PREFABRICATED TUNNEL PRESTRESSED ANCHOR AND MANUFACTURING METHOD AND USE METHOD THEREFOR

Abstract

A prefabricated tunnel prestressed anchor comprises an anchor rod, the anchor rod comprises a free section and a prestressed section which are arranged in sequence; the prestressed section of the anchor rod is sleeved with a steel casing, holes are formed in the steel casing, a filler material is arranged between the steel casing and the anchor rod and filled in a space between the steel casing and the anchor rod after a prestress is applied to the anchor rod on a tensioning bench, and when the filler material is electrified, the structure of the filler material is destroyed; sleeves are arranged at two ends of the steel casing, and grout plugs used for sealing the steel casing are arranged in openings of the sleeves. The prestressed anchor can be directly installed in site to be used, a prestress is applied after the structure of the filler material is destroyed.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent Application No. PCT/CN2023/132512 with a filing date of Nov. 20, 2023, designating the United States, now pending, and further claims priority to Chinese Patent Application No. 202211572033.4 with a filing date of Dec. 8, 2022. The content of the aforementioned applications, including any intervening amendments thereto, is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The invention relates to the technical field of tunnel and underground engineering, in particular to a prefabricated tunnel prestressed anchor and a manufacturing method and use method therefor.

2. Description of Related Art

At present, China is being heading from a country with a great transport demand towards a country with a great transport capacity, the transport industry witnesses a vigorous development, and remarkable achievements have been made in tunnel construction. With the further improvement towards a higher level, the problems in tunnel construction such as faults, soft rock, swelling rock, goafs and karst become increasingly prominent, posing a great challenge to the structural safety of tunnels. Anchors, as parts of tunnel support structures, have an incomparable technical and economical superiority and can adapt to different working conditions. In face of engineering problems such as large deformation of soft rock and rock bursts, prestressed anchors are often recommended by technicians and designers to be used for supporting and have been widely accepted because of their good support capacity.

At present, the construction method for prestressed anchor support is specifically as follows: a hole is drilled for installing an anchor, and grout is injected into an anchoring section; when the anchoring section is full of grout, an oil jack of an anchor puller is disposed around an anchor head; a steel plate and a nut are arranged at the end of the anchor head; and after the oil jack is fixed, a prestress is applied. When the prestress applied by the anchor puller satisfies the design requirement, the anchor is maintained in the prestressed state for a period of time, and then locking is performed, that is, the nut at the root of the anchor head is tightened with a torque wrench by applying a tightening torque. The steel plate and the anchor puller are detached, a redundant portion of the anchor head is removed, and the hole is sealed, such that anchor construction is completed. When such a construction method is used, the working face should be flat, so a tunnel, as an arch structure, needs to be trimmed in advance; in addition, because an operation platform is needed for applying the prestress, this method is only suitable for anchors with horizontal and vertical axes, but it is extremely difficult for anchors within the arch tunnels, the construction quality and efficiency cannot be guaranteed, and the safety risk is high.

BRIEF SUMMARY OF THE INVENTION

In view of the defects in the prior art, the objective of the invention is to provide a prefabricated tunnel prestressed anchor and a manufacturing method and use method therefor to solve the problems that operation is complex and difficult and construction quality cannot be guaranteed when existing tunnel prestressed anchors are constructed.

In a first aspect, the invention provides a prefabricated tunnel prestressed anchor, comprising an anchor rod, wherein the anchor rod comprises a free section and a prestressed section which are arranged in sequence;

• • the prestressed section of the anchor rod is sleeved with a steel casing, holes are formed in the steel casing, a filler material is arranged between the steel casing and the anchor rod and filled in a space between the steel casing and the anchor rod after a prestress is applied to the anchor rod on a tensioning bench, and when the filler material is electrified, a structure of the filler material is destroyed;
  • sleeves are arranged at two ends of the steel casing, and grout plugs used for sealing the steel casing are arranged in openings of the sleeves.

Further, an outer diameter of the steel casing is less than a diameter of a borehole, an inner diameter of the steel casing is 20-25 mm greater than an outer diameter of the anchor rod, and a length of the steel casing is the same as a length of the prestressed section in a tensioned state.

