Construction method for bifurcated tunnel in loess area

Abstract

The invention discloses a construction method for a loess district bifurcated tunnel. The construction method comprises the following steps that S1, a large arch section tunnel is constructed; the whole excavation section of the tunnel is divided into a left part, a middle part and a right part through two temporary middle partition walls, the left excavation section, the right excavation section and the middle excavation section are excavated in sequence, and corresponding supporting measures are taken; s2, a multi-arch section tunnel is constructed; a middle pilot tunnel is excavated, corresponding supporting measures are taken, and a middle partition wall is poured after the middle pilot tunnel is excavated; the positions, on the two sides of the middle partition wall, of the tunnel are each divided into a first hole area and a second hole area in the horizontal direction, first holes and second holes are excavated in sequence, and corresponding supporting measures are taken; s3, small-clear-distance section tunnel construction is carried out; the tunnel is sequentially divided into an upper step section, a middle step section and a lower step section from top to bottom, excavation of the upper step section, the middle step section and the lower step section is sequentially conducted, and corresponding supporting measures are taken. The problems that the transition section of the collapsible loess bifurcated tunnel is complex in structure and settlement control is difficult are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel engineering construction, and particularly to a construction method for a bifurcated tunnel in loess areas. Background Art

[0002] As a relatively novel tunnel form, the bifurcated tunnel is born in the construction of mountain tunnels, bridge-tunnel connections and urban underground road network connection projects under various engineering and geological conditions such as service functions, route selection, and special geology. This bifurcated tunnel with a plane approximately in the shape of a "human" character almost encompasses various structural forms and difficulties of tunnel engineering and has strong representativeness. Its cross-section and structural form have the characteristics of multi-scale and multi-type. Specifically, it is a combination of three tunnel forms: large-span variable cross-section, asymmetric bifurcation, and small spacing.

[0003] Collapsible loess is widely distributed in the northwest region of China, and a large number of loess tunnels have emerged during the construction of high-grade highways. Since the structure of collapsible loess is prone to damage after soaking in water and is likely to generate collapsible deformation, and the disturbance and damage of the construction to the structure of loess will also lead to the deterioration of its long-term mechanical properties. During the later operation of the tunnel, the large deformation caused by the rheological effect of collapsible loess may affect the stability of the tunnel structure. Obviously, the existing project management and design and construction technologies (such as the three-heading method for connected-arch tunnels) can no longer fully meet the needs of constructing bifurcated tunnels in collapsible loess areas.

[0004] Therefore, how to improve the construction quality of bifurcated tunnel projects in collapsible loess areas, improve the design concept and method, and take into account various engineering influencing factors to ensure project safety and stability is one of the frontier topics that urgently need systematic research. Summary of the Invention

[0005] The purpose of the present invention is to provide a construction method for a bifurcated tunnel in loess areas to solve technical problems such as easy deformation and collapse during the construction of bifurcated tunnels in collapsible loess areas, insufficient stability of the support structure, and low construction efficiency.

[0006] To achieve the above purpose, the present invention provides a construction method for a bifurcated tunnel in loess areas, including the following steps:

[0007] S1. Construction of the large-arch section of the tunnel: Use two temporary middle partitions to divide the entire excavation cross-section of the tunnel into three parts: left, middle, and right. Excavate the excavation cross-sections of the left, right, and middle in sequence, and apply corresponding support measures;

[0008] S2. Construction of twin-arch tunnel section: Excavate the middle pilot tunnel and apply corresponding support measures. After the excavation of the middle pilot tunnel is completed, pour the middle partition wall. Divide the tunnels on both sides of the middle partition wall into the advanced tunnel area and the subsequent tunnel area horizontally, and then excavate the advanced tunnel and the subsequent tunnel in sequence, and apply corresponding support measures during the excavation process.

