A flexible hollow anchor rod and construction method integrating digital monitoring

Abstract

A flexible hollow anchor rod and construction method with integrated digital monitoring: Anchor rod: A hollow steel pipe and a steel strand form a flexible hollow rod body; a hollow anti-torsion sleeve is fitted onto the left end of the flexible hollow rod body via a friction-increasing spring; a grouting stopper is installed at the end of the hollow anti-torsion sleeve; a centering positioner is fitted onto the right end of the flexible hollow rod body; a sealing sleeve is fitted onto the outside of the hollow anti-torsion sleeve; an anti-torsion tray is composed of a central tray and four stop columns, and is fitted onto the left end of the anti-torsion connecting section; a fiber optic Bragg grating sensor is arranged on the outside of the rod body. Construction method: Step drilling is performed in the rock mass; anchoring agent is loaded, and the flexible hollow rod body, anti-torsion tray, ribbed tray, self-aligning ball head, friction-reducing washer, and torque nut are placed in sequence; the anchoring agent is stirred and the anchor rod is tightened; the timing of grouting reinforcement is precisely controlled to complete delayed grouting. The present invention utilizes a fiber optic Bragg grating sensor to achieve real-time monitoring of the anchor rod status, while having the advantages of fast installation speed, convenient grouting, and high anchoring quality.

Description

Technical Field

[0001] The invention belongs to the technical field of coal mine tunnel support, and particularly relates to a flexible hollow anchor rod integrated with digital monitoring and a construction method. Background Art

[0002] The development of intelligent tunneling and the trend toward deeper coal mining have placed higher demands on tunnel excavation support. First, it requires safe and efficient maintenance and control of complex tunnels. Deep tunnels, for example, face a series of prominent challenges, including severe deformation, intense mining pressure, and frequent dynamic disasters. Second, it requires increasing tunneling speed and enabling real-time monitoring and feedback of tunnel support status. Building an intelligent, fast-exploration system is an inevitable path for the current intelligent development of coal mines.

[0003] Bolting is the primary support method for coal mine tunnels. However, due to the confines of the tunnels, the maximum anchoring depth of rigid anchor bolts is 2.4-2.8 meters, making it difficult to anchor into deep, stable rock formations, resulting in a weak foundation bearing layer. While cable anchors can address the shortcomings of limited anchoring depth and low strength, their installation is relatively complex, preventing timely post-excavation support. This leads to low construction efficiency and severely restricts excavation speed. To address these issues, existing methods have introduced flexible anchor bolt construction methods, which offer relatively simple installation. However, these methods still require a large number of components, require complex support procedures, and suffer from eccentric anchoring, where the cable anchor bolt is not centered in the drill hole during anchoring, resulting in a maximum anchoring force loss of up to 30%.

[0004] For rock masses with developed fractures, it is difficult to achieve stable control of the tunnel by relying solely on anchor cable support. Combining the anchor cable support function with the grouting reinforcement function, and modifying and reinforcing the broken surrounding rock can significantly improve its strength and bearing capacity, and can better cope with more complex tunnel environments. At present, tunnel anchoring control is mainly achieved through hollow grouting anchor cables, and most grouting sealing devices are of the extrusion sealing type, with the sealing device and the rod body separately set. For example, the patent publication number is CN218563629U, the publication date is March 3, 2023, and the name is a patent for a hollow grouting mining anchor cable embedded expansion sealer. This structure is relatively cumbersome in the implementation process, and has a low sealing success rate and poor sealing effect.

[0005] Anchor stress monitoring is one of the main evaluation indicators of the tunnel support status. The existing dynamometer can only monitor the local stress of the exposed end of the anchor. With the application of optical fiber in coal mines, optical fiber can be used to monitor the stress of the anchor rod body with higher accuracy and sensitivity. The arrangement of optical fiber is mainly achieved by grooving the rod body or attaching it to the outside of the rod body. For example, the patent with the publication number CN113267127B and the publication date of March 8, 2022, entitled "Fiber Bragg Grating Sensing Tunnel Surrounding Rock Safety Monitoring System Using Anchor Rods as Sensing Medium", describes that the optical fiber is arranged by grooving the rod body. However, the grooving method will lead to a decrease in the strength of the rod body, thereby affecting the anchoring strength; the method of arranging the optical fiber on the outside of the rod body will increase the diameter of the rod body, which is easily affected by the scratches of the hole wall, resulting in the breakage of the optical fiber, which will make the monitoring process impossible to implement. Summary of the Invention

[0006] In response to the problems existing in the above-mentioned prior art, the present invention provides a flexible hollow anchor rod and construction method with integrated digital monitoring. The anchor rod can achieve a quick installation process while meeting the support length and strength requirements, can greatly improve the tunnel excavation efficiency, help to build a high-quality support system, and can realize real-time monitoring of the support status, which can effectively ensure the safe production operation of coal mines; this method has simple construction steps, low implementation cost, ideal support effect, and can perform real-time monitoring of the support status, which is conducive to building a high-quality support system.

[0007] In order to achieve the above-mentioned object, the present invention provides a flexible hollow anchor rod with integrated digital monitoring, comprising a flexible hollow rod body, a sealing sleeve, an anti-twist tray, a ribbed tray, a self-aligning ball head, a friction-reducing washer, a torque nut and a fiber grating sensor;

[0008] The flexible hollow rod body is composed of a hollow anti-twist sleeve, a slurry stop ring, a friction spring, a steel strand, a hollow steel pipe, a slurry stop plug and a centering positioner;

[0009] The left half of the hollow anti-twist sleeve is a fastening section, and the right half is an anti-twist connecting section. The outer contour section of the anti-twist connecting section is a regular polygonal structure, and a strip-shaped line groove is provided on each surface of the outer contour. A rod body mounting cavity is provided at the axis of the anti-twist connecting section. The outer contour of the fastening section is a cylindrical structure, and an external thread structure 1 is provided on the outer contour. A core tube mounting hole is provided at the axis of the fastening section, and an internal thread structure is provided inside the left end of the core tube mounting hole; the right end of the core tube mounting hole is connected to the left end of the rod body mounting cavity;

[0010] The outer diameter of the slurry stop ring is adapted to the inner diameter of the rod body installation cavity, and is coaxially assembled at the left end of the rod body installation cavity;

[0011] The outer diameter of the friction spring is adapted to the inner diameter of the rod body installation cavity, and the spring is coaxially assembled in the rod body installation cavity and is located on the right side of the slurry stop ring;

[0012] The steel strand is made of multiple steel wires wound in a spiral shape, and a central cavity is formed at the axial part; a pin is radially inserted in the middle section of the steel strand, and a slurry passage connecting the central cavity and the external space is reserved through the inserted pin;

[0013] The left section of the hollow steel pipe is the main body installation section, and the section to the right of the main body installation section is the rod body installation section; the rod body installation section of the hollow steel pipe is fixedly inserted into the central cavity of the steel strand, and a slurry outlet is opened at a position corresponding to the slurry passage; the connected hollow steel pipe and steel strand together form a flexible hollow rod body;

[0014] The left part of the formed flexible hollow rod body is inserted into the rod body installation cavity inside the hollow anti-twist sleeve, and the left end of the steel strand is inserted into the spring cavity of the friction-increasing wire spring, and is fixedly connected to the anti-twist connecting section through the mutual squeezing action with the friction-increasing wire spring. At the same time, the main body installation section of the hollow steel pipe is fixedly inserted into the core pipe installation hole after passing through the slurry stop ring, and the left end of the main body installation section stops at the right side of the right end of the internal thread structure;

[0015] The outer surface of the slurry stopper body is provided with a second external thread structure, and is assembled to the left end of the core tube mounting hole through threaded cooperation between the second external thread structure and the internal thread structure;

[0016] The centering locator is composed of a positioning sleeve and three positioning clips. The three positioning clips are evenly distributed in a ring shape, and the left ends of the three clips are evenly fixedly connected to the edge of the right end of the positioning sleeve. The centering locator is fixedly sleeved on the outside of the right end of the steel strand through the positioning sleeve.

[0017] The sealing sleeve is made of an elastic sealing material and consists of a continuous undulating section on the left and a necked section on the right. The sealing sleeve is sleeved on the outside of the transition area where the hollow anti-torsion sleeve and the flexible hollow rod are connected. The outer contour of the continuous undulating section is a continuously undulating structure and is sleeved on the outside of the anti-torsion connection section. The outer contour of the necked section is a closing structure with an outer diameter gradually decreasing from left to right and is sleeved on the outside of the steel strand.