Further, the steel casing is configured to be electrically conductive to conduct current to the filler material to destroy the structure of the filler material.

Further, a diameter of the holes is 5-15 mm, and a distance between every two adjacent holes is 20-30 cm.

Further, a wall thickness of the sleeves is 6-10 mm, and each sleeve comprises:

• • a threaded portion connected to the steel casing, wherein an inner diameter of the threaded portion matches an outer dimeter of the steel casing; and
  • a grout plug receiving portion having a space for receiving the corresponding grout plug.

Further, a wall thickness of the steel casing is 4-6 mm, threads are arranged at the two ends of the steel casing respectively, and the two ends of the steel casing are connected to the threaded portions by means of the threads.

Further, the grout plugs are made from an elastic material; middle portions of the grout plugs are protrusive to form spindle structures, an outer diameter of front and rear ends of the grout plugs is the same as an inner diameter of the sleeves, and an outer diameter of the protrusive middle portions is 3-4 mm greater than the inner diameter of the sleeves.

Further, the filler material is an organic material with fluidity, compressive strength after solidification, and bond strength to the anchor rod satisfying preset conditions.

In a second aspect, the invention provides a manufacturing method for the prefabricated tunnel prestressed anchor, comprising:

• • installing the steel casing at a set position on a tensioning bench, wherein an axis of the steel casing pipe is consistent with a tensioning axis and is kept horizontal, a length of the steel casing is the same as a length of the prestressed section in a tensioned state, and the holes in the steel casing are kept facing upwards; installing the sleeves at the two ends of the steel casing, and installing the grout plugs at ends of two sides the sleeves;
  • allowing the anchor rod to penetrate through the steel casing, placing the prestressed section in the steel casing, tensioning the anchor until a set prestress is obtained, and injecting the filler material into a space between the steel casing and the anchor rod by means of the holes; and
  • when the filler material is solidified and satisfies a design strength requirement, relaxing two ends of the anchor rod, and before the prestressed anchor is placed in a warehouse to be further cured, detaching the grout plugs and sleeves from the two ends of the steel casing, such that the prefabricated tunnel prestressed anchor is obtained.

In a third aspect, the invention provides a use method for the prefabricated tunnel prestressed anchor, comprising:

• • installing the prefabricated tunnel prestressed anchor in a borehole, burying a wire in the steel casing, leading out of the wire, allowing the wire to penetrate through a grout plug together with a grouting pipe, connecting the grouting pipe to a reserved grouting hole, and injecting grout into a gap between the anchoring section and the borehole and a gap between the steel casing and the borehole; and
  • after the gaps are full of grout and the grout satisfied a design strength requirement, connecting the prestressed anchor to a power supply by means of the wire to destroy the structure of the filler material to eliminate a gripping effect of the filler material on the prestressed anchor so as to transfer a prestress to surrounding rock, such that prestressed anchor support requirements are satisfied.

Compared with the prior art, the invention has at least one of the following beneficial effects:

The prefabricated tunnel prestressed anchor provided by the invention can be produced in batches on a special tensioning bench according to the anchor production process; and flow-line prefabricated construction is realized, such that the construction quality can be easily guaranteed, and the stress maintaining effect is good. When used, the prefabricated tunnel prestressed anchor is transported to a working surface and directly installed in site to be used; a period of time later after grouting of the anchoring section is completed, the anchor rod is electrified to destroy the structure of the filler material to transfer and apply a prestress to surrounding rock, such that the construction efficiency is high, special equipment and complex operation are not needed, and operation is easy; and even if the axial direction of the anchor faces the center of a tunnel, the prestressed anchor can be quickly constructed above a springing line to reinforce in time surrounding rocks in a bad condition, such as weak and crushed surrounding rock and rock bursts, the prestressed state can be well maintained, the construction safety and structure safety are guaranteed, and the problems of poor operability, low efficiency and high construction safety risks of conventional methods are solved.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

To better clarity other features, purposes and advantages of the invention, non-restrictive embodiments of the invention are described in detail below with reference to the following drawings.

