Round shield tunnel three-dimensional strain and internal force monitoring method

Abstract

The invention provides a circular shield tunnel three-dimensional strain and internal force monitoring method based on a distributed optical fiber sensing technology, and provides a shield tunnel three-dimensional strain measuring method and a force monitoring system based on the distributed optical fiber sensing technology, which are used for measuring strain changes of a shield tunnel in three directions under the action of a complex load in real time. The method comprises the following steps: calculating and analyzing the stress character of a shield tunnel, specifically, embedding nine sensing optical fibers in the pipe wall of the shield tunnel, forming a group by three sensing optical fibers, intersecting three sensing optical fibers in each group at one point and sharing the same cross section at three points, monitoring the linear strain change of each sensing optical fiber at the same time by adopting a Brillouin demodulation technology (BOTDR / BOTDA), and calculating and analyzing the stress character of the shield tunnel according to the measured strain variation. According to a three-way strain rosette calculation principle, three-way linear strain and cutting strain of each section are analyzed, and according to material parameters (elastic modulus E of the shield segment) of the shield segment, axial force (NY), horizontal force (FX), vertical force (FZ), bending moment (MX, MZ), torque (T) and distribution of the axial force, the horizontal force, the vertical force, the bending moment (MX, MZ) and the torque (T) of the shield tunnel are calculated.

Description

Technical Field

[0001] The invention belongs to the technical field of shield tunnel strain and internal force monitoring, and in particular relates to a circular shield tunnel three-dimensional strain and internal force monitoring method based on distributed optical fiber sensing technology. Background Art

[0002] With the acceleration of my country's urbanization process and the rapid and substantial increase in rail transit mileage, the safety protection of operating subway tunnels is becoming increasingly important, especially the deformation of subway tunnel structures caused by the increase in the service life of operating subways. Long-term development may cause serious structural changes and induce major engineering disasters and safety accidents.

[0003] Existing shield tunnel safety monitoring is mostly focused on monitoring tunnel structure deformation (settlement, horizontal displacement and convergence deformation), and rarely monitors the internal force of the shield tunnel structure. The internal force of the shield tunnel structure will affect the deformation development trend of the shield tunnel. If the internal force of the shield tunnel can be mastered, effective remediation measures can be taken in time to change the stress state, so that the deformation rate can be slowed down or develop in a favorable direction. Summary of the invention

[0004] The purpose of the present invention is to provide a method for monitoring three-dimensional strain and internal force of a circular shield tunnel based on distributed optical fiber sensing technology, so as to solve or partially alleviate the above-mentioned technical problems.

[0005] To this end, the above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0006] A method for monitoring three-dimensional strain and internal force of a circular shield tunnel, characterized in that the method comprises the following steps:

[0007] S1. Nine optical sensing fibers are buried along the wall of the circular shield tunnel. The optical sensing fibers are divided into three groups, with three fibers in each group, and arranged as follows:

[0008] -The first group of sensing optical fibers are axial optical fibers, and all three sensing optical fibers are arranged along the axial direction of the circular shield tunnel;

[0009] - The second group of sensing optical fibers are S-shaped optical fibers. All three sensing optical fibers are wound counterclockwise around the wall of the circular shield tunnel, evenly winding from one end of the wall to the other end;

[0010] -The third group of sensing optical fibers are reverse S-shaped optical fibers. All three sensing optical fibers are wound clockwise around the tunnel wall, evenly winding from one end of the wall to the other end;

[0011] The axial optical fiber has several intersection points with the S-type optical fiber and the reverse S-type optical fiber, and the intersection points of each axial optical fiber with the S-type optical fiber and the intersection points of each axial optical fiber with the reverse S-type optical fiber overlap one by one to form test points, and there are three test points at the edge of the circular shield tunnel cross section where each test point is located; the angle between the S-type optical fiber, the reverse S-type optical fiber and the axial optical fiber is θ, 0°<θ<90;

[0012] Nine sensing optical fibers are connected end to end to form one optical fiber. There is no requirement for the order of optical fiber connection. Both ends of the formed optical fiber are connected to a Brillouin demodulator, and the Brillouin demodulator is connected to a computer.

