A low prestress energy absorption anchor rod with expanding shell and construction method thereof

Abstract

The application discloses a kind of low prestress energy-absorbing anchor rod of expansion shell and its construction method, including cone head, expansion shell piece, inner rod and sleeve rod, the rear end of cone head and inner rod are connected in axial direction, wherein: cone head includes conical section, circular table section and cylindrical section connected in axial direction from front to back;Expansion shell piece is cylindrical shell, coaxially sleeved on the outside of cone head;When cone head moves towards the direction of expansion shell piece rear end, the large diameter part of circular table section enters expansion shell piece backwards, and expansion shell piece deforms radially outward;Inner rod is columnar rod body, and a plurality of first arc protrusions are arranged on the upper and lower walls of the rear section, and the first arc protrusions are arranged at intervals;Sleeve rod is columnar shell, and a plurality of second arc protrusions are arranged at intervals on the inner wall of each semicircular cylindrical shell along the length direction;Sleeve rod is coaxially sleeved on the outside of inner rod, and the second arc protrusions and the first arc protrusions are engaged.The anchor rod is firmly anchored, has excellent extension performance, and can be applied in soft rock large deformation or hard rock rock burst stratum reinforcement engineering.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical engineering support technology, specifically relating to an expansion-shell type low-prestress energy-absorbing anchor and its construction method. Background Technology

[0002] In the construction of underground geotechnical engineering projects such as traffic tunnels, mining roadways, and water conservancy tunnels, it is necessary to reinforce the strata to prevent deformation and collapse. Anchor bolt reinforcement is a common method of strata reinforcement. The tension of the anchor bolts can make the strata form a stable whole, thereby restraining strata deformation and preventing extreme engineering disasters such as collapse.

[0003] Energy-absorbing anchors have the following advantages over ordinary anchors: 1. High elongation: Energy-absorbing anchors absorb deformation energy through a special energy-absorbing structure, avoiding the radial shrinkage and fracture phenomenon that occurs with ordinary anchors after stretching. They have a higher overall elongation and are suitable for reinforcement projects in soft rock with large deformation or hard rock burst strata. 2. High frictional resistance: Ordinary anchors experience radial shrinkage after stretching, reducing the contact between the anchor body and the borehole wall, thus lowering the frictional resistance. Energy-absorbing anchors, with their special energy-absorbing structure, not only do not shrink when stretched, but expand, increasing the contact area and pressure between the anchor body and the borehole wall, resulting in higher frictional resistance. 3. High shear resistance: Ordinary anchors are slender and have weak lateral shear resistance. The special energy-absorbing structure of energy-absorbing anchors reduces lateral shear force through deformation, resulting in superior shear resistance.

[0004] The key to the tensile energy absorption function of energy-absorbing anchors is that the anchoring section is firmly anchored to the soil and rock. However, the anchoring performance of common grout anchors is unstable, and the anchoring section often comes off the anchor, leading to the failure of the entire anchor and posing a threat to production safety and project quality. Summary of the Invention

[0005] The purpose of this invention is to provide an expansion-shell type low-prestress energy-absorbing anchor and its construction method. This anchor has a firm anchoring and excellent elongation performance, and can be applied to reinforcement projects of soft rock with large deformation or hard rock burst strata.

[0006] This invention adopts the following technical solution: a shell-type low-prestress energy-absorbing anchor bolt, comprising a cone head, a shell plate, an inner rod, and a sleeve rod, wherein the rear end of the cone head and the inner rod are connected axially, wherein:

[0007] The cone head consists of a conical section, a frustum section, and a cylindrical section connected axially from front to back. The tip of the conical section faces forward, and the small end of the frustum section faces backward.

[0008] The expansion shell is a cylindrical shell that is coaxially fitted around the conical head. Its front end is located at approximately half the length of the frustum section, and its inner diameter is consistent with the outer diameter of the hammer at that location. Its rear end is located near the rear end of the cylindrical section.

[0009] As the cone moves toward the rear expansion shell, the large-diameter part of the frustum section enters the expansion shell rearward, and the expansion shell deforms radially outward, with its outer wall tightly adhering to and being stuck to the inner wall of the borehole.

