A stress structure control type rock burst resistant energy absorbing anchor rod for deep buried hard rock tunnel

Abstract

This invention relates to a rockburst-resistant shear-absorbing anchor bolt for stress-resistant structures in deep-buried hard rock tunnels, comprising a mixing anchor head, a shear-absorbing component, a limiting nut, a rod body, a tray, and a fastening nut. The mixing anchor head is coaxially disposed on one end of the rod body; the tray is coaxially disposed on the other side of the rod body; the fastening nut is located on the outside of the tray and threadedly connected to the rod body; the shear-absorbing component is located between the tray and the mixing anchor head and coaxially sleeved on the outside of the rod body; the limiting nuts are respectively disposed at both ends of the shear-absorbing component and threadedly connected to the rod body. This invention can solve the problems in the prior art that neglect hard rockburst prevention, especially the weak transverse shear resistance and energy absorption capacity of anchor bolts, low anchorage length, failure to consider the need to suppress surrounding rock deformation in hard rock tunnels, and low support reliability. It can achieve the purpose of enhancing transverse shear strength, absorbing transverse deformation energy of rock mass, and increasing the overall anchorage length, thereby preventing structural rockbursts in hard rock tunnels.

Description

Technical Field

[0001] This invention relates to the field of anchor bolt technology, and in particular to a rockburst-resistant shear-absorbing anchor bolt for stress-resistant structures in deep-buried hard rock tunnels. Background Technology

[0002] As geotechnical engineering projects such as tunneling, mining, and hydropower engineering gradually extend to deeper levels, complex geological conditions characterized by high ground stress, high ground temperature, and high permeability pressure become prominent. This leads to the formation of discontinuous interfaces such as faults, joints, and fissures of varying types and scales, posing new challenges to deep support engineering. For example, during the excavation of deeply buried mixed rock tunnels, the surrounding rock exhibits banded, eyeball-shaped, and serpentine joints, with the matrix showing obvious orientation and well-developed foliation. The veins possess semi-euhedral granular melt crystallization structures and replacement structures, with relatively weak orientation. These characteristics reduce the strength of the surrounding rock, making it prone to shear displacement along weak joint surfaces under high ground stress. Once energy accumulates to a certain extent, it can easily induce rockbursts.

[0003] Anchor bolt support is an effective means to ensure the normal operation of rock engineering. As site conditions become increasingly complex, anchor bolt types are also becoming more diverse, such as fully threaded anchor bolts, high-strength anchor bolts, fiberglass anchor bolts, and energy-absorbing anchor bolts that rely on adding special structures or changing the shape of the bolt.

[0004] In deep rock environments, the geological structure of anchor bolt locations is complex, making it difficult for anchor bolts to be in an ideal tensile state, but rather in a combined stress state of tension, bending, and shear. Although existing anchor bolts have high axial strength and large axial bearing capacity, their transverse shear resistance has been neglected, resulting in relatively weak shear strength in most anchor bolts. Existing shear-resistant anchor bolts are usually designed from the following perspectives: (1) High-strength steel casing is used to wrap the bolt body, that is, to resist rock shear force through the properties of the metal itself; however, the anchorage length of the bolt body is reduced, and the bolt body can generate large axial deformation. After the excavation of hard rock in deep-buried tunnels, the rock mass changes from a triaxial stress state to a single-sided unloading state, and the mechanical properties change from ductile to brittle. Rock mass bursting and flying block phenomenon will occur in the axial direction of the free face. Therefore, the design of casing-wrapped bolt body lacks the need to suppress axial deformation of the surrounding rock. (2) The interaction between the casing and the inner tube, that is, the axial resistance is generated by the squeezing friction between the tubes, and the rounded hole set on the outer wall of the inner tube is deformed, which improves the axial shear resistance of the anchor to a certain extent; however, it cannot provide transverse shear strength for the surrounding rock with structural planes. (3) Setting up multi-functional structural splicing, that is, setting up hydraulic sleeves, spiral structures, high-strength connecting rings and necking sleeves between the rods, although it can achieve adaptive multi-rod segment cooperation, the connecting ring structure cannot suppress the rock mass displacement of the structural plane, and the multi-structure design is more idealized, and the anchor is difficult to exert stable mechanical and deformation performance. (4) Increasing the rod diameter and designing through holes around the rod can increase the cross-sectional area to improve shear strength and compact the through holes to release shear stress, but at the same time it will reduce the gap of the surrounding rock, reduce the anchoring effect, and cannot make reasonable use of the on-site threaded steel anchor, increasing the economic cost. In addition, existing anchors mostly consider axial deformation energy absorption, and radial deformation energy absorption design is relatively rare.

