Research On The DFOS-based Monitoring For The Structural Deformation Of Metro Shield Tunnel In Suzhou

With the construction of urban subway transportation hub,shield tunnel construction is developing at an unprecedented speed in China.At the same time,the safety problem caused by deformation during construction and operation period is becoming more and more prominent,so it is important to explore an effective method for tunnel deformation monitoring.On the basis of domestic and foreign related research and the Suzhou metro monitoring tunnel project during operation and construction period,the distributed fiber optical sensing(DFOS)technology and its feasibility for monitoring the structural deformation of Metro Shield Tunnel according to the deformation features of shield tunnel are introduced;The following aspects such as the selection of sensing cable,fixation methods of the cable,temperature compensation techniques,the establishment of monitoring plan,the composition of the monitoring system,data processing analysis and the evaluation of tunnel structure are talked to carry out systematic research on DFOS technology of shield tunnel structure health monitoring.Finally a new and effective way for tunnel structure health monitoring is provided.The achievements are listed as follows:(1)The necessity for deformation monitoring of the subway shield tunnel is discussed,and the present situation and the weakness of the tunnel deformation monitoring technology is analyzed,at last the advantages,development and application of DFOS technology on tunnel structure deformation monitoring are introduced.(2)The principle and technical superiority of FBG,BOTDR,BOTDA and BOFDA are explained,the stability and strain measurement Characteristic for BOFD A and BOTDA technology are compared to adapt to tunnel deformation monitoring.(3)According to the structure and deformation features for the lining of shield tunnel,the advantages of DFOS technology is analyzed,and the section of sensing cable,fixation methods and temperature compensation techniques are discussed.(4)Regarded longitudinal deformation and converge of rings as monitoring contents,the deformation monitoring scheme for the DFOS technology on subway tunnel is designed,the basic framework,data processing and the early warning value for monitoring are respectively described.(5)Combined with the structural deformation features of Suzhou metro line one,the appropriate type of the fixture that can be fixed on the surface of the segment are put forward,then the monitoring scheme is designed so that the sensing cable can go through the waist,top and bottom structure of the shield tunnel.The monitoring results showed that until May 11,2015,there were abnormal deformation intervals in longitudinal structure,the maximum deformation of Segment joints is 1.45mm;The expansion joints of ballast bed gradually close with the raise of temperature,the maximum closure amount is 0.35mm,which is far less than the width of its design value.The above verified the feasibility of the DFOS monitoring technology for the deformation monitoring of tunnel structure.6.The cause for deformation of lining structure in the process of excavation is discussed;According to the monitoring results for the structure monitoring of shield tunnel,Suzhou metro line 4,it is proved that optic cable which has fixed points is easy for positioning,and the strain was stable between two fixed points,therefore it was suitable for long-distance monitoring for tunnel structure.