[0010] The inner rod is a columnar rod body, and multiple first arc-shaped protrusions are provided on the upper and lower walls of its rear section. The multiple first arc-shaped protrusions are spaced apart, and the positions of the arc-shaped protrusions on the upper and lower walls correspond to each other.

[0011] The sleeve rod is a cylindrical shell-shaped structure formed by two semi-cylindrical shells interlocking together. On the inner wall of each semi-cylindrical shell, multiple second arc-shaped protrusions are spaced apart along its length. The sleeve rod is coaxially sleeved on the outside of the inner rod, and the second arc-shaped protrusions and the first arc-shaped protrusions engage with each other. Under the force generated by the deformation of the rock and soil, the sleeve rod can move axially backward along the inner rod. During the movement, the second arc-shaped protrusions and the first arc-shaped protrusions change from an interlocking misaligned state to a consistent position, causing the sleeve rod to expand radially outward and increasing the frictional resistance with the borehole wall.

[0012] Furthermore, a cap nut is screwed onto the rear end of the sleeve rod. The cap nut is used to move the sleeve rod, inner rod, and cone head to the rear end when it is screwed on.

[0013] Furthermore, the expansion shell is composed of multiple arc-shaped shells connected sequentially in the circumferential direction; an expansion shell connecting ring is coaxially sleeved at the rear end of the expansion shell, which is used to fix the multiple arc-shaped shells.

[0014] Furthermore, each arc-shaped pattern surrounds the outer wall of the arc-shaped shell, and multiple arc-shaped patterns are arranged at intervals along the front and back direction of the arc-shaped shell.

[0015] Furthermore, the expansion shell connecting ring is provided with multiple U-shaped notches with openings facing the front or rear end at intervals. The number of notches is the same as the number of arc-shaped shells, and each U-shaped notch is located at the protrusion of the arc-shaped shell.

[0016] Furthermore, the length of the sleeve rod is consistent with the length of the rear section of the inner rod. A conical shell is axially connected to each of the front and rear ends of the sleeve rod, and the sleeve rod is connected to the large end of the conical shell. A cylindrical tube is coaxially and integrally connected to the tip of each conical shell. Both the conical shell and the cylindrical tube are enclosed by half-shells. The inner wall of the cylindrical tube is in contact with the inner rod.

[0017] Furthermore, a washer is fitted on the cylindrical tube at the rear end, and on the cap nut, and a protective sleeve is fitted between the washer and the cylindrical tube.

[0018] Furthermore, a circular grout stop plate is provided at the rear end of the conical shell at the rear end. Multiple grouting holes are provided on the semi-cylindrical tube at the rear end, near the grout stop plate. The end of the cylindrical tube at the rear end is used to connect to the grouting device. Grout overflows from the grouting holes into the borehole for grouting the entire length of the anchor rod in the borehole.

[0019] This invention also discloses a construction method for the above-mentioned expansion-shell type low-prestress energy-absorbing anchor bolt, comprising the following steps:

[0020] Step S1, Drilling: Drill holes into the rock and soil inside the excavated tunnel and place anchoring agent cartridges into the holes;

[0021] Step S2, Anchor Bolt Installation: Insert the pre-installed anchor bolt into the hole, with the pad outside the hole and close to the outer perimeter wall. The cone pushes the anchoring agent cartridge to the bottom of the hole and punctures the anchoring agent cartridge, and the anchoring agent hardens. The pre-installed anchor bolt has the second arc-shaped protrusion and the first arc-shaped protrusion interlocking.

[0022] Step S3, Anchoring: Rotate the cap nut to move the sleeve, inner rod and cone head backward. The large diameter part of the cone head enters the expansion shell plate backward, driving the expansion shell plate to expand. The expansion shell connecting ring breaks at the notch, the expansion shell plate deforms radially, and the outer wall is tightly attached to and stuck to the inner wall of the borehole, thus completing the expansion shell fixing.

