A self-expanding energy-absorbing anchor rod with stepped fracture, and its preparation and use method

Abstract

A self-expanding energy-absorbing anchor bolt with tiered fracture, its preparation, and its use are disclosed. The anchor bolt comprises a rigid part and a flexible part, connected together by a threaded steel rod body. The rigid part includes a threaded steel rod body with several fracture points on its rigid end. The section of the threaded steel rod body with fracture points is located at the bottom of the borehole and fixed with an anchoring agent. A first nut is installed on the portion of the threaded steel rod body near the anchoring agent. The flexible part includes a slotted sleeve fitted onto the flexible end of the threaded steel rod body. A self-expanding explosive charge is installed between the slotted sleeve and the threaded steel rod body. A second nut, screwed onto the threaded steel rod body, is located at the end of the self-expanding explosive charge near the borehole opening. A load-bearing ring is fitted onto the threaded steel rod body. A tray is installed on the portion of the threaded steel rod body extending to the outside of the borehole and fixed with a third nut. By pre-fabricating fracture points, the anchor bolt achieves targeted fracture and continues to provide anchoring capacity after fracture.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical anchoring engineering technology, specifically relating to a self-expanding energy-absorbing anchor rod with stepped fracture, its preparation and application method. Background Technology

[0002] Due to its safety, efficiency, and low cost, rock bolt support has become a major support method in underground engineering. The high-stress environment of deep engineering projects easily induces large deformations, collapses, rock bursts, and other disasters in tunnels and shafts. Conventional rock bolts, due to their low elongation and low bearing capacity, are prone to support failure. For example, resin rock bolts and cement mortar rock bolts commonly used in underground mines have high stiffness and low deformation capacity when anchored along their entire length, resulting in poor yielding capacity and incompatibility with surrounding rock deformation. Under impact loads, threaded steel rods often break or detach from the nut; while slotted pipe rock bolts have a large deformation capacity, their anchoring force is insufficient, making it difficult to effectively control rock mass deformation and instability. Therefore, developing rock bolt support elements with high anchoring force and sufficient deformation capacity is crucial for addressing large deformations and impact disasters in deep engineering projects.

[0003] Therefore, energy-absorbing anchors, also known as yield anchors or extendable anchors, have been proposed both domestically and internationally as a means of support in deep engineering. Typical examples include material deformation-type energy-absorbing anchors such as tapered anchors, MCB-33, and D-bolt. These anchors achieve energy absorption through slippage by releasing the bond between the anchor body and the grout. They offer advantages such as high load capacity, simple structure, and low cost, but their deformation capacity is limited, and they lose their anchoring effect after the anchor body breaks. On the other hand, structural deformation-type energy-absorbing anchors, such as the CN101858225A constant resistance large deformation anchor, Yield-Lok anchor, and Garford anchor, absorb energy through the mutual sliding between structural components. These anchors have a larger deformation capacity and slightly lower sliding resistance. However, the anchor body will undergo tensile fracture after reaching the structural design deformation limit. Some structural slippage-type energy-absorbing anchors are complex in structure and have higher costs. Therefore, existing energy-absorbing anchors cannot simultaneously achieve high anchoring force and large deformation. After the rod breaks, it will lose its anchoring function and will be unable to provide sufficient support when subjected to multiple impact loads.

[0004] Regarding the anchor bolt failure mechanism, the stress on the anchor bolt body of a fully anchored bolt is as follows: Figure 1 As shown. The shear stress on the rod is zero, and the location with the maximum axial stress is called the neutral point. The section of the rod from the neutral point to the roadway sidewall is the load-bearing section, attempting to "grip" the moving surrounding rock; the section from the neutral point to the far end of the anchor is the anchoring section, attempting to remain stationary to prevent the surrounding rock from moving. When the anchor plate bears a load, the neutral point moves forward, the load-bearing section becomes shorter, and the maximum tensile load occurs at the neutral point. Therefore, the failure mode of a fully anchored anchor is usually tensile fracture at the neutral point, i.e., fracture near the borehole opening.

[0005] Based on the above, existing rock bolts have a relatively fixed failure point during the control of surrounding rock deformation. Once the bolt breaks, it immediately loses its anchoring effect on the roadway surface rock mass, making it difficult to suppress the ejection of rock fragments from the roadway surface during rockburst disasters. Therefore, how to control the breakage point of the rock bolt, achieve pinpoint breakage, and continue to absorb deformation energy of the surrounding rock after breakage is a key issue in rockburst disaster prevention and control. Summary of the Invention

[0006] The purpose of this invention is to provide a self-expanding energy-absorbing anchor bolt with stepped fracture, its preparation, and its application method. By pre-fabricating fracture points, the anchor bolt achieves point-to-point fracture and continues to provide anchoring capacity after fracture. This structure can provide a concrete form for the concept of pre-fabricated multi-point fracture and stepped support, and offer a solution for chain rockburst prevention and control.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A self-expanding energy-absorbing anchor bolt with stepped fracture includes a rigid part and a flexible part, which are connected together by a threaded steel rod body.

