Tunnel supporting structure deformation monitoring system based on distributed optical fibers and construction method

Abstract

The invention belongs to the field of tunnel supporting structure deformation monitoring, and discloses a tunnel supporting structure deformation monitoring system based on distributed optical fibers and a construction method, and the system comprises an optical fiber distributed demodulator, a first strain sensing optical cable, a second strain sensing optical cable, and a supporting structure arranged in a tunnel surrounding rock structure. The supporting structure comprises a concrete steel pipe extending along the curved surface of the tunnel and a plurality of flexible grating steel frames, and the concrete steel pipe is arranged in the center of a frame structure formed by the flexible grating steel frames and fixedly connected with the frame structure through weak-rigidity connecting ribs. The first strain sensing optical cable is arranged along the two opposite flexible grating steel frames; the second strain sensing optical cable is bidirectionally arranged along the concrete steel pipe; and the optical fiber distributed demodulator is used for demodulating to obtain the displacement of the tunnel in the horizontal direction and the vertical direction according to the sensing data in the first strain sensing optical cable and the second strain sensing optical cable. According to the invention, real-time accurate monitoring of deformation of the tunnel supporting structure is realized, and the arrangement and maintenance cost of the sensor is greatly reduced.

Description

Technical Field

[0001] The present invention belongs to the field of tunnel support structure deformation monitoring, and specifically relates to a tunnel support structure deformation monitoring system and construction method based on distributed optical fiber, which performs distributed monitoring of tunnel surrounding rock deformation in multi-layer goaf areas based on a new type of intelligent support structure. Background Art

[0002] At present, the design of traditional support structures mainly adopts the concept of first being flexible and then being rigid, and combining rigidity and flexibility. However, under adverse geological conditions, tunnels are prone to deformation. The traditional support structure design focuses too much on rigidity, resulting in insufficient flexibility of the support structure and poor deformation adaptability. After tunnel excavation, the extrusion deformation of local surrounding rock may lead to stress concentration, causing the arch frame to twist, become unstable or even destroyed, thereby causing the failure of the overall support system, and larger deformation problems may occur later. In addition, traditional deformation monitoring methods for tunnel support structures are mostly point measurements, which cannot continuously and effectively monitor the global deformation trend and local deformation status of the structure.

[0003] In view of the defects and shortcomings of the existing tunnel support structure deformation monitoring technology, it is urgent to improve the tunnel support structure deformation monitoring technology to achieve continuous and effective deformation monitoring of the tunnel support structure. Summary of the invention

[0004] In order to solve the above technical problems in the prior art, the present invention proposes a tunnel support structure deformation monitoring system and construction method based on distributed optical fiber to achieve distributed real-time monitoring of tunnel surrounding rock deformation in multi-layer goaf areas.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a tunnel support structure deformation monitoring system based on distributed optical fiber, comprising: an optical fiber distributed demodulator, a first strain sensing optical cable, a second strain sensing optical cable and a support structure arranged in the tunnel surrounding rock structure;

[0006] The support structure includes a concrete steel pipe extending along the tunnel curved surface and a plurality of flexible grid steel frames, wherein the concrete steel pipe is arranged at the center of the frame structure formed by the flexible grid steel frame, and the concrete steel pipe is fixedly connected to the flexible grid steel frame by weak rigid connecting ribs;

[0007] One end of the first strain sensing optical cable is connected to the first output end of the optical fiber distributed demodulator, and the other end is extended along one of the flexible grid steel frames to an end point, then extended to an end point of another opposite flexible grid steel frame, and extended in the opposite direction to another end point and then connected to the first input end of the optical fiber distributed demodulator;

[0008] One end of the second strain sensing optical cable is connected to the first output end of the optical fiber distributed demodulator, and the other end enters the concrete steel pipe through the grouting hole, extends along the concrete steel pipe to the bottom thereof, then returns along the concrete steel pipe and is connected to the second input end of the optical fiber distributed demodulator; concrete is arranged in the concrete steel pipe;

[0009] The optical fiber distributed demodulator is used to demodulate the displacement of the tunnel in the horizontal direction and the vertical direction according to the sensing data in the first strain sensing optical cable and the second strain sensing optical cable.

[0010] The specific method of demodulating the optical fiber distributed demodulator to obtain the displacement of the tunnel in the horizontal direction and the vertical direction is:

[0011] The horizontal displacement of the tunnel is calculated by the strain difference of the relative position of the optical cable sections fixed at the invert and the arch waist section to achieve stable compensation. The vertical displacement of the tunnel is calculated by the strain difference of the outbound and return sections of the optical cable fixed at the arch top section.

