Tunnel high-pull-force group anchor rod and construction method

Abstract

The application discloses a tunnel high-pull-force group anchor rod and a construction method, and belongs to the technical field of tunnel surrounding rock support, which comprises a central anchor rod assembly and at least three peripheral anchor rod assemblies which are uniformly distributed on the outer side of the central anchor rod assembly in the circumferential direction; the central anchor rod assembly and the peripheral anchor rod assemblies each comprise an anchor rod body, an anchor rod cluster joint end rod and a plurality of anchor rod cluster joint ends arranged on the front end face of the anchor rod body; after the group anchor rod is loaded into an anchor rod hole, a limiting part is clamped in the anchor rod hole to provide a counterforce; when the anchor rod cluster joint end rod is pulled backward, the anchor rod cluster joint ends of the central anchor rod assembly and the peripheral anchor rod assemblies are all bent in the radial direction to a reference plane which is perpendicular to the axial direction of the anchor rod body, the group anchor rod is realized to cooperatively bear and uniformly transfer loads, and single anchor rod is prevented from being overloaded and damaged due to stress concentration, so that the overall pull force and support reliability of the group anchor rod are significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of tunnel surrounding rock support technology, specifically relating to a high pull-out resistance group anchor bolt for tunnels and its construction method. Background Technology

[0002] As traffic tunnels, underground civil defense caverns, and deep mine roadways continue to expand into deeply buried and complex geological areas, the proportion of strata with developed faults, soft rock, and joints and fissures is increasing year by year. As the core support component of the surrounding rock, anchor bolts are facing severe challenges in their support effectiveness.

[0003] Conventional anchor bolts rely on the bonding between the bolt body and the grout to achieve anchoring. The pull-out resistance is provided only by the interfacial friction. In loose surrounding rock and water-rich fractured zones, the grout is prone to loss and the consolidation is not dense. The anchoring interface is prone to peeling and slippage. The ultimate pull-out resistance of a single anchor is low, making it difficult to resist the creep and large deformation of the surrounding rock caused by high ground stress.

[0004] Existing anchor bolt support structures are mostly deployed as independent units, resulting in dispersed stress distribution and poor coordination among the anchor bolts. Loads cannot be effectively transferred or evenly distributed, and edge anchor bolts are the first to be pulled out due to overload. This prevents the formation of a unified bearing structure, making it difficult for the surrounding rock to form a continuous load-bearing arch, often leading to excessive local deformation or even the failure of the entire support system. Furthermore, conventional anchor bolt drilling and grouting in stages results in fragmented processes, making borehole collapse prone to occur in fractured surrounding rock. The quality control of borehole formation and grouting is poor, leading to high costs for subsequent maintenance and reinforcement. Summary of the Invention

[0005] To address the shortcomings of the existing technology, this invention provides a high pull-out resistance group anchor bolt for tunnels and its construction method. The anchor bolt cluster ends of the central anchor bolt assembly and the peripheral anchor bolt assembly are radially bent within the front-end enlarged cavity to a reference plane perpendicular to the axial direction of the anchor bolt body, forming an integral load-bearing skeleton. This achieves coordinated load-bearing of the group anchor bolts, preventing individual anchor bolts from failing due to stress concentration and overload failure, thereby significantly improving the overall pull-out resistance and support reliability of the group anchor bolts.

[0006] To achieve the above objectives, the technical solution adopted by this invention is: a high pull-out resistance group anchor bolt for tunnels, comprising a central anchor bolt assembly and at least three peripheral anchor bolt assemblies evenly distributed circumferentially outside the central anchor bolt assembly; both the central anchor bolt assembly and the peripheral anchor bolt assemblies include an anchor bolt body, an anchor bolt cluster end tie rod, multiple anchor bolt cluster ends, and an anchor bolt cluster end limiter; one end of the anchor bolt body used to insert into the anchor bolt hole drilled in the surrounding rock is defined as the front end, and the other end is defined as the rear end; several anchor bolt cluster ends evenly distributed circumferentially are connected to the front end face of the anchor bolt body; the anchor bolt cluster end limiter is disposed on the anchor bolt cluster end, and the anchor bolt cluster end... The front end of the head tie rod passes through the anchor bolt cluster end limiter, and its rear end extends into the axial channel of the anchor bolt body and protrudes from the rear end of the anchor bolt body. The front end of the anchor bolt cluster end tie rod is provided with a pressing part, which is located on the front side of the space enclosed by the anchor bolt cluster ends. The outer side of the front end of the anchor bolt body is also provided with a limiting part that can be locked at the front opening of the anchor bolt hole after the anchor bolt body is installed in the anchor bolt hole. When the anchor bolt cluster end tie rod is pulled backward, the pressing part presses the anchor bolt cluster end, and under the reaction force provided by the limiting part, the anchor bolt cluster ends of the central anchor bolt assembly and the peripheral anchor bolt assembly are all bent radially to a reference plane perpendicular to the axial direction of the anchor bolt body.

[0007] As a further improvement to the technical solution, the anchor bolt cluster end limiter is provided with a central positioning hole and several peripheral positioning holes evenly distributed around the central positioning hole. The anchor bolt cluster end tie rod passes through the central positioning hole, and the anchor bolt cluster ends pass through the corresponding peripheral positioning holes respectively. The anchor bolt cluster ends are fixedly connected to the anchor bolt cluster end limiter at the position where they pass through the peripheral positioning holes.

[0008] As a further improvement to the technical solution, the peripheral anchor bolt assembly has three anchor bolt cluster ends. When the anchor bolt cluster end pull rod is pulled backward, the middle anchor bolt cluster end bends toward the central anchor bolt assembly, and the anchor bolt cluster ends on both sides bend toward the adjacent peripheral anchor bolt assembly. The peripheral anchor bolt assembly has a boss on the rear side of the extrusion part, and the boss faces one of the aforementioned anchor bolt cluster ends on both sides.

