A device and method for in-situ rapid composite shear test of tunnel surrounding rock

Abstract

The application discloses a kind of tunnel surrounding rock in situ rapid composite shear test device and method, including liquid-electric servo control system, data acquisition system and limiting system, utilize surrounding rock natural counterforce support experimental device, avoid additional counterforce system arrangement, simplify experimental operation process, reduce the damage to surrounding rock, while improving experimental efficiency.The design of modular, lightweight experimental device can adapt to various experimental scenarios such as tunnel floor or sidewall, supports quick installation and disassembly, and adapts to complex geological conditions.The introduction of liquid-electric servo control system and high-precision sensor realizes real-time acquisition, transmission and automatic analysis of experimental data, improves the accuracy and repeatability of experimental results.It solves how to efficiently and accurately determine the shear mechanical properties of tunnel surrounding rock in rock mass mechanics in situ experiment, and enhances the portability of experimental device installation, reduces excessive disturbance to surrounding rock during the experiment.

Description

Technical Field

[0001] This invention relates to tunnel engineering, specifically to a rapid in-situ composite shear test device and method for tunnel surrounding rock. Background Technology

[0002] Surrounding rock is a primary research object in tunnel engineering, bearing significant pressure. The purpose of rock strength testing is to evaluate the mechanical properties of rock under various external stresses, thereby providing a scientific basis for engineering design, construction, and safety assessment. Existing rock strength testing methods are mainly divided into two types: laboratory testing methods and in-situ testing methods. In-situ testing, because it can be conducted in the natural environment of the rock, preserving the integrity of the surrounding rock structure, and considering the influence of in-situ stress, confining pressure, rock layer distribution, joints, and fractures, makes the test results more reflective of the actual bearing capacity and strength of the rock mass.

[0003] Currently, there are two main approaches to in-situ rock testing. The first approach involves in-situ borehole testing, where a hole is drilled in the surrounding rock to allow the testing device to be placed directly to test rock strength. Chinese patent application CN118730761 A describes a sampling-free in-situ borehole testing device. This device uses a support shoe to fix the equipment inside the hole, and a hydraulic system drives a cutting tool to continuously cut and test the rock's shear strength. Sensors collect displacement and pressure data to calculate the rock's shear strength parameters. The second approach involves cutting a cubic specimen, placing a shear box on the specimen, and then applying horizontal and vertical loads. The instrument for this approach mainly consists of three parts: a normal loading device, a shear loading device, and a measuring device.

[0004] Normal load application devices generally include four types: surcharge devices, ground anchor devices, horizontal inclined support reaction devices, and top wall support devices. The main equipment should include a surcharge platform or ground anchor or horizontal inclined support reaction device that provides reaction force, as well as supporting I-beams, force transmission columns, hydraulic jacks, upper steel plates, rollers, and lower steel plates, etc. Shear load devices should include shear boxes, top pressure steel plates, rollers, hydraulic jacks, rear seat steel plates, and rear supports, etc. Measuring devices include hydraulic pressure gauges, pressure sensors, dial indicators, electronic displacement gauges, spirit levels, and compasses, etc.

[0005] Patent CN221650110U, authorized by patent number CN221650110U, proposes an anchored in-situ direct shear test device for soil and rock, suggesting a device that uses ground anchors to fix the experimental instruments and provide normal reaction force. Patent CN118464672A, published on application, proposes a device scheme that uses anchor rods to fix a reaction frame and arranges horizontal and vertical loading devices on the reaction frame. Patent CN204330502U, authorized by patent number CN204330502U, proposes a direct shear test device with a built-in counterweight platform, where a counterweight provides vertical reaction force to the vertical jacks; this device requires excavation of an experimental pit for use. Horizontal jacks are placed between the surrounding rock and the sample, with the surrounding rock providing reaction force to the horizontal jacks. Patent CN208937435U, authorized by patent number CN208937435U, proposes a landslide rock mass shear resistance device. This device utilizes the anti-slip device in the sample pit to provide vertical reaction force for the experiment and avoids eccentric moments during the experiment by adding flat jacks; this device also requires excavation of an experimental pit for use.

