Variable pressure grouting anchor rod and grouting method thereof

Abstract

The application discloses a variable-pressure grouting anchor rod and a grouting and anchoring method thereof, and relates to the technical field of roadway support. The grouting anchor rod comprises a hollow grouting anchor rod, a sealing device installed at one end of the grouting anchor rod close to a grouting port and capable of plugging the anchor rod hole, a self-anchoring anchor head installed at the other end of the grouting anchor rod away from the grouting port, a grouting outlet communicated with the inside of the grouting anchor rod and capable of being anchored in the anchor rod hole, and a damping part arranged between the outer wall of the grouting anchor rod and the inner wall of the anchor rod hole and capable of dividing the anchor rod hole into a first grouting section close to the grouting outlet and a second grouting section close to the grouting port. The grouting pressure of the first grouting section is greater than that of the second grouting section, and the damping part is capable of connecting the first grouting section and the second grouting section when the grouting pressure of the first grouting section reaches a set value. The grouting and anchoring method based on the above grouting anchor rod can realize variable-pressure grouting and improve the grouting and anchoring effect on weakly-cemented soft rock roadways.

Description

Technical Field

[0001] This invention relates to the field of tunnel support technology, and in particular to a variable pressure grouting anchor bolt and its grouting method. Background Technology

[0002] Some coal resources are found in Mesozoic Jurassic strata, which are late-formed and consist of weakly cemented soft rocks. These rocks are characterized by low cementation, high degree of joint and fissure development, and are rich in clay minerals (illite, kaolin, etc.), making them prone to swelling, disintegration, or sandification upon contact with water. In mine construction and production processes with such surrounding rock conditions, problems such as roof falls, spalling, and floor heave occur frequently, seriously threatening mine safety. How to effectively support weakly cemented soft rock roadways is a crucial problem that must be solved. Years of research by the inventors have revealed that the key to controlling weakly cemented soft rock roadways is "deep water blocking + shallow reinforcement," namely: sealing deep water-conducting fissures in the surrounding rock and strengthening the shallow surrounding rock.

[0003] One of the key technologies for solving the "deep water plugging + shallow reinforcement" problem is anchor grouting support, which involves using grouting anchor bolts. The existing principle of grouting anchor bolts is to inject high-pressure cement grout into the surrounding rock of the roadway, thereby sealing fissures and reinforcing the roadway. Generally, the higher the grouting pressure, the larger the grout diffusion radius, and the better the fissure sealing effect. However, for roadways with weak cemented soft rock, because the strength of the surrounding rock is much lower than that of ordinary surrounding rock, under the concentrated stress of roadway excavation, the loosening zone is larger and the rock mass is more fragmented. Within this zone, the high-pressure grout pressure will not only fail to reinforce the rock mass but will also further expand the rock fissures, exacerbating the fragmentation. Outside the loosening zone, the surrounding rock is less disturbed by roadway excavation and has relatively higher integrity. High-pressure grouting within this zone can increase the grout diffusion radius, achieving a good water plugging effect. It is evident that effective anchoring support for weakly cemented soft rock roadways requires simultaneous low-pressure grouting reinforcement of the surrounding rock within the loosened zone (shallow surrounding rock) and high-pressure grouting for water plugging of the surrounding rock outside the loosened zone (deep surrounding rock). However, existing grouting anchors cannot achieve variable-pressure grouting, resulting in poor anchoring performance in weakly cemented soft rock roadways. Therefore, it is necessary to develop a variable-pressure grouting anchor and its anchoring method suitable for the anchoring requirements of weakly cemented soft rock roadways. Summary of the Invention

