Variable cross-section high-strength anchoring support method for tunnel construction

Abstract

The invention belongs to the technical field of tunnel supporting, discloses a variable cross-section high-strength anchoring supporting method for tunnel construction, and aims to solve the problems of long construction period and high cost caused by large use amount of tunnel surrounding rock anchor rods and easy generation of cracks caused by concentrated acting force of a single anchor rod on tunnel surrounding rock. The method comprises the following steps: (1) after tunnel surrounding rock is excavated, spraying concrete to form a first concrete protective layer; (2) erecting a steel arch; (3) laying a reinforcing mesh; (4) anchor rod construction; (5) after anchor rod construction is completed, concrete is sprayed again to form a second concrete protection layer; and then secondary lining is constructed according to design requirements. The combined acting force of the single anchor rod and the tunnel surrounding rock can be improved, the number of the tunnel surrounding rock anchor rods is reduced, and the purposes of reducing the construction period and reducing the grouting amount are achieved; and meanwhile, the crack problem caused by overlarge local pressure intensity of the tunnel surrounding rock can be effectively prevented.

Description

Technical Field

[0001] The invention belongs to the field of tunnel support, and in particular relates to a variable-section high-strength anchoring support method used in tunnel construction. Background Art

[0002] With the rapid development of social economy, transportation construction is also advancing rapidly, and transportation routes inevitably pass through mountainous areas. Tunnels are widely used. When building tunnels in mountainous areas, engineers often perform conventional anchor reinforcement on the rock mass around the tunnel.

[0003] For example, the patent with application number 2020108459656 discloses a multi-section, one-time fully recoverable tunnel face advance anchor and its application method, including a mechanical internal anchor head for being set in a hole in the surrounding rock, and an anchor rod body composed of multiple rod-shaped components and connecting parts is installed on the mechanical internal anchor head, and the end of the anchor rod body passing through the surrounding rock hole is sleeved with an anchor tray and an anchor nut is installed; the rod-shaped component is a hot-rolled ribbed steel bar, and both ends of the rod-shaped component are provided with external threads, and the connecting part is a hollow steel pipe and is provided with an internal thread matching the external thread; the rod-shaped component is a left-handed or right-handed fine-rolled threaded steel bar, and the connecting part is a hollow steel pipe and is provided with an internal thread, and the entire length of the rod-shaped component is covered with an external thread matching the internal thread of the connecting part.

[0004] The patent with application number 2021102653500 discloses a tunnel support structure based on active control of surrounding rock deformation and its use method, wherein the tunnel includes a tunnel auxiliary chamber and a tunnel main tunnel, the support structure of the tunnel auxiliary chamber is a sprayed anchor support structure, and the support structure of the tunnel main tunnel includes a sprayed anchor support structure and a reinforced concrete support structure, the sprayed anchor support structure includes a concrete support structure and an anchor rod, the concrete support structure is distributed along the axial direction of the tunnel, one end of the anchor rod is connected to the tunnel surrounding rock, and the other end of the anchor rod is connected to the concrete support structure.

[0005] Patent application number 2022229558533 discloses a support structure for a small-clearance double-hole tunnel passing through a water-rich broken zone, comprising: a plurality of advance small guide tubes, a primary support layer, a plurality of grouting anchors, a plurality of tension anchors, a surface grouting layer and a secondary lining layer; the plurality of advance small guide tubes and the plurality of grouting anchors are arranged in corresponding hole positions on the tunnel vault, the primary support layer and the secondary lining layer are arranged on the tunnel body, and the primary support layer is between the secondary lining layer and the rock surface of the tunnel body; the surface grouting layer is parallel to the tunnel excavation surface, and the plurality of tension anchors are horizontally arranged in the middle rock column between the leading tunnel and the following tunnel.