[0012] The calculation formula of the horizontal displacement is:

[0013] s(x)=∫∫(―Δε(x) / D)dxdx+Cx+E;

[0014] Where s(x) represents the horizontal displacement at position x in the tunnel, Δε(x) represents the measured strain difference at position x, D represents the distance between the outbound and return sections of the corresponding optical cable, and C and E are constants.

[0015] The vertical displacement calculation formula is:

[0016]

[0017] where ε c is the strain of the outbound section of the vault cable, ε D is the strain measured in the return section of the arch optical cable, h is the vertical displacement, i.e., the settlement of the tunnel support structure, and L0 is the distance from the arch top branch protection structure to the nearest fixed point.

[0018] Before the weak rigid node of the flexible grid steel frame fails, the optical fiber distributed demodulator demodulates the horizontal and vertical displacements of the tunnel according to the sensing data in the first strain sensing optical cable;

[0019] After the weak rigid node of the flexible grid steel frame fails, the optical fiber distributed demodulator demodulates the displacement of the tunnel in the horizontal direction and the vertical direction according to the sensing data in the second strain sensing optical cable.

[0020] The first strain sensing optical cable and the second strain sensing optical cable include a fiber core and a protective layer encapsulated outside the fiber core, and the protective layer is polyurethane elastomer or HY material.

[0021] The tunnel support structure deformation monitoring system based on distributed optical fiber also includes a conductor and a counterweight hammer, wherein the conductor is used to connect the two ends of the first strain sensing optical cable and the second strain sensing optical cable to the optical fiber distributed demodulator, and the conductor adopts a metal-based cable-shaped optical cable, and the internal optical fiber is protected by multiple metal reinforcements;

[0022] The counterweight hammer is arranged at the bottom of the concrete steel pipe and is used for performing counterweight stretching on the second strain sensing optical cable.

[0023] The first strain sensing optical cable is fixed to the flexible grid steel frame by a fixing fixture, the fixing fixture includes a fixing ring, a positioning pin and a nut, the fixing ring sleeve is arranged on the outer periphery of the flexible grid steel frame and the first strain sensing optical cable, the positioning pin passes through both ends of the fixing ring, and the fixing ring is fixed to the flexible grid steel frame by tightening the nut;

[0024] The support structure includes four flexible grid steel frames;

[0025] The weak rigidity connecting ribs include a sleeve ring and eight connecting ribs connected to the sleeve ring, wherein four connecting ribs are connected to four flexible grid steel frames above the sleeve ring, and four connecting ribs are connected to four flexible grid steel frames below the sleeve ring.

[0026] The support structure is composed of multiple support units. The flexible grid steel frames between the support units are connected together by connecting plates, and high-strength rubber pads are laid between the connecting plates; the concrete steel pipes between the support units are connected by sleeve welding, and the ends of the concrete steel pipes are closed.

[0027] In addition, the present invention also provides a construction method of a tunnel support structure deformation monitoring system based on distributed optical fiber, comprising the following steps:

[0028] Step 1: Installation of support structure: After excavation of the upper step, spray concrete to seal the face; hang the net, erect the new support structure, and apply the system anchor; after excavation of the lower step, erect the new arch frame, and apply the locking anchor pipe; among them, high-strength and tough rubber pads are laid between each unit steel grid and connected by high-strength bolts, and the concrete steel pipes are connected by sleeve welding, and the end of the sleeve is sealed by a closed ring; install the I20 I-shaped steel arch frame, and connect the units with high-strength bolts and connecting plates;

[0029] Steps: Laying out the first strain sensing optical cable and the second strain sensing optical cable: folding the first strain sensing optical cable and the second strain sensing optical cable into loops respectively, and then fixing the first strain sensing optical cable on the surface of the flexible grid steel frame along the set arrangement position using a fixing fixture, and fixing it with polyacrylic resin glue at the bottom of the loop, and at the same time, placing the second strain sensing optical cable into the concrete steel pipe by a counterweight hammer, and then performing high-pressure grouting on the concrete steel pipe;

[0030] Steps: Connect the fiber optic distributed demodulator: connect the first strain sensing optical cable and the second strain sensing optical cable to the fiber optic distributed demodulator; monitor the overall deformation of the tunnel surrounding rock above the multi-layer complex goaf area through the fiber optic distributed demodulator.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) The present invention utilizes a frame core tube structure as a supporting structure, which can reasonably distribute the stiffness ratio between the flexible grid steel frame and the concrete steel pipe, mobilize the self-bearing capacity of the surrounding rock, and more comprehensively and accurately monitor the deformation of the tunnel surrounding rock.

[0033] (2) The support structure of the present invention has both certain flexibility and certain rigidity, and can resist continuous pressure such as long-term deformation and expansion, and is suitable for deformation monitoring of engineering structures with long periods, large ranges, and large deformations.

