A method for flexible modification of initial support profile of hard rock tunnel main hole and cross hole intersection

Abstract

The application provides a flexible modification method for the initial support profile of a hard rock tunnel main hole and cross hole intersection, and belongs to the technical field of hard rock tunnel construction, and comprises the following steps: S1, measuring point positions; S2, applying auxiliary anchor rods; S3, installing a steel bar mesh; S4, applying main anchor rods; S5, installing a ring-shaped main steel bar; S6, spraying concrete; and S7, concrete curing. The method adopts auxiliary anchor rods, a steel bar mesh, main anchor rods and a ring-shaped main steel bar to form a flexible support structure, the shape of the support structure is more in line with the design, the over-excavated part is modified, and the intersection forming quality is improved.

Description

Technical Field

[0001] This invention belongs to the technical field of hard rock tunnel construction, and specifically discloses a method for flexible trimming of the initial support profile at the intersection of the main tunnel and the cross tunnel in a hard rock tunnel. Background Technology

[0002] Depending on the surrounding rock grade, the lining structure design of the main tunnel and cross tunnels differs. Soft rock sections are designed with steel arch frames and shotcrete support, while hard rock sections are designed with only shotcrete support (partially using anchor bolts, wire mesh, and shotcrete, or only shotcrete). The shape of the intersection cannot be controlled by the steel arch frame because: Assuming the simplest cross tunnel outline design, the orthographic projection (along the cross tunnel axis) is circular (the upper half-circle is acceptable). Then: ① When the cross tunnel is orthogonal to the main tunnel, from a perspective perpendicular to the main tunnel axis, the intersection outline projection is an upper half-circle, the same as the orthographic projection of the cross tunnel, but the side projection of the intersection outline is the same as the main tunnel outline; ② When the cross tunnel intersects the main tunnel at any angle, from a perspective perpendicular to the main tunnel axis, the intersection outline projection is an upper half-ellipse, but the side projection of the intersection outline is the same as the main tunnel outline. Regardless of the angle at which the transverse tunnel and the main tunnel intersect, the outline of the intersection is not in the same plane. If a steel arch frame is to be installed at the intersection outline to control the shape of the intersection, the on-site fabrication of the steel arch frame is extremely difficult. Therefore, it is currently impossible to control the shape of the intersection by using a steel arch frame.

[0003] Because the intersection of the main tunnel and the cross tunnel is a stress concentration zone, the lining at the intersection is under spatial stress, the surrounding rock is disturbed multiple times, the surrounding rock pressure changes are complex, and the surrounding rock may have joints and fissures. As a result, the forming quality after the blasting at the intersection is poor, and there is over-excavation to varying degrees. At the same time, over-excavation will cause construction difficulties and quality risks to the subsequent shotcrete and waterproof layer construction. Summary of the Invention

[0004] This invention provides a flexible trimming method for the initial support profile at the intersection of the main tunnel and the cross tunnel in a hard rock tunnel, which addresses the problem of poor forming quality and varying degrees of over-excavation at the intersection of the main tunnel and the cross tunnel in a hard rock tunnel after blasting.

[0005] The above-mentioned method for flexibly modifying the initial support profile at the intersection of the main tunnel and the cross tunnel of a hard rock tunnel includes the following steps;

[0006] S1, Measurement point

[0007] Within the over-excavation boundary of the intersection of the main tunnel and the cross tunnel, i.e., the outline of the intersection on the side of the main tunnel and the side of the cross tunnel, point measurements are taken, the points are marked and numbered, and the over-excavation value of each marked point is calculated according to the corresponding main tunnel and cross tunnel data.

[0008] S2, Install auxiliary anchor bolts

[0009] Drill holes at the marked points on the side of the main tunnel and the side of the transverse tunnel along the outline of the intersection, with the drilling direction along the radial direction of the main tunnel and the radial direction of the transverse tunnel, respectively.

[0010] Auxiliary anchor rods are fabricated according to the over-excavation value of each marked point. The length of the auxiliary anchor rod is controlled by ensuring that its exposed end does not exceed the design shotcrete surface after installation. The auxiliary anchor rods are then installed in the borehole.

[0011] S3, Install steel mesh

[0012] Based on the over-excavation value of each marked point, on the body of each auxiliary anchor rod, from the designed shotcrete surface inward to the preset position, serve as the welding point for the installation of the reinforcing mesh. The reinforcing mesh is installed at the welding point, and the connection between the reinforcing mesh and the auxiliary anchor rod is made by spot welding. The part of the reinforcing mesh that exceeds the over-excavation boundary is cut off along the contact position between the reinforcing mesh and the surrounding rock. After the reinforcing mesh on the main tunnel side and the reinforcing mesh on the transverse tunnel side are installed, the line connecting the intersection is located on the outline of the intersection, and the excess part is cut off.

[0013] S4, Install the main anchor bolt

[0014] Drill holes into the surrounding rock surface at preset intervals along the intersection line connecting the main tunnel side steel mesh and the transverse tunnel side steel mesh, which is the outline of the intersection. Install the main anchor rods, with the main anchor rods exposed to the preset length of the steel mesh.

