Anchoring rod continuous non-uniform confining pressure applying device and method

Abstract

This invention relates to a device and method for applying continuous non-uniform confining pressure with anchor bolts, belonging to the field of tunnel support technology. The device includes: a pressure chamber filled with a pressurizing medium; an anchor bolt body, which is a non-uniform diameter structure, disposed within the pressure chamber; external confining pressure applied by the pressurizing medium from outside the anchor bolt body; and an anchor bolt tensioning system that applies a tensile load to the end of the anchor bolt body extending out of the pressure chamber from outside the pressure chamber. The anchor bolt body comprises a rock mass resembling surrounding rock and an anchor bolt. The anchor bolt is installed in a simulated borehole of the rock mass resembling surrounding rock, drilled along its height direction at the center of the rock mass resembling surrounding rock, and extends outside the pressure chamber. When testing with the device provided by this invention, only irregularly shaped rock masses of corresponding diameter need to be poured according to the loading requirements. The confining pressure gradient can be adjusted by replacing rock masses of different diameters, eliminating the need for multi-path zoned pressure systems and complex pipeline layouts, significantly reducing equipment manufacturing and maintenance costs.

Description

Technical Field

[0001] This invention belongs to the field of tunnel support technology, and particularly relates to a device and method for applying continuous non-uniform confining pressure to anchor bolts. Background Technology

[0002] Since its introduction to my country in the 1950s, anchor bolt support technology has been widely used in geotechnical engineering support fields such as mines due to its convenient construction, superior economy, and excellent anchoring performance. However, with the gradual depletion of shallow mineral resources and the significant increase in mining depth, the deep ground stress level generally exceeds 10 MPa. Anchor bolt anchoring systems frequently experience fracture failure due to the combined effects of high ground stress and complex stress fields, leading to a decrease in the stability of the support structure. Therefore, confining pressure has become a crucial factor to consider in the design of anchor bolt support systems.

[0003] In deep tunnels, the confining pressure around the anchor bolt gradually decreases along the axial direction of the anchor bolt, that is, from the surface of the tunnel to the depth of the surrounding rock. The confining pressure is a continuous non-uniform distribution, and its theoretical calculation formula is shown in formula (1).

[0004] (1)

[0005] In the formula: The confining pressure at any point on the anchor bolt, in MPa; —In-situ stress of the surrounding rock, MPa; The radius of the tunnel, in meters; The distance from any point on the anchor bolt to the center of the tunnel, in meters (m).

[0006] Chinese patent (publication number: CN116223235A, publication date: June 6, 2023) discloses an anchor pull-out test device and test method for implementing graded confining pressure loading. The graded confining pressure application device implements gradient confining pressure loading on the anchor through pressure chambers at the top, middle and bottom layers. However, it can only simulate three discrete pressure gradients, which cannot meet the actual requirement of continuous non-uniform distribution of confining pressure around the anchor. This results in significant differences between the anchor anchoring performance test results and the engineering site, which restricts the improvement of anchor design theory in deep geotechnical engineering.

[0007] Therefore, there is an urgent need for a simulation device and method that can realize continuous non-uniform loading of confining pressure around anchor bolts, to solve the technical problems that existing graded confining pressure application devices and methods cannot realistically simulate the confining pressure environment of anchor bolts, which is of great significance for improving the reliability of anchor bolt anchoring systems and safe mining in deep mines. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a device and method for applying continuous non-uniform confining pressure to anchor bolts, thereby simulating continuous non-uniform loading of confining pressure around the anchor bolts.

[0009] A device for applying continuous non-uniform confining pressure to an anchor bolt, comprising:

[0010] Pressure chamber, filled with pressurized medium;

[0011] The anchor bolt and anchor body are non-uniform diameter structures and are installed inside the pressure chamber; the pressurizing medium applies external confining pressure from outside the anchor bolt and anchor body.

[0012] The anchor tensioning system applies a tensile load from outside the pressure chamber to the end of the anchor body that extends out of the pressure chamber.

[0013] It also includes a confining pressure control system, which is connected to the pressure chamber and used to regulate the pressure of the pressurizing medium.

