Layered construction method of preliminary bracing structure

Abstract

The invention belongs to the technical field of drilling and blasting method construction, and particularly provides a layered construction method of a tunnel primary support structure, which comprises the following steps: S1, drilling blast holes in a tunnel face according to a designed excavation footage for blasting; s2, a first layer of primary support is constructed on the tunnel wall formed by blasting, and a second layer of primary support space is reserved between the first layer of primary support and the tunnel design contour; s3, a blast hole is drilled in the tunnel face for the next round of blasting by means of the second layer of primary support space; s4, a second-layer primary support of the previous round and a first-layer primary support of the round are constructed synchronously, and a second-layer primary support space is reserved between the first-layer primary support of the round and the tunnel design contour; and S5, the steps S3-S4 are repeated, and the next round of operation is carried out. According to the method, overexcavation and primary support are integrally designed, an overexcavation space serves as a primary support construction space, the overexcavation amount is reduced, and the problems that an operation space is needed for drilling peripheral blast holes and potential safety hazards exist in a free face of a tunnel face are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of drilling and blasting construction, and specifically 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 the construction of infrastructure such as transportation, water conservancy, and energy. Tunnel blasting excavation mostly adopts smooth blasting technology, and blastholes are mainly drilled by rock drilling trolleys and air-leg pneumatic rock drills. In order to ensure the stability of the tunnel surrounding rock and the flatness of the excavation surface after blasting excavation, the positions of the peripheral holes are generally evenly arranged along the design contour line. The drilling machinery needs a certain drilling operation distance when drilling holes in the periphery. Because under-excavation is not allowed, the entire hole needs to be over-excavated in advance to leave space for the drilling machinery to operate. In addition, it is still necessary to drill holes tilted outward, which makes the peripheral drilling holes too large in the external insertion angle. The bottom generally falls outside the design excavation contour line, which further increases the over-excavation after blasting excavation. When supporting, the initial support shotcrete includes shotcrete within the design thickness range and shotcrete of the over-excavated part. The over-excavation of the number of cubic meters of rock requires the over-filling of the number of cubic meters of concrete, which not only increases the cost of the project, but also prolongs the construction period and puts pressure on the progress of the project.

[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 a safety hazard if there is no support construction within the air distance range of the tunnel face.

[0004] In order to solve the safety hazards caused by large over-excavation and large distance between the face and the empty face, the existing technology adopts the scheme of drilling holes one cycle in advance, so that the distance between the face and the empty face can be zero, but this scheme is similar to many technologies of double-row advance peripheral blastholes, which requires an additional row of drilling holes, increasing the blasthole construction time and construction cost. There are also schemes that use mechanical equipment to remove the under-excavation around the tunnel formed by blasting, solving the problem of the distance between the face and the empty face, but the use of mechanical equipment to handle under-excavation in hard rock is inefficient and increases costs. Summary of the invention

[0005] The purpose of the present invention is to overcome the problems in the prior art of large over-excavation volume, large distance between the heading face and the empty face, 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 for blasting according to the designed excavation depth;

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

[0009] S3, using the second layer of initial support space, drill holes on the tunnel face for the next round of blasting;

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

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

[0012] Specifically, the longitudinal external insertion angle of the first layer of initial support along the tunnel is the same as the blasting angle on the face excavation contour line.

[0013] Specifically, the blast hole is constructed 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 by 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 specifically as follows: using the second-layer initial support space to provide advance support for the area to be excavated, and drilling blast holes on the 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 in two times, integrate the over-excavation and the initial support, 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 the 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 surrounding 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 surrounding blastholes and the safety hazards 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 further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the cycle advancement 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 an initial support structure with a steel frame provided by the present invention.

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

[0029] The technical scheme in 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 limited by the attached 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 face for the first round of blasting, and the top is found and the slag is removed after ventilation and smoke exhaust.

[0032] The designed excavation footage is designed according to the actual situation of the construction site. In principle, the performance of the rock drilling rig is fully utilized, and the footage is increased as much as possible under the premise of safety. The over-excavation is related to the footage and the external insertion angle of the rock drilling rig. The larger the footage and the smaller the external insertion angle, the more conducive it is to control the over-excavation.

[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, which is a significant improvement compared with the standard requirements of 3m for grade III, 2 steel frames for grade IV surrounding rock, and 1 steel frame for grade V surrounding rock.