[0009] As a further improvement to the technical solution, the number of anchor bolt cluster ends of the central anchor bolt assembly is greater than or equal to the number of surrounding anchor bolt assemblies.

[0010] As a further improvement to the technical solution, the number of anchor cluster ends of the central anchor bolt assembly is equal to the number of peripheral anchor bolt assemblies. When the anchor cluster end pull rod is pulled backward, the anchor cluster ends of the central anchor bolt assembly bend toward the corresponding peripheral anchor bolt assemblies. The orthographic projections of the anchor cluster ends of the central anchor bolt assembly and the anchor cluster ends of the peripheral anchor bolt assemblies overlap on a reference plane perpendicular to the axial direction of the anchor bolt body, and are spaced apart axially. The orthographic projections of the two anchor cluster ends between adjacent peripheral anchor bolt assemblies overlap on a reference plane perpendicular to the axial direction of the anchor bolt body, and are spaced apart axially.

[0011] As a further improvement to the technical solution, the anchor bolt cluster end includes a plain round steel bar and multiple metal reinforcing collars spaced apart along its length on the plain round steel bar located at the front end of the anchor bolt cluster end limiter. The rear end of the plain round steel bar is connected to the front end face of the anchor bolt body.

[0012] As a further improvement to the technical solution, the anchor bolt cluster end tie rod includes a tie rod body and an extrusion part disposed at the front end of the tie rod body and in the shape of an inverted frustum. The orthographic projection of the extrusion part on a reference plane perpendicular to the axial direction of the anchor bolt body at least partially coincides with the orthographic projection of the metal reinforcing collar on the reference plane.

[0013] As a further improvement to the technical solution, the limiting part includes a tension support limiter, a tension support, and an elastic element. The tension support limiter is located on the outer side of the front end of the anchor rod body to limit the opening angle of the tension support. On the anchor rod body located at the rear end of the tension support limiter, multiple grooves are evenly opened along its circumference. The tension support is hinged in the groove. An elastic element is also provided between the tension support and the bottom of the groove. Under the action of the elastic element, the tension support opens radially and is locked at the front end of the anchor rod hole to limit the displacement of the anchor rod body in the rearward direction and provide a reaction force for pulling the tie rod at the end of the anchor rod cluster.

[0014] As a further improvement to the technical solution, a positioning steel bar is provided between the anchor cluster end limiter of the peripheral anchor bolt assembly and the front end of the anchor bolt body.

[0015] Based on the above structure, this invention proposes a construction method for high pull-out resistance group anchor bolts in tunnels, comprising the following steps: S1. The thickness of the loosened zone of the surrounding rock is determined by on-site acoustic wave velocity testing, and the radius of the plastic zone is obtained. The length of the anchor rod is calculated according to the following formula: L = R + L0 + L1 + L2, where R is the radius of the plastic zone, L0 is the anchoring length extending into the intact rock mass (L0≥0.5m in hard rock, L0≥1.0m in soft rock or under high ground stress), L1 is the length of the anchor rod cluster end (L1≥0.3m), and L2 is the exposed length of the pad, i.e., the length of the rear end of the anchor rod extending beyond the outer side of the outer ring pad, used for installing the nut (L2 is 0.15m). S2. First, drill the central anchor bolt hole, and then expand the hole at the bottom of the central anchor bolt hole through multiple stages to form a cylindrical front expansion cavity. Then, drill several peripheral anchor bolt holes to make the peripheral anchor bolt holes and the front expansion cavity connected. S3. Insert the central anchor bolt assembly into the central anchor bolt hole, so that the limiting part of the central anchor bolt assembly passes through the front end opening of the central anchor bolt hole and is stuck at the front end opening. Pull the anchor bolt cluster end pull rod to make the anchor bolt cluster end of the central anchor bolt assembly bend radially in the front enlarged cavity. S4. Insert the peripheral anchor bolt assemblies into the corresponding peripheral anchor bolt holes, so that the limiting part of the peripheral anchor bolt assembly passes through the front end opening of the corresponding peripheral anchor bolt hole and is stuck at the front end opening. Pull the anchor bolt cluster connection end pull rod of the peripheral anchor bolt assembly to make the anchor bolt cluster connection end of the peripheral anchor bolt assembly bend radially in the front enlarged cavity. S5. Grouting is performed on the anchor bolts of the central anchor bolt assembly and the peripheral anchor bolt assembly, respectively, into the central anchor bolt hole, the peripheral anchor bolt hole and the front end enlarged cavity. S6. Seal the openings of the central anchor bolt hole and the peripheral anchor bolt hole respectively. Pass the rear ends of the central anchor bolt assembly and the peripheral anchor bolt assembly through the inner ring pad and the anchor bolt assembly pad in sequence, and then lock them with nuts after the outer ring pad.

[0016] The present invention provides a high pull-out resistance group anchor bolt and construction method for tunnels, which can achieve the following beneficial effects: (1) After the central anchor bolt assembly and the peripheral anchor bolt assembly of the present invention are installed into the anchor bolt hole, the limiting part is stuck at the hole opening to provide a reaction force, and the anchor bolt cluster end pull rod is pulled to make the anchor bolt cluster end bend radially to a reference plane perpendicular to the axial direction of the anchor bolt body. The bent anchor bolt cluster end is stuck in the enlarged hole cavity to form a mechanical anchoring force. This anchoring force is independent of the interface bonding force between the grout and the rod body. It can still maintain a high anchoring reliability in loose surrounding rock, water-rich fractured zone and other strata where grout is easy to lose and the consolidation is not dense.

