Construction method of super-large-section quasi-circular tunnel

Abstract

The invention discloses a construction method of a super-large-section quasi-circular tunnel, and relates to the technical field of tunnel construction. In order to solve the problem that construction cannot be continued due to the fact that the original structure of the tunnel is damaged by using a blasting excavation mode in the excavation process of the existing super-large section tunnel, the following technical scheme is provided: the method comprises the following steps: S1, advance support arrangement; s2, primary support of the upper pilot tunnel; s3, excavating and supporting left and right upper pilot tunnels; s4, excavating and joining a middle annular pilot tunnel; s5, excavating and supporting a left lower pilot tunnel and a right lower pilot tunnel; s6, excavating and supporting a middle lower pilot tunnel; and S7, bottom excavation and inverted arch closing are conducted, so that the non-blasting excavation and supporting process of the whole tunnel is completed. According to the design and implementation of the method, the overall stability in the tunnel excavation process is improved, the risks of collapse and geological disasters are reduced, and the original structure of the tunnel cannot be damaged in the ultra-large section tunnel excavation process.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel construction, and in particular to a construction method for a super-large cross-section quasi-circular tunnel. Background Art

[0002] In the field of tunnel engineering, with the continuous advancement of infrastructure construction, the demand for large-section circular tunnels is increasing, especially in areas with complex and changeable geological conditions, such as the Quaternary Holocene strata. The Quaternary Holocene strata are mainly composed of artificial fill layers, landslide deposits, residual slope deposits, alluvial and flood deposits, and ancient rock strata. These strata have significant differences in physical and mechanical properties, which brings great challenges to tunnel construction.

[0003] In the Quaternary Holocene strata, the artificial fill layer often has problems of uneven compaction and poor stability due to the different backfilling time and complex material composition; the collapse slope accumulation layer and residual slope accumulation layer have strong weathering of the parent rock and high content of crushed stone, silty clay and other mixtures, resulting in poor self-stability of the strata and easy collapse; and the floating pebble layer in the alluvial layer has a good particle grading, but the particle size is very different, which makes construction difficult and easy to cause wear on the excavation equipment. In addition, the deep rock strata such as the Silurian Hanjiadian Formation slate have different weathering degrees, ranging from strong weathering to moderate weathering, and the rock strength varies greatly, which also increases the difficulty of tunnel excavation and support.

[0004] Traditional tunnel construction methods often have problems such as low excavation efficiency, poor support effect, and high safety risks when facing the Quaternary Holocene strata. Especially for ultra-large cross-section circular tunnels, due to their large cross-section size and wide excavation span, the disturbance to the strata is more significant, so an efficient, safe and reliable construction method is more needed.

[0005] At present, although some tunnel construction technologies for complex geological conditions have been proposed, most of them focus on the optimization of a single stratum or a specific construction stage, and lack a comprehensive construction method that can fully adapt to the characteristics of the Quaternary Holocene strata, especially for ultra-large cross-section quasi-circular tunnels. Therefore, it is of great practical significance and engineering application value to develop a technical solution that can efficiently and safely construct ultra-large cross-section quasi-circular tunnels in the Quaternary Holocene strata. Summary of the invention

[0006] The purpose of the present invention is to provide a construction method for a super-large cross-section quasi-circular tunnel, so as to solve the problem that the existing super-large cross-section tunnel uses blasting excavation during the excavation process, which will destroy the original structure of the tunnel and make it impossible to continue construction.

[0007] The technical solution of the present invention to solve the above technical problems is as follows: A construction method for a super-large cross-section quasi-circular tunnel comprises the following steps: S1. Advanced support setting: Implement advanced small pipe construction on the tunnel vault and grouting to reinforce the stratum; excavate the upper annular pilot pit to form the tunnel top space; S2. Initial support of the upper pilot pit: temporary horizontal and vertical supports are installed in the upper annular pilot pit, and locking anchors are set; initial support is carried out, including installing steel mesh, erecting steel frames, driving system anchors and spraying concrete to close the upper pilot pit; S3, excavation and support of the upper pilot pit: excavate the upper pilot pit from the tunnel upwards, and simultaneously set up temporary supports and locking anchors; then, carry out initial support for the area; S4. Excavation and connection of the middle ring pilot pit: After the construction of the upper pilot pit is completed, the middle ring pilot pit is excavated, and temporary cross braces are set to connect the upper pilot pit support structure to form an overall support system; S5. Excavation and support of lower pilot pit: excavate the lower pilot pit from the tunnel downward, set up temporary supports and locking anchors, and carry out initial support; S6. Excavation and support of the middle lower pilot pit: excavate the middle lower pilot pit from the tunnel downwards, and set up temporary supports and locking anchors; S7, bottom excavation and invert closure: set up a trestle at the bottom of the tunnel to excavate the invert, and form a closed-loop support system through steel frame connection; remove the temporary support and locking anchor rods, and complete the shotcrete construction of the invert to close the bottom of the tunnel, completing the non-blasting excavation and support process of the entire tunnel.

