Straight wall ultra-small clear distance tunnel structure and construction method

Abstract

The invention provides a straight wall ultra-small clear distance tunnel structure and a construction method, and relates to the technical field of tunnel engineering.The straight wall ultra-small clear distance tunnel structure comprises a first hole and a second hole, a middle rock pillar is arranged between the first hole and the second hole, and a plurality of opposite-pulling pre-stressed anchor rods are arranged on the middle rock pillar in the length direction of the first hole and the length direction of the second hole; the opposite-pulling pre-stressed anchor rod penetrates through the middle rock pillar and is of a hollow structure, a plurality of grouting holes are formed in a rod body in a staggered mode, anchoring ends are arranged at the two ends of the opposite-pulling pre-stressed anchor rod and comprise nuts, the nuts are in threaded connection with the opposite-pulling pre-stressed anchor rod, and anchor bearing plates are arranged on the sides, close to the middle rock pillar, of the nuts. A stop-grouting plug is arranged on the side, close to the middle rock pillar, of the anchor bearing plate. Compared with the prior art, the thickness of the middle rock pillar is increased, the construction safety is improved, the construction sequence is optimized to be parallel construction of the left hole and the right hole, the construction efficiency is improved, the construction period is shortened, and material cost and cost are saved.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel engineering, in particular to a straight-wall ultra-small clearance tunnel structure and a construction method. Background Art

[0002] In the design of the entrance and exit of the tunnel connected to the super-large bridge, in order to ensure the smooth line shape, a bifurcated tunnel is usually set at the entrance section. The line spacing of the bifurcated tunnel gradually transitions from wide to narrow. When the line spacing is large, it can be set as a separated tunnel structure. As the line spacing decreases, it needs to be converted into a curved wall small clearance tunnel structure. A middle rock column will be formed between the successively excavated tunnels. In order to ensure the safety of construction, reinforcement measures such as grouting must be taken to enhance the stability of the middle rock column and ensure the smoothness and safety of the construction process. When the line spacing continues to shrink to the point where the curved wall tunnel structure can no longer be used, a straight middle wall arch tunnel is used instead. The straight middle wall arch tunnel is usually constructed by the three-guide tunnel method, but the three-guide tunnel method has several significant defects. First, this method causes the main tunnel to enter the site relatively late, and the overall construction process is cumbersome and complicated, which prolongs the project period. Secondly, the temporary support structure built during the construction of the middle guide tunnel needs to be dismantled in the subsequent stage. This process not only increases the use of materials, but also significantly increases the construction cost. Finally, for the straight-wall continuous-arch tunnel structure, the connection between the top of the partition wall and the main tunnel lining is prone to become a potential risk point for water leakage due to the existence of construction joints, and the construction quality of this area is difficult to meet high standards, thus affecting the overall project quality. Summary of the invention

[0003] The present invention provides a straight wall ultra-small clearance tunnel structure and a construction method, aiming to overcome the difficulties faced by curved wall small clearance tunnels and straight middle wall arch tunnels under narrow line spacing conditions, including the disadvantages of great construction difficulty, increased safety risks, high cost and difficult quality control.

[0004] The present invention provides the following technical solutions to achieve the above objectives: A straight wall ultra-small clearance tunnel structure comprises a leading hole, one side of the leading hole is a trailing hole, a middle rock column is arranged between the leading hole and the trailing hole, the leading hole and the trailing hole are straight walls near the middle rock column, ordinary system anchor rods and extended system anchor rods are arranged at intervals around the excavation faces of the leading hole and the trailing hole; a plurality of tension prestressed anchor rods are arranged on the middle rock column along the length direction of the leading hole and the trailing hole, the tension prestressed anchor rods penetrate the middle rock column, the tension prestressed anchor rods are hollow structures and a plurality of grouting holes are staggered on the rod body, anchoring ends are arranged at both ends of the tension prestressed anchor rods, the anchoring ends comprise nuts, the nuts are threadedly connected to the tension prestressed anchor rods, an anchor pad is arranged on the side of the nut near the middle rock column, and a grouting stopper is arranged on the side of the anchor pad near the middle rock column.

[0005] Furthermore, the diameter of the grouting holes is 8 mm, and the spacing between the holes is 15 to 20 cm.

[0006] Furthermore, the length of the tension prestressed anchor rod is greater than the thickness of the middle rock column by 20 to 30 cm.