[0017] (2) The ends of the anchor clusters of the central anchor assembly and the peripheral anchor assembly are all bent radially to a reference plane perpendicular to the axial direction of the anchor rod body, forming an integral load-bearing skeleton. After the grouting solidifies, they are embedded together in the front-end enlarged cavity. The external load is evenly transmitted between each anchor rod body through this skeleton, so that the group of anchor rods can achieve coordinated bearing, overcoming the defects of uneven load distribution and edge anchor rods being pulled out first due to overload in traditional dispersed anchor installations.

[0018] (3) Furthermore, a boss is provided on the rear side of the compression part of the peripheral anchor bolt assembly. The boss causes the anchor bolt cluster ends facing each other to be staggered in the axial direction between adjacent peripheral anchor bolt assemblies, avoiding interference. At the same time, the central anchor bolt assembly and the peripheral anchor bolt assembly are axially staggered by setting the anchor bolt cluster end limiters at different axial positions. After the anchor bolt cluster ends are bent, their orthographic projections on the reference plane perpendicular to the axial direction of the anchor bolt body are superimposed and spaced in the axial direction to form an overall load-bearing skeleton, further enhancing the collaborative bearing capacity and structural integrity of the group of anchor bolts.

[0019] (4) The group of anchor rods share the front end expansion cavity. Grouting is carried out through the hollow channel of each anchor rod body to complete the installation and anchoring of the group of anchor rods in one go. This avoids the problem of uncontrollable hole quality caused by hole collapse in traditional drilling and grouting. It simplifies the construction process and improves the construction quality and efficiency.

[0020] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in conjunction with the accompanying drawings. Attached Figure Description

[0021] Figure 1 This is a three-dimensional structural diagram of a high-pull-out force group anchor bolt for tunnels according to the present invention; Figure 2 This is a three-dimensional structural schematic diagram of the central anchor assembly of a high pull-out resistance group anchor bolt for tunnels according to the present invention; Figure 3 This is a three-dimensional structural schematic diagram of the peripheral anchor assembly of a high pull-out resistance group anchor bolt for tunnels according to the present invention; Figure 4 This is a three-dimensional structural schematic diagram of a first embodiment of the high pull-out resistance group anchor bolt for tunnels according to the present invention; Figure 5 for Figure 4 A magnified view of a section at point I; Figure 6 This is a three-dimensional structural schematic diagram of a third embodiment of the high pull-out resistance group anchor bolt for tunnels according to the present invention; Figure 7This is a three-dimensional structural diagram of the anchor cluster end tie rod of the peripheral anchor assembly of a high pull-out force group anchor bolt for tunnels according to the present invention; Figure 8 This is a three-dimensional structural diagram of the outer ring pad of a high pull-out resistance group anchor bolt for tunnels according to the present invention; Figure 9 This is a three-dimensional structural diagram of the support system formed by arranging multiple groups of anchor bolts along the longitudinal and circumferential directions of the tunnel according to the present invention; Figure 10 for Figure 9 Enlarged view of a section at point II; Reference numerals: 1. Central anchor bolt assembly; 100. Group anchor bolt; 2. Peripheral anchor bolt assembly; 3. Anchor bolt body; 4. Anchor bolt cluster end tie rod; 41. Extrusion part; 42. Tie rod body; 5. Anchor bolt cluster end; 51. Plain round steel bar; 52. Metal reinforced collar; 6. Anchor bolt cluster end limiter; 61. Central positioning hole; 62. Peripheral positioning hole; 7. Limiting part; 71. Tension-resistant support limiter; 72. Tension-resistant support; 73. Elastic element; 74. Groove; 8. Boss; 9. Positioning steel bar; 10. Inner ring pad; 11. Anchor bolt group pad; 12. Outer ring pad. Detailed Implementation

[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings. Unless otherwise defined, in this application, the end of the anchor rod body that extends into the anchor hole drilled in the surrounding rock is called the front end, and the end of the anchor rod body that protrudes from the anchor hole is called the rear end. The front end of all components refers to the direction towards the front end of the anchor rod body, and the rear end of all components refers to the direction away from the rear end of the anchor rod body. "Axial" refers to the direction parallel to the axis of the anchor rod body itself, that is, the direction from the front end to the rear end; "radial" refers to the direction perpendicular to the axis of the anchor rod body itself; "reference plane perpendicular to the axial direction of the anchor rod body" refers to a plane perpendicular to the axial direction of the anchor rod body.

[0023] This invention achieves coordinated load-bearing by having the anchor bolt cluster ends 5 of the central anchor bolt assembly 1 and the peripheral anchor bolt assembly 2 bend radially within the front end enlarged cavity to a reference plane perpendicular to the axial direction of the anchor bolt body 3, thus forming an integral load-bearing skeleton. This enables the group of anchor bolts 100 to achieve coordinated load-bearing, overcoming the defects of uneven load distribution and premature pull-out of edge anchor bolts in traditional dispersed anchor bolt installations, thereby significantly improving the overall pull-out resistance of the group of anchor bolts 100.

[0024] Reference Figure 1 , Figure 2 , Figure 3 As a first embodiment of the present invention, a high pull-out resistance group anchor bolt for tunnels includes a central anchor bolt assembly 1 and six peripheral anchor bolt assemblies 2 evenly distributed around the central anchor bolt assembly 1.

[0025] The central anchor bolt assembly 1 and the peripheral anchor bolt assembly 2 have basically the same structure, both including anchor bolt body 3, anchor bolt cluster end tie rod 4, anchor bolt cluster end 5 and anchor bolt cluster end limiter 6. The number of anchor bolt cluster end 5 in the central anchor bolt assembly 1 is greater than or equal to the number in the peripheral anchor bolt assembly 2. In this embodiment, both have 6.