[0006] The patent with application number 202020173479X discloses an anchor for tunnel support, an anchor body; a backstop mechanism, detachably connected to the anchoring section of the anchor body, the backstop mechanism is used to abut the surrounding rock and limit the anchor body; a grouting mechanism, arranged on the outer circumference of the anchor body, the grouting mechanism rotates with the help of the anchor body, the grouting mechanism is used to push the anchor in the shallow part of the anchor hole to move to the deep part of the anchor hole; and a grouting mechanism, arranged on the free section of the anchor body, the grouting mechanism abuts against the tunnel wall, and is used to prevent the anchor in the anchor hole from flowing out.

[0007] As in the above-mentioned examples, the existing anchor rod structures for tunnel surrounding rock support all adopt ordinary grouting anchor rods for support. Although ordinary grouting anchor rods can achieve the support function for tunnel surrounding rock, the bearing range of ordinary grouting anchor rods is small. Therefore, in order to achieve the purpose of tunnel support, the number of grouting anchor rods has to be increased. However, when the support stability is achieved by increasing the number of grouting anchor rods, the problems of long anchor rod construction time (i.e., a large number of anchor holes need to be processed) and large grouting amount (i.e., a large number of anchor rods) are brought about.

[0008] At the same time, since the anchor rod and the tunnel surrounding rock are only in contact through the solidified grouting body itself (i.e. the size of the anchor hole) and the size of the anchor rod itself, the contact area with the tunnel surrounding rock is small, and the force application area of ​​a single anchor rod is small. The slurry injected into the cracks of the tunnel surrounding rock by grouting is not continuous due to the irregularity of the cracks, so the solidification of the slurry injected into the tunnel surrounding rock has limited support for the anchor rod, resulting in a small force application area for the anchor rod, and the reaction force of the anchor rod on the tunnel surrounding rock is more concentrated, resulting in poor support stability of the tunnel surrounding rock. Summary of the invention

[0009] The present invention provides a variable-section high-strength anchoring support method for tunnel construction in order to solve the problems of long construction period and high cost caused by large amount of tunnel surrounding rock anchors used, and concentrated force exerted by a single anchor on the tunnel surrounding rock, which easily causes cracks in the tunnel surrounding rock.

[0010] In order to solve the technical problem, the technical solution adopted by the present invention is:

[0011] A variable cross-section high-strength anchoring support method for tunnel construction, characterized by comprising:

[0012] (1) After tunnel surrounding rock is excavated, spray concrete to form the first concrete protective layer;

[0013] (2) Erecting steel arches;

[0014] (3) Laying steel mesh;

[0015] (4) Anchor bolt construction: The anchor bolt construction includes opening an anchor hole along the radial direction of the tunnel surrounding rock, the anchor hole includes an equal diameter anchor hole section, a first-stage hole expansion section and a second-stage hole expansion section, the diameter of the first-stage hole expansion section is larger than the diameter of the equal diameter anchor hole section, the diameter of the second-stage hole expansion section is larger than the diameter of the first-stage hole expansion section, a high-strength threaded anchor is implanted in the anchor hole, the front section of the high-strength threaded anchor extends into the second-stage hole expansion section of the anchor hole, the rear section of the high-strength threaded anchor extends out of a steel mesh to form a locking section, and the locking section of the high-strength threaded anchor is equipped with a first anchor plate and a locking nut; a grouting body is formed between the anchor hole and the high-strength threaded anchor by grouting;

[0016] (5) After the anchor construction is completed, concrete is sprayed again to form a second concrete protective layer; after the second concrete protective layer is completed, the secondary lining is constructed according to the design requirements.

[0017] In some embodiments, the anchor rod construction includes middle anchor rod construction, upper anchor rod construction and lower anchor rod construction, and the number of anchor rods in the upper anchor rod construction is greater than the number of anchor rods in the lower anchor rod construction.

[0018] In some embodiments, when constructing anchor rods during the upper anchor rod construction process, a grouting plug with equal diameter sections of the anchor hole matching each other is provided on the side of the first anchor plate facing the tunnel surrounding rock, a grouting port for installing a grouting pipe is provided on the first anchor plate, a grouting hole is provided at a position corresponding to the grouting port on the grouting plug, a grouting port is provided on the other side of the grouting plug, a return grouting port is provided inside the return grouting port, and a return flow pipe is provided, and the front section of the return flow pipe extends to the top of the anchor hole.