[0014] The pressure chamber includes a pressure chamber body, which is a hollow cylinder without a cover, sealed at the bottom and open at the top. The pressure chamber body is filled with a pressurizing medium, and a pressure chamber cover is fastened to the top of the pressure chamber body.

[0015] The pressure chamber is made of 316L stainless steel.

[0016] The pressure chamber is equipped with a bottom support located at the bottom of the anchor bolt body, serving as a bottom support for the anchor bolt body.

[0017] The bottom bracket is made of 316L stainless steel.

[0018] The anchor body includes a rock mass similar to surrounding rock and an anchor rod. The anchor rod is installed in a simulated borehole of the rock mass similar to surrounding rock, which is drilled along the height direction at the center of the rock mass, and extends out of the pressure chamber.

[0019] The surrounding rock mass is an irregular structure, specifically a non-uniform diameter structure, meaning that the diameter is unequal along the height direction.

[0020] The anchor bolt includes an anchor bolt body and an anchoring agent. The anchor bolt body is bonded to the simulated borehole of the surrounding rock mass by the anchoring agent, and the anchor bolt body is consistent with the actual site.

[0021] A method for applying continuous non-uniform confining pressure to an anchor bolt, using the aforementioned device for applying continuous non-uniform confining pressure to an anchor bolt, specifically includes the following steps:

[0022] Step 1: Establish numerical models of the outer diameter of the cross section at any point A in the surrounding rock mass along the anchor bolt direction, the external confining pressure applied to the anchor bolt anchor body by the confining pressure control system, and the confining pressure at any point B along the anchor bolt direction around the anchor bolt. Determine the dimensions of the anchor bolt anchor body based on field measured data.

[0023] Step 2: Prepare the anchor body for the anchor bolt;

[0024] Step 3: Install the anchor bolt anchor body:

[0025] Install the bottom bracket at the bottom of the pressure chamber;

[0026] Install the anchor bolt anchor body on the upper part of the bottom bracket;

[0027] After filling the pressure chamber with pressurizing medium, the pressure chamber cover is installed on the upper part of the pressure chamber through the anchor bolts and anchor bodies.

[0028] Step 4: Apply confining pressure:

[0029] The confining pressure control system is connected to the pressure chamber, and confining pressure is applied to the inside of the pressure chamber through the confining pressure control system; when the confining pressure reaches the preset value, pressure is maintained.

[0030] Step 5: Pull-out test:

[0031] An anchor bolt tensioning system was installed on the upper part of the pressure chamber cover, and the anchor bolt was pulled out at a stable rate to obtain the anchor bolt pull-out force-displacement curve under continuous non-uniform confining pressure.

[0032] After the pull-out is completed, the anchor bolt tensioning system and the confining pressure of the pressure chamber are removed, and the anchor bolt is taken out to complete the test;

[0033] After the experiment is completed, the data is analyzed.

[0034] By employing the above technical solution, the present invention has at least the following beneficial effects:

[0035] 1. This invention innovatively proposes a device for applying continuous non-uniform confining pressure to anchor bolts. The surrounding rock mass is an irregularly shaped structure with a diameter varying along the length of the anchor bolt. A confining pressure control system is installed to regulate the pressure of the pressurizing medium. This control system has a single constant pressure source, enabling efficient application of continuous, non-uniform confining pressure around the anchor bolt. When testing with the device provided by this invention, only an irregularly shaped surrounding rock mass of the appropriate diameter needs to be poured according to the loading requirements. The confining pressure gradient can be adjusted by changing the surrounding rock mass of different diameters. This eliminates the need for multi-path zoned pressure systems and complex pipeline layouts, significantly reducing equipment manufacturing and maintenance costs.

[0036] 2. This invention, for the first time based on the principle of stress transfer, accurately derives the quantitative mathematical relationship between the outer diameter of the cross-section of the surrounding rock mass at various points along the anchor bolt direction and the confining pressure around the anchor bolt and the uniform external confining pressure of the anchor body. It proposes a new method for precisely controlling the distribution of confining pressure around the anchor bolt by varying the diameter of the surrounding rock mass. This invention overcomes the shortcomings of traditional loading methods, which rely on empirical estimation and are difficult to achieve continuous gradient control. It has a clear physical basis and good applicability. Comparison of experimental results obtained using the device and method provided by this invention with field test data shows an error controlled within 3%, verifying the accuracy and reliability of the method.

