A test device and operating method for on-site shotcrete bond strength testing

Abstract

This invention discloses an on-site shotcrete bond strength testing device and operating method, particularly relating to the field of concrete bond strength testing technology. A novel ring structure is designed to be directly fixed to a rock core, transmitting axial outward tensile force, eliminating the complex and time-consuming processes of rebar installation and pre-embedded parts. A telescopic support frame, precision leveling bolts, and a laser leveling device are designed to ensure an axial outward pull-out force perpendicular to the shotcrete surface. A reaction force frame, operating panel and display screen, hydraulic cylinder, controller, pressure pump, electric pump, and high-precision pressure gauge are designed to achieve simple operation, real-time display, labor saving, improved efficiency, and safety and reliability.

Description

Technical Field

[0001] This invention belongs to the field of concrete bond strength testing technology, specifically a field shotcrete bond strength testing device and operating method. Background Technology

[0002] National standards such as the "Technical Specification for Rock and Soil Anchor and Shotcrete Support Engineering" (GB50086-2015) and the water conservancy industry standard "Technical Specification for Anchor and Shotcrete Support in Water Conservancy and Hydropower Engineering" (SL377-2007) stipulate that the main methods for on-site testing of the bond strength between shotcrete and surrounding rock are the pre-embedded specimen pull-out method and the core drilling pull-out method. The pre-embedded specimen method involves pre-embedding a cylinder with a diameter of 20cm to 50cm during shotcrete construction, embedding a high-strength tie rod in the center of the cylinder, and conducting a pull-out test after the required curing period to calculate the bond strength. The core drilling pull-out method typically involves planting a rebar as a tie rod at a selected test location, then using a small drilling rig to drill into the rock surface from the shotcrete layer, conducting a pull-out test using the pre-embedded rebar, and calculating the bond strength. It can be seen that both testing methods require pre-embedded specimens or rebar installation, and involve processes such as the curing of the rebar adhesive. The preliminary preparation work is complex, time-consuming, and labor-intensive, and there is a risk of rebar detachment causing test failure.

[0003] Application / Patent No.: CN202123285650.X, relating to "a test device for on-site testing of the bond strength of shotcrete," mainly addresses the safety hazards posed by the heavy reaction frame and jacks used in on-site testing due to their weight. It proposes a test device that uses casters to move the test device to a designated position and adjusts the horizontal height of the jacks via a threaded support shaft, thus optimizing the horizontal movement and height adjustment of the test equipment. However, it does not optimize or improve the bond strength testing process itself; only the auxiliary operation aspects of the test are improved.

[0004] Patent application number: 201910354257.X, patent title: Device for on-site testing of the bond strength between shotcrete and surrounding rock. This invention proposes pre-installing steel molds and reaction frames during shotcrete construction, and then conducting bond strength tests on the cured specimens after they have reached the required age. However, it is only applicable to bond strength testing when pre-installed components are present during construction, and not to bond strength testing of hardened shotcrete without pre-installed components. Its applicability is limited, and the preparation work is time-consuming and labor-intensive.

[0005] Patent application number: CN201910552316.4, patent title: A test device and method for testing the bond strength between rock and shotcrete. The method proposes fixing a T-shaped mold onto a T-shaped rock, spraying shotcrete into the mold, curing it to the required age, and then conducting a pull-out test to determine the bond strength. However, this method requires high precision in rock processing and shaping, increasing the workload in the early stages. It is also unsuitable for testing the bond strength of hardened concrete, limiting its applicability and complicating the preliminary preparation.

