System and method for monitoring full-length stress state of pre-stressed anchor cable

Abstract

The invention belongs to the technical field of rock-soil mechanics measurement, and particularly discloses a pre-stressed anchor cable full-length stress state monitoring system and method. Comprising an anchoring section, a free section and an anchor sealing section which are sequentially connected, one end of a pre-stressed anchor cable is embedded in the anchoring section, and the other end of the pre-stressed anchor cable freely penetrates through the free section and then is fixedly connected with the anchoring section; the anchoring section stress monitoring subsystem is used for measuring the stress value of the pre-stressed anchor cable at the anchoring section; one end of the free section stress monitoring subsystem is fixedly communicated with the anchoring section stress monitoring subsystem, and the other end of the free section stress monitoring subsystem sequentially penetrates through the free section and the anchor sealing section to be communicated with the control subsystem and is used for transmitting resistance value information to the control subsystem in the stress process; and the control subsystem is used for calculating the anti-pulling safety coefficient of the anchoring section and the prestress loss of the free section so as to monitor the full-length stress state of the anchor cable. The device is high in testing precision, and stress state monitoring of all parts of the whole length of the anchor cable can be achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of rock and soil mechanics measurement, and more specifically, relates to a system and method for monitoring the full-length stress state of a prestressed anchor cable. Background Art

[0002] Prestressed anchor cables are widely used in slope reinforcement projects because they can improve the stability of rock and soil by applying force to the reinforced rock mass, and have the advantages of small disturbance to the rock and soil mass, fast construction, safety and economy. However, many engineering cases have pointed out that in soft rock slopes, due to factors such as rock rheology, anchor cable relaxation, and construction technology, the prestress of the anchor structure is lost, and the long-term service performance is seriously degraded, thus losing the reinforcement capacity, causing the slope to become unstable, seriously affecting the progress and safety of the project construction, and causing significant economic losses.

[0003] At present, the common practice for monitoring the loss of prestress in the anchoring system of soft rock engineering is to measure the overall stress in the entire anchor cable at the anchor head, which cannot reflect the stress distribution of different sections of the anchor cable. At present, some researchers have embedded optical fibers into anchor cables to try to establish a new system for anchor cable prestressing. However, in practical applications, due to the low tensile performance of optical fibers, which does not match the tensile strength of anchor cables, it is not applicable to ordinary large-tonnage anchor cables (commonly used over 40 tons). At the same time, the deformation of optical fibers and the deformation of anchor cables show a strong nonlinear relationship, resulting in large errors in the measured results. Other factors that limit the further promotion and application of optical fibers in engineering include high cost, complex construction procedures, and difficulties that are not suitable for actual operation by on-site engineering personnel. Therefore, it is urgent to develop a method and equipment for long-term monitoring of the full-length stress of prestressed anchor cables, which has the advantages of low cost, high test accuracy, and simple test process, and can be promoted to engineering practice. Summary of the invention

[0004] In view of the above defects or improvement needs of the prior art, the present invention provides a system and method for monitoring the stress state of a prestressed anchor cable over its entire length. In combination with the characteristics of the prestressed anchor cable itself and its working force characteristics, a method and device for monitoring the stress of the prestressed anchor cable over its entire length is designed accordingly. The structures and specific settings of its key components such as the anchoring section stress monitoring subsystem, the anchoring section stress monitoring subsystem, and the free section stress monitoring subsystem are studied and designed accordingly. Accordingly, the stress state of the prestressed anchor cable can be comprehensively monitored, including the stress distribution of the anchoring section and the free section, and real-time monitoring and prestress loss assessment can be achieved. The method and method have the advantages of low cost, high test accuracy, and simple test process, and can be promoted to engineering practice.

[0005] To achieve the above-mentioned object, according to one aspect of the present invention, a prestressed anchor cable full-length stress state monitoring system is proposed, comprising a device end and a control subsystem, wherein the device end comprises an anchoring section stress monitoring subsystem, an anchoring section stress monitoring subsystem, and a free section stress monitoring subsystem;

[0006] The anchoring section stress monitoring subsystem comprises an anchoring section, a free section and a sealed anchoring section which are connected in sequence, one end of the prestressed anchor cable is buried in the anchoring section, and the other end freely passes through the free section and is fixedly connected to the anchoring section;

[0007] The anchoring section stress monitoring subsystem is arranged in the anchoring section and is used to measure the stress value of the prestressed anchor cable in the anchoring section;

[0008] One end of the free section stress monitoring subsystem is fixedly connected to the anchor section stress monitoring subsystem, and the other end is connected to the control subsystem after passing through the free section and the anchor section in sequence. The free section stress monitoring subsystem is subjected to the same stress as the prestressed anchor cable in the free section, and the resistance value information can be transmitted to the control subsystem during the stress process;

[0009] The control subsystem is used to calculate the pull-out safety factor of the anchor section and the prestress loss of the free section according to the stress value and the resistance value information, and thereby realize the stress state monitoring of the entire length of the anchor cable.

[0010] As further preferred, the free section stress monitoring subsystem includes a pipeline integration module, which integrates an anchor free end stress measurement channel for accommodating an anchor free end stress measurement device, and the anchor free end stress measurement device is made of conductive metal material.