[0037] Compared with the traditional stepped discontinuous loading method, the device provided by the present invention has the advantages of simple structure, high control precision and strong loading continuity, and can more realistically simulate the complex stress field environment in the deep.

[0038] 3. By combining the derived model for real-time verification, the confining pressure loading error of the present invention can be controlled within ±5%, ensuring high accuracy and high repeatability of the test results.

[0039] 4. This invention is applicable to anchor performance testing in complex working conditions in deep mines, tunnels and other geotechnical engineering projects, providing a cost-effective and widely applicable technical approach for accurately designing anchoring support schemes and improving mining safety. Attached Figure Description

[0040] Figure 1 This is an overall schematic diagram of the anchor bolt continuous non-uniform confining pressure application device provided by the present invention.

[0041] Figure 2 This is a schematic diagram of the internal structure of the continuous non-uniform confining pressure application device for anchor bolts provided by the present invention.

[0042] Figure 3 A schematic diagram illustrating the principle of the continuous non-uniform confining pressure application method for anchor bolts provided by the present invention;

[0043] Figure 4 This is a graph showing the pull-out force-displacement curve of a resin anchor bolt obtained by testing using the apparatus and method of the present invention in an embodiment of the present invention.

[0044] in:

[0045] 1-Pressure chamber, 11-Pressure chamber body, 12-Pressure chamber cover, 13-Sealing screw, 14-Pressurizing medium, 2-Bottom support, 3-Anchor bolt anchor body, 31-Class surrounding rock mass, 311-Class surrounding rock mass borehole simulation hole, 32-Anchor bolt, 321-Anchor bolt body, 322-Anchoring agent, 4-Confining pressure control system, 5-Anchor bolt tensioning system. Detailed Implementation

[0046] To better explain and facilitate understanding of the present invention, the technical solution and effects of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0047] This embodiment uses a mine as an example, where a 5m roadway was excavated at a depth of 400m and full-face support was implemented. The support used resin anchors with a diameter of 0.02m, a total length of 2.2m, and an anchoring length of 2.0m, with a borehole diameter of 0.042m. Data on the original rock stress and the confining pressure around the anchors were obtained through field testing. The continuous non-uniform confining pressure application device provided by this invention was used for testing, and the anchoring performance of the resin anchors under continuous non-uniform confining pressure conditions was simulated and evaluated.

[0048] like Figures 1-2 As shown, a continuous non-uniform confining pressure application device for anchor bolts includes a pressure chamber 1, with an anchor bolt anchor body 3 disposed within the pressure chamber 1 and arranged along the height of the pressure chamber 1. An anchor bolt tensioning system 5 is provided at the top of the pressure chamber 1, with one end of the anchor bolt anchor body 3 extending from inside the pressure chamber 1 and connecting to the anchor bolt tensioning system 5. The anchor bolt tensioning system 5 can be any existing tensioning system, applying a tensile load to the anchor bolt of the anchor bolt anchor body 3.

[0049] Furthermore, the pressure chamber 1 includes a pressure chamber body 11, which is a capless hollow cylinder with a sealed bottom and an open top; in this embodiment, the pressure chamber body 11 is made of 316L stainless steel. The pressure chamber body 11 is filled with a pressurizing medium 14, which in this embodiment is 46# hydraulic oil, used to apply confining pressure to the anchor bolt anchor body 3. The top of the pressure chamber body 11 is fastened to a pressure chamber cover 12 by a sealing screw 13, forming a sealed space inside to prevent leakage of the pressurizing medium 14.

[0050] The pressure chamber 1 is connected to the confining pressure control system 4, which regulates the pressure of the pressurizing medium 14 inside the pressure chamber 1 in real time and applies external confining pressure to the anchor bolt anchor body 3.