[0006] The main drawbacks of the above methods are: 1. The pre-preparation work for using embedded parts is complex, time-consuming, and labor-intensive; this is mainly manifested in the need for embedded parts to meet the force support and transmission during pull-out. 2. The applicable time frame is limited, only applicable to the construction period. This is manifested in the need to embed auxiliary test embedded parts before shotcrete, and the embedding of embedded parts cannot be carried out after the shotcrete has hardened. 3. The traditional method of post-installation of rebar is not only time-consuming and complex in preparation, but also cannot guarantee whether the rebar can evenly transmit the tensile force to the shotcrete, resulting in poor test accuracy. 4. On-site leveling is difficult, and it is impossible to guarantee that the specimen is under axial tension, resulting in results that are too large or too small. 5. Manual operation is complex, calculation is inconvenient, and results cannot be displayed in real time. Summary of the Invention

[0007] The purpose of this invention is to provide a test device and operating method for on-site shotcrete bond strength testing.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A field shotcrete bond strength testing device includes a reaction force frame, a telescopic support leg, a hydraulic cylinder mechanism, and a ring hoop structure. The reaction force frame includes a ring support base and a shell. The shell is located on the top of the ring support base. The shell is equipped with a laser leveling device, an operation panel and display screen, and a high-precision pressure gauge. The telescopic support leg is connected to the bottom of the ring support base. A fine-tuning bolt is provided at the connection between the telescopic support leg and the ring support base. The hydraulic cylinder mechanism is located in the center of the ring support base. The ring hoop structure is connected to the bottom of the hydraulic cylinder mechanism. The ring support base contains a pressure pump for supplying hydraulic oil, an electric pump for depressurizing the hydraulic pump and returning hydraulic oil, and a controller. The hydraulic cylinder mechanism, the ring hoop structure, the laser leveling device, the high-precision pressure gauge, the operation panel and display screen, the pressure pump and the electric pump are electrically connected to the controller.

[0010] Preferably, the retractable support frame includes a first connecting rod located at the top and hollowed out in the middle, and a second connecting rod located at the bottom for filling the hollowed-out part of the first connecting rod. The first connecting rod and the second connecting rod can be relatively displaced. The first connecting rod and the second connecting rod are fixed together by fixing bolts. The lower end of the second connecting rod is provided with a frame hole for matching the expansion screw.

[0011] Preferably, the hydraulic cylinder mechanism includes a hydraulic cylinder body, an annular piston rod, an upper support plate, a connecting steel structure for the upper and lower support plates, a lower support plate, an oil return port, and an oil outlet. The annular piston rod of the hydraulic cylinder body is connected to the bottom of the upper support plate. The lower support plate is arranged parallel to the upper support plate directly below it. The upper support plate and the lower support plate are fixedly connected by the connecting steel structure for the upper and lower support plates. The bottom of the lower support plate is provided with a ring-shaped shrink guide rail.

[0012] Preferably, the number of the ring structures is at least three and they are evenly distributed in a ring at the bottom of the lower support plate. Each ring structure includes a retractable support rod, an arc-shaped ring, and a driving mechanism. The upper end of the retractable support rod is connected to the lower support plate through the ring retraction guide rail and is radially displaced along the ring retraction guide rail under the action of the driving mechanism. The lower end of the retractable support rod is connected to the arc-shaped ring. The driving mechanism includes a push rod motor fixed at the center of the bottom of the lower support plate. The push rod of each push rod motor faces the corresponding retractable support rod and is connected to one side of the retractable support rod.

[0013] Preferably, the ring structure is made of high-strength steel.

[0014] An operating method for a field shotcrete bond strength testing device, characterized by comprising the following steps:

[0015] Step 1: Select the test site. The test site should be representative, with at least 5 test points selected.

[0016] Step 2: Prepare test cores. Drill cylindrical cores with shotcrete at the selected location and clean the debris around the cores.

[0017] Step 3: Bond strength test. Bond strength tests were conducted on the five test cores, and the bond strength was calculated.

[0018] Step 4: Determining the Test Results:

[0019] (1) The average value of the five test results is taken as the bond strength between the shotcrete and the surrounding rock, accurate to two significant figures after the decimal point;

[0020] (2) When two or fewer test results exceed 25% of the average of five test results, these results should be discarded, and the average of the remaining valid test results should be used as the bond strength between the shotcrete and the surrounding rock.

[0021] (3) If three or more test results exceed 25% of the average of five test results, the test group is invalid and the reasons should be analyzed and the test should be repeated.

[0022] Preferably, the test site in step 1 above should be free of defects such as cracks, voids, leaks, and exposed aggregates, so as to better reflect the engineering quality of the construction site to be evaluated.