[0004] The purpose of this invention is to provide a variable pressure grouting anchor bolt and its anchoring method to solve the problems existing in the prior art, realize variable pressure grouting, and improve the anchoring effect in weakly cemented soft rock tunnels.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] This invention provides a variable pressure grouting anchor bolt, comprising a hollow grouting anchor bolt for insertion into an anchor bolt hole and for grouting; a sealing device installed at the end of the grouting anchor bolt near the grouting port to seal the anchor bolt hole; a self-anchoring anchor head installed at the end of the grouting anchor bolt away from the grouting port, having a grout outlet communicating with the interior of the grouting anchor bolt, and the self-anchoring anchor head being anchored within the anchor bolt hole; and a damping section disposed between the outer wall of the grouting anchor bolt and the inner wall of the anchor bolt hole, capable of dividing the anchor bolt hole into a first grouting section near the grout outlet and a second grouting section near the grouting port, wherein the grouting pressure of the first grouting section is greater than the grouting pressure of the second grouting section, and when the grouting pressure of the first grouting section reaches a set value, the damping section can connect the first grouting section and the second grouting section.

[0007] Optionally, the grouting anchor has a diameter of 28mm, and both ends of the grouting anchor are threaded.

[0008] Optionally, the sealing device includes a fastening nut, a tray, and a grout-stopping plug. The tray and the grout-stopping plug are sequentially sleeved on the end of the grouting anchor rod near the grouting port. The fastening nut is threadedly connected to the end of the grouting anchor rod near the grouting port. The grout-stopping plug can abut against the opening of the anchor rod hole.

[0009] Optionally, the self-anchoring anchor head includes a hollow locking tongue, the locking tip of which has the grout outlet. A connecting nut is fixedly provided at the end of the locking tongue away from the grout outlet. The connecting nut is threadedly connected to the end of the grouting anchor rod away from the sealing device. The interior of the locking tongue communicates with the interior of the grouting anchor rod. A limiting part is installed on the outer wall of the locking tongue, and the limiting part can be anchored in the anchor rod hole.

[0010] Optionally, the limiting part includes a plurality of expansion shell flaps hinged to the outer wall of the latch, and one end of the expansion shell flaps away from the hinge point is connected to the latch via a flexible wire.

[0011] Optionally, the damping part includes a damping core and a damping sleeve; the damping core is fixedly disposed on the outer wall of the grouting anchor rod, and the damping sleeve includes a sleeve that is sleeved on the outer wall of the grouting anchor rod. A rubber sealing sleeve is fixedly installed on the outer side of the sleeve, and the rubber sealing sleeve can be fixedly abutted against the inner wall of the anchor rod hole; a guide groove is provided on the inner wall of the sleeve, and one end of the damping core can be sealed and snapped into one end of the guide groove; the strength of the damping core is less than the set value of the grouting pressure of the first grouting section. When the grouting pressure in the first grouting section reaches the set value, the damping core breaks, and the guide groove can connect the first grouting section and the second grouting section.

[0012] The present invention also provides an anchoring method for a variable pressure grouting anchor bolt, comprising the following steps:

[0013] S1: In-situ testing of surrounding rock strength and determination of surrounding rock strength grade. Based on the measured results of the surrounding rock strength of the weakly cemented soft rock roadway requiring anchoring support, the surrounding rock strength grade is determined. A small-diameter underground roadway surrounding rock strength in-situ testing device is used to test the surrounding rock strength of the weakly cemented soft rock roadway requiring anchoring support on-site. According to the three grades of weakly cemented soft rock strength: Grade 1 ≤ 10MPa, 10MPa < Grade 2 < 20MPa, and Grade 3 ≥ 20MPa, the surrounding rock strength grade is determined based on the measured results of the surrounding rock strength of the weakly cemented soft rock roadway requiring anchoring support.

[0014] S2: Determination of the thickness of the loosened rock zone and the length of the grouting anchor bolt. An ultrasonic rock fissure detector is used to determine the thickness of the loosened rock zone in the roadway requiring anchor grouting support, and the length of the grouting anchor bolt is selected based on the measured thickness of the loosened rock zone. The length of the grouting anchor bolt according to this invention is selected based on the measured thickness of the loosened rock zone. The length L of the "low-pressure grouting section" of the grouting anchor bolt should be slightly greater than or equal to the measured thickness of the loosened rock zone. Preferably, the length H of the "high-pressure grouting section" is in the range of 500–1000 mm. Grouting anchor bolt length = L + H + 50 mm.