[0051] In this embodiment, the anchor bolt anchor body 3 is installed inside the pressure chamber 1 via a bottom bracket 2. The bottom bracket 2 is located at the bottom of the anchor bolt anchor body 3, serving as a bottom support for the anchor bolt anchor body 3. The bottom bracket 2 is made of 316L stainless steel.

[0052] The anchor body 3 is positioned above the bottom support 2 and includes a rock mass 31 and an anchor 32. The rock mass 31 has an irregular shape, specifically a frustum-shaped structure that is narrower at the top and wider at the bottom, meaning its diameter gradually increases from top to bottom along the height direction, with a height of 2.0m. Its top abuts against the lower surface of the pressure chamber cover 12. A simulated rock mass drilling hole 311 is formed at the center of the rock mass 31 along the height direction for installing the anchor 32. In this embodiment, the diameter of the simulated rock mass drilling hole 311 is 0.042m. The anchor 32 passes through the pressure chamber cover 12, extends out of the pressure chamber body 11, and connects to the anchor tensioning system 5.

[0053] Furthermore, the anchor bolt 32 includes an anchor bolt body 321 and an anchoring agent 322. The anchor bolt body 321 is bonded to the interior of the simulated borehole 311 of the surrounding rock mass by the anchoring agent 322. To maintain consistency with the actual site, in this embodiment, the anchor bolt body 321 is a PSB500-J20 left-hand precision-rolled threaded steel bar with a diameter of 0.02m and a length of 2.2m, and the anchoring agent 322 is an MSK2360 resin anchoring agent with an anchoring length of 2.0m.

[0054] The anchor bolt tensioning system 5 is located on top of the pressure chamber cover 12 and is used to apply tensile load to the anchor bolt 32 and record the pull-out force-displacement curve in real time during the pull-out process.

[0055] On the other hand, this embodiment provides a method for applying continuous non-uniform confining pressure to anchor bolts, which uses the aforementioned device for applying continuous non-uniform confining pressure to anchor bolts, and specifically includes the following steps:

[0056] Step 1: Establish the outer diameter D of the cross section at any point A of the surrounding rock mass 31 along the direction of anchor bolt 32, the external confining pressure p applied to the anchor body 3 by the confining pressure control system 4, and the confining pressure at any point B around anchor bolt 32 along the direction of anchor bolt. The numerical model was used, and the dimensions of the surrounding rock mass 31 were determined based on field measurement data:

[0057] like Figure 3 The schematic diagram shown is based on the Lamé solution for a thick-walled cylinder, and represents the confining pressure at any point B along the anchor bolt direction around anchor bolt 32. The calculation formula is as follows:

[0058] (2)

[0059] In the formula: —Outer diameter D, m, of any point A in the surrounding rock mass 31 along the direction of anchor bolt 32;

[0060] —The confining pressure at any point B along the direction of anchor bolt 32, in MPa; point B and point A are located on the same cross section;

[0061] — The diameter of borehole 311 in the simulated drilling of a type of surrounding rock mass, in meters;

[0062] —The confining pressure control system 4 applies external confining pressure (MPa) to the anchor body 3 of the anchor bolt; The value is the stress of the original underground rock.

[0063] From formula (2), it can be seen that when the diameter b of the simulated borehole 311 of the surrounding rock mass and the external confining pressure p applied to the anchor body 3 by the confining pressure control system 4 are constant, the outer diameter D of the cross section at any point A of the surrounding rock mass 31 along the direction of the anchor 32 and the confining pressure at any point B along the direction of the anchor 32 are... There is a corresponding relationship. Therefore, if the surrounding rock mass 31 is an irregular structure with inconsistent diameters at various points along the length L of the anchor bolt 32, the actual pressure at each point around the anchor bolt 32 is a continuous and non-uniform distribution.

