Combined sleeve pull-out test method

Abstract

The invention discloses a combined sleeve pull-out test method, which comprises the following steps: putting a sample in a combined sleeve pull-out device for pull-out test to obtain the strain of the sample in the pull-out process. Compared with the prior art, the combined sleeve pull-out test method disclosed by the invention has the advantages that the operation is simple, the control is easy, constant displacement and constant force can be applied, the semi-infinite rock rigidity can be accurately simulated, and the response rule and deformation failure characteristics of the sample under the condition of reaction constant rigidity can be accurately simulated.

Description

Technical Field

[0001] The invention relates to the field of geotechnical engineering, and in particular to a combined sleeve pulling test method. Background Art

[0002] Anchor support is one of the most effective rock stability control technologies. Anchors have been widely used and developed in water conservancy and hydropower, transportation tunnels, slope protection, underground engineering, mining engineering, foundation anti-tilting, anti-floating and other projects. Among them, mortar anchors are the most widely used and have excellent support effects. Despite this, due to inaccurate grasp of anchor design parameters, waste caused by excessive support, or failure of stability control caused by insufficient support, such problems often occur, especially in extreme environment rock stability control. The key reason is that people have not yet clearly revealed the mechanical response characteristics of the mortar anchoring system and the interaction mechanism between the anchor and the rock under load, which restricts the formation of a scientific and effective anchor design method.

[0003] The mortar anchor system is a complex system composed of five components (steel bar, mortar, anchor hole surrounding rock, bar-mortar interface, mortar-anchor hole surrounding rock interface) and analyzing the response law and deformation and failure characteristics of this complex system is an important basic work for in-depth understanding of its working mechanism and accurate simulation of its working behavior. The current sleeve pull-out test of the anchor system has the following two problems: (1) Although various sleeves are used to simulate the environmental stiffness of the rock mass, the material properties of the sleeve are different from those of the rock, which leads to the fact that the mechanical properties of the components such as the mortar-sleeve interface and the mortar-rock interface obtained in the test may be different from the anchor system in the actual rock mass of the project; (2) The existing sleeve pull-out test focuses on the pull-out load and displacement response, and the shear dilatancy effect generated during the pull-out process is not well understood. The results of the direct shear test of the bar-mortar interface show that the interface shear dilatancy effect and the evolution characteristics of radial stress play a very important role in the bearing capacity and failure mode of the anchor system.

[0004] Therefore, how to provide a combined sleeve pull-out test method that can achieve the technical effect of equivalently simulating semi-infinite rock stiffness and obtaining the response law and deformation and failure characteristics of the sample under constant stiffness conditions is a technical problem that technical personnel in this field urgently need to solve. Summary of the invention

[0005] In view of the problems existing in the prior art, the technical problem to be solved by the present invention is to provide a combined sleeve pulling test method, which can achieve the technical effect of equivalently simulating semi-infinite rock stiffness and obtaining the response law and deformation and failure characteristics of the sample under constant stiffness conditions.

[0006] To achieve the above-mentioned purpose, the present invention provides a combined sleeve pulling test method, wherein the combined sleeve pulling test method is performed by placing a sample on a combined sleeve pulling device for testing, and the combined sleeve pulling test method comprises: placing the anchor rod of the sample downward and fixing the sample on the combined sleeve pulling device; performing a pulling test on the sample by using the combined sleeve pulling device, monitoring and recording the pulling axial force, pulling displacement, time, and strain of the sample during the pulling process, and analyzing the mechanical response of the sample after the pulling test is completed.

[0007] In the first aspect, the sample preparation method includes: preparing a thick-walled cylindrical rock sample equipped with strain sensors; placing the thick-walled cylindrical rock sample equipped with strain sensors on a centering device, passing one end of the anchor rod through the center of the thick-walled cylindrical rock sample equipped with strain sensors and inserting it into the centering hole of the centering device, then filling the center of the thick-walled cylindrical rock sample equipped with strain sensors with mortar, covering it with a centering cover, and curing to obtain the anchor rod rock sample; sleeveing ​​a steel sleeve on the outer wall of the anchor rod rock sample, and arranging a plurality of first strain sensors on the outer wall of the steel sleeve to obtain the sample.

[0008] In the first aspect, the preparation of a thick-walled cylindrical rock sample provided with a strain sensor specifically includes: using a combination drill bit to produce a thick-walled cylindrical rock sample, using a grinding wheel to grind the surface of the thick-walled cylindrical rock sample to form a smooth surface, and obtaining a test thick-walled cylindrical rock sample; drawing marking lines at equal intervals in the circumference direction of the test thick-walled cylindrical rock sample, and then cutting grooves with a milling cutter to obtain a plurality of strain installation grooves; fixing a second strain sensor in each of the strain installation grooves to obtain the thick-walled cylindrical rock sample provided with a strain sensor.

[0009] In the first aspect, the combined sleeve pull-out test method further includes: after the pull-out test is completed, cutting the sample and analyzing the failure mode of the sample.

