A method for layered construction of a primary support structure

Abstract

The application belongs to the technical field of drilling and blasting construction, and specifically provides a layered construction method of a tunnel primary support structure, comprising the following steps: S1, drilling and blasting holes on the working face according to the designed excavation footage; S2, constructing the first layer of primary support on the tunnel wall formed by blasting, and reserving the space for the second layer of primary support between the first layer of primary support and the tunnel design contour; S3, drilling and blasting holes on the working face for the next round of blasting by using the space for the second layer of primary support; S4, simultaneously constructing the second layer of primary support of the previous round and the first layer of primary support of the current round, and reserving the space for the second layer of primary support between the first layer of primary support of the current round and the tunnel design contour; and S5, repeating steps S3-S4 to perform the next round of operation. The method integrates overbreak and primary support, uses the overbreak space as the primary support construction space, reduces the overbreak amount, and solves the problems of the operation space required for drilling and blasting surrounding holes and the safety hazards of the empty face of the working face.

Description

Technical Field

[0001] The invention belongs to the technical field of drilling and blasting construction, and particularly relates to a layered construction method for an initial support structure. Background Art

[0002] Tunnel engineering refers to the excavation and lining of underground tunnels for infrastructure development, such as transportation, water conservancy, and energy. Tunnel excavation typically utilizes smooth blasting technology, with blastholes primarily drilled using drilling rigs and pneumatic rock drills with air legs. To ensure the stability of the tunnel surrounding rock and a smooth excavation surface after blasting, peripheral holes are typically evenly spaced along the designed contour. Drilling machinery requires a certain operating distance for peripheral holes. Because under-excavation is not permitted, the entire tunnel must be pre-excavated to allow for drilling machinery operating space. Furthermore, the holes must be drilled outward at an angle, resulting in excessively large interpolation angles for the peripheral holes, often causing their bottoms to fall outside the designed excavation contour, further increasing the amount of over-excavation after blasting. During support, the initial support shotcrete includes both shotcrete within the designed thickness range and shotcrete for the over-excavation. Overfilling requires the same amount of concrete as the over-excavation. This not only increases project costs but also extends the construction period, putting pressure on the project schedule.

[0003] In addition, the steel frame is set within the design thickness of the initial support. In principle, the initial support is required to be as close to the tunnel face as possible, but there is no regulation on the air distance between the initial support and the tunnel face. In order to construct blast holes around the tunnel face, the air distance between the tunnel face and the tunnel face is basically more than 0.5m. A small air distance can easily lead to over-excavation exceeding the over-excavation allowed by the design. A large air distance and a small over-excavation, but there is no support construction within the air distance range of the tunnel face, which poses a safety hazard.

[0004] To address the safety risks posed by large overbreak and the large distance between the tunnel and the open face, existing technologies employ a method of drilling holes one cycle in advance to minimize the distance between the tunnel and the open face. However, this approach, similar to many double-row advance peripheral blasthole techniques, requires an additional row of drill holes, increasing blasthole construction time and construction costs. Other approaches use mechanical equipment to remove the underbreak created by blasting, addressing the distance between the tunnel and the open face. However, in hard rock, mechanical equipment is inefficient and increases costs. Summary of the Invention

[0005] The purpose of the present invention is to overcome the problems of large over-excavation volume and large distance between the face of the tunnel and the empty face in the prior art, which lead to potential safety hazards, high construction cost and low efficiency.

[0006] To this end, the present invention provides a layered construction method for an initial tunnel support structure, comprising the following steps:

[0007] S1. Drill blastholes on the tunnel face according to the designed excavation footage and conduct blasting;

[0008] S2. Construct the first layer of primary support on the tunnel wall formed by blasting, and reserve space for the second layer of primary support between the first layer of primary support and the tunnel design outline;

[0009] S3: Using the second layer of primary support space, drill holes on the tunnel face for the next round of blasting.

[0010] S4. Construct the second layer of primary support of the previous round and the first layer of primary support of the current round simultaneously, and reserve space for the second layer of primary support between the first layer of primary support of the current round and the tunnel design outline;

[0011] S5. Repeat steps S3-S4 to proceed to the next round of operations.

[0012] Specifically, the above-mentioned first layer of initial support has an external insertion angle along the longitudinal direction of the tunnel that is the same as the blasting hole construction angle on the excavation contour line of the tunnel face.

