Monitoring and construction method of surrounding rock-support structure properties of tunnel reconstruction and expansion based on flexible piezoelectric strain sensor

Abstract

The present invention discloses a monitoring and construction method for the properties of surrounding rock and support structures of expanded and renovated tunnels based on flexible piezoelectric strain sensors, and relates to the technical field of intelligent sensing and expanded and renovated tunnels. The present invention comprises: a flexible piezoelectric sensing module, which comprises a flexible piezoelectric strain sensor and a temperature compensation sensor, and is used to monitor the stress and strain of surrounding rock support structures and temperature compensation; an existing tunnel monitoring module, which takes a flexible piezoelectric sensor as its core and is used for distributed strain monitoring of the surface of existing tunnel lining concrete; a expanded and renovated tunnel monitoring module, which includes monitoring of anchor axial force, internal force of steel arch frame, internal force of middle partition wall and stress of secondary lining, and which takes a flexible piezoelectric sensing module as its core. The present invention can realize online, dynamic and real-time monitoring of the properties of surrounding rock and support structures of expanded and renovated tunnels, and provide a powerful guarantee measure for the operation and maintenance safety of expanded and renovated tunnels.

Description

Technical Field

[0001] The present invention belongs to the field of intelligent sensing and tunnel reconstruction and expansion, and specifically relates to a tunnel reconstruction and expansion surrounding rock-support structure performance monitoring and construction method based on a flexible piezoelectric strain sensor. Background Art

[0002] With the continued growth of transportation demand, older tunnels are gradually becoming aging and lacking in capacity, making them unable to adapt to the demands of modern transportation. Tunnel renovation and expansion projects have become essential to improving the performance and safety of transportation infrastructure. The primary goals of tunnel renovation and expansion are to extend their service life, enhance safety and carrying capacity, and increase traffic capacity. However, renovation and expansion projects face the complexity of existing tunnel structures, the technical challenges of connecting the old and new structures, and the impact of construction on the existing structure. These factors increase construction difficulty and safety risks, making real-time monitoring of tunnel surrounding rock and support structures particularly important during renovation and expansion.

[0003] Common monitoring methods currently used in tunnel projects, such as displacement meters, inclinometers, laser scanners, and strain gauges, can provide tunnel deformation and stress data. However, due to the limitations of rigid sensors, they are difficult to adapt to complex surrounding rock deformations. Monitoring accuracy and coverage are limited, and they can only provide local data, lacking comprehensive and continuous monitoring capabilities. During tunnel renovation and expansion, construction disturbances and changes in surrounding rock stress increase the difficulty of real-time monitoring. Traditional sensors are susceptible to interference from external factors such as construction vibration and temperature changes, resulting in unstable data. Furthermore, ensuring real-time and reliable monitoring without disrupting construction is a current challenge.

[0004] Distributed fiber-optic sensing technology, due to its high sensitivity, long-distance continuous monitoring, and anti-interference capabilities, is widely used for health monitoring of large structures such as tunnels. However, practical applications still face several shortcomings and technical challenges. These include the fragility of the fiber core, which is prone to breakage or failure due to construction disturbances; high installation and protection requirements; and the difficulty of on-site operation. Furthermore, the high cost of sensing elements and monitoring equipment limits its large-scale application.

[0005] Piezoelectric sensing technology is widely used in fields such as structural health monitoring, biomedicine, environmental monitoring, and energy harvesting. By converting stress into electrical signals through piezoelectric materials, it can accurately monitor parameters such as strain, vibration, and pressure. PZT piezoelectric ceramics, as a core material, have performed outstandingly in sensing applications. However, their brittleness, poor environmental tolerance, and lack of application flexibility limit their widespread use in complex and extreme environments. In contrast, flexible piezoelectric strain sensors, as an emerging technology, offer advantages such as bendability, lightness, and ease of integration. They can adapt to complex and changing environments and are particularly suitable for wearable devices, medical monitoring, the Internet of Things, and engineering structural health monitoring, showing great application prospects. Therefore, the development of a tunnel reconstruction and expansion surrounding rock-support structure performance monitoring and construction method based on flexible piezoelectric strain sensors has important practical significance and application value. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a method for monitoring the properties of surrounding rock and support structures of tunnel renovation and expansion based on flexible piezoelectric strain sensors, thereby solving the problems raised in the above-mentioned background technology.

