A combined sleeve-pull test method

Abstract

The application discloses a combined sleeve drawing test method, which places a sample in a combined sleeve drawing device to carry out a drawing test, and obtains the strain of the sample in the drawing process. Compared with the prior art, the combined sleeve drawing test method has the advantages of simple operation, easy control, constant displacement and constant force, and can accurately simulate the stiffness of semi-infinite rock, and reflect the response law and deformation and failure characteristics of the sample under the constant stiffness condition.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering, and in particular to a method for pull-out testing of a combined sleeve. Background Technology

[0002] Rock bolt support is one of the most effective rock mass stability control technologies. Rock bolts have been widely used and developed in water conservancy and hydropower, transportation tunnels, slope protection, underground engineering, mining engineering, and foundation anti-tilting and anti-buoyancy projects. Among them, mortar rock bolts are the most widely used and have excellent support effects. Nevertheless, due to inaccurate rock bolt design parameters, situations such as excessive support leading to waste or insufficient support causing stability control failures occur frequently, especially in extreme rock mass stability control environments. The key reason is that the mechanical response characteristics of mortar anchoring systems and the interaction mechanism between rock bolts and rock mass under load have not yet been clearly elucidated, hindering the formation of scientifically effective rock bolt design methods.

[0003] The mortar anchoring system is a complex system composed of five components (steel rod, mortar, rock surrounding the anchor hole, rod-mortar interface, and mortar-anchor hole rock surrounding interface). Analyzing the response law and deformation and failure characteristics of this complex system is an important foundation for understanding its working mechanism and accurately simulating its working behavior. The current sleeve pull-out test of the anchoring system has the following two problems: (1) Although various sleeves are used to simulate the stiffness of the rock environment, the material properties of the sleeves are different from those of the rock. As a result, the mechanical properties of the components such as the mortar-sleeve interface and the mortar-rock interface obtained in the test may differ from those of the anchoring 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 does not fully understand the shear dilatation effect generated during the pull-out process. As can be seen from the results of the direct shear test of the rod-mortar interface, the evolution characteristics of the interface shear dilatation effect and radial stress play a very important role in the bearing capacity and failure mode of the anchoring system.

[0004] Therefore, how to provide a combined sleeve pull-out test method that can achieve the technical effect of equivalently simulating the stiffness of semi-infinite rock and obtaining the response law and deformation and failure characteristics of the specimen under constant stiffness conditions is a technical problem that urgently needs to be solved by those skilled in the art. 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 pull-out test method, which can achieve the technical effect of equivalently simulating the stiffness of semi-infinite rock and obtaining the response law and deformation and failure characteristics of the sample under constant stiffness conditions.

[0006] To achieve the above objectives, the present invention provides a combined sleeve pull-out test method. The combined sleeve pull-out test method involves placing the specimen on a combined sleeve pull-out device for testing. The combined sleeve pull-out test method includes: fixing the specimen with its anchor rod facing downwards on the combined sleeve pull-out device; performing a pull-out test on the specimen using the combined sleeve pull-out device; monitoring and recording the pull-out axial force, pull-out displacement, time, and strain of the specimen during the pull-out process; and analyzing the mechanical response of the specimen after the pull-out test is completed.

[0007] In the first aspect, the method for preparing the sample 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, inserting one end of the anchor rod through the center of the thick-walled cylindrical rock sample equipped with strain sensors and 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 it to obtain an anchor rod rock sample; and placing 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 the thick-walled cylindrical rock sample equipped with strain sensors 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, thereby obtaining a test thick-walled cylindrical rock sample; drawing marking lines at equal intervals along the circumference of the test thick-walled cylindrical rock sample, and then using a milling cutter to carve grooves to obtain a plurality of strain mounting grooves; fixing a second strain sensor in each of the strain mounting grooves, thereby obtaining the thick-walled cylindrical rock sample equipped with strain sensors.