[0018] The anti-twist tray consists of a central disk body and four stop posts. The central disk body is a flat plate-shaped structure, with a regular polygonal anti-twist mounting hole adapted to the outer contour of the anti-twist connecting section at its center, and four positioning notches evenly distributed circumferentially on its outer edge surface, with four positioning protrusions formed between the four positioning notches; the four stop posts are evenly distributed circumferentially around the anti-twist mounting hole and are arranged one-to-one corresponding to the four positioning protrusions, and each stop post is vertically fixedly connected to the corresponding positioning protrusion; the anti-twist tray is sleeved on the outside of the left end of the anti-twist connecting section through the anti-twist mounting hole, and the four stop posts are located on the right side of the central disk body;

[0019] The ribbed tray consists of a main body located in the central area and supporting parts located at the edges of the main body, the main body gradually protruding from the edge toward the center in a direction away from the supporting part, and eight raised longitudinal ribs are evenly formed in the circumferential direction. At the same time, a bearing part parallel to the supporting part is formed in the central area of ​​the eight raised longitudinal ribs, and eight octagonal grooves are evenly formed on the inner edges of the eight raised longitudinal ribs, and the size of the space formed inside the eight raised longitudinal ribs is adapted to the size of the central disk body; a small hole for passing the line is provided on one side of the main body; a ball head positioning hole is provided in the center of the bearing part, and the center of the ball head positioning hole is spherical and concave in the direction close to the supporting part; the ribbed tray is mounted on the outside of the fastening section through the ball head positioning hole. At the same time, the four non-adjacent octagonal grooves in the inner surface of the ribbed tray are positioned and matched with the four positioning protrusions on the anti-twist tray;

[0020] The self-aligning ball head is a hemispherical structure with an anchor hole at its axis. The self-aligning ball head is sleeved on the outside of the fastening section through the anchor hole, and the spherical part is inserted into the ball head positioning hole.

[0021] The anti-friction washer is sleeved on the outside of the fastening section and is snugly connected to the flat portion of the self-aligning ball head;

[0022] The torque nut is assembled on the outside of the fastening section through the threaded fit between its internal thread structure and the external thread structure 1, and sequentially presses the anti-friction washer, the self-aligning ball head and the ribbed tray on the right side thereof toward the anti-twist tray;

[0023] The fiber grating sensor consists of an optical fiber and multiple gratings arranged on the optical fiber. The three fiber grating sensors are evenly arranged circumferentially, and each fiber grating sensor is embedded and pasted in a spiral mounting groove formed between two adjacent steel wires, and its right end extends to the left end of the center locator, and its left end ends at the right end of the hollow anti-twist sleeve; the three optical fiber output segments correspondingly connected to the three fiber grating sensors pass through the three strip-shaped wire-passing grooves and then enter the inner cavity of the ribbed tray, and pass out to the outside of the ribbed tray through the wire-passing holes.

[0024] As a preferred embodiment, the outer contour of the anti-twisting connection section is a regular hexagon, and six strip-shaped wire-passing grooves are evenly opened circumferentially on the outer contour of the anti-twisting connection section, wherein the three optical fiber output sections corresponding to the three optical fiber grating sensors are arranged in pairs and not adjacent to each other in the three strip-shaped wire-passing grooves.

[0025] As a preference, the outer diameter of the fastening section is smaller than the outer diameter of the anti-twist connecting section, and the hollow anti-twist sleeve has a transition annular boss between the fastening section and the anti-twist connecting section, and the outer diameter of the transition annular boss is larger than the outer diameter of the fastening section and smaller than the outer diameter of the anti-twist connecting section.

[0026] As a preferred embodiment, the cross-section of the inner hole of the continuous undulating section is a regular polygon that is adapted to the outer contour of the anti-twisting connection section, and its outer contour is a drum-shaped structure with multiple sections arranged continuously. The cross-section of the inner hole of the necking section is a circle that is adapted to the outer contour of the steel strand.

[0027] As a preference, the stop column is fixedly connected to the positioning protrusion by gluing or welding.

[0028] Furthermore, in order to facilitate real-time viewing of the stress state of each part of the anchoring section, a fiber Bragg grating demodulator is also included. The fiber Bragg grating demodulator is respectively connected to the optical fiber output sections of the three fiber Bragg grating sensors.

[0029] Furthermore, in order to ensure that the anti-friction washer has a long service life, the anti-friction washer is made of polytetrafluoroethylene material.

[0030] In order to effectively clamp the anchoring agent and significantly improve the stirring effect, the size of the annular space surrounded by the three positioning clips is consistent with the inner diameter of the positioning sleeve, and the outer edge size of the three positioning clips is larger than the outer diameter of the positioning sleeve.

[0031] In order to improve the sealing effect and ensure that the sealing sleeve has a long service life, the sealing sleeve is made of rubber material.

[0032] In the present invention, a core tube mounting hole and a rod body mounting cavity are connected at the axis of the hollow anti-twist sleeve. When the left end of the steel strand is inserted into the rod body mounting cavity, the exposed main body mounting section of the hollow steel tube is inserted into the core tube mounting hole. In this way, the core tube mounting hole can be used in conjunction with the main body mounting section of the hollow steel tube to achieve a grouting function. A friction-enhancing spring is provided between the steel strand and the hollow anti-twist sleeve. The friction-enhancing spring can be used to significantly increase friction, thereby ensuring that the steel strand can be firmly connected to the interior of the anti-twist sleeve by buckling and pressing, and effectively ensuring the load-bearing capacity of the connection. A slurry-stopping ring is provided at the left end of the rod body mounting cavity, and the root of the main body mounting section of the hollow steel tube is inserted into the slurry-stopping ring. The slurry-stopping ring can be used to block the gap between the outer circular surface of the hollow steel tube and the inner circular surface of the rod body mounting cavity, thereby effectively preventing the slurry injected into the steel strand from overflowing from the gap between the core tube mounting hole and the hollow steel tube. By inserting pins radially in the middle section of the steel strand, slurry passages can be reserved between the multiple steel wires using the pins, and the slurry passages can be effectively prevented from being buried by the steel wires. Since the hollow steel pipe is provided with a slurry outlet inside the steel strand, it is ensured that the slurry entering the central cavity can smoothly flow through the slurry passage to the outer area of ​​the steel strand, thereby effectively filling the gap between the steel strand and the borehole wall. After the slurry solidifies, the flexible hollow rod body can be firmly fixed in the borehole. A centering locator is assembled at the tail end of the steel strand, and three positioning clips are evenly arranged on the right end of the centering locator. This not only facilitates the use of the positioning clips to position and push the anchor agent, but also allows the anchor agent to be fully stirred during the rotation process. In addition, the flexible hollow rod body can be placed in the central area of ​​the borehole during the stirring process, thereby ensuring that the injected slurry can be evenly filled in the gap between the rod body and the borehole, which can significantly improve the anchoring force and help to build a high-quality support system. The outer contour of the anti-twist connection section on the right half of the hollow anti-twist sleeve is a regular polygon, and the anti-twist mounting hole in the center of the anti-twist tray is a regular polygon that matches the anti-twist connection section. In this way, when the anti-twist tray is mounted on the outside of the anti-twist connection section on the hollow anti-twist sleeve, it can be ensured that the anti-twist tray and the hollow anti-twist sleeve will not rotate relative to each other. Since four stop posts are vertically fixedly connected around one side of the anti-twist tray, during the actual installation process, it is only necessary to use the torque nut to provide a locking force to press the four stop posts on the anti-twist tray against the rock wall surface to effectively prevent the flexible hollow rod from rotating during the pre-tightening process, thereby applying a greater pre-tightening force and greatly improving the support effect.The fastening section of the left half of the hollow anti-twist sleeve is a cylindrical structure and is provided with an external thread structure 1, which can facilitate the installation of a ribbed tray, a self-aligning ball head and a torque nut on the fastening section, and can facilitate the application of pre-tightening force by using the torque nut through threaded matching; a strip-shaped wire groove is provided on each surface of the outer contour of the anti-twist connection section, which can ensure that the optical fiber output section of the fiber optic Bragg grating sensor arranged on the surface of the steel strand can be embedded in the strip-shaped wire groove, which can effectively prevent the optical fiber from being scratched by foreign objects and causing damage to the optical fiber. An internal thread structure is provided inside the core tube mounting hole at the end of the fastening section, and at the same time, the plug body surface of the slurry stopper is provided with an external thread structure 2, so that the slurry stopper can be firmly assembled at the end of the core tube mounting hole through threaded matching, thereby effectively sealing the grouting channel and avoiding the slurry overflow after grouting. Wrapping the sealing sleeve as a whole around the outside of the connection between the steel strand and the hollow anti-twist sleeve can not only ensure that the slurry will not overflow from the connection during the grouting process, but also can effectively seal the gap between the anchor rod and the drill hole by utilizing the outer contour of the sealing sleeve that expands due to extrusion, thereby avoiding the slurry from overflowing from the gap between the drill hole and the anchor rod, thereby realizing an integrated and comprehensive sealing operation; making the right end of the continuous undulating section a necking section is conducive to utilizing the necking section to effectively seal the variable diameter transition position in the drill hole during the installation process. The outer surface of the main body of the ribbed tray is uniformly provided with eight raised longitudinal ribs in the circumferential direction, which can effectively improve the load-bearing capacity of the ribbed tray and help to apply a greater preload to the anchor rod. At the same time, since this tray with a raised longitudinal rib structure can provide a greater load-bearing capacity, under the same support requirements, a lighter ribbed tray can be used to replace the traditional butterfly tray, which helps to reduce the labor load of underground workers. The inner surface of the ribbed tray is uniformly provided with eight octagonal grooves in the circumferential direction, which can facilitate the use of four of the octagonal grooves to cooperate with the four positioning protrusions around the anti-twist tray. In this way, when the four stop columns on the anti-twist tray are pressed against the rock wall, they can cooperate with the anti-twist tray to avoid rotation during the application of preload. By providing a small hole for passing the wire on the main body, the output end of the fiber optic Bragg grating sensor can be easily passed through the external space to facilitate connection with the fiber optic Bragg grating regulator. The self-aligning ball head is made into a hemispherical structure, and at the same time, a ball head positioning hole in the shape of a spherical socket is opened in the center of the ribbed tray. In this way, during the application of preload, the spherical portion of the self-aligning ball head and the ball head positioning hole of the ribbed tray are always in annular linear contact, thereby achieving the purpose of automatic centering, ensuring that the ribbed tray will not deviate from the predetermined installation position during the application of preload, which is beneficial to improving the quality of construction and significantly ensuring the support effect. Providing a friction-reducing washer between the torque nut and the flat portion of the self-aligning ball head is beneficial to protecting the torque nut and the self-aligning ball head during the application of preload, avoiding the reduction of support strength due to mutual damage.Placing fiber grating sensors in the spiral mounting grooves formed between adjacent steel wires on the outer surface of the steel strand not only enables stress monitoring along the entire length of the effective anchor rod, facilitating real-time monitoring of the stress conditions within the effective anchor rod, but also avoids the potential for weakening the rod by directly grooving the rod surface without increasing the rod diameter, effectively ensuring the rod's anchoring force. Furthermore, the uniform distribution of three fiber grating sensors across the strand effectively avoids the potential for missed detection that can occur with traditional methods using only one fiber grating sensor.