[0034] (3) The present invention uses distributed optical fiber to monitor the deformation of flexible grid steel frames and concrete steel pipes, and can monitor the deformation of surrounding rocks in a full-process, real-time, efficient and stable manner. Compared with traditional point monitoring methods, distributed sensing optical cables can save the cost of sensor layout and reduce monitoring costs. The optical cables are easy to install and have low maintenance costs. They can operate stably for a long time, reducing the maintenance workload of the monitoring system.

[0035] In summary, the present invention provides a deformation monitoring system and construction method for tunnel support structures based on distributed optical fiber. By using optical fiber sensing technology, real-time deformation monitoring can be performed at key parts of the tunnel. By comparing the strain difference of optical fiber sensors at different positions, accurate displacement monitoring of the tunnel structure in the horizontal and vertical directions can be achieved. The present invention not only improves the accuracy of monitoring, but also provides strong data support for the safety assessment and maintenance of the tunnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 An overall schematic diagram of a tunnel support structure deformation monitoring system based on distributed optical fiber provided in an embodiment of the present invention;

[0037] Figure 2 for Figure 1 Schematic diagram of the local structure;

[0038] Figure 3 is a cross-sectional schematic diagram of the support structure;

[0039] Figure 4 This is a schematic structural diagram of the high-transmission tight-sheathed strain sensing optical cable used in the present invention.

[0040] Figure numerals: 1-fiber optic distributed demodulator; 2-first strain sensing optical cable; 3-fiber optic fixing fixture; 4-conducting wire; 5-tunnel surrounding rock structure; 6-counterweight hammer; 7-flexible grid steel frame; 8-concrete steel pipe; 9-weak rigidity figure eight connecting ribs; 10-grouting port; 11-steel sleeve; 12-connecting plate; 13-second strain sensing optical cable; 14-support structure; 20-polyelastic sheath; 21-optical fiber. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0042] Embodiment 1

[0043] like Figures 1 to 4 As shown, embodiment 1 of the present invention provides a tunnel support structure deformation monitoring system based on distributed optical fiber, including: an optical fiber distributed demodulator 1, a first strain sensing optical cable 2, a second strain sensing optical cable 13 and a support structure 14 arranged in a tunnel surrounding rock structure 5.

[0044] The support structure 14 includes a concrete steel pipe 8 extending along the tunnel curved surface and a plurality of flexible grid steel frames 7. The concrete steel pipe 8 is arranged at the center of a frame structure with a square cross-section formed by the flexible grid steel frame 7, and the concrete steel pipe 8 is fixedly connected to the flexible grid steel frame 7 by weak rigid connecting ribs 9.

[0045] The first strain sensing optical cable 2 is arranged along two opposite flexible grid steel frames; the second strain sensing optical cable 13 is arranged bidirectionally along the concrete steel pipe; specifically, one end of the first strain sensing optical cable 2 is connected to the first output end of the optical fiber distributed demodulator 1, and the other end is extended along one of the flexible grid steel frames 7 to the end point, and then extended to the end point of the other opposite flexible grid steel frame 7, and then extended in the opposite direction to the other end point and connected to the first input end of the optical fiber distributed demodulator 1. The second strain sensing optical cable 13 on one of the flexible grid steel frames 7 is called the outbound section, and the other flexible grid steel frame 7 is called the return section. One end of the second strain sensing optical cable 13 is connected to the first output end of the optical fiber distributed demodulator 1, and the other end enters the concrete steel pipe 8 through the grouting hole 10, extends along the concrete steel pipe 8 to the bottom thereof, and then returns along the concrete steel pipe 8 and is connected to the second input end of the optical fiber distributed demodulator 1; similarly, the second strain sensing optical cable 13 in the concrete steel pipe 8 is also divided into an outbound section and a return section. Concrete is arranged in the concrete steel pipe 8.

[0046] The optical fiber distributed demodulator 1 is used to demodulate the displacement of the tunnel in the horizontal direction and the vertical direction according to the sensing data in the first strain sensing optical cable 2 and the second strain sensing optical cable 13 .

[0047] In this embodiment, the flexible steel grid frame formed by the flexible grid steel frame 7 has excellent deformation coordination ability and can deform together with the surrounding rock. When the deformation of the surrounding rock is small, the weak rigidity node bears and transfers the load; when the deformation increases, the node gradually fails, and the load is taken over by the high-rigidity concrete steel pipe. The multi-level conversion auxiliary bearing mechanism effectively controls the deterioration of the surrounding rock deformation.

[0048] Specifically, in this embodiment, the fiber optic distributed demodulator 1 demodulates the specific method of obtaining the horizontal and vertical displacements of the tunnel as follows: the horizontal displacement of the tunnel is calculated by the strain difference between the outgoing segment and the return segment of the optical cable segment fixed to the invert and the waist segment, thereby achieving temperature compensation; the vertical displacement of the tunnel is calculated by the strain difference between the outgoing segment and the return segment of the optical cable segment fixed to the arch top segment.