[0015] S3. Determining the grouting pressure of the anchor bolt: Based on the strength grade of the surrounding rock, determine the grouting pressure range of the first and second grouting sections of the grouting anchor bolt. When the surrounding rock strength grade determined in step S1 is Grade 1, the grouting pressure range of the "high-pressure grouting section" of the variable pressure grouting anchor bolt suitable for weakly cemented soft rock roadways is 3–3.5 MPa, and the grouting pressure range of the "low-pressure grouting section" is 0.6–0.9 MPa. When the surrounding rock strength grade is Grade 2, the grouting pressure range of the "high-pressure grouting section" is 3.5–4.2 MPa, and the grouting pressure range of the "low-pressure grouting section" is 1.0–1.2 MPa. When the surrounding rock strength grade is Grade 3, the grouting pressure range of the "high-pressure grouting section" is 4.2–5.5 MPa, and the grouting pressure range of the "low-pressure grouting section" is 1.2–1.6 MPa.

[0016] S4. Grouting anchor bolt installation, until the grouting of the anchor bolts is completed.

[0017] Optionally, step S4 includes the following steps:

[0018] S41. Construction of anchor bolt holes: The design length of the anchor bolt hole = the length of the grouting anchor bolt M + 50mm. An anchor bolt drilling machine is used to construct the anchor bolt hole. After drilling reaches the design depth, the drilling is held steady for 1 to 2 minutes. After drilling is completed, high-pressure air is used to remove all rock powder, water and other debris from the hole.

[0019] S42. Using an anchor drilling machine, push the grouting anchor of the present invention into the anchor hole. When the tail of the anchor is about to reach the bottom of the hole, increase the thrust so that the wire binding the locking tongue and the expansion shell flap on the self-anchoring anchor head is broken. The expansion shell flap opens under the action of the locking tongue and tightens the hole wall to achieve self-anchoring. Then, use a fastening nut to fix the tray and the grout stop plug at the hole opening.

[0020] S43. Based on the grouting pressure determined in S3, first perform high-pressure grouting in the high-pressure grouting section, then perform low-pressure grouting in the low-pressure grouting section, until the grouting in the anchor bolt hole is completed.

[0021] Optionally, the grout material and its mass ratio used in the high-pressure grouting section are polyurethane: cement: straw fiber: water: early strength agent = 0.5:1.2:0.38:1:0.006, wherein the fineness of the straw fiber is less than 18μm, and the early strength agent is any one of calcium chloride, gypsum, water glass, and calcium carbonate; after high-pressure grouting for 3-5 minutes, the grouting pressure is increased to the set value of 6.5MPa and maintained for 5 seconds. At this time, the damping core breaks and loses its blocking effect, and the grouting pressure immediately drops to 0.6MPa, and then gradually increased to the low-pressure grouting pressure range of the low-pressure grouting section determined by S3, and grouting is continued for 5-8 minutes until the grouting in the anchor hole is completed.

[0022] The present invention achieves the following technical effects compared to the prior art:

[0023] This invention adds a self-anchoring anchor head device to the tail of a conventional grouting anchor rod. It uses a locking tongue and expansion shell flaps to automatically clamp the hole wall, quickly forming anchoring force, simplifying the construction process, realizing integrated anchoring and grouting operation, and greatly improving the construction efficiency of grouting anchor rods.

[0024] This invention designs a damping sleeve and a damping core structure. Using the damping core as a boundary, the grouting anchor bolt of this invention is divided into a first grouting section and a second grouting section with different grouting pressures, enabling variable pressure grouting. This satisfies the dual requirements of "low-pressure grouting reinforcement of shallow surrounding rock and high-pressure grouting for water plugging of deep surrounding rock" in weakly cemented soft rock roadways, resulting in significant anchoring and grouting support effects.