[0023] Step S4, Prestress Application: Continue to rotate the cap nut to allow the anchor body to elastically elongate. During the anchor retraction process, the axial prestress is transmitted to the rock wall of the anchor hole through the anchor body, cap nut, and washer, thus completing the application of anchor prestress. The anchor body includes: sleeve rod, inner rod, and cone head.

[0024] When the rock and soil mass deforms and moves toward the excavated space of the tunnel, the sleeve in the borehole is subjected to force and moves axially backward along the inner rod. During the movement, the second arc-shaped protrusion and the first arc-shaped protrusion change from an interlocking misaligned state to a consistent position, causing the sleeve to expand radially outward. The frictional resistance between the sleeve and the borehole wall increases, restricting the deformation of the rock and soil mass.

[0025] This invention also discloses a grouting reinforcement method for the above-mentioned expansion-shell type low-prestress energy-absorbing anchor bolt, comprising the following steps:

[0026] Step 1: Drilling: Drill holes into the rock and soil inside the excavated tunnel, ensuring that the inner diameter of the hole matches the diameter of the sleeve.

[0027] Step 2, Anchor Bolt Installation: Insert the pre-installed anchor bolt into the hole, with the pad outside the hole and close to the outer perimeter wall of the hole. The second arc-shaped protrusion of the pre-installed anchor bolt engages with the first arc-shaped protrusion.

[0028] Step 3, Anchoring: Rotate the cap nut to move the sleeve, inner rod and cone head backward. The large diameter part of the cone head enters the expansion shell plate backward, driving the expansion shell plate to expand. This causes the expansion shell connecting ring to break at the notch, and the expansion shell plate deforms radially. The outer wall tightly adheres to and is stuck to the inner wall of the borehole, completing the expansion shell fixing.

[0029] Step 4: Prestressing application: Continue to rotate the cap nut to allow the anchor bolt body to elastically elongate. During the anchor bolt retraction process, the axial prestress is transmitted to the rock wall of the anchor hole through the anchor bolt body, cap nut, and washer, thus completing the application of anchor bolt prestress. The anchor bolt body includes: sleeve, inner rod, and cone.

[0030] Step 5, Grouting: Grout is injected from the rear end of the sleeve rod. The grout overflows from the grouting hole and enters the borehole until the borehole is filled, completing the grouting of the entire length of the anchor rod inside the borehole.

[0031] The beneficial effects of this invention are: 1. By rotating the cap nut, the cone head moves towards the rear expansion shell, pushing the expansion shell to expand, ultimately anchoring the anchor rod to the soil and rock. Continuing to rotate the cap nut applies prestress; this expansion shell structure, through mechanical expansion, enhances the anchoring effect. 2. When the soil and rock deform and move towards the excavated tunnel space, the sleeve expands radially outward, increasing the frictional resistance with the borehole wall, thus strengthening the constraint on the soil and rock and enhancing the restriction on soil and rock deformation. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the overall structure of an expansion-shell type low-prestress energy-absorbing anchor.

[0033] Figure 2 This is a three-dimensional view of the expansion shell plate and the expansion shell connection ring in an expansion shell type low prestress energy-absorbing anchor bolt.

[0034] Figure 3 This is a three-dimensional view of the inner rod in a shell-type low-prestress energy-absorbing anchor bolt.

[0035] Figure 4 This is a three-dimensional view of the sleeve rod in a shell-type low-prestress energy-absorbing anchor bolt.

[0036] Figure 5 This is a diagram illustrating the anchoring process of a shell-type low-prestress energy-absorbing anchor bolt.

[0037] Figure 6 This is a diagram showing the deformation and energy absorption of a shell-type low-prestress energy-absorbing anchor bolt.

[0038] Figure 7 A schematic diagram of a shell-type low-prestress energy-absorbing anchor bolt configured as a full-length grouting anchor bolt.

[0039] Figure 8 A schematic diagram of a low-prestress energy-absorbing rock bolt with an expansion shell type, configured as a pressure-relief rock bolt.