[0019] In some embodiments, when constructing anchor rods during the upper anchor rod construction process, a grouting pipe is installed at the grouting port on the first anchor plate for grouting, and the injected slurry enters the interior of the anchor hole through the grouting hole of the grouting plug until the return slurry in the return pipe is stabilized and the grouting at the grouting port is stopped; after the slurry of the first grouting is initially solidified, the return pipe is pulled out downward for a distance, and after the return pipe no longer flows out fluid, the second grouting is carried out using the return pipe. When the second grouting is carried out using the return pipe, the return pipe is kept stably grouting for a period of time, and then the grouting is continued and the return pipe is slowly and gradually pulled out downward.

[0020] In some embodiments, a second anchor plate is further provided on the locking section of the high-strength threaded anchor rod, a plurality of through holes are opened on the second anchor plate, screws are respectively provided on the left and right sides of the second anchor plate, the screws are respectively provided with clamping grooves for engaging with the steel arch frame, and locking nuts that are compatible with the screws are provided on both sides of the clamping grooves.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The variable-section high-strength anchoring support method for tunnel construction of the present invention constructs the anchor hole into equal-diameter sections, first-order hole expansion sections and second-order hole expansion sections when constructing the anchor hole, so that after the high-strength threaded anchor rod is implanted and grouting is performed, an enlarged head can be formed at the front section of the anchor rod, which improves the bonding force between the single anchor rod and the tunnel surrounding rock and reduces the number of tunnel surrounding rock anchor rods, thereby achieving the purpose of shortening the construction period and reducing the grouting amount. On the other hand, more importantly, the contact area between the front section of the anchor and the tunnel surrounding rock is greatly increased. When the tunnel surrounding rock tends to collapse, the larger grouting body of the second-stage expansion section is used to support the tunnel surrounding rock. First, the force can be quickly transmitted to the entire anchor to use the remaining tunnel surrounding rock (the tunnel surrounding rock closer to the inside of the tunnel) to resist the collapse trend of the tunnel surrounding rock in the front section of the anchor, thereby improving the support stability of the tunnel surrounding rock; second, the larger grouting body of the second-stage expansion section is used to contact the tunnel surrounding rock, which greatly reduces the reverse pressure on the tunnel surrounding rock from the front section of the anchor (i.e. the deepest part of the anchor), so that the reverse pressure on the tunnel surrounding rock in the front section of the anchor is smaller, which can effectively prevent the cracks in the tunnel surrounding rock caused by excessive local pressure, so that the tunnel surrounding rock can maintain its original integrity as much as possible, thereby further improving the safety and stability of the tunnel.

[0023] The anchor hole of the present invention adopts a structural design of a first-order expansion section and a second-order expansion section, so that the interaction force between the anchor rod and the tunnel surrounding rock is gradually transmitted to each other, reducing the risk of fracture between the enlarged head section (i.e., the first-order expansion section and the second-order expansion section) and the equal diameter section due to stress concentration, thereby further improving the support capacity of the anchor rod. Although there are enlarged head anchor rods in the prior art, the cross-sectional area between the equal diameter section and the enlarged head section of the enlarged head anchor rod varies greatly, so the problem of stress concentration between the equal diameter section and the enlarged head section is more serious. The structural design of the first-order expansion section and the second expansion section of the present invention can disperse the stress between the expansion section and the equal diameter section, thereby reducing the risk of fracture between the enlarged head section and the equal diameter section due to stress concentration. More importantly, the design of the first-stage hole section and the second-stage hole expansion section can further increase the contact area between the tunnel surrounding rock and the grouting body, making the bonding ability between the tunnel surrounding rock and the anchor stronger; at the same time, under the premise of the same force, the present invention can reduce the force between a single area of ​​the anchor and the tunnel surrounding rock, thereby making the force between the entire anchor and the tunnel surrounding rock more dispersed and uniform, thereby achieving the purpose of improving the anchor's support capacity for the tunnel surrounding rock. And because the force is more dispersed and uniform, it also reduces the stress between the enlarged head section and the equal diameter section, further reducing the risk of fracture between the equal diameter section and the enlarged head section. Ultimately, the anchor's support capacity for the tunnel surrounding rock is improved.