[0025] The grouting material prepared by this invention through experimental research is polyurethane: cement: straw fiber: water: early strength agent = 0.5:1.2:0.38:1:0.006. Among them, polyurethane has low density, good flowability, and strong water-blocking and seepage-proof performance, which can quickly form a strong waterproof membrane and block water-conducting fissure channels; straw fiber can control the development of cracks in the grout after curing, improve splitting toughness, and avoid the formation of secondary water-conducting fissures. The grouting and water-blocking reinforcement effect is much better than that of traditional cement grout. Attached Figure Description

[0026] To more clearly illustrate the technical solutions in the embodiments of the present invention 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.

[0027] Figure 1 This is a schematic diagram of the structure of the present invention;

[0028] Figure 2 for Figure 1 Sectional view of AA in the middle;

[0029] Figure 3 This is a schematic diagram of a self-anchoring anchor head structure;

[0030] Figure 4 Schematic diagram of the loosened zone of the surrounding rock in the tunnel;

[0031] Figure 5 This is an installation and construction drawing for the present invention;

[0032] Figure 6 This is a schematic diagram illustrating the anchoring effect of the present invention;

[0033] Explanation of reference numerals in the attached drawings: 1-Grouting anchor bolt; 2-Grouting port; 3-Damping core; 4-Damping sleeve; 5-Fastening nut; 6-Plate; 7-Grouting stop plug; 8-Self-anchoring anchor head; 9-Anchor bolt hole; 10-Tunnel; 11-Rock loosening ring; 12-Water plugging layer; 13-Reinforcement layer; H-First grouting section; L-Second grouting section; 41-Sleeve; 42-Guide groove; 43-Rubber sealing sleeve; 81-Lock tongue; 82-Wire; 83-Expansion shell flap; 84-Connecting nut; 85-Grouting outlet. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] The purpose of this invention is to provide a variable pressure grouting anchor bolt and its anchoring method to solve the problems existing in the prior art, realize variable pressure grouting, and improve the anchoring effect in weakly cemented soft rock tunnels.

[0036] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] For roadway 10, which is composed of weakly cemented soft rock, the strength of its surrounding rock is much lower than that of ordinary surrounding rock. Under the concentrated stress of roadway 10 excavation, the loosening zone 11 of the surrounding rock is larger and the degree of rock mass loosening and fragmentation is higher. When the rock mass in this zone is subjected to the pressure of high-pressure grout, it will not only fail to strengthen the rock mass, but will also cause the rock mass fissures to expand further, exacerbating the fragmentation of the surrounding rock. Therefore, low-pressure grouting must be used in the loosening zone 11 (shallow surrounding rock). The surrounding rock outside the loosening zone 11 is less disturbed by roadway excavation and has a relatively higher integrity. High-pressure grouting in this zone can increase the grout diffusion radius and achieve a good water-blocking effect. Therefore, to effectively anchor and reinforce weakly cemented soft rock roadways, it is necessary to simultaneously carry out low-pressure grouting reinforcement of the surrounding rock within the loosening zone 11 (shallow surrounding rock) and high-pressure grouting water-blocking of the surrounding rock outside the loosening zone 11 (deep surrounding rock). Based on this, the present invention can simultaneously meet the dual requirements of "low-pressure grouting reinforcement of shallow surrounding rock and high-pressure grouting for water plugging of deep surrounding rock" in weakly cemented soft rock tunnels.