[0033] The present invention also provides a method for installing a flexible hollow anchor rod with integrated digital monitoring, which uses a flexible hollow anchor rod with integrated digital monitoring, comprising the following steps:

[0034] Step 1: Drilling a stepped borehole in the rock mass, wherein the stepped borehole consists of a large-diameter section drilled near the rock mass surface and a small-diameter section drilled away from the rock mass surface, and the diameter and length of the large-diameter section drilled hole are adapted to the diameter and length of the sealing sleeve, and the diameter and length of the small-diameter section drilled hole are adapted to the diameter and length of the steel strand;

[0035] Step 2: First, three fiber grating sensors whose lengths match the length of the steel strand are evenly arranged on the outer surface of the steel strand, and each fiber grating sensor is adhered to the spiral mounting groove formed between two adjacent steel wires. At the same time, the three corresponding optical fiber output segments of the three fiber grating sensors are embedded in the three strip-shaped wire grooves on the hollow anti-twist sleeve; then, the sealing sleeve is mounted on the outside of the hollow anti-twist sleeve; then, the anti-twist tray is mounted on the outside of the left end of the hollow anti-twist sleeve, and the stop column is located on the side close to the sealing sleeve; finally, the ribbed tray, self-aligning ball head, anti-friction washer and torque nut are mounted on the outside of the fastening section in sequence, and the self-aligning ball head is embedded in the ball head positioning hole;

[0036] Step 3: First, place the anchor in the stepped hole, then use the centering locator fixed on the end of the flexible hollow rod to support the anchor and push it into the bottom of the stepped hole; then start the anchor drill to rotate the torque nut and the flexible hollow rod simultaneously, and then use the three positioning clips on the centering locator to stir the anchor. While the flexible hollow rod rotates, continue to push the anchor drill toward the bottom of the hole to stir the anchor evenly. After pushing it to the bottom of the hole, stay for 30 seconds to allow the anchor to fully solidify.

[0037] Step 4: Continue to turn on the anchor drill rig to destroy the pin on the torque nut, so that the torque nut rotates along the external thread structure on the fastening section in the direction close to the bottom of the hole, and compresses the anti-friction washer and the self-aligning ball head, and then pushes the ribbed tray and the anti-twist tray to move along the axial direction of the fastening section in the direction close to the bottom of the hole, so that the four stop columns on the anti-twist tray are pressed and positioned on the rock wall, and the anti-twist tray is used to push the sealing sleeve toward the bottom of the hole, and the necking section on the outer contour of the sealing sleeve is pushed into the connection between the large-diameter section drilled hole and the small-diameter section drilled hole. In this process, the positioned anti-twist tray is used to position the hollow anti-twist sleeve and the ribbed tray in the rotation direction, and the necking section on the outer contour of the sealing sleeve is used to seal the transition between the large-diameter section drilled hole and the small-diameter section drilled hole. At the same time, the large-diameter section drilled hole is sealed by the continuous undulating section on the outer contour of the sealing sleeve that expands in volume due to extrusion;

[0038] Step 5: Remove the anchor drilling rig and repeat steps 1 to 4 to install the flexible hollow anchor bolts.

[0039] Step 6: For each flexible hollow anchor rod, remove the grouting plug on the hollow anti-torsion sleeve, and install a grouting pipe at the core tube mounting hole at the axis of the fastening section, and use the grouting pipe for grouting; after the flexible hollow anchor rod is installed, the grouting is not carried out immediately. At this time, the cracks in the tunnel surrounding rock are not fully developed. Wait until the tunnel stress is released and re-balanced. At this time, the cracks have developed to a certain extent, but they are not interconnected, which can maintain the stability of the surrounding rock. Grouting is carried out within this time. By accurately controlling the grouting timing, the delayed grouting operation is started, so that the injected slurry enters the central cavity of the steel strand through the core tube mounting hole, the hollow steel pipe and the slurry outlet on the hollow steel pipe, and then fills the space between the steel strand and the small diameter section drilled hole through the slurry channel on the steel strand. After the grouting is completed, the slurry plug is installed at the left end of the core tube mounting hole by threaded fit, and the slurry plug is reset and installed to effectively block the slurry and achieve the closure of the rock cracks;

[0040] Step 7: Connect the three optical fiber output segments corresponding to the three fiber grating sensors on each flexible hollow anchor rod to a fiber grating demodulator, and use the fiber grating demodulator to monitor the stress of each flexible hollow anchor rod.

[0041] In the present invention, a stepped outer hole is drilled in the rock mass. While the small diameter section is used to drill a hole to accommodate the flexible hollow rod, the large diameter section is used to drill a hole to accommodate the hollow anti-twist sleeve with a sealing sleeve. Three fiber optic Bragg grating sensors are evenly arranged on the surface of the steel strand, and each fiber optic Bragg grating sensor is adhered to the spiral installation groove formed between two adjacent steel wires. This allows the anchor rod to have a stress monitoring function without increasing the outer diameter of the rod or damaging the rod structure, thereby enabling stress monitoring along the entire length of the rod. After the anchoring agent is loaded into the borehole, the three positioning clips on the centering locator are used to fully stir the anchoring agent, which can significantly improve the anchoring effect. During the application of preload, the self-aligning ball head is used to push the ribbed tray toward the bottom of the hole, thereby achieving the purpose of automatic centering. During the application of preload, the ribbed tray will not deviate from the predetermined installation position, which is beneficial to improving the quality of construction. By pressing and positioning the four stop columns on the anti-twist tray against the rock wall, the ribbed tray and the hollow anti-twist sleeve that match the anti-twist tray can be radially limited, thereby preventing the ribbed tray and the flexible hollow rod from rotating during the pre-tightening process, which can significantly improve the anchoring strength of the anchor rod. The transition between the large-diameter and small-diameter drilled holes is sealed by the tapered section on the outer contour of the sealing sleeve. At the same time, the large-diameter drilled hole is sealed by the continuous undulating section on the outer contour of the sealing sleeve that expands in volume due to extrusion. In this way, the gap between the rod body and the drilled hole can be multi-sealed, significantly improving the sealing effect. After the grouting is completed, the grouting plug is installed on the left end of the core tube installation hole through the nut, which can effectively seal the core tube installation hole, thereby preventing the slurry from overflowing from the core tube installation hole.

[0042] Compared with existing technologies, this flexible hollow anchor rod and construction method with integrated digital monitoring has the following advantages:

[0043] (1) The rod body is a high-strength steel strand, which only needs to be pre-tightened by twisting the nut during construction. Compared with ordinary anchor rods, it is conducive to achieving high-strength and extended anchoring. At the same time, it has a shorter installation time, can achieve timely support of the tunnel after excavation, can greatly improve the tunnel excavation efficiency, and promote the combination with intelligent fast excavation equipment;

[0044] (2) The flexible hollow anchor integrates the anti-twist device and the grouting and sealing device on the rod body, realizing integrated installation, avoiding cumbersome operation procedures, saving support time and significantly improving grouting efficiency;

[0045] (3) A centering locator is set at the end of the flexible hollow anchor rod, which can fully stir the anchoring agent and keep the rod centered during the stirring process, thereby improving the anchoring force and building a high-quality support system;

[0046] (4) The fiber Bragg grating sensor in the flexible hollow anchor is attached to the groove of the steel strand, which does not increase the diameter of the existing rod body and avoids the reduction of the rod body strength caused by the groove. The three fiber Bragg grating sensors are staggered and arranged together to achieve real-time stress monitoring along the entire length of the rod body, effectively avoiding the problem of missed detection by a traditional single fiber Bragg grating sensor.