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

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

[0011]

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

[0013] In the first aspect, the steel sleeve includes: two half-sleeves, each half-sleeve having a semi-circular structure, and the two half-sleeves being symmetrically arranged; two first bolt connecting plates, the two first bolt connecting plates being symmetrically arranged at both ends of the first half-sleeve; and two second bolt connecting plates, the two second bolt connecting plates being symmetrically arranged at both 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 first strain sensors are evenly distributed on the outer walls of the two half-sleeves.

[0014] In the first aspect, the first bolt connecting plate and the corresponding second bolt connecting plate are spaced 3 mm apart; the diameters of the outer sidewall of the anchor rock sample and the inner sidewalls of the two half-sleeves are the same.

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

[0016] In the first aspect, the combined sleeve pulling device further includes: a pulling system comprising a reaction frame and a power structure; the reaction frame comprising an upper support platform and a lower fixed platform, the upper support platform and the lower fixed platform being symmetrically arranged at intervals; two support rods evenly distributed along the outer edge of the upper support platform; the upper support platform being fixedly connected to the lower fixed platform via the two support rods; and the fixed end of the power structure being fixedly connected to the lower end face of the upper support platform; a sample placement platform fixedly connected to the upper end face of the upper support platform; the sample placement platform being used to place the sample; and a support plate having two sliding through holes along its outer edge; the support plate being connected to the upper fixed platform via the two sliding through holes. A perforated sleeve is fitted onto the two support rods, and the support plate is slidably connected to the two support rods; a power perforation is opened in the center of the support plate, and the support plate is fitted around the output end of the power structure through the power perforation, and the support plate is fixedly connected to the output end of the power structure; a fixing structure is located at the output end of the power structure; wherein, a first perforation is opened in the center of the upper support platform, a second perforation is opened in the center of the power structure, a third perforation is opened in the center of the sample placement platform, and the other end of the anchor rod passes through the third perforation, the first perforation, and the second perforation in sequence, and the anchor rod is fixedly connected to the output end of the power structure through the fixing structure.

[0017] In the first aspect, the fixing structure includes: a nut adapted to the other end of the anchor rod; an anchor plate located at the output end of the power structure, the anchor plate having a fourth through hole at its center; 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 by the nut.

[0018] In the first aspect, the combined sleeve pulling device further includes a rock cuttings collection box located on the upper end face of the lower fixed platform.

[0019] Beneficial effects:

[0020] This invention discloses a combined sleeve pull-out test method. The method involves placing the sample in a combined sleeve pull-out device to perform a pull-out test, thereby obtaining the strain of the sample during the pull-out process. In this method, the sample is placed on a sample placement platform and installed in the combined sleeve pull-out device. A power structure, specifically a hollow jack, is controlled to pull the anchor rod with a constant displacement or constant force. The pull-out displacement and pull-out force are recorded. The hollow jack can be loaded using force control or displacement control via a control system, with a displacement loading rate of 0.0%. The strain rate is 6 mm / min to 50 mm / 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 using a dynamic strain acquisition instrument. The mechanical response of the sample is analyzed by combining pull-out displacement and pull-out force. Simultaneously, the sample, from the inside out, consists of an anchor rod, mortar, the thick-walled cylindrical rock sample, and the steel sleeve, forming a three-body, two-sided structure. The three bodies are the anchor rod, mortar, and the thick-walled cylindrical rock sample; the two sides are the anchor rod-mortar interface and the mortar-thick-walled cylindrical rock sample interface. The thickness of the steel sleeve is determined by the elastic modulus and Poisson's ratio of the steel used in the thick-walled cylindrical rock sample and the steel sleeve, based on the equivalent stiffness. Theoretical calculations show that the combination of steel sleeve and thick-walled cylindrical rock sample effectively simulates the stiffness conditions of an infinitely sized rock environment, avoiding the differences between the mechanical properties of the interface between the mortar and the test thick-walled cylindrical rock sample and the anchoring system in actual engineering rock masses. During the pull-out process, the anchor-mortar interface undergoes an interfacial de-expansion effect, which can be used to study the effects of interfacial de-expansion benefits and the evolution characteristics of radial stress on the bearing capacity and failure mode of the anchorage. The sample is internally fixed to the anchor rod through mortar. During the pull-out process, the mortar strength, steel reinforcement strength, and anchorage length have a certain influence on the peak bearing capacity and failure mode of the sample. This is discussed through the mortar... The influence of strength, reinforcement strength, and anchorage length on the peak bearing capacity and failure mode of the specimen, combined with the strain parameters of the outer wall of the thick-walled cylindrical rock sample and the outer wall of the steel sleeve monitored in the test, can further reveal the radial constraint stress response law of the surrounding rock of the anchor hole during the pull-out process, so as to provide a basis for a deeper understanding of the working mechanism of the anchoring system. In addition, the combined sleeve pull-out test method of the present invention is simple and easy to control. It can apply constant displacement and constant force, and is easy to operate. It can reasonably, objectively and accurately simulate the stiffness of semi-infinite rock and reflect the response law and deformation and failure characteristics of the specimen under constant stiffness conditions. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this specification or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the combined sleeve pulling device of the present invention;

