Study On Differential Settlement Monitoring Of High-speed Railway Bridge Pier By Using A Low-coherence Optical Interferometry

High-speed railway plays a crucial role in Chinese transportation,in which about nearly70% being bridge structures.Because of the quite slow progress in bridge pier settlement(BPS)of high-speed railway,uausally with a velocity of several sub-millimeters annually,we still lack of an automatic monitoring method until now.At present,the BPS monitoring is commonly carried out by operating a digital level or a total station manually to implement a regular inspection.The high requirements of passenger comfortability leads to strict restrictions on differential BPS,and bring out a new challenge of both monitoring theory and novel monitoring methods with an outstanding long-term stability.With the advantages of long transfer distance and anti-electromagnetic interference properties,fiber-optic sensors are more suitable for the BPS monitoring of high-speed railways than the electrical methods.This dissertation studies a differential BPS monitoring at different stages and measurement scales based on the principle of a low coherence fiber-optic sensor.The fiber-optic sensors were designed to measure a very tiny variation of the beam box expansion joint(BEJ)caused by the BPS.A variety of monitoring methods were integrated to obtain the BPS in high-speed railways.The main works of this dissertation were list as the below:1.A low coherent fiber-optic sensor was designed to measure the BEJ.Then we applied them into the one-year monitoring work in Tongzhou section of Beijing-Tianjin Intercity Railway.An accuracy of 50μm for BEJ monitoring was stably achieved by installing temperature compensation sensors.Based on the relationship between the BEJ and the BPS was theoretically derived based on the structure of simply supported beams.Combined with the BEJ-BPS calculation model,the long-term monitoring of the differential BPS in the medium distance range can be realized.2.When monitoring multiple bridge piers in a large-span area,multiple low-coherence optical sensors need to be installed.Thus,we improved the acquisition module of the interferometer.A multi-channel acquisition module was designed to implement a simultaneous acquisition of 12-channel sensors at 50k/s.And then a positioning algorithm for recognition of multiple optical interference peaks was programmed to demodulate the deformed signals of multiple sensors in series connection within one single channel.The optimized demodulation system greatly improved multiplexing and acquisition efficiency of the interferometer,which is crucial for tracing the differential BPS.3.In order to explore differential BPS in the early stage,it is proposed to evaluate BPS by monitoring the load changes of the four bearings at the bottom of the beam.Three sensing fibers were wound around the outside of the pot support of the bearing,so that the three sensors were able to measure the related bearing strain on different positions underlying the same load state.A neural network model based on the correlation between these three sensors was built to compensate the hysteresis effect between stress and strain.So the full-scale error of the loadsensitizing bearing was controlled within ±6%,which basically meets the requirement for the differential BPS early warning.4.It is observed that the abnormal vibration occurs in the beam-box when high-speed train passing through the area in serious a large BPS.In order to monitor this phenomenon,a fiberoptic vibration sensor based on the Sagnac interference principle was designed and implemented.A frequency domain analysis algorithm to recognize the vibration state.Finally,an automatic monitoring system integrating vibration,pier settlement,expansion joint displacement,and bearing load sensors was proposed.This provided a possible scheme for the differential BPS measurement of high-speed railways in different span in space.Based on both the laboratory exploration and practical engineering measurement,this dissertation shows that a low coherence fiber-optic sensor play an important role in high-speed railway BPS monitoring.The integrated differential BPS monitoring includes direct monitoring of local key areas,indirect monitoring of BEJ in large-span areas,early monitoring of abnormal support forces in spherical bearings,and real-time vibration monitoring of beams.These methods have important reference value in practical BPS monitoring.