[0023] Preferably, in step 2 above, a small core drill with a diamond drill bit is used to extract cores at the selected shotcrete location. The diameter of the core tube is in the range of 50 to 200 mm. The core is drilled vertically to the shotcrete layer to a rock depth of not less than 20 mm to form a cylindrical rock core with shotcrete. The debris around the rock core is cleaned with a pressure water gun.

[0024] Preferably, step 3, the bond strength test and the calculation of the bond strength results, specifically includes the following steps:

[0025] (1) Setting test parameters

[0026] Press and hold the power button to start the equipment. Input the test parameters through the operation panel, such as the core diameter, the initial angle between the core fracture and the cross section is set to 0°, and the applied tensile force speed is 0.1 kN / s. You can also select the display content through the operation panel, such as the bond strength, maximum tensile force, tensile force time history curve, pull-out test speed, etc.

[0027] (2) Fixing and leveling

[0028] Select a ring structure of appropriate length according to the thickness of the shotcrete or the length of the rock core, and install it on the lower support plate; fix the telescopic support frame with expansion bolts, perform rough leveling through the telescopic device on it, and perform precise leveling with the help of a laser leveling instrument through the fine leveling bolts;

[0029] (3) Start the equipment

[0030] Briefly press the start / stop button to begin the test. The ring structure contracts radially along the guide rail, pressing against the core surface; the pressure pump provides hydraulic pressure, which is transmitted to the hydraulic cylinder. The annular piston rod of the hydraulic cylinder presses against the upper support plate, and the force is transmitted to the ring structure through the lower support plate, ultimately subjecting the core to an outward axial pull-out force.

[0031] (4) Turn off the equipment

[0032] When the pressure value on the display screen stops increasing, indicating that the contact surface between the sprayed concrete and the rock has broken off, briefly press the start / stop button. The electric pump will then discharge the hydraulic oil back to its own reservoir, and the test is complete.

[0033] (5) Disassembly of equipment

[0034] Remove the test equipment from the sprayed concrete surface;

[0035] (6) Calculation of results

[0036] Measure the angle θ between the fracture surface and the cross section of the rock core and input it into the instrument; the instrument automatically calculates the bond strength between the shotcrete and the surrounding rock according to the following formula and saves it automatically.

[0037]

[0038] In the formula R c — Bond strength between shotcrete and surrounding rock, MPa;

[0039] P c —Core tensile load, N;

[0040] A c — Cross-sectional area of ​​the rock core during tensile testing, mm 2 ;

[0041] θ—Angle between the fracture surface of the rock core and the cross section, °.

[0042] This invention provides a field shotcrete bond strength testing device and operating method. A novel ring structure is designed to be directly fixed to a rock core, transmitting axial outward tensile force, eliminating the complex and time-consuming processes of rebar installation and pre-embedded parts. A telescopic support frame, precision leveling bolts, and a laser leveling device are designed to ensure an axial outward pull-out force perpendicular to the shotcrete surface. A reaction force frame, operating panel and display screen, hydraulic cylinder, controller, pressure pump, electric pump, and high-precision pressure gauge are designed to achieve simple operation, real-time display, labor saving, improved efficiency, and safety and reliability. The advantages of this invention are:

[0043] 1. No need for pre-embedded parts, no need for rebar installation, no need to wait for materials to harden, the rock core is directly fixed with the hoop structure, less preparation work, saving time and improving efficiency;

[0044] 2. The three legs of the base are adjustable in length for coarse leveling and fine leveling using a laser leveling instrument via micro-adjustment bolts, ensuring tension on the shaft and improving detection accuracy.

[0045] 3. The integrated operation screen and display screen can adjust the loading speed and display it in real time, and can also display the force value in real time;

[0046] 4. Input the core diameter and the angle between the core fracture and the cross section, and the bond strength will be automatically calculated.

[0047] 5. It is highly practical and has a wide range of applications. It can also be tested after the concrete has hardened, as long as the test age is met.

