Study On Optical Fiber Monitoring Technology For PCCP Deformation Under Internal Pressure

Prestressed concrete cylinder pipe(PCCP)plays an important role in regional water supply,municipal water supply and drainage and other national infrastructure projects.Because of the Long-distance laying and the complicated engineering geological conditions of cross-over area,PCCP,as a kind of composite pipe,the structural safety in long-term operation service period has been the key issues of attention Pipeline monitoring is the basis of the assessment of PCCP structural safety and the prevention of pipe burst.The traditional monitoring technology is difficult to realize the distributed,long distance,real-time dynamic monitoring for the multi-layer structure of PCCP under internal water pressure.Under the background of the south to North Water Diversion Project,the paper did exploratory study on the structural deformation monitoring of PCCP based on the optical fiber grating technology(FBG)and the Pulse-PrePump Brillouin Optical Time-Domain Analyzer(PPP-BOTDA),Some key technologies of PCCP monitoring based on optical fiber technology were carried out.A prototype test on the embedded PCCP was conducted to monitor the strain response of the five layer structures of PCCP under the action of internal water pressure and broken wires.Besides,a three-dimensional nonlinear finite element model of PCCP was established based on ABAQUS,and the structural deformation of PCCP under different internal water pressure was simulated by using this model,finally the results were compared with that of optical fiber monitoring.The research results are presented as follows:(1)The failure modes of PCCP and pipeline monitoring technology were summarized,and the limitations of various monitoring techniques were analyzed.This paper introduces the basic principle,technical characteristics and application scope of optical fiber sensing technology based on PPP-BOTDA and FBG,and the feasibility of its application in PCCP deformation monitoring was demonstrated.(2)Some key technologies of PCCP monitoring based on PPP-BOTDA and FBG were studied,including the demodulation performance of instrument,temperature compensation methods,installation techniques and so on;The CFRP sensing cloth is developed for strain monitoring of concrete and mortar;A series of calibration experiments were carried out on the pressure gauge,the temperature sensor and the strain gauge that based on FBG;The test of the performance of a variety of optical fiber strain sensors on the steel surface was carried out by using equal intensity beams,the results show that the FBG strain gauge and the 0.9mm polyimide fiber have better strain test performance.and also The influence of installation technology of spot welding and epoxy adhesive on the strain transducing characteristics of FBG strain gauge is analyzed.(3)The strain monitoring scheme of each layer of PCCP under internal water pressure was designed,including the selection of optical fiber sensor,the installation process and the integration of the circuit,and the PCCP structure strain optical fiber monitoring system was established.(4)The PCCP field prototype test was carried out to monitor the structural strain of pipeline concrete,cylinder,steel wire and mortar layer under internal pressure and broken wire.The monitoring results can reflect the strain response of PCCP in the process of compression and wire breaking.basing on the monitoring data,the pipeline deformation process are divided into three stages:the pipeline structure of each layercoordinated deformation stage(0-1.8MPa),in which there was a good linear relationship between the strain and the inter water pressure;fracture initiation phase(1.9MPa).Yield stage of steel wire and cylinder(1.9-2.25MPa),In this stage,the internal pressure is mainly borne by prestressed steel wire.The wire-breaking response patterns are also found.(5)The three-dimensional nonlinear finite element model of PCCP based on ABAQUS was established,which is used to simulate the structural deformation of PCCP under different internal water pressure.The simulated results are compared with that of optical fiber monitoring.The results show that the optical fiber monitoring value and simulation value are in good agreement,and the change trend is also similar.The feasibility and effectiveness of the fiber optic sensing technology used in the structural strain monitoring of PCCP is further verified.