[0011] As a further preferred embodiment, the relationship between the strain and resistance change generated by the anchor free end stress measuring device under tension and compression conditions includes:

[0012]

[0013] Where R is the resistance value, ΔR is the change in resistance value, K is the strain rate, and ε is the strain.

[0014] As a further preferred embodiment, waterproof communication terminals are provided at both ends of the pipeline integrated module;

[0015] The pipeline integrated module also includes a protective layer, an inner steel wire layer and an outer steel wire layer which are arranged in sequence from the inside to the outside. An anchor free end stress measurement channel for placing an anchor free end stress measurement device, a power supply channel for placing a power line, and a communication channel for placing a communication line are arranged in the protective layer along the axial direction.

[0016] As a further preferred embodiment, the anchoring section stress monitoring subsystem includes a bottom shoe, a stress testing section, an electronic collection section and a tensile joint which are fixedly connected in sequence. The stress testing section is bonded to the concrete mortar of the anchoring section to provide sufficient anchoring force with the anchor cable, and the stress testing section is provided with a strain gauge for measuring the stress state of the anchoring section. The electronic collection section is connected to the free section stress monitoring subsystem through the tensile joint, and is used to control the measurement and data collection of the strain gauge, and amplify the collected signal and transmit it to the control subsystem.

[0017] As a further preferred embodiment, the anchoring section includes fixing concrete and a fixing plate and a fixing clamp arranged in the fixing concrete, the fixing plate is used to fix the connection between the prestressed anchor cable and the anchoring section stress monitoring subsystem, one end of the fixing clamp is connected to the fixing plate, and the other end is sleeved on the prestressed anchor cable.

[0018] As a further preferred embodiment, the sealing anchor section includes a concrete sealing anchor and a large sealing plate, a circular pad and an anchor head clamp which are connected in sequence and arranged in the concrete sealing anchor. The concrete sealing anchor is also provided with a measuring port for accommodating the pipeline integrated module to pass through, and a protective cover is also provided at the measuring port.

[0019] As further preferred, the control subsystem includes a power supply and data conversion module, a power supply module and a control module. The power supply and data conversion module is respectively connected to the pipeline integration module and the control module, and is used to receive data, convert the data and transmit it to the control module. The power supply module is connected to the power supply and data conversion module for power supply.

[0020] The control module is used to calculate the pull-out safety factor of the anchoring section and the prestress loss of the free section according to the measurement data, and to calculate and evaluate the pull-out safety factor of the anchoring section.

[0021] According to another aspect of the present invention, there is also provided a method for monitoring the stress state of a prestressed anchor cable over its entire length, comprising the following steps:

[0022] Step 1: Determine the strain rate coefficient K of the free section stress monitoring subsystem at the free section through an indoor uniaxial tensile test;

[0023] Step 2: forming an anchor hole according to design requirements, and installing a prestressed anchor full-length stress state monitoring system according to any embodiment or a combination of multiple embodiments described above in the anchor hole according to design and maintenance requirements;

[0024] Step three, load the prestressed anchor cable and the equipment end, measure the strain change of the prestressed anchor cable at the free section and the anchor section during the loading process, and continue to track and monitor after the loading process is completed until the strain change reaches stability, and read the initial value of the free section resistance measurement after tensioning and locking and the initial value of the axial strain of the concrete in the anchor section;

[0025] Step 4: disconnect the connection between the free section stress monitoring subsystem and the control subsystem, build a measuring anchor head base, protect the anchor head, read the resistance measurement value of the free section and the concrete axial strain measurement value of the anchor section during service, use the resistance change of the free section to evaluate the prestress loss rate, and use the axial strain change value of the anchor section to evaluate the pull-out safety factor.

[0026] As further preferred, in step 3, the calculation of the prestress loss of the free-segment anchor cable according to the measured initial value includes:

[0027] (311) Amplify the voltage signal of the stress measuring device at the free end of the anchor cable:

[0028]

[0029] In the formula, U is voltage, u is output voltage;

[0030] (312) Calculate the relationship between the strain and resistance change of the stress measuring device at the free end of the anchor cable under tension and compression conditions:

[0031]

[0032] Where R is the resistance value, ΔR is the change in resistance value, K is the strain rate coefficient, and ε is the strain;

[0033] (313) The prestress loss of anchor cable is calculated based on the relationship between strain and resistance change:

[0034]

[0035] Where Δσ is the prestress loss of the anchor cable, and E is the elastic modulus;

[0036] Preferably, the calculation model of the prestress loss rate of the anchor cable anchoring section includes:

[0037]

[0038] Where Re is the prestress loss rate of the anchor cable anchorage section; ε v,intial is the initial axial strain of the concrete in the anchorage section after tensioning; v,after To monitor the axial strain of concrete in the anchor section;

[0039] Preferably, the calculation model for evaluating the pull-out safety factor of the anchoring section includes:

[0040]

[0041] Where, Fs is the pull-out safety factor of the anchor section; E concrete is the elastic modulus of concrete; π is the pi; D is the borehole diameter; C is the cohesion between the surrounding rock and concrete; L is the length of the anchor section; S is the cross-sectional area of ​​the anchor section, which is calculated by substituting the diameter into the circular area formula.

[0042] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0043] 1. The present invention can monitor the stress state of each part of the entire length of the prestressed anchor cable, so as to evaluate the loss of prestress of the anchor cable. At the same time, the device can provide the same anchoring force as ordinary prestressed anchor cables and has a temperature measurement function.