[0038] For details, please refer to the appendix. Figure 1 Appendix Figure 2 Appendix Figure 3 Appendix Figure 4 Appendix Figure 5 and attached Figure 6As shown, the present invention provides a variable pressure grouting anchor rod, including a hollow grouting anchor rod 1. The grouting anchor rod 1 is made of Q235-B type hot-rolled hollow round steel, which is used to be inserted into the anchor rod hole 9 and can realize grouting. The diameter of the grouting anchor rod 1 is 28mm, and both ends of the grouting anchor rod 1 are threaded. One end of the grouting anchor rod 1 is provided with a sealing device, which includes a fastening nut 5, a tray 6 and a grout stop plug 7. The tray 6 and the grout stop plug 7 are sequentially sleeved on the end of the grouting anchor rod 1 near the grouting port 2. The fastening nut 5 is threadedly connected to the end of the grouting anchor rod 1 near the grouting port 2, and the grout stop plug 7 can abut against the opening of the anchor rod hole 9. The other end of the grouting anchor rod 1 is provided with a self-anchoring head 8, which includes a hollow locking tongue 81. The locking tip of the locking tongue 81 has a grout outlet 85. A connecting nut 84 is fixedly provided at the end of the locking tongue 81 away from the grout outlet 85. The connecting nut 84 is threadedly connected to the end of the grouting anchor rod 1 away from the sealing device. The interior of the locking tongue 81 is in communication with the interior of the grouting anchor rod 1. Multiple expansion shell flaps 83 are installed on the outer wall of the locking tongue 81. The end of the expansion shell flaps 83 away from the hinge point is connected to the locking tongue 81 through a flexible wire. The flexible wire of the present invention is preferably iron wire 82. The outer wall of the grouting anchor rod 1 is provided with a damping part, which includes a damping core 3 and a damping sleeve 4. The damping core 3 is fixedly installed on the outer wall of the grouting anchor rod 1. The damping sleeve 4 includes a sleeve 41, which is sleeved on the outer wall of the grouting anchor rod 1. A rubber sealing sleeve 43 is fixedly installed on the outside of the sleeve 41, and the rubber sealing sleeve 43 can be fixedly abutted against the inner wall of the anchor rod hole 9. A guide groove 42 is opened on the inner wall of the sleeve 41, and one end of the damping core 3 can be sealed and snapped into one end of the guide groove 42. The strength of the damping core 3 is 6MPa. The grouting anchor rod 1 of the present invention is divided into a first grouting section H and a second grouting section L with the damping core 3 as the boundary. The first grouting section H is a high-pressure grouting section and the second grouting section L is a low-pressure grouting section. The length of the first grouting section H is 500-1000mm. The strength of the damping core 3 is less than that of the sleeve 41. When the grouting pressure in the first grouting section H reaches the set value, the damping core 3 breaks, and the guide groove 42 can connect the first grouting section H and the second grouting section L.

[0039] This invention also discloses a method for anchoring variable pressure grouting anchors. The anchoring method of this invention will be described in detail below in conjunction with the specific surrounding rock conditions of coal mine A.

[0040] The main coal seam in Coal Mine A is located in the Mesozoic Jurassic strata. The surrounding rock of the roadway is characterized by low strength, poor cementation, and tendency to disintegrate upon contact with water, making it a typical weakly cemented rock roadway. The following is a variable pressure grouting anchor bolt method, applicable to weakly cemented soft rock roadways, based on the present invention:

[0041] S1: In-situ testing and determination of surrounding rock strength grade. Using a small-aperture underground roadway surrounding rock strength in-situ testing device, the surrounding rock strength of roadway A in the coal mine was measured to be between 12 and 18 MPa. Based on the three grades of surrounding rock strength for weakly cemented soft rock: Grade I ≤ 10 MPa, 10 MPa < Grade II < 20 MPa, and Grade III ≥ 20 MPa, the surrounding rock strength of roadway A in the coal mine was determined to be Grade II.

[0042] S2: Determination of the thickness of the loosened rock zone 11 and the length of the grouting anchor 1. The thickness of the loosened rock zone 11 in the coal mine A roadway was measured using an ultrasonic rock fissure detector, d = 3000 mm. The length of the second grouting section L of the grouting anchor 1 should be slightly greater than or equal to the measured thickness d of the loosened rock zone 11. In this embodiment, L = d = 3000 mm. Preferably, the length of the first grouting section H should be in the range of 500–1000 mm. In this embodiment, H = 600 mm. Therefore, the length of the grouting anchor 1 is...

[0043] M=L+H+50mm=3000mm+600mm+50mm=3650mm.

[0044] S3. Determination of anchor bolt grouting pressure. The strength grade of the surrounding rock of coal mine A determined in step S1 is level two. In this embodiment, the grouting pressure of the first grouting section H of the grouting anchor bolt 1 is determined to be 4.0 MPa, and the grouting pressure range of the second grouting section L is 1.0 MPa.