[0024] The structural design of the present invention allows that when constructing anchor rods on the upper part of the tunnel surrounding rock, due to the grouting method adopted from bottom to top, after the initial setting after grouting using the first grouting pipe, a separation layer will be formed at the upper top of the second-stage expansion section due to the natural precipitation and separation of the slurry. Therefore, the present invention can ensure that the entire anchor hole is filled with slurry by setting a return pipe on the one hand, and can also use the return pipe to drain the separation layer formed after the first grouting, and then use the return pipe to perform the second grouting for filling. The molding quality of the grouting body after molding is ensured. That is, no cavities will be formed in the first-stage expansion section and the second-stage expansion section, so as to ensure that the grouting body in the first-stage expansion section and the second-stage expansion section can fully play its role.

[0025] The present invention uses the structural design of the second anchor plate, the screw rod and the clamping groove to make the anchor rod not only be locked on the periphery of the steel mesh by the first anchor plate, but also be integrated with the steel arch frame by the structure of the second anchor plate, the screw rod and the clamping groove. Thus, the anchor rod can not only stabilize the surrounding rock of the tunnel, but also transmit the force to the steel arch frame, and use the steel arch frame structure to bear the force from the surrounding rock of the tunnel, further improve the support effect on the surrounding rock of the tunnel, and ensure the safety of the tunnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is a schematic diagram of the cross-sectional structure of the tunnel;

[0027] Figure 2 It is a schematic diagram of the structure of the present invention when constructing anchor holes on the surrounding rock of a tunnel;

[0028] Figure 3 This is a schematic diagram of the structure of implanting a high-strength threaded anchor rod into an anchor hole according to the present invention;

[0029] Figure 4 It is a schematic diagram of the structure after grouting is formed in the anchor hole of the present invention;

[0030] Figure 5 It is a partial structural schematic diagram of the high-strength threaded anchor rod, the first anchor rod and the second anchor plate of the present invention;

[0031] Markings in the figure: 1. tunnel, 2. anchor hole, 21. equal diameter section, 22. first-stage expansion section, 23. second-stage expansion section, 3. high-strength threaded anchor rod, 4. grouting body, 5. first anchor plate, 51. grouting port, 6. grouting plug, 61. grouting hole, 7. return pipe, 8. locking nut, 9. second anchor plate, 10. screw rod, 11. clamping groove, 12. locking nut. DETAILED DESCRIPTION

[0032] The present invention is further described below in conjunction with embodiments, which are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, other embodiments obtained by ordinary technicians in the field without creative work are all within the scope of protection of the present invention.

[0033] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention; the terms "first", "second", and "third" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance; in addition, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0034] In conjunction with the accompanying drawings, the variable cross-section high-strength anchoring support method for tunnel construction of the present invention comprises:

[0035] (1) After the tunnel surrounding rock is excavated, concrete is sprayed to form the first concrete protective layer; the first concrete protective layer mainly serves to enhance the stability of the surrounding rock and prevent water intrusion. After the tunnel surrounding rock is treated with sprayed concrete, it can form a more solid surrounding rock shell, which can effectively enhance the stability of the surrounding rock and reduce the occurrence of landslide accidents. At the same time, sprayed concrete can effectively prevent groundwater and soil from invading the interior of the tunnel, ensuring that the tunnel remains relatively dry for subsequent construction.

[0036] There are many ways to excavate a tunnel, including the full section method, the step method, the center partition wall method (CD method), the cross center partition wall method (CRD method), the double side wall pilot method (glass method) and the circular excavation method with core soil. Those skilled in the art can understand and appreciate that they can select a suitable excavation method according to the actual situation of the tunnel surrounding rock, and will not be described in detail here.

