Self-sensing smart anchor

Abstract

This invention discloses a self-sensing intelligent anchor bolt, comprising a head, a sensing area, and a tail end. The sensing area has straight grooves and spiral grooves, and distributed fiber optic sensors are arranged in the straight grooves and spiral grooves to sense stress and strain information of the surrounding rock in the monitoring area. Based on the stress-strain and strain-deformation relationship expressions of the anchor bolt structure, it senses the deformation information of the tunnel surrounding rock support. The advantage of this invention is that it can not only sense the axial tensile deformation of the anchor bolt, but also obtain local torsional and bending deformation information to a certain extent, thus providing a more comprehensive understanding of the working status of the tunnel support structure.

Description

Technical Field

[0001] This invention relates to the field of tunnel engineering technology, and in particular to a self-sensing intelligent anchor bolt. Background Technology

[0002] In recent years, tunnel construction technology in China has developed rapidly, with many technologies reaching international leading levels. As the deep underground space of Chinese cities continues to expand, the requirements for tunnel construction technology are also gradually increasing. Anchor bolt structures play a crucial role in tunnel surrounding rock support, greatly contributing to the stability of the tunnel support structure. Simultaneously, the failure mode of the anchor bolts directly reflects the failure mode of the surrounding rock, and the stress and deformation state of the anchor bolts indirectly reflects the service condition of the tunnel surrounding rock support structure. Therefore, effectively understanding the working state of the anchor bolt structure can reflect the actual working conditions of the tunnel surrounding rock, thereby ensuring the safety of tunnel engineering.

[0003] Existing anchor bolt structures cannot provide feedback on their own working status, and existing monitoring methods mostly acquire deformation information through point or linear sensors, only obtaining the status information of a certain point or local area of ​​the anchor bolt. Information on the anchor bolt's own torsion and bending is difficult to obtain, making it impossible to effectively perceive the working status of the anchor bolt within the surrounding rock. Furthermore, it cannot effectively assess the service status of tunnel support and the deformation state of the tunnel's surrounding rock. Therefore, it is impossible to make timely adjustments and responses based on the actual situation to ensure tunnel safety and prevent accidents. This invention combines the anchor bolt with a distributed fiber optic sensor, introducing a spiral measuring line. Based on the OFDR technology principle, it proposes a novel self-sensing intelligent anchor bolt that not only acquires deformation information along the anchor bolt's axial direction but also captures torsional and bending deformation information, achieving effective perception and comprehensive understanding of the anchor bolt's own state. This is the area that this application focuses on improving. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a self-sensing intelligent anchor bolt that can acquire the working status of the anchor bolt itself in real time and more comprehensively perceive the working status of the tunnel support structure.

[0005] To address the above technical problems, this invention provides a self-sensing intelligent anchor bolt, comprising a head, a sensing area, and a tail end. The sensing area is provided with a straight groove and a spiral groove, and distributed fiber optic sensors are arranged in the straight groove and spiral groove to sense and monitor stress and strain information of the surrounding rock in the area. Based on the stress-strain and strain-deformation relationship expressions of the anchor bolt structure, the deformation information of the tunnel surrounding rock support is sensed.

[0006] The distributed optical fiber sensors in the straight grooves sense the axial and bending deformation information of the surrounding rock along the anchor bolts, while the distributed optical fiber sensors in the spiral grooves sense the torsional and bending deformation information, thereby obtaining the deformation pattern of the tunnel surrounding rock.

[0007] Based on the theory of mechanics of materials, the stress-strain and strain-deformation relationships of the anchor structure of the present invention under axial tension and compression, bending loads, and torsional loads are given as follows:

[0008] (1) When subjected to an axial force along the length of the anchor rod, the stress-strain of the fiber optic sensor in the straight groove is expressed as:

[0009]

[0010]

[0011] Where: σ is stress, ε is strain, E is the elastic modulus of the material, and N is axial force;

[0012] The stress and strain along the direction of the helical fiber sensor are expressed as:

[0013]

[0014] Where: σ θ and ε θ These represent the stress and strain along the direction of the helical sensor, respectively; N is the axial force; d is the diameter of the anchor rod cross-section; v is the material Poisson's ratio; and θ is the angle between the helical fiber and the anchor rod cross-section.