[0040] The components are as follows: 1. Conical head; 2. Expansion shell plate; 21. Serrated edge; 22. Socket plate; 3. Expansion shell connecting ring; 31. Notch; 4. Inner rod; 41. Inner rod external thread; 42. Inner rod arc-shaped protrusion; 5. Connecting bolt; 6. Sleeve rod; 61. Connecting plate; 62. Sleeve rod arc-shaped protrusion; 63. Sleeve rod external thread; 7. Protective sleeve; 8. Pad plate; 9. Cap nut; 10. Grout stop plate; 11. Grouting hole; 12. Grout stop plug; 13. Pressure relief pad plate; 14. Force measuring spring. Detailed Implementation

[0041] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0042] The present invention discloses an expansion-shell type low prestress energy-absorbing anchor bolt, comprising an anchoring section, an energy-absorbing section, and an anchor head section. The anchoring section is used for anchoring the anchor bolt to the rock and soil, the energy-absorbing section absorbs energy through deformation, and the anchor head section is used for applying prestress.

[0043] The anchoring section includes a cone head 1 and an expansion shell 2; the cone head 1 and the expansion shell 2 are in sliding contact.

[0044] The energy-absorbing section includes the inner rod 4 and the sleeve rod 6; the anchor head section includes the casing 7, the pad 8, and the cap nut 9; the anchor head section is located outside the borehole.

[0045] This invention discloses a shell-type low-prestress energy-absorbing anchor bolt, which can achieve stable anchoring while also deforming to absorb energy. It is suitable for ground reinforcement operations under extreme conditions such as large deformation in soft rock and rockbursts in hard rock. Figure 1 As shown, it includes: a cone head 1, an expansion shell 2, an inner rod 4, and a sleeve rod 6, wherein:

[0046] The rear end of the cone 1 and the inner rod 4 are connected axially;

[0047] The cone 1 consists of a conical segment, a frustum segment, and a cylindrical segment connected axially from front to back. The tip of the conical segment faces forward, and the small end of the frustum segment faces backward.

[0048] like Figure 2 As shown, the expansion shell 2 is a cylindrical shell with a split structure, consisting of multiple arc-shaped shells connected sequentially in the circumferential direction. A connected socket cylindrical shell 22 is integrally connected to the rear end of the expansion shell 2. An expansion shell connecting ring 3 is coaxially sleeved on the socket cylindrical shell 22 and located outside it. The expansion shell connecting ring 3 is used to fix the multiple arc-shaped shells. Multiple raised arc-shaped patterns 22 are provided on the outer wall of each arc-shaped shell. Each arc-shaped pattern 22 surrounds the outer wall of the arc-shaped shell and coincides with the center of the expansion shell 2. The multiple arc-shaped patterns 22 are arranged at intervals along the front and rear direction of the arc-shaped shell.

[0049] The expansion shell connecting ring 3 is provided with a plurality of U-shaped notches 31 with openings facing the front or rear end at intervals. The number of notches 31 is the same as the number of arc-shaped shells, and each U-shaped notch 31 is located at the protrusion of the arc-shaped shell.

[0050] The expansion shell 2 is coaxially sleeved outside the cone head 1, with its front end located at approximately half the length of the frustum section and its inner diameter matching the outer diameter of the hammer head 1 at that location; its rear section is located near the rear end of the cylindrical section.

[0051] As the cone 1 moves toward the rear expansion shell 2, the large-diameter part of the cone 1 enters the expansion shell 2, causing the expansion shell connecting ring 3 to break at the notch 31. The arc-shaped shells are no longer constrained by external forces, and the expansion shell 2 deforms radially, with its outer wall tightly adhering to and stuck to the inner wall of the borehole.

[0052] like Figure 3 As shown, the inner rod 4 is a columnar rod body, and multiple first arc-shaped protrusions are provided on the upper and lower walls of its rear section. The multiple first arc-shaped protrusions are spaced apart, and the positions of the arc-shaped protrusions on the upper and lower walls correspond to each other.

