Tunnel surrounding rock in-situ rapid composite shear testing device and method

Abstract

The invention discloses a tunnel surrounding rock in-situ rapid composite shear test device and method, the device comprises an electro-hydraulic servo control system, a data acquisition system and a limiting system, a surrounding rock natural counter-force support experiment device is utilized, additional counter-force system arrangement is avoided, the experiment operation process is simplified, the damage to surrounding rock is reduced, and meanwhile the experiment efficiency is improved. The design of the modularized and lightweight experiment device can adapt to various experiment scenes such as a tunnel bottom plate or a side wall, supports rapid installation and disassembly, and adapts to complex geological conditions. Due to the introduction of the electro-hydraulic servo control system and the high-precision sensor, real-time acquisition, transmission and automatic analysis of experimental data are realized, and the accuracy and repeatability of experimental results are improved. The shear mechanical property of the tunnel surrounding rock can be efficiently and accurately measured in the rock mass mechanics in-situ experiment, the mounting portability of the experiment device is enhanced, and the excessive disturbance to the surrounding rock in the experiment process is reduced.

Description

Technical Field

[0001] The present invention relates to surrounding rock tunnel engineering, and more specifically to a device and method for rapid in-situ composite shear testing of tunnel surrounding rock. Background Art

[0002] Surrounding rock is the main research object in tunnel engineering and bears a relatively large amount of pressure. The purpose of rock strength testing is to evaluate the mechanical properties of rocks under various external stress actions, so as to provide a scientific basis for engineering design, construction, and safety assessment. The existing rock strength testing methods are mainly divided into two types: indoor experimental testing methods and in-situ experimental testing methods. In-situ testing can be carried out in the natural environment of rocks, maintaining the integrity of the surrounding rock structure. At the same time, considering the influence of in-situ stress, confining pressure, rock layer distribution, joints and fractures, etc., the test results can better reflect the actual bearing capacity and strength of rock masses.

[0003] Currently, there are mainly two schemes for in-situ rock testing experiments. The first scheme is to conduct in-situ in-tunnel experiments, using equipment to drill holes in the surrounding rock to ensure that the testing device can be placed to directly test the strength of rock masses. The Chinese patent with the application number CN118730761 A designs a sampling-free in-situ hole testing device, which uses a shoe device to fix the equipment in the hole, uses a hydraulic system to drive a cutter for continuous cutting testing of rock shear strength, and collects displacement and pressure data through sensors to calculate the shear strength parameters of rocks. The second scheme is to cut a cube specimen and then apply horizontal and vertical loads to the specimen after putting a shear box on it. The instruments of this scheme mainly include three parts: a normal load device, a shear load device, and a measuring device.

[0004] The normal load application device generally has four types: a surcharge device, an anchor device, a horizontal inclined support reaction device, and a top wall support device. The main equipment should include a surcharge platform or an anchor or a horizontal inclined support reaction device that provides reaction force, as well as supporting I-beams, load transfer columns, hydraulic jacks, upper steel plates, roller rows, and lower steel plates, etc. The shear load device should include a shear box, a top pressure steel plate, a roller row, a hydraulic jack, a rear seat steel plate, and a rear support, etc.; the measuring device includes an oil pressure gauge, a pressure sensor, a dial gauge, an electronic displacement gauge, a spirit level, and a compass, etc.

[0005] The patent with the authorization announcement number CN221650110U proposed an in-situ direct shear test device for anchored rock and soil masses, presenting an idea of a device that uses ground anchors to fix experimental instruments and provide normal reaction forces. The patent with the application publication number CN118464672A proposed a device solution that uses anchor bolts to fix the reaction frame and arranges horizontal and vertical loading devices on the reaction frame. The patent with the authorization number CN204330502U proposed a direct shear test device with a built-in weight platform, where counterweight blocks provide vertical reaction forces for vertical jacks. When the device is in use, an experimental foundation pit needs to be excavated; the horizontal jack is placed between the surrounding rock and the specimen, and the surrounding rock provides reaction forces for the horizontal jack. The patent with the patent number CN208937435U proposed a shear resistance device for landslide rock masses. This device uses the anti-sliding device in the specimen pit to provide vertical reaction forces for the experiment and installs flat jacks to avoid eccentric torque during the experiment. When the device is in use, an experimental foundation pit needs to be excavated.