[0045] S4. Grouting Anchor Bolt Installation Steps. The grouting installation includes the following steps:

[0046] ① Construct anchor bolt hole 9. The designed length of anchor bolt hole 9 = the length of grouting anchor bolt 1 M + 50mm = 3700mm; use an anchor bolt drilling machine to construct anchor bolt hole 9. After drilling to the designed depth, hold the drill steady for 1 minute; after drilling is completed, use high-pressure air to remove all rock powder, water and other debris from the hole.

[0047] ② Install the grouting anchor rod 1. Use an anchor drilling machine to push the grouting anchor rod 1 of the present invention into the anchor hole 9. When the tail of the grouting anchor rod 1 is about to reach the bottom of the hole, increase the thrust so that the wire 82 binding the locking tongue 81 and the expansion shell flap 83 on the self-anchoring anchor head 8 is broken. The expansion shell flap 83 opens under the action of the locking tongue 81, and tightens the hole wall of the anchor hole 9 to achieve self-anchoring. Then, use the fastening nut 5 to fix the tray 6 and the grout stop plug 7 at the position of the anchor hole 9.

[0048] ③ Grouting Construction. Following the grouting pressure determined in step S3, high-pressure grouting is first performed in the first grouting section H, followed by low-pressure grouting in the second grouting section L. The grout material and its mass ratio used in the first grouting section H are: polyurethane: cement: straw fiber: water: early-strength agent = 0.5:1.2:0.38:1:0.006. The fineness of the straw fiber is less than 18μm, and the early-strength agent is any one of calcium chloride, gypsum, water glass, or calcium carbonate. After high-pressure grouting for 3–5 minutes, the grouting pressure is increased to 6.5 MPa and maintained for 5 seconds. At this point, the damping core 3 breaks and loses its blocking effect, and the grouting pressure immediately drops to 0.6 MPa. Then, it is gradually increased to the low-pressure grouting pressure range of the second grouting section L determined in S3, and grouting is continued for 5–8 minutes to complete the anchor grouting.

[0049] This invention can simultaneously meet the dual requirements of "shallow surrounding rock low-pressure grouting reinforcement and deep surrounding rock high-pressure grouting water plugging" for weakly cemented soft rock roadways. This invention can rapidly form a water-blocking layer 12 outside the loosened rock zone 11 and a reinforcement layer 13 inside the loosened rock zone 11 in the surrounding rock mass of the roadway. The anchoring and grouting support effect is significant, greatly improving the stability of weakly cemented soft rock roadways and preventing safety accidents.

[0050] In the description of this invention, it should be noted that the terms "center," "top," "bottom," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0051] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A variable pressure grouting anchor bolt, characterized in that: Includes hollow grouting anchors, which are inserted into anchor holes and can be used for grouting; A sealing device is installed at one end of the grouting anchor rod near the grouting port, which can seal the anchor rod hole; The self-anchoring anchor head is installed at the end of the grouting anchor rod away from the grouting port. It has a grout outlet that communicates with the inside of the grouting anchor rod, and the self-anchoring anchor head can be anchored in the anchor rod hole. A damping section is disposed between the outer wall of the grouting anchor and the inner wall of the anchor hole. It can divide the anchor hole into a first grouting section near the grout outlet and a second grouting section near the grout outlet. The grouting pressure of the first grouting section is greater than that of the second grouting section. When the grouting pressure of the first grouting section reaches a set value, the damping section can connect the first grouting section and the second grouting section. The damping part includes a damping core and a damping sleeve; the damping core is fixedly disposed on the outer wall of the grouting anchor rod, and the damping sleeve includes a sleeve that is sleeved on the outer wall of the grouting anchor rod. A rubber sealing sleeve is fixedly installed on the outer side of the sleeve, and the rubber sealing sleeve can be fixedly abutted against the inner wall of the anchor rod hole; a guide groove is provided on the inner wall of the sleeve, and one end of the damping core can be sealed and snapped into one end of the guide groove; the strength of the damping core is less than the set value of the grouting pressure of the first grouting section. When the grouting pressure in the first grouting section reaches the set value, the damping core breaks, and the guide groove can connect the first grouting section and the second grouting section; The self-anchoring anchor head includes a hollow locking tongue, the locking tip of which has the grout outlet, and the interior of the locking tongue is connected to the interior of the grouting anchor rod; a limiting part is installed on the outer wall of the locking tongue, and the limiting part can be anchored in the anchor rod hole.