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

[0024] Figure 3 This is a schematic diagram of the mortar injection for centering a thick-walled cylindrical rock sample according to the present invention;

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

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

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

[0028] Figure label:

[0029] 1. Sample; 11. Anchor bolt; 12. Second strain sensor; 13. Thick-walled cylindrical rock sample for testing; 14. Steel sleeve; 141. Half sleeve; 142. First bolt connection plate; 143. Second bolt connection plate; 15. Strain mounting 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. Fixed structure; 241. Nut; 242. Anchor plate;

[0034] 25. Dynamic strain acquisition instrument;

[0035] 26. Rock cuttings collection box;

[0036] 3. Centering device;

[0037] 4. Center the top cover. Detailed Implementation

[0038] The technical solutions in the embodiments of this specification will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this specification, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments in this specification are within the scope of protection of this invention.

[0039] Example 1

[0040] like Figures 1-4 As shown, this embodiment provides a combined sleeve pull-out test method. The combined sleeve pull-out test method involves placing the sample 1 on a combined sleeve pull-out device for testing. The combined sleeve pull-out test method includes: fixing the sample 1 with the anchor rod 11 facing downwards and fixing the sample 1 on the combined sleeve pull-out device; performing a pull-out test on the sample 1 through the combined sleeve pull-out device; monitoring and recording the pull-out axial force, pull-out displacement, time, and strain of the sample 1 during the pull-out process; and analyzing the mechanical response of the sample 1 after the pull-out test is completed.