[0026] The anchor rod body 3 is a hollow rod made of hollow steel bars, with an internal axial channel that serves as both a grouting channel and a tensioning channel for the anchor rods 4 at the ends of the anchor cluster. The end of the anchor rod body 3 used to insert into the anchor hole drilled into the surrounding rock is defined as the front end, and the other end as the rear end. The diameter of the anchor rod body 3 can be selected according to actual needs, with conventional values ​​being 25mm, 28mm, or 32mm, and the wall thickness being 6mm.

[0027] The anchor bolt assembly 1 has six anchor bolt cluster ends 5 evenly distributed circumferentially on the front end face of the anchor bolt body 3. Each anchor bolt cluster end 5 includes a plain round steel bar 51 and six metal reinforcing collars 52 spaced apart along its length on the plain round steel bar 51 located at the front end of the anchor bolt cluster end limiter 6. The rear end of the plain round steel bar 51 is connected to the front end face of the anchor bolt body 3. The metal reinforcing collars 52 are fixed to the plain round steel bar 51 by spot welding. The diameter of the plain round steel bar 51 is preferably 6 mm.

[0028] The anchor bolt cluster end limiter 6 is made of high-strength steel and is installed on the anchor bolt cluster end 5. The anchor bolt cluster end limiter 6 is disc-shaped and has a central positioning hole 61 and peripheral positioning holes 62 evenly distributed around the central positioning hole 61. The anchor bolt cluster end tie rod 4 passes through the central positioning hole 61, and the anchor bolt cluster end 5 passes through the corresponding peripheral positioning holes 62. The anchor bolt cluster end 5 is fixedly connected to the anchor bolt cluster end limiter 6 at the position where it passes through the peripheral positioning holes 62.

[0029] The front end of the anchor bolt cluster end tie rod 4 passes through the central positioning hole 61, and the rear end extends into the axial channel of the anchor bolt body 3 and protrudes from the rear end of the anchor bolt body 3. The front end of the anchor bolt cluster end tie rod 4 is provided with a pressing part 41, which is located on the front side of the space enclosed by the anchor bolt cluster end 5. The anchor bolt cluster end tie rod 4 includes a tie rod body 42 and a pressing part 41 in the shape of an inverted frustum disposed at the front end of the tie rod body 42. The orthographic projection of the pressing part 41 on a reference plane perpendicular to the axial direction of the anchor bolt body 3 at least partially coincides with the orthographic projection of the metal reinforcing collar 52 on the reference plane.

[0030] The front outer side of the anchor rod body 3 is provided with a limiting part 7 that can be locked at the front opening of the anchor rod hole after the anchor rod body 3 is inserted into the anchor rod hole. The limiting part 7 includes a tension support limiter 71, a tension support 72, and an elastic element 73. The tension support limiter 71 is located on the front outer side of the anchor rod body 3 and is used to limit the opening angle of the tension support 72. On the anchor rod body 3 located at the rear end of the tension support limiter 71, six grooves 74 are evenly opened along its circumference. The tension support 72 is hinged in the grooves 74, and an elastic element 73 is provided between the tension support 72 and the bottom of the groove 74. The elastic element 73 is a wave-shaped elastic gasket with a wavy bend. In its natural state, it has a certain height and can push the tension support 72 outward, so that the tension support 72 maintains its open posture in its natural state.

[0031] Reference Figure 3 , Figure 4 , Figure 5 The structure of the peripheral anchor bolt assembly 2 is basically the same as that of the central anchor bolt assembly 1, except that: firstly, the peripheral anchor bolt assembly 2 has 3 anchor bolt cluster ends. When the anchor bolt cluster end pull rod 4 is pulled backward, the middle anchor bolt cluster end 5 bends toward the central anchor bolt assembly 1, and the anchor bolt cluster ends 5 on both sides bend toward the adjacent peripheral anchor bolt assembly 2 respectively; the peripheral anchor bolt assembly 2 has a boss 8 on the rear side of the extrusion part 41 and the boss 8 faces one of the aforementioned anchor bolt cluster ends 5 on both sides.

[0032] Secondly, a positioning steel bar 9 is provided between the anchor bolt cluster end limiter 6 of the peripheral anchor bolt assembly 2 and the front end of the anchor bolt body 3 to prevent the anchor bolt cluster end limiter 6 from deflecting or shifting when subjected to force.

[0033] Reference Figure 4 , Figure 5 During operation, the tie rod body 42 of the anchor cluster end tie rod 4 of the central anchor bolt assembly 1 is pulled backward. The pressing part 41 presses the metal reinforcing collar 52. Under the reaction force provided by the limiting part 7, the anchor cluster end 5 of the central anchor bolt assembly 1 bends radially outward toward the corresponding 6 peripheral anchor bolt assemblies 2, up to 90°, in a petal-like distribution, and bends to the axial end position defined by the anchor cluster end limiter 6 of the central anchor bolt assembly 1. Due to the constraint of the anchor cluster end limiter 6, the anchor cluster end 5 bends radially outward rather than deflecting arbitrarily.

[0034] Pulling the tie rod body 42 of the peripheral anchor bolt assembly 2 causes the three anchor bolt cluster ends 5 of the peripheral anchor bolt assembly 2 to bend radially outwards. The middle anchor bolt cluster end 5 faces the central anchor bolt assembly 1, while the anchor bolt cluster ends 5 on both sides face the adjacent peripheral anchor bolt assemblies 2, forming a petal-like distribution. Due to the axial positioning effect of the boss 8 on the rear side of the compression part 41 of the peripheral anchor bolt assembly 2, the radial bending starting position of the anchor bolt cluster end 5 corresponding to the boss 8 is lower than the radial bending starting position of the other two anchor bolt cluster ends 5, thus axially offsetting the anchor bolt cluster ends 5 facing each other between adjacent peripheral anchor bolt assemblies 2 and avoiding interference.