[0009] S3. Construction of small clear distance tunnel section: Divide the tunnel into the upper bench stage, the middle bench stage and the lower bench stage from top to bottom in sequence, and then excavate the upper bench stage, the middle bench stage and the lower bench stage in sequence, and apply corresponding support measures during the excavation process.

[0010] Preferably, in the construction of the large-arch tunnel section, the excavation of the excavation section and the applied support measures specifically include the following steps:

[0011] S11. Excavate the upper half section of the left sidewall pilot tunnel and apply the initial support and temporary support for the upper half section of the sidewall pilot tunnel.

[0012] S12. Excavate the lower half section of the left sidewall pilot tunnel and apply the initial support and temporary support for the lower half section of the left sidewall pilot tunnel.

[0013] S13. Excavate the upper half section of the right sidewall pilot tunnel and apply the initial support and temporary support for the upper half section of the right sidewall pilot tunnel.

[0014] S14. Excavate the lower half section of the right sidewall pilot tunnel and apply the initial support and temporary support for the lower half section of the right sidewall pilot tunnel.

[0015] S15. Leave the core soil for the upper bench of the middle rock pillar for circular excavation and apply the initial support for the arch part of the middle rock pillar.

[0016] S16. Excavate the middle bench of the middle rock pillar.

[0017] S17. Excavate the lower bench of the middle rock pillar and apply the initial support for the invert of the middle pilot tunnel.

[0018] S18. Apply the second-layer initial support for the full section.

[0019] S19. Apply the secondary lining for the arch wall of the full section.

[0020] Preferably, the distance from the circular formation section of the second-layer initial support to the excavation face of the pilot tunnel is 40m to 50m, and the distance from the closed section of the secondary lining to the circular formation section of the second-layer initial support is less than 30m.

[0021] Preferably, the distance that step S13 lags behind step S11 is not less than 20m, and the distance that step S15 lags behind step S13 is not less than 15m.

[0022] Preferably, in the construction of the twin-arch tunnel section, the construction of the middle partition wall, the excavation of the advanced tunnel and the subsequent tunnel, and the applied support measures specifically include the following steps:

[0023] S21. Excavate the middle pilot tunnel and construct the initial support for the middle pilot tunnel;

[0024] S22. Pour the middle partition wall after the excavation of the entire middle pilot tunnel in the multi-arch section is completed;

[0025] S23. Excavate the upper half section and the lower half section of the advanced heading of one side tunnel in sequence, and construct the initial support for the side wall and the temporary support;

[0026] S24. Excavate the upper half section and the lower half section of the advanced heading of the other side tunnel in sequence, and construct the initial support for the side wall and the temporary support;

[0027] S25. Excavate the upper half section and the lower half section of the subsequent heading of one side tunnel in sequence, and construct the initial support;

[0028] S26. Excavate the upper half section and the lower half section of the subsequent heading of the other side tunnel in sequence, and construct the initial support;

[0029] S27. Demolish the temporary supports in the tunnels on both sides respectively, and construct the second-layer initial support for the advanced heading and the subsequent heading;

[0030] S28. Construct the secondary lining for the tunnels on both sides respectively in combination with the monitoring and measurement data.

[0031] Preferably, the distance between the faces of the excavation of the lower half section in S23 and the excavation of the upper half section in S24 is not less than 10 m, the distance between the faces of the excavation of the lower half section in S24 and the excavation of the upper half section in S25 is not less than 10 m, and the distance between the faces of the excavation of the lower half section in S25 and the excavation of the upper half section in S26 is not less than 10 m.

[0032] Preferably, during the construction of the multi-arch section tunnel, a transverse support is used to support the middle partition wall on the side of the subsequent heading.

