Variable-length combined jacking pipe, bell mouth tunnel pipe roof structure and construction method of bell mouth tunnel pipe roof structure

Abstract

The invention relates to the field of tunnel engineering, in particular to a variable-length combined jacking pipe, a horn mouth tunnel pipe roof structure and a construction method of the horn mouth tunnel pipe roof structure. The invention aims to provide a variable-length combined jacking pipe suitable for a pipe-roofing pre-building structure of a bell mouth tunnel, the bell mouth tunnel pipe-roofing structure adopting the variable-length combined jacking pipe and a construction method of the bell mouth tunnel pipe-roofing structure, and based on a pipe-roofing pre-building method of double guide pipes, a length-variable structure is adopted between the two guide pipes; therefore, the construction method can adapt to the gradually-changed size of a tunnel structure, solves the problem of construction of a shallow-buried large-span horn mouth tunnel, and can be suitable for pre-construction of horn mouth tunnels under the conditions of large span, poor geological conditions, burying depth and the like.

Description

Technical Field

[0001] The present invention relates to the field of tunnel engineering, and more specifically, to a variable-length combined jacking pipe, a bell-mouth tunnel pipe curtain structure and a construction method thereof. Background Art

[0002] With the continuous advancement of underground space development in my country, tunnel diversion and confluence are gradually increasing to meet the traffic needs in different directions. When underground railways, highways and other lines need to be diverted or merged, the line spacing gradually changes, and the tunnel section clearance also needs to change accordingly, which is a bell-mouth tunnel. Due to the need for line diversion and confluence, bell-mouth tunnels usually have larger cross-sections. When the burial depth is shallow or the surrounding environment is sensitive and complex, there are various difficulties in building bell-mouth tunnels.

[0003] A bell-mouth tunnel is a tunnel with a constantly changing internal clearance. It is widely used in the throat area of ​​railway stations, the junction and divergence area of ​​urban tunnels, etc. In the prior art, shallow buried dark-excavated bell-mouth tunnels in soft soil are generally constructed by open-cut method, which will cause great disturbance to the stratum and the surrounding environment; Japan has adopted the construction method of curved jacking pipe, but the process is relatively cumbersome and is not suitable for highly permeable strata. At present, for shallow buried dark-excavated large-section tunnels, the pipe curtain prefabrication method of double guide pipes has been proposed, which mainly includes the following steps:

[0004] 1. As attached Figure 1 As shown (taking the non-collinear pilot pipe as an example), firstly, the pilot pipe 1 is pushed into the predetermined position along the tunnel contour.

[0005] 2. As attached Figure 2 As shown in (Jumping the first group of interlocking jacking pipes), after the pilot pipe 1 passes through the tunnel longitudinally, a combined pipe body consisting of a fixed joint guide pipe 2-1, a flexible joint guide pipe 2-2, and a steel box 4 is pushed in at the corresponding position. Among them, one end of the steel box 4 is fixedly connected to the fixed joint guide pipe 2-1, and the other end extends into the opening of the flexible joint guide pipe 2-2, and the opening is closed by a water stop device; the guide pipes 2-1 and 2-2 are respectively connected to the pilot pipe 1 in front, and the combined pipe body consisting of the fixed joint guide pipe 2-1, the flexible joint guide pipe 2-2, and the steel box 4 is pushed along the trajectory of the pilot pipe 1 through the jacking machine 3 in front of the steel box 4, until the longitudinal advancement along the tunnel is completed and the pilot pipe 1 is pushed out.

[0006] 3. As attached Figure 3 (In the attached Figure 2The adjacent second group of combined pipe bodies are pushed forward, and their flexible joint guide tubes 2-2 are longitudinally connected to the leading pipe 1 in front, and their double-sided opening guide tubes -3 are longitudinally connected to the flexible joint guide tubes 2-2 of the previous group of combined pipe bodies. The combined pipe bodies are pushed forward longitudinally until the longitudinal advancement along the tunnel is completed, and the flexible joint guide tubes 2-2 of the previous group of combined pipe bodies and the leading pipe 1 in front are pushed out.