[0007] In order to solve the above technical problems, the basic concept of the technical solution adopted by the present invention is:

[0008] A method for monitoring the surrounding rock and support structure of a tunnel under renovation and expansion based on a flexible piezoelectric strain sensor includes:

[0009] Flexible piezoelectric sensing module, which includes a flexible piezoelectric strain sensor and a temperature compensation sensor, is used to monitor the stress and strain of the surrounding rock support structure and perform temperature compensation;

[0010] Existing tunnel monitoring module, which uses flexible piezoelectric sensors as its core and is used for distributed strain monitoring of the concrete surface of existing tunnel linings;

[0011] The monitoring module for the renovation and expansion of tunnels includes monitoring of anchor axial forces, internal forces of steel arch frames, internal forces of middle partition walls and stress of secondary linings. The monitoring module for the renovation and expansion of tunnels is based on a flexible piezoelectric sensor module and is used to monitor the stress and strain of the surrounding rock support structure of the expansion tunnel.

[0012] Optionally, the flexible piezoelectric sensor includes a base layer, a sensitive layer, an electrode layer, and an encapsulation layer. The base layer and encapsulation layer protect the sensor. The sensitive layer is the sensor's core component, capable of converting external physical quantities such as force, temperature, and humidity into electrical signals, which are then transmitted through the electrode layer. The base layer and encapsulation layer are made of PET, the sensitive layer is made of polyvinylidene fluoride piezoelectric material, and the positive and negative electrodes are silver ink electrodes.

[0013] Optionally, temperature compensation sensors are deployed along the depth of the tunnel. These sensors are used to compensate for actual measurements by analyzing the effect of temperature changes on electrical impedance, improving monitoring accuracy. It is important to note that temperature compensation sensors should only be affected by temperature and not stress or strain. Temperature compensation sensors are used to prevent temperature changes within the tunnel caused by construction such as blasting and pouring during tunnel renovation and expansion, which could affect sensor measurements.

[0014] Optionally, existing tunnel monitoring modules and flexible piezoelectric strain sensors are arranged along the longitudinal direction of the tunnel, with the arrangement interval being based on the depth of each excavation for distributed monitoring. At the same time, temperature compensation sensors are arranged for data compensation. The key monitoring locations are generally the arch, side walls and arch waist of the lining structure.

[0015] Optionally, for anchor axial force monitoring in the tunnel monitoring module, distributed flexible piezoelectric strain sensors are fixed along the length of the anchor to monitor axial force changes at different locations. During anchor installation, the sensors must be protected from external forces. Flexible sleeves or other protective measures are used to encase the piezoelectric sensors to prevent damage during anchor grout injection and anchor reinforcement.

[0016] Optionally, the steel arch internal force monitoring and flexible piezoelectric strain sensors in the tunnel renovation and expansion monitoring module are arranged along the surface of the steel arch to monitor the changes in internal forces at different positions of the steel arch, with emphasis on monitoring the stress and strain at the arch crown, arch waist, arch foot, segment connection and other positions.

[0017] Optionally, the internal force monitoring and flexible piezoelectric strain sensors of the middle partition wall in the modified and expanded tunnel monitoring module are arranged longitudinally along the middle partition wall to monitor the stress distribution characteristics of the middle partition wall, and the flexible piezoelectric strain sensors are buried by opening shallow grooves in the middle partition wall.

[0018] Optionally, the secondary lining stress monitoring and distributed flexible piezoelectric strain sensors in the tunnel renovation and expansion monitoring module monitor the internal force changes of the secondary lining. The distributed flexible piezoelectric strain sensors are arranged along the main reinforcement of the steel cage, and the sensors are staggered horizontally and vertically along the steel cage to ensure that the flexible piezoelectric strain sensors can cover the key stress areas. At the same time, the layout path should be as straight as possible to avoid excessive bending. During the concrete pouring process, attention should be paid to the synchronous coordination of construction and monitoring to ensure that the flexible piezoelectric strain sensors always maintain normal function during the construction process.

[0019] Optional, secondary lining stress monitoring within the tunnel renovation and expansion monitoring module is deployed longitudinally along the tunnel, with distributed monitoring intervals based on each excavation depth. After concrete curing is complete and the lining concrete surface is treated, the monitoring layout is identical to the existing tunnel lining surface monitoring. Flexible piezoelectric strain sensors are deployed both within and on the surface of the secondary lining, enhancing the reliability of the monitoring data and ensuring the safety and stability of the structure during the renovation and expansion process.

[0020] A construction method for monitoring the properties of surrounding rock and support structures of a tunnel renovation and expansion based on a flexible piezoelectric strain sensor comprises the following steps:

[0021] Step 1: Flexible piezoelectric strain sensors are deployed along the longitudinal direction of the existing tunnel, with the deployment interval being based on each excavation depth for distributed monitoring. Temperature compensation sensors are also deployed for data compensation.

[0022] Step 2: Remove the primary support and secondary lining of the existing tunnel;

[0023] Step 3: Excavate the upper portion of the left pilot pit of the tunnel, deploy distributed flexible piezoelectric strain sensors on the surface of the anchor rods and steel arches, clarify the transmission lines, ensure the correct placement of the sensors, and construct the initial support and intermediate partition wall in this area.