[0033] Preferably, during the construction of the small clear distance section tunnel, the excavation and the support measures taken in the upper stage, the middle stage and the lower stage specifically include the following steps:

[0034] S31. Leave the core soil and conduct an arc excavation in the upper stage, and construct the initial support for the arch;

[0035] S32. Excavate the core soil in the upper stage;

[0036] S33. Excavate the left and right side walls alternately by 2 m to 3 m in the middle stage, and construct the initial support for the side walls alternately during the construction of the left and right side walls in the middle stage;

[0037] S34. Construct the second-layer initial support for the upper stage;

[0038] S35. Excavate the core soil in the middle stage;

[0039] S36. During the lower bench stage, the left and right sidewalls are excavated staggeredly by 2 m to 3 m, and the initial support for the sidewalls is constructed staggeredly on the left and right sidewalls during the lower bench stage;

[0040] S37. Excavate the core soil during the lower bench stage and construct the primary invert lining;

[0041] S38. Secondary lining for the full-section arch and wall.

[0042] Preferably, the length of the one-time excavation in the upper bench stage does not exceed the distance of three steel arch frames, and the single excavation length in the middle bench stage and the lower bench stage does not exceed the distance of four steel arch frames.

[0043] Preferably, the initial support is carried out by arranging steel arch frames and spraying concrete, and the secondary lining adopts an integral reinforced concrete structure.

[0044] Compared with the prior art, the present invention has the following advantages and technical effects:

[0045] The construction method of the bifurcated tunnel in the loess area provided by the present invention solves the problems of complex structure in the transition section of the collapsible loess bifurcated tunnel and difficult settlement control. By excavating in sections and steps and dynamically adjusting the support parameters, the crown settlement is controlled within 50 mm. The present invention provides a safe, reliable, economical and efficient technical solution for the construction of bifurcated tunnels in the collapsible loess area and has wide engineering application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0047] Figure 1 It is a schematic diagram of the bifurcated tunnel in the loess area of the present invention;

[0048] Figure 2 It is a construction sequence diagram of the tunnel construction in the large-arch section of the present invention;

[0049] Figure 3 It is a construction sequence diagram of the tunnel construction in the multi-arch section of the present invention;

[0050] Figure 4 It is a construction sequence diagram of the tunnel construction in the small clear distance section of the present invention; DETAILED DESCRIPTION OF THE EMBODIMENTS

[0051] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. The described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention. The present invention will be described in detail below with reference to the drawings and in combination with the embodiments.

[0052] As Figure 1 shown, the present invention provides a construction method for a bifurcated tunnel in loess areas, including the following steps:

[0053] S1. Construction of the large-arch section tunnel: The entire excavation section of the tunnel is divided into left, middle, and right parts by two temporary middle partitions, and the excavation of the left, right, and middle excavation sections is carried out in sequence, and the corresponding support measures are constructed.

[0054] S2. Construction of the continuous-arch section tunnel: The middle pilot tunnel is excavated and the corresponding support measures are constructed. After the excavation of the middle pilot tunnel is completed, the middle partition wall is poured. The tunnels on both sides of the middle partition wall are horizontally divided into the advanced tunnel area and the subsequent tunnel area, and the excavation of the advanced tunnel and the subsequent tunnel is carried out in sequence, and the corresponding support measures are constructed during the excavation process.

[0055] S3. Construction of the small clear distance section tunnel: The tunnel is divided into the upper stage, the middle stage, and the lower stage from top to bottom, and the excavation of the upper stage, the middle stage, and the lower stage is carried out in sequence, and the corresponding support measures are constructed during the excavation process.

[0056] Further optimizing the scheme, as Figure 2 shown, in the construction of the large-arch section tunnel, the excavation of the excavation section and the constructed support measures specifically include the following steps:

[0057] S11. Excavate the upper half section of the left sidewall pilot tunnel, and construct the initial support and temporary support for the upper half section of the sidewall pilot tunnel.

[0058] S12. Excavate the lower half section of the left sidewall pilot tunnel, and construct the initial support and temporary support for the lower half section of the left sidewall pilot tunnel.