[0041] This invention discloses a combined sleeve pull-out test method. The strain of the sample 1 during the pull-out process is obtained by placing the sample 1 in a combined sleeve pull-out device. In this method, the sample 1 is placed on a sample placement platform 22 and installed in the combined sleeve pull-out device 2. A power structure 212 (a hollow jack) is controlled to pull the anchor rod 11 with a constant displacement or constant force. The pull-out displacement and pull-out force are recorded. The hollow jack can be loaded using force control or displacement control via a control system, with a displacement loading rate of 0.06 m. m / min~50mm / min; The strain parameters of the outer wall of the thick-walled cylindrical rock sample 13 and the outer wall of the steel sleeve 14 are monitored in real time by a dynamic strain acquisition instrument 25, and the mechanical response of the sample is analyzed by combining the pull-out displacement and pull-out force; At the same time, the sample 1 consists of anchor rod 11, mortar 16, thick-walled cylindrical rock sample 13 and steel sleeve 14 from the inside to the outside, forming a three-body two-sided structure. The three bodies are anchor rod 11, mortar 16 and thick-walled cylindrical rock sample 13, and the two sides are the anchor rod 11-mortar 16 interface and the mortar 16-thick-walled cylindrical rock sample 13 interface. The thickness of the steel sleeve 14 is determined by the elasticity of the steel used in the thick-walled cylindrical rock sample 13 and the steel sleeve. The tensile modulus and Poisson's ratio are calculated using the equivalent stiffness principle, achieving the effect of simulating the stiffness conditions of the environment surrounding an infinitely large rock using the combination of steel sleeve 14 and thick-walled cylindrical rock sample 13. This avoids the difference between the mechanical properties of the interface between mortar 16 and the test thick-walled cylindrical rock sample 13 and the anchoring system in actual engineering rock masses. During the pull-out process, the interface between anchor rod 11 and mortar 16 undergoes an interface de-expansion effect, which can be used to study the effect of interface de-expansion benefits and the evolution characteristics of radial stress on the bearing capacity and failure mode of the anchorage. The sample 1 is fixedly connected to the anchor rod 11 through mortar 16. During the pull-out process, the mortar strength, steel reinforcement strength, and anchorage length have a significant impact on the peak bearing capacity and failure mode of sample 1. This study has a certain impact. By discussing the influence of mortar strength, steel reinforcement strength, and anchorage length on the peak bearing capacity and failure mode of sample 1, and combining the strain parameters of the outer wall of the thick-walled cylindrical rock sample 13 and the outer wall of the steel sleeve 14 monitored during the test, the radial constraint stress response law of the rock surrounding the anchor hole during the pull-out process can be further revealed, in order to provide a basis for a deeper understanding of the working mechanism of the anchorage system. In addition, the combined sleeve pull-out test method of this invention is simple, easy to control, and can apply constant displacement and constant force. It is easy to operate and can reasonably, objectively, and accurately simulate the stiffness of semi-infinite rock, reflecting 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, then filling the center of the thick-walled cylindrical rock sample 13 equipped with strain sensors with mortar 16, covering it with a centering cover 4, and curing it to obtain an anchor rod rock sample; fitting a steel sleeve 14 onto the outer wall of the anchor rod rock sample, and arranging several 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 precision-rolled threaded steel bar. One end of the anchor rod 11 is milled into a smooth round structure with a height of 10mm and a diameter of 10mm by a milling cutter, so that the anchor rod 11 is inserted precisely into the centering hole of the centering device 3 during the centering process, ensuring that the anchor rod 11 is centered in the test thick-walled cylindrical rock sample 13 and remains centered throughout the installation process without any deviation. The mortar 16 injected into the center of the test thick-walled cylindrical rock sample 13 needs to be vibrated and compacted to ensure uniform strength and maximize its strength. The combined sleeve pull-out test of the present invention... The method is not limited to pull-out tests of mortar-anchored specimens. It can also replace the mortar 16 injected into the center of the thick-walled cylindrical rock specimen 13 used for testing with anchoring agent materials such as resin to carry out pull-out tests of anchoring specimens with anchoring agent materials such as resin. The first strain sensor is used to monitor the strain that occurs on the outer wall of the steel sleeve 14 during the pull-out test. The mortar 16 is the proportion planned in the test scheme. After injecting the mortar 16, the curing is carried out as required under room temperature conditions. The diameter of the outer wall of the anchor rock specimen is the same as the diameter of the outer wall of the thick-walled cylindrical rock specimen used for testing.

[0044] In some possible implementations, the preparation of the thick-walled cylindrical rock sample 13 equipped with strain sensors specifically includes: using a combination drill bit to produce the 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, thus obtaining the test thick-walled cylindrical rock sample 13; drawing marking lines at equal intervals along the circumference of the test thick-walled cylindrical rock sample 13, and then using a milling cutter to carve grooves to obtain a plurality of strain mounting grooves 15; fixing a second strain sensor 12 in each of the strain mounting grooves 15, thus obtaining the thick-walled cylindrical rock sample 13 equipped with strain sensors.