[0008] Preferably, in step S2, when excavating the upper guide pit, a step-by-step excavation method is adopted, that is, the right upper guide pit is first excavated to a certain depth, and then the left upper guide pit is excavated, and the excavation surface is kept flat during the excavation process.

[0009] Preferably, in step S5, when excavating the lower guide pit, a step-by-step excavation method is adopted, that is, the right lower guide pit is first excavated to a certain depth, and then the left lower guide pit is excavated. When excavating the right lower guide pit, the left part is reserved as a temporary support area. After the excavation of the right side is completed, the left lower guide pit is excavated.

[0010] Preferably, the initial support includes installation of steel mesh, erection of steel frame, driving of system anchors and shotcrete.

[0011] Preferably, the concrete spraying step is specifically as follows: after the temporary support structure is installed, the tunnel wall is wetted and concrete is sprayed in layers, and each layer is sprayed and then waited for initial setting.

[0012] Preferably, the invert construction step of step S7 includes: after excavating the tunnel bottom to the designed elevation, removing loose rock and soil, constructing the invert steel frame, and spraying concrete.

[0013] Preferably, after the invert construction is completed, step S7, in which the steel frame is connected, further comprises welding or bolting the connection parts.

[0014] Preferably, before excavating the upper annular pilot pit, the excavation area is also accurately measured and marked.

[0015] Preferably, the angle of the advanced small conduit construction implemented on the tunnel vault in step S1 is less than 120°.

[0016] The present invention has the following beneficial effects: Enhanced construction safety: By setting up advance support (S1) and setting up temporary supports and locking anchors (S2, S3, S5) at various stages, the overall stability of the tunnel excavation process is significantly improved, reducing the risk of landslides and geological disasters, and the original structure of the tunnel will not be damaged during the excavation of ultra-large section tunnels.

[0017] Optimize the excavation sequence: Adopt a step-by-step excavation method (S2, S5), such as excavating the right side first and then the left side, which helps to control the stability of the excavation surface and reduce the disturbance to the surrounding rock, optimizes the excavation sequence, and makes the construction more orderly and efficient.

[0018] Improved construction quality: Detailed implementation of the initial support steps (S2, S3, S5), including installation of steel mesh, erection of steel frame, system anchor bolting and shotcrete, ensured the strength and stability of the support structure and improved the overall construction quality of the tunnel.

[0019] Shorten the construction period: Through scientific and reasonable construction process design, such as the connection between the middle annular guide pit and the upper and lower guide pits (S4), and the rapid bottom excavation and invert arch closure (S7), the construction progress can be accelerated and the construction period can be shortened.

[0020] Protecting the surrounding environment: The non-explosive excavation and support process (S7) is adopted to reduce the impact of blasting operations on the surrounding environment and buildings, which is beneficial to environmental protection and ecological protection.

[0021] Economy and efficiency: The systematic design of the overall construction method reduces the frequent disassembly and assembly of temporary supports and supporting structures, reduces construction costs and improves construction efficiency.

