One-time support for excavation of tunnel body

Abstract

The utility model discloses a one-time support for tunnel shaft excavation, and belongs to the technical field of water conveyance engineering. The supporting structure comprises an advance anchor rod, a steel grating, a connector plate, a longitudinal connecting steel bar and a foot-lock bolt. The advance anchor rods are obliquely inserted into the tunnel vault within the range of 120-180 degrees, the annular distance is 0.4 m, the longitudinal distance is 3 m, and the lap joint length is larger than or equal to 1 m; the steel grating is tightly attached to an excavation face, the connector plates are welded in an alternating and staggered mode, the sleeve is welded to the steel grating and connected with the longitudinal steel bars to form an orthogonal grid structure, and concrete is sprayed for full coverage. And two feet-lock bolts are arranged on each truss of steel grating at the arch feet. According to the structure, the supporting strength and stability are remarkably improved, and the construction safety and the surrounding rock stress condition are guaranteed through advance anchor rod grid grouting, surrounding rock deformation restraining, feet-lock bolts for enhancing the anti-sliding capacity, uniform load distribution of the steel grids and the longitudinal steel bars and optimized welding of the connector plates for reducing stress concentration.

Description

Technical Field

[0001] This utility model belongs to the field of water conveyance engineering technology, specifically relating to a primary support system for tunnel excavation that is structurally stable, highly versatile, and provides excellent support. Background Technology

[0002] During the excavation of water conveyance tunnels, local instability, insufficient overall strength of the surrounding rock, localized plastic deformation, or strong groundwater activity are common problems. Without proper support, these conditions can lead to collapses or plastic deformation failures. These geological conditions fall between Class III and Class IV surrounding rock and are referred to as Class III2 surrounding rock. Inadequate primary support measures during tunnel excavation can easily cause loosening of the surrounding rock, collapses, or even overall instability, seriously threatening construction safety and project progress. Therefore, researching reasonable and efficient primary support methods for tunnel excavation under Class III2 surrounding rock conditions has become a critical technical issue that urgently needs to be addressed.

[0003] As a core component of tunnel excavation, the design rationality of primary support directly affects the stability of the surrounding rock, construction efficiency, and project cost. Currently, support technologies such as steel grating and advanced anchor bolts are widely used in practical engineering, but their applicability and optimized design under Class III2 surrounding rock conditions still require further research. Utility Model Content

[0004] This invention, based on Class III2 surrounding rock and combined with engineering practice, provides a primary support method for tunnel excavation. The purpose is to provide technical support for tunnel excavation under similar geological conditions and improve the safety and economy of tunnel construction.

[0005] A primary support system for tunnel excavation is characterized by pre-anchor bolts, steel grating, joint plates, longitudinal connecting steel bars, and anchor bolts. Several pre-anchor bolts are inserted obliquely into the tunnel arch at an outward angle of 10°~15° within a range of 120°-180°, forming a grid-like layout. The circumferential spacing of the pre-anchor bolts is 0.4m, the longitudinal spacing is 3m, and the overlap length between the first and last pre-anchor bolts is not less than 1m. Grouting is performed within the formed pre-anchor bolt grid. Steel grating is arranged close to the tunnel excavation face, with spacing between steel gratings. The steel gratings are 1m apart. The joint plates are welded together at the ends of the steel gratings. The joint plates are arranged alternately and staggered. The number of joint plates in the same section does not exceed 50% of the number of steel gratings. Holes are evenly opened on each steel grating and sleeves are inserted. The sleeves are welded to the steel gratings at the connection. Longitudinal connecting bars are welded on the opposite sleeves. Several longitudinal connecting bars are perpendicular to each other with the steel gratings to form a grid structure. Shotcrete completely covers the steel gratings and longitudinal connecting bars. Two anchor bolts are installed at the tunnel arch foot of each steel grating.

[0006] Furthermore, the advanced anchor rod is a C25 threaded steel bar with a diameter of 25mm and a length of 4.5m.

[0007] Furthermore, the single-sided weld of the joint plate shall be no less than 10d, and the double-sided weld shall be no less than 5d.

[0008] Furthermore, the length of the anchor bolt is 4.5m.