[0047] (5) The ribbed tray in the flexible hollow anchor is lighter than the traditional butterfly tray and has stronger load-bearing capacity, which can effectively reduce the labor intensity of underground workers.

[0048] The present invention can achieve high-strength extended anchoring with simple construction steps, which can effectively improve excavation efficiency; efficient grouting operations can be achieved through an integrated sealing device; and by arranging fiber optic Bragg grating sensors, real-time monitoring of the support status can be achieved without reducing the strength of the rod body, which is conducive to building a high-quality support system. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 Schematic diagram of the supporting state of the flexible hollow anchor rod of the present invention;

[0050] Figure 2 It is a schematic structural diagram of the step drilling in the present invention;

[0051] Figure 3 Schematic diagram of the structure of the flexible hollow anchor rod of the present invention;

[0052] Figure 4 This is a schematic diagram of the assembly of the hollow anti-twist sleeve, the slurry stop ring and the friction-increasing spring in the present invention;

[0053] Figure 5 Schematic diagram of the three-dimensional structure of the hollow anti-twist sleeve of the present invention;

[0054] Figure 6 It is a schematic structural diagram of the flexible hollow rod body in the present invention;

[0055] Figure 7 It is a structural diagram of the centering positioner in the present invention;

[0056] Figure 8 It is a schematic structural diagram of the sealing sleeve in the present invention;

[0057] Figure 9 It is a schematic structural diagram of the anti-twist tray of the present invention;

[0058] Figure 10 It is a schematic structural diagram of the ribbed tray of the present invention;

[0059] Figure 11 It is a structural diagram of the fiber Bragg grating sensor in the present invention;

[0060] Figure 12This is a schematic diagram of the assembly of the anti-twist tray, the hollow anti-twist sleeve, and the fiber grating sensor of the present invention;

[0061] Figure 13 This is a schematic diagram of the assembly of the fiber Bragg grating sensor and the steel strand in the present invention;

[0062] Figure 14 It is a schematic diagram of the assembly of the fiber Bragg grating sensor and the flexible hollow rod in the present invention.

[0063] In the figure: 1. Flexible hollow rod body, 1.1. Hollow anti-twist sleeve, 1.1a. Anti-twist connecting section, 1.1b. Transition annular boss, 1.1c. External thread structure 1, 1.1d. Internal thread structure, 1.1e. Fastening section, 1.1f. Strip-shaped wire groove, 1.1g. Rod body mounting cavity, 1.1h. Core tube mounting hole, 1.2. Steel strand, 1.2a. Slurry outlet, 1.2b. Pin, 1.2c. Hollow steel pipe, 1.2d. Slurry passage, 1.3. Friction-increasing spring, 1.4. Slurry stop ring, 1.5. Slurry stop plug, 1.6. Centering positioner; 1.6a. Positioning sleeve, 1.6b. Positioning clip; 2. Sealing sleeve, 2.1. Drum-shaped section structure, 2.2. Closing structure; 3. Anti-twist tray, 3.1. Center tray, 3.1a. Positioning protrusion, 3.1b. Anti-twist mounting hole, 3.1c. Positioning notch, 3.2. Stop column; 4. Ribbed tray, 4.1. Raised longitudinal rib, 4.2. Octagonal groove, 4.3. Small hole for passing wire, 4.4. Ball head positioning hole, 4.5. Load-bearing part, 4.6. Support part, 4.7. Main body; 5. Self-aligning ball head; 6. Anti-friction washer; 7. Torque nut; 8. Fiber optic Bragg grating sensor, 8.1. Optical fiber, 8.2. Bragg grating; 9. Step drilling, 9.1. Large-diameter section drilling, 9.2. Small-diameter section drilling; 10. Rock mass. DETAILED DESCRIPTION

[0064] The present invention will be further described below.

[0065] like Figures 1 to 14 As shown, the present invention provides a flexible hollow anchor rod with integrated digital monitoring, comprising a flexible hollow rod body 1, a sealing sleeve 2, an anti-twist tray 3, a ribbed tray 4, a self-aligning ball head 5, a friction-reducing washer 6, a torque nut 7 and a fiber grating sensor 8;

[0066] The flexible hollow rod body 1 is composed of a hollow anti-twist sleeve 1.1, a slurry stop ring 1.4, a friction spring 1.3, a steel strand 1.2, a hollow steel pipe 1.2c, a slurry stop plug 1.5 and a centering positioner 1.6;

[0067] The left half of the hollow anti-twist sleeve 1.1 is a fastening section 1.1e, and the right half is an anti-twist connecting section 1.1a. The outer contour section of the anti-twist connecting section 1.1a is a regular polygonal structure, and a strip-shaped line groove 1.1f is provided on each surface of the outer contour. A rod body mounting cavity 1.1g is provided at the axis of the anti-twist connecting section 1.1a. The outer contour of the fastening section 1.1e is a cylindrical structure, and an external thread structure 1.1c is provided on the outer contour. A core tube mounting hole 1.1h is provided at the axis of the fastening section 1.1e, and an internal thread structure 1.1d is provided inside the left end of the core tube mounting hole 1.1h; the right end of the core tube mounting hole 1.1h is connected to the left end of the rod body mounting cavity 1.1g;

[0068] The outer diameter of the slurry stop ring 1.4 is adapted to the inner diameter of the rod body installation cavity 1.1g, and is coaxially assembled at the left end of the rod body installation cavity 1.1g;

[0069] The outer diameter of the friction spring 1.3 matches the inner diameter of the rod mounting cavity 1.1g, and is coaxially assembled in the rod mounting cavity 1.1g and located on the right side of the stop ring 1.4;

[0070] The steel strand 1.2 is made of multiple steel wires wound in a spiral shape, with a central cavity formed at the axial center. A pin 1.2b is radially inserted into the middle section of the steel strand 1.2, and a slurry passage 1.2d is reserved through the inserted pin 1.2b to connect the central cavity with the external space.

[0071] The left section of the hollow steel tube 1.2c is the main body mounting section, and the section to the right of the main body mounting section is the rod body mounting section. The rod body mounting section of the hollow steel tube 1.2c is fixedly inserted into the central cavity of the steel strand 1.2, and a slurry outlet 1.2a is opened at a position corresponding to the slurry passage 1.2d. The connected hollow steel tube 1.2c and the steel strand 1.2 together form a flexible hollow rod body.

[0072] The left portion of the thus formed flexible hollow rod body is inserted into the rod body mounting cavity 1.1g inside the hollow anti-twist sleeve 1.1, and the left end of the steel strand 1.2 is inserted into the spring cavity of the friction-increasing spring 1.3 and fixedly connected to the anti-twist connecting section 1.1a through the mutual squeezing action with the friction-increasing spring 1.3. At the same time, the main body mounting section of the hollow steel tube 1.2c is fixedly inserted into the core tube mounting hole 1.1h after passing through the stop ring 1.4, and the left end of the main body mounting section stops to the right of the right end of the internal thread structure 1.1d.

[0073] The outer surface of the plug body of the slurry stopper 1.5 is provided with an external thread structure 2, and is assembled to the left end of the core tube mounting hole 1.1h through the threaded fit between the external thread structure 2 and the internal thread structure 1.1d;

[0074] The centering locator 1.6 is composed of a positioning sleeve 1.6a and three positioning clips 1.6b. The three positioning clips 1.6b are evenly distributed in a ring shape, and the left ends of the three positioning clips are evenly and annularly fixed to the edge of the right end of the positioning sleeve 1.6a. The centering locator 1.6 is fixedly sleeved on the outside of the right end of the steel strand 1.2 through the positioning sleeve 1.6a.

[0075] The sealing sleeve 2 is made of an elastic sealing material and comprises a continuously undulating section 2.2 on the left and a tapered section 2.1 on the right. The sealing sleeve 2 is sleeved onto the outside of the transition region between the hollow anti-twist sleeve 1.1 and the flexible hollow rod. The continuously undulating section 2.2 has a continuously undulating outer profile and is sleeved onto the outside of the anti-twist connection section 1.1a. The tapered section 2.1 has a gradually decreasing outer diameter from left to right and is sleeved onto the outside of the steel strand 1.2.

[0076] As a preferred embodiment, the length of the continuous undulating section 2.2 is slightly shorter than the length of the anti-twist connecting section 1.1a, so that space can be left for assembling the anti-twist tray 3.