FIG. 1 is a schematic structural diagram of a prefabricated tunnel prestressed anchor according to one embodiment of the invention;

FIG. 2 is a schematic structural diagram of a sleeve according to one embodiment of the invention;

FIG. 3 is a schematic structural diagram of a grout plug according to one embodiment of the invention;

FIG. 4 is a schematic diagram of field installation of the prefabricated tunnel prestressed anchor according to one embodiment of the invention;

In the FIGS.: 1, free section; 2, prestressed section; 3, steel casing; 31, hole; 4, filler material; 5, sleeve; 51, threaded portion; 52, grout plug receiving portion; 6, grout plug; 7, initial support surface; 8, wire; 9, borehole; 10, grout; 11, anchoring section; 12, base plate; 13, bolt.

DETAILED DESCRIPTION OF THE INVENTION

The invention is described in in detail below in conjunction with specific embodiments. With reference to the following embodiments, those skilled in the art can gain a better understanding of the invention, but the invention should not be limited to the following embodiments in any form. Those ordinarily skilled in the art can make some transformations and improvements without departing from the concept of the invention, and all these transformations and improvements also fall within the protection scope of the invention.

One embodiment of the invention provides a prefabricated tunnel prestressed anchor. Referring to FIG. 1, the prefabricated tunnel prestressed anchor comprises an anchor rod, wherein the anchor rod comprises a free section 1 and a prestressed section 2 which are arranged in sequence; the prestressed section 2 of the anchor rod is sleeved with a steel casing 3, holes are formed in the steel casing 3, a filler material 4 is arranged between the steel casing 3 and the anchor rod and filled in a space between the steel casing 3 and the anchor rod via the holes 31 after a prestress is applied to the anchor rod on a tensioning bench, and the filler material 4 is a material, the structure of which will be destroyed under the action of current; and sleeves 5 are arranged at two ends of the steel casing 3, and grout plugs 6 used for sealing the steel casing 3 are arranged in openings in ends of the sleeves 5.

In the above embodiment, the anchor rod may be a conventional tunnel anchor, and the length of the anchor rod, the length of the free section 1 and the length of the prestressed section 2 may be set according to design requirements. The prestress is applied to the anchor rod on the tensioning bench in a factory, the space between the steel casing 5 and the prestressed section 2 of the anchor rod is filled with the filler material 4, and when the strength of the filler material 4 reaches a set value, the anchor rod is relaxed, such that the prefabricated tunnel prestressed anchor is formed. The prefabricated tunnel prestressed anchor is transported to a working face of a tunnel and installed at a design position, and after grouting of the anchoring section is completed, the anchor rod is electrified to destroy the structure of the filler material 4, such that the prestress is transferred and applied to surrounding rock.

In some embodiments, the outer diameter of the steel casing 2 is constrained by the diameter of a borehole. To ensure that the steel casing 3 can be inserted into the borehole, the outer diameter of the steel casing 3 is less than the diameter of the borehole, and the inner diameter of the steel casing 3 is determined according to the diameter of the anchor rod, the wall thickness of the steel casing, the quantity of the filler material and other factors. Preferably, the inner diameter of the steel casing 3 is 20-25 mm greater than the outer diameter of the anchor rod, and the length of the steel casing 3 is the same as the length of the prestressed section 2 in a tensioned state.

In some embodiments, the steel casing 3 is configured to be electrically conductive. Specifically, because the steel casing 3 is made from steel and a body of the steel casing 3 is made from a non-insulating material, when the prestressed anchor is connected to a power supply by means of a wire 8, the steel casing 3 can conduct current to the filler material 4 to destroy the structure of the filler material 4.

Because the filler material 4 has good fluidity and the diameter of the steel casing 3 is generally 55-60 mm, the diameter of the holes 31 should not be too large. In some embodiments, the diameter of the holes 31 is 5-15 mm. To improve filling efficiency, the distance between the holes 31 should be as small as possible. Considering the interaction between adjacent holes when the filler material 4 is injected, the distance between two adjacent holes 31 is preferably 20-30 cm.

In some embodiments, the two ends of the steel casing 3 are sealed by means of the sleeves 5 and the grout plugs 6, and the wall thickness of the sleeves 5 is 6-10 mm. Those skilled in the art can understand that to effectively block the filler material 4 in the steel casing 3, the wall thickness of the sleeves 5 will increase accordingly with the increase in the diameter of the sleeves 5. Referring to FIG. 5, each sleeve 5 sequentially comprises a threaded portion 51 and a grout plug receiving portion 52, wherein the threaded portion 51 is connected to the steel casing 3, the inner diameter of the threaded portion 51 matches the outer diameter of the steel casing 3, and the grout plug receiving portion 52 has a space for receiving the corresponding grout plug 6.