[0006] The rock strength parameters measured by the tool cutting method only apply to the local surrounding rock in front of the tool, and cannot objectively reflect the influence of weak parts such as the rock structure on the rock strength. It is difficult to demonstrate the advantage of the in-situ direct shear test in ensuring the integrity of the surrounding rock structure.

[0007] Direct shear testing methods using shear boxes or shear plates all require specialized reaction devices. Overloading devices require additional normal counterweights; ground anchor devices require specially constructed anchor bolts to provide reaction force; horizontal inclined support reaction devices require machining the sidewalls at a certain angle, and to ensure effective load bearing, a relatively deep foundation pit needs to be excavated; top wall support devices generally require applying shear reaction force using the tunnel arch, and the equipment is complex. All four of these devices require cutting the specimen to create five free surfaces, resulting in a large amount of additional work, and the specimen processing inevitably causes significant disturbance to the surrounding rock.

[0008] Current in-situ direct shear testing methods for rock masses (such as tool cutting or single-shear plane tests) cannot fully reflect the true shear mechanical properties of the surrounding rock, especially in terms of comprehensive evaluation capabilities for complex structural planes and weak points in the surrounding rock. Furthermore, traditional experimental devices (such as surcharge devices and ground anchor devices) require complex reaction force systems for support, causing significant disturbance to the surrounding rock, and making experimental preparation cumbersome and inefficient. Existing experimental devices are typically bulky and complex to install, making them difficult to adapt to diverse field conditions such as tunnel floors or sidewalls, particularly in confined spaces or complex geological environments. Secondly, some devices require excavating large experimental trenches or performing additional sample processing, increasing construction costs and experimental difficulty. Finally, traditional experimental data acquisition methods rely on manual recording or low-precision sensors, making experimental data susceptible to human interference and resulting in insufficient reliability of experimental results. The lack of automated data analysis and real-time monitoring methods further reduces experimental efficiency and fails to meet the demands of modern engineering for rapid and accurate experimental results. Summary of the Invention

[0009] The purpose of this invention is to address the shortcomings of existing technologies by proposing an in-situ rapid composite shear testing device and method for tunnel surrounding rock. This composite shear test method preserves the bottom and side shear surfaces, enabling a more realistic reflection of the overall mechanical properties of the surrounding rock, particularly the impact of complex joints and weak structural surfaces on shear strength. Utilizing the natural reaction force of the surrounding rock to support the experimental device avoids the need for additional reaction system arrangements, simplifies the experimental operation process, reduces damage to the surrounding rock, and improves experimental efficiency. The modular and lightweight design of the experimental device is adaptable to various experimental scenarios, such as tunnel floor slabs or sidewalls, and supports rapid installation and disassembly, adapting to complex geological conditions. The introduction of a hydraulic-electro-servo control system and high-precision sensors enables real-time acquisition, transmission, and automatic analysis of experimental data, improving the accuracy and repeatability of experimental results. This invention solves the problem of how to efficiently and accurately determine the shear mechanical properties of tunnel surrounding rock in in-situ rock mechanics experiments, while enhancing the portability of the experimental device and reducing excessive disturbance to the surrounding rock during the experimental process.

[0010] This invention is achieved through the following technical solution: an in-situ rapid composite shear testing device for tunnel surrounding rock, comprising a hydraulic-electro-servo control system, a data acquisition system, and a limiting system: The electro-hydraulic servo control system includes an axial jack, a normal jack, a hydraulic pump, an intelligent control terminal, cables, hydraulic pipes, and shear plates. The bottoms of the axial jack and the normal jack are both mounted on the device base, and the tops of both are connected to shear plates. The axial jack and the normal jack are connected to the hydraulic pump through hydraulic pipes, and the hydraulic pump is connected to the intelligent control terminal through cables. The data acquisition system includes a displacement sensor, a pressure sensor, and a data relay processor. Displacement sensors are installed on all shear plates, and pressure sensors are installed on both the axial jack and the normal jack. The displacement sensors and pressure sensors are connected to the data relay processor, which is connected to an intelligent control terminal. The limiting system includes a device base, a jack base, and limiting slots. The device base is L-shaped and has limiting slots in the x and y directions. The jack base of the axial jack is installed in the limiting slot in the x direction, and the jack base of the normal jack is installed in the limiting slot in the y direction.