[0037] (2) Erect steel arch frames; the steel arch frames must have sufficient rigidity and strength to withstand the loads that may occur during tunnel construction. The spacing between the steel arch frames is 0.5-1.5 meters, and the specific spacing should be determined according to the design. The number of steel frames used continuously in the section supported by the steel arch frame shall not be less than 3. During the specific implementation process, when there is a large gap between the steel arch frame and the first concrete protective layer (also often called the initial sprayed layer), prefabricated concrete blocks should be used to wedge it tightly, and the back of the steel arch frame should be filled with sprayed concrete. The longitudinal connection of the steel arch frame is connected by steel pipes (rebars).

[0038] (3) Laying steel mesh: The purpose of laying steel mesh is to significantly improve the stability of the tunnel project, improve its earthquake resistance and crack resistance, and effectively prevent the occurrence of cracks and depressions together with the second concrete protective layer poured subsequently.

[0039] (4) Anchor bolt construction: The anchor bolt construction includes opening an anchor hole along the radial direction of the tunnel surrounding rock. The anchor hole includes an equal diameter anchor hole section, a first-stage expansion section and a second-stage expansion section. The diameter of the first-stage expansion section is larger than the diameter of the equal diameter anchor hole section. The diameter of the second-stage expansion section is larger than the diameter of the first-stage expansion section. A high-strength threaded anchor rod (such as the commonly used PSB fine-rolled threaded steel bar) is implanted in the anchor hole. The front section of the high-strength threaded anchor rod extends into the second-stage expansion section of the anchor hole. The rear section of the high-strength threaded anchor rod extends out of the steel mesh to form a locking section. The locking section of the high-strength threaded anchor rod is equipped with a first anchor plate and a locking nut. A grouting body is formed between the anchor hole and the high-strength threaded anchor rod by grouting. The first anchor plate is provided with a threaded hole that matches the high-strength threaded anchor rod. The first anchor plate is threadedly connected to the high-strength threaded anchor rod and then locked by a locking nut to complete the construction of the anchor rod.

[0040] In the specific implementation process, a plurality of bearing plates are arranged at intervals in the front section where the high-strength threaded anchor rod extends into the first-stage hole expansion section and the second-stage hole expansion section.

[0041] Among them, after the anchor hole construction is completed, high-pressure water or wind should be used to clean the anchor hole to improve the molding quality of the grouting body. After the anchor hole is cleaned, high-strength threaded anchor rods are implanted and grouting is performed to form a grouting body, which is connected to the tunnel surrounding rock through the anchor rod to form a whole.

[0042] (5) After the anchor construction is completed, concrete is sprayed again to form a second concrete protective layer; after the second concrete protective layer is completed, the secondary lining is constructed according to the design requirements. The construction of the secondary lining belongs to the prior art, which can be understood by those skilled in the art and will not be described in detail here. Repeat the above steps (1)-(5) to gradually form a tunnel 1 in the surrounding rock.

[0043] The variable-section high-strength anchoring support method for tunnel construction of the present invention constructs the anchor hole into equal-diameter sections, first-order hole expansion sections and second-order hole expansion sections when constructing the anchor hole, so that after the high-strength threaded anchor rod is implanted and grouting is performed, an enlarged head can be formed at the front section of the anchor rod, which improves the bonding force between the single anchor rod and the tunnel surrounding rock and reduces the number of tunnel surrounding rock anchor rods, thereby achieving the purpose of shortening the construction period and reducing the grouting amount. On the other hand, more importantly, the contact area between the front section of the anchor and the tunnel surrounding rock is greatly increased. When the tunnel surrounding rock tends to collapse, the larger grouting body of the second-stage expansion section is used to support the tunnel surrounding rock. First, the force can be quickly transmitted to the entire anchor to use the remaining tunnel surrounding rock (the tunnel surrounding rock closer to the inside of the tunnel) to resist the collapse trend of the tunnel surrounding rock in the front section of the anchor, thereby improving the support stability of the tunnel surrounding rock; second, the larger grouting body of the second-stage expansion section is used to contact the tunnel surrounding rock, which greatly reduces the reverse pressure on the tunnel surrounding rock from the front section of the anchor (i.e. the deepest part of the anchor), so that the reverse pressure on the tunnel surrounding rock in the front section of the anchor is smaller, which can effectively prevent the cracks in the tunnel surrounding rock caused by excessive local pressure, so that the tunnel surrounding rock can maintain its original integrity as much as possible, thereby further improving the safety and stability of the tunnel.