[0035] The axial position of the anchor cluster end limiter 6 of the central anchor bolt assembly 1 is set before the axial position of the anchor cluster end limiter 6 of the peripheral anchor bolt assembly 2, so that the end positions of the two after bending are staggered in the axial direction, thus avoiding interference between the anchor cluster end 5 of the central anchor bolt assembly 1 and the anchor cluster end 5 of the peripheral anchor bolt assembly 2 facing the center.

[0036] Finally, the anchor cluster end 5 of the central anchor bolt assembly 1 and the anchor cluster end 5 of the peripheral anchor bolt assembly 2 overlap on the orthographic projection of the anchor bolts on the reference plane perpendicular to the axial direction of the anchor bolt body 3, and are spaced apart axially to form an overall load-bearing skeleton. The two anchor cluster end 5 of adjacent peripheral anchor bolt assemblies 2 overlap on the orthographic projection of the reference plane perpendicular to the axial direction of the anchor bolt body 3, and are spaced apart axially.

[0037] Reference Figure 1 , Figure 8 The central anchor bolt assembly 1 is located at the center of the group of anchor bolts 100, and the peripheral anchor bolt assemblies 2 are evenly distributed around the outside of the central anchor bolt assembly 1. The rear ends of the central anchor bolt assembly 1 and the peripheral anchor bolt assemblies 2 pass through the inner ring pad 10, the anchor bolt group pad 11, and the outer ring pad 12 in sequence, and are then locked in place with nuts, thus completing the construction of a group of anchor bolts 100.

[0038] The difference between Embodiment 2 and Embodiment 1 is that: the rear side of the compression part 41 of the anchor cluster end tie rod 4 of the peripheral anchor bolt assembly 2 does not have a boss 8, and the bending starting position of its anchor cluster end 5 is the same. The central anchor bolt assembly 1 has 6 or 12 anchor cluster ends 5 evenly distributed circumferentially, corresponding to 6 peripheral anchor bolt assemblies 2 respectively; the peripheral anchor bolt assembly 2 has 2, 3 or 4 anchor cluster ends 5, and the peripheral positioning holes 62 on the central anchor bolt assembly 1 are opened towards the direction closer to the peripheral anchor bolt assembly 2, so that the anchor cluster ends 5 of the central anchor bolt assembly 1 are bent towards the direction closer to the peripheral anchor bolt assembly 2; the peripheral positioning holes 62 of the peripheral anchor bolt assembly 2 are opened towards the direction closer to the central anchor bolt assembly 1, so that the anchor cluster ends 5 of the peripheral anchor bolt assembly 2 are bent towards the direction closer to the central anchor bolt assembly 1. The axial position of the anchor cluster end limiter 6 of the central anchor bolt assembly 1 is positioned before the axial position of the anchor cluster end limiter 6 of the peripheral anchor bolt assembly 2. This ensures that the axial endpoint of the bent anchor cluster end 5 of the central anchor bolt assembly 1 is located before the axial endpoint of the bent anchor cluster end 5 of the peripheral anchor bolt assembly 2, with the two staggered axially to avoid interference. After each anchor cluster end 5 is bent, it extends into the front-end enlarged cavity, forming an integral load-bearing skeleton. After the grout solidifies, this skeleton is encapsulated and solidified, enhancing its stability.

[0039] Reference Figure 6 The difference between Embodiment 3 and Embodiment 1 is that: the rear side of the compression part 41 of the anchor cluster end tie rod 4 of the peripheral anchor bolt assembly 2 does not have a boss 8, and the bending starting position of its anchor cluster end 5 is the same. The front end face of the anchor bolt body 3 of the central anchor bolt assembly 1 is connected to 6 or 12 anchor cluster ends 5 evenly distributed in the circumferential direction, which correspond to 6 peripheral anchor bolt assemblies 2 respectively; the anchor cluster ends 5 of the central anchor bolt assembly 1 bend towards the peripheral anchor bolt assembly 2, and the anchor cluster ends 5 of the peripheral anchor bolt assembly 2 are 2, 3 or 4. The anchor cluster ends 5 of the peripheral anchor bolt assembly 2 do not bend towards the central anchor bolt assembly 1, nor towards the adjacent peripheral anchor bolt assembly 2, and extend into the front end enlarged cavity, naturally avoiding each other, forming an overall force-bearing skeleton.

[0040] It is understood that the number, distribution direction, and bending angle of the anchor bolt cluster ends 5 are not limited to the specific forms described in the above embodiments. When the extrusion part 41 of the peripheral anchor bolt assembly 2 is provided with a boss 8, the anchor bolt cluster ends 5 facing each other between adjacent peripheral anchor bolt assemblies 2 are axially staggered by the boss 8. The anchor bolt cluster ends 5 of the central anchor bolt assembly 1 and the anchor bolt cluster ends 5 of the peripheral anchor bolt assemblies 2 facing the central anchor bolt assembly 1 are axially staggered by setting the anchor bolt cluster end limiters 6 at different axial positions. After each anchor bolt cluster end 5 is bent, it does not interfere with each other, forming an integral load-bearing skeleton.

[0041] When the compression part 41 of the peripheral anchor bolt assembly 2 does not have a boss 8, the anchor bolt cluster end limiter 6 can be set at different axial positions to make the anchor bolt cluster end 5 of the central anchor bolt assembly 1 and the peripheral anchor bolt assembly 2 axially staggered, or to prevent the anchor bolt cluster end 5 of the peripheral anchor bolt assembly 2 from bending towards the central anchor bolt assembly 1 and adjacent peripheral anchor bolt assemblies 2, thus achieving natural avoidance. Regardless of the method used, as long as each anchor bolt cluster end 5 forms an integral load-bearing skeleton after bending, and can realize the transfer and distribution of load among the group of anchor bolts 100, it does not deviate from the design concept of this invention.