[0049] Specifically, in this embodiment, before the weak rigid node of the flexible grid steel frame 7 fails, the optical fiber distributed demodulator 1 demodulates the horizontal and vertical displacements of the tunnel according to the sensing data in the first strain sensing optical cable 2; after the weak rigid node of the flexible grid steel frame 7 fails, the optical fiber distributed demodulator 1 demodulates the horizontal and vertical displacements of the tunnel according to the sensing data in the second strain sensing optical cable 13.

[0050] Specifically, Figure 4As shown, in this embodiment, the first strain sensing optical cable 2 and the second strain sensing optical cable 13 include a fiber core and a protective layer encapsulated outside the fiber core, and the protective layer is polyurethane elastomer or HY material.

[0051] Furthermore, a tunnel support structure deformation monitoring system based on distributed optical fiber in this embodiment also includes a conductor 4 and a counterweight 6, wherein the conductor 4 is used to connect the two ends of the first strain sensing optical cable 2 and the second strain sensing optical cable 13 to the optical fiber distributed demodulator 1, and the conductor 4 adopts a metal-based rope-shaped optical cable, and the internal optical fiber is protected by multiple metal reinforcements. Its cross-sectional size is Φ5mm, the weight is 38kg / km, and the strain test range is -15000με~+15000με; the counterweight 6 is arranged at the bottom of the concrete steel pipe 8, and is used to perform counterweight stretching on the second strain sensing optical cable 13.

[0052] Furthermore, the diameter of the first strain sensing optical cable 2 and the second strain sensing optical cable 13 is 2 mm, the weight is 1.2 kg / km, and the strain test range is -15000 με to +15000 με.

[0053] Furthermore, in the present embodiment, the first strain sensing optical cable 2 is fixed to the flexible grid steel frame 7 by a fixing clamp 3, the fixing clamp 3 comprises a fixing ring, a positioning pin and a nut, the fixing ring sleeve is arranged on the outer periphery of the flexible grid steel frame 7 and the first strain sensing optical cable 2, the positioning pin passes through both ends of the fixing ring, and the fixing ring is fixed to the flexible grid steel frame 7 by tightening the nut; the major diameter of the fixing ring is the same as the diameter of the flexible grid steel frame, and the minor diameter is the same as the diameter of the optical cable, the optical cable is clamped into the fixing ring, and then the nut is tightened to achieve the fixing purpose.

[0054] Further, in this embodiment, the support structure 14 includes four flexible grid steel frames 7; the four flexible grid steel frames 7 form a square accommodation space, the concrete steel pipe 8 is arranged in the accommodation space, and the two sections of the first strain sensing optical cable 2 are respectively arranged on the two flexible grid steel frames 7 located on the diagonal of the square. The first strain sensing optical cable is laid on the two flexible grid steel frames on the diagonal of the square, which can more evenly cover the entire support structure and effectively capture the omnidirectional distribution of strain. The diagonal arrangement helps to accurately reflect the overall strain transmission of the structure, reduce the measurement error caused by structural asymmetry or local load, and thus improve the accuracy and reliability of strain measurement. In addition, this arrangement enhances the monitoring effect of the structural health status. The weak rigid connecting rib 9 includes a ring and eight connecting ribs connected to the ring, the ring is set on the concrete steel pipe 8, wherein four connecting ribs are connected to the four flexible grid steel frames 7 above the ring, and four connecting ribs are connected to the four flexible grid steel frames 7 below the ring.

[0055] Furthermore, in this embodiment, the support structure is composed of a plurality of support units, the flexible grid steel frames 7 between the support units are connected together by connecting plates 12, and high-strength rubber pads are laid between the connecting plates 12; the concrete steel pipes 8 between the support units are connected by sleeve welding, and the ends of the concrete steel pipes 8 are closed. Furthermore, the connecting plates 12 at the ends of the flexible grid steel frames 7 are connected together by bolts.

[0056] The measuring principle of the present invention is described below.

