| With the rapid development of rail transportation in China,shield tunnel technology has been widely used in subway tunnels because of its advantages of concealed construction,rapidity and low impact on ground traffic.However,subway tunnels often traverse large areas with complex geological conditions,especially in the eastern soft soil areas.During the operation of subway shield tunnels,diseases such as convergence deformation and tunnel uneven settlement likely to occur,which seriously threaten the safe operation of the subway.Traditional tunnel monitoring means are still difficult to meet the monitoring needs of modern shield tunnels,so it is imperative to explore an advanced safety monitoring technology for shield tunnels.In this paper,the types,characteristics,monitoring elements and monitoring means of shield tunnel deformation were summarized based on the previous research;the principles of several fiber optic sensing(FOS)technologies and sensing fiber optic(FO)cables commonly used for tunnel health monitoring were introduced,and the principles and implementation methods of tunnel uneven settlement based on distributed fiber optic sensing(DFOS)technologies were proposed;indoor experiments were conduted to study the monitoring effects and usage conditions of different sensing cables and installation methods.The calculation method of tunnel uneven settlement was proposed,and the accuracy of the monitoring effect was evaluated through the long-distance model test of tunnel uneven settlement;combined with structural health monitoring of Ningbo Metro Line 1,the monitoring and analysis of the uneven settlement deformation of this shield tunnel was carried out.The main contents and research results of the paper are summarized as follows:(1)The deformation types,characteristics and monitoring elements of shield tunnel were analyzed;the sensing principles of Brillouin optical frequency domain analysis(BOFDA)and optical frequency domain reflectometer(OFDR)technology and Bragg fiber grating(FBG)were introduced;sensing FO cables commonly used for tunnel deformation monitoring and methods of cables were introduced;the principle and method of shield tunnel uneven settlement monitoring based on DFOS were proposed.(2)The principle of uneven settlement monitoring with obliquely-pulled sensing fiber optic cable was proposed,and the indoor model test of uneven settlement of shield tunnel was carried out with 0.9 mm tight-buffered strain sensing cable,2 mm polyurethane tight-buffered strain sensing cable and Kevlar sheath strain sensing cable,respectively;and the relationship between displacement and the strain in cables was analyzed;the results showed that: the larger the displacement caused by uneven settlement,the larger slanting angle and the strain caused by unit displacement change of the cable is;when the displacement change is within ±5 mm,the calculated value of the strain ratio is almost the same as the theoretical strain value,and the maximum error is only 3 με;the 2 mm polyurethane tight-buffered train sensing cable has the best performance in the monitoring of settlement deformation.(3)The calculation model of shield tunnel uneven settlement was proposed,and the relationship between the settlement displacement of the shield tunnel and the strain of sensing cable was quantitatively analyzed;a long-distance tunnel uneven settlement monitoring model test was carried out,and the local relative displacement and the overall displacement change were quantitatively calculated;the results showed that the displacement error of each point was less than 1 mm when the displacement change range of each point was not greater than ±2 mm,and the monitoring accuracy met the requirements of the safety monitoring requirements of the tunnel.(4)Based on the structural health monitoring project of the shield tunnel of Ningbo Metro Line 1,the research results of this paper were applied to the actual monitoring of the uneven settlement of the tunnel,and the results showed that the strain variation of the fiber optic cable was within 175 με,excluding the influence of axial displacement and temperature.Until this May,the tunnel as a whole is in a safe and stable condition. |
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