[0048] 6. The supporting structure has high rigidity and is fixed with expansion bolts, ensuring high safety and preventing the equipment from suddenly falling and causing damage after the test.

[0049] 7. Integrated design, simple operation, easy to carry, and only one person is needed to complete the experiment on site. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the structure during the experiment of this invention.

[0051] Figure 2 This is a front view of the present invention.

[0052] Figure 3 This is a top view of the present invention.

[0053] Figure 4 This is a partial structural diagram of the retractable support leg of the present invention.

[0054] Figure 5 This is a schematic diagram of the hydraulic cylinder mechanism of the present invention.

[0055] Figure 6 This is a bottom view of the connection between the support plate and the hoop structure of the present invention.

[0056] The attached figures are labeled as follows: 1-Reaction force frame, 11-Annular support base, 12-Outer shell, 2-Retractable support leg, 21-First connecting rod, 22-Second connecting rod, 221-Leg hole, 222-Expansion bolt, 23-Fixing bolt, 3-Hydraulic cylinder mechanism, 31-Hydraulic cylinder body, 32-Annular piston rod, 33-Upper support plate, 34-Upper and lower support plate connecting steel structure, 35-Lower support plate, 351-Ring hoop retractable guide rail, 36-Oil return port, 37-Oil outlet, 4-Ring hoop structure, 41-Retractable support rod, 42-Arc-shaped ring hoop, 43-Drive mechanism, 431-Push rod motor, 432-Push rod, 5-Laser leveling instrument, 6-Operation panel and display screen, 7-Pressure pump, 8-Electric pump, 9-Controller, 10-High-precision pressure gauge. Detailed Implementation

[0057] To make the technical means, creative features, objectives and effects of this invention easy to understand, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention.

[0058] Example

[0059] A field shotcrete bond strength testing device includes a reaction force frame 1, a telescopic support leg 2, a hydraulic cylinder mechanism 3, and a ring structure 4. The reaction force frame 1 includes an annular support base 11 and a shell 12. The shell 12 is located on the top of the annular support base 11. The shell 12 is equipped with a laser leveling device 5, an operation panel and display screen 6, and a high-precision pressure gauge 10. The telescopic support leg 2 is connected to the bottom of the annular support base 11. Fine-tuning bolts are provided at the connection between the telescopic support leg 2 and the annular support base 11. The hydraulic cylinder mechanism 3 is located in the center of the annular support base 11. The ring structure 4 is connected to the bottom of the hydraulic cylinder mechanism 3. The annular support base 11 contains a pressure pump 7 for supplying hydraulic oil, an electric pump 8 for depressurizing the hydraulic pump and returning hydraulic oil, and a controller 9. The hydraulic cylinder mechanism 3, the ring structure 4, the laser leveling device 5, the high-precision pressure gauge 10, the operation panel and display screen 6, the pressure pump 7, the electric pump 8, and the controller 9 are electrically connected.

[0060] The retractable support leg 2 can be fixed to the shotcrete surface by expansion bolts 222 passing through the leg holes 221 at the bottom, providing a fixed fulcrum; the length of the retractable support leg 2 can be adjusted by fixing bolts 23 to coarsely level the reaction force frame 1 and provide axial pull-out force perpendicular to the shotcrete surface; the upper part of the retractable support leg 2 is connected to the reaction force frame 1 by bolts, and the direction can be adjusted 360° to adjust the angle with the reaction force frame 1; the connection between the retractable support leg 2 and the reaction force frame 1 is provided with fine-tuning bolts, which can accurately level the equipment and ensure that the pull-out force on the rock core is a non-eccentric force.

[0061] The retractable support frame 2 includes a first connecting rod 21 located at the top and hollowed out in the middle, and a second connecting rod 22 located at the bottom for filling the hollowed-out part of the first connecting rod 21. The first connecting rod 21 and the second connecting rod 22 can be displaced relative to each other to change the length of the support frame.