[0044] 2. The present invention does not increase the workload of on-site construction personnel, adopts an independent construction process, and does not need to be processed on the existing anchor cable. The monitoring equipment is light and easy to carry, and can be performed by one person during the monitoring process. The testing process is simple and easy, and only requires connecting to the monitoring system to achieve one-key collection and real-time processing functions.

[0045] 3. The equipment cost of the present invention is low, and the test accuracy is high, and it has broad market application prospects.

[0046] 4. The present invention improves monitoring accuracy and reliability. The system can comprehensively monitor the stress state of the prestressed anchor cable, including the stress distribution of the anchor cable and the free section, by setting up stress monitoring subsystems in the anchor section and the free section respectively. The anchor cable free end stress measuring device made of strain gauges and conductive metal materials can accurately measure and convert stress data into resistance values, thereby improving the accuracy of the data. The system design takes environmental adaptability into consideration, such as the use of waterproof communication terminals and special materials, to ensure stable operation even in harsh environments and enhance the reliability of the system.

[0047] 5. The present invention realizes real-time monitoring and prestress loss assessment. It can receive and process stress data from the anchor section and the free section in real time, and realize real-time monitoring of the stress state of the entire length of the prestressed anchor cable. The system can calculate the prestress loss of the anchor section and the free section based on the measured stress value and resistance value information, providing important reference data for engineering safety assessment. Through intelligent data processing, such as machine learning and artificial intelligence algorithms, the system can predict potential structural problems and issue early warnings in a timely manner, improving the safety management level of prestressed anchor cables. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a structural schematic diagram of a full-length stress state monitoring system for a prestressed anchor cable involved in an embodiment of the present invention;

[0049] Figure 2 is a structural schematic diagram of an anchoring section stress monitoring subsystem involved in an embodiment of the present invention;

[0050] Figure 3 is a schematic structural diagram of a tensile joint involved in an embodiment of the present invention;

[0051] Figure 4 is a schematic structural diagram of a free segment stress monitoring subsystem involved in an embodiment of the present invention;

[0052] Figure 5 is a schematic diagram of the structure of a pipeline integration module involved in an embodiment of the present invention;

[0053] Figure 6 is a schematic structural diagram of a fixed disk involved in an embodiment of the present invention;

[0054] Figure 7 It is a flow chart of a method for monitoring the full-length stress state of a prestressed anchor cable involved in an embodiment of the present invention.

[0055] In all the drawings, the same reference numerals represent the same technical features, specifically: 100-control subsystem, 200-free section stress monitoring subsystem, 300-anchor section stress monitoring subsystem, 400-anchoring equipment subsystem, 101-power supply and data conversion module, 102-power module, 103-control module, 201-waterproof communication terminal, 202-pipeline integration module, 2021-outer steel wire layer, 2022-inner steel wire layer, 2023-protective layer, 2024-anchor free end stress measurement channel, 2 025-power supply channel, 2026-backup channel, 2027-communication channel, 301-tensile joint, 302-bottom shoe, 303-stress test section, 304-electronic collection section, 401-fixed concrete, 402-fixed plate, 403-fixed clamp, 404-prestressed anchor cable, 405-cavity section, 406-anchor head clamp, 407-concrete sealing anchor, 408-large sealing plate, 409-round pad, 410-measuring port, 411-protective cover, 4021-anchor cable fixing hole, 4022-equipment fixing hole. DETAILED DESCRIPTION

[0056] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0057] like Figure 1 As shown, a prestressed anchor cable full-length stress state monitoring system provided by an embodiment of the present invention includes an equipment end and a control subsystem 100, wherein the equipment end includes an anchoring section stress monitoring subsystem 400, an anchoring section stress monitoring subsystem 300, and a free section stress monitoring subsystem 200; the anchoring section stress monitoring subsystem 400 includes an anchoring section, a free section, and a sealed anchor section connected in sequence, one end of a prestressed anchor cable 404 is buried in the anchoring section, and the other end freely passes through the free section and is fixedly connected to the anchoring section; the anchoring section stress monitoring subsystem 300 is arranged in the anchoring section, and is used to measure the prestressed anchor cable 404. The stress value of the prestressed anchor cable 404 in the anchoring section; one end of the free section stress monitoring subsystem 200 is fixedly connected to the anchoring section stress monitoring subsystem 300, and the other end is connected to the control subsystem 100 after passing through the free section and the sealing anchor section in sequence. The free section stress monitoring subsystem 200 is subjected to the same stress as the prestressed anchor cable 404 in the free section, so as to transmit the resistance value information to the control subsystem 100 during the stress process; the control subsystem 100 is used to calculate the pull-out safety factor of the anchoring section and the prestress loss of the free section according to the stress value and the resistance value information, so as to realize the stress state monitoring of the entire length of the anchor cable.

[0058] Based on any of the above embodiments or a combination of multiple embodiments, the free section stress monitoring subsystem 200 includes a pipeline integration module 202, which is integrated with an anchor free end stress measurement channel 2024 for placing an anchor free end stress measurement device, and the anchor free end stress measurement device is made of conductive metal material.