[0024] Step 4: Use a cutting machine to create shallow grooves on the surface of the middle partition wall, arrange distributed flexible piezoelectric strain sensors along the longitudinal direction of the middle partition wall, and fill them with epoxy resin;

[0025] Step 5: Excavate the lower part of the left pilot pit of the tunnel and deploy distributed flexible piezoelectric strain sensors on the surface of the anchor rods and steel arches. Clarify the transmission lines to ensure the correct placement of the sensors. Construct the initial support and intermediate partition wall. Grooves are cut in the intermediate partition wall surface to embed the flexible piezoelectric strain sensors.

[0026] Step 6: Excavate the upper part of the right pilot pit of the tunnel, deploy distributed flexible piezoelectric strain sensors on the surface of the anchor rods and steel arches, clarify the transmission lines, ensure the correct placement of the sensors, and implement initial support for this area.

[0027] Step 7: Excavate the lower part of the right pilot pit of the tunnel, deploy distributed flexible piezoelectric strain sensors on the surface of the anchor rods and steel arches, clarify the transmission lines, ensure the correct placement of the sensors, and implement initial support for this area.

[0028] Step 8: Excavate the tunnel inverted arch, construct the tunnel inverted arch and inverted arch filling, remove the middle partition wall and the flexible piezoelectric strain sensor thereon, and construct the tunnel waterproof layer;

[0029] Step 9: Construct the secondary lining of the tunnel and lay distributed flexible piezoelectric strain sensors on the main reinforcement of the steel cage. Use nylon rolled strips for preliminary positioning and then use adhesive and epoxy resin to fix them. The sensor layout path should be as straight as possible to avoid excessive bending. Then pour the concrete. Attention should be paid to the synchronization and coordination of construction and monitoring to ensure the normal function of the flexible piezoelectric strain sensors.

[0030] Step 10: After the concrete is cured, use a grinder to grind the concrete surface, place the distributed flexible piezoelectric strain sensor on the concrete surface, fix it with an adhesive, and finally protect the flexible piezoelectric strain sensor with epoxy resin.

[0031] After adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art. Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described below at the same time:

[0032] 1. Flexible piezoelectric strain sensors have the advantages of being bendable, lightweight, and easy to integrate, and can adapt to the complex and changeable monitoring of tunnel renovation and expansion projects.

[0033] 2. Compared with distributed optical fiber, distributed flexible piezoelectric strain sensor has a larger strain measurement range, cheaper acquisition instrument, better durability, and more convenient on-site construction.

[0034] 3. The construction method for monitoring the properties of surrounding rock and support structure of expanded and renovated tunnels based on flexible piezoelectric strain sensors fills the gaps in the monitoring process of expanded and renovated tunnel construction, can significantly improve the safety of expanded and renovated tunnel operation and maintenance, and has great application prospects in expanded and renovated tunnel monitoring.

[0035] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The drawings described below are only some embodiments. A person skilled in the art can derive other drawings based on these drawings without inventive effort. In the drawings:

[0037] Figure 1 Schematic diagram of the construction method for monitoring the properties of surrounding rock and support structure of a tunnel renovation and expansion based on flexible piezoelectric strain sensors;

[0038] Figure 2 Schematic diagram of the flexible piezoelectric sensor structure;

[0039] Figure 3 Schematic diagram of the layout of distributed flexible piezoelectric sensors for existing tunnel monitoring modules;

[0040] Figure 4 This is a schematic diagram of the sensor layout for monitoring the existing tunnel lining;

[0041] Figure 5 This is a schematic diagram of the flexible sensor layout for anchor monitoring;

[0042] Figure 6 Schematic diagram of flexible sensor layout for steel arch monitoring;

[0043] Figure 7 This is a schematic diagram of the flexible sensor layout for monitoring the middle partition wall;

[0044] Figure 8 Schematic diagram of flexible sensor layout for monitoring secondary lining steel mesh;

[0045] Figure 9 This is the construction flow chart for tunnel renovation and expansion monitoring.

[0046] In the accompanying drawings, the components represented by the reference numerals are as follows:

[0047] 1- existing tunnel lining, 2- existing tunnel lining monitoring module, 3- surrounding rock, 4- anchor rod, 5- anchor rod monitoring module, 6- steel arch, 7- steel arch monitoring module, 8- middle partition wall, 9- middle partition wall monitoring module, 10- primary support, 11- secondary lining, 12- secondary lining monitoring module, 13- solar panel, 14- data acquisition instrument, 15- data processing platform, 16- multi-core signal transmission wire, 17- PET packaging material, 18- silver ink electrode, 19- polyvinylidene fluoride piezoelectric material, 20 -PET substrate material, 21-distributed flexible piezoelectric strain sensor, 22-distributed flexible piezoelectric temperature compensation sensor, 23-clip, 24-carbon fiber cloth, 25-flexible piezoelectric strain sensor, 26-insulating sleeve, 27-welding wire, 28-waterproof heat shrink sleeve, 29-V-notch, 30-nut, 31-pad, 32-connecting plate, 33-single-point flexible piezoelectric strain sensor, 34-U-groove, 35-concrete mortar, 36-lining steel mesh, 37-cross-shaped fixing clip.