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

[0007] The direct shear test methods with additional shear boxes or shear plates all require special reaction devices. The surcharge device needs to provide additional normal counterweights; the ground anchor device needs to specially install anchor bolts to provide reaction forces; the horizontal inclined support reaction device needs to process the side wall at a certain angle, and in order to ensure the effective force of the inclined support, a deeper foundation pit needs to be excavated; the top wall support device generally needs to use the tunnel vault to apply shear reaction forces, and the equipment is complex. When these four devices are applied, they all need to cut the specimen to generate five free surfaces, resulting in a large amount of additional work, and it is inevitable to cause greater disturbance to the surrounding rock during the specimen processing.

[0008] Currently, the in-situ direct shear test methods for rock masses (such as tool cutting or single shear plane experiments) cannot comprehensively reflect the true shear mechanical properties of the surrounding rock, especially the limited ability to comprehensively evaluate the complex structural planes and weak parts of the surrounding rock. In addition, traditional experimental devices (such as surcharge devices, ground anchor devices, etc.) require complex reaction systems to support, causing greater disturbance to the surrounding rock, with cumbersome experimental preparations and low efficiency. Existing experimental devices are usually large in size and complex in installation, making it difficult to adapt to diverse on-site conditions such as tunnel floors or side walls, especially with poor applicability in narrow spaces or complex geological environments. Secondly, some devices need to excavate large experimental troughs or carry out additional specimen processing, increasing construction costs and experimental difficulties. Finally, traditional experimental data acquisition methods rely on manual recording or low-precision sensors, resulting in experimental data being easily interfered by humans and insufficient reliability of experimental results. The lack of automated data analysis and real-time monitoring means leads to low experimental efficiency and difficulty in meeting the requirements of modern engineering for rapid and accurate experimental results. Summary of the Invention

[0009] The object of the present invention is to address the deficiencies existing in the above-mentioned prior art, and propose a device and method for in-situ rapid composite shear testing of tunnel surrounding rock, which is a composite shear experiment method that retains the shear surfaces of the bottom and side surfaces, and can more truly reflect the overall mechanical properties of the surrounding rock, especially the influence of complex joints and weak structural planes on the shear strength. By using the natural reaction force of the surrounding rock to support the experimental device, the arrangement of an additional reaction force system can be avoided, the experimental operation process can be simplified, the damage to the surrounding rock can be reduced, and at the same time, the experimental efficiency can be improved. The design of the modular and lightweight experimental device can be adapted to various experimental scenarios such as tunnel floors or sidewalls, support rapid installation and disassembly, and adapt to complex geological conditions. The introduction of a liquid-electric servo control system and high-precision sensors realizes the real-time acquisition, transmission, and automatic analysis of experimental data, improving the accuracy and repeatability of experimental results. It solves the problem of how to efficiently and accurately measure the shear mechanical properties of tunnel surrounding rock in in-situ rock mechanics experiments, enhances the portability of the installation of the experimental device, and reduces the excessive disturbance to the surrounding rock during the experiment.

