Construction method for quickly determining fastening force of low prestressed anchor rod

Abstract

The present application relates to the technical field of tunnel initial support, more particularly, to a construction method for rapidly measuring low pre-stressed anchor rod fastening force, which improves the anchor pad with a groove type, passes the strain wire of a dynamometer into the anchor pad, starts the instrument, and the strain gauge with a strong magnetic suction head can be attached to the anchor rod, the strong magnetic suction head is made of high-resistance and low-current material, is convenient and durable, is easy to install, can directly measure the anchor rod fastening force, and realizes instant and accurate control of the on-site anchor rod mechanical index; after the construction is completed, the detection work is also completed, then the power of the dynamometer is turned off, the strain gauge with the strong magnetic suction head will naturally fall off, and the anchor rod construction can be transferred to the next anchor rod construction. The present application integrates the detection and construction, greatly reduces the process test time in the early and process stages of construction, and improves the anchor rod construction efficiency. The present application is mainly applied to the measurement of low pre-stressed anchor rod fastening force.

Description

Technical Field

[0001] This invention relates to the field of tunnel initial support technology, and more specifically, to a construction method for rapidly determining the fastening force of low-prestressed anchor bolts. Background Technology

[0002] The tightening force of low-prestressed anchor bolts is achieved by applying torque to the tail of the anchor bolt. The torque acts on the bolt, but the tightening force of the anchor bolt does not change linearly during the process of applying torque to the bolt with a torque wrench. The torque applied to the bolt by the torque wrench must first overcome the frictional resistance between the bolt and the washer, the biting force between the anchor head and the surrounding rock or the anchoring force between the anchor bolt and the resin anchoring agent, and other force values. Only the remaining torque value can be effectively converted into the tightening force of the anchor bolt. However, the frictional resistance between the bolt and the washer, the biting force between the anchor head and the surrounding rock, and the anchoring force of the resin anchoring agent are not linearly changing. Ultimately, the effective torque that can be converted into the anchor bolt is uncertain. Moreover, according to past engineering experience, the effective torque value only accounts for about 10% of the total applied torque. The effective torque is affected by several factors, including: 1) the contact surface between the bolt and the thread; 2) the coefficient of friction between the bolt and the washer / washer; 3) the varying biting force of the surrounding rock on the anchor head or the anchoring force of the resin anchor as the strength and joint development of the surrounding rock change; 4) poor matching between the absolute torque error and the tightening force error, with no fundamental regularity; and 5) the torque coefficient of the torque wrench is not fixed as the ambient temperature inside the tunnel changes. Given that the effective torque of low-prestressed anchors is limited by these five factors and its value is not fixed, the relationship between torque and tightening force cannot be determined solely through testing, as this does not reflect the actual working conditions on site.

[0003] The traditional method for controlling anchor bolt tightening force is to determine the relationship between torque and anchor bolt force values ​​based on test data collected before construction. Subsequent construction directly controls the torque value. However, the relationship between torque and anchor bolt force is actually influenced by multiple factors and lacks a fundamental pattern. Traditional anchor bolt quality inspection is lagging behind; if the anchor bolt tightening force fails to meet requirements, a large number of anchor bolts will need to be reworked, hindering the stable control of anchor bolt mechanical properties on-site.

[0004] Meanwhile, traditional anchor bolt construction requires extensive process tests on torque and anchor bolt tightening force before large-scale construction can proceed. Furthermore, there are many types of surrounding rock in tunnels, and it is impossible to encounter them all in a short period of time during actual construction. Only one process test can be conducted for each type of surrounding rock. The parameters summarized have inherent defects in the accuracy and timeliness of on-site guidance. Summary of the Invention