[0034] S2. Anchors are driven into the tunnel wall formed by blasting, steel frames 5 are set up as needed, and concrete is sprayed obliquely to wrap the anchors and steel frames 5 to form the first layer of initial support 1, so that the first layer of initial support 1 has the same external insertion angle along the longitudinal direction of the tunnel as the blasthole construction angle on the excavation contour line of the face. The longitudinal length of the first layer of initial support 1 along the tunnel is preferably the same as the designed footage, so that one end of the first layer of initial support 1 is close to the face, that is, there is no need to reserve empty space facing the face, which greatly improves construction safety.

[0035] Since the blastholes set on the excavation contour line of the face have a certain angle of operation, generally 5-10°, the tunnel contour formed by blasting exceeds the tunnel design contour 4, that is, there is a certain amount of over-excavation. The thickness of the first layer of initial support 1 is not less than the design thickness of the initial support to ensure construction safety. At the same time, the thickness does not exceed the preset thickness and the actual over-excavation thickness, ensuring that the second layer of initial support space 3 is reserved between the first layer of initial support 1 and the tunnel design contour.

[0036] If the initial support needs to set up a steel frame 5, according to the angle of the surrounding blastholes, the steel frame 5 also adopts different steel frame 5 radii according to the location. Although the change of the steel frame 5 diameter increases the types of steel frames 5, all the steel frames 5 in a single footage can be assembled at the same time through the steel frame assembly trolley, so the construction progress is faster.

[0037] S3. Using the second layer of initial support space 3, drill blast holes on the 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 penetration rate.

[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 contour, ensuring that the surface of the initial support structure finally formed coincides with the tunnel design contour 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 of this round 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 synchronously 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 initial tunnel support structure of the present invention is studied below through specific examples.

[0044] Embodiment 1:

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

[0046] S1. According to the tunnel design drawings, determine the tunnel excavation contour line, use the rock drilling rig to evenly drill blastholes on the excavation contour line and the face surface, and the length of the blastholes on the excavation contour line is designed according to the footage and the blasthole operation angle. The operation angle is 6°, the excavation footage per cycle of grade III surrounding rock is 4m, the footage of grade IV surrounding rock is 3 steel frames, and the footage of grade V surrounding rock is 2 steel frames.

[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 in 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 obliquely sprayed with concrete to form the first layer of initial support 1. The first layer of initial support 1 has an external insertion 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 heading 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 for 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, and fill the gap between the first layer of initial support 1 of the first round and the tunnel design contour to ensure that the surface of the initial support structure finally formed coincides with the tunnel design contour 4, so that the initially designed initial support thickness range and the over-excavation part are all sprayed with concrete to ensure the flatness of the initial support and improve the toughness of the initial support.

[0052] A second-layer initial support space 3 for 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 the entire tunnel is 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, a steel frame 5 is erected, and concrete is sprayed synchronously 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 constitute a limitation on the protection scope of the present invention. All designs that are the same or similar to the present invention fall within the protection scope 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 for blasting according to the designed excavation depth; S2. Construct the first layer of initial support on the tunnel wall formed by blasting, and reserve space for the second layer of initial support between the first layer of initial support and the tunnel design outline; S3, using the second layer of initial support space, drill holes on the tunnel face for the next round of blasting; S4. Construct the second layer of initial support of the previous round and the first layer of initial support of this round simultaneously, and reserve space for the second layer of initial support between the first layer of initial support of this 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 initial support structure according to claim 1, characterized in that: The longitudinal external insertion angle of the first layer of initial support along the tunnel is the same as the blasting angle on the excavation contour line of the face.

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

4. The layered construction method of the initial support structure according to claim 2, characterized in that: The first layer of initial support is constructed as follows: anchor rods are driven into the tunnel wall and the anchor rods are wrapped with a layer of sprayed concrete; 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.

5. The layered construction method of the initial support structure according to claim 4, characterized in that: After driving the anchor rods, a steel frame is erected and a sprayed concrete layer is used to wrap the anchor rods and the steel frame.

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

7. The layered construction method of the initial 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.

8. The layered construction method of the initial support structure according to claim 1, characterized in that: The step S3 specifically includes: utilizing the second-layer initial support space to provide advance support for the area to be excavated, and drilling blast holes on the face for the next round of blasting.

9. The layered construction method of the initial 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.

10. The layered construction method of the initial 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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