[0010] The present invention is achieved through the following technical solutions: A device for in-situ rapid composite shear testing of tunnel surrounding rock, comprising a liquid-electric servo control system, a data acquisition system, and a limiting system:

[0011] The liquid-electric servo control system includes an axial jack, a normal jack, a hydraulic pump, an intelligent control terminal, a cable, a hydraulic pipeline, and a shear plate. The bottoms of the axial jack and the normal jack are both installed on the device base, and the tops are both connected to the shear plate; the axial jack and the normal jack are connected to the hydraulic pump through the hydraulic pipeline, and the hydraulic pump is connected to the intelligent control terminal through the cable;

[0012] The data acquisition system includes a displacement sensor, a pressure sensor, and a data relay processor. Displacement sensors are installed on the shear plate, pressure sensors are installed on the axial jack and the normal jack, the displacement sensors and the pressure sensors are connected to the data relay processor, and the data relay processor is connected to the intelligent control terminal;

[0013] The limiting system includes a device base, a jack base, and a limiting slot. The device base is L-shaped, with x-direction and y-direction limiting slots provided on the device base. The jack base of the axial jack is installed in the x-direction limiting slot, and the jack base of the normal jack is installed in the y-direction limiting slot.

[0014] Further, a strain sensor is also connected to the data relay processor.

[0015] Further, a limiter is provided in the limiting slot of the axial jack, and a slide rail and a roller row are provided in the limiting slot of the normal jack.

[0016] Furthermore, an end limit block is provided at the end of the device base.

[0017] Furthermore, a hard rubber backing plate is connected to the shear plate.

[0018] The present invention also provides a method for rapid in-situ composite shear testing of tunnel surrounding rock, including the following steps:

[0019] (1) Test preparation:

[0020] Select the test location, determine the specimen specifications and normal loads of different grades, and estimate the shear loads required for different test blocks.

[0021] (2) Specimen preparation:

[0022] Fabricate cube-shaped rock specimens, each specimen having four free planes of front, back, top, and side, with the surfaces of each plane being flat, and excavate a test groove.

[0023] (3) Formal test:

[0024] Install the above-mentioned device to ensure that the forces of the normal jack and the axial jack both pass through the centroid of the specimen. Issue an instruction on the intelligent control terminal for initial pushing, so that both the axial jack and the normal jack are jacked up until the shear plate or the hard rubber backing plate is in close contact with the rock specimen; conduct the test according to the normal load set in the test preparation stage, and control the axial jack to push until the rock specimen undergoes shear failure.

[0025] (4) Method for obtaining the shear parameters of the specimen:

[0026] Assume that the surrounding rock is an isotropic material. The sum of the normal stress σ and the shear stress τ applied to the specimen can be calculated according to the following formula:

[0027]

[0028] T1 + T2 = F - μN (2)

[0029]

[0030] τ = τ d + τ c (4)

[0031] In the formula: σ—the normal stress on the side surface of the specimen (MPa);

[0032] τ d —the shear stress on the bottom surface of the specimen (MPa);

[0033] τ c —the shear stress on the side surface of the specimen (MPa);

[0034] τ—the sum of the shear stress at the bottom surface and the shear stress at the side surface of the specimen;

[0035] μ—the friction coefficient of the limiting device;

[0036] F—the thrust of the axial jack during the shearing process (N);

[0037] N—the thrust of the normal jack (N);

[0038] T1—the shear force (N) on the side shear plane of the specimen;

[0039] T2—the axial shear force (N) on the bottom shear plane of the specimen;

[0040] T3—the normal shear force (N) on the bottom shear plane;

[0041] A—the area of the cube specimen (mm 2 );

[0042] During the experiment, different normal forces N are set for multiple direct shear failure tests. During the test, the shear displacement s of the specimen and the sum of the bottom shear stress and the side shear stress τ are recorded in real time. After the test, with the shear displacement s as the abscissa and the shear stress τ as the ordinate, the relationship curve between the shear stress τ and the shear displacement s under different normal forces is plotted. In the result image, the normal stress and the peak shear stress on its corresponding curve are taken, and the cohesion c and the internal friction angle of the rock and soil mass of the rock mechanics parameters are respectively derived using formula (5) and formula (6).

[0043]

[0044] Furthermore, in the step (1), the experimental positions include the tunnel floor, the tunnel side wall or the tunnel excavation face, and the surface of the selected position is processed to make the surface flat.