[0015] The axial deformation Δl of the anchor bolt and the strain ε of the helical sensor θ The relationship is represented as:

[0016]

[0017] (2) When subjected to torsional load and undergoing torsional deformation, the linear sensor cannot capture deformation information; only the helical sensor acquires deformation information caused by torsion.

[0018] ① When the rotation direction of the spiral sensor is the same as the rotation direction of the torsional force, the stress-strain relationship is expressed as:

[0019]

[0020] Where: T is torque;

[0021] The arc θ0 caused by the torsion of the anchor bolt is expressed as:

[0022]

[0023] Where: G is the shear modulus;

[0024] ② When the rotation direction of the helical sensor is opposite to the direction of the applied torsional force, the stress-strain relationship is expressed as:

[0025]

[0026] The arc θ0 caused by the torsional deformation of the anchor bolt is expressed as:

[0027]

[0028] (3) Subjected to bending load M z When deformation occurs, the deformation of the linear sensor under force is expressed as follows:

[0029]

[0030]

[0031] Where: y is the distance from the sensor to the center axis of the anchor bolt;

[0032] The stress-strain of the helical sensor is expressed as follows:

[0033]

[0034] The change in anchor bolt rotation angle Δθ(x) and deflection Δy(x) are expressed as follows:

[0035]

[0036] Where: ε + ε represents the strain of the fiber in the tension region. - Let represent the strain of the fiber in the pressure zone, and D represent the distance between the linear fiber optic sensors.

[0037] The straight grooves are arranged along the circumference of the anchor rod.

[0038] The tail end is provided with a through hole, through which the distributed optical fiber sensor leads out a connecting line to connect with the optical fiber demodulator.

[0039] The connecting line is directly replaced by a distributed optical fiber sensor, and the length can be flexibly selected according to the actual situation, with the reserved length sufficient for effective connection with the optical fiber demodulator.

[0040] The widths of the straight and spiral grooves are set according to the distributed optical fiber sensor.

[0041] The depths of the straight and spiral grooves are selected based on the depth difference of the distributed optical fiber sensors, so that each distributed optical fiber sensor can independently sense mechanical parameters.

[0042] The sensing length of the spiral groove along the anchor rod axis is the same as that of the straight groove, which facilitates data comparison and theoretical analysis.

[0043] The pitch of the spiral groove is customized according to the site requirements.

[0044] The distributed optical fiber sensor is a customized dedicated optical fiber sensor to ensure the accuracy of the sensed data.

[0045] The beneficial effects of this invention are as follows:

[0046] (1) It has a self-sensing function to obtain the working status of the anchor bolt itself in real time;

[0047] (2) It can not only sense the axial tensile deformation of the anchor rod, but also obtain information on local torsional and bending deformation to a certain extent, so as to more comprehensively sense the working status of the tunnel support structure. Attached Figure Description

[0048] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0049] Figure 1 This is a structural schematic diagram of a specific embodiment of the present invention;

[0050] Explanation of the labels in the diagram

[0051] 1—Self-sensing intelligent anchor bolt; 2—Straight groove;

[0052] 3—Helical groove; 4—Through hole;

[0053] 5—Distributed fiber optic sensor; 6—Connecting cable;

[0054] 7—Fiber Optic Demodulator. Detailed Implementation

[0055] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0056] Based on the theory of mechanics of materials, the stress-strain and strain-deformation relationships of the anchor structure of the present invention under axial tension and compression, bending loads, and torsional loads are given as follows:

[0057] (1) When subjected to an axial force along the length of the anchor rod, the stress-strain of the fiber optic sensor in the straight groove is expressed as:

[0058]

[0059] Where: σ is stress, ε is strain, E is the elastic modulus of the material, and N is axial force;

[0060] The stress and strain along the direction of the helical fiber sensor are expressed as:

[0061]

[0062] Where: σ θ and εθ These represent the stress and strain along the direction of the helical sensor, respectively; N is the axial force; d is the diameter of the anchor rod cross-section; v is the material Poisson's ratio; and θ is the angle between the helical fiber and the anchor rod cross-section.