[0013] S2. The strain variation of three test points A, B, and C on a cross section of a circular shield tunnel is measured by a Brillouin demodulator. Test point B is between test point A and test point C. The strain values ​​of the inverted S-type optical fiber, axial optical fiber, and S-type optical fiber at points A, B, and C are ε A1 , ε A2 , ε A3 , ε B1 , ε B2 , ε B3 , ε C1 , ε C2 , ε C3 , using three-dimensional strain rosette analysis calculation;

[0014] The strain test value and the force in the rectangular coordinate system of the circular shield tunnel are used to establish the test equation group as follows:

[0015]

[0016] In the above formula, d is the diameter of the shield tunnel, F X 、F Z 、N Y , T, M X and M Z They are three forces and three moments in the rectangular coordinate system of the shield tunnel, among which F X is the X-direction force, N Y is the Y-direction force, F Z is the Z-direction force, T is the torque, M X is the bending moment relative to the X-axis, M Z is the bending moment relative to the Z axis; E is the elastic modulus of the shield segment, and μ is the Poisson’s ratio of the shield tunnel;

[0017] According to the strain test principle, the strain test value is expressed by six force components in the rectangular coordinate system of the shield tunnel as follows:

[0018]

[0019] In the above formula, k represents the kth row of the matrix, k=3(i-1)+j, i=1,2,3; j is the number of the test hole corresponding to the test value equation, j=1,2,3; is the test value; A k1 ~A k6 is the force coefficient of the test value equation, and its expressions are:

[0020]

[0021]

[0022]

[0023]

[0024]

[0025]

[0026]

[0027]

[0028]

[0029] In the above formula, d is the diameter of the shield tunnel, and E is the elastic modulus of the shield segment;

[0030] The number of equations in the test equation group is greater than the number of unknown spatial forces (6 components) that need to be solved. The least squares method is used to solve the optimal value of the force component. The calculation can use no less than 6 equations, and then the calculation results are comprehensively analyzed to determine the value to be used. The calculation equation is as follows:

[0031]

[0032] F X 、F Z 、N Y , T, M X and M Z They are three forces and three moments in the rectangular coordinate system of the shield tunnel, among which F X is the X-direction force, N Y is the Y-direction force, F Z is the Z-direction force, T is the torque, M X is the bending moment relative to the X-axis, M Z is the bending moment relative to the Z axis; is the test value; A k1 ~A k6 is the force coefficient of the test value equation.

[0033] The present invention provides a three-dimensional strain and internal force monitoring method of a circular shield tunnel based on distributed optical fiber sensing technology, and provides a three-dimensional strain measurement method and force monitoring system for a shield tunnel based on distributed optical fiber sensing technology, which are used for real-time measurement of strain changes in three directions of a shield tunnel under complex loads, calculation and analysis of the stress characteristics of the shield tunnel, etc. Specifically, 9 sensing optical fibers are buried in the shield tunnel wall, three sensing optical fibers form a group, and the three sensing optical fibers in each group intersect at one point, and the three points have a common cross-section. Brillouin demodulation technology (BOTDR / BOTDA) is used to simultaneously monitor the linear strain changes of each sensing optical fiber, and then according to the measured strain changes and the three-dimensional strain rosette calculation principle, the three-dimensional linear strain and shear strain of each cross section are analyzed, and according to the material parameters of the shield segment (the shield segment elastic modulus E), the axial force (N Y ), horizontal force (F X ), vertical force (F Z ), bending moment (M X 、M Z ), torque (T) and its distribution. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of a circular shield tunnel three-dimensional strain and internal force monitoring system based on distributed optical fiber sensing technology provided by the present invention.

[0035] Figure 2 Schematic diagram of the layout of distributed sensing optical cables.

[0036] Figure 3 This is a side view of the distributed sensing optical cable arranged in a circular shield tunnel.

[0037] Figure 4 Schematic diagram of the strain gauge rosette principle.

[0038] Figure 5 It is a schematic diagram of the i cross section. DETAILED DESCRIPTION

[0039] The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

[0040] like Figure 1-2 As shown, 9 sensing optical fibers are buried along the surface of the shield tunnel wall. The sensing optical fibers are divided into three groups, with 3 fibers in each group, and are arranged as follows:

[0041] - The first group of sensing optical fibers are axial optical fibers, and the three sensing optical fibers are arranged along the axial direction of the circular shield tunnel, as shown by reference numeral 3 in the figure;

[0042] - The second group of sensing optical fibers are S-shaped optical fibers, and the three sensing optical fibers are all wound counterclockwise around the wall of the circular shield tunnel, evenly winding from one end of the wall to the other end, as shown by reference numeral 2 in the figure;

[0043] - The third group of sensing optical fibers are inverted S-shaped optical fibers. All three sensing optical fibers are wound clockwise around the tunnel wall, evenly winding from one end of the wall to the other end, as shown by reference numeral 1 in the figure;

[0044] The axial optical fiber has several intersection points with the S-type optical fiber and the reverse S-type optical fiber, and the intersection points with the S-type optical fiber and the intersection points with the reverse S-type optical fiber on each axial optical fiber correspond to each other and overlap to form test points. There are three test points at the edge of the cross-section of the shield tunnel where each test point is located; the angle between the S-type optical fiber, the reverse S-type optical fiber and the axial optical fiber is θ, 0°<θ<90°.