[0077] The anti-twist tray 3 consists of a central disk body 3.1 and four stop posts 3.2. The central disk body 3.1 is a flat plate-like structure, with a regular polygonal anti-twist mounting hole 3.1b at its center that matches the outer contour of the anti-twist connecting section 1.1a. Four positioning notches 3.1c are evenly distributed circumferentially on its outer edge surface, and four positioning protrusions 3.1a are formed between the four positioning notches 3.1c; the four stop posts 3.2 are evenly distributed circumferentially around the anti-twist mounting hole 3.1b and are arranged one-to-one corresponding to the four positioning protrusions 3.1a, and each stop post 3.2 is vertically fixedly connected to the corresponding positioning protrusion 3.1a; the anti-twist tray 3 is sleeved on the outside of the left end of the anti-twist connecting section 1.1a through the anti-twist mounting hole 3.1b, and the four stop posts 3.2 are located on the right side of the central disk body 3.1;

[0078] The ribbed tray 4 is composed of a main body 4.7 located in the central area and a support portion 4.6 located on the edges of the main body 4.7. The main body 4.7 gradually protrudes from the edge to the center in a direction away from the support portion 4.6, and eight raised longitudinal ribs 4.1 are evenly formed in the circumferential direction. At the same time, a bearing portion 4.5 parallel to the support portion 4.6 is formed in the central area of ​​the eight raised longitudinal ribs 4.1, and eight octagonal grooves 4.2 are evenly formed on the inner edges of the eight raised longitudinal ribs 4.1. The dimensions of the space formed are compatible with those of the central disc body 3.1; a small hole 4.3 for passing the line is provided on one side of the main body 4.7; a ball head positioning hole 4.4 is provided in the center of the bearing portion 4.5, the center of which is recessed in a spherical socket shape toward the supporting portion 4.6; the ribbed tray 4 is fitted onto the exterior of the fastening section 1.1e through the ball head positioning hole 4.4, and at the same time, four non-adjacent octagonal grooves 4.2 on the inner surface of the ribbed tray 4 are positioned and matched with the four positioning protrusions 3.1a on the anti-twist tray 3;

[0079] The self-aligning ball head 5 is a hemispherical structure with an anchor hole at its axis. The self-aligning ball head 5 is sleeved on the outside of the fastening section 1.1e through the anchor hole, and its spherical part is inserted into the ball head positioning hole 4.4;

[0080] The anti-friction washer 6 is mounted on the outside of the fastening section 1.1e and is snugly connected to the flat portion of the self-aligning ball head 5;

[0081] The torque nut 7 is assembled on the outside of the fastening section 1.1e through the threaded cooperation between its internal thread structure and the external thread structure 1.1c, and sequentially presses the anti-friction washer 6, the self-aligning ball head 5 and the ribbed tray 4 located on the right side thereof toward the anti-twist tray 3. As a preferred embodiment, the anchoring length of the flexible hollow anchor is 1800 to 11000 mm, that is, when tightened, the length of the rock mass clamped between the support portion 4.6 of the ribbed tray 4 and the centering locator 1.6 is 1800 to 11000 mm, thus ensuring that the flexible hollow anchor can have a longer anchoring length.

[0082] The fiber grating sensor 8 is composed of an optical fiber 8.1 and a plurality of gratings 8.2 arranged on the optical fiber 8.1. The three fiber grating sensors 8 are evenly arranged circumferentially, and each fiber grating sensor 8 is embedded and pasted in a spiral mounting groove formed between two adjacent steel wires, and its right end extends to the left end of the center locator 1.6, and its left end ends at the right end of the hollow anti-twist sleeve 1.1; the three optical fiber output segments correspondingly connected to the three fiber grating sensors 8 pass through the three strip-shaped wire-passing grooves 1.1f and then enter the inner cavity of the ribbed tray 4, and pass out to the outside of the ribbed tray 4 through the wire-passing hole 4.3.

[0083] As a preferred embodiment, the outer contour of the anti-twisting connection section 1.1a is a regular hexagon, and six strip-shaped wire grooves 1.1f are evenly opened circumferentially on the outer contour of the anti-twisting connection section 1.1a, wherein the three optical fiber output sections corresponding to the three optical fiber grating sensors 8 are arranged in pairs and not adjacent to each other in the three strip-shaped wire grooves 1.1f.

[0084] As a preferred embodiment, the outer diameter of the fastening section 1.1e is smaller than the outer diameter of the anti-twist connection section 1.1a, and the hollow anti-twist sleeve 1.1 has a transition annular boss 1.1b between the fastening section 1.1e and the anti-twist connection section 1.1a, and the outer diameter of the transition annular boss 1.1b is larger than the outer diameter of the fastening section 1.1e and smaller than the outer diameter of the anti-twist connection section 1.1a.

[0085] As a preferred embodiment, the cross-section of the inner hole of the continuous undulating section 2.2 is a regular polygon that is adapted to the outer contour of the anti-twisting connecting section 1.1a, and its outer contour is a drum-shaped structure with multiple sections arranged continuously. The cross-section of the inner hole of the necking section 2.1 is a circle that is adapted to the outer contour of the steel strand.

[0086] As a preference, the stop post 3.2 is fixedly connected to the positioning protrusion 3.1a by gluing or welding.

[0087] In order to facilitate real-time viewing of the stress state of each part of the anchoring section, a fiber Bragg grating demodulator is also included, and the fiber Bragg grating demodulator is connected to the optical fiber output sections of the three fiber Bragg grating sensors 8 respectively.

[0088] In order to ensure that the anti-friction washer has a long service life, the anti-friction washer 6 is made of polytetrafluoroethylene material.

[0089] In order to effectively clamp the anchoring agent and significantly improve the stirring effect, the size of the annular space surrounded by the three positioning clips 1.6b is consistent with the inner diameter of the positioning sleeve 1.6a, and the outer edge size of the three positioning clips 1.6b is larger than the outer diameter of the positioning sleeve 1.6a.

[0090] In order to improve the sealing effect and ensure that the sealing sleeve has a long service life, the sealing sleeve 2 is made of rubber material.

[0091] In the present invention, a core tube mounting hole and a rod body mounting cavity are connected at the axis of the hollow anti-twist sleeve. When the left end of the steel strand is inserted into the rod body mounting cavity, the exposed main body mounting section of the hollow steel tube is inserted into the core tube mounting hole. In this way, the core tube mounting hole can be used in conjunction with the main body mounting section of the hollow steel tube to achieve a grouting function. A friction-enhancing spring is provided between the steel strand and the hollow anti-twist sleeve. The friction-enhancing spring can be used to significantly increase friction, thereby ensuring that the steel strand can be firmly connected to the interior of the anti-twist sleeve by buckling and pressing, and effectively ensuring the load-bearing capacity of the connection. A slurry-stopping ring is provided at the left end of the rod body mounting cavity, and the root of the main body mounting section of the hollow steel tube is inserted into the slurry-stopping ring. The slurry-stopping ring can be used to block the gap between the outer circular surface of the hollow steel tube and the inner circular surface of the rod body mounting cavity, thereby effectively preventing the slurry injected into the steel strand from overflowing from the gap between the core tube mounting hole and the hollow steel tube. By inserting pins radially in the middle section of the steel strand, slurry passages can be reserved between the multiple steel wires using the pins, and the slurry passages can be effectively prevented from being buried by the steel wires. Since the hollow steel pipe is provided with a slurry outlet inside the steel strand, it is ensured that the slurry entering the central cavity can smoothly flow through the slurry passage to the outer area of ​​the steel strand, thereby effectively filling the gap between the steel strand and the borehole wall. After the slurry solidifies, the flexible hollow rod body can be firmly fixed in the borehole. A centering locator is assembled at the tail end of the steel strand, and three positioning clips are evenly arranged on the right end of the centering locator. This not only facilitates the use of the positioning clips to position and push the anchor agent, but also allows the anchor agent to be fully stirred during the rotation process. In addition, the flexible hollow rod body can be placed in the central area of ​​the borehole during the stirring process, thereby ensuring that the injected slurry can be evenly filled in the gap between the rod body and the borehole, which can significantly improve the anchoring force and help to build a high-quality support system. The outer contour of the anti-twist connection section on the right half of the hollow anti-twist sleeve is a regular polygon, and the anti-twist mounting hole in the center of the anti-twist tray is a regular polygon that matches the anti-twist connection section. In this way, when the anti-twist tray is mounted on the outside of the anti-twist connection section on the hollow anti-twist sleeve, it can be ensured that the anti-twist tray and the hollow anti-twist sleeve will not rotate relative to each other. Since four stop posts are vertically fixedly connected around one side of the anti-twist tray, during the actual installation process, it is only necessary to use the torque nut to provide a locking force to press the four stop posts on the anti-twist tray against the rock wall surface to effectively prevent the flexible hollow rod from rotating during the pre-tightening process, thereby applying a greater pre-tightening force and greatly improving the support effect.The fastening section of the left half of the hollow anti-twist sleeve is a cylindrical structure and is provided with an external thread structure 1, which can facilitate the installation of a ribbed tray, a self-aligning ball head and a torque nut on the fastening section, and can facilitate the application of pre-tightening force by using the torque nut through threaded matching; a strip-shaped wire groove is provided on each surface of the outer contour of the anti-twist connection section, which can ensure that the optical fiber output section of the fiber optic Bragg grating sensor arranged on the surface of the steel strand can be embedded in the strip-shaped wire groove, which can effectively prevent the optical fiber from being scratched by foreign objects and causing damage to the optical fiber. An internal thread structure is provided inside the core tube mounting hole at the end of the fastening section, and at the same time, the plug body surface of the slurry stopper is provided with an external thread structure 2, so that the slurry stopper can be firmly assembled at the end of the core tube mounting hole through threaded matching, thereby effectively sealing the grouting channel and avoiding the slurry overflow after grouting. Wrapping the sealing sleeve as a whole around the outside of the connection between the steel strand and the hollow anti-twist sleeve can not only ensure that the slurry will not overflow from the connection during the grouting process, but also can effectively seal the gap between the anchor rod and the drill hole by utilizing the outer contour of the sealing sleeve that expands due to extrusion, thereby avoiding the slurry from overflowing from the gap between the drill hole and the anchor rod, thereby realizing an integrated and comprehensive sealing operation; making the right end of the continuous undulating section a necking section is conducive to utilizing the necking section to effectively seal the variable diameter transition position in the drill hole during the installation process. The outer surface of the main body of the ribbed tray is uniformly provided with eight raised longitudinal ribs in the circumferential direction, which can effectively improve the load-bearing capacity of the ribbed tray and help to apply a greater preload to the anchor rod. At the same time, since this tray with a raised longitudinal rib structure can provide a greater load-bearing capacity, under the same support requirements, a lighter ribbed tray can be used to replace the traditional butterfly tray, which helps to reduce the labor load of underground workers. The inner surface of the ribbed tray is uniformly provided with eight octagonal grooves in the circumferential direction, which can facilitate the use of four of the octagonal grooves to cooperate with the four positioning protrusions around the anti-twist tray. In this way, when the four stop columns on the anti-twist tray are pressed against the rock wall, they can cooperate with the anti-twist tray to avoid rotation during the application of preload. By providing a small hole for passing the wire on the main body, the output end of the fiber optic Bragg grating sensor can be easily passed through the external space to facilitate connection with the fiber optic Bragg grating regulator. The self-aligning ball head is made into a hemispherical structure, and at the same time, a ball head positioning hole in the shape of a spherical socket is opened in the center of the ribbed tray. In this way, during the application of preload, the spherical portion of the self-aligning ball head and the ball head positioning hole of the ribbed tray are always in annular linear contact, thereby achieving the purpose of automatic centering, ensuring that the ribbed tray will not deviate from the predetermined installation position during the application of preload, which is beneficial to improving the quality of construction and significantly ensuring the support effect. Providing a friction-reducing washer between the torque nut and the flat portion of the self-aligning ball head is beneficial to protecting the torque nut and the self-aligning ball head during the application of preload, avoiding the reduction of support strength due to mutual damage.Placing fiber grating sensors in the spiral mounting grooves formed between adjacent steel wires on the outer surface of the steel strand not only enables stress monitoring along the entire length of the effective anchor rod, facilitating real-time monitoring of the stress conditions within the effective anchor rod, but also avoids the potential for weakening the rod by directly grooving the rod surface without increasing the rod diameter, effectively ensuring the rod's anchoring force. Furthermore, the uniform distribution of three fiber grating sensors across the strand effectively avoids the potential for missed detection that can occur with traditional methods using only one fiber grating sensor.