[0045] Furthermore, in the step (2), the side length of the cube rock sample is slightly larger than the shear plate, and the size of the test tank is 50 cm wide and 100 cm long.

[0046] Furthermore, in the step (3), after the test, according to the need, the test tank is continuously excavated along the test axis, a new specimen is cut, and other normal loads are set for the test.

[0047] 10. For a method for in-situ rapid composite shear test of tunnel surrounding rock according to claim 6, in the step (4), the influence of T3 is ignored, that is, it is assumed in formula (1) that

[0048] The beneficial effects of the present invention are as follows:

[0049] (1) The present invention provides a direct shear test device for rock mass in-situ that only utilizes the natural reaction force of the surrounding rock as the normal support without the need for external reaction force, simplifies the experimental preparation work in the construction environment, and reduces the disturbance to the surrounding rock.

[0050] (2) The present invention provides a direct shear test method with a composite shear surface, which applies shear forces simultaneously to the bottom shear surface and the side shear surface of the same specimen to more comprehensively reflect the shear strength characteristics of the surrounding rock under actual conditions.

[0051] (3) Based on the composite shear surface theory, a calculation formula for shear strength parameters is proposed, comprehensively considering experimental data such as normal stress, axial thrust, and shear displacement, to improve the accuracy of experimental results.

[0052] (4) A modular-designed limit structure is adopted to ensure the accuracy of the loading direction. At the same time, a roller row system is used to reduce the friction force during the experiment and improve the stability of the device operation.

[0053] (5) The combination of a hydraulic-electric servo system and an intelligent terminal is adopted to realize the automatic operation of the whole experimental process, including real-time data acquisition, feedback, and analysis, and accurately control the loading process through the hydraulic-electric servo system.

[0054] (6) The device supports rapid installation and disassembly, adapts to complex experimental environments such as tunnel floors and side walls, and meets the convenience and diversification requirements of in-situ experiments. It can conveniently and quickly conduct direct shear tests on rock mass in-situ.

[0055] (7) The present invention also provides a corresponding derivation method for rock shear strength parameters. A device is proposed in addition to the four normal loading devices of the surcharge device, the ground anchor device, the horizontal inclined support reaction device, and the top wall support device, which uses the reaction force of the pit wall to provide the support reaction force required when applying normal load. The experimental device is simple to operate, has a simple structure, and a clear principle, and minimizes the disturbance to the surrounding rock during the experiment, improving the accuracy of the experiment.

[0056] (8) The novel in-situ direct shear test method designed by the present invention retains the original characteristics of the rock sample during the implementation process, making the experimental results more capable of reflecting the true shear mechanical properties of the surrounding rock.

[0057] (9) During the equipment installation process, only four free surfaces need to be cut, and only an experimental groove for placing the device needs to be made, with less engineering work, reducing the workload during the experiment and the disturbance to the specimen during the specimen preparation process.

[0058] (10) During the experiment, the experimental data is automatically recorded, and some parameters are automatically calculated, simplifying the experimental process.

[0059] (11) An in-situ experiment is carried out using an intelligent control system to ensure a uniform increase in the force on the specimen during the experiment process, reducing experimental errors. Description of the Drawings

[0060] Figure 1 This is a schematic diagram of the overall device of the present invention.

[0061] Figure 2 This is a schematic diagram of the jack of the present invention.

[0062] Figure 3 This is a schematic diagram of the limit system of the present invention.

[0063] Figure 4 This is a schematic diagram of the limiter of the present invention.

[0064] Figure 5 This is a schematic diagram of the end limit block of the present invention.

[0065] Figure 6 This is a schematic diagram of the specimen and the experimental tank after cutting during the test of the present invention.

[0066] Figure 7 This is a schematic diagram of the installed and operating state of the present invention.

[0067] Figure 8 This is a schematic diagram of the force analysis of the specimen of the present invention.