[0005] To overcome the shortcomings of the existing technology, this invention provides a construction method for rapidly determining the fastening force of low-prestressed anchor bolts. This method utilizes resistance strain gauge measurement technology, directly integrating the measurement of the anchor bolt's fastening force with the construction process, thereby achieving precise control of the initial active support indicators for tunnels and improving the construction efficiency of the anchor bolts.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A construction method for rapidly determining the fastening force of low-prestressed anchor bolts includes the following steps: S1. Prepare the necessary equipment and tools before construction begins; S2. Locate the borehole positions on the surrounding rock mass. Before construction, surveyors shall lay out the positions according to the designed borehole spacing. S3. Use an air gun to drill the holes. The drilling angle should be perpendicular to the initial sprayed concrete surface. The length and diameter of the holes should be constructed according to the design requirements. S4. Use the high-pressure air gun to clean the hole and thoroughly remove the surrounding rock debris, rock powder and other impurities from the hole. S5. Insert the prestressed anchor rod into the hole and fix the prestressed anchor rod; S6. Insert the signal wire of the strong magnetic strain gauge into the central hole of the anchor plate, start the force measuring instrument. Once the force measuring instrument is started, the strong magnetic head will have a strong magnetism. Attach the strong magnetic head to the anchor body inside the hole and press the anchor plate tightly against the rock surface. Then insert the bolt and tighten it initially. Be careful to pull the lead wire into the groove on one side of the center circle of the anchor plate to avoid damaging the lead wire during the bolt tightening process. S7. Apply torque to the bolt at the end of the anchor rod using an electric torque wrench. Apply the torque value quickly at first and then slowly, while observing the value displayed on the stress tester, until it reaches 1.1 times the design tightening force. S8. Turn off the force gauge. Once the force gauge is turned off, the magnetism of the strong magnetic head disappears. Carefully remove the strong magnetic strain gauge through the hole in the anchor plate and move to the next hole for construction. S9. Use M20 cement grout for anchor bolt grouting. The grouting pressure should be determined in advance through process tests. Stop grouting when the grout flows out continuously from the gap between the rock surface and the anchor plate. S10, Move to the next hole for construction.

[0007] In step S2, the anchor bolt drilling positions are marked with red paint.

[0008] In step S5, the prestressed anchor bolt is an expansion-shell type hollow grouting anchor bolt.

[0009] The installation steps for the expansion-shell type hollow grouting anchor are as follows: S11. Assemble the expansion shell anchor head and the hollow anchor body of the expansion shell hollow grouting anchor bolt. The expansion shell anchor head and the hollow anchor body should be on the same axis. S12. Insert the assembled anchor head and anchor bolt assembly into the hole and into the bottom of the hole. The expansion-shell anchor head should be in close contact with the surrounding rock surface at the bottom of the hole. The anchor bolt assembly should be perpendicular to the initial shotcrete surface and suspended in the hole. To prevent hole collapse, the assembly installation should be carried out immediately after hole cleaning. S13. Use an electric torque wrench to rotate the expansion-shell anchor head counterclockwise until the anchor head is fully opened and firmly locked into the surrounding rock at the bottom of the hole.

[0010] In step S5, the prestressed anchor rod is a resin hollow grouting anchor rod.

[0011] The installation steps for the resin hollow grouting anchor are as follows: S21. Assemble the solid rod body, anchor connecting sleeve, and hollow anchor body of the low prestressed resin hollow anchor rod. The assembly should be on the same axis. S22. Send the resin anchoring agent into the bottom of the hole. The anchoring agent is ultra-fast setting. The anchor assembly is pushed into the hole at a uniform speed while rotating the anchor rod until the anchor rod is inserted into the bottom of the hole. The number of anchoring agent segments, anchor rod drilling speed, mixing time and other parameters should be determined according to the process test. The bottom of the anchor rod should be in close contact with the surrounding rock surface at the bottom of the hole. The anchor assembly should be perpendicular to the initial sprayed surface of the shotcrete and suspended in the hole. To prevent the hole from collapsing, the assembly should be installed immediately after cleaning the hole. S23. Wait for gelation time. The gelation time should be determined based on the process test. S24. After the gelation time reaches the required level, connect a strong magnetic strain gauge for measurement.

