| In the construction of the urban subway in China,shallow excavation method is widely used because of its low cost and wide stratum adaptability.However,Due to the numerous construction steps of shallow excavation method,the mechanical transformation in the tunnel primary lining and secondary lining structure is frequent.Therefore,the construction safety and operation maintenance of the tunnel are also facing great challenges.Therefore,it is very important to carry out the whole life cycle monitoring of the tunnel.At present,point sensors,total stations and three-dimensional laser scanners are usually used in engineering to monitor the deformation of the tunnel.Although these monitoring technologies have mature experience,they have some problems,such as high cost,unable to lay on a large scale,cumbersome operation,time-consuming and laborious,and affected by environmental visibility,which seriously affect the efficiency of tunnel structure health monitoring.In order to solve this problem,this thesis applies distributed optical fiber sensing technology to tunnel excavation deformation monitoring.However,at present,most monitoring codes at home and abroad take tunnel settlement/convergence deformation as the main index to judge tunnel safety and guide on-site construction,while the distributed optical fiber technology can only directly measure the strain of the structure according to its original design principle.How to indirectly calculate the longitudinal settlement and lateral convergence deformation of the tunnel through the strain monitoring data and various mechanical and geometric principles,as well as a series of key scientific problems derived therefrom,still need to be solved.In this thesis,by means of literature research,theoretical analysis,numerical simulation,indoor test and field test,the following research is carried out: firstly,the basic working performance of optical fiber(Research(1))is studied to determine whether optical fiber can be used in underground tunnel monitoring.Secondly,the research on the noise reduction of optical fiber monitoring data based on wavelet analysis(Research(2))and the research on the deformation coordination and strain transmission mechanism between optical fiber and tunnel lining(Research(3))are carried out to ensure the accuracy and reliability of optical fiber monitoring data.On this basis,Tunnel settlement deformation inversion based on the distributed optical fiber technology(Research(4))and tunnel convergent deformation inversion based on the distributed optical fiber technology(Research(5))are studied.The theory of distributed optical fiber monitoring tunnel deformation is proposed and verified by indoor experiments.Finally,the application of distributed optical fiber technology in deformation monitoring of Beijing metro tunnel(Research(6))is studied,and all the results are tested through field tests.The main research achievements of this thesis are as follows:(1)Through the experimental research on the basic working performance of optical fiber,the strain measurement accuracy and spatial resolution of BOTDR and BOFDA are explored,and the ultimate tensile,compressive,bending and shear properties of different kinds of optical fiber are obtained,which provides a basis for the selection of optical fiber in the field.(2)Through the research on noise reduction of the optical fiber monitoring data,it is found that when sym6 wavelet is used to decompose the signal in six layers,then the threshold based on penaly strategy is used to reduce the signal noise,and the soft threshold action mode is selected,the noise reduction effect is the most ideal.Compared with the signal-to-noise ratio of 9.6d B of the original data and the root mean square error of 0.99 ℃,the signal-to-noise ratio of the signal after noise reduction is increased by 59.7%,The root mean square error is reduced by 48.5%,suggesting that the noise reduction effect is significant.(3)By studying the deformation coordination and strain transfer mechanism between the optical fiber and tunnel lining,the strain transfer theoretical models of optical fiber embedded layout and fixed-point layout are established,and the distribution law of the strain transfer efficiency of optical fiber under the two layout modes is explored.The effects of the embedded length of the optical fiber,the shear modulus of the protective sleeve,the thickness of the protective sleeve and the pre-tensile strain of the optical fiber on the strain transmission efficiency and cooperative deformation ability of the optical fiber are revealed.(4)Through the research on the sensing algorithm of the tunnel longitudinal settlement deformation based on the distributed optical fiber,the longitudinal settlement law of the tunnel under different working conditions is obtained,and the parabola inversion algorithm,curvature superposition inversion algorithm and neural network inversion algorithm based on optical fiber strain curves are proposed.Through the simulated loading test in the laboratory,the three deformation inversion algorithms are tested respectively.From the error analysis results,the relative errors of the algorithm are within 10%,which meets the requirements of the international survey association for the monitoring accuracy of engineering projects.(5)Through the research of tunnel convergence deformation sensing algorithm based on the distributed optical fiber,the convergence deformation inducing mechanism and deformation mode of tunnel are obtained.Two algorithms for the inversion of tunnel convergence deformation based on the optical fiber strain curve are proposed,which are based on the theoretical analysis and neural network.Through the simulated loading test in the laboratory,the proposed convergent deformation inversion algorithms are tested respectively.From the error analysis results,the relative errors of the algorithm are within 10%,which meets the requirements of the international survey association for the monitoring accuracy of engineering projects.(6)The application of the distributed optical fiber technology in the deformation monitoring of Beijing metro tunnel is carried out.Based on the strain monitoring curve of the initial support of the tunnel,the longitudinal settlement deformation of the tunnel is inversed.The results show that the maximum error between the maximum settlement of the tunnel obtained by strain inversion and the measured value of the field total station is 0.84 mm.Based on the strain monitoring curve of tunnel secondary lining,the transverse convergence deformation of tunnel is inversed.The results show that the maximum error between the maximum transverse convergence deformation of the tunnel obtained by strain inversion and the measured value of the field total station is 0.5mm.It is proved that it is feasible to apply the distributed optical fiber technology to the tunnel deformation monitoring. |
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