Expansion shell type low-prestress energy absorption anchor rod and construction method thereof

Abstract

The invention discloses an expansion shell type low-prestress energy-absorbing anchor rod and a construction method thereof.The expansion shell type low-prestress energy-absorbing anchor rod comprises a conical head, expansion shell pieces, an inner rod and a sleeve rod, the rear end of the conical head is connected with the inner rod in the axial direction, and the conical head 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 expansion shell piece is a cylindrical shell and is coaxially arranged outside the conical head in a sleeving manner; when the conical head moves towards the shell expansion piece at the rear end, the large-diameter part of the circular truncated cone section backwards enters the shell expansion piece, and the shell expansion piece outwards deforms in the radial direction; the inner rod is a columnar rod body, the upper wall and the lower wall of the rear section of the inner rod are each provided with a plurality of first arc-shaped protrusions, and the first arc-shaped protrusions are arranged at intervals; the sleeve rod is in a columnar shell shape, and a plurality of second arc-shaped protrusions are arranged on the inner wall of each semi-cylindrical shell at intervals in the length direction of the semi-cylindrical shell; the sleeve rod is coaxially arranged outside the inner rod in a sleeving mode, and the second arc-shaped protrusion and the first arc-shaped protrusion are meshed. The anchor rod is firm in anchoring, excellent in extension performance and suitable for soft rock large deformation or hard rock rockburst stratum reinforcement engineering.

Description

Technical Field

[0001] The invention belongs to the technical field of geotechnical engineering support, and particularly relates to an expansion shell type low prestressed energy absorbing anchor rod and a construction method thereof. Background Art

[0002] During the construction of underground geotechnical engineering projects such as transportation tunnel projects, mining tunnel projects, and water conservancy and water supply cavern projects, the strata need to be reinforced to prevent deformation and collapse. Anchor reinforcement is a common method of stratum reinforcement. The tension of the anchor rods can form a stable whole for the stratum, thereby restraining stratum deformation and preventing extreme engineering disasters such as landslides.

[0003] Compared with ordinary anchor rods, energy-absorbing anchor rods have the following advantages: 1. High elongation. Energy-absorbing anchor rods absorb deformation energy through special energy-absorbing structures, and will not experience the phenomenon of diameter shrinkage and fracture after stretching of ordinary anchor rods. The overall elongation is larger, and it can be used in soft rock large deformation or hard rock rock burst strata reinforcement projects; 2. High friction resistance. After ordinary anchor rods are stretched, the anchor rod body will shrink in diameter, resulting in reduced contact between the rod body and the hole wall, which in turn leads to reduced friction resistance of the rod body. However, energy-absorbing anchor rods, with their special energy-absorbing structure, will not shrink in diameter when stretched, but will expand instead, increasing the contact area and contact pressure between the rod body and the hole wall. Therefore, the friction resistance of energy-absorbing anchor rods is greater; 3. High shear resistance. Ordinary anchor rods have slender rod bodies and weak lateral shear resistance. The special energy-absorbing structure of energy-absorbing anchor rods can reduce lateral shear force through deformation, and have better shear resistance.

[0004] The key to the tensile energy absorption effect of the energy-absorbing anchor is that the anchoring section is firmly anchored to the rock and soil. However, the anchoring performance of common slurry anchoring is unstable, and the anchoring section often becomes detached, resulting in the overall failure of the anchor, posing a hidden danger to production safety and project quality. Summary of the invention

[0005] The purpose of the present invention is to provide a shell expansion type low prestressed energy absorbing anchor rod and a construction method thereof. The anchor rod has a firm anchoring and excellent elongation performance and can be applied to reinforcement engineering of soft rock large deformation or hard rock rock burst strata.