[0007] Furthermore, locking foot anchor rods are provided at the arch foot positions on both sides of the steel arch frame.

[0008] The aforementioned construction method of the straight wall ultra-small clearance tunnel structure comprises the following steps: S1. First, dig a pilot hole and install common system anchor rods, extended system anchor rods and steel arch frames; S2. Drill holes on the side of the pilot hole close to the middle rock column, install tension prestressed anchor rods in the holes, and install nuts, anchor pads and grouting plugs on one side of the pilot hole. After installation, perform grouting operations; S3. After the slurry solidifies and hardens, tighten the nuts to tighten the tension prestressed anchor rods, and carry out the secondary lining structure construction of the pilot hole; S4. After the secondary lining structure of the pilot tunnel reaches the designed strength, the rear tunnel is excavated and the installation of ordinary system anchor rods, extended system anchor rods and steel arch frames is carried out; S5. Break the end concrete of the tension prestressed anchor rod on the rear tunnel side and install nuts, anchor pads and grout stoppers; S6. Perform grouting work on the tension prestressed anchor rods on the rear tunnel side. After the grout reaches the designed strength, tighten the nuts to apply prestress, and then carry out the secondary lining structure construction of the rear tunnel; S7, repeat steps S1 to S6 until exiting the hole.

[0009] Furthermore, the drilling operation in S2 is arranged in a plum blossom shape, the vertical spacing of the drilling holes is 1m, and the longitudinal spacing of the drilling holes is consistent with the arrangement spacing of the steel arch frame.

[0010] Furthermore, in the excavation operation of the rear tunnel in S4, controlled blasting is first used to excavate away from the middle rock pillar side, and then mechanical cold excavation is used to excavate close to the middle rock pillar side.

[0011] Furthermore, in the excavation operation of the back tunnel in S4, controlled blasting is first used to excavate away from the middle rock column side, and then mechanical cold excavation is used to excavate close to the middle rock column side. When the excavation is about 30 cm close to the middle rock column, a steel bar detector is used to determine the position of the tension prestressed anchor rod, and manual excavation is used. Compared with the prior art, the present invention has the following beneficial effects: Compared with the curved wall small clearance tunnel, the present invention significantly increases the thickness of the middle rock column by designing the tunnel as a straight wall near the surveying baseline, thereby improving the safety during the construction process. Compared with the straight middle wall arch tunnel, the present invention eliminates the setting of the middle guide hole and the middle partition wall, optimizes the construction sequence, and realizes the parallel construction of the left and right holes. This not only improves the construction efficiency, but also shortens the overall construction period, while effectively reducing the material cost and overall cost. In addition, the drainage system of the first and second holes and the independent ring of the secondary lining effectively solve the construction problems such as easy seepage, and further improve the construction quality of the project. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below only relate to some embodiments of the present invention, and for those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative labor.

[0013] Figure 1 It is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the tension prestressed anchor structure of the present invention; Figure 3 This is a schematic diagram of the locking foot anchor structure of the present invention; Figure numerals: 1-preliminary tunnel; 2-rear tunnel; 3-middle rock column; 4-steel arch frame; 5-second lining structure; 6-tension prestressed anchor rod; 7-nut; 8-anchor plate; 9-grouting plug; A-locking anchor rod. DETAILED DESCRIPTION

[0014] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0015] It should be noted that in the present invention: the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or apparatuses; the directions or positional relationships indicated by the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inside", "outside", "middle", "vertical", "horizontal", "lateral", "longitudinal" and the like are based on the directions or positional relationships shown in the drawings. These The terms are mainly used to better describe the present invention and its embodiments, and are not used to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation; the terms "first", "second", etc. are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence; the terms "install", "set", "provided with", "connected", "connected", "sleeved", etc. should be understood in a broad sense; for example, it can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection, or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or it can be an internal connection between two devices, elements or components. In addition, some terms can be used to express other meanings in addition to indicating orientation or positional relationships. For example, the term "on" may also be used to express a certain dependency or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in the present invention can be understood according to specific circumstances.