[0048] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but rather to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0049] The present invention will now be described in further detail with reference to the accompanying drawings.

[0050] See also Figure 1-9 As shown, in this embodiment, a method for monitoring the surrounding rock and support structure of a tunnel under renovation and expansion based on a flexible piezoelectric strain sensor is provided, including:

[0051] Flexible piezoelectric sensing module, which includes a flexible piezoelectric strain sensor and a temperature compensation sensor, is used to monitor the stress and strain of the surrounding rock support structure and perform temperature compensation;

[0052] Existing tunnel monitoring module, which uses flexible piezoelectric sensors as its core and is used for distributed strain monitoring of the concrete surface of existing tunnel linings;

[0053] The monitoring module for the renovation and expansion of tunnels includes monitoring of anchor axial forces, internal forces of steel arch frames, internal forces of middle partition walls and stress of secondary linings. The monitoring module for the renovation and expansion of tunnels is based on a flexible piezoelectric sensor module and is used to monitor the stress and strain of the surrounding rock support structure of the expansion tunnel.

[0054] The flexible piezoelectric sensor of this embodiment includes a base layer, a sensitive layer, an electrode layer, and an encapsulation layer. The base layer and encapsulation layer protect the sensor. The sensitive layer is the sensor's core component, capable of converting external physical quantities such as force, temperature, and humidity into electrical signals, which are then transmitted through the electrode layer. The base layer and encapsulation layer are made of PET, the sensitive layer is made of polyvinylidene fluoride piezoelectric material, and the positive and negative electrodes are silver ink electrodes.

[0055] In this embodiment, temperature compensation sensors are deployed along the depth of the tunnel. They utilize the influence of temperature changes on electrical impedance to compensate for actual measurements and improve monitoring accuracy. It is important to note that temperature compensation sensors should be affected only by temperature, not stress or strain. Construction projects such as tunnel expansion and renovation, such as blasting and pouring, can cause temperature fluctuations within the tunnel, which in turn can affect sensor measurements. To obtain accurate structural strain information, temperature compensation must be addressed in flexible piezoelectric strain sensor measurements.

[0056] In this embodiment, the existing tunnel monitoring modules and flexible piezoelectric strain sensors are arranged along the longitudinal direction of the tunnel, with the arrangement interval being based on the depth of each excavation for distributed monitoring. At the same time, temperature compensation sensors are arranged for data compensation. The key monitoring positions are generally the arch, side walls and arch waist of the lining structure.

[0057] In this embodiment, the anchor axial force monitoring module for tunnel expansion and renovation uses distributed flexible piezoelectric strain sensors fixed along the length of the anchor to monitor axial force changes at different locations. During anchor installation, care should be taken to protect the sensors from damage by external forces. Flexible sleeves or other protective measures should be used to encase the piezoelectric sensors to prevent damage during anchor grout injection and anchor reinforcement.

[0058] The steel arch internal force monitoring and flexible piezoelectric strain sensors in the tunnel renovation and expansion monitoring module of this embodiment are arranged along the surface of the steel arch to monitor the changes in internal forces at different positions of the steel arch, with emphasis on monitoring the stress and strain at positions such as the arch crown, arch waist, arch foot, and segment connections.

[0059] The internal force monitoring and flexible piezoelectric strain sensors of the middle partition wall in the tunnel renovation and expansion monitoring module of this embodiment are arranged longitudinally along the middle partition wall to monitor the stress distribution characteristics of the middle partition wall. The flexible piezoelectric strain sensors are buried by opening shallow grooves in the middle partition wall.

[0060] The secondary lining stress monitoring and distributed flexible piezoelectric strain sensor in the tunnel renovation and expansion monitoring module of this embodiment monitor the internal force changes of the secondary lining. The distributed flexible piezoelectric strain sensor is arranged along the main reinforcement of the steel cage, and the sensors are staggered horizontally and vertically along the steel cage to ensure that the flexible piezoelectric strain sensor can cover the key stress areas. At the same time, the layout path should be as straight as possible to avoid excessive bending. During the concrete pouring process, attention should be paid to the synchronous coordination of construction and monitoring to ensure that the flexible piezoelectric strain sensor always maintains normal function during the construction process.