[0010] In the first aspect, the steel sleeve is a cylindrical structure, and the calculation formula of the outer radius c of the steel sleeve is:

[0011]

[0012] Among them, E s is the Young's modulus of the steel sleeve; μ s is the Poisson's ratio of the steel sleeve; E r is the Young's modulus of the thick-walled cylindrical rock sample used in the test; μ r is the Poisson's ratio of the thick-walled cylindrical rock sample for the test; b is the outer radius of the thick-walled cylindrical rock sample for the test; the thickness of the steel sleeve d=cb.

[0013] In the first aspect, the steel sleeve includes: two half sleeves, each of which is a semicircular structure, and the two half sleeves are symmetrically arranged; two first bolt connecting plates, and the two first bolt connecting plates are symmetrically arranged at the two ends of the first half sleeve; two second bolt connecting plates, and the two second bolt connecting plates are symmetrically arranged at the two ends of the second half sleeve; wherein each first bolt connecting plate is fixedly connected to a corresponding second bolt connecting plate by bolts; and a plurality of the first strain sensors are evenly arranged on the outer walls of the two half sleeves.

[0014] In the first aspect, the first bolt connection plate is spaced 3 mm from the corresponding second bolt connection plate; the diameters of the circles where the outer wall of the anchor rock sample and the inner walls of the two half sleeves are located are the same.

[0015] In the first aspect, the combined sleeve drawing device includes a dynamic strain collector, and a plurality of the first strain sensors and a plurality of the second strain sensors are all connected to the dynamic strain collector.

[0016] In the first aspect, the combined sleeve pulling device also includes: a pulling system, the pulling system includes a reaction frame and a power structure, the reaction frame includes an upper support platform and a lower fixed platform, the upper support platform and the lower fixed platform are symmetrically arranged at upper and lower intervals, two support rods are evenly arranged on the outer edge of the upper support platform, the upper support platform is fixedly connected to the lower fixed platform through the two support rods, and the fixed end of the power structure is fixedly connected to the lower end surface of the upper support platform; a sample placing platform, the sample placing platform is fixedly connected to the upper end surface of the upper support platform, and the sample placing platform is used to place the sample; a support plate, the outer edge of the support plate is provided with two sliding through holes, and the support plate is provided with two sliding through holes. A through hole is provided on the two support rods, and the support plate is slidably connected to the two support rods; a power through hole is provided in the center of the support plate, and the support plate is provided on the periphery of the output end of the power structure through the power through hole, and the support plate is fixedly connected to the output end of the power structure; a fixed structure, the fixed structure is located at the output end of the power structure; wherein a first through hole is provided at the center of the upper support platform, a second through hole is provided at the center of the power structure, and a third through hole is provided at the center of the sample placement platform, and the other end of the anchor rod passes through the third through hole, the first through hole, and the second through hole in sequence, and the anchor rod is fixedly connected to the output end of the power structure through the fixed structure.

[0017] In the first aspect, the fixing structure includes: a nut, which is adapted to the other end of the anchor rod; an anchor plate, which is located at the output end of the power structure, and a fourth through hole is opened in the center of the anchor plate; wherein the other end of the anchor rod passes through the fourth through hole, and the anchor rod is fixedly connected to the output end of the power structure through the nut.

[0018] In the first aspect, the combined sleeve pulling device further comprises a cuttings collection box, and the cuttings collection box is located on the upper end surface of the lower fixed platform.

[0019] Beneficial effects:

[0020] A combined sleeve pulling test method of the present invention is to place a sample in a combined sleeve pulling device for a pulling test to obtain the strain of the sample during the pulling process; in the combined sleeve pulling test method of the present invention, the sample is placed on a sample placing platform, the sample is installed in the combined sleeve pulling device, a power structure is controlled to pull the anchor rod, the power structure is a hollow jack, the hollow jack is used to pull the anchor rod with a constant displacement or a constant force, and the pulling displacement and pulling force during the pulling process are recorded. The hollow jack can realize force control or displacement control loading through a control system, and the displacement loading rate is 0.0 6mm / min~50mm / min; the strain parameters of the outer wall of the thick-walled cylindrical rock sample and the outer wall of the steel sleeve are monitored in real time by a dynamic strain collector, and the mechanical response of the sample is analyzed by combining the pull-out displacement and the pull-out force; at the same time, the sample is composed of anchor rod, mortar, thick-walled cylindrical rock sample for test and steel sleeve from the inside to the outside, forming a three-body two-face structure, the three bodies are anchor rod, mortar and thick-walled cylindrical rock sample for test, and the two faces are anchor rod-mortar interface and mortar-thick-walled cylindrical rock sample interface, in which the thickness of the steel sleeve is determined by the elastic modulus and Poisson's ratio of the steel used for the thick-walled cylindrical rock sample and the steel sleeve from the equivalent stiffness principle Theoretical calculations show that the combination of steel sleeves and thick-walled cylindrical rock samples can simulate the stiffness conditions of the surrounding environment of infinite-sized rocks, avoiding the difference between the mechanical properties of the interface between the mortar and the thick-walled cylindrical rock sample used in the test and the anchoring system in the actual rock mass of the project; during the pulling process, the interface swelling effect occurs at the anchor-mortar interface, which can be used to study the effects of the interface swelling effect and the evolution characteristics of radial stress on the bearing capacity and failure mode of the anchor; the inside of the sample is fixedly connected to the anchor by mortar. During the pulling process, the mortar strength, steel bar strength and anchoring length have a certain influence on the peak bearing capacity and failure mode of the sample. By discussing the mortar The influence of strength, steel bar strength, and anchoring length on the peak bearing capacity and failure mode of the specimen, combined with the monitored strain parameters of the outer wall of the thick-walled cylindrical rock specimen and the outer wall of the steel sleeve used in the test, can further reveal the radial constraint stress response law of the surrounding rock of the anchor hole during the pulling process, in order to provide a basis for in-depth understanding of the working mechanism of the anchoring system; in addition, a combined sleeve pulling test method of the present invention is simple and easy to control, can apply constant displacement and constant force, is simple to operate, and can reasonably, objectively and accurately simulate semi-infinite rock stiffness, reflecting the response law and deformation and failure characteristics of the specimen under constant stiffness conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of this specification or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 It is a structural schematic diagram of the combined sleeve drawing device of the present invention;