[0053] like Figure 4 As shown, the sleeve 6 is a cylindrical shell-shaped structure formed by two semi-cylindrical shells fastened together. On the inner wall of each semi-cylindrical shell, a plurality of second arc-shaped protrusions 62 are spaced apart along its length. The size of each second arc-shaped protrusion 62 is such that half of its upper and lower protrusion portions can be accommodated in the groove between two adjacent first arc-shaped protrusions. The front-to-back distance between two adjacent second arc-shaped protrusions 62 is consistent with the front-to-back span of a first arc-shaped protrusion. The diameter of the sleeve 6 is the same as the diameter of the largest part of the conical section and the frustum section.

[0054] The length of the sleeve rod 6 is consistent with the length of the rear section of the inner rod 4, and it is coaxially sleeved outside the inner rod 4. The outer wall of the rear section of the sleeve rod 6 is provided with external threads. Its inner diameter satisfies the following: the end of the protruding part of a second arc-shaped protrusion 62 is located in the groove between two adjacent first arc-shaped protrusions and is attached to the inner rod wall in the space, that is, the second arc-shaped protrusion 62 and the first arc-shaped protrusion are engaged. When the rock and soil mass deforms and moves toward the excavated space of the tunnel, the force generated by the deformation acts on the sleeve rod 6. Under the action of the generated force, the sleeve rod 6 can move axially backward along the inner rod 4. During the movement, the second arc-shaped protrusion 62 and the first arc-shaped protrusion change from an engaged and misaligned state to a consistent position, so that the sleeve rod 6 expands radially outward, the frictional resistance with the hole wall increases, and the effect of restricting the deformation of the rock and soil mass is enhanced. After continuing to move, the second arc-shaped protrusion 62 moves to the next groove. Due to the pressure inside the hole, the sleeve rod 6 shrinks in diameter, and the second arc-shaped protrusion 62 and the first arc-shaped protrusion re-engage.

[0055] The sleeve rod 6 is axially connected to a conical shell at both its front and rear ends, and is connected to the large end of the conical shell. A cylindrical tube is coaxially and integrally connected to the tip of each conical shell. Both the conical shell and the cylindrical tube are enclosed by half-shells. The end of the cylindrical tube at the rear end is provided with an external thread.

[0056] A connecting plate 61 is provided at the end of the front semi-cylindrical shell, and a connecting plate 61 is also provided on the rear semi-cylindrical shell. Each connecting plate 61 has bolt holes, and the bolt holes on the connecting plate 61 at the same end are in corresponding positions. When each semi-shell is fastened together, it is connected and fixed by the connecting bolts 5 provided in the bolt holes.

[0057] A protective sleeve 7 is coaxially fitted onto the cylindrical tube at the rear end, close to the rear end. The outer wall of the protective sleeve 7 is tightly fitted against the inner wall of the borehole. A pad 8 is coaxially fitted onto the outside of the protective sleeve 7. A cap nut 9 is screwed onto the end of the cylindrical tube at the rear end, behind the pad 8. In use, the front and rear ends of the protective sleeve 7 are positioned inside and outside the borehole opening, respectively, serving to support and fix the anchor rod. The pad 8 is located outside the borehole and tightly fitted against the outer wall of the borehole. Figure 8 As shown, the pad 8 can be replaced with a spring-loaded pressure pad 13, and the spring in the pressure pad 13 can be replaced with a force-measuring spring 14. The signal line is then led out to obtain a pressure-absorbing anchor rod that can measure soil pressure.

[0058] like Figure 7 As shown, a circular grout stop plate 10 is provided at the rear end inside the conical shell at the rear end. Multiple grouting holes 11 are provided on the semi-cylindrical tube at the rear end, near the grout stop plate 10. The end of the cylindrical tube at the rear end is used to connect the grouting device. Grout overflows from the grouting holes 11 into the borehole, thereby realizing full-length grouting of the anchor rod.

[0059] A grout stop plug 12 is coaxially sleeved on the semi-cylindrical tube at the rear end, and the grout stop plug 12 is located in front of the grout stop plate 10.