[0068] Figure 9 This is a shear stress-displacement curve graph of the present invention.

[0069] Figure 10 This is a schematic diagram of the test process in Embodiment 2 of the present invention.

[0070] Figure 11 This is a shear stress-displacement curve graph in Embodiment 2 of the present invention.

[0071] In the figures: 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 row, 15 - shear plate, 16 - hard rubber cushion plate, 17 - limiter, 18 - end limit block. Detailed Description of the Invention

[0072] The specific embodiments of the present invention will be described below to facilitate those skilled in the art of the present technology to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art of the present technology, as long as various changes are within the spirit and scope of the present invention defined and determined by the appended claims, these changes are obvious, and all inventions created using the concept of the present invention are within the scope of protection.

[0073] Example 1

[0074] The electro-hydraulic servo control system includes:

[0075] (1). The bottom of the axial jack 1 is installed 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 specimen, causing the specimen to undergo shear failure. For convenient transportation, the entire experimental device can be disassembled and installed, and the jack base 6 is designed as a groove-shaped that can fit closely with the device base 12.

[0076] (2). The normal jack 2 is installed on the vertical limiting device and can move synchronously with the shear deformation of the specimen while providing a normal pressure to the specimen.

[0077] (3). The hydraulic pump 3, using a high-precision electro-hydraulic servo control system to control the axial jack 1 and the normal jack 2 respectively. After the intelligent control terminal 7 issues an operation instruction, the system adjusts the pressures of the axial jack 1 and the normal jack 2 through the hydraulic pump 3. The hydraulic pump 3 is connected to the jack through a hydraulic pipeline 11.

[0078] (4). The 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 closely 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 in real time data such as thrust, displacement, and strain during the failure process.

[0079] The data acquisition system includes:

[0080] (1). The displacement sensor 4, using a linear variable differential transformer (LVDT) displacement sensor as the measurement device for shear displacement. The displacement sensor 4 is installed on the shear plate 15, and the directly measured data is the jack lifting distance during the experiment.

[0081] (2). The pressure sensor 5, using a high-precision spoke-type pressure sensor to measure in real time the thrust applied by the jack to the specimen during the experiment. The pressure sensor 5 on the axial jack 1 is used to measure the axial thrust during the shear failure process, and the pressure sensor 5 on the normal jack 2 is used to measure the normal thrust applied by the jack to the rock sample during the direct shear test.

[0082] (3) Strain sensor 8. A resistive strain sensor is selected to measure the strain of the rock specimen during the shear failure process.

[0083] (4) Data relay processor 10. It is connected to the displacement sensor 4, pressure sensor 5, and strain sensor 8 through the cable 9, receives the sensor signals, and feeds back the experimental data to the intelligent control terminal 7.

[0084] The limit system includes:

[0085] (1) Device base 12. It is an L-shaped device base, and its main function is to carry the jack. For easy disassembly, transportation, and installation, a limit slot 13 is provided on the device base 12 for the axial jack 1. To ensure that the axial jack 1 can be adjusted in the x-direction during the installation process so that its acting force passes through the centroid of the specimen, a limiter 17 is set. The limiter 17 adopts a mechanical clamping type limit device to fix the position of the axial jack 1. The device base 12 also has a limit slot 13 for restricting the z-direction movement of the normal jack 2. A slide rail is provided in the limit slot 13, and a corresponding chute is provided on the jack base 6 of the normal jack 2 to be installed on the slide rail to ensure that the normal jack 2 can move along with the shear failure direction of the specimen.

[0086] (2) Roller row 14. To further ensure that the normal jack 2 can move forward along the shear direction together with the shear box 15 during the direct shear test, a roller row 14 is provided behind the normal jack base to reduce the friction force of the normal jack 2 during movement.

[0087] (3) Limiter 17. To ensure that the thrust of the axial jack 1 passes through the centroid of the specimen during the experiment, a mechanical clamping type limit device is set to facilitate the adjustment of the x-direction movement of the axial jack 1.