[0011] Furthermore, a strain sensor is also connected to the data relay processor.

[0012] Furthermore, a limiter is provided in the limiting slot of the axial jack, and a slide rail and rollers are provided in the limiting slot of the normal jack.

[0013] Furthermore, an end limiting block is provided at the end of the device base.

[0014] Furthermore, a rigid rubber pad is connected to the shear plate.

[0015] This invention also provides a method for in-situ rapid composite shear testing of tunnel surrounding rock, comprising the following steps: (1) Experimental preparation: Select the test location, determine the specimen specifications and different levels of normal load, and estimate the shear load required for different specimens; (2) Sample preparation: Prepare cubic rock samples, each with four free planes (front, back, top, and sides), and ensure that the surfaces of each plane are flat. Also, excavate test trenches. (3) Formal test: Install the above-mentioned device to ensure that the forces of the normal jack and the axial jack pass through the centroid of the sample. Issue a command at the intelligent control terminal to perform an initial push, so that both the axial jack and the normal jack are lifted until the shear plate or hard rubber pad is in close contact with the rock sample. Conduct the test according to the normal load set in the test preparation stage, and control the axial jack to push the rock sample until shear failure occurs. (4) Method for obtaining the shear parameters of the specimen: Assuming the surrounding rock is an isotropic material, the normal stress on the specimen... sum of shear stress It can be calculated using the following formula: In the formula: --Normal stress (MPa) on the side of the specimen; --Shear stress at the bottom of the specimen (MPa); --Side shear stress of the specimen (MPa); --The sum of the shear stress on the bottom surface and the shear stress on the side surface of the specimen; --The coefficient of friction of the limiting device; F--The axial thrust of the jack during shearing (N); N -- the thrust of the normal jack (N); T1 -- Shear force (N) on the shear surface of the specimen. T2 -- Axial shear force (N) on the bottom shear surface of the specimen; T3 -- Normal shear force (N) on the bottom shear surface; A -- Area of ​​the cube sample (mm²) 2 ); During the experiment, multiple direct shear failure tests were conducted with different normal forces N. The shear displacement s and the sum of the bottom and side shear stresses of the specimens were recorded in real time during the tests. After the test, the shear displacement s was plotted as the abscissa and the shear stress was plotted as the ordinate. Plot the shear stress under different normal forces, with the vertical axis as the ordinate. The relationship curve between shear displacement s and the normal stress is obtained from the result image. The peak shear stress on each curve is taken, and the rock mechanics parameters cohesion c and internal friction angle of the soil are derived by using formulas (5) and (6), respectively. ; (5) (6).

[0016] Furthermore, in step (1), the experimental location includes the tunnel floor, tunnel sidewall, or tunnel excavation face, and the surface of the selected location is processed to make the surface flat.

[0017] Furthermore, in step (2), the side length of the cube rock sample is slightly larger than that of the shear plate, and the dimensions of the test groove are 50cm wide and 100cm long.

[0018] Furthermore, in step (3), after the test is completed, the test trench is excavated along the test axis as needed, new specimens are cut, and other normal loads are set for the test.

[0019] In step (4), the influence of T3 is ignored, that is, the assumption in formula (1) is that... .

[0020] The beneficial effects of this invention are as follows: (1) This invention proposes an in-situ direct shear test device for rock mass that uses only the natural reaction force of the surrounding rock as normal support and does not require external reaction force, which simplifies the experimental preparation work in the construction environment and reduces the disturbance of the surrounding rock.