[0060] The construction method of the above-mentioned expansion-shell type low prestressed energy-absorbing anchor bolt includes the following steps:

[0061] Step S1, Drilling: Using a rock drilling rig or an integrated anchor injection machine, drill holes outwards within the excavated tunnel and inject clean water into the holes for cleaning. The drilling spacing and depth are determined by the design requirements of different tunnels; pre-place anchoring agent cartridges into the holes.

[0062] Step S2, Anchor Bolt Installation: Insert the pre-installed anchor bolt into the hole. The pad 8 is located outside the hole and is tightly against the outer perimeter wall of the hole. A grout stopper 12 is installed at the hole opening and is fitted onto the rear end of the sleeve rod 6. The cone head 1 pushes the anchoring agent cartridge to the bottom of the hole and punctures the anchoring agent cartridge, and the anchoring agent begins to gradually harden. The pre-installed anchor bolt has its second arc-shaped protrusion 62 interlocking with the first arc-shaped protrusion.

[0063] Step S3, Anchoring: Rotate the cap nut 9, causing the anchor rod body to rotate outward, moving the cone head 1 towards the rear expansion shell 2. That is, the larger diameter portion of the cone head 1 enters the expansion shell 2, causing the expansion shell 2 to expand and adhere tightly to the hole wall, completing the expansion shell fixation. The anchor rod body includes: sleeve 6, inner rod 4, and cone head 1, as shown... Figure 5 As shown.

[0064] Step S4, Prestress Application: Continue to rotate the cap nut 9 to allow the anchor rod body to elastically elongate. During the retraction of the anchor rod body, the axial prestress is transmitted to the rock wall of the anchor hole through the anchor rod body, cap nut 9 and pad 8, thus completing the anchor rod prestress application action.

[0065] When the rock and soil mass deforms and moves toward the excavated space of the tunnel, the sleeve 6 inside the borehole is subjected to force, such as... Figure 6 As shown, the sleeve 6 moves axially backward along the inner rod 4. During the movement, the second arc-shaped protrusion 62 and the first arc-shaped protrusion change from an interlocking misaligned state to a position that is consistent, causing the sleeve 6 to expand radially outward. This increases the frictional resistance between the sleeve 6 and the hole wall, thus limiting the deformation of the rock and soil.

[0066] The above-mentioned grouting reinforcement method for expansion-shell type low prestressed energy-absorbing anchor bolts includes the following steps:

[0067] Step 1, Drilling: Drill a hole into the rock and soil inside the excavated tunnel, with the inner diameter of the hole matching the diameter of sleeve 6;

[0068] Step 2, Anchor Bolt Installation: Insert the pre-installed anchor bolt into the hole. The pad 8 is located outside the hole and is in close contact with the outer perimeter wall of the hole. The second arc-shaped protrusion 62 of the pre-installed anchor bolt engages with the first arc-shaped protrusion.

[0069] Step 3, Anchoring: Rotate the cap nut 9 to move the sleeve rod 6, inner rod 4 and cone 1 backward. The large diameter part of the cone 1 enters the expansion shell plate 2 backward, driving the expansion shell plate 2 to expand. This causes the expansion shell connecting ring 3 to break at the notch 31. The expansion shell plate 2 deforms radially, and its outer wall tightly adheres to and is stuck to the inner wall of the borehole, thus completing the expansion shell fixing.

[0070] Step 4: Prestressing application: Continue to rotate the cap nut 9 to allow the anchor body to elastically elongate. During the anchor retraction process, the axial pre-tightening force is transmitted to the rock wall of the anchor hole through the anchor body, cap nut 9 and pad 8, thus completing the application of anchor prestress. The anchor body includes: sleeve 6, inner rod 4 and cone 1.

[0071] Step 5, Grouting: Grout is injected from the rear end of sleeve rod 6. The grout overflows from grouting hole 11 and enters the borehole until the borehole is filled, completing the grouting of the entire length of the anchor rod in the borehole, which plays a role in reinforcing the rock and soil.