[0088] (4) End limit block 18. To facilitate the installation and disassembly of the jack, an end limit block 18 is provided.

[0089] (5) Shear plate 15. Its main function is to evenly apply the jack thrust on the specimen.

[0090] (6) Hard rubber cushion 16. It is adhered to the shear plate 15, and its main purpose is to ensure that the shear plate 15 is in close contact with the specimen during the shear process.

[0091] The experimental process is as follows:

[0092] 1. Test preparation:

[0093] (1) According to the requirements of the specification "Field Direct Shear Test Procedure" (YS / T 5221-2019), measure the friction coefficient μ between the normal jack 2 and the slide rail and / or roller row 14.

[0094] (2) Before the experiment starts, first select the experimental location, which can be the tunnel floor, tunnel sidewall, or tunnel excavation face. Process the surface of the selected location to make it as flat as possible.

[0095] (3) According to the engineering properties of the experimental rock and soil mass and combined with the experience of similar projects, determine the specimen specifications and normal loads of different grades, and estimate the shear loads to be applied to different specimens based on this.

[0096] 2. Specimen preparation

[0097] At the beginning of the experiment, first use rock-breaking equipment, grooving equipment, cutting equipment, etc. to make cubic rock specimens (about 30 cm in side length). The side length of the specimen should be slightly larger than the shear plate. Each rock specimen has four free planes of front, back, top, and side. During the cutting process, try to ensure that the surface of the rock specimen is flat. If it is not flat, use mortar or concrete for leveling. The excavated test groove should be adapted to the size of the equipment (about 50 cm in width and about 100 cm in length). The cut specimens and the excavated test grooves are as Figure 6 shown.

[0098] 3. Formal experiment

[0099] (1) Install the equipment to ensure that the acting forces of the normal jack 2 and the axial jack 1 both pass through the centroid of the specimen. The installed equipment is as Figure 7 shown.

[0100] (2) Issue an instruction at the control terminal to perform the initial push of the jacks, so that both the axial jack 1 and the normal jack 2 are jacked up until the hard rubber cushion 16 is in close contact with the rock specimen.

[0101] (3) Conduct the experiment according to the normal load set in the test preparation stage, control the axial jack 1 to push until the rock specimen undergoes shear failure, and the system will automatically record the experimental data in real time during the experiment.

[0102] (4) According to actual needs, continue to excavate the test groove along the test axis, cut new specimens, and set other normal loads for testing.

[0103] 4. Method for obtaining specimen shear resistance parameters

[0104] The force analysis diagram of the specimen is as Figure 8 shown. Assume that the surrounding rock is an isotropic material. During the shear process, the thrust of the axial jack 1 acting on the rear free surface is F, the normal force of the jack acting on the side free surface normally is N, and the frictional force suffered by the normal jack during the forward movement 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 acting on the side shear surface is N1. The shear stress on the bottom shear surface of the specimen is τ d , and the shear stress on the side shear surface of the specimen is τc The sum of the two is τ. Then, the normal stress σ and the sum of shear stresses τ applied to the specimen can be calculated according to the following formulas respectively:

[0105]

[0106] T1 + T2 = F - μN (2)

[0107]

[0108] τ = τ d + τ c (4)

[0109] Where: σ—the normal stress on the side of the specimen (MPa);

[0110] τ d —the shear stress on the bottom surface of the specimen (MPa);

[0111] τ c —the shear stress on the side surface of the specimen (MPa);

[0112] τ—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 "sum of shear stresses" (MPa);

[0113] μ—the friction coefficient of the limiting device;

[0114] F—the thrust of the axial jack during the shearing process (N);

[0115] N—the thrust of the normal jack (N);

[0116] T1—the shear force on the side shear surface of the specimen (N);

[0117] T2—the axial shear force on the bottom shear surface of the specimen (N);

[0118] T3—the normal shear force on the bottom shear surface (N);