[0092] The present invention also provides a method for installing a flexible hollow anchor rod with integrated digital monitoring, which uses a flexible hollow anchor rod with integrated digital monitoring, comprising the following steps:

[0093] Step 1: If Figure 2 As shown, a stepped borehole 9 is drilled in a rock mass 10, wherein the stepped borehole 9 consists of a large-diameter section borehole 9.1 close to the surface of the rock mass 10 and a small-diameter section borehole 9.2 away from the surface of the rock mass 10, and the diameter and length of the large-diameter section borehole 9.1 are adapted to the diameter and length of the sealing sleeve 2, and the diameter and length of the small-diameter section borehole 9.2 are adapted to the diameter and length of the steel strand 1.2;

[0094] Step 2: If Figure 14 As shown, three fiber grating sensors 8, each of which has a length matching that of the steel strand 1.2, are first evenly arranged circumferentially on the outer surface of the steel strand 1.2, with each fiber grating sensor 8 adhered to a spiral mounting groove formed between two adjacent steel wires. Simultaneously, the three corresponding optical fiber output segments of the three fiber grating sensors 8 are embedded in the three strip-shaped wire-passing grooves 1.1f of the hollow anti-twist sleeve 1.1. Next, the sealing sleeve 2 is fitted onto the exterior of the hollow anti-twist sleeve 1.1. Next, the anti-twist tray 3 is fitted onto the exterior of the left end of the hollow anti-twist sleeve 1.1, with the stopper 3.2 located on the side near the sealing sleeve 2. Finally, the ribbed tray 4, the self-aligning ball head 5, the anti-friction washer 6, and the torque nut 7 are sequentially fitted onto the exterior of the fastening section 1.1e, with the self-aligning ball head 5 embedded in the ball head positioning hole 4.4.

[0095] Step 3: First, place the anchoring agent in the stepped hole 9, and then use the centering positioner 1.6 fixed to the end of the flexible hollow rod 1 to support the anchoring agent and push it into the bottom of the stepped hole 9; then start the anchor drill to drive the torque nut 7 to rotate and synchronously drive the flexible hollow rod 1 to rotate, and then use the three positioning clips 1.6b on the centering positioner 1.6 to stir the anchoring agent. While the flexible hollow rod 1 rotates, continue to push the anchor drill toward the bottom of the hole to stir the anchoring agent evenly. After pushing it to the bottom of the hole, stay for 30 seconds to allow the anchoring agent to fully solidify;

[0096] Step 4: Continue to turn on the anchor drill to destroy the pin on the torque nut 7, so that the torque nut 7 rotates along the external thread structure 1.1c on the fastening section 1.1e toward the bottom of the hole, and presses the anti-friction washer 6 and the self-aligning ball head 5, and then pushes the ribbed tray 4 and the anti-twist tray 3 along the axial direction of the fastening section 1.1e toward the bottom of the hole, so that the four stop columns 3.2 on the anti-twist tray 3 are pressed and positioned on the rock wall, and the anti-twist tray 3 is used to push the sealing sleeve 2 toward the bottom of the hole, and the sealing sleeve The tapered section 2.1 on the outer contour of the sealing sleeve 2 is pushed into the connection between the large-diameter section drilled hole 9.1 and the small-diameter section drilled hole 9.2. During this process, the already positioned anti-twist tray 3 is used to position the hollow anti-twist sleeve 1.1 and the ribbed tray 4 in the rotational direction. The tapered section 2.1 on the outer contour of the sealing sleeve 2 is used to seal the transition between the large-diameter section drilled hole 9.1 and the small-diameter section drilled hole 9.2. At the same time, the continuously undulating section 2.2 on the outer contour of the sealing sleeve 2, which has expanded in volume due to extrusion, is used to seal the large-diameter section drilled hole 9.1.

[0097] Step 5: Remove the anchor drilling rig and repeat steps 1 to 4 to install the flexible hollow anchor bolts.

[0098] Step 6: For each flexible hollow anchor rod, remove the stop plug 1.5 on the hollow anti-torsion sleeve 1.1, and install a grouting pipe at the core pipe installation hole 1.1h at the axis of the fastening section 1.1e, and use the grouting pipe to perform grouting; after the flexible hollow anchor rod is installed, grouting is not carried out immediately. At this time, the cracks in the tunnel surrounding rock are not fully developed. Wait until the tunnel stress is released and re-balanced. At this time, the cracks have developed to a certain extent, but are not interconnected, which can maintain the stability of the surrounding rock. Grouting is carried out during this time. By accurately controlling the grouting timing, the implementation Perform delayed grouting operations, allowing the injected slurry to enter the central cavity of the steel strand 1.2 through the core tube mounting hole 1.1h, the hollow steel tube 1.2c, and the slurry outlet 1.2a on the hollow steel tube 1.2c, and then flow through the slurry passage 1.2d on the steel strand 1.2 to fill the space between the steel strand 1.2 and the small-diameter drilled hole 9.2. After the grouting is completed, a slurry stopper 1.5 is installed at the left end of the core tube mounting hole 1.1h through threaded engagement, and the slurry stopper 1.5 is reinstalled to effectively block the slurry and seal the rock mass fissures.

[0099] Step 7: Connect the three optical fiber output segments corresponding to the three fiber grating sensors 8 on each flexible hollow anchor rod to a fiber grating demodulator, and use the fiber grating demodulator to monitor the stress of each flexible hollow anchor rod.

[0100] In the present invention, a stepped outer hole is drilled in the rock mass. While the small diameter section is used to drill a hole to accommodate the flexible hollow rod, the large diameter section is used to drill a hole to accommodate the hollow anti-twist sleeve with a sealing sleeve. Three fiber optic Bragg grating sensors are evenly arranged on the surface of the steel strand, and each fiber optic Bragg grating sensor is adhered to the spiral installation groove formed between two adjacent steel wires. This allows the anchor rod to have a stress monitoring function without increasing the outer diameter of the rod or damaging the rod structure, thereby enabling stress monitoring along the entire length of the rod. After the anchoring agent is loaded into the borehole, the three positioning clips on the centering locator are used to fully stir the anchoring agent, which can significantly improve the anchoring effect. During the application of preload, the self-aligning ball head is used to push the ribbed tray toward the bottom of the hole, thereby achieving the purpose of automatic centering. During the application of preload, the ribbed tray will not deviate from the predetermined installation position, which is beneficial to improving the quality of construction. By pressing and positioning the four stop columns on the anti-twist tray against the rock wall, the ribbed tray and the hollow anti-twist sleeve that match the anti-twist tray can be radially limited, thereby preventing the ribbed tray and the flexible hollow rod from rotating during the pre-tightening process, which can significantly improve the anchoring strength of the anchor rod. The transition between the large-diameter and small-diameter drilled holes is sealed by the tapered section on the outer contour of the sealing sleeve. At the same time, the large-diameter drilled hole is sealed by the continuous undulating section on the outer contour of the sealing sleeve that expands in volume due to extrusion. In this way, the gap between the rod body and the drilled hole can be multi-sealed, significantly improving the sealing effect. After the grouting is completed, the grouting plug is installed on the left end of the core tube installation hole through the nut, which can effectively seal the core tube installation hole, thereby preventing the slurry from overflowing from the core tube installation hole.