[0006] The present invention adopts the following technical solution: an expansion shell type low prestressed energy absorbing anchor rod, comprising a cone head, an expansion shell sheet, an inner rod and a sleeve rod, the rear end of the cone head and the inner rod are connected in the axial direction, wherein:

[0007] The cone head includes a cone section, a truncated cone section and a cylindrical section connected axially from front to back, the tip of the cone section faces forward, and the small head end of the truncated cone section faces backward;

[0008] The shell expansion piece is a cylindrical shell, which is coaxially sleeved outside the cone head, with its front end located at nearly half the length of the truncated cone section, and its inner diameter is consistent with the outer diameter of the hammer head where it is located; its rear end is located near the rear end of the cylindrical section;

[0009] When the cone head moves toward the rear end expansion piece, the large diameter part of the truncated cone section enters the expansion piece backward, the expansion piece deforms radially outward, and the outer wall is closely attached to and stuck on the inner wall of the drill hole;

[0010] The inner rod is a columnar rod body, and a plurality of first arc-shaped protrusions are arranged on the upper and lower walls of the rear section thereof, and the plurality of 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;

[0011] The sleeve rod is in the shape of a columnar shell, which is formed by buckling two semi-cylindrical shells. On the inner wall of each semi-cylindrical shell, a plurality of second arc-shaped protrusions are arranged at intervals along its length direction; the sleeve rod is coaxially sleeved outside the inner rod, and the second arc-shaped protrusion and the first arc-shaped protrusion are engaged with each other; under the action of the force generated by the deformation of the rock and soil body, the sleeve rod can move axially backward along the inner rod, and when moving, the second arc-shaped protrusion and the first arc-shaped protrusion change from an engaged and misaligned state to a consistent position, so that the sleeve rod expands radially outward, and the friction resistance with the hole wall increases.

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

[0013] Furthermore, the shell expansion piece is composed of a plurality of arc-shaped shells, which are connected in sequence in a ring direction; an expansion shell connecting ring is coaxially sleeved at the rear end outside the shell expansion piece, and the expansion shell connecting ring is used to fix the plurality of arc-shaped shells.

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

[0015] Furthermore, the expansion shell connecting ring is provided with a plurality of U-shaped notches with openings toward the front end or the rear end at intervals, the number of the notches is the same as the number of the arc-shaped shell, and each U-shaped notch is located at a 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, the front and rear ends of the sleeve rod are each axially connected to a conical shell, and are connected to the large end of the conical shell, and a cylindrical tube is coaxially and integrally connected to the tip of each conical shell, and the conical shell and the cylindrical tube are both surrounded by half shells; the inner wall of the cylindrical tube fits with that of the inner rod.

[0017] Furthermore, a backing plate is sleeved on the cylindrical tube at the rear end and on the cap head nut, and a protective tube is sleeved between the backing plate and the cylindrical tube.

[0018] Furthermore, a circular grouting plate is provided at the rear end of the conical shell at the rear end, and a plurality of grouting holes are opened on the semi-cylindrical tube at the rear end and close to the grouting plate. The end of the cylindrical tube at the rear end is used to connect the grouting device, and the slurry overflows from the grouting hole into the borehole for grouting the entire length of the anchor rod in the borehole.

[0019] The present invention also discloses a construction method of the above-mentioned shell expansion type low prestressed energy absorbing anchor rod, comprising the following steps:

[0020] Step S1, drilling: drilling a hole into the rock and soil in the excavated tunnel, and placing an anchoring agent roll into the hole;

[0021] Step S2, anchor rod installation: insert the pre-installed anchor rod into the hole, the backing plate is located outside the hole and close to the peripheral wall outside the hole, the cone head pushes the anchor agent roll to the bottom of the hole and punctures the anchor agent roll, and the anchor agent hardens; the second arc-shaped protrusion of the pre-installed anchor rod is engaged with the first arc-shaped protrusion;

[0022] Step S3, anchoring: rotating the cap head nut to move the sleeve rod, the inner rod and the cone head backwards, and the large diameter part of the cone head enters the shell expansion piece backwards, driving the shell expansion piece to expand, so that the shell expansion connecting ring breaks at the notch, the shell expansion piece is radially deformed, and the outer wall is tightly attached to and stuck on the inner wall of the drill hole, completing the expansion fixation;

[0023] Step S4, applying prestress: continue to rotate the cap nut to make the anchor rod body elastically elongate. During the retraction of the anchor rod, the axial prestressing force is transmitted to the rock wall of the anchor hole through the anchor rod body, the cap nut and the pad to complete the application of prestress to the anchor rod. The anchor rod body includes: a sleeve rod, an inner rod and a cone head;

[0024] When the rock and soil body deforms and moves toward the excavated space of the tunnel, the sleeve rod 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 engaged and misaligned state to a consistent position, causing the sleeve rod to expand radially outward, increasing the friction resistance between the sleeve rod and the hole wall, and limiting the deformation of the rock and soil body.