[0023] Figure 2 It is a schematic diagram of the connection structure of the dynamic strain acquisition instrument of the present invention;

[0024] Figure 3 It is a schematic diagram of injecting mortar into the center of a thick-walled cylindrical rock sample of the present invention;

[0025] Figure 4 It is a structural schematic diagram of the steel sleeve of the present invention;

[0026] Figure 5 This is a schematic diagram of radial stress and deformation of the surrounding rock of the bolt hole in semi-infinite surrounding rock;

[0027] Figure 6 It is a schematic diagram of radial stress and deformation analysis of the rock sample-steel sleeve assembly.

[0028] Reference numerals:

[0029] 1. Test specimen; 11. Anchor rod; 12. Second strain sensor; 13. Thick-walled cylindrical rock sample for test; 14. Steel sleeve; 141 Half sleeve; 142. First bolt connection plate; 143. Second bolt connection plate; 15. Strain installation groove; 16. Mortar;

[0030] 21. Pulling system; 211. Reaction frame; 2111. Upper support platform; 2112. Lower fixed platform; 2113. Support rod; 212. Power structure;

[0031] 22. Sample placement platform;

[0032] 23. Support plate;

[0033] 24. Fixing structure; 241. Nut; 242. Anchor plate;

[0034] 25. Dynamic strain acquisition instrument;

[0035] 26. Cuttings collection box;

[0036] 3. Centering device;

[0037] 4. Center the upper cover. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of this specification to clearly and completely describe the technical solutions in the embodiments of this specification. Obviously, the described embodiments are only part of the embodiments of this specification, not all of the embodiments. Based on the embodiments in this specification, all other embodiments obtained by ordinary technicians in this field belong to the scope of protection of the present invention.

[0039] Embodiment 1

[0040] like Figures 1 to 4 As shown, this embodiment 1 provides a combined sleeve pulling test method, the combined sleeve pulling test method is tested by placing a sample 1 on a combined sleeve pulling device, and the combined sleeve pulling test method includes: placing the anchor rod 11 of the sample 1 downward and fixing the sample 1 on the combined sleeve pulling device; performing a pulling test on the sample 1 through the combined sleeve pulling device, monitoring and recording the pulling axial force, pulling displacement, time, and strain of the sample 1 during the pulling process, and analyzing the mechanical response of the sample 1 after the pulling test is completed.