[0015] S5, Install circumferential main reinforcing bars

[0016] Along the outline of the intersection, starting from the arch foot on one side, the circumferential main steel bars and the exposed ends of the main anchor rods are welded to form the circumferential main skeleton;

[0017] S6, Shotcrete

[0018] According to the design, the sprayed concrete will eventually form the intersection shape with the designed outline.

[0019] S7, concrete curing.

[0020] In step S1, a total station is used to conduct point surveys, and the points are marked with paint.

[0021] In steps S2 and S4, both the auxiliary anchor bolts and the main anchor bolts are made of molten metal.

[0022] In step S3, the excess portion of the reinforcing mesh is cut using electric welding.

[0023] The present invention has the following beneficial effects:

[0024] 1. A flexible support structure is formed by auxiliary anchors, steel mesh, main anchors and circumferential main steel bars. The structure is simple, the materials are readily available, and the shape of the support structure fits the design better. Shotcrete is sprayed on the basis of the flexible support structure, which can fill and repair the over-excavated part, improve the forming quality of the intersection, and at the same time provide better construction conditions for the waterproof layer.

[0025] 2. No large processing equipment is required; installation can be completed on-site, and the operation is simple.

[0026] 3. It greatly reduces the difficulty of construction. Attached Figure Description

[0027] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 A flowchart illustrating the process of flexible trimming of the initial support profile at the intersection of the main tunnel and the cross tunnel in a hard rock tunnel.

[0029] Figure 2 Plan view of the intersection of the main tunnel and the cross tunnel (taking the lower left corner as an example to illustrate the over-excavation shape and the shape after trimming);

[0030] Figure 3 Elevation layout of the intersection of the main tunnel and the transverse tunnel;

[0031] Figure 4 A partial layout of the marked points at the intersection (the view is a plan view unfolded along the intersection outline on the main tunnel side and the cross tunnel side);

[0032] Figure 5 A partial layout diagram of the anchor bolts at the intersection (the view is a plan view unfolded along the outline of the intersection on the main tunnel side and the transverse tunnel side);

[0033] Figure 6 This is a partial layout diagram of the steel mesh at the intersection (the view is a plan view unfolded along the outline of the intersection on the side of the main opening and the side of the transverse opening).

[0034] Figure 7 Partial layout of the main anchor bolts at the intersection (the view is a plan view unfolded along the outline of the intersection on the side of the main tunnel and the side of the transverse tunnel);

[0035] Figure 8 This is a partial layout of the circumferential main reinforcement at the intersection (the view is a plan view unfolded along the outline of the intersection on the side of the main opening and the side of the transverse opening).

[0036] In the diagram: 1-Auxiliary anchor bolt; 2-Reinforcing mesh; 3-Main anchor bolt; 4-Circumferential main reinforcement; 101-Main tunnel; 102-Transverse tunnel; 103-Intersection outline; 104-Main tunnel side; 105-Transverse tunnel side; 106-Over-excavation boundary; 107-Marker point; 108-Main tunnel centerline; 109-Transverse tunnel centerline; 110-Shotcrete; 111-Arch foot; 112-Ground surface. Detailed Implementation

[0037] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] This embodiment takes a hard rock tunnel as an example to provide specific steps and parameters for a flexible trimming method of the initial support profile at the intersection of the main tunnel and the cross tunnel of a hard rock tunnel.

[0039] S1, Measurement point

[0040] Using a total station, measurements were taken around the intersection of the main tunnel 101 and the transverse tunnel 102, specifically within the over-excavation boundary 106 of the intersection outline 103 on the side of the main tunnel 104 and the side of the transverse tunnel 105 (i.e., between the over-excavation boundary 106 of the main tunnel side 104 and the intersection outline 103, and between the over-excavation boundary 106 of the transverse tunnel side 105 and the intersection outline 103). Measurements were taken in a staggered pattern of 80×80cm, and the layout was adjusted according to the actual site conditions to ensure that the points were within the over-excavation boundary 106. The points were marked with paint and numbered, and the over-excavation value of each marked point 107 was calculated based on the corresponding data of the main tunnel 101 and the transverse tunnel 102, providing a basis for subsequent construction.

[0041] S2, Install auxiliary anchor bolts

[0042] At the intersection outline 103, on the side 104 near the main tunnel and on the side 105 near the transverse tunnel, drill holes according to the marked point 107. The drilling direction is along the radial direction of the main tunnel 101 and the radial direction of the transverse tunnel 102, respectively, and the hole depth is 50-100cm.

[0043] According to the over-excavation value of 107 for each marked point, auxiliary anchor bolt 1 is manufactured. The anchor bolt type is a cartridge anchor bolt, and the bolt body is made of... For steel bar processing, the length is controlled so that the exposed end after installation does not exceed the design sprayed concrete surface. Auxiliary anchor rod 1 is installed in the drilled hole.