[0042] Based on the above structure, this embodiment also proposes a construction method for high pull-out resistance group anchor bolts in tunnels.

[0043] First, based on the physical and mechanical properties of the engineering rock mass and the support requirements, the length of the individual anchor rod 3 in a group of anchor rods 100 is determined. The thickness of the loosened zone of the surrounding rock is determined by on-site sonic wave velocity testing, obtaining the radius R of the plastic zone. Then, the length L of the anchor rod 3 is calculated according to the following formula: L = R + L0 + L1 + L2, where R is the radius of the plastic zone, L0 is the anchoring length extending into the intact rock mass (L0 ≥ 0.5m in hard rock, L0 ≥ 1.0m in soft rock or under high ground stress), L1 is the length of the anchor rod cluster end 5 (L1 ≥ 0.3m), and L2 is the exposed length of the pad, i.e., the length of the rear end of the anchor rod 3 extending beyond the outer side of the outer ring pad 12, used for installing the nut; L2 is taken as 0.15m.

[0044] The anchor rod body 3 adopts a hollow structure, with a diameter typically of 25mm, 28mm, or 32mm and a wall thickness of 6mm. Adjustments or customization are possible based on actual conditions. After determining the length of a single anchor rod body 3, anchor holes are drilled (the anchor hole includes a drilled section and an enlarged section at the bottom). The central anchor hole is drilled first, using an enlarger drill. The initial drilling length is R + L0, with a minimum diameter of φ45, φ48, or φ52mm. When using a customized anchor rod body 3, the drilling diameter must be at least 20mm larger than the anchor rod body 3 diameter, or adjusted appropriately for ease of subsequent construction. The enlarged section drilling length is L1 + L2, with a minimum enlarged diameter of 0.3m (0.4m in this embodiment). When drilling the peripheral anchor holes, since the diameter and length of the anchor rod body 3 are the same, the drilling length is the same as the central anchor hole. The peripheral anchor holes must be connected to the enlarged cavity at the front end of the central anchor hole.

[0045] After drilling is completed, the central anchor bolt assembly 1 is installed into the central anchor bolt hole. During installation, the tension support 72 is radially compressed by the hole wall, compressing the wave-shaped elastic gasket and retracting into the groove 74, thus closing the hole. When the tension support 72, along with the anchor bolt body 3, passes the front end opening of the central anchor bolt hole (i.e., the junction of the drilling section and the reaming section) and enters the front reaming cavity, the radial constraint of the central anchor bolt hole on the tension support 72 disappears. The wave-shaped elastic gasket rebounds and resets under its own elastic force, pushing the tension support 72 radially outward, causing it to open. The opened tension support 72 is then locked at the front end opening of the central anchor bolt hole, and its maximum rotation angle is limited to 90° by the tension support limiter 71. At this time, the anti-tension support 72, which is stuck at the front end of the hole, provides a reaction force for the pulling of the anchor bolt cluster end rod 4. Then, the anchor bolt cluster end rod 4 is pulled, and the extrusion part 41 extrudes the anchor bolt cluster end 5, so that the anchor bolt cluster end 5 is bent in the front end expansion cavity to form a 90° angle with the anchor bolt body 3, and is distributed in a petal shape.

[0046] The peripheral anchor bolt assembly 2 is installed into the peripheral anchor bolt hole, and the working process of its tension support 72 is the same as that of the central anchor bolt assembly 1. Under the guidance of the positioning steel bar 9, the anchor bolt cluster end tie rod 4 of the peripheral anchor bolt assembly 2 is pulled, causing the anchor bolt cluster end 5 of the peripheral anchor bolt assembly 2 to bend in the front end enlarged cavity. Because the rear side of the compression part 41 of the peripheral anchor bolt assembly 2 is provided with a boss 8, and the rear side of the boss 8 corresponds to an anchor bolt cluster end 5, the radial bending starting position of the anchor bolt cluster end 5 is lower than the radial bending starting position of the other two anchor bolt cluster end 5. And because the anchor bolt cluster end limiters 6 of the central anchor bolt assembly 1 and the peripheral anchor bolt assembly 2 are staggered in the axial direction, the radial bending of the anchor bolt cluster end 5 of the central anchor bolt assembly 1 and the peripheral anchor bolt assembly 2 on the orthographic projection portion perpendicular to the axial reference plane of the anchor bolt body 3 overlaps, and is spaced apart in the axial direction. The orthographic projection portions of the two anchor bolt cluster end 5 between adjacent peripheral anchor bolt assemblies 2 on the reference plane perpendicular to the axial direction of the anchor bolt body 3 overlap, and are spaced apart in the axial direction, forming an overall load-bearing skeleton.

[0047] Grouting is performed on the anchor rods 3 of the central anchor bolt assembly 1 and the peripheral anchor bolt assembly 2, respectively, into the central anchor bolt hole, each peripheral anchor bolt hole, and the front end enlarged cavity.

[0048] After grouting is completed, the openings of the central anchor bolt hole and the peripheral anchor bolt holes are sealed respectively. The inner ring pad 10 and the outer ring pad 12 are respectively placed on both sides of the anchor bolt group pad 11. The rear ends of the central anchor bolt assembly 1 and the peripheral anchor bolt assembly 2 pass through the inner ring pad 10, the anchor bolt group pad 11 and the outer ring pad 12 in sequence, and are locked with nuts to complete the installation of a group of anchor bolts 100.