[0057] The Brillouin frequency shift (BFS) in optical fiber is related to the effective refractive index of the medium and the speed of acoustic wave transmission. In addition, it is also affected by the working wavelength of the incident light. Its specific expression is shown in formula (1):

[0058]

[0059] where v B is BFS, n is the refractive index of the fiber medium, v a is the acoustic wave field velocity of the optical fiber, and λ0 is the working wavelength of the incident light. From formula (1), it can be seen that the Brillouin frequency shift is proportional to the refractive index and the acoustic wave field transmission velocity, and inversely proportional to the wavelength of the incident light. The formula is used to characterize the acoustic wave field velocity in the optical fiber:

[0060]

[0061] Where k is Poisson's ratio, an elastic constant used to describe the lateral deformation of the material, ρ is the fiber medium density, E is the Young's modulus that describes the material's resistance to deformation, and v a is the acoustic wave field velocity of the optical fiber. The above parameters and the medium refractive index n can be expressed as functions of temperature and strain, namely k(T,ε), E(T,ε), ρ(T,ε) and n(T,ε). Substituting formula (2) into formula (1), the relationship between BFS and temperature and strain can be obtained, as shown in formula (3):

[0062]

[0063] where v Bis BFS, k(T,ε) is the relationship function between Poisson's ratio and temperature and strain changes, n(T,ε) is the relationship function between the refractive index of the optical fiber medium and temperature and strain changes, ρ(T,ε) is the relationship function between the density of the optical fiber medium and temperature and strain changes, k0 is the working wavelength of the incident light, and E(T,ε) is the relationship function between the Young's modulus of the material's resistance to deformation and temperature and strain changes. Assuming that the external environment temperature is constant and only strain is applied to the optical fiber, the microscopic particles in the medium will produce different refractive indices due to the stress, which will ultimately affect BFS. Therefore, when the temperature is constant (assuming T = T0) and the stress is changed, formula (3) can be written as:

[0064]

[0065] where v B is BFS, k(T,ε) is the relationship function between Poisson's ratio and temperature and strain changes, n(T,ε) is the relationship function between the refractive index of the optical fiber medium and temperature and strain changes, ρ(T,ε) is the relationship function between the density of the optical fiber medium and temperature and strain changes, λ0 is the working wavelength of the incident light, and E(T,ε) is the relationship function between the Young's modulus of the material's resistance to deformation and temperature and strain changes. Further, in the case of stress changes, formula (4) can be expressed as:

[0066] v B (T0,ε)≈v B (T0,0)[1+Δε(Δn ε +Δk ε +ΔE ε +Δρ ε )] (5)

[0067] Among them, Δk ε is the value of Poisson's ratio as a function of strain, Δn ε is the value of the refractive index of the optical fiber medium changing with strain, Δρ ε is the value of the fiber medium density changing with strain, ΔE ε It is the value of the Young's modulus of the material's resistance to deformation as the strain changes. Therefore, under the condition of constant temperature, the value of BFS that changes linearly with stress is Δv B It can be expressed as:

[0068] Δv B =C v,ε Δε

[0069] Among them, C v,ε is the strain coefficient of BFS changing linearly with stress, and Δε is the strain change. Similarly, from formula (4), when the optical fiber is under zero stress and only the temperature changes, the BFS is:

[0070] v B(T,0)≈v B (T0,0)[1+ΔT(Δn T +Δk T +ΔE T +Δρ T )] (6)

[0071] Where k is Poisson's ratio, an elastic constant used to describe the lateral deformation of the material, Δk T is the value of Poisson's ratio changing with temperature, Δn T is the value of the refractive index of the optical fiber medium changing with temperature, Δρ T is the value of the fiber medium density changing with temperature, ΔE T It is the value of the Young's modulus of the material's resistance to deformation as it changes with temperature. Therefore, it is in a zero-stress state, and the BFS change Δv is caused only by temperature changes. B It can be expressed as:

[0072] Δv B =C v,T ΔT (7)

[0073] Among them C v,T is the linear variation coefficient of BFS with temperature, and ΔT is the temperature variation. In summary, BFS is approximately linearly related to the temperature sensed by the optical fiber and the applied strain value, which can be expressed as:

[0074] Δv B =C v,T ΔT+C v,ε Δε (8)

[0075] Among them, C v,T is the linear variation coefficient of BFS with temperature, C v,ε is the gauge coefficient of BFS that changes linearly with stress. When the wavelength of incident light is 1553.8nm, C v,T =1.1MHz / ℃,C v,ε =0.0483MHz / με.

[0076] Therefore, by using redundant sections of the optical cable loop to perform temperature compensation on the optical cable monitoring, it can be approximated to monitor under constant temperature conditions. The new support structure fixed to the invert and arch waist sections calculates and monitors the horizontal displacement of the tunnel based on the strain difference of the two optical fibers, and the new support structure fixed to the arch top section can monitor the vertical displacement of the tunnel based on the strain difference of the two optical fibers. This method can evaluate the strain state of the high-transmission tight-sheathed strain sensing optical cable installed on the new tunnel support structure, thereby achieving the purpose of monitoring the deformation of the new tunnel support structure.