[0063] The axial deformation Δl of the anchor bolt and the strain ε of the helical sensor θ The relationship is represented as:

[0064]

[0065] (2) When subjected to torsional load and undergoing torsional deformation, the linear sensor cannot capture deformation information; only the helical sensor acquires deformation information caused by torsion.

[0066] ① When the rotation direction of the spiral sensor is the same as the rotation direction of the torsional force, the stress-strain relationship is expressed as:

[0067]

[0068] Where: T is torque;

[0069] The arc θ0 caused by the torsion of the anchor bolt is expressed as:

[0070]

[0071] Where: G is the shear modulus;

[0072] ② When the rotation direction of the helical sensor is opposite to the direction of the applied torsional force, the stress-strain relationship is expressed as:

[0073]

[0074] The arc θ0 caused by the torsional deformation of the anchor bolt is expressed as:

[0075]

[0076] (3) Subjected to bending load M z When deformation occurs, the deformation of the linear sensor under force is expressed as follows:

[0077]

[0078] Where: y is the distance from the sensor to the center axis of the anchor bolt;

[0079] The stress-strain of the helical sensor is expressed as follows:

[0080]

[0081] The change in anchor bolt rotation angle Δθ(x) and deflection Δy(x) are expressed as follows:

[0082]

[0083] Where: ε + ε represents the strain of the fiber in the tension region. - Let represent the strain of the fiber in the pressure zone, and D represent the distance between the linear fiber optic sensors.

[0084] like Figure 1 As shown, the present invention provides a self-sensing intelligent anchor bolt, including three regions A, B, and C, which are the head, sensing region, and tail end, respectively. The sensing region is provided with a straight groove 2 and a spiral groove 3. Distributed optical fiber sensors 5 are arranged in the straight groove 2 and the spiral groove 3 to sense and monitor the stress and strain information of the surrounding rock in the region. Based on the stress-strain and strain-deformation relationship expressions of the anchor bolt structure, the deformation information of the tunnel surrounding rock support is sensed.

[0085] The distributed optical fiber sensor 5 in the straight groove 2 senses the axial and bending deformation information of the surrounding rock along the anchor bolt, and the distributed optical fiber sensor 5 in the spiral groove 3 senses the torsional and bending deformation information, thereby obtaining the deformation law of the tunnel surrounding rock.

[0086] The anchor rod 1 is 3m long, and the sensing area is 0.5m to 2.5m long. Four straight grooves 2 are arranged around the anchor rod at a gradient of 90° along the circumference of the rod body in the sensing area and at the tail end. The width × depth is 5mm × 10mm. A spiral groove 3 is prefabricated in the sensing area. The width × depth is 5mm × 5mm and the pitch is 40mm. The straight groove at the tail end is directly used as a through hole 4.

[0087] A dedicated distributed optical fiber sensor 5 with a length of 15m and coated with polyimide (PI) is selected. It is encapsulated in a straight groove 2 and a spiral groove 3 using epoxy resin. Finally, the remaining distributed optical fiber sensor is led out through the straight groove at the tail end as a connecting line 6.

[0088] Use a fiber optic fusion splicer to splice the patch cord and the distributed fiber optic sensor 5, which will facilitate subsequent connection with the fiber optic demodulator 7. Protect the connecting cable 6 and the patch cord to prevent damage during construction.