[0005] In summary, existing shear anchors are not ideal in terms of shear strength and lateral energy absorption. Furthermore, it is difficult to simultaneously achieve end anchoring and suppression of surrounding rock deformation. In addition, some anchors have the disadvantages of complex structure and high cost, which leads to premature failure of anchor support methods and the inability of the surrounding rock to exert its self-bearing capacity, resulting in frequent stress structure-controlled rockbursts in deep-buried hard rock tunnels. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to provide a rockburst-resistant shear-absorbing anchor bolt for stress-resistant structures in deep-buried hard rock tunnels. This anchor bolt effectively solves the technical problems in existing technologies, such as neglecting rockburst prevention in hard rock, particularly the weak transverse shear resistance and energy absorption capacity of the anchor bolt, low anchoring length, failure to consider the need to suppress surrounding rock deformation in hard rock tunnels, and low support reliability. This invention can enhance transverse shear strength, absorb transverse deformation energy of the rock mass, and simultaneously increase the overall anchoring length, thereby preventing rockbursts on the structural surface of hard rock tunnels.

[0007] The technical solution adopted in this invention is as follows:

[0008] The present invention proposes a rockburst-resistant shear-absorbing anchor bolt for stress-resistant structures in deep-buried hard rock tunnels, comprising a mixing anchor head, a shear-absorbing component, a limiting nut, a rod body, a tray, and a fastening nut. The mixing anchor head is coaxially disposed on one end of the rod body; the tray is coaxially disposed on the other side of the rod body; the fastening nut is located on the outside of the tray and threadedly connected to the rod body; the shear-absorbing component is located between the tray and the mixing anchor head and coaxially sleeved on the outside of the rod body; the limiting nuts are respectively disposed at both ends of the shear-absorbing component and threadedly connected to the rod body, for limiting the axial position of the shear-absorbing component.

[0009] Furthermore, the shear-resistant energy-absorbing component includes n axially extended columnar equal-thickness walls. The axial cross-section of the columnar equal-thickness walls has a radially symmetrical trapezoidal tooth-shaped geometric configuration. A ring-shaped deformation cavity with a constant gap is formed between its inner wall surface and the outer surface of the rod. Both ends of the shear-resistant energy-absorbing component in the axial direction are respectively provided with rings with a diameter larger than the ring-shaped deformation cavity.

[0010] Furthermore, the number and length of the columnar equal-thickness walls depend on the location and length of faults and joints within the surrounding rock obtained from advanced geological exploration; where n≥2.

[0011] Furthermore, the stirring anchor head includes a thin-walled cylinder, a piercing cone, and helical blades; the front side of the thin-walled cylinder is coaxially sleeved on the end of the rod; the piercing cone is disposed in the inner cavity of the thin-walled cylinder; the helical blades are disposed on the front side of the thin-walled cylinder and coaxially fixed to the radial outer surface of the tail of the rod, and extend spirally around the central axis of the rod to the piercing cone; the tip of the piercing cone is arranged in a direction away from the helical blades.

[0012] Furthermore, at least three axially elongated slots are provided on the sidewall of the thin-walled cylinder.

[0013] Furthermore, both the limiting nut and the fastening nut are hexagonal nuts.