Claims

1. A swelling shell low prestressed energy absorbing anchor, characterized in that, The application relates to a drill rod, which comprises a cone head (1), a shell expanding piece (2), an inner rod (4) and a sleeve rod (6), the rear end of the cone head (1) is connected with the inner rod (4) in the axial direction, wherein: The cone head (1) comprises a conical section, a circular truncated cone section and a cylindrical section which are connected in the axial direction from front to back, the tip of the conical section is directed forward, and the small end of the circular truncated cone section is directed backward; The shell expanding piece (2) is a cylindrical shell which is coaxially sleeved on the cone head (1), the front end of the shell expanding piece (2) is located at the position close to the half length of the circular truncated cone section, and the inner diameter of the shell expanding piece (2) is consistent with the outer diameter of the cone head (1) at the position; the rear end of the shell expanding piece (2) is located at the position close to the rear end of the cylindrical section; When the cone head (1) moves towards the rear end of the shell expanding piece (2), the large diameter part of the circular truncated cone section enters the shell expanding piece (2) backward, the shell expanding piece (2) is deformed radially outward, and the outer wall is tightly clamped on the inner wall of the drill hole; The inner rod (4) is a columnar rod body, a plurality of first arc-shaped protrusions are arranged on the upper and lower walls of the rear section of the inner rod (4), the first arc-shaped protrusions are arranged at intervals, and the positions of the arc-shaped protrusions on the upper and lower walls correspond to each other; The sleeve rod (6) is a columnar shell, which is formed by buckling two half-cylindrical shells, a plurality of second arc-shaped protrusions (62) are arranged at intervals on the inner walls of the half-cylindrical shells along the length direction; the sleeve rod (6) is coaxially sleeved on the outer wall of the inner rod (4), the second arc-shaped protrusions (62) and the first arc-shaped protrusions are engaged; under the action of the force generated by the deformation of the rock-soil body, the sleeve rod (6) can move axially backward along the inner rod (4), and when the sleeve rod (6) moves, the second arc-shaped protrusions (62) and the first arc-shaped protrusions change from the engaged dislocation state to the position consistent state, so that the sleeve rod (6) expands radially outward, and the frictional resistance with the hole wall increases; A cap nut (9) is screwed on the rear end of the sleeve rod (6), the cap nut (9) is used for driving the sleeve rod (6), the inner rod (4) and the cone head (1) to move to the rear end when the cap nut (9) is screwed; The length of the sleeve rod (6) is consistent with the length of the rear section of the inner rod (4), the front and rear ends of the sleeve rod (6) are respectively connected with a conical shell in the axial direction, and the large end of the conical shell is connected, a cylindrical pipe is coaxially and integrally connected to the tip of each conical shell, and the conical shell and the cylindrical pipe are both formed by half shells; the inner wall of the cylindrical pipe is tightly fitted with the inner rod (4); A backing plate (8) is sleeved on the cylindrical pipe at the rear end and on the cap nut (9), and a casing (7) is sleeved between the backing plate (8) and the cylindrical pipe.

2. A low prestressed energy absorbing expanding shell anchor according to claim 1, characterized in that The shell expanding piece (2) is composed of a plurality of arc-shaped shells which are sequentially connected in the circumferential direction; a shell connecting ring (3) is coaxially sleeved on the rear end of the shell expanding piece (2), and the shell connecting ring (3) is used for fixing the plurality of arc-shaped shells.

3. A low prestressed energy absorbing expanding shell anchor according to claim 2, characterized in that The outer wall of the arc-shaped shell is surrounded by a plurality of arc-shaped lines (22), and the plurality of arc-shaped lines (22) are arranged at intervals along the front and rear directions.

4. A swelling cased low pre-stressed energy absorbing anchor rod as claimed in claim 3, wherein, A plurality of U-shaped notches (31) with the opening directed to the front end or the rear end are arranged at intervals on the shell connecting ring (3), the number of the U-shaped notches (31) is the same as that of the arc-shaped shells, and each U-shaped notch (31) is located at the protruding position of the arc-shaped shell.