[0059] In the above embodiment, the method for monitoring the stress state of the free end of the anchor cable is as follows:

[0060] The resistance of a metal is inversely proportional to its cross-sectional area and directly proportional to its length. After a metal wire is stretched, its resistance increases because its cross-sectional area decreases and its length increases. Similarly, after a metal wire is compressed, its resistance decreases. There is a certain coefficient relationship between the strain caused by the stretching and compression of a metal and the change in resistance, and its expression is:

[0061]

[0062] In the formula: R is the resistance value, ΔR is the resistance change value, K is the strain rate, and ε is the strain. Generally, since the resistance change is very small, it is necessary to collect the voltage signal after processing through the amplifier circuit, and its expression is:

[0063]

[0064] Where: U is voltage, u is output voltage.

[0065] Generally speaking, it is difficult to directly know the stress of an object or material, so the stress can be obtained by measuring the strain generated by the stress. Stress and strain are proportional in the elastic domain, which conforms to Hu Ke's law. The stress can be obtained by the strain, so the expression of the anchor cable prestress loss is

[0066]

[0067] Where Δσ is the prestress loss of the anchor cable and E is the elastic modulus.

[0068] Based on any of the above embodiments or a combination of multiple embodiments, such as Figure 4 and Figure 5 As shown, waterproof communication terminals 201 are provided at both ends of the pipeline integrated module 202; the pipeline integrated module 202 also includes a protective layer 2023, an inner steel wire layer 2022 and an outer steel wire layer 2021 arranged in sequence from the inside to the outside, and the protective layer 2023 is provided with an anchor free end stress measurement channel 2024 for placing an anchor free end stress measurement device, a power supply channel 2025 for placing an energized line, and a communication channel 2027 for placing a communication line along the axial direction. Correspondingly, in order to more conveniently replace or replace the pipeline, a spare channel 2026 is also provided in the protective layer 2023 along the axial direction. In the above embodiment, the protective layer 2023 is made of flexible material, and the inner steel wire layer 2022 and the outer steel wire layer 2021 are evenly arranged along the circumference of the outer wall of the protective layer.

[0069] Based on any of the above embodiments or a combination of multiple embodiments, such as Figure 2 and Figure 3 As shown, the anchoring section stress monitoring subsystem 300 includes a bottom shoe 302, a stress testing section 303, an electronic acquisition section 304 and a tensile joint 301 which are fixedly connected in sequence. The stress testing section 303 is bonded to the concrete mortar of the anchoring section to provide sufficient anchoring force with the anchor cable, and the stress testing section 303 is provided with a strain gauge for measuring the stress state of the anchoring section. The electronic acquisition section 304 is connected to the free section stress monitoring subsystem 200 through the tensile joint 301, and is used to control the measurement and data acquisition of the strain gauge, and amplify the collected signal and transmit it to the control subsystem 100.

[0070] Among them, the stress state monitoring method of the anchor cable anchorage end is as follows:

[0071] After placing the measuring device at the bottom of the anchor hole, injecting concrete and waiting for the concrete age to arrive, the measuring device will deform together with the concrete. Therefore, the expression of the prestress loss rate of the anchor cable anchoring section is:

[0072]

[0073] Where Re is the prestress loss rate of the anchor cable anchorage section; ε v,initial is the initial axial strain of the concrete body after tensioning; v,after is the initial axial strain of the concrete body during monitoring.

[0074] The expression for evaluating the pull-out safety factor of the anchor section is:

[0075]

[0076] Where, Fs is the pull-out safety factor of the anchor section; E concrete is the elastic modulus of concrete; π is the pi; D is the diameter of the borehole; C is the cohesion between the surrounding rock and concrete; L is the length of the anchoring section; S is the cross-sectional area of ​​the anchoring section.

[0077] Based on any of the above embodiments or a combination of multiple embodiments, the anchoring section includes a fixed concrete 401 and a fixed plate 402 and a fixed clamp 403 arranged in the fixed concrete 401, the fixed plate 402 is used to fix the prestressed anchor cable 404 and the anchoring section stress monitoring subsystem 300, one end of the fixed clamp 403 is connected to the fixed plate 402, and the other end is sleeved on the prestressed anchor cable 404. The sealing anchor section includes a concrete sealing anchor 407 and a large sealing plate 408, a circular pad 409 and an anchor head clamp 406 which are connected in sequence and arranged in the concrete sealing anchor 407. The concrete sealing anchor 407 is also provided with a measuring port 410 for accommodating the pipeline integrated module 202 to pass through, and a protective cover 411 is also provided at the measuring port 410. Specifically, as Figure 6 As shown, the fixing plate 402 is provided with a plurality of through holes, anchor fixing holes 4021 for the anchor cables to pass through, and equipment fixing holes 4022 for the anchoring section stress monitoring subsystem 300 to pass through.

[0078] Based on any of the above embodiments or a combination of multiple embodiments, the control subsystem 100 includes a power supply and data conversion module 101, a power supply module 102 and a control module 103. The power supply and data conversion module 101 is connected to the pipeline integration module 202 and the control module 103 respectively, and is used to receive data and transmit the data to the control module 103 after converting the data. The power supply module 102 is connected to the power supply and data conversion module 101 for power supply; the control module 103 is used to calculate the pull-out safety factor of the anchor section and the prestress loss of the free section according to the measurement data, and calculate and evaluate the pull-out safety factor of the anchor section.