[0009] The rigid part includes a threaded steel rod, an anchoring agent, and a first nut. The rigid end of the threaded steel rod has several fracture points of fixed shape and depth. When an impact load occurs, the anchor rod will break at the fracture points to absorb a large amount of impact energy and can continue to provide high-strength anchoring force after breaking. The threaded steel rod with fracture points is located at the bottom of the borehole, and the threaded steel rod and the borehole are anchored and fixed by the anchoring agent of the rigid part. The first nut is installed on the part of the threaded steel rod near the anchoring agent.

[0010] The flexible part includes a slotted sleeve, a self-expanding propellant charge, a load-bearing ring, and a second nut. The slotted sleeve is fitted onto the flexible end of the threaded steel rod. A self-expanding propellant charge is installed between the slotted sleeve and the threaded steel rod. A second nut, screwed onto the threaded steel rod, is located at the end of the self-expanding propellant charge near the borehole opening. The load-bearing ring is fitted onto the threaded steel rod and located between the first nut and the slotted sleeve. A tray is installed on the portion of the threaded steel rod extending to the outside of the borehole and is fixed by a third nut installed on the threaded steel rod.

[0011] The slotted sleeve is a thin-walled steel pipe with a longitudinal slot, its outer diameter is larger than the borehole diameter, and its tail is processed into a tapered shape for easy on-site installation.

[0012] The load-bearing ring is installed 3-5cm away from the tail of the slotted sleeve. Its thickness is 12-20mm. The outer diameter of the load-bearing ring is smaller than the borehole diameter and larger than the diameter of the tapered opening at the tail of the slotted sleeve.

[0013] The anchoring agent is a resin anchoring agent, a quick-drying cement mortar anchoring agent, or an expansion anchoring agent.

[0014] The self-expanding propellant charge includes a hollow cylinder, a self-expanding anchoring agent, absorbent paper, and a second annular cap. The self-expanding propellant charge is continuously installed inside a slotted sleeve via a threaded steel rod and is secured in a fixed position by a second nut. The hollow cylinder is filled with a self-expanding anchoring agent, and a second annular cap is provided on the top of the self-expanding anchoring agent at the open end of the hollow cylinder. The outer wall of the hollow cylinder is wrapped with absorbent paper.

[0015] The hollow cylinder is made by blow molding and includes an outer cylinder with several water absorption holes to increase water permeability. An inner cylinder is coaxially fitted inside the outer cylinder, and a self-expanding anchoring agent installation space is formed between the outer cylinder and the inner cylinder. A first annular cap is installed at one end of the outer cylinder and the inner cylinder. The outer diameter of the outer cylinder is smaller than the inner diameter of the slotted sleeve, and the inner diameter of the inner cylinder is larger than the outer diameter of the threaded steel rod.

[0016] The self-expanding anchoring agent is made of calcium sulfoaluminate, calcium oxide, or metal. When used, it can quickly output a certain amount of expansion pressure, which greatly increases the friction between the slotted sleeve and the borehole wall, thereby improving the anchoring performance.

[0017] The threaded steel rod is left-handed or right-handed, made of high-strength manganese steel, with a yield strength greater than the ultimate strength of the slotted sleeve, ensuring that the slotted sleeve can slide without breaking. The front end of the threaded steel rod protrudes 30-60cm from the slotted sleeve for installing the anchoring agent, and the rear end protrudes 10-20cm from the drill hole opening for installing the tray and the third nut. The third nut is matched with the threaded steel rod.

[0018] A method for preparing a self-expanding energy-absorbing anchor bolt with stepped fracture includes the following steps:

[0019] Step 1: Fabricate the threaded steel rod body, first nut, second nut, third nut, and break point.

[0020] The threaded steel rod is made of high-strength precision-rolled manganese steel, with a length of 2.0-2.4m and a diameter of 18-26mm. The internal threads of the first nut, second nut, and third nut match the external threads of the threaded steel rod. The outer diameter of the first nut, second nut, and third nut is 34-38mm, and the length is 25-45mm. The fracture point is prefabricated 0.3-0.7m from the end of the threaded steel rod and located on the rigid part of the rod. The fracture point is made by drilling, shearing, and cutting, with a diameter or depth in the range of 4-15mm. When multiple fracture points are prefabricated, the diameter difference between adjacent fracture points is 2-4mm, and the strength of the fracture point closer to the flexible part is higher than that of the adjacent fracture points.