[0044] However, in the existing tunnel surrounding rock support process, equal-diameter anchor rods are used to reinforce the tunnel surrounding rock. On the one hand, the bonding force between a single anchor rod and the tunnel surrounding rock is poor, resulting in a large number of anchor rods, which greatly increases the construction period and grouting volume, and ultimately leads to high construction costs. More importantly, due to the small contact area between the front section of the equal-diameter anchor rod (i.e., the anchor rod extends to the deepest part of the tunnel surrounding rock) and the tunnel surrounding rock, the tunnel surrounding rock transmits less force to the anchor rod, so that the anchoring force of the anchor rod cannot be fully exerted; and when the tunnel surrounding rock has a tendency to collapse, the pressure between the front section of the anchor rod and the tunnel surrounding rock is large due to the small contact area, which accelerates the generation of cracks in the tunnel surrounding rock, and thus provides limited support to the tunnel surrounding rock.

[0045] At the same time, the anchor hole of the present invention adopts the structural design of the first-order expansion section and the second-order expansion section, so that the interaction force between the anchor rod and the tunnel surrounding rock is gradually transmitted to each other, reducing the risk of fracture between the enlarged head section (i.e., the first-order expansion section and the second-order expansion section) and the equal diameter section due to stress concentration, thereby further improving the support capacity of the anchor rod. Although there are enlarged head anchor rods in the prior art, the cross-sectional area between the equal diameter section and the enlarged head section of the enlarged head anchor rod varies greatly, so the problem of stress concentration between the equal diameter section and the enlarged head section is more serious. The structural design of the first-order expansion section and the second expansion section of the present invention can disperse the stress between the expansion section and the equal diameter section, thereby reducing the risk of fracture between the enlarged head section and the equal diameter section due to stress concentration. More importantly, the design of the first-stage hole section and the second-stage hole expansion section can further increase the contact area between the tunnel surrounding rock and the grouting body, making the bonding ability between the tunnel surrounding rock and the anchor stronger; at the same time, under the premise of the same force, the present invention can reduce the force between a single area of ​​the anchor and the tunnel surrounding rock, thereby making the force between the entire anchor and the tunnel surrounding rock more dispersed and uniform, thereby achieving the purpose of improving the anchor's support capacity for the tunnel surrounding rock. And because the force is more dispersed and uniform, it also reduces the stress between the enlarged head section and the equal diameter section, further reducing the risk of fracture between the equal diameter section and the enlarged head section. Ultimately, the anchor's support capacity for the tunnel surrounding rock is improved.

[0046] In some embodiments, the anchor bolt construction includes middle anchor bolt construction, upper anchor bolt construction and lower anchor bolt construction, and the number of anchor bolts in the upper anchor bolt construction is greater than the number of anchor bolts in the lower anchor bolt construction. Among them, the anchor bolts in the lower anchor bolt construction are also often called locking foot anchor bolts.

[0047] In some embodiments, when constructing anchor rods during the upper anchor rod construction process, a grouting plug with equal diameter sections of the anchor hole matching each other is provided on the side of the first anchor plate facing the tunnel surrounding rock, a grouting port for installing a grouting pipe is provided on the first anchor plate, a grouting hole is provided at a position corresponding to the grouting port on the grouting plug, a grouting port is provided on the other side of the grouting plug, a return grouting port is provided inside the return grouting port, and a return flow pipe is provided, and the front section of the return flow pipe extends to the top of the anchor hole.

[0048] In the specific implementation process, a through hole or a bayonet that is compatible with the return pipe is opened on the bearing plate of the front section of the anchor rod, so that the return pipe can be supported by the grouting plug and the bearing plate.