Because the steel casing 3 is mainly used for restraining the filler material 4 to guarantee the prestress, the strength and stiffness of the steel casing 3 should be high enough, which means that the wall of the steel casing 3 should not be too thin; however, if the wall of the steel casing 3 is too thick, the quantity of the filler material 4 in the steel casing 4 will be too small, making it difficult to obtain a designed prestress. Preferably, the wall thickness of the steel casing 3 is 4-6 mm, and threads are arranged at the two ends of the steel casing 3 respectively. Specifically, the range of the threads at the two ends of the steel casing 3 is 3 cm, the thread angle is 75°, the thread pitch of 3.0, and the threads are connected to the threaded portions 51.

To ensure that the grout plugs 6 can fulfill a good sealing effect, the grout plugs 6 are made from an elastic material. Referring to FIG. 3, before grouting, the grout plugs 6 made from an elastic material need to be inserted into the sleeves 5 to block grout and will suffer from a pressure from the filler material 6, so in order to prevent the grout plugs 6 from being pushed out of the sleeves 5, middle portions of the grout plugs 6 are protrusive to form spindle structures, the outer diameter of front and rear ends of the grout plugs 6 is the same as the inner diameter of the sleeves 5, and the outer diameter of the protrusive middle portions of the grout plugs 6 is 3-4 mm greater than the inner diameter of the sleeves 5, such that the openings in the ends of the sleeves 5 can be completely sealed by the grout plugs 6, thus fulfilling a good sealing and grout blocking effect.

In some embodiments, the sleeves 5 and the grout plugs 6 are installed before the anchor rod is tensioned and are detached after the prestressed anchor is prefabricated, such that the sleeves 5 and the grout plugs 6 can be reused.

In one specific embodiment, each sleeve 5 has a length of 8 cm and a wall thickness of 6-10 mm, and is divided into two parts; one end of each sleeve 5 is provided with the threaded portion 51, has a length of 3 cm, is connected to the steel casing 3, and has an inner diameter matching the outer diameter of the steel casing 3; and the other end of each sleeve 5 is provided with the grout plug receiving portion 52 and has a length of 5 cm. The grout plugs 6 in the sleeves 5 are made from an elastic material, have a length of 6 cm and are configured as spindle structures, each section of the grout plugs 6 has a length of 2 cm, the outer diameter of the front and rear ends of the grout plugs 6 is the same as the inner diameter of the sleeves 5, the outer diameter of the protrusive (bulging) middle portions of the grout plugs 6 is 3-4 mm greater than the inner diameter of the sleeves 5, and the grout plugs 6 are installed in the sleeves 5 before the anchor rod is tensioned.

In the above embodiment, the filler material 4 is an organic material, the fluidity, the compressive strength after solidification, and the bond strength to the anchor rod of which satisfy preset conditions, and the preset conditions are set according to specific construction requirements. Because the filler material has good fluidity, high compressive strength after solidification, and high bond strength to the anchor rod, the structure of the filler material will be destroyed under the action of current conducted by the steel casing 3, such that the prestress is effectively transferred and applied to surrounding rock.

The prefabricated tunnel prestressed anchor in the above embodiment can be transported to a working surface and directly installed in site to be used; a period of time later after grouting of the anchoring section is completed, the anchor rod is electrified to destroy the structure of the filler material 4 to transfer and apply a prestress to surrounding rock, such that the construction efficiency is high, special equipment and complex operation are not needed, and operation is easy; and even if the axial direction of the anchor faces the center of a tunnel, the prestressed anchor can be quickly constructed above a springing line to reinforce in time surrounding rocks in a bad condition, such as weak and crushed surrounding rock and rock bursts, the prestressed state can be well maintained, the construction safety and structure safety are guaranteed, and the problems of poor operability, low efficiency and high construction safety risks of conventional methods are solved.