[0059] S13. Excavate the upper half section of the right sidewall pilot tunnel, and construct the initial support and temporary support for the upper half section of the right sidewall pilot tunnel.

[0060] S14. Excavate the lower half section of the right sidewall pilot tunnel, and construct the initial support and temporary support for the lower half section of the right sidewall pilot tunnel.

[0061] S15. Leave the core soil for circular excavation of the upper bench of the middle rock pillar and construct the initial support for the arch part of the middle rock pillar.

[0062] S16. Excavate the middle bench of the middle rock pillar.

[0063] S17. Excavate the lower bench of the middle rock pillar and construct the initial support for the inverted arch of the middle pilot tunnel;

[0064] S18. Conduct the initial support for the second layer of the full section;

[0065] S19. Install the secondary lining for the arch wall of the full section.

[0066] Further optimize the plan. The distance between the circular section of the initial support for the second layer and the excavation face of the pilot tunnel is 40m to 50m, and the distance between the closed section of the secondary lining and the circular section of the initial support for the second layer is less than 30m.

[0067] Further optimize the plan. The distance by which step S13 lags behind step S11 is not less than 20m, and the distance by which step S15 lags behind step S13 is not less than 15m.

[0068] Further optimize the plan. During the construction of the tunnel in the large arch section, the stage from the standard section to the excavation of the split - arch section is the enlarged - excavation section of the tunnel. The excavation of the enlarged - excavation section of the tunnel must be carried out after the advanced support is completed to ensure construction safety. The cyclic footage of the excavation of the enlarged - excavation section of the tunnel is controlled within 0.5m to 0.75m, and the initial support and temporary support closely follow the excavation face. The excavation is carried out using small - scale machinery in cooperation with manual labor to ensure construction safety.

[0069] Further optimize the plan. As Figure 3 shown, during the construction of the split - arch section of the tunnel, the construction of the middle partition wall, the excavation of the leading and trailing tunnels on both sides, and the support measures implemented specifically include the following steps:

[0070] S21. Excavate the middle pilot tunnel and construct the initial support for the middle pilot tunnel;

[0071] S22. Pour the middle partition wall after the excavation of the entire middle pilot tunnel of the split - arch section is completed;

[0072] S23. Sequentially excavate the upper and lower half - sections of the leading tunnel on one side and construct the initial support for the side wall and the temporary support;

[0073] S24. Sequentially excavate the upper and lower half - sections of the leading tunnel on the other side and construct the initial support for the side wall and the temporary support;

[0074] S25. Sequentially excavate the upper and lower half - sections of the trailing tunnel on one side and construct the initial support;

[0075] S26. Sequentially excavate the upper and lower half - sections of the trailing tunnel on the other side and construct the initial support;

[0076] S27. Remove the temporary supports inside the tunnels on both sides respectively and construct the initial support for the second layer of the leading and trailing tunnels;

[0077] S28. Apply the secondary lining for both sides of the tunnel respectively in combination with the monitored measurement data.

[0078] Further optimize the plan. The distance between the excavation faces of the lower half section excavation in S23 and the upper half section excavation in S24 shall be not less than 10 m. The distance between the excavation faces of the lower half section excavation in S24 and the upper half section excavation in S25 shall be not less than 10 m. The distance between the excavation faces of the lower half section excavation in S25 and the upper half section excavation in S26 shall be not less than 10 m.

[0079] Further optimize the plan. During the construction of the multi-arch tunnel section, use horizontal supports on the side of the later-driven tunnel to support the middle partition wall.

[0080] Further optimize the plan. As Figure 4 shown, during the construction of the small clear distance tunnel section, the excavation and the applied support measures in the upper bench stage, middle bench stage and lower bench stage specifically include the following steps:

[0081] S31. Leave a core soil and conduct an arc excavation in the upper bench stage, and apply the initial support for the arch part.

[0082] S32. Excavate the core soil in the upper bench stage.