[0021] (2) The present invention proposes a direct shear test method with composite shear surface, which applies shear force to the bottom shear surface and the side shear surface of the same sample at the same time, so as to more comprehensively reflect the shear strength characteristics of the surrounding rock under actual conditions.

[0022] (3) Based on the composite shear surface theory, a calculation formula for shear strength parameters is proposed, taking into account experimental data such as normal stress, axial thrust and shear displacement, to improve the accuracy of experimental results.

[0023] (4) The modular design of the limiting structure ensures the accuracy of the loading direction, while the use of the rolling system reduces friction during the experiment and improves the stability of the device operation.

[0024] (5) The combination of the electrohydraulic servo system and the intelligent terminal is adopted to realize the automated operation of the entire experimental process, including real-time data acquisition, feedback and analysis, and precise control of the loading process through the electrohydraulic servo system.

[0025] (6) The device supports rapid installation and disassembly, adapts to complex experimental environments such as tunnel floor and sidewalls, and meets the convenience and diverse needs of in-situ experiments. It facilitates and enables convenient and quick in-situ direct shear tests on rock masses.

[0026] (7) This invention also proposes a corresponding method for deriving rock shear strength parameters. In addition to the four types of normal loading devices—surcharge devices, ground anchor devices, horizontal inclined support reaction devices, and top wall support devices—a device is proposed that utilizes the pit wall reaction force to provide the required support reaction force when applying normal loads. The experimental device is simple to operate, has a simple structure, and a clear principle. During the experiment, it minimizes disturbance to the surrounding rock and improves the accuracy of the experiment.

[0027] (8) The novel in-situ direct shear test method designed in this invention retains the original characteristics of the rock sample during the implementation process, so that the test results can better reflect the true shear mechanical properties of the surrounding rock.

[0028] (9) Only four free surfaces need to be cut during the equipment installation process, and only experimental grooves for placing the device need to be made. The workload is small, which reduces the workload during the experiment and the disturbance to the sample during the sample preparation process.

[0029] (10) The experimental data is automatically recorded during the experiment, and some parameters are automatically calculated, which simplifies the experimental process.

[0030] (11) An intelligent control system was used to conduct in-situ experiments to ensure that the stress on the sample increased uniformly during the experiment and to reduce experimental errors. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the overall device of the present invention.

[0032] Figure 2 This is a schematic diagram of the jack of the present invention.

[0033] Figure 3 This is a schematic diagram of the limiting system of the present invention.

[0034] Figure 4 This is a schematic diagram of the limiter of the present invention.

[0035] Figure 5 This is a schematic diagram of the end limiting block of the present invention.

[0036] Figure 6This is a schematic diagram of the sample and experimental groove after cutting during the experiment of this invention.

[0037] Figure 7 This is a schematic diagram of the installed and used state of the present invention.

[0038] Figure 8 This is a schematic diagram of the force analysis of the sample of the present invention.

[0039] Figure 9 This is a shear stress-displacement curve diagram of the present invention.

[0040] Figure 10 This is a schematic diagram of the test process in Embodiment 2 of the present invention.

[0041] Figure 11 This is a shear stress-displacement curve diagram in Embodiment 2 of the present invention.

[0042] In the diagram: 1-Axial jack, 2-Normal jack, 3-Hydraulic pump, 4-Displacement sensor, 5-Pressure sensor, 6-Jack base, 7-Intelligent control terminal, 8-Strain sensor, 9-Cable, 10-Data relay processor, 11-Hydraulic pipeline, 12-Device base, 13-Limit slot, 14-Roller, 15-Shearing plate, 16-Hard rubber pad, 17-Limiter, 18-End limit block. Detailed Implementation

[0043] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0044] Example 1

[0045] The electro-hydraulic servo control system includes: (1) The bottom of the axial jack 1 is mounted on the device base 12, and the top is connected to the shear plate 15. During the experiment, the axial jack 1 pushes the shear plate 15 to apply a thrust to the sample, causing the sample to be sheared and broken. For convenient transportation, the entire experimental device can be disassembled and installed. The jack base 6 is designed as a groove that can fit tightly with the device base 12.