[0049] In some embodiments, when grouting is performed using the grouting port, the grouting pipe can also pass through the grouting port of the first anchor plate and the grouting hole of the stop plug and extend into the anchor hole for pressure grouting. When the grouting pipe is extended into the anchor hole for grouting, the grouting pipe gradually extends upward to the inner top of the anchor hole and then gradually pulls back downward. During the process of pulling the grouting pipe back downward, grouting is also required to fill the gap generated when the grouting pipe is pulled back.

[0050] In some embodiments, when constructing anchor rods during the construction of upper anchor rods, the grouting pipe is installed at the grouting port on the first anchor plate for grouting, and the injected slurry enters the interior of the anchor hole through the grouting hole of the grouting stopper until the return slurry of the return pipe is stabilized and the grouting of the grouting port is stopped; after the slurry of the first grouting is initially solidified, the return pipe is pulled out downward for a distance (generally controlled at 10-20cm), and the return pipe is used for the second grouting after the return pipe no longer flows out of the fluid. When the return pipe is used for the second grouting, the return pipe is kept stable for a period of time, and then the grouting is continued and the return pipe is slowly and gradually pulled out downward. In the specific implementation process, the slurry grade of the second grouting is greater than the slurry grade of the first grouting.

[0051] The structural design of the present invention allows that when constructing anchor rods on the upper part of the surrounding rock of a tunnel, since a grouting method from bottom to top is adopted, after the initial setting after grouting is completed using the first grouting pipe, a separation layer (mainly water) will be formed on the upper top of the second-order expansion section (or even the first-order expansion section) due to the natural precipitation and separation of the slurry. Therefore, the present invention can ensure that the entire anchor hole is filled with slurry by setting a return pipe, and can also use the return pipe to drain the separation layer (mainly water) formed after the first grouting, and then use the return pipe to perform the second grouting for filling. The molding quality of the grouting body after molding is ensured. That is, there will be no cavities in the first-order expansion section and the second-order expansion section, so as to ensure that the grouting body in the first-order expansion section and the second-order expansion section can fully play its role.

[0052] At the same time, the return pipe of the present invention can also be used as a basis for judging whether the grouting fills the entire anchor hole. In the specific implementation process, when the return pipe no longer refluxes after the first grouting is completed, it can be determined that the slurry of the first grouting has filled the entire anchor hole. Then, after the first grouting is initially solidified (a separation layer has been formed), the return pipe is pulled down for a distance. By measuring the volume of the fluid flowing out of the return pipe, the volume of the cavity formed after the initial solidification of the first grouting slurry can be determined. Therefore, when the return pipe is used for the second grouting, the time when the return pipe remains stable, that is, the volume of the injected slurry is at least not less than the volume of the fluid flowing out after the return pipe is pulled down, thereby ensuring that the space formed after the initial solidification of the first grouting can be backfilled and filled by the second grouting of the return pipe.

[0053] However, the tunnel surrounding rock anchor construction in the prior art all adopts a one-time grouting method, which will result in a cavity in the grouting body after the slurry solidifies (i.e., the separation layer mainly formed after the initial setting of the slurry is water), so that there is a certain height distance between the grouting body and the tunnel surrounding rock, thereby reducing the supporting force of the anchor on the tunnel surrounding rock.

[0054] In some embodiments, a second anchor plate is further provided on the locking section of the high-strength threaded anchor rod, a plurality of through holes are opened on the second anchor plate, screws are respectively provided on the left and right sides of the second anchor plate, the screws are respectively provided with clamping grooves for engaging with the steel arch frame, and locking nuts that are compatible with the screws are provided on both sides of the clamping grooves.

[0055] In a specific implementation process, the front side and the rear side of the second anchor plate are both provided with locking nuts threadedly connected to the high-strength threaded anchor rod, so as to lock the second anchor plate on the high-strength threaded anchor rod.

[0056] The present invention uses the structural design of the second anchor plate, the screw rod and the clamping groove to make the anchor rod not only be locked on the periphery of the steel mesh by the first anchor plate, but also be integrated with the steel arch frame by the structure of the second anchor plate, the screw rod and the clamping groove. Thus, the anchor rod can not only stabilize the surrounding rock of the tunnel, but also transmit the force to the steel arch frame, and use the steel arch frame structure to bear the force from the surrounding rock of the tunnel, further improve the support effect on the surrounding rock of the tunnel, and ensure the safety of the tunnel.