[0007] 4. Repeat the above steps until the combined pipe body is pushed forward within the predetermined range.

[0008] 5. Construct the internal structure of the combined pipe body to form a prefabricated lining, and excavate the soil in the tunnel under the protection of the prefabricated lining.

[0009] The tunnel lining obtained by the pipe curtain prefabrication method of the above double guide pipe is as shown in the attached figure. Figure 4 As mentioned above (taking the horseshoe section as an example), however, since the configuration of the combined pipe body and the interlocking pipe jacking machine is related to the section size, once the configuration of the combined pipe body and the interlocking pipe jacking machine is formulated according to the tunnel section, this combination can basically only be applied to the construction of this one tunnel section, that is, this technology can only be applied to tunnel sections with constant section sizes, and cannot be used in gradient sections. Summary of the invention

[0010] The purpose of the present invention is to provide a variable-length combined jacking pipe suitable for a bell-mouth tunnel pipe curtain prefabrication structure, a bell-mouth tunnel pipe curtain structure and a construction method thereof using the variable-length combined jacking pipe, a pipe curtain prefabrication method based on double guide pipes, a variable-length structure between the two guide pipes, thereby being able to adapt to the gradual size of the tunnel structure, solving the difficult problem of shallow-buried large-span bell-mouth tunnel construction, and being suitable for the prefabrication of bell-mouth tunnels with large spans, poor geological conditions, shallow burial depths and the like.

[0011] In order to achieve these purposes and other advantages according to the present invention, there is provided a variable-length combined jacking pipe, including a steel box, a movable joint guide pipe and a fixed joint guide pipe, one end of the movable joint guide pipe and the fixed joint guide pipe are respectively connected to a first transition section steel pipe and a second transition section steel pipe, one side of the first transition section steel pipe and the second transition section steel pipe close to each other is respectively provided with a first accommodating groove and a second accommodating groove, the movable joint guide pipe is provided with an opening, one end of the steel box passes through the opening and is slidably connected to the movable joint guide pipe, and the other end thereof is fixedly connected to the fixed joint guide pipe.

[0012] Furthermore, in the variable-length combined jacking pipe, one end of the steel box is connected to an extension section.

[0013] Furthermore, in the variable-length combined jacking pipe, the cross-section of the first transition section steel pipe is C-shaped.

[0014] The present invention also provides a bell-mouth tunnel pipe-roof structure, wherein the parts of the pipe-roof prefabricated structure located at the tunnel vault and invert are composed of a plurality of groups of variable-length combined jacking pipes described in any one of the above items.

[0015] The present invention also provides a construction method of the bell-mouth tunnel pipe curtain structure, comprising the following steps:

[0016] S1. Pushing a pilot pipe into the stratum until it penetrates, the distance between two adjacent pilot pipes varies with the cross-sectional dimensions of the dark excavation structure;

[0017] S2, carrying out the jacking of the first group of variable length combined jacking pipes:

[0018] S2.1. Connect one end of the first transition section steel pipe and the second transition section steel pipe to two adjacent pilot pipes respectively, and arrange a combined pipe jacking machine between the first transition section steel pipe and the second transition section steel pipe, with both ends of the combined pipe jacking machine extending into the first receiving tank and the second receiving tank respectively;

[0019] S2.2, connecting one end of the movable joint guide tube and the fixed joint guide tube to the other end of the first transition section steel pipe and the second transition section steel pipe respectively, and connecting the steel box to the plurality of pipe jacking machines respectively;

[0020] S2.3, the plurality of pipe jacking machines start to work, and push the first group of variable-length combined pipe jacking machines along the path of the pilot pipe, and the pilot pipe, the first transition section steel pipe and the second transition section steel pipe are gradually pushed out, and as the spacing between the two pilot pipes changes, one end of the steel box slides in the flexible joint guide pipe, and drives one end of the combined pipe jacking machine to move in the first receiving groove;

[0021] S3, repeat S2, and complete the jacking of other variable-length combined jacking pipes in sequence until the end.