[0041] A combined sleeve pulling test method of the present invention is to place a sample 1 in a combined sleeve pulling device for a pulling test to obtain the strain of the sample 1 during the pulling process; in the combined sleeve pulling test method of the present invention, the sample 1 is placed on a sample placement platform 22, the sample 1 is installed in the combined sleeve pulling device 2, and a power structure 212 is controlled to pull the anchor rod 11, the power structure 212 is a hollow jack, and the hollow jack is used to pull the anchor rod 11 with a constant displacement or a constant force, and the pulling displacement and the pulling force during the pulling process are recorded. The hollow jack can realize force control or displacement control loading through a control system, and the displacement loading rate is 0.06m m / min~50mm / min; the strain parameters of the outer wall of the test thick-walled cylindrical rock sample 13 and the outer wall of the steel sleeve 14 are monitored in real time by the dynamic strain collector 25, and the mechanical response of the sample is analyzed in combination with the pull-out displacement and the pull-out force; at the same time, the sample 1 is composed of the anchor rod 11, the mortar 16, the test thick-walled cylindrical rock sample 13 and the steel sleeve 14 from the inside to the outside, forming a three-body two-face structure, the three bodies are the anchor rod 11, the mortar 16 and the test thick-walled cylindrical rock sample 13, the two faces are the anchor rod 11-mortar 16 interface, the mortar 16-test thick-walled cylindrical rock sample 13 interface, wherein the thickness of the steel sleeve 14 is determined by the elastic properties of the steel used for the test thick-walled cylindrical rock sample 13 and the steel sleeve The elastic modulus and Poisson's ratio are calculated by the equivalent stiffness principle, so that the combination of the steel sleeve 14 and the thick-walled cylindrical rock sample 13 can simulate the stiffness conditions of the surrounding environment of the infinite-size rock, avoiding the difference between the mechanical properties of the interface between the mortar 16 and the experimental thick-walled cylindrical rock sample 13 and the anchoring system in the actual rock mass of the project; during the pulling process, the interface swelling effect occurs at the interface of the anchor rod 11-mortar 16, which can be used to study the effects of the interface swelling effect and the evolution characteristics of the radial stress on the bearing capacity and failure mode of the anchor; the interior of the sample 1 is fixedly connected to the anchor rod 11 by the mortar 16. During the pulling process, the mortar strength, the steel bar strength, and the anchoring length have a significant effect on the peak bearing capacity and failure mode of the sample 1. It has a certain influence. By discussing the influence of mortar 16 strength, steel bar strength and anchoring length on the peak bearing capacity and failure mode of sample 1, combined with the monitored strain parameters of the outer wall of the thick-walled cylindrical rock sample 13 and the outer wall of the steel sleeve 14 used in the test, the radial constraint stress response law of the surrounding rock of the anchor hole during the pulling process can be further revealed, in order to provide a basis for in-depth understanding of the working mechanism of the anchoring system; in addition, a combined sleeve pulling test method of the present invention is simple in test method, easy to control, can apply constant displacement and constant force, is simple to operate, can reasonably, objectively and accurately simulate semi-infinite rock stiffness, and reflect the response law and deformation and failure characteristics of the sample under constant stiffness conditions.

[0042] In some possible implementations, the preparation method of the sample 1 includes: preparing a thick-walled cylindrical rock sample 13 equipped with strain sensors; placing the thick-walled cylindrical rock sample 13 equipped with strain sensors on a centering device 3, passing one end of the anchor rod 11 through the center of the thick-walled cylindrical rock sample 13 equipped with strain sensors and inserting it into the centering hole of the centering device 3, and then filling the center of the thick-walled cylindrical rock sample 13 equipped with strain sensors with mortar 16, covering it with a centering upper cover 4, and curing it to obtain the anchor rod rock sample; sleeveing ​​a steel sleeve 14 on the outer wall of the anchor rod rock sample, and arranging a plurality of first strain sensors on the outer wall of the steel sleeve 14 to obtain the sample 1.

[0043] Specifically, the anchor rod 11 is a finely rolled threaded steel bar, and one end of the anchor rod 11 is milled by a milling cutter into a smooth round structure with a height of 10 mm and a diameter of 10 mm, so that the anchor rod 11 can be just inserted into the centering hole of the centering device 3 during the centering process, so that the anchor rod 11 is centered in the test thick-walled cylindrical rock sample 13, so that the anchor rod 11 always remains centered during the installation process without deviation; the mortar 16 injected into the center of the test thick-walled cylindrical rock sample 13 needs to be vibrated and compacted to make the strength uniform and reach the maximum; the combined sleeve pull-out test of the present invention The method is not limited to the pull-out test of the mortar anchored specimen, but the mortar 16 in the center of the thick-walled cylindrical rock sample 13 for injection test can also be replaced with an anchoring material such as resin to carry out a pull-out test of the anchored specimen with an anchoring material such as resin; the first strain sensor is used to monitor the strain of the outer wall of the steel sleeve 14 during the pull-out test; the mortar 16 is the ratio planned in the test plan, and the curing after the mortar 16 is injected is carried out as required at room temperature, and the diameter of the outer wall of the anchor rod rock sample is the same as the diameter of the outer wall of the thick-walled cylindrical rock sample for the test.

[0044] In some possible implementations, the preparation of the thick-walled cylindrical rock sample 13 equipped with strain sensors specifically includes: using a combined drill bit to produce a thick-walled cylindrical rock sample 13, using a grinding wheel to grind the surface of the thick-walled cylindrical rock sample 13 to form a smooth surface, and obtaining a test thick-walled cylindrical rock sample 13; drawing marking lines at equal intervals in the circumference direction of the test thick-walled cylindrical rock sample 13, and then cutting grooves with a milling cutter to obtain a plurality of strain installation grooves 15; fixing a second strain sensor 12 in each of the strain installation grooves 15 to obtain the thick-walled cylindrical rock sample 13 equipped with strain sensors.

[0045] Specifically, the strain installation groove 15 on the outer wall of the test thick-walled cylindrical rock sample 13 is used to install the second strain sensor 12, which can avoid the friction and extrusion between the steel sleeve 14 and the outer wall of the test thick-walled cylindrical rock sample 13 during the pull-out test, thereby preventing the test of the second strain sensor 12 from being affected.