[0021] Step 2: Fabricate the slotted sleeve

[0022] The slotted sleeve is made of high-elasticity steel. The slotted sleeve is 1.2-1.8m long, 43-47mm in outer diameter, and 2-4mm in wall thickness. It has a 10-15mm wide slit along the longitudinal direction. The load-bearing ring is a metal ring with an outer diameter that is larger than the tapered diameter at the front end of the slotted sleeve and smaller than the diameter of the drill hole. Its inner diameter is larger than the diameter of the threaded steel rod.

[0023] Step 3: Prepare self-expanding propellant charges

[0024] The hollow cylinder for the self-expanding propellant cartridge is manufactured using a blow molding process. The inner diameter of the inner cylinder is 19-27 mm, the outer diameter is 38-40 mm, the wall thickness of both the inner and outer cylinders is 0.2-0.5 mm, and the height of both the inner and outer cylinders is 10-15 cm. Several 1 mm diameter absorbent holes are formed on the outer cylinder wall, and the outer wall is lined with absorbent paper. The installation space formed by the outer and inner cylinders contains 1.5-2.0 g / cm³ of [unspecified substance]. 3 Expansion anchoring agent;

[0025] Among them, calcium sulfoaluminate expansive agents are made of alunite, anhydrous gypsum, anhydrous calcium sulfoaluminate, cement, and water absorbent; calcium oxide expansive agents are made of CaO, water absorbent, silicate cement, and S95 grade mineral powder; and metal expansive agents are made of iron powder, perchromate, and permanganate oxidant.

[0026] Step 4: Assemble the self-expanding energy-absorbing anchor bolt

[0027] First, immerse the self-expanding explosive charge prepared in step 3 in water for 10-15 minutes or spray it with water for 15-18 minutes. Then, remove the self-expanding explosive charge and insert it into the threaded steel rod. After that, insert the rod and the self-expanding explosive charge into the slotted sleeve. The end of the sleeve near the round opening should protrude 10-15 cm to install the tray and nut. The end of the tapered part should protrude 50-70 cm to expose the pre-made fracture point. Then, install the load-bearing ring and nut on the threaded steel rod. After that, install 40-60 cm of anchoring agent on the remaining part of the threaded steel rod and use nuts to restrain both ends. The anchor installation is now complete.

[0028] A method for using a self-expanding energy-absorbing anchor bolt with tiered fracture includes the following three stages:

[0029] (1) Rigid stage; After the anchor is installed and put into use, the anchoring agent anchors the threaded steel rod body into the borehole, the self-expanding explosive charge expands and hardens, and outputs radial pressure to tightly fit the slotted sleeve with the rock wall; When the threaded steel rod body is subjected to axial tensile force generated by the deformation of the surrounding rock, the tensile load is less than the fracture load of the threaded steel rod body with the pre-fabricated fracture point, and neither the rigid part nor the flexible part moves. The self-expanding energy-absorbing anchor relies on the extension capacity of the rod body to resist the deformation and failure of the rock mass.

[0030] (2) Static-dynamic transition stage; When rockburst or rock burst disaster strikes, the load on the threaded steel rod reaches the threshold of the fracture point setting, and the stress will be transmitted to the fracture point through the threaded steel rod, and tensile fracture will occur at the fracture point; during the fracture process, some impact energy is absorbed and the ejection speed of the rock block is greatly reduced; after the fracture, the rigid part loses its function, and the threaded steel rod is pulled out from the self-expanding explosive charge and moves towards the borehole side under the action of the pull-out force. At this time, the bearing ring fixedly connected to the threaded steel rod will contact the tail of the slotted sleeve, and the self-expanding energy-absorbing anchor rod begins to transition from a static state to a sliding state;

[0031] (3) Flexible stage: After the anchor rod breaks at the fracture point under the action of impact load, the anchor rod does not fail. Instead, under the tension of the threaded steel rod body and the bearing ring, the flexible part slides continuously in the borehole and provides high anchoring force, thereby controlling the deformation and collapse of the rock mass. After the impact load is completed, the anchor rod stops sliding. When the next rock mass deformation occurs, the slotted sleeve can continue to slide to absorb the deformation energy of the surrounding rock until the deformation of the entire rock mass reaches the maximum deformation limit of the anchor rod.

[0032] The anchor bolt of this invention can produce the following beneficial effects:

[0033] (1) In this invention, by pre-fabricating a fracture point in the anchor rod body, the invented anchor rod can be broken at a predetermined position, and the energy absorption capacity of the rod body can be maximized when it breaks.

[0034] (2) By setting multiple fracture points with different degrees of damage, the present invention can achieve stepped fracture of the anchor bolt support and absorb the deformation energy of the surrounding rock multiple times.