[0077] Specifically, when the surrounding rock deformation is small, in order to obtain the deep horizontal displacement of the frame formed by the flexible grid steel frame 7, it is assumed that the bottom of the frame structure, i.e., the inverted arch, is a fixed point. The horizontal displacement ds(x) of any point x of the support structure is:

[0078] ds(x)=(ε a ―ε b )·dx·dx / D1; (9)

[0079] Where: dx is any micro-segment on the new support structure (flexible grid steel frame 7), ε a and ε b is the measured strain measured at the same height of the outgoing and return sections of the first strain sensing optical cable 2, and D1 represents the distance between the outgoing and return sections of the first strain sensing optical cable, that is, the distance between the two diagonal positions of the flexible grid steel frame 7. The horizontal displacement of the flexible grid steel frame 7 and the axial strain have the following relationship:

[0080] s1(x)=∫∫(―Δε1(x) / D1)dxdx+Cx+E; (10)

[0081] Where: s1(x) is the horizontal displacement of each point, C and E are unknown constants. If the bottom of the flexible grid steel frame 7 is assumed to be a fixed point, C and E are both 0. Where Δε1(x) represents the actual strain difference measured by the first strain sensing optical cable 2, that is, Δε1(x) = ε a ―ε b , through formula (8), the distribution curve of the horizontal displacement of the support structure at different periods with the tunnel excavation depth can be calculated.

[0082] When the surrounding rock deformation is large, the weak rigid node is transformed from rigid to weak until it fails. At this time, the load is completely borne by the high-rigidity core steel pipe filled with concrete mortar. In order to obtain the deep horizontal displacement of the concrete steel pipe structure, the bottom of the counterweight hammer is assumed to be a fixed point. Similarly, the horizontal displacement of the concrete steel pipe structure has the following relationship with the axial strain:

[0083] s2(x)=∫∫(―Δε2(x) / D2)dxdx+Cx+E; (11)

[0084] Where: s2(x) is the horizontal displacement of each point x, C and E are unknown constants. If the bottom of the counterweight is assumed to be a fixed point, C and E are both 0. D2 is the distance between the outbound section and the return section of the second strain sensing optical cable 13; Δε2(x) represents the measured strain difference measured by the second strain sensing optical cable 13. Through formula (11), the distribution curve of the horizontal displacement of the support at different periods with the tunnel excavation depth can be calculated.

[0085] The support structure fixed to the invert and arch haunch sections can accurately measure the horizontal displacement of the tunnel support structure through two fiber optic sensors installed at these locations. These fiber optic sensors can detect the strain differences caused by external loads, geological changes or construction activities, and thus calculate the value of horizontal displacement.

[0086] Specifically, combining equations (9) and (10), the calculation formula for the horizontal displacement is:

[0087] s(x)=∫∫(―Δε(x) / D)dxdx+Cx+E; (12)

[0088] Wherein, s(x) represents the horizontal displacement of each point x in the tunnel, Δε(x) represents the strain difference corresponding to the point x on the optical fiber of the outbound and return segments, D represents the distance between the outbound and return segments of the corresponding strain sensing optical cable, dx represents the micro segment in the horizontal direction, and C and E are constants. In this embodiment, the displacement is calculated by the strain difference corresponding to the point x on the optical fiber of the outbound and return segments, which can eliminate the influence of temperature change on the measurement and realize temperature self-compensation.

[0089] At the same time, the new support structure fixed to the arch section can monitor the vertical displacement of the tunnel support structure through two optical fibers at the arch position on the outbound and return sections. These optical fiber sensors also obtain vertical displacement data by measuring strain differences, thus providing important information for the stability of the tunnel.

[0090] The calculation method of the vertical settlement of the supporting structure is as follows: assuming that the settlement of the tunnel supporting structure is h, and the distance between the arch top branch protection structure and the nearest anchor rod (the nearest fixed point of the optical cable) is L0, then when no settlement occurs, the length of the optical cable between the anchor rod and the supporting structure is also L0. Due to the settlement of the supporting structure, the length of this section of optical fiber increases by ΔL. The relationship between ε(x) at the same position x of the optical fiber inlet and outlet caused by settlement and the increased length ΔL of the optical cable is:

[0091]

[0092] At this time, the vertical settlement of the optical cable before settlement, the optical cable after settlement and the supporting structure can be abstracted as a right triangle, and the relationship between the strain caused by settlement and the vertical displacement of the supporting structure is:

[0093]

[0094] The strain measured in the outbound section of the optical cable monitoring the vertical settlement of the support structure is set as ε c , the strain measured in the return section of the optical cable monitoring the vertical settlement of the support structure is set as ε D , then the relationship between the settlement of the tunnel support structure, that is, the displacement h of the support structure in the vertical direction and the strain measured by the optical cable is:

[0095]

[0096] Then, through the above equations (12) and (15), the horizontal and vertical strains of the tunnel support structure can be converted into the horizontal deformation and vertical settlement of the tunnel support structure.