[0079] like Figure 7 According to another aspect of the present invention, a method for monitoring the stress state of a prestressed anchor cable over its entire length is provided, comprising the following steps:

[0080] Step 1: Determine the strain rate coefficient K of the free section stress monitoring subsystem at the free section through an indoor uniaxial tensile test;

[0081] Step 2: forming an anchor hole according to design requirements, and installing a prestressed anchor full-length stress state monitoring system involved in any of the above embodiments in the anchor hole according to design and maintenance requirements;

[0082] Step 3: Load the prestressed anchor cable and the equipment end, measure the strain change of the prestressed anchor cable at the free section and the anchor section during the loading process, and continue to track and monitor after the loading process ends until the strain change reaches stability, and read the initial measurement value, and calculate the prestress loss of the free section anchor cable and the prestress loss of the fixed section anchor cable based on the initial measurement value. In this step, the calculation of the prestress loss of the free section anchor cable based on the initial measurement value includes:

[0083] (311) Amplify the voltage signal of the stress measuring device at the free end of the anchor cable:

[0084]

[0085] In the formula, U is voltage, u is output voltage;

[0086] (312) Calculate the relationship between the strain and resistance change of the stress measuring device at the free end of the anchor cable under tension and compression conditions:

[0087]

[0088] Where R is the resistance value, ΔR is the change in resistance value, K is the strain rate coefficient, and ε is the strain;

[0089] (313) The prestress loss of anchor cable is calculated based on the relationship between strain and resistance change:

[0090]

[0091] Where Δσ is the prestress loss of the anchor cable and E is the elastic modulus.

[0092] Step 4: disconnect the connection between the free section stress monitoring subsystem 200 and the control subsystem 100, tension the prestressed anchor cable 404, reassemble the joint, build a measuring anchor head base, protect the anchor head, and evaluate the safety factor and loss rate based on the measured values ​​of the anchoring section stress monitoring subsystem 300 during service, wherein the calculation model of the prestress loss rate of the anchor cable anchoring section includes:

[0093]

[0094] Where Re is the prestress loss rate of the anchor cable anchorage section; ε v,intialis the initial axial strain of the concrete in the anchorage section after tensioning; v,after To monitor the axial strain of concrete in the anchor section.

[0095] The calculation model for evaluating the pull-out safety factor of the anchor section includes:

[0096]

[0097] Where, Fs is the pull-out safety factor of the anchor section; E concrete is the elastic modulus of concrete; π is the pi; D is the diameter of the borehole; C is the cohesion between the surrounding rock and concrete; L is the length of the anchoring section; S is the cross-sectional area of ​​the anchoring section.

[0098] In one embodiment of the present invention, the prestressed anchor cable full-length stress state monitoring device mainly realizes the following functions:

[0099] (1) Realize stress monitoring and prestress loss assessment at different positions of prestressed anchor cables.

[0100] (2) Realize the temperature measurement of the anchor section

[0101] According to the above functional requirements, the full-length stress state monitoring equipment of prestressed anchor cable mainly includes four subsystems: prestressed anchor cable free section stress state monitoring subsystem, prestressed anchor cable anchoring section stress state monitoring subsystem, prestressed anchor cable stress state monitoring portable collection subsystem and other supporting subsystems. The prestressed anchor cable anchoring section stress state monitoring subsystem is located at the bottom of the system, fixed to other anchor cables through the anchor cable / equipment fixing plate and the anchor cable / equipment fixing clamp, and connected to the prestressed anchor cable free section stress state monitoring subsystem through the tensile joint at the top. After passing through the ground, the prestressed anchor cable free section stress state monitoring subsystem is fixed to the anchor head through the anchor head clamp, and after the prestress is applied, the anchor is sealed with concrete. It is connected to the prestressed anchor cable stress state monitoring portable collection subsystem through the measuring cable.

[0102] Among them, according to the principle of stress state monitoring of the free section of prestressed anchor cable, the corresponding prestressed anchor cable free section stress state monitoring subsystem needs to have the following functions:

[0103] (1) The subsystem itself has the same stress-bearing performance as the original anchor cable, that is, the tensile strength is similar to that of the anchor cable. For the prestressed anchor cable free section stress state monitoring subsystem used for 4 cables, the anchoring force provided is at least 12 tons. For the prestressed anchor cable free section stress state monitoring subsystem used for 6 cables, the anchoring force provided is at least 15 tons.

[0104] (2) The subsystem needs to be able to measure the change in resistance, obtain the change in anchor cable length through equation (1-3), and then convert the stress loss state of the anchor cable based on the elastic modulus of the anchor cable. Therefore, a path needs to be established between the anchor head and the anchoring section, and the change in resistance must be captured by a high-precision resistance tester.

[0105] (3) The subsystem also needs to supply power to the anchor section monitoring subsystem located below, and transmit signals to the prestress monitoring system at the anchor head.

[0106] (4) The subsystem needs to be corrosion-resistant and fatigue-resistant.