[0046] (2) The normal jack 2 is installed on the vertical limiting device, which can move synchronously with the shear deformation of the sample while providing normal pressure to the sample.

[0047] (3) The hydraulic pump 3 uses a high-precision hydraulic-electro-servo control system to control the axial jack 1 and the normal jack 2 respectively. After the intelligent control terminal 7 issues the operation command, the system adjusts the pressure of the axial jack 1 and the normal jack 2 through the hydraulic pump 3. The hydraulic pump 3 is connected to the jacks through the hydraulic pipeline 11.

[0048] (4) Intelligent control terminal 7: During the experiment, the intelligent control terminal 7 can control the axial jack 1 and the normal jack 2 to fit tightly with the rock sample; control the normal jack 2 to apply a fixed normal force on the rock sample; control the axial jack 1 to push the rock sample to undergo shear failure, and record the thrust, displacement, strain and other data in real time during the failure process.

[0049] The data acquisition system includes: (1) Displacement sensor 4: A linear variable differential transformer (LVDT) displacement sensor is used as the shear displacement measuring device. The displacement sensor 4 is installed on the shear plate 15, and the data it directly measures is the lifting distance of the jack during the experiment.

[0050] (2) Pressure sensor 5, a high-precision spoke-type pressure sensor is used to measure the thrust applied to the sample by the jack in real time during the experiment. The pressure sensor 5 on the axial jack 1 is used to measure the axial thrust during the shear failure process. The pressure sensor 5 on the normal jack 2 is used to measure the normal thrust applied to the rock sample by the jack during the direct shear test.

[0051] (3) Strain sensor 8: Select a resistive strain sensor to measure the strain of the rock sample during the shear failure process.

[0052] (4) The data relay processor 10 is connected to the displacement sensor 4, pressure sensor 5 and strain sensor 8 via cable 9, receives sensor signals and feeds back experimental data to the intelligent control terminal 7.

[0053] The limit system includes: (1) The device base 12 is an L-shaped device base, whose main function is to support the jacks. To facilitate disassembly and transportation, a limiting slot 13 is provided on the device base 12 for the axial jack 1. To ensure that the axial jack 1 can be adjusted along the x-direction during device installation so that its force passes through the centroid of the sample, a limiter 17 is provided. The limiter 17 is a mechanical clamping limiting device to fix the position of the axial jack 1. The device base 12 is also provided with a limiting slot 13 for the normal jack 2 to restrict its movement in the z-direction. A slide rail is provided in the limiting slot 13. The jack base 6 of the normal jack 2 is provided with a corresponding slide rail and installed on the slide rail to ensure that the normal jack 2 can move in the direction of sample shear failure.

[0054] (2) Roller 14: In order to further ensure that the normal jack 2 can move along the shearing direction together with the shear box 15 during the straight shearing experiment, a roller 14 is set behind the base of the normal jack to reduce the friction of the normal jack 2 during movement.

[0055] (3) Limiter 17: In order to ensure that the thrust of the axial jack 1 passes through the centroid of the sample during the experiment, a mechanical clamping limit device is set to facilitate the adjustment of the x-direction movement of the axial jack 1.

[0056] (4) End limit block 18: To facilitate the installation and disassembly of the jack, an end limit block 18 is provided.

[0057] (5) Shear plate 15, whose main function is to apply the jack thrust evenly to the sample.

[0058] (6) Hard rubber pad 16 is attached to shear plate 15. Its main purpose is to ensure that shear plate 15 and sample are closely attached during shearing.