[0101] Compared with existing technologies, this flexible hollow anchor rod and construction method with integrated digital monitoring has the following advantages:

[0102] (1) The rod body is a high-strength steel strand, which only needs to be pre-tightened by twisting the nut during construction. Compared with ordinary anchor rods, it is conducive to achieving high-strength and extended anchoring. At the same time, it has a shorter installation time, can achieve timely support of the tunnel after excavation, can greatly improve the tunnel excavation efficiency, and promote the combination with intelligent fast excavation equipment;

[0103] (2) The flexible hollow anchor integrates the anti-twist device and the grouting and sealing device on the rod body, realizing integrated installation, avoiding cumbersome operation procedures, saving support time and significantly improving grouting efficiency;

[0104] (3) A centering locator is set at the end of the flexible hollow anchor rod, which can fully stir the anchoring agent and keep the rod centered during the stirring process, thereby improving the anchoring force and building a high-quality support system;

[0105] (4) The fiber Bragg grating sensor in the flexible hollow anchor is attached to the groove of the steel strand, which does not increase the diameter of the existing rod body and avoids the reduction of the rod body strength caused by the groove. The three fiber Bragg grating sensors are staggered and arranged together to achieve real-time stress monitoring along the entire length of the rod body, effectively avoiding the problem of missed detection by a traditional single fiber Bragg grating sensor.

[0106] (5) The ribbed tray in the flexible hollow anchor is lighter than the traditional butterfly tray and has stronger load-bearing capacity, which can effectively reduce the labor intensity of underground workers.

[0107] The present invention can achieve high-strength extended anchoring with simple construction steps, which can effectively improve excavation efficiency; efficient grouting operations can be achieved through an integrated sealing device; and by arranging fiber optic Bragg grating sensors, real-time monitoring of the support status can be achieved without reducing the strength of the rod body, which is conducive to building a high-quality support system.

Claims

1. A flexible hollow anchor rod with integrated digital monitoring, comprising a flexible hollow rod body (1), characterized in that: It also includes a sealing sleeve (2), an anti-twist tray (3), a ribbed tray (4), a self-aligning ball head (5), a friction-reducing washer (6), a torque nut (7) and a fiber optic Bragg grating sensor (8); The flexible hollow rod body (1) is composed of a hollow anti-twist sleeve (1.1), a slurry stop ring (1.4), a friction-increasing spring (1.3), a steel strand (1.2), a hollow steel pipe (1.2c), a slurry stop plug (1.5) and a centering positioner (1.6); The left half of the hollow anti-twist sleeve (1.1) is a fastening section (1.1e), and the right half is an anti-twist connection section (1.1a). The outer contour section of the anti-twist connection section (1.1a) is a regular polygonal structure, and a strip-shaped line groove (1.1f) is provided on each surface of the outer contour. A rod body mounting cavity (1.1g) is provided at the axis of the anti-twist connection section (1.1a). The outer contour of the fastening section (1.1e) is a cylindrical structure, and an external thread structure (1.1c) is provided on the outer contour. A core tube mounting hole (1.1h) is provided at the axis of the fastening section (1.1e), and an internal thread structure (1.1d) is provided inside the left end of the core tube mounting hole (1.1h); the right end of the core tube mounting hole (1.1h) is connected to the left end of the rod body mounting cavity (1.1g). The outer diameter of the slurry-stopping ring (1.4) is adapted to the inner diameter of the rod body installation cavity (1.1g), and is coaxially assembled at the left end of the rod body installation cavity (1.1g); The outer diameter of the friction-increasing spring (1.3) matches the inner diameter of the rod body installation cavity (1.1g), and is coaxially assembled in the rod body installation cavity (1.1g) and is located on the right side of the slurry stop ring (1.4); The steel strand (1.2) is made of a plurality of steel wires wound in a spiral shape, and a central cavity is formed at the axial center. A pin (1.2b) is radially inserted into the middle section of the steel strand (1.2), and a slurry passage (1.2d) is reserved through the inserted pin (1.2b) to connect the central cavity and the external space. A left section of the hollow steel pipe (1.2c) is a main body installation section, and a portion to the right of the main body installation section is a rod body installation section; the rod body installation section of the hollow steel pipe (1.2c) is fixedly inserted into the central cavity of the steel strand (1.2), and a slurry outlet (1.2a) is provided at a position corresponding to the slurry passage (1.2d); the connected hollow steel pipe (1.2c) and the steel strand (1.2) together form a flexible hollow rod body; The left portion of the formed flexible hollow rod body is inserted into the rod body installation cavity (1.1g) inside the hollow anti-twist sleeve (1.1), and the left end of the steel strand (1.2) is inserted into the spring cavity of the friction-increasing wire spring (1.3), and is fixedly connected to the anti-twist connection section (1.1a) through the mutual squeezing action with the friction-increasing wire spring (1.3). At the same time, the main body installation section of the hollow steel pipe (1.2c) is fixedly inserted into the core pipe installation hole (1.1h) after passing through the slurry stop ring (1.4), and the left end of the main body installation section stops at the right side of the right end of the internal thread structure (1.1d); The outer surface of the plug body of the slurry stopper (1.5) is provided with an external thread structure 2, and is assembled to the left end of the core tube mounting hole (1.1h) through threaded cooperation between the external thread structure 2 and the internal thread structure (1.1d); The centering positioner (1.6) is composed of a positioning sleeve (1.6a) and three positioning clips (1.6b). The three positioning clips (1.6b) are evenly distributed in a ring shape, and the left ends thereof are evenly fixedly connected to the edge of the right end of the positioning sleeve (1.6a). The centering positioner (1.6) is fixedly sleeved on the outer side of the right end of the steel strand (1.2) through the positioning sleeve (1.6a). The sealing sleeve (2) is made of an elastic sealing material and is composed of a continuously undulating section (2.2) located on the left and a constricted section (2.1) located on the right. The sealing sleeve (2) is sleeved on the outside of the transition area where the hollow anti-twist sleeve (1.1) and the flexible hollow rod are connected. The outer contour of the continuously undulating section (2.2) is a continuously undulating changing structure and is sleeved on the outside of the anti-twist connection section (1.1a). The outer contour of the constricted section (2.1) is a closing structure with an outer diameter gradually decreasing from left to right and is sleeved on the outside of the steel strand (1.2). The anti-twist tray (3) is composed of a central tray body (3.1) and four stop posts (3.2). The central tray body (3.1) is a planar plate-shaped structure, the center of which is provided with a regular polygonal anti-twist mounting hole (3.1b) that matches the outer contour of the anti-twist connection section (1.1a). Four positioning notches (3.1c) are evenly arranged on the outer edge surface thereof in a circumferential direction, and four positioning protrusions (3.1a) are formed between the four positioning notches (3.1c). Four stop columns (3.2) are evenly distributed circumferentially around the anti-twist mounting hole (3.1b) and are arranged one-to-one corresponding to the four positioning protrusions (3.1a), and each stop column (3.2) is vertically fixedly connected to the corresponding positioning protrusion (3.1a); the anti-twist tray (3) is sleeved on the outside of the left end of the anti-twist connecting section (1.1a) through the anti-twist mounting hole (3.1b), and the four stop columns (3.2) are located on the right side of the central tray body (3.1); The ribbed tray (4) is composed of a main body (4.7) located in the central area and a support portion (4.6) located at the edges of the main body (4.7). The main body (4.7) gradually protrudes from the edge to the center in a direction away from the support portion (4.6), and eight raised longitudinal ribs (4.1) are evenly formed in the circumferential direction. At the same time, a bearing portion (4.5) parallel to the support portion (4.6) is formed in the central area of ​​the eight raised longitudinal ribs (4.1), eight octagonal grooves (4.2) are evenly formed on the inner edges of the eight raised longitudinal ribs (4.1), and a groove (4.5) is formed inside the eight raised longitudinal ribs (4.1). The spatial dimensions are adapted to the dimensions of the central disk (3.1); a small hole (4.3) for passing the line is provided on one side of the main body (4.7); a ball head positioning hole (4.4) is provided at the center of the bearing portion (4.5), and the center of the ball head positioning hole (4.4) is spherical and recessed toward the supporting portion (4.6); the ribbed tray (4) is sleeved on the outside of the fastening section (1.1e) through the ball head positioning hole (4.4), and at the same time, four non-adjacent octagonal grooves (4.2) on the inner surface of the ribbed tray (4) are positioned and matched with the four positioning protrusions (3.1a) on the anti-twist tray (3); The self-aligning ball head (5) is a hemispherical structure, and an anchor hole is provided at its axis. The self-aligning ball head (5) is sleeved on the outside of the fastening section (1.1e) through the anchor hole, and its spherical body is inserted into the ball head positioning hole (4.4); The anti-friction washer (6) is sleeved on the outside of the fastening section (1.1e) and is snugly connected to the plane portion of the self-aligning ball head (5); The torque nut (7) is assembled on the outside of the fastening section (1.1e) through the threaded fit between its internal threaded structure and the external threaded structure (1.1c), and sequentially presses the anti-friction washer (6), the self-aligning ball head (5) and the ribbed tray (4) located on the right side thereof toward the anti-twist tray (3); The fiber grating sensor (8) is composed of an optical fiber (8.1) and a plurality of gratings (8.2) arranged on the optical fiber (8.1). The three fiber grating sensors (8) are evenly arranged circumferentially, and each fiber grating sensor (8) is embedded and pasted in a spiral mounting groove formed between two adjacent steel wires, and its right end extends to the left end of the centering positioner (1.6), and its left end stops at the right end of the hollow anti-twist sleeve (1.1); the three optical fiber output segments correspondingly connected to the three fiber grating sensors (8) pass through the three strip-shaped wire grooves (1.1f) and then penetrate into the inner cavity of the ribbed tray (4), and pass out to the outside of the ribbed tray (4) through the wire hole (4.3).

