A columnar jointed rock mass in-situ direct shear test device and method

Abstract

The application provides a columnar jointed rock mass in-situ direct shear test device and method. The device comprises a cavity anchor rod, an anchor head, a screw rod, a vertical loading system and a horizontal loading system. The screw rod is arranged in the cavity anchor rod and can control the extension and retraction of the tail anchor head; the anchor head is composed of four wedge-shaped steel blocks which are uniformly distributed around the tail of the anchor rod; the vertical loading system comprises a ball system, a hollow jack and a nut lock; and the horizontal loading system is fixed to the side wall rock mass. The application can quickly test the shear strength parameters of the undisturbed columnar jointed rock mass under the in-situ conditions on site, and the results are more real, accurate and reliable. In addition, the application also has the characteristics of simple structure, easy operation and convenient carrying.

Description

Technical Field

[0001] This invention belongs to the field of rock and soil mechanical parameter testing, and specifically relates to an in-situ direct shear test device and method for columnar jointed rock mass. Background Technology

[0002] Columnar jointed rock mass, as a special type of rock mass, differs significantly from other materials in that it is a multi-fractured body with longitudinal and transverse structural planes. The interior of this fractured rock mass is rich in various defects, including microcracks, pores, and macroscopic discontinuities such as joints and fissures. These defects not only significantly alter the mechanical properties of the rock mass but also severely affect its permeability, exhibiting anisotropy in both mechanical and permeability properties. Especially in geotechnical engineering projects constructed under columnar jointed rock mass conditions, the excavation process alters the stress and expands the joints and fissures, leading to significant changes in the strength of the columnar jointed rock mass and directly impacting the construction and safe operation of the project.

[0003] Currently, obtaining "undisturbed" specimens of columnar jointed rock masses typically involves using a sleeve in the field, then pressing the specimen into a shear box with a jack, or using a manual pickaxe. However, after excavation, the specimens are easily disturbed due to the excavation method and unloading relaxation, and therefore cannot fully reflect the actual state of the columnar jointed rock mass in the field. In-situ field tests, compared to laboratory tests, can determine the strength parameters of undisturbed columnar jointed rock masses, avoid disturbance to the specimens during sampling, and provide more accurate test values ​​that are closer to reality.

[0004] Most direct shear testing machines use hydraulic loading systems; the frames mainly include box-beam integral frame type and column-box-beam composite type; the measurement systems mainly include mechanical type, sensor digital display type, and computer automatic measurement and acquisition type. Field testing of the strength parameters of columnar jointed rock masses typically uses large-scale field shear testing equipment, which has high requirements for test site conditions. Furthermore, the instruments are bulky and the tests are time-consuming, significantly limiting the practical application effectiveness of this type of equipment.

[0005] Therefore, developing a simple, rapid, economical direct shear test device capable of obtaining shear performance indicators of columnar jointed rock masses in their natural state, and providing more accurate and reliable parameter suggestions for structural design and geological hazard prediction in geotechnical engineering, is an urgent problem to be solved. Summary of the Invention

[0006] The purpose of this invention is to provide an in-situ direct shear test device for columnar jointed rock mass, so as to solve the technical problems of commonly used in-situ direct shear instruments in the prior art, such as large mass, high test cost, non-disassembly, and inconvenience in transportation and carrying.

[0007] An in-situ direct shear test device for columnar jointed rock mass is characterized by comprising a cavity anchor rod, an anchor head, a screw rod, a vertical loading system, and a horizontal loading system; the cavity anchor rod is a steel column with a central hole and a closed head, and the side wall of the anchor rod head has a hole in which the anchor head is movably connected; the screw rod is slidably connected to the anchor rod, and the bottom end of the screw rod is inserted into the central hole of the anchor rod and movably connected to the anchor head; the screw rod can move up and down to control the opening and closing of the anchor head; when the anchor head is closed, it is located in the hole on the side wall of the anchor rod head; when the anchor head is open, the anchor rod protrudes from the hole in a tooth-like shape and can be embedded in the columnar jointed rock wall.

[0008] The vertical loading system is detachably installed in the test equipment. The vertical loading system is sleeved on the screw and includes a bearing, a hollow jack and a nut lock. The nut lock is threadedly connected to the screw. A perforated partition is provided at the bottom of the vertical loading system, and the partition is pressed against the rock mass to be tested by the vertical loading system.