[0119] A—the area of the cube specimen (mm 2 )

[0120] For simplicity of calculation, the influence of T3 is ignored (the actual influence of T3 on the calculation results needs to be determined through experiments), that is, it is assumed that During the experiment, different normal forces N are set for multiple direct shear failure experiments. During the experiment, the shear displacement s of the specimen and the sum of the shear stresses on the bottom surface and the side surface τ are recorded in real time. After the experiment, with the shear displacement s as the abscissa and the shear stress τ as the ordinate, the relationship curve between the shear stress τ and the shear displacement s under different normal forces is plotted, as shown in Figure 9As shown. In the result image, take the normal stresses σ1, σ2, σ3, σ4 and the peak shear stresses τ1, τ2, τ3, τ4 on their corresponding curves. Using formula (5) and formula (6), the rock mechanics parameters c and

[0121] the cohesion c and the internal friction angle of the rock and soil mass can be calculated by the least squares method:

[0122]

[0123]

[0124] Example 2:

[0125] The experimental process of a direct shear test on the surrounding rock of a tunnel mainly composed of sandstone is as follows:

[0126] (1) Before the test starts, based on the experience of similar projects, the selected specimen size is 30cm × 30cm × 30cm. Four levels of normal stress, 10MPa, 20MPa, 30MPa, and 40MPa, are planned to be set. To ensure the normal progress of the experiment, it is estimated that the maximum thrust that the axial jack can provide should not be less than the shear force of 1800kN required to cause the specimen to fail.

[0127] (2) Before the experiment starts, first select the experimental location, choose a relatively flat tunnel floor or tunnel sidewall. Then process the surface to make it as flat as possible.

[0128] (3) At the beginning of the experiment, first use rock-breaking equipment, grooving equipment, cutting equipment, etc. to excavate the experimental groove (about 50cm wide and about 100cm long), and make a cube rock sample (30cm × 30cm × 30cm). The top surface of the specimen and the side surface where the shear load acts should be leveled with mortar after cutting.

[0129] (4) Install the equipment, and adjust the thrust directions of the axial jack and the normal jack to pass through the axis of the specimen. Ensure that all parts of the equipment are stably connected and turn on the power.

[0130] (5) Issue an instruction on the intelligent terminal, initially push the jack to make the shear plate close to the rock sample and the reaction plate of the device close to the sidewall of the rock pit. Then clear the experimental data and push the normal jack to apply a 10MPa normal stress to the specimen.

[0131] (6) Apply pressure to the axial jack to start the shearing experiment. The axial jack pushes the specimen to cause shear failure. During the experiment, the system automatically records the jacking displacement value and the corresponding thrust, and automatically calculates the shear stress corresponding to each jacking displacement value.

[0132] After one experiment is completed, return the jack to its original position, clean the grooving, continue to cut along the original axis of the experimental foundation pit to form a specimen, move the device to conduct the experiment, as Figure 10 shown. Continue to measure the experimental data when the normal force is 20 MPa, 30 MPa, and 40 MPa.

[0133] (8) After the experiment is completed, plot the shear stress-displacement curve as Figure 11 shown. Calculate respectively according to formula (5) and formula (6):

[0134] Cohesion

[0135]

[0136] Internal friction angle

[0137] Those of ordinary skill in the art will realize that the embodiments described herein are to assist the reader in understanding the principles of the present invention, and should be understood that the protection scope of the present invention is not limited to such specific statements and embodiments. Those of ordinary skill in the art can make various other specific deformations and combinations that do not depart from the essence of the present invention based on the technical revelations disclosed in the present invention, and these deformations and combinations are still within the protection scope of the present invention.