[0025] The present invention also discloses a grouting reinforcement method for the above-mentioned shell expansion type low prestressed energy absorbing anchor rod, comprising the following steps:

[0026] Step 1: Drilling: Drill a hole into the rock and soil in the excavated tunnel, with the inner diameter of the hole matching the diameter of the casing rod;

[0027] Step 2: Anchor rod installation: insert the pre-installed anchor rod into the hole, with the backing plate located outside the hole and close to the peripheral wall of the hole, and the second arc-shaped protrusion of the pre-installed anchor rod is engaged with the first arc-shaped protrusion;

[0028] Step 3: Anchoring: Rotate the cap nut to move the sleeve rod, inner rod and cone head backwards, and the large diameter part of the cone head enters the shell expansion piece backwards, driving the shell expansion piece to expand, so that the shell expansion connecting ring breaks at the notch, the shell expansion piece deforms radially, and the outer wall is tightly attached to and stuck on the inner wall of the drill hole, completing the fixing of the shell expansion;

[0029] Step 4: Apply prestress: Continue to rotate the cap nut to elastically extend the anchor rod body. During the retraction of the anchor rod, the axial preload force is transmitted to the rock wall of the anchor hole through the anchor rod body, the cap nut and the pad to complete the application of prestress to the anchor rod. The anchor rod body includes: a sleeve rod, an inner rod and a cone head.

[0030] Step 5: Grouting: Grouting liquid is injected from the rear end of the casing rod. The grouting liquid 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 in the borehole.

[0031] The beneficial effects of the present invention are as follows: 1. The cone head is driven to move toward the rear end expansion shell plate by rotating the cap head nut, pushing the expansion shell plate to expand, and finally anchoring the anchor rod to the rock and soil body. The cap head nut is continued to be rotated to apply prestress. The expansion shell structure strengthens the anchoring effect through mechanical expansion. 2. Under the action of the force generated by the deformation when the rock and soil body deforms and moves toward the excavated space of the tunnel, the sleeve rod expands radially outward, the friction resistance with the hole wall increases, the restraining effect on the rock and soil body is enhanced, and the effect of limiting the deformation of the rock and soil body is enhanced. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of the overall structure of the expansion shell type low prestressed energy-absorbing anchor rod.

[0033] Figure 2 It is a three-dimensional diagram of the expansion shell piece and the expansion shell connecting ring in the expansion shell type low prestressed energy-absorbing anchor.

[0034] Figure 3 It is a three-dimensional diagram of the inner rod of the expansion shell type low prestressed energy-absorbing anchor rod.

[0035] Figure 4 It is a three-dimensional diagram of the middle sleeve rod of the expansion shell type low prestressed energy-absorbing anchor rod.

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

[0037] Figure 6 This is the deformation and energy absorption diagram of the expanding shell type low prestressed energy-absorbing anchor.

[0038] Figure 7 Schematic diagram of the expansion shell type low prestressed energy-absorbing anchor rod set as a full-length grouting anchor rod.

[0039] Figure 8 This is a schematic diagram of the expansion shell type low prestressed energy-absorbing anchor rod set as a compression anchor rod.

[0040] Among them: 1. cone head; 2. shell expansion plate; 21. serration; 22. socket plate; 3. shell expansion connecting ring; 31. notch; 4. inner rod; 41. inner rod external thread; 42. inner rod arc bulge; 5. connecting bolt; 6. sleeve rod; 61. connecting plate; 62. sleeve rod arc bulge; 63. sleeve rod external thread; 7. casing; 8. pad; 9. cap head nut; 10. grouting plate; 11. grouting hole; 12. grouting plug; 13. pressure pad; 14. force measuring spring. DETAILED DESCRIPTION

[0041] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0042] The invention discloses an expansion shell type low prestressed energy absorbing anchor rod, comprising an anchoring section, an energy absorbing section and an anchor head section. The anchoring section is used for anchoring the anchor rod to a rock and soil body, the energy absorbing section absorbs energy by deformation, and the anchor head section is used for applying prestress.