[0009] Based on the above technical solutions, the present invention may also employ the following further technical solutions, or combine these further technical solutions:

[0010] The bottom end of the screw is connected to the anchor head via a movable rod. Bolts are provided at both ends of the movable rod, which are respectively hinged to the screw and the anchor head.

[0011] The bottom end of the screw is detachably connected and installed.

[0012] The anchor head consists of multiple (e.g., four) wedge-shaped steel blocks, evenly distributed around the head of the anchor rod, and the steel blocks are hinged to the anchor rod by bolts.

[0013] Both ends of the horizontal loading system are equipped with grooved bearing plates.

[0014] The vertical loading system also includes an upper cover and a partition, with the upper cover, the bearing, and the partition arranged sequentially from top to bottom; the hollow jack is placed on the upper cover, and a perforated pressure plate is provided between the upper end of the hollow jack and the nut lock and at the lower end.

[0015] The bearing uses a ball bearing arranged in a circle around the outer periphery of the screw.

[0016] The vertical loading system is equipped with a displacement sensor that cooperates with the partition plate, and the horizontal loading system is equipped with a displacement sensor that cooperates with the pressure plate. The sensors are connected to a computer data acquisition system.

[0017] Another objective of this invention is to provide a method for in-situ direct shear testing of columnar jointed rock masses using the aforementioned testing equipment. To this end, this invention employs the following technical solution:

[0018] A method for in-situ direct shear testing of columnar jointed rock mass, characterized by: employing the in-situ direct shear testing equipment for columnar jointed rock mass as described in any one of claims 1-7, and comprising the following steps:

[0019] Step 1: Select the rock mass to be tested, level it, and drill holes in the base of the rock mass to provide shear test seams for the test.

[0020] Step 2: With the anchor head closed, insert the assembled anchor rod, anchor head, and screw into the borehole. Once it reaches the designated position, press the screw downwards to open the anchor head and secure it to the rock wall. Then, install the partition plate, bearing, top cover, and hollow jack sequentially on the anchor rod above the borehole opening, ensuring the entire system is coaxial in the loading direction. Finally, lock it with a nut lock. The horizontal loading system is then fixed to the sidewall rock mass.

[0021] Step 3: Start the computer data acquisition system and zero it. Then start the vertical loading system and the horizontal loading system, and use micro-motion to alternately make the working surfaces of the horizontal loading system and the vertical loading system fit tightly against the rock surface.

[0022] Step 4: Conduct a rapid shear test using the horizontal pushing method: Apply vertical pressure through the vertical loading system and apply horizontal shear force in stages through the horizontal loading system to capture the peak value, so that the in-situ specimen is sheared within 3 to 5 minutes. When the shear deformation reaches the predetermined value, stop loading of the horizontal loading system to complete a set of tests, and record the stress and strain data throughout the process through the computer data acquisition system.

[0023] Compared to other rock masses, the equipment of this invention is more suitable for in-situ direct shear tests on columnar jointed rock masses. Because softer rocks (such as mudstone) are inherently soft, the borehole wall cannot provide sufficient anchoring force, resulting in an inability to provide stable vertical loads. Similarly, the borehole wall of hard rocks (such as granite) is hard and smooth, preventing the anchor head from embedding into the rock wall, also resulting in an inability to provide stable vertical loads. However, columnar jointed rock masses have a hard but well-developed joint and fracture structure, allowing the anchor head to embed within the rock joints and provide sufficient vertical loads. Therefore, this invention is more suitable for in-situ direct shear tests on columnar jointed rock masses.

[0024] Compared with traditional technologies, this invention optimizes and improves upon traditional large-scale in-situ rock shear testing instruments. It features a simple structure and eliminates the need for grouting techniques or large reaction steel frames, enabling the testing of shear strength parameters of rock masses under in-situ conditions. The in-situ direct shear testing equipment for columnar jointed rock masses provided by this invention can be disassembled into easily transportable components and readily assembled on-site. It accurately reflects the actual state of the rock mass through in-situ testing, providing test values ​​that are closer to the actual conditions and are more accurate and reliable. Furthermore, this invention requires minimal technical skill; the vertical load can be provided using the anchoring force of the anchor head on the rock wall, making operation convenient. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the in-situ direct shear test equipment for rock mass according to the present invention;

[0026] Figure 2 This is a top view of the in-situ direct shear test equipment for rock mass according to the present invention;

[0027] Figure 3 This is a schematic diagram of the anchor bolt in the open and closed states of the present invention; wherein: (a) shows the structural state when the anchor head is closed, and (b) shows the structural state when the anchor head is open;

