using optical fibers as vibration sensors,through continuous detection of track plate reveals two aspects of the defect effects on the slab dynamic response: the amplification of the dynamic response when the train is arriving and leaving the monitoring section and also to cause extreme resonance when the train is passing increasing largely the vibration signal.The impact image method can accurately inspect the defects distribution on the track slab,and it is favored for defects quantification and repair quality management. |
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