[0013] Specifically, the blasthole is made at an angle of 5-10°.

[0014] Specifically, the first layer of initial support for the above construction is as follows: anchor rods are driven into the tunnel wall and the anchor rods are wrapped with a sprayed concrete layer; the angle of the concrete layer inserted in the longitudinal direction of the tunnel is the same as the angle of the blastholes on the excavation contour line of the face.

[0015] Specifically, after the anchor rods are driven in, a steel frame is erected, and the anchor rods and the steel frame are wrapped with a sprayed concrete layer.

[0016] Specifically, all the steel frames within a single footage are assembled simultaneously using a steel frame assembly trolley.

[0017] Specifically, the thickness of the above concrete layer shall not be less than the initial support design thickness.

[0018] Specifically, the construction of the second layer of initial support is specifically to spray concrete in the reserved second layer of initial support space.

[0019] Specifically, the above step S3 is as follows: using the second-layer initial support space to provide advance support for the area to be excavated, and drilling blastholes on the tunnel face for the next round of blasting.

[0020] Specifically, the excavation depth for the above-mentioned Grade III surrounding rock is designed to be 4m, the excavation depth for Grade IV surrounding rock is designed to be 3 steel frames, and the excavation depth for Grade V surrounding rock is designed to be 2 steel frames.

[0021] Specifically, it also includes: S6. After the last round of blasting, the second layer of initial support of the previous round and the first layer and second layer of initial support of this round are constructed simultaneously.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0023] The layered construction method of the initial support structure provided by the present invention is to construct the initial support twice, integrate the over-excavation and the initial support into an integrated design, and use the over-excavation space as the initial support construction space. The first layer of initial support constructed for the first time uses the over-excavation part to ensure that the support thickness meets the design requirements and ensures construction safety. The second layer of initial support is constructed later. On the one hand, it provides construction space for drilling blastholes around the face, so that the distance between the face and the empty space can be zero, which greatly improves construction safety. On the other hand, it plays a role in leveling the initial support and toughening. The larger the footage, the smaller the external insertion angle of the peripheral blastholes, which reduces the amount of over-excavation and solves the problem of the need for operating space for the drilling rig to drill the peripheral blastholes and the safety hazard of the face of the empty space. A steel frame assembly machine is used to lay multiple steel frames at the same time, giving full play to the advantages of mechanized construction and increasing the cycle footage under the premise of safety.

[0024] The present invention will be described in further detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the cycle advance of the layered construction method provided by the present invention.

[0026] Figure 2 It is a schematic diagram of the initial support structure provided by the present invention.

[0027] Figure 3 It is a schematic diagram of the initial support structure with a steel frame provided by the present invention.

[0028] Figure numerals: 1. First layer of initial support; 2. Second layer of initial support; 3. Second layer of initial support space; 4. Tunnel design outline; 5. Steel frame. DETAILED DESCRIPTION

[0029] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Although the representative embodiments of the present invention have been described in detail, it will be understood by those skilled in the art that various modifications and changes can be made to the present invention without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the embodiments, but should be defined by the appended claims and their equivalents.

[0030] Reference Figure 1-3 The present invention provides a layered construction method for an initial tunnel support structure, comprising the following steps:

[0031] S1. According to the designed excavation depth, blastholes are drilled on the tunnel face for the first round of blasting. After ventilation and smoke exhaust, the top is found and the slag is removed.

[0032] The designed excavation footage is based on the actual conditions of the construction site. In principle, the drilling rig's performance is fully utilized, and the footage is increased as much as possible while maintaining safety. Overbreak is related to the footage and the drilling rig's external insertion angle. A greater footage and a smaller external insertion angle are more conducive to controlling overbreak.

[0033] By adopting the method provided by the present invention, the excavation advance per cycle for Grade III surrounding rock is 4m, the advance for Grade IV surrounding rock is 3 steel frames, and the advance for Grade V surrounding rock is 2 steel frames. This is a significant improvement compared to the standard requirements of 3m for Grade III surrounding rock, 2 steel frames for Grade IV surrounding rock, and 1 steel frame for Grade V surrounding rock.