[0028] Figure 4 This is a schematic diagram of the connection between the anchor head and the tension / compression rod screw of the present invention; wherein: (a) shows the structural fit when the anchor head is closed, and (b) shows the structural fit when the anchor head is open;

[0029] Figure 5 This is a stress analysis diagram of the rock mass sample during the test of this invention;

[0030] The markings in the diagram are as follows: 1-Cavity anchor rod; 2-Anchor head; 3-Screw rod; 4-Vertical loading system; 5-Upper cover; 6-Ball bearing row; 7-Partition plate; 8-Locking nut; 9-Horizontal loading system; 10-Rock mass to be tested; 11-First bearing plate; 12-Second bearing plate; 13-Third bearing plate; 14-Fourth bearing plate; 15-Displacement sensor; 16-Moving rod; 17-Rock mass shear surface. Detailed Implementation

[0031] The basic principle of this invention is based on the Coulomb principle of classical geotechnical mechanics, and is proposed according to the Coulomb strength criterion. Where, τ f σ refers to the shear strength (kPa) of the soil and rock mass, where σ is the normal pressure (kPa) acting on the shear surface. The internal friction angle (°) of the soil / rock mass is given by τ, and the cohesion (kPa) of the soil / rock mass is given by τ, which is related to the shear strength τ. f Plot the shear strength τ with the vertical pressure σ as the x-axis and the vertical pressure σ as the y-axis. fThe relationship curve between the vertical pressure σ and the rock mass is plotted as a line based on the points on the graph. The inclination angle of the line is the internal friction angle of the rock mass. The intercept of the straight line on the vertical axis represents the cohesion c of the soil and rock mass. In this invention, a certain load is applied vertically, along with a horizontal force. When the displacement sensor reading changes abruptly, the sample shears (in this test, a displacement greater than 4 mm is generally considered sample failure). The shear force of the sample at this point is the shear strength τ of the soil and rock mass. f .

[0032] Please refer to Figures 1 to 5 The in-situ direct shear test equipment for columnar jointed rock mass provided by this invention includes a hollow anchor rod 1, an anchor head 2, a screw rod 3, a vertical loading system 4, and a horizontal loading system 9. The hollow anchor rod 1 has an outer diameter of 80 mm and is a steel column with a central hole and a closed lower end. The head sidewall of the anchor rod 1 has a hole corresponding to the anchor head 2, and the anchor head 2 is installed in the hole. The anchor head 2 consists of four wedge-shaped steel blocks, evenly distributed around the head of the anchor rod 1. The lower part of the wedge-shaped steel blocks is hinged to the anchor rod 1 by bolts. A screw rod 3 is provided in the central hole of the anchor rod 1. The bottom end of the screw rod 3 is connected to the anchor head 2 via a movable rod 16. Bolts are provided at both ends of the movable rod 16, respectively connected to the screw rod. 3 is hinged to the anchor head 2. The screw 3 can move up and down to control the opening and closing of the anchor head 2. When the anchor head 2 is closed, it is located in the hole on the side wall of the anchor head. When the anchor head 2 is open, the anchor 1 protrudes from the hole, forming a toothed snap-fit ​​structure on the surface of the anchor 1. When the test equipment needs to be dismantled, the nut is unscrewed, and the anchor head 2 can be retracted into the hole by pressing the screw 3 downwards. The vertical loading system 4 includes a ball bearing 6 arranged in a circle around the screw 3 and a vertical hollow jack (in Figure 1 The structure located around number 4) and the nut lock 8, the nut lock 8 being sleeved on the outside of the screw 3, can provide a downward reaction force for the hollow jack; the horizontal loading system 9 adopts a horizontally arranged jack, one end of which acts on the side of the sampled rock mass during sampling.

[0033] The outer diameter of the screw 3 and the inner diameter of the center hole of the anchor rod 1 are matched, so that the screw 3 and the anchor rod 1 are in sliding fit. The anchor rod 1 can play a centering role for the screw 3. The screw 3 and the anchor rod 1 remain coaxial during the test.

[0034] Both the cavity anchor rod 1 and the anchor head 2 are made of ultra-high strength special steel, which can provide sufficient reaction force. The diameter of the cavity anchor rod is 80mm. The material strength can meet the stress requirements.

[0035] When the screw 3 is pulled upward, the anchor head 2 opens outward through the hole protruding from the head of the anchor rod. The anchor head 2 is in the open state, at which time the anchor head 2 can be embedded in the columnar jointed rock wall, providing sufficient anchoring force for the superstructure.