[0062] The reaction force frame 1 consists of a high-strength annular support base 11 and an outer shell 12. The annular support base 11 is connected to the telescopic support leg 2 by bolts, and the inner wall of the annular frame is integrated with the hydraulic cylinder. The outer shell 12 is equipped with a laser leveling device 5, an operation panel, and a display screen 6. The laser leveling device 5 is used to ensure that the force is perpendicular to the sprayed concrete surface during the pulling operation; the operation panel and display screen 6 can be used to control the equipment operation and display relevant data.

[0063] The operation panel and display screen 6 include a display screen, power switch, settings, playback, start / stop, and directional buttons. The display screen shows the bond strength, maximum tensile force, time history curve of tensile force, pull-out test speed, etc. The settings panel allows input of information such as the core diameter, the angle between the core fracture and the cross-section, and the design strength. The settings panel also allows setting the pull-out test speed and recording the axial displacement of the core. The settings panel allows selection of displaying the bond strength, maximum tensile force, time history curve of tensile force, pull-out test speed, etc. The playback panel is used to view the data or images of the test. The start / stop buttons control the start and stop of the electric pump 8, pressure pump 7, hydraulic cylinder mechanism 3, etc. The directional buttons are used to move the cursor, increase or decrease values, and confirm.

[0064] The hydraulic cylinder mechanism 3 includes a hydraulic cylinder body 31, an annular piston rod 32, an upper support plate 33, a connecting steel structure 34 for the upper and lower support plates, a lower support plate 35, an oil return port 36, and an oil outlet 37. The annular piston rod 32 of the hydraulic cylinder body 31 is connected to the bottom of the upper support plate 33, and the force is mainly provided by oil pressure. The lower support plate 35 is arranged parallel to the upper support plate 33. The upper support plate 33 and the lower support plate 35 are fixedly connected by the connecting steel structure 34 for the upper and lower support plates, which can transmit the force. The bottom of the lower support plate 35 is provided with a ring-shaped retraction guide rail 351. When the test starts, the controller 9 will control the push rod 432 of the push rod motor 431 to move and drive the retractable support rod 41 to retract radially along the ring-shaped retraction guide rail 351 to ensure that the ring force between the rod and the rock core is large enough.

[0065] Furthermore, the materials used in the hydraulic cylinders are all high-rigidity and high-strength materials, and they do not deform due to their own reasons when subjected to pressure, thus affecting the test results.

[0066] The controller 9 can issue commands such as start and stop to the hydraulic cylinder mechanism 3, the ring structure 4, the pressure pump 7, the electric pump 8, and the high-precision pressure gauge 10. Upon receiving a start command from the controller 9, the hydraulic pressure from the pressure pump 7 is transmitted to the cylinder body of the hydraulic cylinder through the oil pipe. The pressure acts directly on the upper support plate 33 through the ring piston rod, and is transmitted to the lower support plate 35 through the steel structure connecting the upper and lower support plates 34. The ring structure 4 then transmits the force to the rock core, providing it with an axial force perpendicular to the sprayed concrete surface and pulling outwards. After the test, the controller 9 issues a stop command, and the electric pump 8 discharges the hydraulic oil from the hydraulic cylinder back to its reservoir through the oil pipe, restoring the hydraulic cylinder to its original state. The force value on the rock core during the process is recorded by the high-precision pressure gauge 10. The controller 9 also controls the equipment's parameter settings, operating speed, and display items.

[0067] The number of the ring structures 4 is at least three, and they are evenly distributed in a ring shape at the bottom of the lower support plate 35. Each ring structure 4 includes a retractable support rod 41, an arc-shaped ring 42, and a driving mechanism 43. The upper end of the retractable support rod 41 is connected to the lower support plate 35 via the ring retraction guide rail 351, and under the action of the driving mechanism 43, it moves radially along the ring retraction guide rail 351 to ensure the fit between the ring structure 4 and the rock core. The lower end of the retractable support rod 41 is connected to the arc-shaped ring 42. The driving mechanism 43 includes components fixed to the lower support plate 35. A push rod motor 431 is located at the center of the bottom of plate 35. Each push rod 432 of the push rod motor 431 faces the corresponding retractable support rod 41 and is connected to one side of the retractable support rod 41. An arc-shaped hoop 42 is connected to the retractable support rod 41, primarily used to increase the contact area with the rock core. Different friction-increasing patterns are distributed on the inner surfaces of both the arc-shaped hoop 42 and the retractable support rod 41 to increase the friction between the hoop structure and the rock core, preventing relative displacement. The outer surfaces of the arc-shaped hoop 42 and the retractable support rod 41 are relatively smooth to reduce the influence of the rock on the experiment. The hoop structure 4 is selected with different lengths according to the thickness of the shotcrete to ensure effective force transmission.