[0061] The secondary lining stress monitoring system in this embodiment's tunnel renovation and expansion monitoring module is deployed longitudinally along the tunnel, with distributed monitoring intervals based on each excavation depth. After concrete curing is completed and the lining concrete surface is treated, the monitoring arrangement is identical to that used for existing tunnel lining surface monitoring. Flexible piezoelectric strain sensors are deployed both within and on the surface of the secondary lining, enhancing the reliability of the monitoring data and ensuring the safety and stability of the structure during renovation and expansion.

[0062] A construction method for monitoring the properties of surrounding rock and support structures of a tunnel renovation and expansion based on a flexible piezoelectric strain sensor comprises the following steps:

[0063] Step 1: Flexible piezoelectric strain sensors are deployed along the longitudinal direction of the existing tunnel (generally on the vault, side walls, and haunches of the lining structure), with the deployment interval being based on each excavation depth for distributed monitoring. Temperature compensation sensors are also deployed for data compensation.

[0064] Step 2: Remove the primary support and secondary lining of the existing tunnel;

[0065] Step 3: Excavate the upper portion of the left pilot pit of the tunnel, deploy distributed flexible piezoelectric strain sensors on the surface of the anchor rods and steel arches, clarify the transmission lines, ensure the correct placement of the sensors, and construct the initial support and intermediate partition wall in this area.

[0066] Step 4: Use a cutting machine to create shallow grooves on the surface of the middle partition wall, arrange distributed flexible piezoelectric strain sensors along the longitudinal direction of the middle partition wall, and fill them with epoxy resin;

[0067] Step 5: Excavate the lower part of the left pilot pit of the tunnel and deploy distributed flexible piezoelectric strain sensors on the surface of the anchor rods and steel arches. Clarify the transmission lines to ensure the correct placement of the sensors. Construct the initial support and intermediate partition wall. Grooves are cut in the intermediate partition wall surface to embed the flexible piezoelectric strain sensors.

[0068] Step 6: Excavate the upper part of the right pilot pit of the tunnel, deploy distributed flexible piezoelectric strain sensors on the surface of the anchor rods and steel arches, clarify the transmission lines, ensure the correct placement of the sensors, and implement initial support for this area.

[0069] Step 7: Excavate the lower part of the right pilot pit of the tunnel, deploy distributed flexible piezoelectric strain sensors on the surface of the anchor rods and steel arches, clarify the transmission lines, ensure the correct placement of the sensors, and implement initial support for this area.

[0070] Step 8: Excavate the tunnel inverted arch, construct the tunnel inverted arch and inverted arch filling, remove the middle partition wall and the flexible piezoelectric strain sensor thereon, and construct the tunnel waterproof layer;

[0071] Step 9: Construct the secondary lining of the tunnel and lay distributed flexible piezoelectric strain sensors on the main reinforcement of the steel cage. Use nylon rolled strips for preliminary positioning and then use adhesive and epoxy resin to fix them. The sensor layout path should be as straight as possible to avoid excessive bending. Then pour the concrete. Attention should be paid to the synchronization and coordination of construction and monitoring to ensure the normal function of the flexible piezoelectric strain sensors.

[0072] Step 10: After the concrete is cured, use a grinder to grind the concrete surface, place the distributed flexible piezoelectric strain sensor on the concrete surface, fix it with an adhesive, and finally protect the flexible piezoelectric strain sensor with epoxy resin.

[0073] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings.

[0074] Figure 1 This diagram illustrates a construction method for monitoring the surrounding rock and support structure properties of a tunnel renovation and expansion project based on flexible piezoelectric strain sensors. First, distributed flexible piezoelectric strain sensors 21 and distributed flexible piezoelectric temperature compensation sensors 22 are deployed on the surface of the existing tunnel lining 1 to form the existing tunnel lining monitoring module 2. During the renovation and expansion of the tunnel, distributed flexible piezoelectric strain sensors 21 are deployed on the surfaces of anchor bolts 4 and pressed into the surrounding rock 3 to form the anchor bolt monitoring module 5. Distributed flexible piezoelectric strain sensors 21 are deployed as required on the steel arch 6, intermediate partition wall 8, and secondary lining 11 to form the steel arch monitoring module 7, intermediate partition wall monitoring module 9, and secondary lining monitoring module 12. All sensors are connected to a data acquisition device 14 via multi-core signal transmission cables 16. The data acquisition device is powered by solar panels 13 and wirelessly transmits monitoring data to a data processing platform 15 in real time.