[0046] In some possible implementations, the combined sleeve pull-out test method further includes: after the pull-out test is completed, cutting the sample 1 and analyzing the failure mode of the sample 1.

[0047] Specifically, the inside of the thick-walled cylindrical rock sample 13 used for the test will be affected during the pulling test. Cutting the sample 1 can intuitively obtain the damage inside the thick-walled cylindrical rock sample 13, providing a phenomenological basis for analyzing the mechanical response of the sample 1 during the pulling process.

[0048] In some possible implementations, the steel sleeve 14 is a cylindrical structure, and the calculation formula of the outer radius c of the steel sleeve 14 is:

[0049]

[0050] Among them, E s is the Young's modulus of the steel sleeve 14; μ s is the Poisson's ratio of the steel sleeve 14; E r is the Young's modulus of the thick-walled cylindrical rock sample 13 used in the test; μ r is the Poisson's ratio of the test thick-walled cylindrical rock sample 13; b is the outer radius of the test thick-walled cylindrical rock sample 13; and the thickness of the steel sleeve 14 is d=cb.

[0051] Specifically, for a single anchor in an actual project, the surrounding rock of the anchor support is semi-infinite compared to the anchor hole. It is very costly to directly use large-sized rocks as surrounding rocks in indoor tests. Therefore, a steel sleeve 14 with equivalent stiffness is proposed to be placed on the outer shell of the finite-sized rock to simulate the stiffness conditions of the surrounding environment of the finite-sized rock, so as to achieve the stiffness conditions of the combination of the rock and the steel sleeve 14 to be equal to the semi-infinite rock, that is, to achieve the stiffness conditions of the rock sample-steel sleeve combination to be equal to the semi-infinite rock; for the semi-infinite surrounding rock, its deformation analysis under the radial force of the hole wall is as follows: Figure 5 As shown in the figure, since the surrounding rock is an infinite body, the pressure at infinity can be set to 0, and the radius of the anchor hole in the surrounding rock is a; the length direction of the anchor hole is much larger than the diameter of the anchor hole, so the axial direction of the anchor hole can be assumed to be a plane strain problem. According to the plane strain Lamé solution of the outer diameter thick-walled cylinder problem in semi-infinite space in elastic mechanics, when the inner wall of the anchor hole acts with a uniform pressure q a When , the radial expansion displacement of the anchor hole in the rock mass can be obtained as:

[0052]

[0053] Among them, u e is the radial displacement of the bolt hole wall in the actual rock mass; the surrounding rock is the same as the thick-walled cylindrical rock sample used in the test of the present invention, E r , μ rare Young's modulus and Poisson's ratio of the thick-walled cylindrical rock sample used in the test; a is the radius of the anchor hole, q a is the radial pressure on the inner wall of the anchor hole;

[0054] For the rock sample-steel sleeve assembly, the deformation analysis of the assembly under the radial force of the anchor hole is as follows: Figure 6 As shown in FIG. 1 , the radial displacement of the inner side of the thick-walled cylindrical rock sample 13 used in the test in the assembly can be obtained from the plane strain Lamé solution of the thick-walled cylinder problem in elastic mechanics:

[0055]

[0056] The radial displacement of the outer side of the thick-walled cylindrical rock sample 13 used in the test is:

[0057]

[0058] Among them, u r (r=a),u r (r=b) are the radial displacements of the inner and outer sides of the test thick-walled cylindrical rock sample 13; b is the outer radius of the test thick-walled cylindrical rock sample 13; q a ,q b are the radial pressures on the inner and outer walls of the thick-walled cylindrical rock sample 13 used in the test;

[0059] The pressure on the inner side of the steel sleeve 14 and the pressure on the outer side of the test thick-walled cylindrical rock sample 13 q b Similarly, the outer side of the steel sleeve 14 is a free surface with no stress (q c =0), so the radial displacement of the inner side of the steel sleeve 14 is:

[0060]

[0061] Among them, u s (r=b) is the radial displacement of the inner side of the steel sleeve 14; E s , μ s are Young's modulus and Poisson's ratio of the steel sleeve 14 respectively; c is the outer radius of the steel sleeve 14;

[0062] The inner wall of the steel sleeve 14 fits tightly with the outer wall of the test thick-walled cylindrical rock sample 13, and the radial displacement is continuous, that is, the radial displacement of the inner side of the steel sleeve 14 is equal to the radial displacement of the outer side of the test thick-walled cylindrical rock sample 13, so: u r (r=b)=u s (r = b);

[0063] In the actual rock environment, when the bolt hole wall is subjected to uniform internal pressure q a When the radial expansion displacement of the anchor hole wall is u eIn the rock sample-steel sleeve assembly, when the inner wall of the test thick-walled cylindrical rock sample 13 is subjected to the internal pressure q a When the radial expansion displacement of the inner wall of the thick-walled cylindrical rock sample 13 is u r According to the principle of equivalent stiffness, the consistency of the internal pressure and radial expansion displacement between the rock sample-steel sleeve assembly and the actual rock mass must be ensured, that is, when the internal pressure is q a When the actual radial displacement of the anchor hole wall is e The radial displacement u of the inner wall of the thick-walled cylindrical rock sample of the rock sample-steel sleeve assembly under test r Equal, that is: u r (r=a)=u e (r=a); In summary, the calculation formula for the outer radius c of the steel sleeve 14 is:

[0064]

[0065] This results in a thickness d=cb of the steel sleeve 14 .