2. The flexible hollow anchor rod with integrated digital monitoring according to claim 1, characterized in that: The outer contour of the anti-twist connection section (1.1a) is a regular hexagon, and six strip-shaped wire-passing grooves (1.1f) are evenly arranged circumferentially on the outer contour of the anti-twist connection section (1.1a), wherein three optical fiber output sections correspondingly connected to the three optical fiber grating sensors (8) are arranged in pairs in the three strip-shaped wire-passing grooves (1.1f) without being adjacent to each other.

3. The flexible hollow anchor rod with integrated digital monitoring according to claim 2, characterized in that: The outer diameter of the fastening section (1.1e) is smaller than the outer diameter of the anti-twist connecting section (1.1a); the hollow anti-twist sleeve (1.1) has a transition annular boss (1.1b) between the fastening section (1.1e) and the anti-twist connecting section (1.1a); the outer diameter of the transition annular boss (1.1b) is larger than the outer diameter of the fastening section (1.1e) and smaller than the outer diameter of the anti-twist connecting section (1.1a).

4. The flexible hollow anchor rod with integrated digital monitoring according to claim 3, characterized in that: The cross section of the inner hole of the continuous undulating section (2.2) is a regular polygon that matches the outer contour of the anti-twist connection section (1.1a), and its outer contour is a drum-shaped structure with multiple sections arranged continuously. The cross section of the inner hole of the necking section (2.1) is a circle that matches the outer contour of the steel strand.

5. The flexible hollow anchor rod with integrated digital monitoring according to claim 4, characterized in that: The stop column (3.2) is fixedly connected to the positioning protrusion (3.1a) by gluing or welding.

6. The flexible hollow anchor rod with integrated digital monitoring according to claim 5, characterized in that: It also includes a fiber Bragg grating demodulator, which is respectively connected to the optical fiber output sections of the three fiber Bragg grating sensors (8).

7. The flexible hollow anchor rod with integrated digital monitoring according to claim 6, characterized in that: The anti-friction washer (6) is made of polytetrafluoroethylene material.

8. The flexible hollow anchor rod with integrated digital monitoring according to claim 7, characterized in that: The size of the annular space enclosed by the three positioning clips (1.6b) is consistent with the inner diameter of the positioning sleeve (1.6a), and the outer edge size of the three positioning clips (1.6b) is larger than the outer diameter of the positioning sleeve (1.6a).

9. The flexible hollow anchor rod with integrated digital monitoring according to claim 8, characterized in that: The sealing sleeve (2) is made of rubber material.

10. A method for installing a flexible hollow anchor rod with integrated digital monitoring, using the flexible hollow anchor rod with integrated digital monitoring according to any one of claims 1 to 9, characterized in that: The following steps are involved: Step 1: Drilling a stepped borehole (9) in the rock mass (10), wherein the stepped borehole (9) consists of a large-diameter borehole (9.1) close to the surface of the rock mass (10) and a small-diameter borehole (9.2) away from the surface of the rock mass (10), and the diameter and length of the large-diameter borehole (9.1) are adapted to the diameter and length of the sealing sleeve (2), and the diameter and length of the small-diameter borehole (9.2) are adapted to the diameter and length of the steel strand (1.2); Step 2: First, three fiber optic Bragg grating sensors (8) whose lengths match the length of the steel strand (1.2) are evenly arranged on the outer surface of the steel strand (1.2) in the circumferential direction, and each fiber optic Bragg grating sensor (8) is adhered to the spiral installation groove formed between two adjacent steel wires. At the same time, the three corresponding optical fiber output sections of the three fiber optic Bragg grating sensors (8) are embedded in the three strip-shaped wire grooves (1.1f) on the hollow anti-twist sleeve (1.1); then , the sealing sleeve (2) is mounted on the outside of the hollow anti-twist sleeve (1.1); then, the anti-twist tray (3) is mounted on the outside of the left end of the hollow anti-twist sleeve (1.1), and the stop column (3.2) is located on the side close to the sealing sleeve (2); finally, the ribbed tray (4), the self-aligning ball head (5), the anti-friction washer (6) and the torque nut (7) are mounted on the outside of the fastening section (1.1e) in sequence, and the self-aligning ball head (5) is embedded in the ball head positioning hole (4.4); Step 3: First, place the anchoring agent in the stepped borehole (9), and then use the centering positioner (1.6) fixed to the end of the flexible hollow rod (1) to support the anchoring agent and push it into the bottom of the stepped borehole (9); then start the anchor drilling machine to drive the torque nut (7) to rotate and synchronously drive the flexible hollow rod (1) to rotate, and then use the three positioning clips (1.6b) on the centering positioner (1.6) to stir the anchoring agent. While the flexible hollow rod (1) is rotating, the anchor drilling machine is continued to be pushed towards the bottom of the hole to stir the anchoring agent evenly. After it is pushed to the bottom of the hole, it is kept for 30 seconds to allow the anchoring agent to fully solidify; Step 4: Continue to open the anchor drill to destroy the pin on the torque nut (7), so that the torque nut (7) rotates along the external thread structure 1 (1.1c) on the fastening section (1.1e) toward the bottom of the hole, and presses the anti-friction washer (6) and the self-aligning ball head (5), and then pushes the ribbed tray (4) and the anti-twist tray (3) along the axial direction of the fastening section (1.1e) toward the bottom of the hole, so that the four stop columns (3.2) on the anti-twist tray (3) are pressed and positioned on the rock wall, and the anti-twist tray (3) is used to push the sealing sleeve (2) toward the bottom of the hole, so that the sealing sleeve The shrinking section (2.1) on the outer contour of the hole sleeve (2) is pushed into the connection between the large diameter section drill hole (9.1) and the small diameter section drill hole (9.2), and the already positioned anti-twist tray (3) is used to position the hollow anti-twist sleeve (1.1) and the ribbed tray (4) in the rotation direction. The shrinking section (2.1) on the outer contour of the sealing sleeve (2) is used to seal the transition between the large diameter section drill hole (9.1) and the small diameter section drill hole (9.2). At the same time, the continuous undulating section (2.2) on the outer contour of the sealing sleeve (2) that expands in volume due to extrusion is used to seal the large diameter section drill hole (9.1); Step 5: Remove the anchor drilling rig and repeat steps 1 to 4 to install the flexible hollow anchor bolts. Step 6: For each flexible hollow anchor rod, remove the stop plug (1.5) on the hollow anti-torsion sleeve (1.1), and install a grouting pipe at the core pipe installation hole (1.1h) at the axis of the fastening section (1.1e), and use the grouting pipe to perform grouting; after the flexible hollow anchor rod is installed, do not immediately perform grouting. At this time, the cracks in the tunnel surrounding rock are not fully developed. Wait until the tunnel stress is released and re-balanced. At this time, the cracks have developed to a certain extent, but are not interconnected, and the stability of the surrounding rock can be maintained. Perform grouting during this time. By accurately controlling the grouting timing, start the delayed grouting operation. The injected slurry is passed through the core tube mounting hole (1.1h), the hollow steel tube (1.2c), and the slurry outlet (1.2a) on the hollow steel tube (1.2c) into the central cavity of the steel strand (1.2), and then is filled into the space between the steel strand (1.2) and the small diameter section borehole (9.2) through the slurry passage (1.2d) on the steel strand (1.2). After the grouting is completed, the slurry stopper (1.5) is installed at the left end of the core tube mounting hole (1.1h) through threaded engagement, and the slurry stopper (1.5) is reset and installed to effectively block the slurry and seal the rock mass fissures. Step 7: Connect the three optical fiber output segments corresponding to the three optical fiber Bragg grating sensors (8) on each flexible hollow anchor rod to the optical fiber Bragg grating demodulator, and use the optical fiber Bragg grating demodulator to monitor the stress of each flexible hollow anchor rod.

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