[0045] The nine sensing optical fibers are connected end to end to form one optical fiber. There is no requirement for the order of optical fiber connection. Both ends of the formed optical fiber are connected to the Brillouin demodulator 5 , and the Brillouin demodulator 5 is connected to the computer 4 .

[0046] The following describes in detail the method for monitoring three-dimensional strain and internal force of a shield tunnel using this embodiment:

[0047] 1) Basic principles of Brillouin demodulation technology (BOTDR / BOTDA)

[0048] BOTDR / BOTDA is a new type of sensing technology developed on the basis of optical fiber and optical fiber communication technology, which uses light as a carrier and optical fiber as a medium to sense and transmit external signals. Its working principle is to inject pulsed light and continuous light from both ends of the optical fiber to create the Brillouin amplification effect (stimulated Brillouin), based on the linear change relationship between the Brillouin frequency shift of the optical signal and the optical fiber temperature and axial strain, as shown in formula (1).

[0049] Δv B =C vt ·Δt+C ve ·Δε (1)

[0050] In the above formula, Δv B is the Brillouin frequency shift; C νt is the Brillouin frequency shift temperature coefficient; C νe is the Brillouin frequency shift strain coefficient; Δt is the temperature change; Δε is the strain change.

[0051] The Brillouin frequency shift caused by temperature change can be compensated by the frequency shift obtained by standing still in the non-test section.

[0052] 2) Calculation principle of three-dimensional strain rosette

[0053] like Figure 4 , Figure 5As shown, OXYZ is defined as the rectangular coordinate system of the shield tunnel, oxyz is the local coordinate system of the measuring point, the Y axis is along the axial direction of the tunnel, the X axis is along the horizontal direction of the tunnel section, the Y axis is along the vertical direction of the tunnel section, the local coordinate system of the test point is the coordinate origin, the x axis is along the direction of the tunnel section, and the y axis is along the axial optical fiber arrangement direction, wherein the angles between the x axis and the y axis and the X axis and the Y axis are respectively D, and the z axis is perpendicular to the Y axis.

[0054] Assume that the x-strain, y-strain and shear strain at point G on the shield tunnel section are ε x , ε y , γ xy , then the strains in the 0°, θ, and -θ directions are:

[0055] ε 0° =ε y (2)

[0056]

[0057]

[0058] Solving the simultaneous equations of (2), (3) and (4) yields:

[0059]

[0060] ε y =ε 0° (6)

[0061]

[0062] Assumptions Figure 3 A i The strain values ​​measured at points θ (anti-S-type fiber), 0° (axial fiber), and -θ (S-type fiber) are ε A1 , ε A2 , ε A3 , B i The strain values ​​measured at points θ (anti-S-type fiber), 0° (axial fiber), and -θ (S-type fiber) are ε B1 , ε B2 , ε B3 , C i The strain values ​​measured at points θ (anti-S-type fiber), 0° (axial fiber), and -θ (S-type fiber) are ε C1 , ε C2 , ε C3 .

[0063] The six strain components in the OXYZ coordinate system are represented by {ε}, and the six strain components in the oxyz coordinate system are represented by {ε'}. The following coordinate transformation relationship should be satisfied between the two sets of strain components.

[0064]

[0065] The direction cosines of the coordinate axis of the measuring point and the rectangular coordinate system of the shield tunnel can be expressed as follows:

[0066]

[0067] The azimuths of points A, B, and C are 0°, 120°, and 240°, respectively, and the inclinations are all 90°. Based on the three-dimensional strain rosette principle and the spatial coordinate transformation formula, the relationship between the three-dimensional linear strain of the measuring point and the spatial strain parameters of the shield tunnel is established as follows:

[0068]

[0069]

[0070]

[0071] 3) Calculation theory and principle of axial force, bending moment and torque

[0072] According to the calculated three-dimensional linear strain and shear strain, the horizontal force, vertical force, bending moment and torque of the shield tunnel in the rectangular coordinate system can be obtained from the material mechanics theory:

[0073]

[0074] Then the spatial strain component is expressed in terms of force as:

[0075]

[0076] The strain test value and the force in the rectangular coordinate system of the shield tunnel are used to establish the test equation group as follows:

[0077]

[0078] In the above formula, d is the diameter of the shield tunnel, F X 、F Z 、N Y , T, M X and M Z They are three forces and three moments in the rectangular coordinate system of the shield tunnel, among which F X is the X-direction force, N Y is the Y-direction force, F Z is the Z-direction force, T is the torque, M X is the bending moment relative to the X-axis, M Z is the bending moment relative to the Z axis; E is the elastic modulus of the shield segment, and μ is the Poisson’s ratio of the shield tunnel;

[0079] According to the strain test principle, the strain test value is expressed by six force components in the rectangular coordinate system of the shield tunnel as follows:

[0080]