[0066] In some possible implementations, the steel sleeve 14 includes: two half sleeves 141, each of the half sleeves 141 is a semicircular structure, and the two half sleeves 141 are symmetrically arranged; two first bolt connecting plates 142, the two first bolt connecting plates 142 are symmetrically arranged at the two ends of the first half sleeve 141; two second bolt connecting plates 143, the two second bolt connecting plates 143 are symmetrically arranged at the two ends of the second half sleeve 141; wherein each first bolt connecting plate 142 is fixedly connected to a corresponding second bolt connecting plate 143 by bolts; a plurality of the first strain sensors are evenly arranged on the outer walls of the two half sleeves 141; the first bolt connecting plate 142 and the corresponding second bolt connecting plate 144 are spaced 3 mm apart; the outer wall of the anchor rock sample, the inner wall of the two half sleeves 141, and the diameter of the circle in which they are located are all the same.

[0067] Specifically, the two half sleeves are mainly obtained by axially symmetrically cutting a steel cylinder whose inner radius is the same as the outer radius of the test thick-walled cylindrical rock sample 13. The inner radius of the two half sleeves 141 is the same as the outer radius of the test thick-walled cylindrical rock sample 13, so that when the two half sleeves 141 are on the outer wall of the test thick-walled cylindrical rock sample 13, the inner walls of the two half sleeves 141 can be tightly attached to the test thick-walled cylindrical rock sample 13, and the two first bolt connecting plates 142 are fixedly connected with the corresponding two second bolt connecting plates 144 by bolts, so that the two half sleeves 141 are set tightly against the test thick-walled cylindrical rock sample 13, so that the connection between the first half sleeve 141 and the second half sleeve 141 is approximately a rigid connection, wherein the number and diameter of the bolts are calculated according to the simulated stiffness of the steel sleeve 14; in addition, the first bolt connecting plates 142 and the corresponding second bolt connecting plates 144 are fixedly connected by bolts, so that the two half sleeves 141 are set tightly against the test thick-walled cylindrical rock sample 13, and the connection between the first half sleeve 141 and the second half sleeve 141 is approximately a rigid connection, wherein the number and diameter of the bolts are calculated according to the simulated stiffness of the steel sleeve 14; in addition, the first bolt connecting plates 142 and the corresponding second bolt connecting plates 144 are fixedly connected by bolts. The bolt connection plate 142 is spaced 3 mm from the corresponding second bolt connection plate 143, which can further make the two half sleeves 141 fit tightly against the test thick-walled cylindrical rock sample 13, avoiding the existence of gaps that lead to looseness between the steel sleeve 14 and the test thick-walled cylindrical rock sample 13 and affect the test data; the thickness of the two half sleeves 141 is calculated by the elastic modulus and Poisson's ratio of the test thick-walled cylindrical rock sample 13 and the steel material according to the equivalent stiffness principle; by putting the steel sleeve 14 on the outer wall of the finite-size rock test thick-walled cylindrical rock sample 13, the stiffness conditions of the surrounding environment of the infinite-size rock can be simulated, so that the stiffness conditions of the rock sample-steel sleeve combination are equal to those of the semi-infinite rock. At the same time, the response law and deformation and failure characteristics of the anchoring system under constant stiffness conditions can be obtained through a pull-out test.

[0068] In some possible implementations, the combined sleeve drawing device includes a dynamic strain collector 25 , and a plurality of the first strain sensors and a plurality of the second strain sensors 12 are connected to the dynamic strain collector 25 .

[0069] Specifically, the second strain sensor 12 and the first strain sensor are connected to the dynamic strain collector 25 through strain connecting lines. The dynamic strain collector 25 is used to receive the strain data of the outer wall of the test thick-walled cylindrical rock sample 13 and the outer wall of the steel sleeve 14 measured by the second strain sensor 12 and the first strain sensor on the sample 1.