[0009] The beneficial effects of this utility model are as follows: This support is suitable for Class III2 surrounding rock with poor local stability, insufficient overall strength of the surrounding rock, local plastic deformation, or strong groundwater activity, where failure to support may lead to collapse or plastic deformation failure. The advanced anchor bolts, arranged in a grid pattern and grouted, effectively reinforce the arch-top surrounding rock, suppress plastic deformation, and prevent local collapse. Locking anchor bolts are installed at the arch foot to enhance the tunnel bottom's anti-slip capacity and prevent overall instability. The steel grid and longitudinal connecting steel bars form a grid structure, evenly distributing the load and improving support strength. Alternating staggered welding of joint plates reduces stress concentration, ensures connection reliability, and extends the support's service life. This primary support structure is stable, versatile, flexible in construction, and provides excellent support effects, effectively improving the stability of primary support during tunnel excavation, significantly improving the stress conditions of the surrounding rock, and ensuring safety and reliability during the excavation stage. It is a type of primary support for the excavation of water conveyance tunnels in Class III2 surrounding rock sections where the surrounding rock strength is insufficient, plastic deformation is easily generated, or groundwater activity is strong. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the structural elevation of this utility model.

[0011] Figure 2 This is a longitudinal cross-sectional view of the structure of this utility model.

[0012] Figure 3 This is a schematic diagram of the longitudinal connection of the steel grating.

[0013] Among them: 1-steel grating, 2-advanced anchor rod, 3-longitudinal connecting steel bar, 4-joint plate, 5-sleeve, 6-locking anchor rod. Detailed Implementation

[0014] Example 1: A primary support system for tunnel excavation includes pre-anchor bolts 2, steel grating 1, joint plates 4, longitudinal connecting steel bars 3, and anchor bolts 6. The pre-anchor bolts 2 are C25 threaded steel bars with a diameter of 25mm and a length of 4.5m. Several pre-anchor bolts 2 are inserted obliquely into the tunnel arch within a range of 120°-180° at an outward insertion angle of 10°~15°, forming a grid-like layout. The circumferential spacing of the pre-anchor bolts 2 is 0.4m, and the longitudinal spacing is 3m. The overlap length between the first and last pre-anchor bolts 2 is not less than 1m. Grouting is performed within the grid formed by the pre-anchor bolts 2. Steel grating 1 is arranged close to the tunnel excavation face, with a spacing of 1m between steel gratings 1. The first and last joints of the steel grating 1 are connected by welding with joint plates 4. The joint plates 4 are arranged alternately and staggered. The number of joint plates 4 in the same cross section does not exceed 50% of the number of steel gratings 1. The single-sided weld of the joint plate 4 is not less than 10d, and the double-sided weld is not less than 5d. Each steel grating 1 has evenly spaced holes and a sleeve 5 is inserted. The sleeve 5 is welded to the steel grating 1 at the connection point. Longitudinal connecting steel bars 3 are welded to the opposite sleeve 5. Several longitudinal connecting steel bars 3 are perpendicularly connected to the steel grating 1 to form a grid structure. Shotcrete completely covers the steel grating 1 and the longitudinal connecting steel bars 3. Two anchor bolts 6 are installed at the tunnel arch foot of each steel grating 1. The length of the anchor bolts 6 is 4.5m.

[0015] During tunnel excavation, the next cycle of excavation can only begin after a section of support has been installed and completely covered with shotcrete to form the support.

Claims

1. A one-time support for the excavation of a tunnel body, characterized in that The advanced anchor rod, the steel grid, the joint plate, the longitudinal connecting steel bar and the locking foot anchor rod, several advanced anchor rods are inserted into the range of 120°-180° of the tunnel vault at an outward insertion angle of 10°-15° to form a grid layout, the circumferential spacing of the advanced anchor rod is 0.4 m, the longitudinal spacing is 3 m, the overlapping length between the advanced anchor rods connected at the head and tail is not less than 1 m, and grouting is carried out in the formed advanced anchor rod grid; the steel grid is arranged close to the tunnel excavation face, the interval distance of the steel grid is 1 m, the joint plate is welded and connected at the head and tail of the steel grid, the joint plates are arranged alternately staggered, the number of the joint plates in the same section is not more than 50% of the number of the steel grids, each steel grid is uniformly holed and inserted into the sleeve, the connection between the sleeve and the steel grid is welded and fixed, the longitudinal connecting steel bars are welded on the opposite sleeves, and several longitudinal connecting steel bars are connected with the steel grid to form a grid structure, and the sprayed concrete completely covers the steel grid and the longitudinal connecting steel bars; two locking foot anchor rods are arranged at the tunnel arch foot of each steel grid.

2. A primary support for the excavation of a tunnel bore according to claim 1, characterised in that The advanced anchor rod is a C25 threaded steel with a diameter of 25 mm and a length of 4.5 m.

3. A primary support for a tunnel excavation according to claim 1, wherein The joint plate is welded on one side by not less than 10d or on both sides by not less than 5d.

4. A primary support for the excavation of a tunnel bore according to claim 1, wherein The locking foot anchor rod has a length of 4.5 m.

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