[0014] Furthermore, the rod body, tray, and fastening nut are all standard 22mm threaded steel anchor rod components.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. The anchor rod of the present invention can make full use of the deformation characteristics of the metal material. The design of the gap between the shear energy absorbing component and the rod body makes the shear energy absorbing component first plastically deform to absorb energy when the anchor rod is subjected to shear action, rather than directly transferring it to the rod body.

[0016] 2. The anchor bolt of this invention can be anchored in three ways according to site requirements: end anchoring, grouting anchoring, or end-grouting anchoring. When end anchoring is used, prestress can be applied to increase the cohesion of the surrounding rock, thereby improving the shear resistance of the anchor body. When grouting anchoring is used, since the diameters of the shear energy absorbing elements at both ends are larger than the diameter of the bolt body but smaller than the borehole diameter, and they are embedded in the grout, the combination of multiple shear energy absorbing elements achieves a multi-point anchoring effect, improving the cohesion between the anchor bolt and the surrounding rock and suppressing the axial deformation of the surrounding rock. Furthermore, the end-grouting anchoring method combines the advantages of both methods.

[0017] 3. When the anchor rod of the present invention is subjected to tension, the design of the inclined surface of the shear energy-absorbing component can enhance the contact area with the grouting body and improve the tensile strength of the anchor rod. When the load is too large, the multiple trapezoidal toothed conical structures squeeze each other with the grouting body, and absorb the deformation energy of the surrounding rock through the rupture of the grouting body and its own plastic deformation. When subjected to shear, the design of multiple trapezoidal toothed conical structures inside the shear energy-absorbing element can cope with joint surfaces of multiple angles and multiple sets, and absorb the deformation energy of the surrounding rock through crushing deformation. The shear energy absorption performance of the shear energy-absorbing element can also be improved by filling the annular deformation cavity with shear energy-absorbing material or by adding ribs.

[0018] 4. The shear-absorbing energy-absorbing component in the anchor bolt of the present invention can be set as needed according to the location of faults and joints inside the surrounding rock obtained from advanced geological exploration. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the overall structure of a rockburst-resistant shear-absorbing anchor bolt for stress-resistant structure of a deep-buried hard rock tunnel proposed in this invention. Figure 2 for Figure 1 A schematic diagram of the front sectional structure; Figure 3 This is a schematic diagram of the shear-absorbing energy-absorbing component in section 1; Figure 4 This is a schematic diagram illustrating the effect of end anchoring in this invention; Figure 5 This is a schematic diagram illustrating the effect of grouting anchoring in this invention.

[0020] In the attached drawings, the following labels are used: 1-mixing anchor head; 2-shear energy absorption component; 3-limiting nut; 4-rod body; 5-tray; 6-fastening nut; 7-grouting body; 8-surrounding rock; 9-resin anchoring agent. Detailed Implementation

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] It should be noted that in the description of this invention, the terms "upper", "lower", "top", "bottom", "one side", "the other side", "left", "right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not mean that the device or element must have a specific orientation, or be constructed and operated in a specific orientation.

[0023] See appendix Figures 1-2 The present invention proposes a rockburst-resistant shear-absorbing anchor bolt for stress-resistant structures in deep-buried hard rock tunnels, comprising a mixing anchor head 1, a shear-absorbing component 2, a limiting nut 3, a rod body 4, a tray 5, and a fastening nut 6. The rod body 4, tray 5, and fastening nut 6 are all standard 22mm threaded steel anchor bolt components. The limiting nut 3 and fastening nut 5 are both hexagonal nuts.

[0024] The stirring anchor head 1 is coaxially disposed at the tail end of the rod body 4; the tray 5 is coaxially disposed at the head end of the rod body 4; the fastening nut 6 is located on the outside of the tray 5 and threadedly connected to the rod body 4; the shear-absorbing component 2 is located between the tray 5 and the stirring anchor head 1 and is coaxially sleeved on the outer surface of the rod body 4; the limiting nuts 3 are respectively disposed at both ends of the shear-absorbing component 2 and threadedly connected to the rod body 4, used to limit the axial position of the shear-absorbing component 2.