[0035] (3) The self-expanding energy-absorbing anchor prepared by the present invention can still provide a high anchoring force after the rod body breaks, thereby controlling the ejection of rock blocks on the roadway surface and reducing the risk level of impact disasters;

[0036] (4) The present invention uses self-expanding explosive charge and slotted sleeve to enhance the sliding resistance of the anchor rod, so that the anchor rod has both high anchoring force and adaptability to large deformation.

[0037] (5) The present invention uses threaded steel rod body and pipe gap sleeve to improve the overall shear resistance of anchor rod, and at the same time solves the defects of conventional pipe gap anchor rod welded retaining ring easy to break and low strength, and improves the upper limit of anchoring force of anchor rod. Attached Figure Description

[0038] Figure 1 A schematic diagram of the forces acting on the anchor rod for full-length anchoring;

[0039] Figure 2 This is a schematic diagram of the self-expanding energy-absorbing anchor bolt according to Embodiment 1 of the present invention;

[0040] Figure 3 This is a cross-sectional view and an axial view of the slotted sleeve of the self-expanding energy-absorbing anchor bolt according to Embodiment 1 of the present invention;

[0041] Figure 4 This is a schematic diagram of a self-expanding propellant column from Embodiment 1 of the present invention;

[0042] Figure 5 This is a schematic diagram of a tray according to Embodiment 1 of the present invention;

[0043] Figure 6 This is a schematic diagram of the self-expanding energy-absorbing anchor bolt with multi-stage fracture according to Embodiment 2 of the present invention;

[0044] Among them: 1-Anchoring agent, 201-First nut, 202-Second nut, 203-Third nut, 3-Fracturing point, 31-Fourth-level fracture point, 32-Third-level fracture point, 33-Second-level fracture point, 34-First-level fracture point, 4-Bearing ring, 5-Self-expanding explosive charge, 51-Outer cylinder, 52-Self-expanding anchoring agent, 53-Second annular cap, 54-Water absorption hole, 55-Water absorption paper, 56-Inner cylinder, 6-Slit sleeve, 7-Threaded steel rod body, 8-Pattern. Detailed Implementation

[0045] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0046] Example 1

[0047] like Figures 2 to 5 As shown, a self-expanding energy-absorbing anchor bolt with stepped fracture is provided. The self-expanding energy-absorbing anchor bolt with stepped fracture includes a rigid part and a flexible part, which are connected together by a threaded steel rod body 7.

[0048] The rigid part includes a threaded steel rod 7, an anchoring agent 1, and a first nut 201. The rigid end of the threaded steel rod 7 is provided with several fracture points 3 of fixed shape and depth. When an impact load comes, the anchor rod will break at the fracture point 3 to absorb a large amount of impact energy, and can continue to provide high-strength anchoring force after breaking. The threaded steel rod 7 with the fracture point part is located at the bottom of the borehole, and the threaded steel rod 7 and the borehole are fixed by the anchoring agent 1. In this embodiment, the anchoring agent 1 is a resin anchoring agent, wherein the anchoring agent 1 tightly anchors the threaded steel rod 7 in the borehole through bonding or expansion. The first nut 201 is installed on the part of the threaded steel rod 7 near the anchoring agent 1.

[0049] The flexible part includes a slotted sleeve 6, a self-expanding propellant charge 5, a bearing ring 4, and a second nut 202. The slotted sleeve 6 is a thin-walled steel pipe with a longitudinal slot, its outer diameter being larger than the borehole diameter, and its tail is machined into a tapered shape for easy on-site installation. The slotted sleeve 6 is fitted onto the flexible end of the threaded steel rod 7. A self-expanding propellant charge 5 is installed between the slotted sleeve 6 and the threaded steel rod 7. The self-expanding propellant charge 5 can provide radial expansion pressure, causing the slotted sleeve 6 to be pressed against the rock wall, providing high frictional resistance. One end of the self-expanding propellant charge 5 abuts against the tapered part of the slotted sleeve 6, near the borehole opening. The other end is provided with a second nut 202 screwed onto the threaded steel rod body 7. The position of the self-expanding explosive charge 5 is fixed by the second nut 202 cooperating with the conical part. The load-bearing ring 4 is fitted on the threaded steel rod body 7 and is set close to the first nut 201. In this embodiment, the load-bearing ring 4 is installed 3cm away from the tail of the slotted sleeve 6, and its thickness is 12mm. The outer diameter of the load-bearing ring 4 is smaller than the diameter of the drill hole and larger than the diameter of the conical opening at the tail of the slotted sleeve 6. The threaded steel rod body 7 extends to the outer part of the drill hole and is equipped with a tray 8, which is fixed by a third nut 203 installed on the threaded steel rod body 7. When the anchor rod is subjected to a large impact load, the load is transferred to the threaded steel rod body 7 through the tray 8. The threaded steel rod body 7 transfers the load to the rigid part, and the pre-fabricated fracture point 3 begins to concentrate stress and break, thereby absorbing part of the impact energy. The anchoring agent 1 does not move throughout the process. After the threaded steel rod body 7 breaks at the fracture point 3, at the same time, under the action of the pull-out force, the threaded steel rod body 7 is pulled out from the self-expanding explosive charge 5 and moves towards the orifice side, which drives the bearing ring 4 to contact the slotted sleeve 6, and gradually drives the slotted sleeve 6 to begin to slide and absorb energy, thereby achieving "explosion without bounce".