[0044] S3, Install steel mesh

[0045] Based on the over-excavation value of each marker point 107, on the body of each auxiliary anchor rod 1, 8cm inward from the designed shotcrete surface, a welding point for the installation of the reinforcing mesh 2 is marked with spray paint. The reinforcing mesh 2 is installed on the welding point. The reinforcing mesh 2 uses φ6 steel mesh with a mesh spacing of 25×25cm. The reinforcing mesh 2 is connected to the auxiliary anchor rod 1 by spot welding. The excess part of the reinforcing mesh 2 beyond the over-excavation boundary 106 is cut off by electric welding at the contact position between the reinforcing mesh 2 and the surrounding rock. The line connecting the intersection of the reinforcing mesh on the main tunnel side and the reinforcing mesh on the transverse tunnel side after installation is located on the outline line 103 of the intersection, and the excess part is cut off.

[0046] S4, Install the main anchor bolt

[0047] Drill holes 50-150cm deep into the surrounding rock surface at 80cm intervals, around the intersection line connecting the main tunnel side reinforcement mesh and the transverse tunnel side reinforcement mesh (i.e., the intersection outline line 103). Install main anchor bolts 3; the anchor bolt type is explosive cartridge anchor bolt, and the bolt body is made of... Rebar processing: 5cm of exposed rebar mesh on the main anchor rod 3.

[0048] S5, Install circumferential main reinforcing bars

[0049] Along the intersection outline 103, starting from the single arch foot 111, the circumferential main steel bar 4 and the exposed end of the main anchor rod 3 are welded to form the circumferential main skeleton.

[0050] S6, Shotcrete

[0051] Using a flexible structure consisting of auxiliary anchor bolts 1, steel mesh 2, main anchor bolts 3 and circumferential main steel bars 4 as the skeleton, the sprayed concrete is used to finally form the design outline of the intersection shape. The surface of the intersection is the design sprayed concrete surface mentioned above.

[0052] Step S7, Concrete Curing

[0053] Two hours after the final setting of the shotcrete, a reasonable curing method should be selected based on the site conditions, and the curing time should not be less than 14 days.

[0054] The above-mentioned flexible trimming method for the initial support outline of the main tunnel cross passage intersection in hard rock tunnels solves the problem of poor forming quality of the initial support outline at the tunnel cross passage intersection. It adopts a flexible structure composed of auxiliary anchor rod 1, steel mesh 2, main anchor rod 3 and circumferential main steel bar 4. The trimming of the over-excavated part of the intersection can be completed on the construction site, with good forming quality, providing better construction conditions for the waterproof layer construction, and has extremely wide promotion value.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for flexibly adjusting the initial support profile at the intersection of the main tunnel and the cross tunnel in a hard rock tunnel, characterized in that, Includes the following steps; S1, Measurement point Within the over-excavation boundary of the intersection of the main tunnel and the cross tunnel, i.e., the outline of the intersection on the side of the main tunnel and the side of the cross tunnel, a total station is used to conduct point measurements, the points are marked with paint and numbered, and the over-excavation value of each marked point is calculated according to the corresponding main tunnel and cross tunnel data. S2, Install auxiliary anchor bolts Drill holes at the marked points on the side of the main tunnel and the side of the transverse tunnel along the outline of the intersection, with the drilling direction along the radial direction of the main tunnel and the radial direction of the transverse tunnel, respectively. Auxiliary anchor bolts are fabricated according to the over-excavation value of each marked point. The auxiliary anchor bolts are made of molten metal. The length of the auxiliary anchor bolt is controlled so that its exposed end does not exceed the surface of the designed shotcrete after installation. The auxiliary anchor bolts are installed in the borehole. S3, Install steel mesh Based on the over-excavation value of each marked point, on the body of each auxiliary anchor rod, from the designed shotcrete surface inward to the preset position, serve as the welding point for the installation of the reinforcing mesh. The reinforcing mesh is installed at the welding point, and the connection between the reinforcing mesh and the auxiliary anchor rod is made by spot welding. The part of the reinforcing mesh that exceeds the over-excavation boundary is cut off along the contact position between the reinforcing mesh and the surrounding rock. After the reinforcing mesh on the main tunnel side and the reinforcing mesh on the transverse tunnel side are installed, the line connecting the intersection is located on the outline of the intersection, and the excess part is cut off. S4, Install the main anchor bolt Drill holes into the surrounding rock surface at preset intervals along the intersection line connecting the main tunnel side steel mesh and the transverse tunnel side steel mesh, which is the outline of the intersection. Install the main anchor rods. The main anchor rods are made of explosive cartridges, and the main anchor rods are exposed to the steel mesh for a preset length. S5, Install circumferential main reinforcing bars Along the outline of the intersection, starting from the arch foot on one side, the circumferential main steel bars and the exposed ends of the main anchor rods are welded to form the circumferential main skeleton; S6, Shotcrete According to the design, the sprayed concrete will eventually form the intersection shape with the designed outline.

2. The method for flexibly adjusting the initial support profile at the intersection of the main tunnel and the transverse tunnel of a hard rock tunnel according to claim 1, characterized in that, In step S3, the excess portion of the steel mesh is cut using electric welding.

3. The method for flexibly adjusting the initial support profile at the intersection of the main tunnel and the cross tunnel of a hard rock tunnel according to claim 2, characterized in that, It also includes step S7, concrete curing.

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