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

[0044] The energy absorbing section comprises an inner rod 4 and a sleeve rod 6; the anchor head section comprises a casing 7, a backing plate 8, and a cap head nut 9; and the anchor head section is located outside the borehole.

[0045] The invention discloses an expansion shell type low prestressed energy absorbing anchor rod, which can realize stable anchoring and can be deformed to absorb energy, and is suitable for stratum reinforcement operations under extreme conditions such as large deformation of soft rock and rock burst of hard rock. Figure 1 As shown, it includes: a cone head 1, a shell expansion piece 2, an inner rod 4 and a sleeve rod 6, wherein:

[0046] The rear end of the cone head 1 is connected to the inner rod 4 in the axial direction;

[0047] The cone head 1 includes a cone section, a truncated cone section and a cylindrical section connected in the axial direction from front to back, the tip of the cone section faces forward, and the small head end of the truncated cone section faces backward;

[0048] like Figure 2 As shown, the shell expansion piece 2 is a cylindrical shell, which is a split structure, and is composed of a plurality of arc shells, which are connected in sequence in the ring direction; a connected socket cylindrical shell 22 is integrally connected to the rear end of the shell expansion piece 2, and a shell expansion connecting ring 3 is coaxially sleeved on the socket cylindrical shell 22 and located outside thereof, and the shell expansion connecting ring 3 is used to fix a plurality of arc shells; a plurality of raised arc patterns 22 are arranged on the outer wall of each arc shell, and each arc pattern 22 surrounds the outer wall of the arc shell and coincides with the center of the shell expansion piece 2, and a plurality of arc patterns 22 are arranged at intervals along the front and rear direction of the arc shell;

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

[0050] The shell expansion piece 2 is coaxially sleeved outside the cone head 1, with its front end located at nearly half the length of the truncated cone section, and its inner diameter is consistent with the outer diameter of the hammer head 1 where it is located; and its rear section is located near the rear end of the cylindrical section;

[0051] When the cone head 1 moves toward the rear end expansion piece 2, the large diameter part of the cone head 1 enters the expansion piece 2 backward, causing the expansion connecting ring 3 to break at the notch 31. Each arc-shaped shell is no longer constrained by external force, the expansion piece 2 is radially deformed, and the outer wall is tightly attached to and stuck on the inner wall of the drilled hole.

[0052] like Figure 3 As shown, the inner rod 4 is a columnar rod body, and a plurality of first arc-shaped protrusions are arranged on the upper and lower walls of the rear section thereof, and the plurality of 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;

[0053] like Figure 4 As shown, the sleeve rod 6 is in the shape of a columnar shell, which is formed by buckling two semi-cylindrical shells. On the inner wall of each semi-cylindrical shell, a plurality of second arc-shaped protrusions 62 are arranged at intervals along its length direction. The size of each second arc-shaped protrusion 62 is such that half of its upper and lower protruding parts can be accommodated in the groove between two adjacent first arc-shaped protrusions; the front-to-back spacing 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 rod 6 is the same as the diameter of the largest part of the conical section and the truncated cone 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 an external thread; its inner diameter satisfies: the end of the convex part of a second arc-shaped protrusion 62 is located in the groove between the 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 with each other; when the rock and soil body deforms and moves toward the excavated space of the tunnel, the force generated by the deformation acts on the sleeve rod 6, and under the action of the generated force, the sleeve rod 6 can move axially backward along the inner rod 4, and when moving, 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 friction resistance with the hole wall increases, and the effect of limiting the deformation of the rock and soil body is enhanced; after continuing to move, the second arc-shaped protrusion 62 moves to the next groove, and due to the pressure in the hole, the sleeve rod 6 shrinks in diameter, and the second arc-shaped protrusion 62 and the first arc-shaped protrusion are engaged again.

[0055] The front and rear ends of the sleeve rod 6 are axially connected to a conical shell, and are connected to the large end of the conical shell. The tip of each conical shell is coaxially connected to a cylindrical tube. The conical shell and the cylindrical tube are surrounded by a half shell. The end of the rear cylindrical tube 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 a bolt hole. The positions of the bolt holes on the connecting plate 61 at the same end correspond to each other. When the half shells are buckled together, they are connected and fixed by connecting bolts 5 set in the bolt holes.