[0050] The self-expanding propellant 5 includes a hollow cylinder, a self-expanding anchoring agent 52, absorbent paper 55, and a second annular cap 53; the self-expanding propellant 5 is continuously installed inside the slotted sleeve 6 by a threaded steel rod 7 and is constrained in a fixed position by a second nut 202; the hollow cylinder is filled with self-expanding anchoring agent 52, and a second annular cap 53 is provided on the top of the self-expanding anchoring agent 52 at the open end of the hollow cylinder, and absorbent paper 55 is wrapped around the outer wall of the hollow cylinder.

[0051] The hollow cylinder is made by blow molding and includes an outer cylinder 51 with several water absorption holes. The water absorption holes 54 are designed to increase water permeability. An inner cylinder 56 is coaxially fitted inside the outer cylinder 51. A space for self-expanding anchoring agent 52 is formed between the outer cylinder 51 and the inner cylinder 56. A first annular cap is installed at one end of the outer cylinder 51 and the inner cylinder 56. The outer diameter of the outer cylinder 51 is smaller than the inner diameter of the slotted sleeve 6, and the inner diameter of the inner cylinder 56 is larger than the outer diameter of the threaded steel rod body 7.

[0052] The self-expanding anchoring agent 52 is a calcium oxide-based expanding agent, which can quickly output a certain amount of expansion pressure when applied, greatly increasing the friction between the slotted sleeve 6 and the borehole wall, thereby improving the anchoring performance.

[0053] The threaded steel rod 7 is made of high-strength manganese steel. The threaded steel rod 7 is left-handed, and its yield strength is greater than the ultimate strength of the slotted sleeve 6, which can ensure that the slotted sleeve 7 will not break while sliding. The front end of the threaded steel rod 7 protrudes 30cm from the slotted sleeve 6 for installing the anchoring agent 1, and the rear end protrudes 10cm from the drill hole opening for installing the tray 8 and the third nut 203. The third nut 203 is matched with the threaded steel rod 1.

[0054] The fracture point 3 is located on the rigid part of the threaded steel rod 7. The fracture point 3 is created on the threaded steel rod 7 by drilling, shearing, or cutting to form a circular hole, groove, or slit. The cross-sectional area of ​​the rod at the fracture point 3 is smaller, and the strength of the rod at the fracture point 3 is lower than that of the rod without the fracture point 3. During impact loading, stress concentration occurs at the fracture point 3, leading to pre-failure and releasing impact energy. When there are two or more fracture points 3, the fracture point 3 closest to the flexible part between adjacent fracture points 3 must have higher strength.

[0055] In this embodiment, the threaded steel rod 7 has a diameter of 20mm and a length of 2400mm, and is made of high-strength, ribless threaded steel; the first nut 201, the second nut 202, and the third nut 203 are all hexagonal nuts with an outer diameter of 36mm and a length of 45mm; the tray 8 is made of square steel plate with a side length of 200mm, a thickness of 5mm, and a central hole diameter of 25mm; the fracture point 3 is in the form of a circular hole, with one hole pre-fabricated at 60cm from the threaded steel rod 7 with a hole diameter of 8mm.

[0056] like Figure 3 As shown, the slotted sleeve 6 is made of a steel pipe with a length of 1.5m, a thickness of 3mm, and a longitudinal slot width of 10mm. The outer diameter of the slotted sleeve 6 is 47mm, the outer diameter of the tapered front end is 43mm, and the tapered part is 10cm long.

[0057] like Figure 4 As shown, the self-expanding drug column 5 includes a hollow cylinder 51 made of plastic. The inner cylinder 56 has an inner diameter of 24 mm, the outer cylinder 51 has an outer diameter of 40 mm, a thickness of 0.5 mm, and a height of 100 mm. The outer cylinder 51 has circular water absorption holes 54 on its wall. The water absorption holes have a diameter of 1 mm and are distributed axially and circumferentially at intervals of 20 mm. The outer wall of the outer cylinder 51 is wrapped with absorbent paper 55 with a wall thickness of 1 mm. The hollow cylinder is filled with a self-expanding anchoring agent 52. The top end is sealed with a second annular cap 53.