[0045] Specifically, the strain mounting groove 15 on the outer wall of the thick-walled cylindrical rock sample 13 is used to install the second strain sensor 12, which can avoid the steel sleeve 14 from being rubbed and squeezed against the outer wall of the thick-walled cylindrical rock sample 13 during the pull-out test, thus avoiding the impact on the test of the second strain sensor 12.

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

[0047] Specifically, the pull-out test will affect the interior of the thick-walled cylindrical rock sample 13. Cutting the sample 1 open will allow a direct view of the damage inside the thick-walled cylindrical rock sample 13, providing a phenological basis for analyzing the mechanical response of the sample 1 during the pull-out process.

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

[0049]

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

[0051] Specifically, for a single anchor bolt in actual engineering, the surrounding rock supported by the anchor bolt is a semi-infinite mass relative to the anchor bolt hole. Using large-sized rocks directly as the surrounding rock in laboratory tests is very costly. Therefore, it is proposed to coat a finite-sized rock with a steel sleeve 14 of equivalent stiffness to simulate the stiffness conditions of the environment surrounding the finite-sized rock. This will ensure that the stiffness conditions of the rock-steel sleeve 14 assembly are equal to those of the semi-infinite rock, i.e., that the stiffness conditions of the rock sample-steel sleeve assembly are equal to those of the semi-infinite rock. For the semi-infinite surrounding rock, its deformation analysis under the radial force of the borehole wall is as follows: Figure 5 As shown, since the surrounding rock is infinitely large, the pressure at infinity can be assumed to be 0, and the radius of the anchor hole inside the surrounding rock is a. The length of the anchor hole is much larger than its diameter, so the axial direction of the anchor hole can be assumed to be a plane strain problem. According to the plane strain Lamé solution for the semi-infinite space thick-walled cylinder problem in elasticity, when a uniform pressure q is applied to the inner wall of the anchor hole... a At that time, the radial expansion displacement of the anchor bolt hole in the rock mass can be obtained as follows:

[0052]

[0053] Among them, u e This represents the radial displacement of the actual rock mass anchor hole wall; the surrounding rock and the thick-walled cylindrical rock sample used in the experiment of this invention are the same type of rock, E. r μ rThese represent the Young's modulus and Poisson's ratio of the thick-walled cylindrical rock sample used in the experiment; a is the radius of the anchor bolt hole, and q is the value of the value of the anchor bolt hole. a This refers to the radial pressure on the inner wall of the anchor bolt hole;

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

[0055]

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

[0057]

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

[0059] The pressure on the inner side of the steel sleeve 14 and the pressure q on the outer side of the thick-walled cylindrical rock sample 13 used in the test b Similarly, the outer side of steel sleeve 14 is a free surface, without stress (q) c =0), therefore the radial displacement of the inner side of the steel sleeve 14 is:

[0060]

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

[0062] The inner wall of the steel sleeve 14 is in close contact with the outer wall of the thick-walled cylindrical rock sample 13 used in the test, and the radial displacement is continuous. That is, the radial displacement inside the steel sleeve 14 is equal to the radial displacement outside the thick-walled cylindrical rock sample 13 used in the test. Therefore, we have: u r (r=b)=u s (r=b);

[0063] In actual rock environments, when the anchor bolt hole wall is subjected to a uniform internal pressure q a When the radial expansion displacement of the anchor bolt hole wall is u, eIn the rock sample-steel sleeve assembly, when the inner wall of the thick-walled cylindrical rock sample 13 used in the experiment is subjected to an internal pressure q... a At that time, the radial expansion displacement of the inner wall of the thick-walled cylindrical rock sample 13 used in the experiment was u. r According to the principle of equivalent stiffness, it is necessary to ensure the consistency between the rock sample-steel sleeve assembly and the actual rock mass in terms of internal pressure and radial expansion displacement, that is, when the internal pressure is q... a At that time, the actual radial displacement u of the anchor bolt hole wall e The radial displacement u of the inner wall of the thick-walled cylindrical rock sample in the rock sample-steel sleeve assembly during the test should correspond to the radial displacement u of the inner wall of the rock sample. r Equal, that is: u r (r=a)=u e (r=a); In summary, the formula for calculating the outer radius c of the 14 steel sleeve is:

[0064]

[0065] Therefore, the thickness d = cb of the steel sleeve 14 is obtained.