Another embodiment of the invention provides a manufacturing method for the prefabricated tunnel prestressed anchor, comprising: installing the steel casing 3 on a tensioning bench, forming the holes 31 in the steel casing 3, keeping the holes 31 facing upward when the steel casing 3 is installed, and connecting the sleeves 5 and the grout plugs 6 to two ends of the steel casing 3 respectively; tensioning the anchor to a preset prestress, then injecting the filler material 4 via the holes 31 in the steel casing 3; and when the strength of the filler material reaches a design value after the filler material is solidified, relaxing the anchor rod, such that the prefabricated tunnel prestressed anchor is obtained. The manufacturing method specifically comprises the following steps:

• • S1, installing the steel casing 3 at a set position of a steel casing locating rack on a tensioning bench, wherein the axis of the steel casing 3 is consistent with a tensioning axis and keeps horizontal, the length of the steel casing 3 is the same as the length of the prestressed section 2 in a tensioned state, and the holes 31 in the steel casing 3 face upward; installing the sleeves 5 at two ends of the steel casing 3, and installing the grout plugs 6 at ends of two sides the sleeves 5;
  • S2, allowing the anchor rod to penetrate through the steel casing 3, placing the prestressed section 2 in the steel casing 3, tensioning the anchor, and when the anchor is tensioned to a preset prestress, maintaining the anchor rod in the prestressed state for a period of time; fine adjusting the position of the steel casing 3 until the position of the steel casing 2 is identical with the position of the to the prestressed section 2; then, injecting the filler material 4 into the space between the steel casing 3 and the anchor rod via the holes 31, wherein the filler material 4 is injected every a hole, and the holes not used for injecting the filler material 4 are used for discharging gas; and
  • S3, when the strength of the filler material 4 reaches a design value a period time later after injection is completed, relaxing two ends of the anchor rods; and before the prestressed anchor is placed in a warehouse to be further cured, detaching the grout plugs 6 and the sleeves 5 from the two ends of the steel casing 3, such that the prefabricated tunnel prestressed anchor is obtained.

Another embodiment of the invention further provides a use method for the prefabricated tunnel prestressed anchor. Referring to FIG. 4, the use method comprises:

• • S1, installing the prefabricated tunnel prestressed anchor in a borehole 9, burying the wire 8 in the steel casing 3 and leading the wire 8 out, and installing a grout plug 6, a base plate 12 and a bolt 13 on an initial support surface 7, wherein the base plate 12 and the bolt 13 are mounted at an end of the anchor rod and are close to a rock surface, and the bolt 13 and the base plate 12 prevent the anchor rod from retracting; allowing the wire 8 to penetrate through the grout plug 6 together with a grouting pipe, connecting the grouting pipe to a reserved grouting hole, and injecting grout into a gap between the anchoring section 11 (the free section 1 of the prefabricated tunnel prestressed anchor) and the borehole 9 and a gap between the steel casing 3 and the borehole 9; and
  • S2, when the gap between the anchoring section 11 and the borehole 9 and the gap between the steel casing 3 and the borehole 9 are full of grout 10 and the grout satisfied a design strength requirement, connecting the prestressed anchor to a low-voltage power supply by means of the wire 8 to destroy the structure of the filler material 4 by current to eliminate a gripping effect of the filler material 4 on the prestressed anchor so to transfer a prestress to surrounding rock, such that prestressed anchor support requirements are satisfied.

When the prefabricated tunnel prestressed anchor provided by the above embodiments are used, the anchor is transported to a working surface and directly installed in site to be used; a period of time later after grouting of the anchoring section is completed, the anchor rod is electrified to destroy the structure of the filler material to transfer and apply a prestress to surrounding rock, such that the construction quality is guaranteed, a good support stress is maintained, the construction efficiency is high, and special equipment and complex operation are not needed on the construction site; and even if the axial direction of the anchor faces the center of a tunnel, the prestressed anchor can be quickly constructed above a springing line to reinforce in time surrounding rocks in a bad condition, such as weak and crushed surrounding rock and rock bursts, the prestressed state can be well maintained, the construction safety and structure safety are guaranteed, and the problems of poor operability, low efficiency and high construction safety risks of conventional methods are solved.

The specific embodiments of the invention are described above. It should be understood that the invention is not limited to the above specific embodiments. Those skilled in the art can make various transformations or modifications within the scope of the claims without affecting the essential contents of the invention. The above preferred features can be combined freely without conflicts.