[0049] Reference Figure 9 , Figure 10As a fourth embodiment of the present invention, during actual construction, based on the physical and mechanical properties of the engineering rock mass and the support requirements, the number and length of individual anchor rods 3 in a group of anchor rods 100, as well as the total number and arrangement of the group of anchor rods 100, are determined. Several groups of anchor rods 100 are arranged along the longitudinal and circumferential directions of the tunnel to form a systematic support system. In the figure, the direction of arrow AB is the circumferential direction of the tunnel, and the direction of arrow CD is the longitudinal direction of the tunnel.

[0050] Based on the equilibrium calculation of the surrounding rock's stable plastic zone, and taking into account the synergistic effect of the group of anchor bolts 100, the distribution design of the group of anchor bolts 100 is based on the principle of preventing local collapse arches, and must also meet the maximum spacing S between the group of anchor bolts 100. max ≤0.5L ＇ L ＇ This refers to the effective anchorage length of the anchor rod 3 excluding exposed sections. This ensures that adjacent groups of anchor rods 100 form a continuous, integral load-bearing structure.

[0051] For a circular tunnel with a cross-section diameter of 10m and Class III surrounding rock, when the loosening range of the surrounding rock is determined to be 1.1m using the on-site acoustic wave velocity test method, according to the formula L = R + L0 + L1 + L2, R is 1.1m, L0 is 1.55m, L1 is 0.3m, L2 is 0.15m, and the total length of the anchor rod 3 can be 3.0m. To increase the pull-out resistance, the anchor rod 3 is selected with a diameter of φ32mm and a wall thickness of 6mm. When drilling the central anchor hole of the group of anchor rods 100, a larger diameter of φ110 is selected for drilling to facilitate subsequent hole enlargement. When drilling to the design depth, multiple stages of hole enlargement are used to finally form a front-end enlarged cavity of a cylinder with a diameter of 400mm and a height of 400mm. The peripheral anchor holes are drilled with a diameter of φ76mm and intersect and connect with the front-end enlarged cavity of the central anchor hole.

[0052] Insert the central anchor bolt assembly 1 and the peripheral anchor bolt assembly 2 into the central anchor bolt hole and the peripheral anchor bolt hole respectively, and grout them until the installation of a group of anchor bolts 100 is completed. The specific steps are not described here.

[0053] Based on the maximum spacing S between 100 anchor bolts in the group max ≤0.5L ＇ Based on the requirements and the common arrangement principles of group anchor bolts 100 in engineering, the spacing of group anchor bolts 100 can be selected as 1.5m, while the row spacing is selected according to 1.5×sin60°=1.3m. At this time, each group anchor bolt 100 will be able to bear the surrounding rock stress evenly, forming the best support structure system.

[0054] The above modifications do not change the core technical solution of the present invention and fall within the protection scope of the present invention.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the design and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A high-pull-out resistance group anchor bolt for tunnels, characterized in that: Includes a central anchor bolt assembly (1) and at least three peripheral anchor bolt assemblies (2) evenly distributed around the central anchor bolt assembly (1) in the circumferential direction; both the central anchor bolt assembly (1) and the peripheral anchor bolt assembly (2) include an anchor bolt body (3), an anchor bolt cluster end tie rod (4), multiple anchor bolt cluster ends (5), and an anchor bolt cluster end limiter (6); one end of the anchor bolt body (3) used to insert into the anchor bolt hole drilled in the surrounding rock is defined as the front end, and the other end is defined as the rear end; the anchor bolt body (3) The front end face of the anchor bolt cluster is connected with several anchor bolt cluster ends (5) evenly distributed in the circumferential direction; the anchor bolt cluster end limiter (6) is set on the anchor bolt cluster end (5); the front end of the anchor bolt cluster end pull rod (4) passes through the anchor bolt cluster end limiter (6), and its rear end extends into the axial channel of the anchor bolt rod body (3) and extends out from the rear end of the anchor bolt rod body (3); the front end of the anchor bolt cluster end pull rod (4) is provided with a pressing part (41), and the pressing part (41) is located in the anchor bolt cluster The front side of the space enclosed by the connecting ends (5); the outer side of the front end of the anchor rod body (3) is also provided with a limiting part (7) that can be locked at the front end of the anchor rod hole after the anchor rod body (3) is inserted into the anchor rod hole; when the anchor rod cluster connecting end pull rod (4) is pulled backward, the squeezing part (41) squeezes the anchor rod cluster connecting end (5), and under the reaction force provided by the limiting part (7), the anchor rod cluster connecting end (5) of the central anchor rod assembly (1) and the peripheral anchor rod assembly (2) are all bent radially to On a reference plane perpendicular to the axial direction of the anchor rod body (3), the anchor cluster end (5) of the central anchor rod assembly (1) and the anchor cluster end (5) of the peripheral anchor rod assembly (2) overlap on the orthographic projection portion of the reference plane perpendicular to the axial direction of the anchor rod body (3), and are spaced apart in the axial direction. The two anchor cluster ends (5) between adjacent peripheral anchor rod assemblies (2) overlap on the orthographic projection portion of the reference plane perpendicular to the axial direction of the anchor rod body (3), and are spaced apart in the axial direction.

2. The tunnel high pull-out resistance group anchor bolt according to claim 1, characterized in that: The anchor bolt cluster end limiter (6) is provided with a central positioning hole (61) and a number of peripheral positioning holes (62) evenly distributed around the central positioning hole (61). The anchor bolt cluster end pull rod (4) passes through the central positioning hole (61), and the anchor bolt cluster end (5) passes through the corresponding peripheral positioning holes (62). The anchor bolt cluster end (5) is fixedly connected to the anchor bolt cluster end limiter (6) at the position where it passes through the peripheral positioning holes (62).