[0058] A method for preparing a self-expanding energy-absorbing anchor bolt with stepped fracture includes the following steps:

[0059] Step 1: Fabricate the threaded steel rod, nut, and break point.

[0060] A threaded steel rod 7 with a length of 2.4m and a diameter of 20mm is made of left-hand precision rolled ribless threaded steel. The first nut 201, the second nut 202 and the third nut 203 are hexagonal, and their internal threads match those of the threaded steel rod 7. The outer diameter is 36mm and the length is 45mm. A fracture point with a diameter of 8mm is drilled at 60cm of the threaded steel rod 7 using a drilling machine.

[0061] Step 2, make the slotted sleeve

[0062] A 3mm thick high-elasticity steel plate is cut to a length of 1.5m and made into a tube with an outer diameter of 47mm using conventional rolling methods. A 10mm gap is left during the rolling process. After completion, one end is pressed into a cone shape using a pipe pressing machine. The cone part is 100mm long.

[0063] Step 3, Prepare self-expanding propellant columns

[0064] A hollow cylinder for self-expanding precipitate 5 and matching first and second annular caps 53 are manufactured using a blow molding process. The inner cylinder 56 of the hollow cylinder has an inner diameter of 24 mm, the outer cylinder 51 has an outer diameter of 40 mm, the wall thickness of both the inner and outer cylinders 56 and 51 is 0.5 mm, and the height of both is 100 mm. The outer cylinder 51 has 1 mm diameter absorbent holes on its wall. Absorbent paper 55 with a wall thickness of 0.1 mm is pasted onto the outer wall of the outer cylinder 51. Then, precipitate with a density of 1.7 g / cm³ is filled into the installation space between the outer cylinder 51 and the inner cylinder 56. 3 The calcium oxide-based expanding agent is sealed with a second annular cap 53, and the self-expanding explosive column 5 is completed; the calcium oxide-based expanding agent is made of CaO, water absorbent, silicate cement and S95 grade mineral powder;

[0065] Step 4: Assemble the self-expanding energy-absorbing anchor bolt.

[0066] Take the eight self-expanding explosive charges 5 prepared in step 3, soak them in water for 12 minutes, then take them out and continuously insert them into the threaded steel rod body 7. After limiting them with the second nut 202, insert them into the slotted sleeve 6. Install the tray 8 and the third nut 203 with 15cm protruding from the round end of the slotted sleeve 6. Protrude 75cm from the conical end of the conical part to expose the pre-made fracture point 3. Install the load-bearing ring 4 and the first nut 201 on the threaded steel rod body 7. Then install 50cm of anchoring agent 1 on the remaining part of the threaded steel rod body 7 and constrain both ends with the third nut 203. The anchor rod installation is now complete.

[0067] A method for using a self-expanding energy-absorbing anchor bolt with tiered fracture includes the following three stages:

[0068] (1) Rigid stage; After the anchor rod is installed and put into use, the anchoring agent 1 anchors the threaded steel rod body 7 into the borehole, the self-expanding explosive 5 expands and hardens, and outputs radial pressure to tightly fit the slotted sleeve 6 with the rock wall; When the threaded steel rod body 7 is subjected to axial tensile force generated by the deformation of the surrounding rock, the tensile load is less than the fracture load of the threaded steel rod body 7 with the prefabricated fracture point 3, and neither the rigid part nor the flexible part moves. The self-expanding energy-absorbing anchor rod relies on the rod body extension capacity to resist the deformation and damage of the rock mass.

[0069] (2) Static-dynamic transition stage; When rockburst or rock burst disaster occurs, the load on the threaded steel rod 7 reaches the threshold set at the fracture point 3. The stress will be transmitted to the fracture point 3 through the threaded steel rod 7 and tensile fracture will occur at the fracture point 3. During the fracture process, some impact energy is absorbed and the ejection speed of the rock block is greatly reduced. After the fracture, the rigid part loses its function. Under the action of the pull-out force, the threaded steel rod 7 is pulled out from the self-expanding explosive 5 and moves towards the orifice side. At this time, the load-bearing ring 4, which is fixedly connected to the threaded steel rod 7, will contact the tail of the slotted sleeve 6. The self-expanding energy-absorbing anchor rod begins to transition from a static state to a sliding state.

[0070] (3) Flexible stage; after the anchor rod breaks at the fracture point 3 under the action of impact load, the anchor rod does not fail. Instead, under the tension of the threaded steel rod body 7 and the bearing ring 4, the flexible part slides continuously in the borehole and provides high anchoring force, thereby controlling the deformation and collapse of the rock mass. After the impact load is completed, the anchor rod stops sliding. When the next rock mass deformation occurs, the slotted sleeve 6 can continue to slide to absorb the deformation energy of the surrounding rock until the deformation of the entire rock mass reaches the maximum deformation limit of the anchor rod.