[0070] In some possible implementations, the combined sleeve drawing device also includes: a drawing system 21, the drawing system 21 includes a reaction frame 211 and a power structure 212, the reaction frame 211 includes an upper support platform 2111 and a lower fixed platform 2112, the upper support platform 2111 and the lower fixed platform 2112 are symmetrically arranged at upper and lower intervals, two support rods 2113 are evenly arranged on the outer edge of the upper support platform 2111, the upper support platform 2111 is fixedly connected to the lower fixed platform 2112 through the two support rods 2113, and the fixed end of the power structure 212 is fixedly connected to the lower end surface of the upper support platform 2111; 22 sample placing platform, the sample placing platform 22 is fixedly connected to the upper end surface of the upper support platform 2111, and the sample placing platform 22 is used to place the sample 1; a support plate 23, the outer edge of the support plate 23 is provided with two sliding through holes , the support plate 23 is sleeved on the two support rods 2113 through the two sliding through holes, and the support plate 23 is slidably connected to the two support rods 2113; a power through hole is opened in the center of the support plate 23, and the support plate 23 is sleeved on the periphery of the output end of the power structure 212 through the power through hole, and the support plate 23 is fixedly connected to the output end of the power structure 212; a fixed structure 24, the fixed structure 24 is located at the output end of the power structure 212; wherein, a first through hole is opened in the center of the upper support platform 2111, a second through hole is opened in the center of the power structure 212, and a third through hole is opened in the center of the sample placement platform 22, and the other end of the anchor rod 11 passes through the third through hole, the first through hole, and the second through hole in sequence, and the anchor rod 11 is fixedly connected to the output end of the power structure 212 through the fixed structure 24.

[0071] Specifically, in the present invention, the reaction frame 211 serves as the main supporting structure, the support plate 23 serves as the auxiliary supporting structure, the fixed end of the power structure 212 is fixed on the reaction frame 211, the middle of the output end of the power structure 212 is fixed on the support plate 23, the sample placement platform 22 is fixed on the reaction frame 211, the sample 1 is placed on the sample placement platform 22, the anchor rod 11 on the sample 1 passes through the third through hole, the first through hole, and the second through hole in sequence, the anchor rod 11 is fixed to the output end of the power structure 212 through the fixing structure 24, the power structure 212 is connected to the control system, and the sample placement platform 22 is fixed on the reaction frame 211. The control system controls the output end of the power structure 212 to extend and retract to pull the anchor rod 11 of the sample 1; when the output end of the power structure 212 pulls the anchor rod 11 with a constant displacement or a constant force, the test thick-walled cylindrical rock sample 13 inside the sample 1 changes due to the anchor rod 11 being pulled downward, and the outer wall of the test thick-walled cylindrical rock sample 13 will be strained. When the outer wall of the test thick-walled cylindrical rock sample 13 is strained, the steel sleeve 14 outside the sample 1 will be strained accordingly; the inside of the test thick-walled cylindrical rock sample 13 is fixed to the anchor rod 11 by the mortar 16. During the pulling process, the strength of the mortar 16, the strength of the steel bars of the anchor rod 11, and the length of the anchor rod 11 all have an impact on the peak bearing capacity and failure mode of the sample 1; the pulling force and pulling displacement applied by the dynamic structure 212 can be used to analyze the mechanical response of the sample 1, and the influence of the strength of the mortar 16, the strength of the steel bars of the anchor rod 11, and the length of the anchor rod 11 on the peak bearing capacity and failure mode of the sample 1 is discussed. At the same time, combined with the strain data of the outer wall of the test thick-walled cylindrical rock sample 13 and the outer wall of the steel sleeve 14 monitored by the dynamic strain collector 25, it can be revealed that the anchor hole in the pulling process The radial constraint stress response law of the surrounding rock provides a basis for in-depth understanding of the working mechanism of the anchoring system; the combined sleeve pulling device has a simple structure, low cost, simple operation and easy implementation. It simulates environmental conditions by combining the steel sleeve 14 with the thick-walled cylindrical rock sample 13 for the test, and can simulate semi-infinite rock stiffness, so that the pulling test is carried out under constant stiffness conditions to reflect the response law and deformation and failure characteristics of the sample. At the same time, it has important significance for the research and application of anchoring support in the fields of water conservancy and hydropower, transportation tunnels, slope protection, underground engineering, mining engineering, foundation anti-tilt, anti-floating and other engineering.

[0072] In some possible implementations, the fixing structure 24 includes: a nut 241, which is adapted to the other end of the anchor rod 11; an anchor plate 242, which is located at the output end of the power structure 212, and a fourth through hole is opened in the center of the anchor plate 242; wherein the other end of the anchor rod 11 passes through the fourth through hole, and the anchor rod 11 is fixedly connected to the output end of the power structure 212 through the nut 241.

[0073] Specifically, the nut 241 is adapted to the anchor rod 11, and the nut 241 is sleeved on the threaded end of the anchor rod 11 to fixedly connect the anchor rod 11 with the output end of the power structure 212, so that the elongation of the output end of the power structure 212 drives the anchor rod 11 to be pulled.

[0074] In some possible implementations, the combined sleeve pulling device further includes a cuttings collection box 26 , and the cuttings collection box 26 is located on the upper end surface of the lower fixed platform 2112 .

[0075] Specifically, the rock debris collection box 26 is used to collect rock sample debris generated by the friction between the inside of the sample 1 and the anchor rod 11 during the pulling process.