[0068] Furthermore, the ring structure 4 is preferably made of high-strength steel, which can withstand sufficient tensile force without deformation, and can meet the requirements of the ring core and provide sufficient friction.

[0069] Furthermore, the hoop structure 4 is replaceable. The inner surfaces of the arc-shaped hoop 42 and the retractable support rod 41 can be selected with friction threads, friction protrusions, etc. The hoop structure 4 has different lengths, and the appropriate length and type can be selected according to the thickness of the shotcrete, the size of the rock core, etc.

[0070] The pressure pump 7 mainly provides hydraulic oil to ensure that the hydraulic cylinder can provide sufficient force; the electric pump 8 is mainly used for depressurization of the hydraulic pump and hydraulic oil return; the high-precision pressure gauge 10 can record the force value.

[0071] The laser leveling device 5 emits a laser beam parallel to the axial direction of the ring structure 4 and the ring piston rod 32. After leveling, the device should be perpendicular to the sprayed concrete test surface to ensure that it provides an axial force perpendicular to the test surface during the pull-out test, thus ensuring the accuracy and effectiveness of the test values. First, rough leveling is performed using the telescopic support legs, so that the laser beam is nearly perpendicular to the test surface; then, with the aid of tools such as a triangle ruler, the device is precisely leveled using fine leveling bolts.

[0072] On the other hand, the present invention also provides a test method for the bond strength of shotcrete in situ, comprising the following steps:

[0073] Step 1: Selection of test sites. The selection of test sites should be representative, with at least 5 measuring points selected.

[0074] Step 2: Prepare test cores. Drill cylindrical cores with shotcrete at the selected location and clean the area around the cores to remove debris.

[0075] Step 3: Bond strength test. Bond strength tests were conducted on each of the five test cores, and the bond strength was calculated.

[0076] Step 4: Determining the Test Results:

[0077] (1) The average value of the five test results is taken as the bond strength between the shotcrete and the surrounding rock, accurate to two significant figures after the decimal point.

[0078] (2) When two or fewer test results exceed 25% of the average of five test results, these results should be discarded, and the average of the remaining valid test results should be used as the bond strength between the shotcrete and the surrounding rock.

[0079] (3) If three or more test results exceed 25% of the average of five test results, the test group is invalid and the reasons should be analyzed and the test should be repeated.

[0080] In some preferred implementation schemes, representative test sites are selected under the joint witness of the owner, supervisor, and testing unit. The test sites should be free of defects such as cracks, voids, leaks, and exposed aggregates, and should be able to reflect the engineering quality of the construction site to be evaluated.

[0081] In some preferred implementations, a small coring machine with a diamond drill bit is used to extract cores at selected shotcrete locations. The diameter of the core tube ranges from 50 to 200 mm. The core is drilled vertically into the shotcrete layer to a depth of not less than 20 mm into the rock to form a cylindrical rock core with shotcrete. The area around the rock core is then cleaned with a pressure water gun to remove debris.

[0082] In some preferred implementations, step 3, the bond strength test and the calculation of the bond strength results, specifically includes the following steps:

[0083] (1) Set test parameters. Press and hold the power button to start the equipment. Input the test parameters through the operation panel, such as the core diameter, the initial angle between the core fracture and the cross section is set to 0°, and the applied tensile force speed is 0.1 kN / s. You can also select the display content through the operation panel, such as the bond strength, maximum tensile force, time history curve of tensile force, pull-out test speed, etc.