[0097] In general, the present invention can monitor the deformation of key parts of the tunnel in real time by improving the support structure and combining it with the use of optical fiber sensing technology. By comparing the strain difference of optical fiber sensors at different positions, accurate displacement monitoring of the tunnel structure in the horizontal and vertical directions can be achieved. This method not only improves the accuracy of monitoring, but also provides strong data support for the safety assessment and maintenance of the tunnel.

[0098] Embodiment 2

[0099] Embodiment 2 of the present invention provides a method for arranging a tunnel support structure deformation monitoring system based on distributed optical fiber, comprising the following steps:

[0100] Step 1: Installation of support structure: After excavation of the upper step, spray concrete to seal the face; hang the net, erect a new support structure, and apply system anchors; after excavation of the lower step, erect a new arch frame, and apply locking anchor pipes; high-strength and tough rubber pads are laid between each unit steel grille and connected by high-strength bolts, and concrete steel pipes are connected by sleeve welding, and the side ends of the sleeves are sealed by closed rings; install I20 I-beam inverted arch frames, and connect the units with high-strength bolts and connecting plates.

[0101] Step 2: Laying out the first strain sensing optical cable 2 and the second strain sensing optical cable 13: Fold the first strain sensing optical cable 2 and the second strain sensing optical cable 13 into a U-shaped loop respectively, and the U-shaped bottom corresponding to the first strain sensing optical cable 2 is set at the bottom of the supporting structure 14, fixed with polyacrylic resin glue, and then use the fixing clamp 3 to fix the two sections of the first strain sensing optical cable 2 on the surface of the corresponding flexible grid steel frame 7, and fix it with polyacrylic resin glue at the bottom of the loop. At the same time, the second strain sensing optical cable 13 is placed in the concrete steel pipe 8 by a counterweight hammer, and then high-pressure grouting is performed in the concrete steel pipe 8.

[0102] Specifically, in this embodiment, a certain prestressed elongation should be applied to the first strain sensing optical cable 2 and the second strain sensing optical cable 13 when they are fixed, and the second strain sensing optical cable 13 is fixed under the concrete steel pipe in a fixed-point manner.

[0103] Step 3: Connect the fiber optic distributed demodulator 1: Connect the first strain sensing optical cable 2 and the second strain sensing optical cable 13 to the fiber optic distributed demodulator 1; monitor the overall deformation of the tunnel surrounding rock above the multi-layer complex goaf area through the fiber optic distributed demodulator 1.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A tunnel support structure deformation monitoring system based on distributed optical fiber, characterized in that: include: An optical fiber distributed demodulator (1), a first strain sensing optical cable (2), a second strain sensing optical cable (13), and a support structure (14) arranged in a tunnel surrounding rock structure (5); The support structure (14) comprises a concrete steel pipe (8) extending along the tunnel curved surface and a plurality of flexible grid steel frames (7), wherein the concrete steel pipe (8) is arranged at the center of a frame structure formed by the flexible grid steel frame (7), and the concrete steel pipe (8) and the flexible grid steel frame (7) are fixedly connected via weak rigid connecting ribs (9); One end of the first strain sensing optical cable (2) is connected to a first output end of the optical fiber distributed demodulator (1), and the other end is extended along one of the flexible grid steel frames (7) to an end point, then extended to an end point of another opposite flexible grid steel frame (7), and extended in the opposite direction to another end point, and then connected to a first input end of the optical fiber distributed demodulator (1); One end of the second strain sensing optical cable (13) is connected to the first output end of the optical fiber distributed demodulator (1), and the other end enters the concrete steel pipe (8) through the grouting hole (10), extends along the concrete steel pipe (8) to the bottom thereof, then returns along the concrete steel pipe (8) and is connected to the second input end of the optical fiber distributed demodulator (1); concrete is arranged in the concrete steel pipe (8); The optical fiber distributed demodulator (1) is used to demodulate and obtain the displacement of the tunnel in the horizontal direction and the vertical direction according to the sensing data in the first strain sensing optical cable (2) and the second strain sensing optical cable (13).

2. A tunnel support structure deformation monitoring system based on distributed optical fiber according to claim 1, characterized in that: The specific method of demodulating the optical fiber distributed demodulator (1) to obtain the displacement in the horizontal direction and the vertical direction of the tunnel is: The horizontal displacement of the tunnel is calculated by the strain difference of the relative position of the optical cable sections fixed at the invert and the arch waist section to achieve stable compensation. The vertical displacement of the tunnel is calculated by the strain difference of the outbound and return sections of the optical cable fixed at the arch top section.