[0057] On the rear cylindrical tube, a casing 7 is coaxially sleeved near the rear end, and the outer wall of the casing 7 is closely attached to the inner wall of the borehole; a backing plate 8 is coaxially sleeved outside the casing 7, and a cap nut 9 is screwed on the end of the cylindrical tube behind the backing plate 8 and located at the rear end. When in use, the front and rear ends of the casing 7 are respectively located inside and outside the borehole, playing the role of supporting and fixing the anchor rod. The backing plate 8 is located outside the borehole and closely attached to the outer wall of the borehole. Figure 8 As shown, the pad 8 can be replaced by a yield pad 13 with a spring, the spring in the yield pad 13 can be replaced by a force measuring spring 14, and the signal line is led out to obtain a yield energy absorbing anchor rod capable of measuring soil pressure.

[0058] like Figure 7 As shown, a circular grouting plate 10 is provided at the rear end of the conical shell at the rear end, and a plurality of grouting holes 11 are opened on the semi-cylindrical tube at the rear end and close to the grouting plate 10. The end of the cylindrical tube at the rear end is used to connect the grouting device, and the slurry overflows from the grouting hole 11 into the borehole, thereby realizing grouting of the entire length of the anchor rod.

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

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

[0061] Step S1, drilling: drilling holes outwards in the excavated tunnel through a rock drilling rig or an anchoring and injection machine, and injecting clean water into the holes for cleaning. The drilling spacing and depth are determined by the design requirements of different tunnels; anchoring agent rolls are placed in the holes in advance.

[0062] Step S2, anchor rod installation: insert the pre-installed anchor rod into the hole, the backing plate 8 is located outside the hole and close to the peripheral wall of the hole, the grout stopper 12 is set at the hole mouth, and the grout stopper 12 is sleeved on the rear end of the sleeve rod 6; the cone head 1 pushes the anchor agent roll to the bottom of the hole and punctures the anchor agent roll, and the anchor agent begins to harden gradually. The second arc-shaped protrusion 62 of the pre-installed anchor rod is engaged with the first arc-shaped protrusion.

[0063] Step S3, anchoring: Rotate the cap nut 9 to drive the anchor rod body to rotate outward, so that the cone head 1 moves toward the expansion piece 2 at the rear end, that is, the large diameter part of the cone head 1 enters the expansion piece 2, driving the expansion piece 2 to expand and adhere to the hole wall to complete the expansion and fixing. The anchor rod body includes: a sleeve rod 6, an inner rod 4 and a cone head 1, such as Figure 5 shown.

[0064] Step S4, applying prestress: continue to rotate the cap nut 9 to elastically stretch the anchor rod body. During the retraction of the anchor rod body, the axial prestressing force is transmitted to the rock wall of the anchor hole through the anchor rod body, the cap nut 9 and the pad 8, completing the anchor rod prestressing action.

[0065] When the rock mass deforms and moves toward the excavated space of the tunnel, the sleeve rod 6 in the borehole is subjected to force, such as Figure 6 As shown, the sleeve rod 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 a state of occlusal misalignment to a consistent position, so that the sleeve rod 6 expands radially outward, the friction resistance between the sleeve rod 6 and the hole wall increases, and the deformation of the rock and soil is limited.

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

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

[0068] Step 2: Anchor rod installation: insert the pre-installed anchor rod into the hole, with the backing plate 8 located outside the hole and close to the peripheral wall of the hole. The second arc-shaped protrusion 62 of the pre-installed anchor rod is engaged with the first arc-shaped protrusion;

[0069] Step 3: Anchoring: Rotate the cap nut 9 to move the sleeve rod 6, the inner rod 4 and the cone head 1 backwards, and the large diameter part of the cone head 1 enters the shell expansion piece 2 backwards, driving the shell expansion piece 2 to expand, so that the shell expansion connecting ring 3 breaks at the notch 31, and the shell expansion piece 2 is radially deformed, and the outer wall is tightly attached to and stuck on the inner wall of the drill hole, completing the fixing of the shell expansion;

[0070] Step 4: Apply prestress: Continue to rotate the cap nut 9 to elastically extend the anchor rod body. During the retraction of the anchor rod, the axial prestressing force is transmitted to the rock wall of the anchor hole through the anchor rod body, the cap nut 9 and the pad 8 to complete the application of prestress to the anchor rod. The anchor rod body includes: a sleeve rod 6, an inner rod 4 and a cone head 1;

[0071] Step 5, grouting: Grouting liquid is injected from the rear end of the sleeve rod 6, and the grouting liquid overflows from the 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, thereby playing the role of reinforcing the rock and soil body.