[0071] Example 2

[0072] like Figure 6 As shown, the differences between Example 2 and Example 1 are as follows:

[0073] In this embodiment, four levels of fracture points are set on the threaded steel rod body: level 4 fracture point 31, level 32, level 2 fracture point 33, and level 1 fracture point 34. The level 1, 2, 3, and 4 fracture points on the threaded steel rod body 7 are all in the form of circular holes, pre-drilled at 30cm, 40cm, 50cm, and 60cm positions on the threaded steel rod body, with hole diameters of 14mm, 12mm, 10mm, and 8mm, respectively. When a self-expanding energy-absorbing anchor rod with multi-level fracture points is used, the anchor rod will begin to break at the level 1 fracture point farthest from the flexible part, followed by the level 2, 3, and 4 fracture points breaking sequentially, thereby withstanding multiple impact loads and absorbing more rock mass strain energy.

Claims

1. A self-expanding energy-absorbing anchor bolt with stepped fracture, characterized in that, It includes a rigid part and a flexible part, which are connected together by a threaded steel rod. The rigid part includes a threaded steel rod, an anchoring agent, and a first nut; the rigid end of the threaded steel rod has several fracture points, the threaded steel rod with fracture points is located at the bottom of the borehole, and the threaded steel rod and the borehole are anchored and fixed by the anchoring agent of the rigid part, and the first nut is installed on the part of the threaded steel rod near the anchoring agent; The flexible part includes a slotted sleeve, a self-expanding propellant charge, a load-bearing ring, and a second nut. The slotted sleeve is fitted onto the flexible end of the threaded steel rod. A self-expanding propellant charge is installed between the slotted sleeve and the threaded steel rod. A second nut, screwed onto the threaded steel rod, is located at the end of the self-expanding propellant charge near the borehole opening. The load-bearing ring is fitted onto the threaded steel rod and located between the first nut and the slotted sleeve. A tray is installed on the portion of the threaded steel rod extending to the outside of the borehole and is fixed by a third nut installed on the threaded steel rod.

2. The self-expanding energy-absorbing anchor bolt with stepped fracture according to claim 1, characterized in that: The slotted sleeve is a thin-walled steel pipe with a longitudinal slot, its outer diameter is larger than the borehole diameter, and its tail is processed into a tapered shape for easy on-site installation.

3. The self-expanding energy-absorbing anchor bolt with stepped fracture according to claim 1, characterized in that: The load-bearing ring is installed 3-5cm away from the tail of the slotted sleeve. Its thickness is 12-20mm. The outer diameter of the load-bearing ring is smaller than the borehole diameter and larger than the diameter of the tapered opening at the tail of the slotted sleeve.

4. The self-expanding energy-absorbing anchor bolt with stepped fracture according to claim 1, characterized in that: The anchoring agent is a resin anchoring agent, a quick-drying cement mortar anchoring agent, or an expansion anchoring agent.

5. The self-expanding energy-absorbing anchor bolt with stepped fracture according to claim 1, characterized in that: The self-expanding propellant charge includes a hollow cylinder, a self-expanding anchoring agent, absorbent paper, and a second annular cap. The self-expanding propellant charge is continuously installed inside a slotted sleeve via a threaded steel rod and is secured in a fixed position by a second nut. The hollow cylinder is filled with a self-expanding anchoring agent, and a second annular cap is provided on the top of the self-expanding anchoring agent at the open end of the hollow cylinder. The outer wall of the hollow cylinder is wrapped with absorbent paper.

6. A self-expanding energy-absorbing anchor bolt with stepped fracture according to claim 5, characterized in that: The hollow cylinder includes an outer cylinder with several water absorption holes to increase water permeability. An inner cylinder is coaxially fitted inside the outer cylinder, forming a space for self-expanding anchoring agent installation between the outer and inner cylinders. A first annular cap is installed at one end of the outer and inner cylinders. The outer diameter of the outer cylinder is smaller than the inner diameter of the slotted sleeve, and the inner diameter of the inner cylinder is larger than the outer diameter of the threaded steel rod.

7. A self-expanding energy-absorbing anchor bolt with stepped fracture as described in claim 5, characterized in that: The self-expanding anchoring agent is a calcium sulfoaluminate-based expander, a calcium oxide-based expander, or a metal expander.

8. The self-expanding energy-absorbing anchor bolt with stepped fracture according to claim 1, characterized in that: The front end of the threaded steel rod protrudes 30-60 cm from the slotted sleeve for installing the anchoring agent, and the rear end protrudes 10-20 cm from the drill hole opening for installing the tray and the third nut.