[0025] The stirring anchor head 1 includes a thin-walled cylinder 1-1, a piercing cone 1-2, and a spiral blade 1-3. The front side of the thin-walled cylinder 1-1 is coaxially sleeved at the end of the rod body 4. In this invention, at least three circumferentially distributed axially narrow slots are provided on the side wall of the thin-walled cylinder 1-1 for clamping and centering the resin anchoring agent 9. The piercing cone 1-2 is disposed in the inner cavity of the thin-walled cylinder 1-1, with its tip facing away from the spiral blade 1-3, for piercing the packaging bag of the resin anchoring agent 9. The spiral blade 1-3 is disposed on the front side of the thin-walled cylinder 1-1 and coaxially fixed to the radial outer surface of the tail of the rod body 4, and the spiral blade 1-3 extends spirally around the central axis of the rod body 4 to the piercing cone 1-2.

[0026] The stirring anchor head 1 is designed such that when it rotates and moves axially with the rod body 4, it punctures the packaging bag of the resin anchoring agent 9 in the thin-walled cylinder 1-1 through the cone body 1-2; the slotted structure of the thin-walled cylinder 1-1 undergoes plastic expansion deformation when the rod body 4 is inserted into the thin-walled cylinder 1-1 and axially compressed, forming a stable interference fit connection with the surrounding rock 8.

[0027] like Figure 3 As shown, the shear-absorbing energy member 2 includes n axially extended columnar equal-thickness walls; the number and length of the columnar equal-thickness walls depend on the location and length of faults and joints inside the surrounding rock obtained from advanced geological exploration, wherein n≥2, and in this invention, n is 8; the axial cross-section of the columnar equal-thickness walls has a radially symmetrical trapezoidal tooth-shaped geometric configuration; a constant gap annular deformation cavity is formed between the inner wall surface of the columnar equal-thickness walls and the outer surface of the rod 4; the shear-absorbing energy member 2 is provided with rings at both ends with a diameter larger than the annular deformation cavity to increase the axial contact area with the grouting body.

[0028] The shear-absorbing component 2 achieves lateral shear resistance as follows: when the surrounding rock deformation is small, the trapezoidal toothed cone structure of the shear-absorbing component 2 is subjected to the shear action of the surrounding rock, and the annular deformation cavity resists the lateral shear; when the surrounding rock deformation is large, multiple annular deformation cavities are crushed and undergo plastic deformation, providing reaction force; when the surrounding rock deformation continues to increase, the annular deformation cavity is compacted, the shear-absorbing component 2 is tightly attached to the rod 4, and relies on the material properties to resist the shear force of the surrounding rock together with the rock mass until it breaks before the rod 4, and the shear resistance performance of the shear-absorbing component 2 is fully utilized.

[0029] The energy absorption mechanism of the shear-resistant energy-absorbing component 2 is as follows: When the rod 4 is subjected to a transverse shear load and the surrounding rock deformation is small, the trapezoidal toothed conical structure of the shear-resistant energy-absorbing component 2 crushes the surrounding rock and releases some shear energy; when the surrounding rock deformation is large, the trapezoidal toothed conical structure of the shear-resistant energy-absorbing component 2 crushes and deforms to dissipate energy, and the annular deformation cavity can accommodate rheological materials or add ribs to increase the plastic deformation energy of the structure; when the surrounding rock deformation continues to increase, the shear-resistant energy-absorbing component 2 absorbs the deformation energy of the surrounding rock by the plastic deformation of the material itself.