[0066] In some possible implementations, the steel sleeve 14 includes: two semi-sleeves 141, each of which is semi-circular, and the two semi-sleeves 141 are symmetrically arranged; two first bolt connecting plates 142, which are symmetrically arranged at both ends of the first semi-sleeve 141; and two second bolt connecting plates 143, which are symmetrically arranged at both ends of the second semi-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 first strain sensors are evenly distributed on the outer sidewalls of the two semi-sleeves 141; the first bolt connecting plate 142 and the corresponding second bolt connecting plate 144 are spaced 3 mm apart; the outer sidewall of the anchor rock sample, the inner sidewall of the two semi-sleeves 141, and the diameter of the circle they form are all the same.

[0067] Specifically, the two semi-sleeves are mainly obtained by symmetrically cutting a steel cylinder with the same inner radius as the outer radius of the test thick-walled cylindrical rock sample 13 along the axial direction. The inner radius of the two semi-sleeves 141 is the same as the outer radius of the test thick-walled cylindrical rock sample 13, so that when the two semi-sleeves 141 are on the outer wall of the test thick-walled cylindrical rock sample 13, the inner sidewalls of the two semi-sleeves 141 can be tightly attached to the test thick-walled cylindrical rock sample 13. The two first bolt connecting plates 142 are fixedly connected to the corresponding two second bolt connecting plates 144 by bolts, so that the two semi-sleeves 141 are tightly attached to the test thick-walled cylindrical rock sample 13, and the connection between the first semi-sleeve 141 and the second semi-sleeve 141 is approximately a rigid connection. The number and diameter of the bolts are calculated based on the simulated stiffness of the steel sleeve 14. In addition, the first bolt... The bolt connecting plate 142 is spaced 3mm apart from the corresponding second bolt connecting plate 143, which further ensures that the two half-sleeves 141 are tightly fitted to the test thick-walled cylindrical rock sample 13, avoiding gaps that would cause the steel sleeve 14 to be loosely fitted to 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 equivalent stiffness principle based on the elastic modulus and Poisson's ratio of the test thick-walled cylindrical rock sample 13 and the steel. By fitting the steel sleeve 14 onto the outer wall of the finite-sized rock test thick-walled cylindrical rock sample 13, the stiffness conditions of the environment surrounding the infinite-sized rock can be simulated, thereby achieving the same stiffness conditions for the rock sample-steel sleeve assembly as for the semi-infinite rock. At the same time, the response law and deformation failure characteristics of the anchoring system under constant stiffness conditions can be obtained through pull-out tests.

[0068] In some possible implementations, the combined sleeve pulling device includes a dynamic strain acquisition device 25, with several first strain sensors and several second strain sensors 12 all connected to the dynamic strain acquisition device 25.

[0069] Specifically, the second strain sensor 12 and the first strain sensor are both connected to the dynamic strain acquisition instrument 25 via strain connection lines. The dynamic strain acquisition instrument 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 pulling device further includes: a pulling system 21, which 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 vertical intervals. Two support rods 2113 are evenly distributed along 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. The fixed end of the power structure 212 is fixedly connected to the lower end face of the upper support platform 2111; a sample placement platform 22, which is fixedly connected to the upper end face of the upper support platform 2111 and is used to place the sample 1; and a support plate 23, which has two sliding perforations along its outer edge. The support plate 23 is sleeved on the two support rods 2113 through two sliding through holes, and the support plate 23 and the two support rods 2113 are slidably connected. The support plate 23 has a power through hole in its center, and the support plate 23 is sleeved on the periphery of the output end of the power structure 212 through the power through hole. The support plate 23 is fixedly connected to the output end of the power structure 212. The fixing structure 24 is located at the output end of the power structure 212. The upper support platform 2111 has a first through hole in its center, the power structure 212 has a second through hole in its center, and the sample placement platform 22 has a third through hole in its center. 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. The anchor rod 11 is fixedly connected to the output end of the power structure 212 through the fixing structure 24.