[0076] In summary, the combined sleeve pull-out test method of the present invention has the following advantages: 1. The combined sleeve pull-out test method of the present invention is simple to operate, easy to implement and control, can apply constant displacement and constant force, can reasonably, objectively and accurately simulate semi-infinite rock stiffness, and reflect the response law and deformation failure characteristics of the sample under constant stiffness conditions; 2. By sleeved with a steel sleeve 14 on the outer wall of the thick-walled cylindrical rock sample 13, the thickness of the steel sleeve 14 is calculated by the elastic modulus and Poisson's ratio of the thick-walled cylindrical rock sample 13 and the steel material by the equivalent stiffness principle, so that the rock sample-steel sleeve combination composed of the thick-walled cylindrical rock sample 13 and the upper steel sleeve 14 can simulate the stiffness conditions of the surrounding environment of the infinite size rock, and at the same time, the response law and deformation failure characteristics of the anchoring system under constant stiffness conditions can be obtained through the pull-out test; 3. During the pulling process, the interface swelling effect occurring at the interface of the anchor rod 11-mortar 16 can be used to study the effects of the interface swelling effect and the evolution characteristics of the radial stress on the bearing capacity and failure mode of the anchoring.

[0077] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A combined sleeve pull-out test method, characterized in that: The combined sleeve pulling test method is to place a sample on a combined sleeve pulling device for testing, and the combined sleeve pulling test method includes: The anchor rod of the sample is directed downward and the sample is fixed on the combined sleeve pulling device; The sample is subjected to a pulling test by the combined sleeve pulling device, and the pulling axial force, pulling displacement, time, and strain of the sample during the pulling process are monitored and recorded. After the pulling test is completed, the mechanical response of the sample is analyzed.

2. A combined sleeve pull-out test method as claimed in claim 1, characterized in that: The sample preparation method comprises: preparing a thick-walled cylindrical rock sample equipped with strain sensors; The thick-walled cylindrical rock sample provided with the strain sensor is placed on a centering device, one end of the anchor rod is passed through the center of the thick-walled cylindrical rock sample provided with the strain sensor and inserted into the centering hole of the centering device, and then the center of the thick-walled cylindrical rock sample provided with the strain sensor is filled with mortar, covered with a centering upper cover, and cured to obtain the anchor rod rock sample; A steel sleeve is sleeved on the outer side wall of the anchor rock sample, and a plurality of first strain sensors are arranged on the outer side wall of the steel sleeve to obtain the sample.

3. A combined sleeve pull-out test method as claimed in claim 2, characterized in that: The preparation of a thick-walled cylindrical rock sample provided with a strain sensor specifically comprises: A thick-walled cylindrical rock sample is produced by using a combined drill bit, and a surface of the thick-walled cylindrical rock sample is polished by using a grinding wheel to form a smooth surface, thereby obtaining a thick-walled cylindrical rock sample for testing; Marking lines are drawn at equal intervals in the circumference direction of the thick-walled cylindrical rock sample used in the test, and then grooves are cut with a milling cutter to obtain a plurality of strain installation grooves; A second strain sensor is fixed in each of the strain installation grooves to obtain the thick-walled cylindrical rock sample on which the strain sensors are arranged.

4. A combined sleeve pull-out test method as claimed in claim 3, characterized in that: The combined sleeve pull-out test method further includes: after the pull-out test is completed, cutting the sample and analyzing the failure mode of the sample.

5. A combined sleeve pull-out test method as claimed in claim 4, characterized in that: The steel sleeve has a cylindrical structure, and the calculation formula of the outer radius c of the steel sleeve is: Among them, E s is the Young's modulus of the steel sleeve; μ s is the Poisson's ratio of the steel sleeve; E r is the Young's modulus of the thick-walled cylindrical rock sample used in the test; μ r is the Poisson's ratio of the thick-walled cylindrical rock sample used in the test; b is the outer radius of the thick-walled cylindrical rock sample used in the test; The thickness of the steel sleeve is d=cb.

6. A combined sleeve pulling test method as claimed in claim 5, characterized in that: The steel sleeve comprises: Two half sleeves, each of which is in a semicircular structure, and the two half sleeves are symmetrically arranged; Two first bolt connection plates, which are symmetrically arranged at two ends of the first half sleeve; Two second bolt connection plates, the two second bolt connection plates are symmetrically arranged at two ends of the second half sleeve; Wherein, each of the first bolt connecting plates is fixedly connected to a corresponding second bolt connecting plate by bolts; and a plurality of the first strain sensors are evenly distributed on the outer side walls of the two half sleeves.

7. A combined sleeve pull-out test method as claimed in claim 6, characterized in that: The first bolt connection plate and the corresponding second bolt connection plate are spaced 3 mm apart; the diameters of the circles where the outer wall of the anchor rock sample and the inner walls of the two half sleeves are located are the same.

8. A combined sleeve pull-out test method as claimed in claim 7, characterized in that: The combined sleeve drawing device comprises a dynamic strain collector, and a plurality of the first strain sensors and a plurality of the second strain sensors are all connected to the dynamic strain collector.

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