[0036] The horizontal loading system 9 is provided with a first bearing plate 11 and a second bearing plate 12 with grooves at both ends. The grooves prevent the horizontal loading system from slipping and provide a stable horizontal force. The vertical loading system 4 is also provided with a third bearing plate 13 and a fourth bearing plate 14 with holes at both ends for the screw 3 to pass through.

[0037] The vertical loading system 4 also includes an upper cover 5 and a partition 7, with the upper cover 5, ball bearing 6, and partition 8 arranged sequentially from top to bottom. During the shearing process, the in-situ specimen always receives the force applied by the vertical jack from the vertical loading system 4 through the ball bearing 6. At the same time, the partition 7 moves horizontally under the action of the ball bearing 6, thus not hindering the horizontal movement of the in-situ specimen during shearing.

[0038] The nut lock 8 is located above the vertical jack and is threadedly connected to the screw 3. When the screw 3 is locked by the anchor head (at which time the anchor head is in the open state), the nut lock 8 is screwed down to press the vertical hollow jack, providing a downward reaction force for the vertical loading system.

[0039] The vertical loading system 4 is equipped with a displacement sensor 15 that cooperates with the partition 7, and the horizontal loading system 9 is equipped with a displacement sensor 15 that cooperates with the pressure plate 11. The displacement sensor 15 is connected to the computer acquisition system.

[0040] This invention also provides a testing method using the above-mentioned in-situ direct shear test equipment for columnar jointed rock mass, comprising the following steps:

[0041] Step 1: Select the rock mass 10 to be tested, level it, and drill a hole in the base of the rock mass. The diameter of the hole is 108mm, which is the standard diameter for drilling, to provide sufficient shear test slots for the test. Preferably, the hole depth is not less than the length of the anchor rod 1, so that the anchor rod 1 can be completely inside the hole.

[0042] Step 2: Install anchor rod 1. With the anchor rod 1, anchor head 2 and screw rod 3 assembled, insert the assembly into the borehole with the anchor head 2 in the closed state. After reaching the designated position, pull the screw rod 3 upward to open the anchor head 2 and embed it into the rock wall. Then, install the partition plate 7, ball bearing 6, top cover 5 and hollow jack 4 in sequence on the screw rod 3 above the borehole opening, so that the entire vertical loading system surrounds the screw rod and ensures that the entire system is coaxial in the loading direction. Then, lock it with nut lock 8.

[0043] Step 3: Start the computer data acquisition system and zero it. Then start the horizontal loading system 9 and the vertical loading system 4, and use micro-motion to alternately make the working surfaces of the horizontal loading system 9 and the vertical loading system 4 fit tightly against the surface of the rock mass 10 to be tested.

[0044] Step 4: Conduct a rapid shear test using the horizontal pushing method: Apply vertical pressure through the vertical loading system 4 and apply horizontal shear force in stages through the horizontal loading system 9 to capture the peak value, so that the in-situ specimen is sheared within 3 to 5 minutes. When the shear deformation reaches the predetermined value, stop loading of the horizontal loading system 9 to complete a set of tests, and record the stress and strain data throughout the process through the computer data acquisition system.

[0045] Step 5: Remove the horizontal loading system and the vertical loading system in sequence, press down the screw 3, retract the anchor head, and pull the entire anchor rod out of the borehole.

[0046] Repeat the above steps to conduct at least five sets of experiments for data processing. The data can be processed using the following methods:

[0047] Throughout the experiment, the normal stress σ and shear stress τ on the shear surface 17 of the rock mass specimen were determined according to... Figure 5 The force equilibrium conditions of the rock mass sample are obtained as follows:

[0048] The normal stress σ on the shear plane is calculated using the following formula:

[0049]

[0050] The shear stress τ on the shear plane is calculated using the following formula:

[0051]

[0052] In the formula, G is the gravity of the vertical loading system and the ball bearing system (kN); P is the pressure value measured by the vertical pressure gauge (kN); F is the pressure value measured by the horizontal pressure gauge (kN); and A is the shear area (m²). 2 A0 is the borehole area (m²). 2 ).

[0053] Shear strength was calculated based on the Coulomb strength criterion:

[0054]

[0055] In the formula, τ f σ refers to the shear strength of the rock mass (kPa); σ is the normal stress acting on the shear plane (kPa); c refers to the internal friction angle of the rock mass (°); c refers to the cohesion of the rock mass (kPa).