5. A swelling cased low prestressed energy absorbing anchor rod as claimed in claim 4, wherein, A circular stop plate (10) is arranged at the rear end of the conical shell in the rear end, a plurality of grouting holes (11) are arranged on the rear end semi-cylindrical tube and close to the stop plate (10), and the end of the rear end cylindrical tube is used for connecting a grouting device. Grouting liquid is overflowed into the borehole from the grouting holes (11) to realize full-length grouting of the anchor rod in the borehole.

6. A method of constructing a swelling shell low prestressed energy absorbing anchor according to any one of claims 1 to 5, wherein, The method comprises the following steps: Step S1, drilling: drilling a hole in the rock-soil body in the excavated tunnel hole, and placing an anchoring agent cartridge in the hole; Step S2, anchor rod installation: inserting a preassembled anchor rod into the hole, the backing plate (8) being located outside the hole and closely attached to the peripheral wall surface of the hole, the tapered head (1) pushing the anchoring agent cartridge to the bottom of the hole and piercing the anchoring agent cartridge, and the anchoring agent hardening; the preassembled anchor rod, the second arc-shaped protrusion (62) and the first arc-shaped protrusion being engaged with each other; Step S3, anchoring: rotating the cap nut (9) to move the sleeve rod (6), the inner rod (4) and the tapered head (1) backward, the large-diameter part of the tapered head (1) entering the expansion shell piece (2) backward, driving the expansion shell piece (2) to expand, breaking the expansion shell connecting ring (3) at the gap (31), the expansion shell piece (2) being radially deformed, the outer wall being closely attached to and clamped on the inner wall of the borehole, and the expansion shell fixation being completed; Step S4, prestress application: continuing to rotate the cap nut (9) to make the anchor rod body elastically elongate, and the axial pretightening force being transmitted to the rock wall surface of the anchor hole through the anchor rod body, the cap nut (9) and the backing plate (8) in the retraction process of the anchor rod, the prestress application of the anchor rod being completed, and the anchor rod body comprising the sleeve rod (6), the inner rod (4) and the tapered head (1); When the rock-soil body deforms and moves towards the excavated space of the tunnel, the sleeve rod (6) in the hole is stressed, the sleeve rod (6) moves axially backward along the inner rod (4), in the moving process, the second arc-shaped protrusion (62) and the first arc-shaped protrusion are disengaged from the engaged state and are in the same position, the sleeve rod (6) expands radially outward, the frictional resistance between the sleeve rod (6) and the hole wall increases, and the deformation of the rock-soil body is limited.

7. The grouting reinforcement method of the expansion shell type low-prestress energy-absorbing anchor rod according to any one of claims 1-5, characterized in that Step one, drilling: drilling a hole in the rock-soil body in the excavated tunnel hole, the inner diameter of the hole matching the diameter of the sleeve rod (6); Step two, anchor rod installation: inserting a preassembled anchor rod into the hole, the backing plate (8) being located outside the hole and closely attached to the peripheral wall surface of the hole, the preassembled anchor rod, the second arc-shaped protrusion (62) and the first arc-shaped protrusion being engaged with each other; Step three, anchoring: rotating the cap nut (9) to move the sleeve rod (6), the inner rod (4) and the tapered head (1) backward, the large-diameter part of the tapered head (1) entering the expansion shell piece (2) backward, driving the expansion shell piece (2) to expand, breaking the expansion shell connecting ring (3) at the gap (31), the expansion shell piece (2) being radially deformed, the outer wall being closely attached to and clamped on the inner wall of the borehole, and the expansion shell fixation being completed; Step four, prestress application: continue to rotate the cap nut (9), so that the anchor rod body is elastically elongated, and the axial pretightening force is transmitted to the anchor hole wall surface through the anchor rod body, the cap nut (9) and the backing plate (8) in the retraction process of the anchor rod, the prestress application of the anchor rod is completed, and the anchor rod body comprises a sleeve rod (6), an inner rod (4) and a taper head (1); Step five, grouting: grouting liquid is injected from the rear end of the sleeve rod (6), the grouting liquid overflows from the grouting hole (11) and enters the drill hole until the drill hole is filled, and the full-length grouting of the anchor rod in the drill hole is completed.

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