[0064] Based on formula (2), the formula for calculating the outer diameter D of the cross section at any point A of the surrounding rock mass 31 along the direction of anchor bolt 32 can be derived as follows:

[0065] (3)

[0066] In this embodiment, through on-site measurement, the underground original rock stress was found to be 10 MPa, the diameter of the anchor rod body 321 was 0.02 m, and the diameter of the simulated borehole 311 in the rock mass was 0.042 m. The confining pressures at ten points around the anchor rod 32 along the anchor rod direction were 30.0 MPa, 27.2 MPa, 24.9 MPa, 23.0 MPa, 21.5 MPa, 20.2 MPa, 19.1 MPa, 18.2 MPa, 17.4 MPa, 16.8 MPa, and 16.2 MPa, respectively. The confining pressure control system 4 applied external confining pressure to the anchor body 3 of the anchor rod. The stress in the original underground rock is 10 MPa.

[0067] Finally, based on formula (3), the outer diameters D of the cross sections of the ten points on the same cross section of the rock mass 31 and the anchor 32 along the direction of the anchor 32 are obtained as follows: 0.02828m, 0.02944m, 0.03063m, 0.03186m, 0.03312m, 0.03441m, 0.03572m, 0.03706m, 0.03841m, 0.03979m, and 0.04119m. By fitting or interpolating the data of the ten points, the diameters of all points of the rock mass 31 are obtained, thus forming the size profile of the rock mass 31.

[0068] Step 2: Pour the surrounding rock mass 31 and install the anchor bolts 32.

[0069] Based on the calculation results in step 1, a cement slurry is prepared and then poured. Specifically, when preparing the cement slurry, it is mixed evenly according to the ratio of cement:coarse sand:fine sand:water = 50:57:114:25 to form a cement slurry, which is then poured to form the surrounding rock mass 31. After the surrounding rock mass 31 is poured, it is cured for 28 days according to standard. Then, PSB500-J20 left-handed precision-rolled threaded steel bars are bonded to the inside of the surrounding rock mass 31 using MSK2360 resin anchoring agent to form the anchor bolt anchor body 3.

[0070] Step 3: Install the anchor bolt anchor body 3.

[0071] Install the bottom bracket 2 at the bottom of the pressure chamber 11; then install the anchor bolt 3 on the top of the bottom bracket 2; after filling the pressure chamber 11 with pressurizing medium 14, install the pressure chamber cover 12 through the anchor bolt 3 on the top of the pressure chamber 11.

[0072] Step 4: Apply confining pressure.

[0073] The confining pressure control system 4 is connected to the pressure chamber 11, and confining pressure is applied to the interior of the pressure chamber 1 through the confining pressure control system 4; when the confining pressure reaches the design value of 10MPa, pressure is maintained. At this time, the confining pressure on all points outside the anchor body 3 is consistent, but because the diameter of each point of the surrounding rock mass 31 along the length of the anchor 32 is different, based on the stress transfer principle, the stress transmitted to the interface of the anchor 32 is not the same, thereby realizing the application of continuous non-uniform confining pressure around the anchor 32, and realistically simulating the confining pressure environment of the anchor 32.

[0074] Step 5: Pull-out test.

[0075] The anchor bolt tensioning system 5 was installed on the upper part of the pressure chamber cover 12, and the anchor bolt 32 was pulled out at a tensioning rate of 1 mm / min to obtain the anchor bolt pull-out force-displacement curve under continuous non-uniform confining pressure, as shown in the figure. Figure 4 As shown. After the pull-out is completed, the confining pressure in the anchor bolt tensioning system 5 and pressure chamber 1 is removed, and the anchor bolt 32 is taken out to complete the test.

[0076] This embodiment analyzes the data after the experiment is completed: by Figure 4 Analysis shows that under non-uniform continuous confining pressure, the maximum pull-out force of the resin anchor body 3 is 133.04 kN, and the maximum displacement is 130 mm. The error rate between the experimental results and the field test results is less than 3%, proving that the anchor continuous non-uniform confining pressure application device and method proposed in this invention are reliable.