[0030] The following specific examples further illustrate the method of using this invention: like Figure 4As shown, when using end anchoring to support jointed and fractured rock masses, firstly, based on the results of advanced geological exploration, boreholes are drilled in the surrounding rock. The borehole depth should penetrate the fractured zone of the surrounding rock to ensure that the anchor is anchored in stable surrounding rock. Subsequently, based on the core sampling results, the distance between the joints and fractures and the bottom of the hole is calculated. Shear energy absorbing components 2, limit nuts 3, and stirring anchor heads 1 are then installed sequentially at the corresponding positions on the rod body 4, thereby completing the assembly of the shear energy absorbing anchor. Then, resin anchoring agent 9 is inserted into the thin-walled cylinder 1-1, ensuring that the three centers are aligned. Subsequently, the assembled anchor rod, along with the anchoring agent, is driven into the surrounding rock borehole. After ensuring that the thin-walled cylinder 1-1 is in contact with the bottom of the hole, the load is increased to continue pushing the rod body 4 in, ensuring that the outer packaging of the resin anchoring agent 9 is punctured. Then, the rod body 4 is rotated for four to six minutes to ensure that the resin anchoring agent 9 is fully stirred and solidified. Finally, the tray 5 and the fastening nut 6 are installed on the head of the rod body 4, and the on-site installation of the end-anchored shear-absorbing anchor rod support is completed.

[0031] When the fractured rock mass displaces along the joints and fractures, the anchor rod is subjected to a combination of tension and shear. Axially, because the rod body 4 is anchored at the ends, it can be freely stretched and deformed, thus absorbing a large amount of axial deformation energy of the surrounding rock. Laterally, when the deformation of the surrounding rock is small, the trapezoidal toothed conical structure of the shear-absorbing component 2 effectively resists the shear displacement of the surrounding rock when the shear force of the surrounding rock does not exceed the shear strength of the shear-absorbing component 2.

[0032] When the surrounding rock deformation is large, the shear force of the surrounding rock approaches the shear strength of the shear-resistant energy-absorbing component 2. Multiple trapezoidal tooth-like structures generate plastic deformation through crushing, absorbing the lateral deformation energy of the surrounding rock and protecting the rod body 4 from shear failure.

[0033] As the deformation of the surrounding rock continues to increase, the shear force of the surrounding rock exceeds the shear strength of the shear-resistant energy-absorbing component 2. The annular deformation cavity is compacted and continues to resist the shear action of the surrounding rock together with the rod 4 until it breaks before the rod 4. The shear resistance of the shear-resistant energy-absorbing component 2 is fully utilized, thereby making full use of the deformation energy absorption characteristics and high shear resistance of the metal material structure.

[0034] like Figure 5 As shown, when using grouting anchoring for anchor support of jointed and fractured rock masses, the preliminary geological exploration results and the assembly of shear-absorbing anchors are the same as when using end anchoring. First, the mixing anchor head 1 is inserted to the bottom of the hole, and then the load is applied to push the rod body 4 in, causing the thin-walled cylinder 1-1 to undergo plastic deformation. Then, grout is injected into the hole, and finally, the tray 5 and the fastening nut 6 are installed on the head of the rod body 4. The on-site installation of the grouting anchored shear-absorbing anchor support is completed.

[0035] When the fractured rock mass displaces along the joints and fractures, the anchor bolt is subjected to a combination of tension and shear forces. When the deformation of the surrounding rock is small, the axial component of the frictional force between the trapezoidal toothed conical structure of the shear-resistant energy-absorbing component 2 and the grouting body 7 resists the axial tensile force on the rod body 4, and the lateral component resists the lateral shear force.

[0036] When the surrounding rock deforms significantly, the grout 7 between the shear-absorbing component 2 and the borehole is sheared and destroyed. The grout 7 absorbs the deformation energy of the surrounding rock through plastic deformation. At the same time, since the shear-absorbing component 2 is sleeved with the rod 4, the sleeved part of the rod 4 absorbs the axial deformation energy of the surrounding rock through tensile deformation. The trapezoidal toothed conical structure of the shear-absorbing component 2 absorbs the lateral deformation energy of the surrounding rock through the compression deformation of the annular deformation cavity. This offsets the influence of shear force on the rod 4, improves the overall shear strength of the anchor bolt, and ensures that the anchor bolt is not sheared and destroyed.