[0022] Flexibility and adaptability: Multiple steps in the technical solution, such as step-by-step excavation and detailed steps of initial support, can be adjusted and optimized according to actual geological conditions and construction requirements, reflecting strong flexibility and adaptability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the steps of the construction method of the super-large cross-section quasi-circular tunnel of the present invention; Figure 2 It is a schematic diagram of the construction sequence of the construction method of the super-large cross-section quasi-circular tunnel of the present invention; Figure 3 It is a schematic diagram of advance support of the construction method of the super-large cross-section quasi-circular tunnel of the present invention; Figure 4a It is a schematic diagram of excavation and initial support of the upper annular pilot pit and the upper right pilot pit of the construction method of the super-large cross-section quasi-circular tunnel of the present invention; Figure 4b It is a schematic diagram of the upper left pilot pit excavation and initial support of the construction method of the super-large cross-section quasi-circular tunnel of the present invention; Figure 5 It is a schematic diagram of the excavation and connection of the middle annular pilot pit of the construction method of the super-large cross-section quasi-circular tunnel of the present invention; Figure 6a It is a schematic diagram of the excavation and initial support of the right lower pilot pit of the construction method of the super-large cross-section quasi-circular tunnel of the present invention; Figure 6b It is a schematic diagram of the left side lower pilot pit excavation and initial support of the construction method of the super-large cross-section quasi-circular tunnel of the present invention; Figure 7 It is a schematic diagram of excavation of the middle lower pilot pit of the construction method of the super-large cross-section quasi-circular tunnel of the present invention; Figure 8 The present invention is a schematic diagram of the construction method of the super-large cross-section quasi-circular tunnel, which shows the erection of the trestle and the excavation of the invert.

[0024] The reference numerals shown in the figure represent respectively: 1-system anchor rod, 2-temporary support, 3-locking anchor rod, 4-lateral support, 5-vertical support. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0026] Reference Figure 1-2 This embodiment provides a construction method for a super-large cross-section quasi-circular tunnel, which aims to solve the technical problem that the use of blasting excavation in the excavation process of the existing super-large cross-section tunnel will destroy the original structure of the tunnel and make it impossible to continue construction. It explains each step one by one to ensure that each link of the construction process is clearly and specifically described.

[0027] 1. Advanced support setting (S1) Reference Figure 3First of all, setting up advance support is the first step to ensure the safety of tunnel construction. The construction team needs to implement advance small pipe construction within 120° of the tunnel vault. The small pipe uses a steel pipe with a suitable diameter, and grouting holes are drilled on the pipe wall to ensure that the grouting slurry can evenly penetrate into the stratum and reinforce the surrounding stratum. The grouting material is usually cement slurry or cement-water glass double liquid slurry, which is injected into the small pipe by a grouting machine, and the grouting pressure is used to diffuse the slurry into the stratum cracks to improve the bearing capacity and stability of the stratum.

[0028] While grouting to reinforce the stratum, the upper annular pilot pit is excavated to form the top space of the tunnel. During this stage, the excavation progress must be strictly controlled to avoid over-excavation or under-excavation and keep the excavation surface flat and stable. During the excavation process, geological surveys and monitoring should be strengthened, and abnormal situations should be handled in a timely manner to ensure construction safety.

[0029] 2. Initial support of upper pilot tunnel (S2) Reference Figure 4a-4b After the excavation of the upper annular pilot pit is completed, initial support is immediately carried out to prevent deformation and collapse of the surrounding rock. First, temporary horizontal supports 4 and vertical supports 5 are installed in the pilot pit. The support structure needs to be designed and calculated according to geological conditions and design requirements to ensure sufficient strength and rigidity. At the same time, locking anchor rods 3 are set to further strengthen the support structure.

[0030] Next, the specific construction of the initial support is carried out. First, the steel mesh is installed. The mesh needs to be tightly connected to the supporting structure to form an overall force system. Then, the steel frame is erected. The steel frame should be firmly connected to the supporting structure and the steel mesh to ensure the overall stability of the support structure. After that, the system anchor rod 1 is driven in. The length and spacing of the anchor rod should be determined according to the geological conditions and design requirements to ensure that the anchor rod can be effectively anchored in the stable stratum. Finally, the concrete is sprayed. The concrete needs to be sprayed in layers. After each layer is sprayed, wait for initial setting until the design thickness and strength requirements are reached.

[0031] In step S2, the upper pilot pit is excavated in a step-by-step manner. That is, the upper pilot pit on the right is excavated to a certain depth first, and then the upper pilot pit on the left is excavated after the support structure is completed and reaches a certain strength. This method is conducive to controlling the deformation of the surrounding rock and the stability of the support structure during the excavation process.