[0059] The experimental procedure is as follows: 1. Experimental preparation: (1) According to the requirements of the standard "Specification for On-site Direct Shear Test" (YS / T 5221-2019), the coefficient of friction between the normal jack 2 and the slide rail and / or roller 14 is determined as follows: .

[0060] (2) Before the experiment begins, the experimental location should be selected, such as the tunnel floor, tunnel sidewall, or tunnel excavation face. The surface of the selected location should be processed to make it as flat as possible.

[0061] (3) Based on the engineering characteristics of the experimental soil and rock mass and combined with the experience of similar projects, the specifications of the test specimens and the normal loads of different levels are determined, and the shear loads required for different test blocks are estimated based on these specifications.

[0062] 2. Sample preparation At the start of the experiment, cube-shaped rock samples (approximately 30cm on each side) were prepared using rock-breaking, grooving, and cutting equipment. The side length of the sample should be slightly larger than that of the shear plate. Each rock sample has four free planes: front, back, top, and sides. During the cutting process, the surface of the rock sample should be kept as flat as possible; if uneven, it should be leveled with mortar or concrete. The excavated test trench should be adapted to the dimensions of the equipment (approximately 50cm wide and 100cm long). The cut sample and the excavated test trench are shown below. Figure 6 As shown.

[0063] 3. Formal Trial (1) Install the equipment, ensuring that the forces exerted by the normal jack 2 and the axial jack 1 both pass through the centroid of the sample. The installed equipment should look like this: Figure 7 As shown.

[0064] (2) The control terminal issues an instruction to push the jacks initially, so that the axial jack 1 and the normal jack 2 are both lifted to the point where the hard rubber pad 16 fits tightly against the rock sample.

[0065] (3) The test is conducted according to the normal load set in the test preparation stage. The axial jack 1 is controlled to push the rock sample until shear failure occurs. The system will automatically record the experimental data in real time during the test.

[0066] (4) According to actual needs, continue to excavate the test trench along the test axis, cut new specimens, and set other normal loads for testing.

[0067] 4. Method for obtaining shear parameters of specimens The force analysis diagram of the specimen is as follows Figure 8 As shown, assuming the surrounding rock is an isotropic material, the axial thrust of jack 1 on the rear free surface during shearing is F, the normal force of jack 1 on the side free surface is N, and the frictional force experienced by the normal jack during its advance is P. The axial shear force on the bottom shear surface of the specimen is T2, the normal shear force on the bottom shear surface is T3, the shear force on the side shear surface of the specimen is T1, and the normal reaction force of the surrounding rock on the side shear surface is N. 1。 The shear stress on the bottom shear surface of the specimen is The shear stress on the side shear surface of the sample is The sum of the two is The normal stress on the specimen. sum of shear stress The following formulas can be used for calculation: In the formula: --Normal stress (MPa) on the side of the specimen; --Shear stress at the bottom of the specimen (MPa); --Side shear stress of the specimen (MPa); --The sum of the shear stress on the bottom surface and the shear stress on the side surface of the specimen, hereinafter referred to as "shear stress sum" (MPa); --The coefficient of friction of the limiting device; F--The axial thrust of the jack during shearing (N); N -- the thrust of the normal jack (N); T1 -- Shear force (N) on the shear surface of the specimen. T2 -- Axial shear force (N) on the bottom shear surface of the specimen; T3 -- Normal shear force (N) on the bottom shear surface; A -- Area of ​​the cube sample (mm²) 2 ) To simplify the calculation, the effect of T3 is ignored (the actual effect of T3 on the calculation results needs to be determined experimentally), that is, it is assumed that... During the experiment, multiple direct shear failure experiments were conducted with different normal forces N. The shear displacement s and the sum of the bottom and side shear stresses of the specimens were recorded in real time during the experiment. After the experiment, the shear displacement s was plotted as the abscissa and the shear stress as the ordinate. Plot the shear stress under different normal forces, with the vertical axis as the ordinate. The curve showing the relationship between the shear displacement s and the shear displacement s is as follows: Figure 9 As shown in the result image, the normal stresses are taken. and the peak shear stress on the corresponding curve Using formulas (5) and (6), the rock mechanical parameters c and c can be derived respectively. .