[0057] In the construction process of the tunnel surrounding rock anchor of the prior art, since the position of the anchor and the steel arch are staggered, the second concrete protective layer is formed by spraying concrete after the anchor construction is completed. Therefore, the anchor and the steel arch are independent of each other. However, the present invention uses the second anchor plate to organically form the anchor and the steel arch into a whole, and uses the structural strength of the steel arch to provide an additional support force for the anchor, and this support force does not affect the locking effect of the anchor and the tunnel surrounding rock itself through the first anchor plate, thereby further improving the support stability of the tunnel surrounding rock.

Claims

1. A variable cross-section high-strength anchoring support method for tunnel construction, characterized in that: include: (1) After tunnel surrounding rock is excavated, spray concrete to form the first concrete protective layer; (2) Erecting steel arches; (3) Laying steel mesh; (4) Anchor bolt construction: The anchor bolt construction includes opening an anchor hole along the radial direction of the tunnel surrounding rock, the anchor hole includes an equal diameter anchor hole section, a first-stage hole expansion section and a second-stage hole expansion section, the diameter of the first-stage hole expansion section is larger than the diameter of the equal diameter anchor hole section, the diameter of the second-stage hole expansion section is larger than the diameter of the first-stage hole expansion section, a high-strength threaded anchor is implanted in the anchor hole, the front section of the high-strength threaded anchor extends into the second-stage hole expansion section of the anchor hole, the rear section of the high-strength threaded anchor extends out of a steel mesh to form a locking section, and the locking section of the high-strength threaded anchor is equipped with a first anchor plate and a locking nut; a grouting body is formed between the anchor hole and the high-strength threaded anchor by grouting; (5) After the anchor construction is completed, concrete is sprayed again to form a second concrete protective layer; after the second concrete protective layer is completed, the secondary lining is constructed according to the design requirements.

2. The variable cross-section high-strength anchoring support method for tunnel construction according to claim 1 is characterized in that: The anchor rod construction includes middle anchor rod construction, upper anchor rod construction and lower anchor rod construction, and the number of anchor rods in the upper anchor rod construction is greater than the number of anchor rods in the lower anchor rod construction.

3. The variable cross-section high-strength anchoring support method for tunnel construction according to claim 2 is characterized in that: When constructing the anchor during the construction of the upper anchor, a grouting plug with equal diameter sections of the anchor hole matching each other is provided on the side of the first anchor plate facing the tunnel surrounding rock, a grouting port for installing a grouting pipe is provided on the first anchor plate, a grouting hole is provided at a position corresponding to the grouting port on the grouting plug, a return grouting port is provided on the other side of the grouting plug, a return grouting port is sleeved with a return pipe, and the front section of the return pipe extends to the top of the anchor hole.

4. The variable cross-section high-strength anchoring support method for tunnel construction according to claim 3 is characterized in that: During the construction of the upper anchor bolt, the grouting pipe is installed at the grouting port on the first anchor plate for grouting. The injected slurry enters the interior of the anchor hole through the grouting hole of the grouting plug until the return slurry in the return pipe is stabilized and the grouting at the grouting port is stopped. After the slurry of the first grouting is initially solidified, the return pipe is pulled out downward for a distance, and the second grouting is carried out using the return pipe after the fluid no longer flows out of the return pipe. When the second grouting is carried out using the return pipe, the return pipe is kept stably grouting for a period of time, and then the grouting is continued and the return pipe is slowly and gradually pulled out downward.

5. The variable cross-section high-strength anchoring support method for tunnel construction according to claim 1, characterized in that: The locking section of the high-strength threaded anchor rod is also provided with a second anchor plate, on which a plurality of through holes are opened, and screws are respectively arranged on the left and right sides of the second anchor plate, and the screws are respectively provided with clamping grooves for engaging with the steel arch frame, and both sides of the clamping grooves are provided with locking nuts that are compatible with the screws.

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