Claims

1. A rapid in-situ composite shear test device for tunnel surrounding rock, characterized in that, It includes a hydraulic-electric servo control system, a data acquisition system and a limit system: The hydraulic-electric 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 installed 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 displacement sensor (4) is installed on the shear plate (15), the pressure sensor (5) is installed on the axial jack (1) and the normal jack (2). 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 limit system includes a device base (12), a jack base (6) and a limit slot (13). The device base (12) is L-shaped, and limit slots (13) in the x-direction and y-direction are provided on the device base (12). The jack base (6) of the axial jack (1) is installed in the limit slot (13) in the x-direction, and the jack base (6) of the normal jack (2) is installed in the limit slot (13) in the y-direction.

2. The in-situ rapid composite shear test device for tunnel surrounding rock according to claim 1, wherein A strain sensor (8) is also connected to the data relay processor (10).

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

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

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

6. A rapid in-situ composite shear test method for tunnel surrounding rock, characterized in that, It includes the following steps: (1) Test preparation: Select the test location, draw up the specimen specifications and normal loads of different grades, and estimate the shear loads required to be applied to different test blocks; (2) Specimen preparation: Make cube rock specimens. Each rock specimen has four free planes of front, back, top and side, and the surfaces of each plane are flat, and test grooves are excavated; (3) Formal test: Install the device according to any one of claims 1-7, ensure that the acting forces of the normal jack (2) and the axial jack (1) both pass through the centroid of the specimen, and issue an instruction on the intelligent control terminal (7) for initial pushing, so that both the axial jack (1) and the normal jack (2) are jacked up until the shear plate (15) or the hard rubber cushion plate (16) is in close contact with the rock specimen; 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 specimen undergoes shear failure; (4) Method for obtaining the shear parameters of the specimen: Assume that the surrounding rock is an isotropic material, and the sum of the normal stress σ and the shear stress τ received by the specimen can be calculated according to the following formula: T1 + T2 = F - μN (2) τ = τ d + τ c (4) Where: σ——Normal stress on the side surface of the specimen (MPa); τ d —— Shearing stress at the bottom surface of the specimen (MPa); τ c —— Shearing stress on the side of the specimen (MPa); τ——Sum of the shear stress on the bottom surface and the shear stress on the side surface of the specimen; μ——Friction coefficient of the limiting device; F——Thrust of the axial jack during the shearing process (N); N——Thrust of the normal jack (N); T1——Shearing force on the side shear surface of the specimen (N); T2——Axial shearing force on the bottom shear surface of the specimen (N); T3——Normal shearing force on the bottom shear surface (N); A—— Area of the cube specimen (mm 2 ); During the experiment, multiple direct shear failure tests were carried out by setting different normal forces N. During the test, the shear displacement s of the specimen and the shear stress τ (the sum of the bottom shear stress and the side shear stress) were recorded in real time. After the test, with the shear displacement s as the abscissa and the shear stress τ as the ordinate, the relationship curves of the shear stress τ and the shear displacement s under different normal forces were plotted. In the result image, the normal stresses and the peak shear stresses on their corresponding curves were taken, and the cohesion c and the internal friction angle of the rock and soil mass of the rock mechanics parameters were respectively derived using formulas (5) and (6).

7. A method for in-situ rapid composite shear test of tunnel surrounding rock according to claim 6, characterized in that In the said step (1), the experimental positions include the tunnel floor, tunnel side wall or tunnel excavation face, and the surface of the selected position is processed to make it flat.

8. A method for in-situ rapid composite shear test of tunnel surrounding rock according to claim 6, characterized in that In the said step (2), the side length of the cube rock sample is slightly larger than the shear plate, and the size of the test tank is 50 cm in width and 100 cm in length.

9. A method for in-situ rapid composite shear test of tunnel surrounding rock according to claim 6, characterized in that In the said step (3), after the test is completed as required, the test tank is continuously excavated along the test axis, a new specimen is cut, and other normal loads are set for the test.

10. A method for in-situ rapid composite shear test of tunnel surrounding rock according to claim 6, characterized in that, In step (4), the influence of T3 is ignored, that is, it is assumed in formula (1)

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