[0032] 3. Excavation and support of upper pilot pit (S3) With the completion of the construction of the upper annular pilot pit, the full excavation of the upper pilot pit began. During the excavation process, temporary supports 2 and locking anchors 3 need to be set up simultaneously to ensure the stability of the excavation surface. The excavation footage and support speed need to be strictly controlled to maintain the coordination of excavation and support.

[0033] After each excavation, the initial support construction of the area is immediately carried out. The support construction is the same as S2, including installing steel mesh, erecting steel frame, driving system anchor 1 and spraying concrete. After the support is completed, the support structure needs to be inspected and accepted to ensure that it meets the design requirements.

[0034] 4. Excavation and connection of the central ring pilot pit (S4) Reference Figure 5 After the upper pilot pit is constructed, the middle ring pilot pit is excavated. Before excavation, the excavation area needs to be accurately measured and marked to ensure the accuracy of the excavation position. During the excavation process, the excavation surface should be kept flat and stable to avoid over-excavation or under-excavation.

[0035] After excavation to a certain depth, temporary cross braces are set to connect the upper pilot pit support structure to form an overall support system. The selection and installation of temporary cross braces need to be designed and calculated according to geological conditions and design requirements to ensure sufficient strength and rigidity. At the same time, the connection between the cross brace and the support structure needs to be reinforced to improve the stability of the overall support system.

[0036] 5. Excavation and support of lower pilot pit (S5) Reference Figure 6a-6b After the construction of the central annular pilot pit is completed, the lower pilot pit is excavated. Similar to the excavation of the upper pilot pit, the lower pilot pit is also excavated in steps. That is, the right lower pilot pit is excavated to a certain depth first, and the left part is reserved as a temporary support 2 area. After the right excavation is completed and the support is completed, the left lower pilot pit is excavated.

[0037] During the excavation process, temporary supports 2 and locking anchors 3 need to be set up simultaneously to ensure the stability of the excavation surface. After each excavation distance, the initial support construction of the area is immediately carried out. The support construction steps are the same as S2 and S3, including installing steel mesh, erecting steel frames, driving system anchors 1 and spraying concrete.

[0038] VI. Bottom excavation and invert closure (S6-S7) Reference Figure 7-8 , excavate the middle lower pilot pit from the tunnel downward, set up temporary support 2 and locking anchor 3; set up a trestle at the bottom of the tunnel for arch excavation. The setting of the trestle needs to consider the influence of construction load and geological conditions to ensure the stability and safety of the trestle. During the excavation process, the excavation surface needs to be kept flat and stable to avoid over-excavation or under-excavation.

[0039] After excavation to the design elevation, loose soil is removed, the inverted steel frame is constructed, and concrete is sprayed. Before pouring concrete, the base needs to be cleaned and moistened to ensure good bonding between the concrete and the base. When pouring concrete, the pouring speed and vibration quality need to be controlled to ensure that the density and strength of the concrete meet the design requirements.

[0040] After the invert construction is completed, the steel frame connection step is carried out. The steel frame connection parts need to be welded or bolted to ensure that the connection is firm and reliable. At the same time, the connection parts need to be reinforced to improve the stability of the overall support system.

[0041] During the construction of the invert and the connection of the steel frame, it is necessary to strengthen construction monitoring and inspection, and timely discover and deal with abnormal situations to ensure the quality and safety of the invert construction.

[0042] 7. Construction precautions During the construction process, please pay attention to the following points: The left and right side walls and temporary cross braces are temporary support structures, which need to be designed and calculated according to geological conditions and design requirements. After the support structure is completed, it needs to be inspected and accepted to ensure that it meets the design requirements.

[0043] When excavating each part, the strength of the shotcrete in the adjacent parts should reach more than 70% of the design strength to ensure the overall stability of the support structure. When using mechanical excavation, care should be taken not to damage the temporary support structure of the side wall guide pit.

[0044] When the self-stability of the surrounding rock is poor, the excavation face can be sealed with 10 cm thick sprayed concrete to improve the stability and safety of the face.

[0045] The temporary steel frame should be removed after the initial support construction of the main structure is completed and stabilized. Before and after the removal, the monitoring of the arch settlement and surrounding deformation should be strengthened to ensure construction safety.