[0107] To achieve the above four functions, the entire anchor cable free section stress monitoring subsystem consists of two parts: transmission and measurement components and waterproof communication connectors at both ends. The transmission and measurement components are composed of outer and inner steel strands as bearing layers and protective layers, which are used to bear the role of prestress and protect internal electrical components. The inner side is the measurement transmission circuit and protective layer. The protective layer wraps the measurement transmission circuit, which plays a role of corrosion and moisture resistance, and can shield the signal interference between the measurement transmission circuits. The measurement transmission circuit is the core of the entire subsystem. There are 7 channels, two of which are the stress state measurement channels of the free end of the anchor cable, which are used to measure the stress loss of the entire anchor cable. When the stress monitoring subsystem of the free section of the anchor cable is connected to the stress state monitoring subsystem of the anchoring section of the prestressed anchor cable below through the tensile joint, the two channels will be connected. After the portable acquisition subsystem is powered on, a loop is formed, and the resistance change of the two channels is measured to realize the monitoring of prestress loss. Two channels are power supply channels, which are used to power the stress state monitoring subsystem of the anchoring section of the prestressed anchor cable below. The two channels are communication channels, used to transmit the signal of the stress state monitoring subsystem of the anchoring section of the prestressed anchor cable. The middle channel is a spare channel, which forms a passage with the remaining channels when one channel is damaged due to various reasons.

[0108] The waterproof communication connectors at both ends connect the prestressed anchor free section stress state monitoring subsystem with the tensile connector and the prestressed anchor stress state monitoring portable acquisition subsystem respectively, and have waterproof capabilities.

[0109] Furthermore, according to the stress state monitoring principle of the anchoring section of the prestressed anchor cable, the corresponding stress state monitoring subsystem of the anchoring section of the prestressed anchor cable needs to have the following functions:

[0110] (1) The subsystem can measure the stress state of the anchor section of the anchor cable to evaluate the service performance of the prestressed anchor cable.

[0111] (2) The subsystem can bond well with the concrete mortar and provide sufficient anchoring force for the anchor cable.

[0112] (3) The subsystem can work normally after the concrete solidifies and has corrosion resistance and waterproof capabilities.

[0113] (4) Since the subsystem is a one-time deep-buried part, the selected materials should be as low-cost and easy to install as possible.

[0114] The stress state monitoring subsystem of the anchoring section of the prestressed anchor cable consists of three parts: the bottom shoe, the stress test section and the electronic acquisition section. Among them, the bottom shoe is located at the bottom of the equipment, and its purpose is to prevent the stress test section from being too close to the bottom of the hole, resulting in large stress change measurement errors. The stress test section is located in the middle of the subsystem, and its function is to measure the stress state of the anchoring section through the strain gauge in the stress test section, and calculate the change of the prestress of the anchoring section through formula (4-5). The electronic acquisition section is located at the top of the subsystem, and is connected to the stress state monitoring subsystem of the free section of the prestressed anchor cable through a tensile joint. Its function is to adjust the voltage to a low voltage of 12V for strain gauge measurement and data acquisition, and transmit the amplified signal through the anchor cable free section stress monitoring subsystem to the prestressed anchor cable stress state monitoring portable acquisition subsystem on the surface for real-time data processing and analysis.

[0115] Furthermore, the portable acquisition subsystem for monitoring the stress state of prestressed anchor cables should have the following functions:

[0116] (1) The subsystem can be carried to the site by engineering personnel according to monitoring needs, and through simple wiring, it can achieve rapid measurement of anchor cable prestress loss.

[0117] (2) The subsystem can work independently and does not require on-site matching power supply.

[0118] The portable acquisition subsystem for monitoring the stress state of prestressed anchor cable consists of a monitoring tablet, a portable power module, a power supply and data conversion module, a measuring cable, a power connection line and a data connection line. Among them, the power supply and data conversion module is connected to the prestressed anchor cable free section stress state monitoring subsystem through a measuring cable, and is connected to the portable power module through a power connection line, which is used to power the prestressed anchor cable full-length stress state monitoring equipment; it is connected to the monitoring tablet through a data connection line, which is used to convert data into the monitoring tablet for data processing. The monitoring tablet is used to perform real-time analysis of the monitoring data of the prestressed anchor cable anchor section stress state monitoring subsystem and the prestressed anchor cable free section stress state monitoring subsystem. The portable power module adopts a lightweight design to provide power for the entire device.

[0119] Furthermore, other supporting subsystems mainly include anchor cable / equipment fixing devices and measuring anchor head systems, wherein the main function of the anchor cable / equipment fixing device is to fix the anchor cable and the equipment on several discs, which, on the one hand, facilitates the smooth lowering of the entire anchor cable into the anchor cable hole, and on the other hand, prevents the equipment from shaking and displacing during the lowering process, and is not parallel to the hole axis after reaching the bottom of the hole, resulting in large subsequent measurement errors. The anchor cable fixing plate determines the number of holes according to the anchor cable used. When n-cable anchor cables are used, the number of anchor cable fixing holes is n-1, and the equipment fixing hole is located below the anchor cable fixing hole. After the equipment and anchor cable pass through the corresponding holes, the anchor cable / equipment fixing fixture is used to fix the equipment and anchor cable on the fixing plate. The anchor cable / equipment fixing fixture consists of a fixing buckle and a fixing cap, and its diameter matches the diameter of the equipment and anchor cable. When in use, the fixing buckle and the fixing cap are respectively inserted into the equipment and anchor cable at both ends of the chuck, and then locked to achieve the fixing purpose.