Claims

1. An expansion shell type low prestressed energy absorbing anchor, characterized in that: It comprises a cone head (1), a shell expansion plate (2), an inner rod (4) and a sleeve rod (6), wherein the rear end of the cone head (1) and the inner rod (4) are connected in the axial direction, wherein: The cone head (1) comprises, from front to back, a cone section, a truncated cone section and a cylindrical section connected in the axial direction, the tip of the cone section faces forward, and the small head of the truncated cone section faces backward; The shell expansion piece (2) is a cylindrical shell, coaxially sleeved outside the cone head (1), with its front end located at nearly half the length of the truncated cone section, and its inner diameter is consistent with the outer diameter of the hammer head (1) where it is located; and its rear end is located near the rear end of the cylindrical section; When the cone head (1) moves toward the rear end expansion piece (2), the large diameter portion of the truncated cone section enters the expansion piece (2) backwards, and the expansion piece (2) deforms radially outward, with the outer wall tightly attached to and stuck on the inner wall of the drill hole; The inner rod (4) is a columnar rod body, and a plurality of first arc-shaped protrusions are arranged on the upper and lower walls of the rear section thereof. The plurality of 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 in the shape of a columnar shell, which is formed by buckling two semi-cylindrical shells. On the inner wall of each semi-cylindrical shell, a plurality of second arc-shaped protrusions (62) are arranged at intervals along the length direction thereof; the sleeve rod (6) is coaxially sleeved outside the inner rod (4), and the second arc-shaped protrusion (62) and the first arc-shaped protrusion are engaged with each other; under the action of the force generated by the deformation of the rock and soil body, the sleeve rod (6) can move axially backward along the inner rod (4), and when moving, the second arc-shaped protrusion (62) and the first arc-shaped protrusion change from an engaged and misaligned state to a position consistent with each other, so that the sleeve rod (6) expands radially outward, and the friction resistance with the hole wall increases.

2. The expansion shell type low prestressed energy absorbing anchor rod according to claim 1, characterized in that: A cap nut (9) is screwed onto the rear end of the sleeve rod (6). The cap nut (9) is used to drive the sleeve rod (6), the inner rod (4) and the cone head (1) to move toward the rear end when it is screwed.

3. The shell expansion type low prestressed energy absorbing anchor rod according to claim 2, characterized in that: The shell expansion piece (2) is composed of a plurality of arc-shaped shells, which are connected in sequence in a ring direction; a shell expansion connecting ring (3) is coaxially sleeved at the rear end outside the shell expansion piece (2), and the shell expansion connecting ring (3) is used to fix the plurality of arc-shaped shells.

4. The expansion shell type low prestressed energy absorbing anchor rod according to claim 3, characterized in that: Each of the arc-shaped patterns (22) surrounds the outer wall of the arc-shaped shell, and a plurality of the arc-shaped patterns (22) are arranged at intervals along the front-to-back direction of the arc-shaped shell.

5. The shell expansion type low prestressed energy absorbing anchor rod according to claim 4, characterized in that: The expansion shell connecting ring (3) is provided with a plurality of U-shaped notches (31) with openings facing the front end or the rear end at intervals, the number of the notches (31) is the same as the number of the arc-shaped shell, and each of the U-shaped notches (31) is located at a protrusion of the arc-shaped shell.

6. The expansion shell type low prestressed energy absorbing anchor rod according to claim 5, characterized in that: 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 axially connected to a conical shell and connected to the large end of the conical shell; the tip of each conical shell is coaxially connected to a cylindrical tube; the conical shell and the cylindrical tube are both surrounded by half shells; the inner wall of the cylindrical tube is in contact with the inner rod (4).