[0046] When constructing the invert, a trestle should be laid for full-width segmented construction. The setting of the trestle should take into account the influence of construction load and geological conditions to ensure the stability and safety of the trestle.

[0047] During the construction process, geological survey and monitoring work needs to be strengthened to timely discover and deal with abnormal situations. At the same time, construction management and quality control work needs to be strengthened to ensure construction quality and safety.

[0048] In summary, the construction method of the super-large section quasi-circular tunnel includes the following steps: advance support setting, initial support of the upper pilot pit, excavation and support of the upper pilot pit, excavation and connection of the middle annular pilot pit, excavation and support of the lower pilot pit, and bottom excavation and invert closure. Each step must be carried out strictly in accordance with the design requirements and construction specifications to ensure construction quality and safety.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A construction method for a super-large cross-section quasi-circular tunnel, characterized in that: The following steps are involved: S1. Advanced support setting: Implement advanced small pipe construction on the tunnel vault and grouting to reinforce the stratum; excavate the upper annular pilot pit to form the tunnel top space; S2. Initial support of the upper annular pilot pit: temporary horizontal and vertical supports are installed in the upper annular pilot pit, and foot locking anchors are set; initial support is performed to close the upper pilot pit; S3, excavation and support of the upper pilot pit: excavate the upper pilot pit from the tunnel upwards, and simultaneously set up temporary supports and locking anchors; carry out initial support for the upper pilot pit; S4. Excavation and connection of the middle ring pilot pit: After the construction of the upper pilot pit is completed, the middle ring pilot pit is excavated, and temporary cross braces are set to connect the upper pilot pit support structure to form an overall support system; S5. Excavation and support of lower pilot pit: excavate the lower pilot pit from the tunnel downward, set up temporary supports and locking anchors, and carry out initial support; S6. Excavation and support of the middle lower pilot pit: excavate the middle lower pilot pit from the tunnel downwards, and set up temporary supports and locking anchors; S7, bottom excavation and invert closure: a trestle is set up at the bottom of the tunnel to excavate the invert, and a closed-loop support system is formed through steel frame connection; Temporary supports and locking anchors were removed, and the shotcrete construction of the invert was completed to seal the bottom of the tunnel, completing the non-explosive excavation and support process of the entire tunnel.

2. The construction method of a super-large cross-section quasi-circular tunnel according to claim 1, characterized in that: In step S2, when excavating the upper pilot pit, a step-by-step excavation method is adopted, that is, the right upper pilot pit is first excavated to a certain depth, and then the left upper pilot pit is excavated, and the excavation surface is kept flat during the excavation process.

3. The construction method of a super-large cross-section quasi-circular tunnel according to claim 1, characterized in that: In step S5, when excavating the lower guide pit, a step-by-step excavation method is adopted, that is, the right lower guide pit is excavated to a certain depth first, and then the left lower guide pit is excavated. When excavating the right lower guide pit, the left part is reserved as a temporary support area. After the excavation of the right side is completed, the left lower guide pit is excavated.

4. The construction method of a super-large cross-section quasi-circular tunnel according to claim 1, characterized in that: Initial support includes installation of steel mesh, erection of steel frame, system anchor bolting and shotcrete spraying.

5. The construction method of a super-large cross-section quasi-circular tunnel according to claim 4, characterized in that: The specific steps of shotcrete spraying are as follows: after the temporary support structure is installed, the tunnel wall is moistened and the concrete is sprayed in layers, and each layer is waited for initial setting after spraying.

6. The construction method of a super-large cross-section quasi-circular tunnel according to claim 1, characterized in that: The invert construction steps of step S7 include: after excavating the tunnel bottom to the designed elevation, removing loose rock and soil, constructing the invert steel frame, and spraying concrete.

7. The construction method of a super-large cross-section quasi-circular tunnel according to claim 1, characterized in that: Step S7: After the invert construction is completed, the step of connecting the steel frame also includes welding or bolting the connecting parts.

8. The construction method of a super-large cross-section quasi-circular tunnel according to claim 1, characterized in that: Prior to excavating the upper ring pilot pit, this also includes precise measurement and marking of the excavation area.

9. The construction method of a super-large cross-section quasi-circular tunnel according to claim 1, characterized in that: In step S1, the angle of the advanced small conduit construction on the tunnel vault is less than 120°.

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