[0089] The working principle of this invention is as follows: The self-sensing intelligent anchor rod 1 is installed into the support structure as the construction progresses. After the on-site construction is completed, the jumper is connected to the fiber optic demodulator 7, and reference files and test parameters are set and saved. As needed, the stress and strain parameters of the anchor rod are acquired over a long period of time to achieve effective sensing of the working state of the anchor rod and effective assessment of the deformation state of the surrounding rock support structure.

[0090] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A self-sensing intelligent anchor bolt, characterized in that: It includes a head, a sensing area and a tail end. The sensing area is equipped with straight grooves and spiral grooves. Distributed fiber optic sensors are arranged in the straight grooves and spiral grooves to sense and monitor the stress and strain information of the surrounding rock in the area. Based on the stress-strain and strain-deformation relationship expressions of the anchor structure, it senses the deformation information of the tunnel surrounding rock support. The distributed optical fiber sensors in the straight groove sense the axial and bending deformation information of the surrounding rock along the anchor bolt, and the distributed optical fiber sensors in the spiral groove sense the torsional and bending deformation information to obtain the deformation law of the tunnel surrounding rock. The stress-strain and strain-deformation relationships of the anchor structure are expressed as follows: (1) When subjected to an axial force along the length of the anchor bolt, the stress-strain of the distributed optical fiber sensor in the straight groove is expressed as: ； in: For stress, Where E is the strain, E is the elastic modulus of the material, and N is the axial force; The stress and strain along the direction of the helical fiber sensor are expressed as: ； in: and Let N be the stress and strain along the direction of the spiral sensor, d be the diameter of the anchor rod cross-section, and v be the Poisson's ratio of the material. The angle between the spiral optical fiber and the cross-section of the anchor rod; Axial deformation of anchor bolt Strain along the direction of the helical sensor The relationship is represented as: ； (2) When subjected to torsional load and undergoing torsional deformation, the spiral sensor acquires information on the deformation caused by torsion: ① When the rotation direction of the spiral sensor is the same as the rotation direction of the torsional force, the stress-strain relationship is expressed as: ； ； Where: T is torque; Curvature caused by anchor bolt torsion Represented as: ； Where: G is the shear modulus; ② When the rotation direction of the helical sensor is opposite to the direction of the applied torsional force, the stress-strain relationship is expressed as: ； The curvature of the anchor bolt due to torsional deformation Represented as: ； (3) Subjected to bending load When deformation occurs, the deformation of the linear sensor under force is expressed as follows: ； Where: y is the distance from the sensor to the center axis of the anchor bolt; The stress-strain of the helical sensor is expressed as follows: ； ； Anchor bolt rotation change and deflection They are represented as follows: ； ； in: For the strain of the fiber in the tension region, Let represent the strain of the fiber in the pressure zone, and D represent the distance between the linear fiber optic sensors.

2. The self-sensing intelligent anchor bolt according to claim 1, characterized in that: The straight grooves are arranged along the circumference of the anchor rod.

3. The self-sensing intelligent anchor bolt according to claim 1, characterized in that: The tail end is provided with a through hole, through which the distributed optical fiber sensor leads out a connecting line to connect with the optical fiber demodulator.

4. The self-sensing intelligent anchor bolt according to claim 3, characterized in that: The connecting line, as part of the distributed optical fiber sensor, has a reserved length to allow for effective connection with the optical fiber demodulator.

5. The self-sensing intelligent anchor bolt according to claim 1, characterized in that: The widths of the straight and spiral grooves are set according to the distributed optical fiber sensor.

6. The self-sensing intelligent anchor bolt according to claim 1, characterized in that: The depths of the straight and spiral grooves are selected based on the depth difference of the distributed optical fiber sensors, so that each distributed optical fiber sensor can independently sense mechanical parameters.

7. The self-sensing intelligent anchor bolt according to claim 6, characterized in that: The sensing length of the spiral groove along the anchor rod axis is the same as that of the straight groove, which facilitates data comparison and theoretical analysis.

8. The self-sensing intelligent anchor bolt according to claim 7, characterized in that: The pitch of the spiral groove is customized according to the site requirements.

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