Claims

1. A prefabricated tunnel prestressed anchor, comprising an anchor rod, wherein the anchor rod comprises a free section and a prestressed section which are arranged in sequence;

the prestressed section of the anchor rod is sleeved with a steel casing, holes are formed in the steel casing, a filler material is arranged between the steel casing and the anchor rod and filled in a space between the steel casing and the anchor rod after a prestress is applied to the anchor rod on a tensioning bench, and when the filler material is electrified, a structure of the filler material is destroyed;

sleeves are arranged at two ends of the steel casing, and grout plugs used for sealing the steel casing are arranged in openings of the sleeves.

2. The prefabricated tunnel prestressed anchor according to claim 1, wherein an outer diameter of the steel casing is less than a diameter of a borehole, an inner diameter of the steel casing is 20-25 mm greater than an outer diameter of the anchor rod, and a length of the steel casing is the same as a length of the prestressed section in a tensioned state.

3. The prefabricated tunnel prestressed anchor according to claim 1, wherein the steel casing is configured to be electrically conductive to conduct current to the filler material to destroy the structure of the filler material.

4. The prefabricated tunnel prestressed anchor according to claim 1, wherein a diameter of the holes is 5-15 mm, and a distance between every two adjacent said holes is 20-30 cm.

5. The prefabricated tunnel prestressed anchor according to claim 1, wherein a wall thickness of the sleeves is 6-10 mm, and each said sleeve comprises:

a threaded portion connected to the steel casing, wherein an inner diameter of the threaded portion matches an outer dimeter of the steel casing; and

a grout plug receiving portion having a space for receiving the corresponding grout plug.

6. The prefabricated tunnel prestressed anchor according to claim 5, wherein a wall thickness of the steel casing is 4-6 mm, threads are arranged at the two ends of the steel casing respectively, and the two ends of the steel casing are connected to the threaded portions by means of the threads.

7. The prefabricated tunnel prestressed anchor according to claim 1, wherein the grout plugs are made from an elastic material; middle portions of the grout plugs are protrusive to form spindle structures, an outer diameter of front and rear ends of the grout plugs is the same as an inner diameter of the sleeves, and an outer diameter of the protrusive middle portions is 3-4 mm greater than the inner diameter of the sleeves.

8. The prefabricated tunnel prestressed anchor according to claim 1, wherein the filler material is an organic material with fluidity, compressive strength after solidification, and bond strength to the anchor rod satisfying preset conditions.

9. A manufacturing method for the prefabricated tunnel prestressed anchor according to claim 1, comprising:

installing the steel casing at a set position on a tensioning bench, wherein an axis of the steel casing pipe is consistent with a tensioning axis and is kept horizontal, a length of the steel casing is the same as a length of the prestressed section in a tensioned state, and the holes in the steel casing are kept facing upwards; installing the sleeves at the two ends of the steel casing, and installing the grout plugs at ends of two sides of the sleeves;

allowing the anchor rod to penetrate through the steel casing, placing the prestressed section in the steel casing, tensioning the anchor until a set prestress is obtained, and injecting the filler material into a space between the steel casing and the anchor rod by means of the holes; and

when the filler material is solidified and satisfies a design strength requirement, relaxing two ends of the anchor rod, and before the prestressed anchor is placed in a warehouse to be further cured, detaching the grout plugs and sleeves from the two ends of the steel casing, such that the prefabricated tunnel prestressed anchor is obtained.

10. A use method for the prefabricated tunnel prestressed anchor according to claim 1, comprising:

installing the prefabricated tunnel prestressed anchor in a borehole, burying a wire in the steel casing, leading out of the wire, allowing the wire to penetrate through a grout plug together with a grouting pipe, connecting the grouting pipe to a reserved grouting hole, and injecting grout into a gap between the anchoring section and the borehole and a gap between the steel casing and the borehole; and

after the gaps are full of grout and the grout satisfied a design strength requirement, connecting the prestressed anchor to a power supply by means of the wire to destroy the structure of the filler material to eliminate a gripping effect of the filler material on the prestressed anchor so as to transfer a prestress to surrounding rock, such that prestressed anchor support requirements are satisfied.