[0075] Figure 2 This is a schematic diagram of the flexible piezoelectric sensor structure. From bottom to top, the flexible piezoelectric sensor consists of a PET substrate 20, a PVDF piezoelectric material 19, silver ink electrodes 18, and a PET packaging material 17. The core component is the PVDF piezoelectric material 19, a polymer material that can be fabricated into any shape or size. The electrodes are riveted or bonded, ensuring surface electrode protection. The PET substrate 20 and PET packaging material 17 protect the PVDF piezoelectric material 19 from mechanical damage. The piezoelectric signal is transmitted via a transmission wire, and subsequent data analysis and processing yield physical information such as stress and strain.

[0076] Figure 3 and Figure 4 The following is a schematic diagram of the layout of the distributed flexible piezoelectric sensors for the existing tunnel monitoring module and the existing tunnel lining monitoring sensor layout. The distributed flexible piezoelectric strain sensors 21 are laid out along the longitudinal direction of the tunnel, and the layout interval is based on the depth of each excavation. The monitoring positions include the arch, side walls and waist of the lining structure. At the same time, a distributed flexible piezoelectric temperature compensation sensor 22 is arranged at the waist for data compensation. After all the sensors are laid out, they are led out from the exit of the renovation and expansion construction tunnel through a multi-core signal transmission wire 16, so that monitoring can continue when the existing tunnel lining is removed on the side of the entrance. The multi-core signal transmission wire 16 is fixed to the entrance lining by a buckle 23. The specific flexible piezoelectric sensor layout plan is as follows. First, use a grinder to grind the surface of the existing tunnel lining 1 to ensure that the surface is clean, flat, and free of debris. Then draw lines to locate and mark the sensor laying position. Use 502 glue to preliminarily fix the flexible piezoelectric strain sensor 25 to the lining surface. Then connect the welding wire 27 and encapsulate it with an insulating sleeve 26. The welding wire 27 is led to the multi-core signal transmission wire 16 and encapsulated with a waterproof heat shrink sleeve 28 to ensure that the sensor is protected from interference from the external environment. Use the buckle 23 to fix the multi-core signal transmission wire 16 to the lining concrete surface. Finally, the surface is covered with a layer of carbon fiber cloth 24 and coated with epoxy resin to ensure that the sensor is not subject to secondary interference from external construction.

[0077] Figure 5This is a schematic diagram of the flexible sensor layout for anchor monitoring. Distributed flexible piezoelectric strain sensors 21 are arranged longitudinally along the anchor 4. Before sensor installation, the surface of the anchor 4 should be cleaned with industrial alcohol. The distributed flexible piezoelectric strain sensor 21 is initially secured to the anchor 4 using a rolled strip, then secured with 502 glue. Finally, epoxy resin is applied throughout to ensure proper coupling between the sensor and the anchor and prevent damage to the anchor during construction. To minimize the effect of the sensor on the mounting bolt 30 and backing plate 31, a V-shaped notch 29 is cut into the head of the anchor 4 using a cutting machine. The sensor at the interface is placed within the notch, and the remaining gap is filled with epoxy resin. The anchor 4 is slowly inserted into the drilled hole to the desired depth, taking care to avoid damaging the sensor. A backing plate 31 is placed between the head of the anchor 4 and the structural surface. Finally, the nut 30 is tightened until it makes firm contact with the backing plate 31. Care should be taken to protect the sensor leads during this process.

[0078] Figure 6 This diagram shows the flexible sensing arrangement for monitoring steel arches. Distributed flexible piezoelectric strain sensors 21 are laid along the main beams of the steel arches 6. They are initially secured to the steel arches 6 using tape and then secured with 502 glue to ensure their stability and unaffected by the construction process. The steel arches are then installed in their intended locations. Monitoring should be focused on the connection plates 32 of each steel arch 6. To this end, single-point flexible piezoelectric strain sensors 33 are installed at these connection plates 32. Welded wires 27 are connected to the multi-core signal transmission wires 16 of the distributed flexible piezoelectric strain sensors 21. The multi-core signal transmission wires 16 should have corresponding connection channels reserved and well-marked.

[0079] Figure 7 This diagram shows the flexible sensor layout for monitoring the middle partition wall. Distributed flexible piezoelectric strain sensors 21 are laid longitudinally along the middle partition wall 8. A 2mm-deep U-shaped groove 34 is pre-cut in the surface of the middle partition wall 8 using a concrete cutter. Debris is removed from the groove, ensuring it is smooth and tidy. The distributed flexible piezoelectric strain sensors 21 are secured in the groove using 502 glue, and the wiring is straightened. Finally, the U-shaped groove 34 is filled with concrete mortar 35.

[0080] Figure 8 Schematic diagram of the flexible sensor layout for monitoring the secondary lining reinforcement mesh. Distributed flexible piezoelectric strain sensors 21 are arranged horizontally and vertically in a staggered pattern across the lining reinforcement mesh 36. The steel surfaces are cleaned with industrial alcohol and then placed along the mesh at predetermined locations. 502 glue is then used to secure the sensors, followed by a full coating of epoxy resin. Cross-shaped fixing clamps 37 are used to reinforce the sensors when they are staggered. To prevent damage to the piezoelectric sensors during construction, PVC pipes are installed at the transmission line outlets. Mechanical damage to the piezoelectric sensors should be minimized during concrete pouring and vibration.