[0012] The anchor plate is machined into a hole-like structure with protrusions in the middle, and a rectangular groove is opened at the position of the hole-like structure. The protrusions are surrounded by flat plates.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention improves the anchor plate with a grooved design. By threading the strain gauge wire of the force gauge through the anchor plate and activating the instrument, the strain gauge with a strong magnetic head can be attached to the anchor rod. The strong magnetic head is made of a high-resistance, low-current material, making it convenient, durable, and easy to install. It can directly measure the anchor rod's tightening force, achieving real-time and accurate control of the anchor rod's mechanical properties on-site. After construction is completed, the inspection work also ends. Afterwards, the power of the force gauge is turned off, and the strain gauge with the strong magnetic head will naturally detach, making disassembly convenient and allowing for the next anchor rod installation. The raised part of the anchor plate effectively reduces the friction between the bolt and the raised part of the plate during installation, effectively improving the efficiency of torque conversion into anchor rod tightening force. The flat part can evenly distribute the pressure of the bolt on the plate onto the rock surface. The groove in the raised part allows the strain gauge wire of the force gauge to be easily threaded into the plate, and after the force gauge is activated, the strong magnetic head directly and firmly adheres to the anchor rod surface without manual intervention, ultimately achieving accurate, efficient, and real-time measurement of the anchor rod's anchoring force.

[0014] This invention integrates the direct measurement of anchor bolt tightening force into the anchor bolt construction process management, thus improving the efficiency of anchor bolt construction. By combining testing and construction, this invention significantly reduces the time spent on process testing during the pre-construction and in-process stages, and also improves the overall efficiency of anchor bolt construction. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the construction process of the present invention; Figure 2 This is a schematic diagram of the internal structure of the expansion-shell type hollow grouting anchor bolt used in this invention; Figure 3 This is a schematic diagram of the internal structure of the resin hollow grouting anchor rod used in this invention; Figure 4 This is a schematic diagram of the anchor plate portion of the present invention; Figure 5 This is a schematic diagram of the structure of the high-strength magnetic strain gauge in this invention; Figure 6 This is a schematic diagram of the arrangement of the strong magnetically attracted strain gauges in this invention; In the figure: 1 is the surrounding rock mass, 2 is the expansion shell type anchor head, 3 is the hollow anchor rod body, 4 is the anchor rod pad, 5 is the bolt, 6 is the force gauge, 7 is the solid rod body, 8 is the anchor rod connecting sleeve, 9 is the high-strength magnetic strain gauge, 10 is the signal line, and 11 is the high-strength magnetic head. Detailed Implementation

[0016] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0017] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0018] like Figures 1 to 5 As shown, a construction method for rapidly determining the fastening force of low-prestressed anchor bolts includes the following steps: S1. Prepare the necessary equipment and tools before construction begins; S2. Locate the borehole positions on the surrounding rock mass 1. Before construction, the surveyors shall lay out the positions according to the designed borehole spacing. S3. Use an air gun to drill the holes. The drilling angle should be perpendicular to the initial sprayed concrete surface. The length and diameter of the holes should be constructed according to the design requirements. S4. Use the high-pressure air gun to clean the hole and thoroughly remove the surrounding rock debris, rock powder and other impurities from the hole. S5. Insert the prestressed anchor rod into the hole and fix the prestressed anchor rod; S6. Insert the strong magnetic strain gauge 9 and signal line 10 into the central hole of the anchor plate 4, start the force measuring instrument 6. Once the force measuring instrument 6 is started, the strong magnetic head 11 will have strong magnetism. Attract the strong magnetic head 11 to the anchor body in the hole, and press the anchor plate 4 tightly against the rock surface. Then insert the bolt and tighten it initially. Be careful to pull the lead wire into the groove on one side of the center circle of the anchor plate 4 to avoid damaging the lead wire during the bolt tightening process. S7. Apply torque to bolt 5 at the end of the anchor rod using an electric torque wrench. Apply the torque value quickly at first and then slowly, while observing the value displayed on the stress tester, until it reaches 1.1 times the design tightening force. S8. Close the force gauge 6. Once the force gauge 6 is closed, the magnetism of the strong magnetic head 11 disappears. Carefully remove the strong magnetic strain gauge 9 through the hole in the anchor plate 4 and move to the next hole for construction. S9. Use M20 cement grout for anchor bolt grouting. The grouting pressure is determined in advance through process tests. Stop grouting when the grout flows out continuously from the gap between the rock surface and the anchor plate 4. S10, Move to the next hole for construction.