[0120] Furthermore, the main functions of the anchor head base system include (1) protecting the anchor head from damage and corrosion; and (2) facilitating the collection of monitoring data. The anchor head base mainly includes a large pad, a circular pad, an anchor head clamp, a concrete anchor seal structure, a measuring port and a protective cover. The large pad is located at the bottom and is used to increase the force-bearing area to prevent the lower structure and rock and soil from being damaged during the anchor cable loading process; the circular pad is used to raise the anchor head clamp and increase the length exposed to the surface; the anchor head clamp is used to fix the anchor cable and the prestressed anchor cable free section stress state monitoring subsystem through the wedge-shaped anchor cable clamp for loading and prestress maintenance. The concrete anchor seal structure is a structure cast after the prestressed anchor cable is tensioned, which is used to protect the anchor head. A measuring port and a protective cover are left on the concrete anchor seal structure. The measuring port is used to provide a connection channel between the measuring cable and the prestressed anchor cable free section stress state monitoring subsystem. The protective cover is used to protect the interface inside the measuring port from rain erosion and prevent short circuit.

[0121] According to another aspect of the present invention, a method for calibrating and monitoring the stress state of a prestressed anchor cable over its entire length is provided, comprising:

[0122] (1) Indoor calibration process of monitoring equipment: The strain rate coefficient K in the stress state monitoring subsystem of the free section of the prestressed anchor cable is determined through indoor uniaxial tensile tests.

[0123] (2) Anchor hole forming process: Anchor holes are formed according to design requirements.

[0124] (3) Equipment on-site assembly process. The stress state monitoring subsystem of the free section of the prestressed anchor cable and the stress state monitoring subsystem of the anchoring section of the prestressed anchor cable are connected on-site through a tensile joint, and the anchor cable and the equipment are fixed through the anchor cable / equipment fixing device and sent into the anchor cable hole.

[0125] (4) Grouting and curing process: According to the design requirements, concrete is injected into the hole and the concrete age is waited for.

[0126] (5) On-site tensioning and initial readings. According to the design requirements, the prestressed anchor cable and the prestressed anchor cable full-length stress state monitoring equipment are loaded with a jack. During this process, the prestressed anchor cable free section stress state monitoring subsystem is connected to the prestressed anchor cable stress state monitoring portable acquisition subsystem through a measuring cable to measure the strain changes of the free section and the anchoring section during the loading process. After the loading process is completed, continuous tracking and monitoring are performed until the strain changes are stable and the initial value is read. Disconnect the connection between the prestressed anchor cable free section stress state monitoring subsystem and the prestressed anchor cable stress state monitoring portable acquisition subsystem.

[0127] (6) Anchor head fixation and construction of measuring anchor head base. After the tensioning is completed, the overlong anchor cable is cut off, the prestressed anchor cable free section stress state monitoring subsystem is reassembled, and the measuring anchor head base is constructed to protect the anchor head.

[0128] (7) Continuous tracking monitoring and evaluation. According to the monitoring needs, the prestressed anchor cable stress state monitoring portable acquisition subsystem is used to measure the full-length prestress loss of the prestressed anchor cable, and the safety factor and loss rate are evaluated according to formula (5).

[0129] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A prestressed anchor cable full-length stress state monitoring system, characterized in that: It comprises a device end and a control subsystem (100), wherein the device end comprises an anchoring section stress monitoring subsystem (400), an anchoring section stress monitoring subsystem (300), and a free section stress monitoring subsystem (200); The anchoring section stress monitoring subsystem (400) comprises an anchoring section, a free section and a sealed anchoring section which are connected in sequence, one end of the prestressed anchor cable (404) is buried in the anchoring section, and the other end freely passes through the free section and is fixedly connected to the anchoring section; The anchoring section stress monitoring subsystem (300) is arranged in the anchoring section and is used to measure the stress value of the prestressed anchor cable (404) in the anchoring section; One end of the free section stress monitoring subsystem (200) is fixedly connected to the anchor section stress monitoring subsystem (300), and the other end is connected to the control subsystem (100) after passing through the free section and the anchor section in sequence. The free section stress monitoring subsystem (200) is subjected to the same stress as the prestressed anchor cable (404) in the free section, so that the resistance value information is transmitted to the control subsystem (100) during the stress process; The control subsystem (100) is used to calculate the pull-out safety factor of the anchoring section and the prestress loss of the free section respectively according to the stress value and the resistance value information, thereby realizing the stress state monitoring of the entire length of the anchor cable.

2. A prestressed anchor cable full-length stress state monitoring system according to claim 1, characterized in that: The free segment stress monitoring subsystem (200) comprises a pipeline integrated module (202), wherein the pipeline integrated module (202) is integrated with an anchor free end stress measurement channel (2024) for accommodating an anchor free end stress measurement device, wherein the anchor free end stress measurement device is made of a conductive metal material.

3. A prestressed anchor cable full-length stress state monitoring system according to claim 2, characterized in that: The relationship between the strain and resistance change generated by the anchor free end stress measuring device under tension and compression conditions includes: Where R is the resistance value, ΔR is the change in resistance value, K is the strain rate coefficient, and ε is the strain.