7. The shell expansion type low prestressed energy absorbing anchor rod according to claim 6, characterized in that: A backing plate (8) is sleeved on the cylindrical tube at the rear end and located on the cap head nut (9), and a protective tube (7) is sleeved between the backing plate (8) and the cylindrical tube.

8. The expansion shell type low prestressed energy absorbing anchor rod according to claim 7, characterized in that: A circular grouting plate (10) is arranged at the rear end of the conical shell at the rear end, and a plurality of grouting holes (11) are opened on the semi-cylindrical tube at the rear end and close to the grouting plate (10). The end of the cylindrical tube at the rear end is used to connect the grouting device, and the grout overflows from the grouting hole (11) into the borehole for grouting the entire length of the anchor rod in the borehole.

9. A construction method for an expansion shell type low prestressed energy absorbing anchor rod as claimed in any one of claims 1 to 7, characterized in that: The steps include: Step S1, drilling: drilling a hole into the rock and soil in the excavated tunnel, and placing an anchoring agent roll into the hole; Step S2, anchor rod installation: insert the pre-installed anchor rod into the hole, the pad (8) is located outside the hole and close to the peripheral wall of the hole, the cone head (1) pushes the anchoring agent roll to the bottom of the hole and punctures the anchoring agent roll, and the anchoring agent hardens; the second arc-shaped protrusion (62) of the pre-installed anchor rod is engaged with the first arc-shaped protrusion; Step S3, anchoring: the cap head nut (9) is rotated to move the sleeve rod (6), the inner rod (4) and the cone head (1) backwards, and the large diameter portion of the cone head (1) enters the shell expansion piece (2) backwards, driving the shell expansion piece (2) to expand, so that the shell expansion connecting ring (3) breaks at the notch (31), the shell expansion piece (2) is radially deformed, and the outer wall is tightly attached to and stuck on the inner wall of the drill hole, thereby completing the expansion fixation; Step S4, applying prestress: continue to rotate the cap head nut (9) to make the anchor rod body elastically elongate. During the retraction of the anchor rod, the axial prestressing force is transmitted to the rock wall surface of the anchor hole through the anchor rod body, the cap head nut (9) and the pad (8), thereby completing the application of prestress to the anchor rod. The anchor rod body comprises: a sleeve rod (6), an inner rod (4) and a cone head (1); When the rock and soil body deforms and moves toward the excavated space of the tunnel, the sleeve rod (6) in the borehole is subjected to force, and the sleeve rod (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 a state of occlusal misalignment to a state of being aligned in position, so that the sleeve rod (6) expands radially outward, and the friction resistance between the sleeve rod (6) and the hole wall increases, thereby limiting the deformation of the rock and soil body.

10. A grouting reinforcement method for an expansion shell type low prestressed energy absorbing anchor rod according to any one of claims 1 to 8, characterized in that: Step 1: Drilling: Drilling a hole into the rock and soil in the excavated tunnel, the inner diameter of the hole matching the diameter of the sleeve rod (6); Step 2, anchor rod installation: insert the pre-installed anchor rod into the hole, the pad (8) is located outside the hole and is in close contact with the peripheral wall of the hole, and the second arc-shaped protrusion (62) of the pre-installed anchor rod is engaged with the first arc-shaped protrusion; Step 3: Anchoring: Rotate the cap nut (9) to move the sleeve rod (6), the inner rod (4) and the cone head (1) backwards, and the large diameter portion of the cone head (1) enters the shell expansion piece (2) backwards, driving the shell expansion piece (2) to expand, so that the shell expansion connecting ring (3) breaks at the notch (31), the shell expansion piece (2) is radially deformed, and the outer wall is tightly attached to and stuck on the inner wall of the drill hole, thereby completing the fixing of the shell expansion piece; Step 4: Applying prestress: Continue to rotate the cap nut (9) to allow the anchor rod body to elastically extend. During the retraction of the anchor rod, the axial prestressing force is transmitted to the rock wall of the anchor hole through the anchor rod body, the cap nut (9) and the pad (8), thereby completing the application of prestress to the anchor rod. The anchor rod body comprises: a sleeve rod (6), an inner rod (4) and a cone head (1); Step 5: Grouting: Grouting liquid is injected from the rear end of the sleeve rod (6), and the grouting liquid overflows from the 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.

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