Claims

1. A device for applying continuous non-uniform confining pressure to anchor bolts, characterized in that, include: Pressure chamber, filled with pressurized medium; The anchor bolt anchor body is a non-uniform diameter structure and is installed inside the pressure chamber; The pressurizing medium applies external confining pressure from outside the anchor body of the anchor bolt; The anchor tensioning system applies a tensile load from outside the pressure chamber to the end of the anchor body extending out of the pressure chamber; The anchor bolt anchor body includes a rock mass similar to surrounding rock and an anchor bolt. The anchor bolt is installed in a simulated borehole of the rock mass similar to surrounding rock, which is drilled along the height direction at the center of the rock mass similar to surrounding rock and extends out of the pressure chamber. The formula for calculating the outer diameter D of the cross section at any point A in the surrounding rock mass along the anchor bolt direction is as follows: In the formula: —Outer diameter D, m, of the cross section at any point A in the surrounding rock mass along the anchor bolt direction; —The confining pressure at any point B along the anchor bolt direction, in MPa; point B and point A are located on the same cross section; — The diameter of the simulated borehole in the surrounding rock mass, in meters; —The confining pressure control system applies external confining pressure to the anchor body of the anchor bolt. This refers to the stress in the original underground rock.

2. The anchor bolt continuous non-uniform confining pressure application device according to claim 1, characterized in that: It also includes a confining pressure control system, which is connected to the pressure chamber and used to regulate the pressure of the pressurizing medium.

3. The anchor bolt continuous non-uniform confining pressure application device according to claim 1, characterized in that: The pressure chamber includes a pressure chamber body, which is a hollow cylinder without a cover, sealed at the bottom and open at the top. The pressure chamber body is filled with a pressurizing medium, and a pressure chamber cover is fastened to the top of the pressure chamber body.

4. The anchor bolt continuous non-uniform confining pressure application device according to claim 3, characterized in that: The pressure chamber is made of 316L stainless steel.

5. The anchor bolt continuous non-uniform confining pressure application device according to claim 1, characterized in that: The pressure chamber is equipped with a bottom support located at the bottom of the anchor bolt body, serving as a bottom support for the anchor bolt body.

6. The anchor bolt continuous non-uniform confining pressure application device according to claim 5, characterized in that: The bottom bracket is made of 316L stainless steel.

7. The anchor bolt continuous non-uniform confining pressure application device according to claim 1, characterized in that: The surrounding rock mass is an irregular structure, specifically a non-uniform diameter structure, meaning that the diameter is unequal along the height direction.

8. The anchor bolt continuous non-uniform confining pressure application device according to claim 1, characterized in that: The anchor bolt includes an anchor bolt body and an anchoring agent. The anchor bolt body is bonded to the simulated borehole of the surrounding rock mass by the anchoring agent, and the anchor bolt body is consistent with the actual site.

9. A method for applying continuous non-uniform confining pressure to an anchor bolt, using the continuous non-uniform confining pressure application device for an anchor bolt as described in claim 1, characterized in that, Specifically, the following steps are included: Step 1: Establish numerical models of the outer diameter of the cross section at any point A in the surrounding rock mass along the anchor bolt direction, the external confining pressure applied to the anchor bolt anchor body by the confining pressure control system, and the confining pressure at any point B along the anchor bolt direction around the anchor bolt. Determine the dimensions of the anchor bolt anchor body based on field measured data. Step 2: Prepare the anchor body for the anchor bolt; Step 3: Install the anchor bolt anchor body: Install the bottom bracket into the inner bottom of the pressure chamber. Install the anchor bolt anchor body on the upper part of the bottom bracket; After filling the pressure chamber with pressurizing medium, the pressure chamber cover is installed on the upper part of the pressure chamber through the anchor bolts and anchor bodies. Step 4: Apply confining pressure: The confining pressure control system is connected to the pressure chamber, and confining pressure is applied to the inside of the pressure chamber through the confining pressure control system; when the confining pressure reaches the preset value, pressure is maintained. Step 5: Pull-out test: An anchor bolt tensioning system was installed on the upper part of the pressure chamber cover, and the anchor bolt was pulled out at a stable rate to obtain the anchor bolt pull-out force-displacement curve under continuous non-uniform confining pressure. After the pull-out is completed, the anchor bolt tensioning system and the confining pressure of the pressure chamber are removed, and the anchor bolt is taken out to complete the test; After the experiment is completed, the data is analyzed.

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