[0034] S2. Anchor bolts are driven into the tunnel wall formed by blasting. Steel frames 5 are erected as needed. Concrete is then sprayed over the anchor bolts and steel frames 5 at an angle to form the first layer of primary support 1. The longitudinal extension angle of the first layer of primary support 1 along the tunnel is aligned with the blasthole angle along the tunnel face excavation contour. The longitudinal length of the first layer of primary support 1 along the tunnel is preferably aligned with the designed footage, ensuring that one end of the first layer of primary support 1 is in close contact with the tunnel face. This eliminates the need for leaving empty space facing the tunnel face, greatly improving construction safety.

[0035] Because the blastholes set along the face excavation contour are set at a certain angle (generally 5-10°), the tunnel contour formed by blasting exceeds the tunnel design contour 4, resulting in a certain amount of overexcavation. The thickness of the first layer of primary support 1 must be no less than the designed thickness to ensure construction safety. At the same time, the thickness must not exceed the preset thickness or the actual overexcavation thickness, ensuring that space 3 for the second layer of primary support is reserved between the first layer of primary support 1 and the tunnel design contour.

[0036] If steel frames 5 are required for initial support, their radius can be adjusted based on the angles of the surrounding blastholes. While these diameter variations increase the number of steel frame types, all steel frames 5 within a single shot can be assembled simultaneously using a steel frame assembly trolley, accelerating construction progress.

[0037] S3. Utilize the second layer of initial support space 3 to drill blastholes on the tunnel face for the next round of blasting.

[0038] For broken rock formations, the second layer of initial support space 3 can be utilized, and measures such as advanced support can be set up before blasting to increase the advance.

[0039] S4. Construct the first layer of initial support 1 on the tunnel wall formed by this round of blasting. The construction method is the same as that in S2. When spraying the concrete of the first layer of initial support 1 of this round, simultaneously spray concrete in the second layer of initial support space 3 reserved in the previous round to form the second layer of initial support 2 of the previous round, filling the gap between the first layer of initial support 1 of the previous round and the tunnel design outline, ensuring that the surface of the initial support structure finally formed coincides with the tunnel design outline 4, so that the initially designed initial support thickness range and the over-excavation part are all sprayed with concrete, ensuring the flatness of the initial support and improving the toughness of the initial support.

[0040] The second layer of initial support space 3 is still reserved between the first layer of initial support 1 of this round and the tunnel design outline.

[0041] S5. Repeat steps S3-S4 to carry out the next round of operations until the tunnel drilling is completed.

[0042] S6. After the last round of blasting, since there is no need to continue blasting, anchor rods are driven into the tunnel wall formed in this round, steel frames 5 are erected as needed, and concrete is sprayed simultaneously to form the second layer of initial support 2 of the previous round and the first layer of initial support 1 and the second layer of initial support 2 of this round.

[0043] The effect of the layered construction method of the tunnel initial support structure of the present invention is studied below through specific examples.

[0044] Example 1:

[0045] This embodiment, based on the Jiaozhou Bay Second Subsea Tunnel Project, provides a layered method for constructing the initial tunnel support structure, including the following steps:

[0046] S1. Determine the tunnel excavation outline based on the tunnel design drawings. Use a drilling rig to evenly drill blastholes along the excavation outline and on the tunnel face. The blasthole length along the excavation outline is designed based on the penetration depth and the blasthole drilling angle. The drilling angle is 6°. Each cycle of excavation requires 4 meters of penetration for Grade III surrounding rock, 3 steel frames for Grade IV surrounding rock, and 2 steel frames for Grade V surrounding rock.

[0047] Load explosives into the blasthole, detonate the explosives, carry out the first round of blasting, and then find the top and remove the slag after ventilation and smoke exhaust.

[0048] S2. All the steel frames 5 within a single footage are assembled simultaneously by means of a steel frame assembly trolley. Anchor rods are driven into the tunnel wall formed by blasting, the steel frames 5 are erected, and the anchor rods and the steel frames 5 are wrapped with inclined sprayed concrete to form the first layer of initial support 1. The first layer of initial support 1 has an outward interpolation angle of 6° along the longitudinal direction of the tunnel, the thickness of the sprayed concrete is not less than the designed thickness, and the longitudinal length is the length of this round of footage, so that one end of the first layer of initial support 1 is close to the tunnel face.

[0049] A second layer of initial support space 3 is reserved between the first layer of initial support 1 and the tunnel design outline.

[0050] S3. Use the second layer of initial support space 3 to carry out advance support for the next round of excavation area. According to the advance, drill holes on the newly formed face and the designed excavation contour line to carry out the second round of blasting. After ventilation and smoke exhaust, find the top and remove the slag.