[0019] Preferably, in step S2, the location of the anchor bolt drilling hole is marked with red paint.

[0020] Preferably, in step S5, the prestressed anchor bolt is an expansion-shell type hollow grouting anchor bolt.

[0021] Preferably, the installation steps for expansion-shell type hollow grouting anchor bolts are as follows: S11. Assemble the expansion-shell type anchor head 2 and the hollow anchor body 3 of the expansion-shell type hollow grouting anchor bolt. The expansion-shell type anchor head 2 and the hollow anchor body 3 should be on the same axis. S12. Insert the assembled anchor head and anchor bolt assembly into the hole and into the bottom of the hole. The expansion-shell anchor head 2 should be in close contact with the surrounding rock surface at the bottom of the hole. The anchor bolt assembly should be perpendicular to the initial sprayed concrete surface and suspended in the hole. To prevent hole collapse, the assembly installation should be carried out immediately after cleaning the hole. S13. Use an electric torque wrench to rotate the expansion-shell anchor head 2 counterclockwise until the anchor head is fully opened and firmly locked into the surrounding rock at the bottom of the hole.

[0022] Preferably, in step S5, the prestressed anchor rod is a resin hollow grouting anchor rod.

[0023] Preferably, the installation steps for resin hollow grouting anchors are as follows: S21. Assemble the solid rod body 7, anchor connecting sleeve 8, and hollow anchor body 3 of the low prestressed resin hollow anchor rod. The assembly should be on the same axis. S22. Send the resin anchoring agent into the bottom of the hole. The anchoring agent is ultra-fast setting. The anchor assembly is pushed into the hole at a uniform speed while rotating the anchor rod until the anchor rod is inserted into the bottom of the hole. The number of anchoring agent segments, anchor rod drilling speed, mixing time and other parameters should be determined according to the process test. The bottom of the anchor rod should be in close contact with the surrounding rock surface at the bottom of the hole. The anchor assembly should be perpendicular to the initial sprayed surface of the shotcrete and suspended in the hole. To prevent the hole from collapsing, the assembly should be installed immediately after cleaning the hole. S23. Wait for gelation time. The gelation time should be determined based on the process test. S24. After the gelation time reaches the required level, connect the strong magnetic strain gauge 9 for measurement.

[0024] Preferably, the middle part of the anchor plate 4 is processed into a hole-like structure with protrusions, and a rectangular groove is opened at the position of the hole-like structure, and the protrusions are surrounded by flat plates.

[0025] The above description only illustrates the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention, and all such changes should be included within the protection scope of the present invention.