[0016] Embodiment. A straight wall ultra-small clearance tunnel structure and construction method, the structure reference Figures 1 to 3 , including a leading hole 1, one side of the leading hole 1 is a rear hole 2, a middle rock column 3 is arranged between the leading hole 1 and the rear hole 2, and the leading hole 1 and the rear hole 2 are straight walls near the middle rock column 3; ordinary system anchor rods and extended system anchor rods are arranged at intervals around the excavation surface of the leading hole 1 and the rear hole 2, and the extended system anchor rods are arranged near the center of the two holes; a plurality of tension prestressed anchor rods 6 are arranged on the middle rock column 3 along the length direction of the leading hole 1 and the rear hole 2, the tension prestressed anchor rods 6 are arranged through the middle rock column 3, the tension prestressed anchor rods 6 are hollow structures and a plurality of grouting holes are staggered on the rod body, anchoring ends are arranged at both ends of the tension prestressed anchor rod 6, the anchoring ends include nuts 7, the nuts 7 are threadedly connected to the tension prestressed anchor 6, an anchor pad 8 is arranged on the side of the nut 7 close to the middle rock column 3, and a grouting stopper 9 is arranged on the side of the anchor pad 8 close to the middle rock column 3. The grouting holes have a diameter of 8 mm and a spacing of 15 to 20 cm between the holes. The grouting holes are provided to facilitate the diffusion of slurry in the surrounding rock mass during the grouting operation.

[0017] The length of the tension prestressed anchor rod 6 is 20 to 30 cm greater than the thickness of the middle rock column 3. By setting the length of the tension prestressed anchor rod 6 to be greater than the thickness of the middle rock column 3, it is convenient to install nuts 7, anchor pads 8 and grouting plugs 9 at both ends of the tension prestressed anchor rod 6, and at the same time facilitate grouting operations.

[0018] The arch foot positions on both sides of the steel arch frame 4 are provided with locking foot anchor rods A. The locking foot anchor rods A are provided to improve the bearing capacity and reduce the deformation of the tunnel excavation surface.

[0019] The construction method of the straight wall ultra-small clearance tunnel structure comprises the following steps: S1, first excavate the pilot hole 1, and install the common system anchor rods, extended system anchor rods and steel arch frame 4; S2. Drill holes on the side of the pilot hole 1 close to the middle rock column 3, install the tension prestressed anchor rod 6 in the hole, and install the nut 7, anchor plate 8 and grout stopper 9 on one side of the pilot hole 1. After the installation is completed, perform grouting. When drilling, the hole depth is greater than the thickness of the middle rock column 3 by 20 cm, and the borehole diameter is slightly greater than the diameter of the tension prestressed anchor rod 6, leaving enough installation space for installing the tension prestressed anchor rod 6. S3, after the slurry solidifies and hardens, tighten the nut 7 to tighten the tension prestressed anchor rod 6, and carry out the construction of the secondary lining structure 5 of the pilot hole 1; S4, after the secondary lining structure 5 of the leading tunnel 1 reaches the designed strength, the trailing tunnel 2 is excavated, and the ordinary system anchor rods, the extended system anchor rods and the steel arch frame 4 are installed; the leading tunnel 1 and the trailing tunnel 2 are staggered and constructed in parallel, and the leading tunnel 1 is ahead of the trailing tunnel 2 by a certain distance to avoid the surrounding rock instability caused by the close distance between the leading tunnel 1 and the trailing tunnel 2; S5, breaking the end concrete of the tension prestressed anchor rod 6 on the side of the rear tunnel 2, and installing the nut 7, anchor plate 8 and grout stopper 9; S6. Perform grouting operation on the tension prestressed anchor rod 6 on the side of the rear tunnel 2. After the grout reaches the designed strength, tighten the nut 7 to apply prestress, and then construct the secondary lining structure 5 of the rear tunnel 2; apply prestress to the middle rock column 3 by tightening the nut 7, reinforce the middle rock column 3, and improve the strength of the middle rock column 3.

[0020] S7, repeat steps S1 to S6 until exiting the hole.

[0021] The drilling operation in S2 is arranged in a plum blossom shape, the vertical spacing of the drilling holes is 1m, and the longitudinal spacing of the drilling holes is consistent with the arrangement spacing of the steel arch frame 4.

[0022] In the excavation operation of the rear tunnel 2 in S4, controlled blasting is first used to excavate the side away from the middle rock pillar 3, and then mechanical cold excavation is used to excavate the side close to the middle rock pillar 3; the excavation operation is carried out in a combination of controlled blasting and mechanical cold excavation to reduce the construction interference caused by the close distance between the first and second tunnels; when the excavation is about 30 cm close to the middle rock pillar 3, a steel bar detector is used to determine the position of the tension prestressed anchor rods 6, and manual excavation operations are performed to avoid damaging the constructed tension prestressed anchor rods.