[0081] In the above formula, k represents the kth row of the matrix, k=3(i-1)+j, i=1,2,3; j is the number of the test hole corresponding to the test value equation, j=1,2,3; is the test value; A k1 ~A k6 is the force coefficient of the test value equation. The number of equations in the test equation group (14) is greater than the number of unknown spatial forces (6 components) to be solved, and the principle of least squares method is used to solve the optimal value of the force component. The calculation can use no less than 6 equations, and then conduct a comprehensive analysis of the calculation results to determine the value to be used. The calculation equation is as follows:

[0082]

[0083] The above-mentioned specific implementation methods are used to explain the present invention and are only preferred embodiments of the present invention, rather than limiting the present invention. Any modifications, equivalent substitutions, improvements, etc. made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A method for monitoring three-dimensional strain and internal force of a circular shield tunnel, characterized in that: The method comprises the following steps: S1. Nine optical sensing fibers are buried along the wall of the circular shield tunnel. The optical sensing fibers are divided into three groups, with three fibers in each group, and arranged as follows: -The first group of sensing optical fibers are axial optical fibers, and all three sensing optical fibers are arranged along the axial direction of the circular shield tunnel; - The second group of sensing optical fibers are S-shaped optical fibers. All three sensing optical fibers are wound counterclockwise around the wall of the circular shield tunnel, evenly winding from one end of the wall to the other end; -The third group of sensing optical fibers are reverse S-shaped optical fibers. All three sensing optical fibers are wound clockwise around the tunnel wall, evenly winding from one end of the wall to the other end; The axial optical fiber has several intersection points with the S-type optical fiber and the reverse S-type optical fiber, and the intersection points of each axial optical fiber with the S-type optical fiber and the intersection points of each axial optical fiber with the reverse S-type optical fiber overlap one by one to form test points, and there are three test points at the edge of the circular shield tunnel cross section where each test point is located; the angle between the S-type optical fiber, the reverse S-type optical fiber and the axial optical fiber is θ, 0°<θ<90; Nine sensing optical fibers are connected end to end to form one optical fiber. There is no requirement for the order of optical fiber connection. Both ends of the formed optical fiber are connected to a Brillouin demodulator, and the Brillouin demodulator is connected to a computer. S2. The strain variation of three test points A, B, and C on a cross section of a circular shield tunnel is measured by a Brillouin demodulator. Test point B is between test point A and test point C. The strain values ​​of the inverted S-type optical fiber, axial optical fiber, and S-type optical fiber at points A, B, and C are ε A1 , ε A2 , ε A3 , ε B1 , ε B2 , ε B3 , ε C1 , ε C2 , ε C3 , using three-dimensional strain rosette analysis calculation; The strain test value and the force in the rectangular coordinate system of the circular shield tunnel are used to establish the test equation group as follows: In the above formula, d is the diameter of the shield tunnel, F X 、F Z 、N Y , T, M X and M Z They are three forces and three moments in the rectangular coordinate system of the shield tunnel, among which F X is the X-direction force, N Y is the Y-direction force, F Z is the Z-direction force, T is the torque, M X is the bending moment relative to the X-axis, M Z is the bending moment relative to the Z axis; E is the elastic modulus of the shield segment, and μ is the Poisson’s ratio of the shield tunnel; According to the strain test principle, the strain test value is expressed by six force components in the rectangular coordinate system of the shield tunnel as follows: In the above formula, k represents the kth row of the matrix, k=3(i-1)+j, i=1,2,3; j is the number of the test hole corresponding to the test value equation, j=1,2,3; is the test value; A k1 ~A k6 is the force coefficient of the test value equation, and its expressions are: A 12 =0, A 14 =0, A 16 =0, A 21 =0,A 22 =0, A 24 =0,A 25 =0,A 26 =0, A 32 =0, A 34 =0, A 36 =0, A 51 =0,A 52 =0, A 54 =0,A 55 =0,A 56 =0, A 81 =0,A 82 =0, A 84 =0,A 85 =0,A 86 =0, In the above formula, d is the diameter of the shield tunnel, and E is the elastic modulus of the shield segment; The number of equations in the test equation group is greater than the number of unknown spatial forces to be solved. The principle of least squares method is used to solve the optimal value of the force component. The calculation can use no less than 6 equations, and then a comprehensive analysis is performed on the calculation results to determine the value to be used. The calculation equation is as follows: In the above formula, F X 、F Z 、N Y , T, M X and M Z They are three forces and three moments in the rectangular coordinate system of the shield tunnel, among which F X is the X-direction force, N Y is the Y-direction force, F Z is the Z-direction force, T is the torque, M X is the bending moment relative to the X-axis, M Z is the bending moment relative to the Z axis; is the test value; A k1 ~A k6 is the force coefficient of the test value equation.

Images