Design And Application Of The Fiber-optic Low Coherent Ground Settlement Sensor In The Accuracy Of Micrometer

Along with the rapid growth of the national economy of China,a large number of infrastructures and constructions were built or renovated.Thus,the quality control on these infrastructures required the new monitoring or testing methods to evaluate their structural health status during its building procedures or its services.In the case of the high-speed railway,the situation becomes more urgent.The the bridge piers,which supported the high-speed railway,act as the first cause of track irregularity and therefore being the focus monitoring place.The difficulties were not only from the high accuracy requirement,usually sub-millimeters,but also its thousands of kilometers extension on the earth.The ground settlement must happen in this span.Therefore,in order to ensure the long-term safety service of high speed railway,an automatic monitoring method of the ground settlement was required.There are two difficulties in the ground settlement monitoring of high-speed railway.One is the large span in space and the other is the high precision requirement.The traditional electrical monitoring system could not satisfy the sub-millimeters in a long term,because it is susceptible to the electromagnetic interference from the railway power supply system.It is difficult to achieve the required high precision.The conventional monitoring method was to set up a monitoring basis on the rock,and employed the theodolite to carry out a manual monitoring.Even if this done were able to achieve the monitoring precision at about 10 microns,it was time-consuming and difficult to obtain all-day data,thereby,unable to meet the needs of high-speed rail safety operation.Thus,an automatic monitoring method was necessary.Optical fiber sensor bears the advantages of anti-electromagnetic interference and long distance measurement merits together.In this paper,we designed and fabricated a kind of fiber-optic low coherent micrometer ground settlement sensor.And the relative performance of the system was studied under laboratory conditions.Based on the practical application of the system in a span of the high-speed railway from Hefei to BengBu,we observed that the system could provide us a micrometer accuracy monitoring on the ground settlement measurement.The main work of this dissertation were list as the below three aspects:1.A practical configuration of the fiber-optic ground settlement methodology was proposed by using a scanning low-coherent Michelson interferometer.In this design,the sensor was combined the static liquid level sensor with the fiber-optic method.One of the paths of the interferometer is formed by the liquid surface,and therefore the read out of the interferometer can make the measurement of the surface approach micrometer scale.Theliquid-contained chambers are hydraulically connected together at the bottom by using a water-filled tube.The liquid surface inside each chamber is at the same level initially.One of the chambers is located on stable ground or is at a point that can be easily surveyed to.The others are located at the points where settlement or heave is to be measured.Differential settlement,or heave,between the chambers will result in an apparent rise or fall of the liquid level,which biased the initial equal status.The experimental results demonstrated that an accuracy of ten of micrometers accuracy for ground settlement monitoring was obtained with a reference compensation sensor.2.Underlying the laboratory conditions,we employed a feeler gauge to simulate the ground settlement happened in the accuracy of several micrometers.As the measurand reflecting surface formed by the liquid surface inside the fiber-optic liquid level sensor,we implemented a study on the anti-tilt performance of the fiber-optic liquid level sensor.The results demonstrated that in the tilt range between +5° and-5°,the sensor worked well.The designed sensor was applied to the practical monitoring of the high-speed railway,from Hefei to Bengbu.During the 3 months observation the sensor was proved effective on the monitoring with a accuracy of tens of micrometer.In the mean time,the system connected to the 4G wireless through a phone card transmission and by which a remote control was carried out.Thus,the problem of abnormal turn off the power supply was solved in a convenient way.After the test of the sensor,the designed filtering algorithm etc,were effectiveness on the noise remove,which caused by the running of the high speed railway.