[0071] Specifically, in this invention, the reaction frame 211 serves as the main support structure, the support plate 23 serves as the auxiliary support structure, the fixed end of the power structure 212 is fixed to the reaction frame 211, the middle part of the output end of the power structure 212 is fixed to the support plate 23, the sample placement platform 22 is fixed to the reaction frame 211, the sample 1 is placed on the sample placement platform 22, and 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 by the fixing structure 24. The power structure 212 is connected to the control system. The control system controls the output end of the power structure 212 to extend and retract, pulling the anchor rod 11 of the sample 1. During the pulling process of the anchor rod 11 with a constant displacement or constant force, the thick-walled cylindrical rock sample 13 inside the sample 1 changes due to the downward pull of the anchor rod 11. The outer wall of the thick-walled cylindrical rock sample 13 will experience strain, and the steel sleeve 14 outside the sample 1 will also experience corresponding strain changes. The thick-walled cylindrical rock sample 13 is fixed to the anchor rod 11 by mortar 16. During the pull-out process, the strength of mortar 16, the strength of the reinforcing steel in anchor rod 11, and the length of anchor rod 11 all affect the peak bearing capacity and failure mode of specimen 1. The mechanical response of specimen 1 can be analyzed by the pull-out force and displacement applied by the dynamic structure 212. The influence of the strength of mortar 16, the strength of the reinforcing steel in anchor rod 11, and the length of anchor rod 11 on the peak bearing capacity and failure mode of specimen 1 can be discussed. Simultaneously, by combining the strain data of the outer wall of the thick-walled cylindrical rock sample 13 and the outer wall of the steel sleeve 14 monitored by the dynamic strain acquisition instrument 25, the strain of the anchor hole during the pull-out process can be revealed. The radial constraint stress response law of the surrounding rock provides a basis for a deeper understanding of the working mechanism of the anchoring system. The combined sleeve pull-out device has a simple structure, low cost, simple operation, and is easy to implement. By combining the steel sleeve 14 with the test thick-walled cylindrical rock sample 13 to simulate environmental conditions, it can simulate the stiffness of semi-infinite rock and conduct pull-out tests under constant stiffness conditions to reflect the response law and deformation and failure characteristics of the sample. At the same time, it is of great significance for the research and application of anchoring support in fields such as water conservancy and hydropower, transportation tunnels, slope protection, underground engineering, mining engineering, and foundation anti-tilting and anti-buoyancy engineering.

[0072] In some possible implementations, the fixing structure 24 includes: a nut 241 adapted to the other end of the anchor rod 11; an anchor plate 242 located at the output end of the power structure 212, the anchor plate 242 having a fourth through hole in its center; 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 by the nut 241.

[0073] Specifically, the nut 241 is adapted to the anchor rod 11. The nut 241 is sleeved on the threaded end of the anchor rod 11 to fix the anchor rod 11 to the output end of the power structure 212, so that the extension 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 rock cuttings collection box 26 located on the upper end face of the lower fixed platform 2112.