[0037] As the deformation of the surrounding rock continues to increase, most of the trapezoidal toothed cone structure of the shear-absorbing component 2 is crushed and the annular deformation cavity is compacted. At this time, the shear-absorbing component 2 is in close contact with the rod 4. Through the material's own properties, it and the rod 4 jointly resist the shearing action of the rock mass until it breaks before the rod 4. The shear resistance of the shear-absorbing component 2 is fully utilized, thereby making full use of the deformation energy absorption characteristics and high shear resistance of the metal material structure.

[0038] Since the grout 7 fills the entire borehole and the diameters of both ends of the shear-absorbing component 2 are larger than the diameter of the rod 4, the two ends of the shear-absorbing component 2 are restricted by the grout 7, and the anchoring method is multi-point anchoring; under tension, the rod 4 is only allowed to extend freely between the two ends, ensuring that after the anchor is damaged at one point, the other parts still play the role of connecting the fractured rock mass.

[0039] Matters not covered in this invention are common knowledge.

[0040] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A rockburst-resistant shear-absorbing anchor bolt for stress-resistant structures in deeply buried hard rock tunnels, characterized in that: The anchor bolt includes a stirring anchor head, a shear-absorbing component, a limiting nut, a rod body, a tray, and a fastening nut. The stirring anchor head is coaxially disposed on one end of the rod body. The tray is coaxially disposed on the other side of the rod body. The fastening nut is located on the outside of the tray and threadedly connected to the rod body. The shear-absorbing component is located between the tray and the stirring anchor head and is coaxially sleeved on the outside of the rod body. The limiting nuts are respectively disposed at both ends of the shear-absorbing component and threadedly connected to the rod body to limit the axial position of the shear-absorbing component.

2. The stress-structure-controlled rock-burst-resisting energy-absorbing anchor rod for deep-buried hard rock tunnel according to claim 1, characterized in that: The shear-resistant energy-absorbing component includes n axially extended columnar equal-thickness walls. The axial cross-section of the columnar equal-thickness walls has a radially symmetrical trapezoidal tooth-shaped geometric configuration. A ring-shaped deformation cavity with a constant gap is formed between its inner wall surface and the outer surface of the rod. Both ends of the shear-resistant energy-absorbing component in the axial direction are respectively provided with rings with a diameter larger than the ring-shaped deformation cavity.

3. The stress-structure-controlled rockburst-resisting energy-absorbing anchor rod for deep-buried hard rock tunnel according to claim 2, characterized in that: The number and length of the columnar, equal-thickness-walled bodies depend on the location and length of faults and joints within the surrounding rock obtained from advanced geological exploration; where n≥2.

4. The stress-structure-controlled anti-shear energy-absorbing anchor rod for preventing rock burst in deep-buried hard rock tunnel according to claim 1, characterized in that: The stirring anchor head includes a thin-walled cylinder, a piercing cone, and helical blades; the front side of the thin-walled cylinder is coaxially sleeved on the end of the rod; the piercing cone is disposed in the inner cavity of the thin-walled cylinder; the helical blades are disposed on the front side of the thin-walled cylinder and coaxially fixed to the radial outer surface of the tail of the rod, and extend spirally around the central axis of the rod to the piercing cone; the tip of the piercing cone is arranged in a direction away from the helical blades.

5. The rockburst shear-absorbing anchor bolt for stress-resistant structure control in deep-buried hard rock tunnels according to claim 4, characterized in that: The thin-walled cylinder has at least three axially elongated slots on its sidewall.

6. The rockburst shear-absorbing anchor bolt for stress-resistant structure control in deep-buried hard rock tunnels according to claim 1, characterized in that: Both the limiting nut and the fastening nut are hexagonal nuts.

7. The rockburst shear-absorbing anchor bolt for stress-resistant structure control in deep-buried hard rock tunnels according to claim 1, characterized in that: The rod body, tray, and fastening nut are all standard 22mm threaded steel anchor rod components.

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