[0068] Cohesion of soil and rock mass and internal friction angle The least squares method can be used to calculate: (5) (6) Example 2:

[0069] The experimental procedure for a direct shear test on tunnel surrounding rock mainly composed of sandstone is as follows: (1) Before the test, based on experience from similar projects, the selected specimen size was 30cm×30cm×30cm. Four levels of normal stress were to be set: 10MPa, 20MPa, 30MPa, and 40MPa. To ensure the normal progress of the test, it was estimated that the maximum thrust that the axial jack could provide should not be less than the shear force of 1800kN required for the specimen to fail.

[0070] (2) Before the experiment begins, the experimental location is first selected, choosing a relatively flat tunnel floor or tunnel sidewall. The surface is then processed to make it as flat as possible.

[0071] (3) At the beginning of the experiment, first use rock breaking equipment, trenching equipment, cutting equipment, etc. to excavate the experimental trench (about 50cm wide and about 100cm long), and make a cube rock sample (30cm×30cm×30cm). After the cutting is completed, the top surface of the sample and the side subjected to shear load should be leveled with mortar.

[0072] (4) Install the equipment and adjust the thrust direction of the axial jack and the normal jack to pass through the center of the sample shaft. Ensure that all parts of the equipment are stably connected and turn on the power.

[0073] (5) Issue a command on the smart terminal to initially push the jack so that the shear plate is in close contact with the rock sample and the reaction plate of the device is in close contact with the side wall of the rock pit. Then, clear the experimental data and push the normal jack to apply a normal stress of 10 MPa to the sample.

[0074] (6) Apply pressure to the axial jack and begin the shearing test. The axial jack pushes the specimen and causes shearing failure. During the experiment, the system automatically records the lifting displacement value of the jack and the corresponding thrust, and automatically calculates the shear stress corresponding to each lifting displacement value.

[0075] (7) After each experiment, return the jack to its original position, clean the groove, continue cutting along the original axis of the experimental pit to form a sample, move the device to conduct the test, such as Figure 10 As shown. Continue to measure the experimental data when the normal force is 20MPa, 30MPa, and 40MPa.

[0076] (8) After the test, plot the shear stress-displacement curve as follows: Figure 11 As shown. Calculate according to formulas (5) and (6) respectively: Cohesion , =0.64, internal friction angle =32.62°.