[0081] Figure 9 This is a flow chart for monitoring the construction of a tunnel renovation and expansion project. First, flexible piezoelectric sensors are fabricated according to construction requirements. Distributed flexible piezoelectric strain sensors are deployed along the longitudinal direction of the existing tunnel, with each excavation depth used as a unit for distributed monitoring. Temperature sensors and compensation sensors are also deployed for data compensation. The existing tunnel unit sensors are removed, along with the single excavation support and lining structures. Initial support and lining are installed, and distributed flexible piezoelectric sensors are deployed, including anchor rods, steel arches, intermediate partition walls, and secondary linings. Monitoring data is transmitted via multi-channel transmission lines to an electrical impedance acquisition instrument. Sensor monitoring data is collected in real time, processed and analyzed by a data processing platform, providing real-time monitoring feedback on construction and maintenance status.

[0082] The present invention utilizes the sensitivity of flexible piezoelectric sensors to stress and strain, and collects the electrical impedance value of distributed flexible piezoelectric sensors through an electrical impedance acquisition instrument. When subjected to stress and strain, the electrical impedance value changes. The change in the electrical impedance value is analyzed and a corresponding relationship is established with the stress and strain, and the corresponding construction damage location is analyzed and determined.

[0083] Specifically, a construction method for monitoring the properties of surrounding rock and support structure of a modified and expanded tunnel based on flexible piezoelectric strain sensors is provided. First, flexible piezoelectric sensors are manufactured according to construction requirements. Distributed flexible piezoelectric strain sensors are arranged along the longitudinal direction of the existing tunnel. The arrangement interval is based on the depth of each excavation for distributed monitoring. At the same time, temperature sensing compensation sensors are arranged for data compensation. The existing tunnel unit sensors are removed, the single excavation support and lining structure are removed, initial support and lining are implemented, and distributed flexible piezoelectric sensors are arranged, including anchor rods, steel arch frames, middle partition walls, and secondary linings. The monitoring data is transmitted to the electrical impedance acquisition instrument via a multi-channel transmission line. The sensor monitoring data is collected in real time, and the data is processed and analyzed by the data processing platform to monitor and feedback the construction and operation and maintenance status in real time.

[0084] Specifically, after the flexible piezoelectric sensing module, the existing tunnel monitoring module and the expanded tunnel monitoring module are laid, they are connected to the electrical impedance acquisition instrument via wires to collect data in real time.

[0085] The present invention is not limited to the above-described embodiments. Any structural changes made under the guidance of the present invention, which have the same or similar technical solutions as the present invention, should be understood to fall within the scope of protection of the present invention. The technologies, shapes, and structures not described in detail in the present invention are all well-known technologies.

Claims

1. A method for monitoring the surrounding rock and support structure of a tunnel under renovation and expansion based on a flexible piezoelectric strain sensor, characterized in that: include: Flexible piezoelectric sensing module, which includes a flexible piezoelectric strain sensor and a temperature compensation sensor, is used to monitor the stress and strain of the surrounding rock support structure and perform temperature compensation; Existing tunnel monitoring module, which uses flexible piezoelectric strain sensors as its core and is used for distributed strain monitoring of the concrete surface of existing tunnel linings; Tunnel expansion and renovation monitoring module. This includes monitoring of anchor axial forces, steel arch internal forces, intermediate partition wall internal forces, and secondary lining stress. The module, with a flexible piezoelectric sensor module as its core, is used to monitor stress and strain in the surrounding rock support structure of the expanded tunnel. Among them, the flexible piezoelectric strain sensor includes a base layer, a sensitive layer, an electrode layer and a packaging layer. The base layer and the packaging layer are used to protect the sensor. The sensitive layer is the core component of the sensor, which can convert external physical quantities such as force, temperature, humidity, etc. into electrical signals and transmit the electrical signals through the electrode layer. Anchor bolt axial force monitoring in the tunnel renovation and expansion monitoring module uses distributed flexible piezoelectric strain sensors fixed to the anchor bolt surface along its length to monitor axial force changes at different anchor bolt locations. The steel arch internal force monitoring and flexible piezoelectric strain sensors in the tunnel renovation and expansion monitoring module are arranged along the surface of the steel arch to monitor the internal force changes at different locations of the steel arch, with a focus on monitoring the stress and strain at the arch crown, arch waist, arch foot, and segment connections. The internal force monitoring and flexible piezoelectric strain sensors for the middle partition wall in the tunnel expansion and renovation monitoring module are arranged longitudinally along the middle partition wall to monitor the stress distribution characteristics of the middle partition wall. The flexible piezoelectric strain sensors are buried in shallow grooves in the middle partition wall. The secondary lining stress monitoring and distributed flexible piezoelectric strain sensors in the tunnel renovation and expansion monitoring module monitor the internal force changes of the secondary lining. The distributed flexible piezoelectric strain sensors are arranged along the main reinforcement of the steel cage. The sensors are staggered horizontally and vertically along the steel cage to ensure that the flexible piezoelectric strain sensors can cover the key stress areas. At the same time, the layout path should be as straight as possible to avoid excessive bending.