4. A prestressed anchor cable full-length stress state monitoring system according to claim 2, characterized in that: Waterproof communication terminals (201) are provided at both ends of the pipeline integrated module (202); The pipeline integrated module (202) further comprises a protective layer (2023), an inner steel wire layer (2022) and an outer steel wire layer (2021) which are arranged in sequence from the inside to the outside, wherein the protective layer (2023) is provided with an anchor free end stress measurement channel (2024) for placing an anchor free end stress measurement device, a power supply channel (2025) for placing an energized line, and a communication channel (2027) for placing a communication line along the axial direction.

5. A prestressed anchor cable full-length stress state monitoring system according to any one of claims 2 to 4, characterized in that: The anchoring section stress monitoring subsystem (300) comprises a bottom shoe (302), a stress testing section (303), an electronic acquisition section (304) and a tensile joint (301) which are fixedly connected in sequence. The stress testing section (303) is bonded to the concrete mortar of the anchoring section to provide sufficient anchoring force with the anchor cable, and the stress testing section (303) is provided with a strain gauge for measuring the stress state of the anchoring section. The electronic acquisition section (304) is connected to the free section stress monitoring subsystem (200) through the tensile joint (301) to control the measurement and data acquisition of the strain gauge, and transmits the collected signal to the control subsystem (100) after amplification.

6. A prestressed anchor cable full-length stress state monitoring system according to claim 5, characterized in that: The anchoring section comprises a fixing concrete (401), a fixing plate (402) and a fixing clamp (403) arranged in the fixing concrete (401); the fixing plate (402) is used for fixing the connection between the prestressed anchor cable (404) and the anchoring section stress monitoring subsystem (300); one end of the fixing clamp (403) is connected to the fixing plate (402), and the other end is sleeved on the prestressed anchor cable (404).

7. A prestressed anchor cable full-length stress state monitoring system according to claim 5, characterized in that: The sealing anchor section comprises a concrete sealing anchor (407) and a large sealing plate (408), a circular pad (409) and an anchor head clamp (406) which are arranged in the concrete sealing anchor (407) and are connected in sequence. The concrete sealing anchor (407) is also provided with a measuring port (410) for accommodating the pipeline integrated module (202) to pass through, and a protective cover (411) is also provided at the measuring port (410).

8. A prestressed anchor cable full-length stress state monitoring system according to claim 1, characterized in that: The control subsystem (100) comprises a power supply and data conversion module (101), a power supply module (102) and a control module (103); the power supply and data conversion module (101) is connected to the pipeline integration module (202) and the control module (103) respectively, and is used to receive data, convert the data and transmit it to the control module (103); the power supply module (102) is connected to the power supply and data conversion module (101) and is used to supply power; The control module (103) is used to calculate the pull-out safety factor of the anchoring section and the prestress loss of the free section according to the measurement data, and to calculate and evaluate the pull-out safety factor of the anchoring section.

9. A method for monitoring the stress state of a prestressed anchor cable over its entire length, characterized in that: The following steps are involved: Step 1: Determine the strain rate coefficient K of the free section stress monitoring subsystem (200) through an indoor uniaxial tensile test; Step 2: forming an anchor hole according to design requirements, and installing a prestressed anchor full-length stress state monitoring system as described in any one of claims 1 to 8 in the anchor hole according to design and maintenance requirements; Step three, loading the prestressed anchor cable (404) and the equipment end, measuring the strain change of the prestressed anchor cable (404) at the free section and the anchor section during the loading process, and continuously tracking and monitoring after the loading process is completed until the strain change reaches stability, and reading the initial value of the resistance measurement of the free section after tensioning and locking and the initial value of the axial strain of the concrete in the anchor section; Step 4, disconnect the connection between the free section stress monitoring subsystem (200) and the control subsystem (100), build a measuring anchor head base, protect the anchor head, read the resistance measurement value of the free section and the concrete axial strain measurement value of the anchor section during service, use the resistance change of the free section to evaluate the prestress loss rate, and use the axial strain change value of the anchor section to evaluate the pull-out safety factor.

10. A method for monitoring the full-length stress state of a prestressed anchor cable according to claim 9, characterized in that: In step 3, the calculation of the prestress loss of the free-segment anchor cable according to the measured initial value includes: (311) Amplify the voltage signal of the stress measuring device at the free end of the anchor cable: Where U is voltage, u is output voltage, and ε is strain; (312) Calculate the relationship between the strain and resistance change of the stress measuring device at the free end of the anchor cable under tension and compression conditions: Where R is the resistance value, ΔR is the change in resistance value, K is the strain rate coefficient, and ε is the strain; (313) The prestress loss of anchor cable is calculated based on the relationship between strain and resistance change: Where Δσ is the prestress loss of the anchor cable, and E is the elastic modulus; Preferably, the calculation model of the prestress loss rate of the anchor cable anchoring section includes: Where Re is the prestress loss rate of the anchor cable anchorage section; ε v,intial is the initial axial strain of the concrete in the anchorage section after tensioning; v,after To monitor the axial strain of concrete in the anchoring section; Preferably, the calculation model for evaluating the pull-out safety factor of the anchoring section includes: Where, Fs is the pull-out safety factor of the anchor section; E concrete is the elastic modulus of concrete; π is the circumference of a circle; D is the diameter of the borehole; C is the cohesion between the surrounding rock and concrete; L is the length of the anchoring section; S is the cross-sectional area of ​​the anchoring section.

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