[0051] S4. Construct the first layer of initial support 1 on the tunnel wall formed by the second round of blasting. The construction method is the same as the construction method of the first layer of initial support 1 on the tunnel wall formed by the first round of blasting in S2. When spraying the concrete of the first layer of initial support 1 of the second round, simultaneously spray concrete in the second layer of initial support space 3 reserved in the first round to fill the second layer of initial support space 3 to form the second layer of initial support 2 of the first round, filling the gap between the first layer of initial support 1 of the first round and the tunnel design outline, ensuring that the surface of the initial support structure finally formed coincides with the tunnel design outline 4, so that the initially designed initial support thickness range and the over-excavation part are all sprayed with concrete, ensuring the flatness of the initial support and improving the toughness of the initial support.

[0052] The second-layer initial support space 3 of this round is still reserved between the first-layer initial support 1 of the second round and the tunnel design outline.

[0053] S5. Repeat the above steps to carry out the third round of blasting, construct the first layer of initial support 1 of the third round and the second layer of initial support 2 of the second round, and reserve space 3 for the second layer of initial support of the third round.

[0054] The fourth, fifth, ..., and Nth rounds of construction are completed in sequence until all tunnels are drilled.

[0055] S6. After the last round of blasting is completed, since there is no need to continue blasting, anchor rods are driven into the tunnel wall formed in this round, steel frame 5 is erected, and concrete is sprayed simultaneously to form the second layer of initial support 2 of the previous round and the first layer of initial support 1 and the second layer of initial support 2 of this round.

[0056] The above examples are merely illustrative of the present invention and do not limit the scope of protection of the present invention. Any design that is identical or similar to the present invention falls within the scope of protection of the present invention.

Claims

1. A layered construction method for an initial tunnel support structure, characterized in that: The following steps are involved: S1. Drill blastholes on the tunnel face according to the designed excavation footage and conduct blasting; S2. Construct the first layer of primary support on the tunnel wall formed by blasting, and reserve space for the second layer of primary support between the first layer of primary support and the designed tunnel outline. The first layer of primary support has the same angle of extension along the longitudinal direction of the tunnel as the angle of blastholes on the tunnel face excavation outline. The first layer of primary support has the same longitudinal length as the designed excavation footage, ensuring that one end of the first layer of primary support is in close contact with the tunnel face, i.e., no empty space is required on the tunnel face. S3: Using the second layer of primary support space, drill holes on the tunnel face for the next round of blasting. S4. Construct the second layer of primary support of the previous round and the first layer of primary support of the current round simultaneously, and reserve space for the second layer of primary support between the first layer of primary support of the current round and the tunnel design outline; S5. Repeat steps S3-S4 to proceed to the next round of operations.

2. The layered construction method of the primary support structure according to claim 1, characterized in that: The blast hole is made at an angle of 5-10°.

3. The layered construction method of the primary support structure according to claim 1, characterized in that: The first layer of initial support is constructed as follows: anchor rods are driven into the tunnel wall and wrapped with a layer of sprayed concrete; the angle of the concrete layer inserted longitudinally along the tunnel is the same as the angle of the blastholes on the excavation contour line of the face.

4. The layered construction method of the primary support structure according to claim 3, characterized in that: After driving the anchor rods, the steel frame is erected and the anchor rods and steel frame are wrapped with a sprayed concrete layer.

5. The layered construction method of the primary support structure according to claim 4, characterized in that: All steel frames within a single footage are assembled simultaneously using the steel frame assembly trolley.

6. The layered construction method of the primary support structure according to claim 1, characterized in that: The construction of the second layer of initial support specifically involves spraying concrete in the reserved second layer of initial support space.

7. The layered construction method of the primary support structure according to claim 1, characterized in that: The step S3 specifically includes: using the second layer of initial support space to provide advance support for the area to be excavated, and drilling blastholes on the tunnel face for the next round of blasting.

8. The layered construction method of the primary support structure according to claim 1, characterized in that: The designed excavation depth for Grade III surrounding rock is 4m, the designed excavation depth for Grade IV surrounding rock is 3 steel frames, and the designed excavation depth for Grade V surrounding rock is 2 steel frames.

9. The layered construction method of the primary support structure according to claim 1, characterized in that: Also includes: S6. After the last round of blasting, the second layer of initial support of the previous round and the first and second layers of initial support of this round are constructed simultaneously.

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