[0023] Obviously, the above is only a part of the embodiments of the present invention, not all of the embodiments. The above embodiments are not intended to limit the present invention. For those skilled in the art, the present invention may have various changes and variations. Any combination, modification, equivalent replacement, improvement and all other embodiments that can be made by those of ordinary skill in the art within the spirit and principle of the present invention should be within the protection scope of the present invention.

Claims

1. A straight wall ultra-small clearance tunnel structure, comprising a leading tunnel (1), one side of the leading tunnel (1) being a trailing tunnel (2), a middle rock pillar (3) being arranged between the leading tunnel (1) and the trailing tunnel (2), and the sides of the leading tunnel (1) and the trailing tunnel (2) close to the middle rock pillar (3) being straight walls, characterized in that: Ordinary system anchor rods and extended system anchor rods are arranged at intervals around the excavation surface of the advance hole (1) and the rear hole (2); a plurality of tension prestressed anchor rods (6) are arranged on the middle rock column (3) along the length direction of the advance hole (1) and the rear hole (2); the tension prestressed anchor rods (6) penetrate the middle rock column (3); the tension prestressed anchor rods (6) are hollow structures and a plurality of grouting holes are staggered on the rod body; anchoring ends are arranged at both ends of the tension prestressed anchor rod (6); the anchoring ends include nuts (7); the nuts (7) are threadedly connected to the tension prestressed anchor rod (6); an anchor pad (8) is arranged on the side of the nut (7) close to the middle rock column (3); and a grouting stopper (9) is arranged on the side of the anchor pad (8) close to the middle rock column (3).

2. The straight wall ultra-small clearance tunnel structure according to claim 1 is characterized in that: The diameter of the grouting holes is 8 mm, and the spacing between the grouting holes is 15 to 20 cm.

3. The straight wall ultra-small clearance tunnel structure according to claim 1 is characterized in that: The length of the tension prestressed anchor rod (6) is 20 to 30 cm greater than the thickness of the middle rock column (3).

4. The straight wall ultra-small clearance tunnel structure according to claim 1 is characterized in that: Foot locking anchor rods are provided at the arch foot positions on both sides of the steel arch frame (4).

5. The construction method of the straight wall ultra-small clearance tunnel structure according to claim 1 is characterized by: The following steps are involved: S1. First, a pilot hole (1) is excavated, and ordinary system anchor rods, extended system anchor rods and steel arch frames (4) are installed; S2, drilling a hole on the side of the pilot hole (1) close to the middle rock column, installing a tension prestressed anchor rod (6) in the hole, and installing a nut (7), an anchor plate (8) and a grout stopper (9) on one side of the pilot hole (1), and performing grouting after the installation is completed; S3, after the slurry solidifies and hardens, tighten the nut (7) to tighten the tension prestressed anchor rod (6), and carry out the construction of the secondary lining structure (5) of the pilot hole (1); S4, after the secondary lining structure (5) of the advance tunnel (1) reaches the designed strength, the rear tunnel (2) is excavated, and the ordinary system anchor rods, the extended system anchor rods and the steel arch frame (4) are installed; S5, breaking the end concrete of the tension prestressed anchor rod (6) on the side of the rear tunnel (2), and installing the nut (7), anchor pad (8) and grout stopper (9); S6, performing grouting operations on the tension prestressed anchor rods (6) on the side of the rear tunnel (2), tightening the nuts (7) to apply prestress after the grout reaches the designed strength, and then constructing the secondary lining structure (5) of the rear tunnel (2); S7, repeat steps S1 to S6 until exiting the hole.

6. The construction method according to claim 5, characterized in that: The drilling operation in S2 is arranged in a plum blossom shape, the vertical spacing of the drilling holes is 1 m, and the longitudinal spacing of the drilling holes is consistent with the arrangement spacing of the steel arch frame (4).

7. The construction method according to claim 5, characterized in that: The excavation operation of the rear tunnel (2) in the S4 is first performed by using controlled blasting to excavate the side away from the middle rock column (3), and then by using mechanical cold excavation to excavate the side close to the middle rock column (3). When the excavation is about 30 cm close to the middle rock column (3), a steel bar detector is used to determine the position of the tension prestressed anchor rod (6), and manual excavation is performed.

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