[0083] S33. Excavate the left and right sidewalls of the middle bench stage staggeredly by 2 m to 3 m, and construct the initial support for the sidewalls of the left and right sidewalls of the middle bench stage staggeredly.

[0084] S34. Apply the second layer of initial support for the upper bench stage.

[0085] S35. Excavate the core soil in the middle bench stage.

[0086] S36. Excavate the left and right sidewalls of the lower bench stage staggeredly by 2 m to 3 m, and construct the initial support for the sidewalls of the left and right sidewalls of the lower bench stage staggeredly.

[0087] S37. Excavate the core soil in the lower bench stage, and apply the primary inverted arch lining.

[0088] S38. Apply the full-section arch wall secondary lining.

[0089] Further optimize the plan. The length of the one-time excavation in the upper bench stage shall not exceed the distance of three steel arch frames. The single excavation length in the middle bench stage and the lower bench stage shall not exceed the distance of four steel arch frames.

[0090] Further optimize the plan. The initial support adopts the method of arranging steel arch frames and spraying concrete, and the secondary lining adopts the integral reinforced concrete structure.

[0091] The construction method of the bifurcated tunnel in the loess area provided by the present invention solves the problems of complex structure in the transition section of the collapsible loess bifurcated tunnel and difficult settlement control. By excavating in zones and steps and dynamically adjusting the support parameters, the crown settlement is controlled within 50 mm. The present invention provides a safe, reliable, economical and efficient technical solution for the construction of bifurcated tunnels in the collapsible loess area and has wide engineering application value.

[0092] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A construction method for bifurcated tunnels in loess areas, characterized in that, It includes the following steps: S1. Construction of the large-arch section tunnel: The entire excavation section of the tunnel is divided into left, middle, and right parts by two temporary middle diaphragms, and the excavation of the left, right, and middle excavation sections is carried out in sequence, and corresponding support measures are constructed. S2. Construction of the connected-arch section tunnel: The middle pilot tunnel is excavated and corresponding support measures are constructed. After the excavation of the middle pilot tunnel is completed, the middle diaphragm is poured. The tunnels on both sides of the middle diaphragm are horizontally divided into the advanced tunnel area and the subsequent tunnel area, and the excavation of the advanced tunnel and the subsequent tunnel is carried out in sequence, and corresponding support measures are constructed during the excavation process. S3. Construction of the small clear distance section tunnel: The tunnel is divided into the upper stage, the middle stage, and the lower stage from top to bottom in sequence, and the excavation of the upper stage, the middle stage, and the lower stage is carried out in sequence, and corresponding support measures are constructed during the excavation process.

2. The construction method of the bifurcated tunnel in the loess area according to claim 1, characterized in that, In the construction of the large-arch section tunnel, the excavation of the excavation section and the constructed support measures specifically include the following steps: S11. Excavate the upper half section of the left sidewall pilot tunnel and construct the initial support and temporary support for the upper half section of the sidewall pilot tunnel. S12. Excavate the lower half section of the left sidewall pilot tunnel and construct the initial support and temporary support for the lower half section of the left sidewall pilot tunnel. S13. Excavate the upper half section of the right sidewall pilot tunnel and construct the initial support and temporary support for the upper half section of the right sidewall pilot tunnel. S14. Excavate the lower half section of the right sidewall pilot tunnel and construct the initial support and temporary support for the lower half section of the right sidewall pilot tunnel. S15. Leave the core soil for the upper bench of the middle rock pillar for circular excavation and construct the initial support for the arch part of the middle rock pillar. S16. Excavate the middle bench of the middle rock pillar. S17. Excavate the lower bench of the middle rock pillar and construct the initial support for the inverted arch of the middle pilot tunnel. S18. The second layer of initial support for the full section. S19. The secondary lining of the arch wall for the full section.