9. The method for preparing a self-expanding energy-absorbing anchor bolt with stepped fracture according to claim 1, characterized in that, Includes the following steps: Step 1: Fabricate the threaded steel rod body, first nut, second nut, third nut, and break point. The threaded steel rod is made of high-strength precision-rolled manganese steel, with a length of 2.0-2.4m and a diameter of 18-26mm. The internal threads of the first nut, second nut, and third nut match the external threads of the threaded steel rod. The outer diameter of the first nut, second nut, and third nut is 34-38mm, and the length is 25-45mm. The fracture point is prefabricated 0.3-0.7m from the end of the threaded steel rod and located on the rigid part of the rod. The fracture point is made by drilling, shearing, and cutting, with a diameter or depth in the range of 4-15mm. When multiple fracture points are prefabricated, the diameter difference between adjacent fracture points is 2-4mm, and the strength of the fracture point closer to the flexible part is higher than that of the adjacent fracture points. Step 2: Fabricate the slotted sleeve The slotted sleeve is made of high-elasticity steel. The slotted sleeve is 1.2-1.8m long, 43-47mm in outer diameter, and 2-4mm in wall thickness. It has a 10-15mm wide slit along the longitudinal direction. The load-bearing ring is a metal ring with an outer diameter that is larger than the tapered diameter at the front end of the slotted sleeve and smaller than the diameter of the drill hole. Its inner diameter is larger than the diameter of the threaded steel rod. Step 3: Prepare self-expanding propellant charges The hollow cylinder of the self-expanding catalytic charge is manufactured using a blow molding process. The inner diameter of the inner cylinder is 19-27 mm, the outer diameter of the outer cylinder is 38-40 mm, the wall thickness of both the inner and outer cylinders is 0.2-0.5 mm, and the height of both the inner and outer cylinders is 10-15 cm. Several 1 mm diameter water absorption holes are opened on the outer cylinder wall, and the outer cylinder wall is wrapped with absorbent paper. The installation space formed by the outer and inner cylinders is filled with 1.5-2.0 g / cm³ of expansion anchoring agent. Step 4: Assemble the self-expanding energy-absorbing anchor bolt First, immerse the self-expanding explosive charge prepared in step 3 in water for 10-15 minutes or spray it with water for 15-18 minutes. Then, remove the self-expanding explosive charge and insert it into the threaded steel rod. After that, insert the rod and the self-expanding explosive charge into the slotted sleeve. Expose 10-15 cm of the round end of the slotted sleeve to install the tray and nut. Expose 50-70 cm of the conical end of the conical part to expose the pre-made fracture point. Install the load-bearing ring and nut on the threaded steel rod. Then, install 40-60 cm of anchoring agent on the remaining part of the threaded steel rod and use nuts to restrain both ends. The anchor installation is now complete.

10. The method of using a self-expanding energy-absorbing anchor bolt with stepped fracture as described in claim 1, characterized in that, It includes the following three stages: (1) Rigid stage; After the anchor is installed and put into use, the anchoring agent anchors the threaded steel rod body into the borehole, the self-expanding explosive charge expands and hardens, and outputs radial pressure to tightly fit the slotted sleeve with the rock wall; When the threaded steel rod body is subjected to axial tensile force generated by the deformation of the surrounding rock, the tensile load is less than the fracture load of the threaded steel rod body with the pre-fabricated fracture point, and neither the rigid part nor the flexible part moves. The self-expanding energy-absorbing anchor relies on the extension capacity of the rod body to resist the deformation and damage of the rock mass. (2) Static-dynamic transition stage; When rockburst or rock burst disaster strikes, the load on the threaded steel rod reaches the threshold of the fracture point setting, and the stress will be transmitted to the fracture point through the threaded steel rod, and tensile fracture will occur at the fracture point; during the fracture process, some impact energy is absorbed and the ejection speed of the rock block is greatly reduced; after the fracture, the rigid part loses its function, and the threaded steel rod is pulled out from the self-expanding explosive charge and moves towards the borehole side under the action of the pull-out force. At this time, the bearing ring fixedly connected to the threaded steel rod will contact the tail of the slotted sleeve, and the self-expanding energy-absorbing anchor rod begins to transition from the static state to the sliding state; (3) Flexible stage; after the anchor rod breaks at the fracture point under the action of impact load, the anchor rod does not fail. Instead, under the tension of the threaded steel rod body and the bearing ring, the flexible part slides continuously in the borehole and provides high anchoring force, thereby controlling the deformation and collapse of the rock mass. After the impact load is completed, the anchor rod stops sliding. When the next rock mass deformation occurs, the slotted sleeve can continue to slide to absorb the deformation energy of the surrounding rock until the deformation of the entire rock mass reaches the maximum deformation limit of the anchor rod.

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