[0075] Specifically, the rock debris collection box 26 is used to collect rock debris generated by friction between 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, and can apply constant displacement and constant force, which can reasonably, objectively and accurately simulate the stiffness of semi-infinite rock and reflect the response law and deformation failure characteristics of the sample under constant stiffness conditions; 2. By fitting 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 equivalent stiffness principle based on the elastic modulus and Poisson's ratio of the thick-walled cylindrical rock sample 13 and the steel material, 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 environment surrounding infinite-sized 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 pull-out tests; 3. During the pull-out process, the interface anti-expansion effect occurring at the interface of the anchor rod 11-mortar 16 can be used to study the effect of interface anti-expansion benefits and the evolution characteristics of radial stress on the bearing capacity and failure mode of the anchoring.

[0077] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A combined sleeve-pull test method, characterized by, The combined sleeve pull-out test method is performed by placing a sample on a combined sleeve pull-out device, and the combined sleeve pull-out test method comprises: The anchor rod of the sample is downward and the sample is fixed on the combined sleeve pull-out device; The sample is subjected to a pull-out test by the combined sleeve pull-out device, the pull-out axial force, the pull-out displacement, the time and the strain of the sample during the pull-out process are monitored and recorded, and the mechanical response of the sample is analyzed after the pull-out test is completed; The sample preparation method comprises: A thick-walled cylindrical rock sample provided with a strain sensor is prepared; The thick-walled cylindrical rock sample provided with a strain sensor is placed on a centering device, one end of the anchor rod is inserted into the center of the thick-walled cylindrical rock sample provided with a strain sensor and inserted into the centering hole of the centering device, then the center of the thick-walled cylindrical rock sample provided with a strain sensor is filled with mortar, and the centering upper cover is covered, and the anchor rod rock sample is obtained after curing; A steel sleeve is sleeved on the outer wall of the anchor rod rock sample, a plurality of first strain sensors are arranged on the outer wall of the steel sleeve, and the sample is obtained; The thick-walled cylindrical rock sample provided with a strain sensor specifically comprises: A thick-walled cylindrical rock sample is prepared by using a combined drill bit, and the surface of the thick-walled cylindrical rock sample is polished by using a grinding wheel to form a smooth surface, thereby obtaining a test thick-walled cylindrical rock sample; Marking lines are drawn at equal intervals in the circumferential direction of the test thick-walled cylindrical rock sample, and then a milling cutter is used to mill grooves to obtain a plurality of strain installation grooves; A second strain sensor is fixed in each strain installation groove to obtain the thick-walled cylindrical rock sample provided with a strain sensor; The combined sleeve pull-out test method further comprises: after the pull-out test is completed, the sample is cut open, and the failure mode of the sample is analyzed; The steel sleeve comprises: Two half sleeves, each half sleeve is in a semicircular structure, and the two half sleeves are symmetrically arranged; Two first bolt connection plates, the two first bolt connection plates are symmetrically arranged at the two ends of the first half sleeve; Two second bolt connection plates, the two second bolt connection plates are symmetrically arranged at the two ends of the second half sleeve; Each first bolt connection plate is fixedly connected with a corresponding second bolt connection plate by a bolt; a plurality of first strain sensors are arranged on the outer side walls of the two half sleeves; The interval between the first bolt connection plate and the corresponding second bolt connection plate is 3mm; the diameters of the circles in which the outer side wall of the anchor rod rock sample and the inner side walls of the two half sleeves are located are the same; The steel sleeve is in a cylindrical structure, and the calculation formula of the outer radius c of the steel sleeve is: ； wherein, E s E is the Young's modulus of the steel sleeve; μ s v is the Poisson's ratio of the steel sleeve; E r E is the Young's modulus of the test thick-walled cylinder rock sample; μ r v is the Poisson's ratio of the test thick-walled cylinder rock sample; b R is the outer radius of the test thick-walled cylinder rock sample; The thickness of the steel sleeve d=c-b .

2. A combined sleeve-pull test method as claimed in claim 1, characterized in that: The combined sleeve pull-out device comprises a dynamic strain acquisition instrument, and a plurality of first strain sensors and a plurality of second strain sensors are connected with the dynamic strain acquisition instrument.

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