Claims

1. A construction method for rapidly determining the fastening force of low-prestressed anchor bolts, characterized in that, Includes the following steps: S1. Prepare the necessary equipment and tools before construction begins; S2. The borehole positions are located on the surrounding rock mass (1). Before construction, the surveyors shall lay out the positions according to the designed hole spacing. S3. Use an air gun to drill the holes. The drilling angle should be perpendicular to the initial sprayed concrete surface. The length and diameter of the holes should be constructed according to the design requirements. S4. Use the high-pressure air gun to clean the hole and thoroughly remove the surrounding rock debris, rock powder and other impurities from the hole. S5. Insert the prestressed anchor rod into the hole and fix the prestressed anchor rod; S6. Insert the signal line (10) of the strong magnetic strain gauge (9) into the central hole of the anchor plate (4), start the force measuring instrument (6), and the strong magnetic head (11) will have strong magnetism as soon as the force measuring instrument (6) is started. Then, the strong magnetic head (11) will be attracted to the anchor body in the hole and the anchor plate (4) will be pressed tightly against the rock surface. Then, insert the bolt and tighten it initially. Be careful to pull the lead wire into the groove on one side of the center circle of the anchor plate (4) to avoid damaging the lead wire during the bolt tightening process. S7. Apply torque to the bolt (5) at the end of the anchor rod using an electric torque wrench. Apply the torque value quickly at first and then slowly, while observing the value displayed on the stress tester until it reaches 1.1 times the design tightening force. S8. Close the force measuring instrument (6). Once the force measuring instrument (6) is closed, the magnetism of the strong magnetic suction head (11) disappears. Carefully remove the strong magnetic suction strain gauge (9) through the hole in the anchor plate (4) and move to the next hole position for construction. S9. Use M20 cement grout for anchor bolt grouting. The grouting pressure is determined in advance through process test. Stop grouting when the grout flows out continuously from the gap between the rock surface and the anchor plate (4). S10, Move to the next hole for construction.

2. The construction method for rapidly determining the fastening force of low-prestressed anchor bolts according to claim 1, characterized in that: In step S2, the anchor bolt drilling positions are marked with red paint.

3. The construction method for rapidly determining the fastening force of low-prestressed anchor bolts according to claim 1, characterized in that: In step S5, the prestressed anchor bolt is an expansion-shell type hollow grouting anchor bolt.

4. The construction method for rapidly determining the fastening force of low-prestressed anchor bolts according to claim 3, characterized in that: The installation steps for the expansion-shell type hollow grouting anchor are as follows: S11. Assemble the expansion-shell type anchor head (2) and the hollow anchor body (3) of the expansion-shell type hollow grouting anchor rod. The expansion-shell type anchor head (2) and the hollow anchor body (3) should be on the same axis. S12. Insert the assembled anchor head and anchor rod assembly into the hole and into the bottom of the hole. The expansion-shell type anchor head (2) should be in close contact with the surrounding rock surface at the bottom of the hole. The anchor rod assembly should be perpendicular to the initial sprayed concrete surface and suspended in the hole. To prevent the hole from collapsing, the assembly should be installed immediately after cleaning the hole. S13. Use an electric torque wrench to rotate the expansion-shell anchor head (2) counterclockwise until the anchor head is fully opened and firmly locked into the surrounding rock at the bottom of the hole.

5. The construction method for rapidly determining the fastening force of low-prestressed anchor bolts according to claim 1, characterized in that: In step S5, the prestressed anchor rod is a resin hollow grouting anchor rod.

6. The construction method for rapidly determining the fastening force of low-prestressed anchor bolts according to claim 5, characterized in that: The installation steps for the resin hollow grouting anchor are as follows: S21. Assemble the solid rod body (7), anchor connecting sleeve (8), and hollow anchor body (3) of the low prestressed resin hollow anchor rod. The assembly should be on the same axis. S22. Send the resin anchoring agent into the bottom of the hole. The anchoring agent is ultra-fast setting. The anchor assembly is pushed into the hole at a uniform speed while rotating the anchor rod until the anchor rod is inserted into the bottom of the hole. The number of anchoring agent segments, anchor rod drilling speed, mixing time and other parameters should be determined according to the process test. The bottom of the anchor rod should be in close contact with the surrounding rock surface at the bottom of the hole. The anchor assembly should be perpendicular to the initial sprayed surface of the shotcrete and suspended in the hole. To prevent the hole from collapsing, the assembly should be installed immediately after cleaning the hole. S23. Wait for gelation time. The gelation time should be determined based on the process test. S24. After the gelation time reaches the required level, connect the strong magnetic strain gauge (9) for measurement.

7. The construction method for rapidly determining the fastening force of low-prestressed anchor bolts according to claim 1, characterized in that: The anchor plate (4) is processed into a hole-like structure with protrusions in the middle. A rectangular groove is opened at the position of the hole-like structure, and the protrusions are surrounded by flat plates.

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