3. The construction method of the bifurcated tunnel in the loess area according to claim 2, characterized in that, The distance between the ring-forming section of the second layer of initial support and the excavation face of the pilot tunnel is 40m to 50m, and the distance between the closed section of the secondary lining and the ring-forming section of the second layer of initial support is less than 30m.

4. The construction method of the bifurcated tunnel in the loess area according to claim 2, characterized in that, The distance that step S13 lags behind step S11 is not less than 20m, and the distance that step S15 lags behind step S13 is not less than 15m.

5. The construction method of the bifurcated tunnel in the loess area according to claim 1, characterized in that, In the construction of the connected-arch section tunnel, the construction of the middle diaphragm, the excavation of the advanced tunnel and the subsequent tunnel, and the constructed support measures specifically include the following steps: S21. Excavate the middle pilot tunnel and construct the initial support for the middle pilot tunnel. S22. Pour the middle diaphragm after the excavation of the entire connected-arch section middle pilot tunnel is completed. S23. Sequentially excavate the upper half section and the lower half section of the advanced tunnel on one side of the tunnel, and construct the initial support and temporary support for the side wall. S24. Sequentially excavate the upper half section and the lower half section of the advanced tunnel on the other side of the tunnel, and construct the initial support and temporary support for the side wall. S25. Sequentially excavate the upper half section and the lower half section of the subsequent tunnel on one side of the tunnel, and construct the initial support. S26. Sequentially excavate the upper half section and the lower half section of the subsequent tunnel on the other side of the tunnel, and construct the initial support. S27. Remove the temporary supports in the tunnels on both sides respectively, and construct the second layer of initial support for the advanced tunnel and the subsequent tunnel. S28. Construct the secondary lining for the tunnels on both sides respectively in combination with the monitoring data.

6. The construction method of the bifurcated tunnel in the loess area according to claim 5, characterized in that The distance between the excavation face of the lower half section of S23 and the excavation face of the upper half section of S24 shall be not less than 10 m. The distance between the excavation face of the lower half section of S24 and the excavation face of the upper half section of S25 shall be not less than 10 m. The distance between the excavation face of the lower half section of S25 and the excavation face of the upper half section of S26 shall be not less than 10 m.

7. The construction method of the bifurcated tunnel in the loess area according to claim 5, characterized in that, During the construction of the twin-arch tunnel section, transverse supports are used on the side of the subsequent tunnel to support the middle partition wall.

8. The construction method of the bifurcated tunnel in the loess area according to claim 1, characterized in that, During the construction of the small clear distance tunnel section, the excavation and support measures for the upper bench stage, middle bench stage and lower bench stage shall specifically include the following steps: S31: Leave the core soil and conduct an arc excavation in the upper bench stage, and apply the initial support for the arch part. S32: Excavate the core soil in the upper bench stage. S33: Excavate the left and right sidewalls of the middle bench stage staggeredly by 2 m to 3 m, and construct the initial support for the sidewalls of the left and right sidewalls of the middle bench stage staggeredly. S34: Apply the second layer of initial support for the upper bench stage. S35: Excavate the core soil in the middle bench stage. S36: Excavate the left and right sidewalls of the lower bench stage staggeredly by 2 m to 3 m, and construct the initial support for the sidewalls of the left and right sidewalls of the lower bench stage staggeredly. S37: Excavate the core soil in the lower bench stage and apply the primary invert lining. S38: Conduct the secondary lining for the full cross-section arch and wall.

9. The construction method of the bifurcated tunnel in the loess area according to claim 8, characterized in that, The length of the one-time excavation in the upper bench stage shall not exceed the distance of three steel arch frames. The single excavation length in the middle bench stage and the lower bench stage shall not exceed the distance of four steel arch frames.

10. The construction method of the bifurcated tunnel in the loess area according to claim 2 or 5 or 8, characterized in that, The initial support is carried out by arranging steel arch frames and spraying concrete. The secondary lining adopts a monolithic reinforced concrete structure.

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