2. The method for monitoring the surrounding rock and support structure of a tunnel under renovation and expansion based on a flexible piezoelectric strain sensor according to claim 1 is characterized in that: Temperature compensation sensors are arranged along the depth direction of the tunnel to compensate for the actual measurement value and improve the monitoring accuracy by observing the influence of temperature changes on the electrical impedance value.

3. The method for monitoring the surrounding rock and support structure of a tunnel under renovation and expansion based on a flexible piezoelectric strain sensor according to claim 1 is characterized in that: Existing tunnel monitoring modules and flexible piezoelectric strain sensors are arranged along the longitudinal direction of the tunnel. The arrangement interval is based on the excavation depth of each time for distributed monitoring. At the same time, temperature compensation sensors are arranged for data compensation. The key monitoring locations are generally the arch, side walls and arch waist of the lining structure.

4. The method for monitoring the surrounding rock and support structure of a tunnel under renovation and expansion based on a flexible piezoelectric strain sensor according to claim 1 is characterized in that: The secondary lining stress monitoring system in the tunnel renovation and expansion monitoring module is arranged along the longitudinal direction of the tunnel, with the intervals of each excavation depth as the unit for distributed monitoring. Flexible piezoelectric strain sensors are arranged inside and on the surface of the secondary lining, which enhances the reliability of the monitoring data and ensures the safety and stability of the structure during the renovation and expansion process.

5. A construction method for monitoring the properties of surrounding rock and support structure of a tunnel renovation and expansion based on a flexible piezoelectric strain sensor, characterized in that: The steps include: Step 1: Flexible piezoelectric strain sensors are deployed along the longitudinal direction of the existing tunnel, with the deployment interval being based on each excavation depth for distributed monitoring. Temperature compensation sensors are also deployed for data compensation. Step 2: Remove the primary support and secondary lining of the existing tunnel; Step 3: Excavate the upper portion of the left pilot pit of the tunnel, deploy distributed flexible piezoelectric strain sensors on the surface of the anchor rods and steel arches, clarify the transmission lines, ensure the correct placement of the sensors, and construct the initial support and intermediate partition wall in this area. Step 4: Use a cutting machine to create shallow grooves on the surface of the middle partition wall, arrange distributed flexible piezoelectric strain sensors along the longitudinal direction of the middle partition wall, and fill them with epoxy resin; Step 5: Excavate the lower part of the left pilot pit of the tunnel and deploy distributed flexible piezoelectric strain sensors on the surface of the anchor rods and steel arches. Clarify the transmission lines to ensure the correct placement of the sensors. Construct the initial support and intermediate partition wall. Grooves are cut in the intermediate partition wall surface to embed the flexible piezoelectric strain sensors. Step 6: Excavate the upper part of the right pilot pit of the tunnel, deploy distributed flexible piezoelectric strain sensors on the surface of the anchor rods and steel arches, clarify the transmission lines, ensure the correct placement of the sensors, and implement initial support for this area. Step 7: Excavate the lower part of the right pilot pit of the tunnel, deploy distributed flexible piezoelectric strain sensors on the surface of the anchor rods and steel arches, clarify the transmission lines, ensure the correct placement of the sensors, and implement initial support for this area. Step 8: Excavate the tunnel inverted arch, construct the tunnel inverted arch and inverted arch filling, remove the middle partition wall and the flexible piezoelectric strain sensor thereon, and construct the tunnel waterproof layer; Step 9: Construct the secondary lining of the tunnel and lay distributed flexible piezoelectric strain sensors on the main reinforcement of the steel cage. Use nylon rolled strips for preliminary positioning and then use adhesive and epoxy resin to fix them. The sensor layout path should be as straight as possible to avoid excessive bending. Then pour the concrete. Attention should be paid to the synchronization and coordination of construction and monitoring to ensure the normal function of the flexible piezoelectric strain sensors. Step 10: After the concrete is cured, use a grinder to grind the concrete surface, place the distributed flexible piezoelectric strain sensor on the concrete surface, fix it with an adhesive, and finally protect the flexible piezoelectric strain sensor with epoxy resin.

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