[0084] (2) Fixing and leveling. Select a ring structure of appropriate length according to the thickness of the shotcrete or the length of the rock core, and install it on the lower support plate; fix the telescopic support frame with expansion bolts, perform rough leveling through the telescopic device on it, and perform precise leveling with the help of a laser leveling instrument through the fine leveling bolts.

[0085] (3) Start the equipment. Briefly press the start / stop button to begin the test. The ring structure contracts radially along the guide rail and presses against the core surface; the pressure pump provides hydraulic pressure and transmits it to the hydraulic cylinder. The annular piston rod of the hydraulic cylinder presses against the upper support plate, and the force is transmitted to the ring structure through the lower support plate, ultimately causing the core to be subjected to an outward axial pull-out force.

[0086] (4) Shut down the equipment. When the pressure value on the display screen no longer increases, that is, when the contact surface between the sprayed concrete and the rock breaks off, briefly press the start / stop button, and the electric pump will discharge the hydraulic oil back to its own oil tank, and the test is completed.

[0087] (5) Dismantle the equipment. Remove the test device from the sprayed concrete surface.

[0088] (6) Result Calculation. Measure the angle θ between the fracture surface and the cross-section of the rock core and input it into the instrument. The instrument automatically calculates the bond strength between the shotcrete and the surrounding rock according to the following formula and saves the result automatically.

[0089]

[0090] In the formula R c — Bond strength between shotcrete and surrounding rock, MPa;

[0091] P c —Core tensile load, N;

[0092] A c — Cross-sectional area of ​​the rock core during tensile testing, mm 2 ;

[0093] θ—Angle between the fracture surface of the rock core and the cross section, °.

[0094] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. An apparatus for testing the bond strength of shotcrete in situ, characterised in that, Including counterforce skeleton (1), telescopic support foot stand (2), hydraulic cylinder mechanism (3), hoop structure (4), the counterforce skeleton (1) includes annular support base (11) and shell (12), the top of annular support base (11) is equipped with the shell (12), the shell (12) is equipped with laser leveling instrument (5), operating panel and display screen (6) and high-precision pressure gauge (10), the bottom of annular support base (11) is connected with telescopic support foot stand (2), the connecting part of telescopic support foot stand (2) and annular support base (11) is provided with fine adjustment flat bolt, the center of annular support base (11) is equipped with hydraulic cylinder mechanism (3), the bottom of hydraulic cylinder mechanism (3) is connected with hoop structure (4), hoop structure (4) is made of high-strength steel material, the number of hoop structure (4) is at least three and is evenly distributed in the bottom of lower support plate (35), hoop structure (4) includes retractable support rod (41), arc hoop (42) and drive mechanism (43), the upper end of retractable support rod (41) is connected with lower support plate (35) through hoop contraction guide rail (351) and is displaced along hoop contraction guide rail (351) under the action of drive mechanism (43), the lower end of retractable support rod (41) is connected with arc hoop (42), drive mechanism (43) includes push rod motor (431) fixed at the bottom center of lower support plate (35), the push rod (432) of each push rod motor (431) is connected with retractable support rod (41) on the side corresponding to retractable support rod (41), the inside of annular support base (11) is provided with pressure pump (7) for providing hydraulic oil, electric pump (8) for pressure relief and hydraulic oil backflow of hydraulic pump and controller (9), hydraulic cylinder mechanism (3), hoop structure (4), laser leveling instrument (5), high-precision pressure gauge (10), operating panel and display screen (6), pressure pump (7) and electric pump (8) are electrically connected with controller (9).

2. A device for testing the bond strength of shotcrete in situ according to claim 1, characterized in that Telescopic support foot stand (2) includes first connecting rod (21) located in upper portion and middle hollow and second connecting rod (22) located in lower portion for filling hollow part of first connecting rod (21), first connecting rod (21) and second connecting rod (22) can be relatively displaced, first connecting rod (21) and second connecting rod (22) are fixed by fixed bolt (23), the lower end of second connecting rod (22) is provided with foot stand hole (221) matched with expansion screw (222).