3. A distributed optical fiber based tunnel support structure deformation monitoring system according to claim 2, characterized in that: The calculation formula of the horizontal displacement is: s(x)=∫∫(―Δε(x) / D)dxdx+Cx+E; Where s(x) represents the horizontal displacement at position x in the tunnel, Δε(x) represents the measured strain difference at position x, D represents the distance between the outbound and return sections of the corresponding optical cable, and C and E are constants; The vertical displacement calculation formula is: where ε c is the strain of the outbound section of the vault cable, ε D is the strain measured in the return section of the arch optical cable, h is the vertical displacement, i.e., the settlement of the tunnel support structure, and L0 is the distance from the arch top branch protection structure to the nearest fixed point.

4. The distributed optical fiber-based tunnel support structure deformation monitoring system according to claim 1, characterized in that: Before the weak rigidity node of the flexible grid steel frame (7) fails, the optical fiber distributed demodulator (1) demodulates the displacement of the tunnel in the horizontal direction and the vertical direction according to the sensing data in the first strain sensing optical cable (2); After the weak rigidity node of the flexible grid steel frame (7) fails, the optical fiber distributed demodulator (1) demodulates the displacement of the tunnel in the horizontal direction and the vertical direction according to the sensing data in the second strain sensing optical cable (13).

5. The distributed optical fiber-based tunnel support structure deformation monitoring system according to claim 1, characterized in that: The first strain sensing optical cable (2) and the second strain sensing optical cable (13) comprise a fiber core and a protective layer encapsulated outside the fiber core, and the protective layer is polyurethane elastomer or HY material.

6. The distributed optical fiber-based tunnel support structure deformation monitoring system according to claim 1, characterized in that: It also comprises a conductor (4) and a counterweight (6), wherein the conductor (4) is used to connect the two ends of the first strain sensing optical cable (2) and the second strain sensing optical cable (13) to the optical fiber distributed demodulator (1), and the conductor (4) is a metal-based cable-shaped optical cable, and the internal optical fiber is protected by a plurality of metal reinforcements; The counterweight (6) is arranged at the bottom of the concrete steel pipe (8) and is used to perform counterweight stretching on the second strain sensing optical cable (13).

7. The distributed optical fiber-based tunnel support structure deformation monitoring system according to claim 1, characterized in that: The first strain sensing optical cable (2) is fixed to the flexible grid steel frame (7) by a fixing fixture (3), the fixing fixture (3) comprising a fixing ring, a positioning pin and a nut, the fixing ring sleeve is arranged on the outer periphery of the flexible grid steel frame (7) and the first strain sensing optical cable (2), the positioning pin passes through both ends of the fixing ring, and the fixing ring is fixed to the flexible grid steel frame (7) by tightening the nut; The support structure (14) comprises four flexible grid steel frames (7); The weak rigidity connecting ribs (9) comprise a sleeve ring and eight connecting ribs connected to the sleeve ring, wherein four connecting ribs are connected to four flexible grid steel frames (7) above the sleeve ring, and four connecting ribs are connected to four flexible grid steel frames (7) below the sleeve ring.

8. The distributed optical fiber-based tunnel support structure deformation monitoring system according to claim 1, characterized in that: The support structure is formed by splicing a plurality of support units, wherein the flexible grid steel frames (7) between the support units are connected together via connection plates (12), and high-strength rubber pads are laid between the connection plates (12); the concrete steel pipes (8) between the support units are connected via sleeve welding, and the ends of the concrete steel pipes (8) are closed.

9. The construction method of a tunnel support structure deformation monitoring system based on distributed optical fiber according to claim 1, characterized in that: The following steps are involved: Step 1: Installation of support structure: After excavation of the upper step, spray concrete to seal the face; hang the net, erect the new support structure, and apply the system anchor; after excavation of the lower step, erect the new arch frame, and apply the locking anchor pipe; among them, high-strength and tough rubber pads are laid between each unit steel grid and connected by high-strength bolts, and the concrete steel pipes are connected by sleeve welding, and the end of the sleeve is sealed by a closed ring; install the I20 I-shaped steel arch frame, and connect the units with high-strength bolts and connecting plates; Step 2: Laying out the first strain sensing optical cable (2) and the second strain sensing optical cable (13): folding the first strain sensing optical cable (2) and the second strain sensing optical cable (13) into loops respectively, and then using a fixing fixture (3) to fix the first strain sensing optical cable (2) on the surface of the flexible grid steel frame (7) along the set layout position, and fixing it with polyacrylic resin glue at the bottom of the loop, and at the same time, placing the second strain sensing optical cable (13) into the concrete steel pipe (8) by a counterweight hammer, and then performing high-pressure grouting in the concrete steel pipe (8); Step 3: Connecting the optical fiber distributed demodulator (1): connecting the first strain sensing optical cable (2) and the second strain sensing optical cable (13) to the optical fiber distributed demodulator (1); monitoring the overall deformation of the tunnel surrounding rock above the multi-layer complex goaf area through the optical fiber distributed demodulator (1).

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