[0077] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A method for in-situ rapid composite shear testing of tunnel surrounding rock, characterized in that, The in-situ rapid composite shear test device for tunnel surrounding rock includes a hydraulic-electric servo control system, a data acquisition system, and a limit system; The electro-hydraulic servo control system includes an axial jack (1), a normal jack (2), a hydraulic pump (3), an intelligent control terminal (7), a cable (9), a hydraulic pipeline (11), and a shear plate (15). The bottoms of the axial jack (1) and the normal jack (2) are both mounted on the device base (12), and the tops are both connected to the shear plate (15). The axial jack (1) and the normal jack (2) are connected to the hydraulic pump (3) through the hydraulic pipeline (11), and the hydraulic pump (3) is connected to the intelligent control terminal (7) through the cable (9). The data acquisition system includes a displacement sensor (4), a pressure sensor (5) and a data relay processor (10). The shear plate (15) is equipped with a displacement sensor (4), and the axial jack (1) and the normal jack (2) are equipped with a pressure sensor (5). The displacement sensor (4) and the pressure sensor (5) are connected to the data relay processor (10), and the data relay processor (10) is connected to the intelligent control terminal (7). The limiting system includes a device base (12), a jack base (6), and a limiting slot (13). The device base (12) is L-shaped and has limiting slots (13) in the x and y directions. The jack base (6) of the axial jack (1) is installed in the limiting slot (13) in the x direction, and the jack base (6) of the normal jack (2) is installed in the limiting slot (13) in the y direction. The in-situ rapid composite shear test method for tunnel surrounding rock includes the following steps: (1) Experimental preparation: Select the test location, determine the specimen specifications and different levels of normal load, and estimate the shear load required for different specimens; (2) Sample preparation: Prepare cubic rock samples, each with four free planes (front, back, top, and sides), and ensure that the surfaces of each plane are flat. Also, excavate test trenches. (3) Formal test: Ensure that the forces of the normal jack (2) and the axial jack (1) pass through the centroid of the sample. Issue a command at the intelligent control terminal (7) to perform an initial push, so that both the axial jack (1) and the normal jack (2) are lifted until the shear plate (15) or hard rubber pad (16) is in close contact with the rock sample. Conduct the test according to the normal load set in the test preparation stage, and control the axial jack (1) to push until the rock sample undergoes shear failure. (4) Method for obtaining the shear parameters of the specimen: Assuming the surrounding rock is an isotropic material, the normal stress on the specimen... sum of shear stress Calculate using the following formula: In the formula: --Normal stress (MPa) on the side of the specimen; --Shear stress at the bottom of the specimen (MPa); --Side shear stress of the specimen (MPa); --The sum of the shear stress on the bottom surface and the shear stress on the side surface of the specimen; --The coefficient of friction of the limiting device; F--The axial thrust of the jack during shearing (N); N -- the thrust of the normal jack (N); T1 -- Shear force (N) on the shear surface of the specimen. T2 -- Axial shear force (N) on the bottom shear surface of the specimen; T3 -- Normal shear force (N) on the bottom shear surface; A -- Area of ​​the cube sample (mm²) 2 ); During the experiment, multiple direct shear failure tests were conducted with different normal forces N. The shear displacement s and the sum of the bottom and side shear stresses of the specimens were recorded in real time during the tests. After the test, the shear displacement s was plotted as the abscissa and the shear stress was plotted as the ordinate. Plot the shear stress under different normal forces, with the vertical axis as the ordinate. The relationship curve between shear displacement s and the normal stress is obtained from the result image. The peak shear stress on each curve is taken, and the rock mechanics parameters cohesion c and internal friction angle of the soil are derived by using formulas (5) and (6), respectively. ; （5） （6）。 2. The in-situ rapid composite shear test method for tunnel surrounding rock according to claim 1, characterized in that, The data relay processor (10) is also connected to a strain sensor (8).

3. The in-situ rapid composite shear test method for tunnel surrounding rock according to claim 1, characterized in that, A limiter (17) is provided in the limiting slot (13) of the axial jack (1), and a slide rail and a roller (14) are provided in the limiting slot (13) of the normal jack (2).

4. The in-situ rapid composite shear test method for tunnel surrounding rock according to claim 1, characterized in that, An end limit block (18) is provided at the end of the device base (12).

5. The in-situ rapid composite shear test method for tunnel surrounding rock according to claim 1, characterized in that, A rigid rubber pad (16) is connected to the shear plate (15).

6. The in-situ rapid composite shear test method for tunnel surrounding rock according to claim 1, characterized in that, In step (1), the experimental location includes the tunnel floor, tunnel sidewall, or tunnel excavation face. The surface of the selected location is processed to make the surface flat.

7. The in-situ rapid composite shear test method for tunnel surrounding rock according to claim 1, characterized in that, In step (2), the side length of the cube rock sample is slightly larger than that of the shear plate, and the dimensions of the test trough are 50cm wide and 100cm long.

8. The in-situ rapid composite shear test method for tunnel surrounding rock according to claim 1, characterized in that, In step (3), after the test is completed, the test trench is excavated along the test axis as needed, new specimens are cut, and other normal loads are set for the test.

9. The in-situ rapid composite shear test method for tunnel surrounding rock according to claim 1, characterized in that, In step (4), the influence of T3 is ignored, that is, the assumption in formula (1) is that... .

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