[0056] The in-situ natural direct shear test of rock completed through the embodiments of the present invention can obtain reliable test data that is closer to the actual test data.

[0057] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An in-situ direct shear test device for columnar jointed rock mass, characterized in that: This includes hollow anchor bolts, anchor heads, bolts, vertical loading systems, and horizontal loading systems; The cavity anchor is a steel column with a central hole and a closed head. The side wall of the cavity anchor head has a hole, and the anchor head is movably connected inside the hole. The anchor head is composed of multiple wedge-shaped steel blocks, which are evenly distributed around the head of the hollow anchor rod. The wedge-shaped steel blocks are hinged to the hollow anchor rod by bolts. The screw is slidably connected to the cavity anchor rod. The bottom end of the screw rod is inserted into the central hole of the cavity anchor rod and is movably connected to the anchor head. The screw rod can move up and down to control the opening and closing of the anchor head. When the anchor head is closed, it is located in the hole on the side wall of the anchor rod head. When the anchor head is open, it protrudes from the hole in the shape of convex teeth to the cavity anchor rod, so as to be embedded in the columnar jointed rock wall. The vertical loading system is detachably installed in the test equipment and sleeved on the screw. The vertical loading system includes an upper cover, a bearing, a hollow jack, a nut lock, and a partition. The upper cover, the bearing, and the partition are arranged sequentially from top to bottom. The hollow jack is installed on the upper cover. The nut lock is threadedly connected to the screw and presses the hollow jack tightly. The anchoring force of the anchor head on the columnar jointed rock wall provides a reaction force for the vertical loading system, and applies vertical pressure to the rock mass to be tested through the upper cover and the partition. The bearing uses a ball bearing arranged in a circle around the outer periphery of the screw; The baffle can move horizontally under the action of the ball bearings so as not to hinder the horizontal displacement of the rock mass under test during the shearing process; The horizontal loading system is fixed to the sidewall rock mass and is used to apply horizontal shear force to the rock mass to be tested.

2. The in-situ direct shear test equipment for columnar jointed rock mass as described in claim 1, characterized in that: The bottom end of the screw is detachably connected and installed.

3. The in-situ direct shear test equipment for columnar jointed rock mass as described in claim 1, characterized in that: Both ends of the horizontal loading system are equipped with grooved bearing plates.

4. The in-situ direct shear test equipment for columnar jointed rock mass as described in claim 1, characterized in that: The hollow jack has perforated pressure plates at its upper end and between its upper and lower ends, allowing the screw to pass through.

5. The in-situ direct shear test equipment for columnar jointed rock mass as described in claim 1, characterized in that: The vertical loading system is equipped with a displacement sensor that cooperates with the partition plate, and the horizontal loading system is equipped with a displacement sensor that cooperates with the pressure plate. The sensors are connected to a computer data acquisition system.

6. A method for in-situ direct shear testing of columnar jointed rock mass, characterized in that: The in-situ direct shear test equipment for columnar jointed rock mass as described in any one of claims 1-5 is employed, and the test includes the following steps: Step 1: Select the rock mass to be tested, level it, and drill holes in the base of the rock mass to provide shear test seams for the test. Step 2: With the assembled hollow anchor rod, anchor head, and screw rod in the closed state, insert them into the borehole. Once they reach the designated position, pull the screw rod upwards to open the anchor head and secure it to the rock wall. Then, install the partition plate, ball bearing, bearing, top cover, and hollow jack sequentially on the screw rod above the borehole opening, ensuring the entire system is coaxial in the loading direction. Finally, tighten the hollow jack with a nut lock to utilize the anchoring force of the anchor head on the columnar jointed rock wall to provide a reaction force for vertical loading. Simultaneously, fix the horizontal loading system to the sidewall rock mass. Step 3: Start the computer data acquisition system and zero it. Then start the horizontal loading system and the vertical loading system, and use micro-motion to alternately make the working surfaces of the horizontal loading system and the vertical loading system fit tightly against the rock surface. Step 4: Conduct a rapid shear test using the horizontal pushing method: Apply vertical pressure through the vertical loading system and apply horizontal shear force in stages through the horizontal loading system to capture the peak value, so that the in-situ specimen is sheared within 3 to 5 minutes. When the shear deformation reaches the predetermined value, stop loading of the horizontal loading system to complete a set of tests, and record the stress and strain data throughout the process through the computer data acquisition system.

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