3. The tunnel high-pull-out resistance group anchor bolt according to claim 1, characterized in that: The peripheral anchor bolt assembly (2) has three anchor bolt cluster ends (5). When the anchor bolt cluster end pull rod (4) is pulled backward, the middle anchor bolt cluster end (5) bends toward the central anchor bolt assembly (1), and the anchor bolt cluster ends (5) on both sides bend toward the adjacent peripheral anchor bolt assembly (2). The extrusion part (41) of the peripheral anchor bolt assembly (2) has a boss (8) on the rear side, and the boss (8) faces one of the aforementioned anchor bolt cluster ends (5) on both sides.

4. A high-pull-out resistance group anchor bolt for tunnels according to claim 3, characterized in that: The number of anchor cluster ends (5) of the central anchor assembly (1) is greater than or equal to the number of the surrounding anchor assemblies (2).

5. A high-pull-out resistance group anchor bolt for tunnels according to claim 4, characterized in that: The number of anchor cluster ends (5) of the central anchor assembly (1) is equal to the number of the surrounding anchor assemblies (2). When the anchor cluster end pull rod (4) is pulled backward, the anchor cluster ends (5) of the central anchor assembly (1) bend toward the corresponding surrounding anchor assemblies (2).

6. A high-pull-out resistance group anchor bolt for tunnels according to claim 1, characterized in that: The anchor bolt cluster end (5) includes a plain round steel bar (51) and a plurality of metal reinforcing collars (52) spaced apart along its length on the plain round steel bar (51) located at the front end of the anchor bolt cluster end limiter (6). The rear end of the plain round steel bar (51) is connected to the front end face of the anchor bolt body (3).

7. A high-pull-out resistance group anchor bolt for tunnels according to claim 6, characterized in that: The anchor bolt cluster end tie rod (4) includes a tie rod body (42) and a pressing part (41) disposed at the front end of the tie rod body (42) and in the shape of an inverted frustum. The orthographic projection of the pressing part (41) on a reference plane perpendicular to the axial direction of the anchor bolt body (3) at least partially coincides with the orthographic projection of the metal reinforcing collar (52) on the reference plane.

8. A high-pull-out resistance group anchor bolt for tunnels according to claim 1, characterized in that: The limiting part (7) includes a tension support limiter (71), a tension support (72), and an elastic element (73). The tension support limiter (71) is located on the outer side of the front end of the anchor rod body (3) to limit the opening angle of the tension support (72). On the anchor rod body (3) located at the rear end of the tension support limiter (71), a plurality of grooves (74) are evenly opened along its circumference. The tension support (72) is hinged in the groove (74). An elastic element (73) is also provided between the tension support (72) and the bottom of the groove (74). The tension support (72) opens radially under the action of the elastic element (73) and is locked at the front end of the anchor rod hole to provide a reaction force for pulling the anchor rod cluster end pull rod (4).

9. A high-pull-out resistance group anchor bolt for tunnels according to claim 1, characterized in that: A positioning steel bar (9) is provided between the anchor cluster end limiter (6) of the peripheral anchor assembly (2) and the front end of the anchor rod body (3).

10. A construction method for a high-pull-out resistance group anchor bolt for tunnels as described in any one of claims 1-9, characterized in that, Includes the following steps: S1. The thickness of the loosened zone of the surrounding rock is determined by on-site acoustic wave velocity test, and the radius of the plastic zone is obtained. The length of the anchor rod (3) is calculated according to the following formula: L = R + L0 + L1 + L2, where R is the radius of the plastic zone, L0 is the anchoring length extending into the complete rock mass, L0≥0.5m in hard rock, L0≥1.0m in soft rock or high ground stress, L1 is the length of the anchor rod cluster end (5), L1≥0.3m; L2 is the exposed length of the pad, that is, the length of the rear end of the anchor rod (3) extending out of the outer side of the outer ring pad (12), used for installing nuts, L2 is 0.15m; S2. First, drill the central anchor bolt hole, and then expand the hole at the bottom of the central anchor bolt hole through multiple stages to form a cylindrical front expansion cavity. Then, drill several peripheral anchor bolt holes so that the peripheral anchor bolt holes are connected to the front expansion cavity. S3. Insert the central anchor bolt assembly (1) into the central anchor bolt hole, so that the limiting part (7) of the central anchor bolt assembly (1) passes through the front end opening of the central anchor bolt hole and is stuck at the front end opening. Pull the anchor bolt cluster end pull rod (4) so ​​that the anchor bolt cluster end (5) of the central anchor bolt assembly (1) is bent radially in the front end enlarged cavity. S4. Insert the peripheral anchor bolt assembly (2) into the corresponding peripheral anchor bolt hole, so that the limiting part (7) of the peripheral anchor bolt assembly (2) passes through the front end opening of the corresponding peripheral anchor bolt hole and is stuck at the front end opening. Pull the anchor bolt cluster end pull rod (4) of the peripheral anchor bolt assembly (2) respectively, so that the anchor bolt cluster end (5) of the peripheral anchor bolt assembly (2) is bent radially in the front end enlarged cavity. S5. Grouting is performed on the anchor rods (3) of the central anchor bolt assembly (1) and the peripheral anchor bolt assembly (2) to the central anchor bolt hole, the peripheral anchor bolt hole and the front end enlarged cavity, respectively. S6. Seal the openings of the central anchor bolt hole and each peripheral anchor bolt hole respectively. Pass the rear ends of the central anchor bolt assembly (1) and the peripheral anchor bolt assembly (2) through the inner ring pad (10), the anchor bolt assembly pad (11), and the outer ring pad (12) in sequence and then lock them with nuts.

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