2. The variable pressure grouting anchor bolt according to claim 1, characterized in that: The grouting anchor has a diameter of 28mm, and both ends of the grouting anchor are threaded.

3. The variable pressure grouting anchor bolt according to claim 2, characterized in that: The sealing device includes a fastening nut, a tray, and a grout-stopping plug. The tray and the grout-stopping plug are sequentially sleeved on the end of the grouting anchor rod near the grouting port. The fastening nut is threadedly connected to the end of the grouting anchor rod near the grouting port. The grout-stopping plug can abut against the opening of the anchor rod hole.

4. The variable pressure grouting anchor bolt according to claim 2, characterized in that: The locking tongue is fixedly provided with a connecting nut at the end away from the grout outlet, and the connecting nut is threadedly connected to the end of the grouting anchor rod away from the sealing device.

5. The variable pressure grouting anchor bolt according to claim 4, characterized in that: The limiting part includes a plurality of expansion shell flaps hinged to the outer wall of the latch, and the end of the expansion shell flaps away from the hinge point is connected to the latch via a flexible wire.

6. An anchoring method based on the variable pressure grouting anchor bolt according to any one of claims 1 to 5, characterized in that: Includes the following steps: S1: In-situ testing of surrounding rock strength and determination of surrounding rock strength grade. Based on the actual test results of the surrounding rock strength of the weakly cemented soft rock roadway with anchoring support as needed, the surrounding rock strength grade is determined. S2: Determination of the thickness of the loosened zone of the surrounding rock and the length of the grouting anchor bolt. The thickness of the loosened zone of the surrounding rock in the roadway that needs to be anchored and grouted is determined by using an ultrasonic rock fissure detector, and the length of the grouting anchor bolt is selected based on the actual thickness of the loosened zone. S3. Determine the grouting pressure of the anchor bolt. Based on the strength grade of the surrounding rock, determine the grouting pressure range of the first and second grouting sections of the grouting anchor bolt. S4. Grouting anchor bolt installation, until the grouting of the anchor bolts is completed.

7. The anchoring method for variable pressure grouting anchors according to claim 6, characterized in that: Step S4 includes the following steps: S41. When drilling the anchor bolt hole, after the drilling reaches the designed depth, hold the drill steady for 1 to 2 minutes. After drilling is completed, use high-pressure air to remove all rock powder and water debris from the anchor bolt hole. S42. Push the grouting anchor into the anchor hole. When the tail of the grouting anchor is about to reach the bottom of the hole, increase the thrust so that the flexible wire binding the locking tongue and the expansion shell flap on the self-anchoring anchor head breaks. The expansion shell flap opens under the action of the locking tongue and tightens the hole wall to achieve self-anchoring. Then, use the fastening nut to fix the tray and the grout stop plug at the hole opening. S43. Based on the grouting pressure determined in S3, first perform high-pressure grouting in the high-pressure grouting section, then perform low-pressure grouting in the low-pressure grouting section, until the grouting in the anchor bolt hole is completed.

8. The anchoring method for variable pressure grouting anchors according to claim 7, characterized in that: The grout material and its mass ratio used in the high-pressure grouting section are polyurethane: cement: straw fiber: water: early strength agent = 0.5:1.2:0.38:1:0.

006. The fineness of the straw fiber is less than 18μm, and the early strength agent is any one of calcium chloride, gypsum, water glass, and calcium carbonate. After high-pressure grouting for 3-5 minutes, the grouting pressure is increased to the set value and maintained for 5 seconds. At this time, the damping core breaks and loses its blocking effect, and the grouting pressure immediately drops. Then, it is gradually increased to the low-pressure grouting pressure range of the low-pressure grouting section determined by S3, and grouting is continued for 5-8 minutes until the grouting in the anchor hole is completed.

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