3. A device for testing the bond strength of shotcrete as claimed in claim 1, wherein The hydraulic cylinder mechanism (3) comprises a hydraulic cylinder body (31), an annular piston rod (32), an upper support plate (33), an upper and lower support plate connecting steel structure (34), a lower support plate (35), an oil return port (36), and an oil outlet (37), the annular piston rod (32) of the hydraulic cylinder body (31) is connected with the bottom of the upper support plate (33), the lower support plate (35) is arranged in parallel below the upper support plate (33), the upper support plate (33) and the lower support plate (35) are fixedly connected through the upper and lower support plate connecting steel structure (34), and the bottom of the lower support plate (35) is provided with a ring hoop contraction guide rail (351).

4. The method of operating a field sprayed concrete bond strength test device of claim 1, wherein, The method comprises the following steps: Step 1: test site selection, the test site selection should be representative, and at least 5 test points are selected; Step 2: making test cores, drilling cylindrical cores with sprayed concrete at the selected positions, and cleaning the peripheral impurities of the cores; Step 3: bonding strength test, respectively testing the bonding strength of the 5 test cores, and calculating the bonding strength; Step 4: test result determination: (1) taking the average value of the 5 test results as the bonding strength of the sprayed concrete and the surrounding rock, accurate to two decimal places; (2) when 2 or fewer test results exceed 25% of the average value of the 5 test results, the results should be discarded, and the average value of the remaining valid test results is taken as the bonding strength of the sprayed concrete and the surrounding rock; (3) when 3 or more test results exceed 25% of the average value of the 5 test results, the test is invalid, and the test should be retested after analyzing the reasons.

5. The method of operating a field sprayed concrete bond strength test device of claim 4, wherein, The test site in step 1 should be free of defects such as cracking, cavities, water leakage, and exposed aggregate, and can better reflect the engineering quality of the construction site to be evaluated.

6. The method of operating a field sprayed concrete bond strength test device of claim 4, wherein, In step 2, a small coring machine with a diamond drill bit is used to take cores at the selected sprayed concrete positions, the core barrel diameter ranges from 50 to 200 mm, and the drilling depth into the rock is not less than 20 mm perpendicular to the sprayed concrete layer, forming a cylindrical core with sprayed concrete, and the peripheral impurities of the core are cleaned with a pressure water gun.

7. The method of operating a field sprayed concrete bond strength test device of claim 4, wherein, The bonding strength test in step 3 and the bonding strength result calculation specifically comprise the following steps: (1) setting test parameters Hold the key, start the device, and input test parameters through the operation panel, such as core diameter, initial angle of core fracture cross section 0°, applied tension speed 0.1 kN / s, etc.; the display content can also be selected through the operation panel, such as bonding strength, maximum tension, tension time curve, and pull-out test speed, etc.; (2) fixing and leveling According to the thickness of the sprayed concrete or the length of the core, select the appropriate length of the ring hoop structure and install it on the lower support plate; use expansion screws to fix the telescopic support legs, coarsely adjust the level through the telescopic device, and accurately adjust the level through the precision leveling screw with the help of the laser leveling instrument; (3) starting the device Short press the start-stop button to start the test. The ring structure is shrunk along the guide rail and is pressed on the surface of the core. The pressure pump provides hydraulic pressure to the hydraulic cylinder. The annular piston rod of the hydraulic cylinder pushes against the upper support plate. The force is transmitted to the ring structure through the lower support plate. Finally, the core is subjected to an outward axial pulling force. (4) Turn off the equipment When the pressure value on the display screen no longer increases, that is, the shotcrete and the rock contact surface are pulled apart and separated, short press the start-stop button. The electric pump discharges the hydraulic oil back to its own oil tank, and the test is completed. (5) Disassemble the equipment Remove the test device from the shotcrete surface. (6) Result calculation Measuring the intersection angle of core fracture plane and cross section and input into the instrument; the instrument automatically calculates the bond strength of the shotcrete and surrounding rock according to the following formula and automatically saves it; ； In the formula — Bond strength of shotcrete to surrounding rock, MPa; - Core break load, N; Core tensile cross-sectional area, mm2 2 ; Core fracture plane intersection with cross section, °.

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