[0022] Furthermore, in the construction method of the bell-mouth tunnel pipe curtain structure, the combined pipe jacking machine includes a first pipe jacking machine and at least one second pipe jacking machine, and the first pipe jacking machine and the second pipe jacking machine are arranged in parallel along the transverse direction of the steel box.

[0023] Furthermore, in the construction method of the bell-mouth tunnel pipe curtain structure, two adjacent groups of the variable-length combined jacking pipes share a double-sided opening guide pipe, one side of the double-sided opening guide pipe is provided with the opening, and the other side thereof is fixedly connected to the corresponding steel box.

[0024] Furthermore, in the construction method of the bell-mouth tunnel pipe-roof structure, S2 also includes:

[0025] S2.4. When one end of the steel box slides outward to the opening, a steel box extension section is connected to the one end of the steel box.

[0026] Furthermore, in the construction method of the bell-mouth tunnel pipe curtain structure, S2.4 specifically includes:

[0027] S2.4.1. Reinforce the stratum where the first transition section steel pipe is located, and open a notch on the first transition section steel pipe, place the third pipe jacking machine into the first transition section steel pipe through the notch, and then seal the notch;

[0028] S2.4.2. As the variable-length combined jacking pipe is advanced, the third jacking machine is gradually pulled out of the first transition section steel pipe, and then the steel box extension section is connected to one end of the steel box, and the steel box extension section is connected to the third jacking machine.

[0029] Furthermore, in the construction method of the bell-mouth tunnel pipe-roof structure, the notch is detachably connected with an inner steel plate.

[0030] The beneficial effects of the present invention are:

[0031] The present invention, based on the double-guide pipe curtain prefabrication structure method, adopts a variable-length combined jacking pipe whose transverse dimension can be linearly changed, and a tunnel pipe curtain structure is formed by connecting multiple groups of variable-length combined jacking pipes. The two ends of the variable-length combination are guide pipes, and the structure between the two guide pipes can adapt to the change of the length of the combined structure according to the length of the guide pipe entering, so that the double-guide pipe curtain prefabrication structure can adapt to the change of the tunnel section size on the basis of the unchanged number of the guide pipe and the guide pipe. When the tunnel profile is a curve, such as a horseshoe-shaped cross-section tunnel, the tunnel profile can be simplified into multiple broken lines, and each group of pipe bodies is distributed along the broken lines, and can be extended or shortened in the direction of the broken lines, so that the length of the broken line segment is variable, and finally the purpose of tunnel bell mouth construction is achieved. The present invention solves the difficult problem of shallow buried large-span bell mouth tunnel construction, can avoid the open excavation construction of bell mouth tunnels in sensitive environments, and is suitable for the prefabrication of bell mouth tunnels with large spans, poor geological conditions, shallow burial depths, etc.

[0032] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the layout of the pilot pipe of the double-guide pipe curtain prefabrication method in the background technology;

[0034] Figure 2It is a schematic diagram of the arrangement of the guide pipe, the pipe jacking machine and the steel box structure of the double guide pipe pipe curtain prefabrication method in the background technology (jacking the first group of bite jacking pipes);

[0035] Figure 3 The schematic diagram of the layout of the guide pipe, pipe jacking machine and steel box structure of the double guide pipe curtain prefabrication method in the background technology (see the attached Figure 2 On the basis of the jacking of the adjacent second group of bite jacking pipes);

[0036] Figure 4 It is a schematic diagram of the cross section of a double-guide tube curtain prefabrication method tunnel in the background technology;

[0037] Figure 5 It is a schematic diagram of the cross-section arrangement of the prefabricated structure of the pipe curtain according to the present invention;

[0038] Figure 6 It is a schematic plan view of the initial state of the variable-length combined jacking pipe according to the present invention;

[0039] Figure 7 for Figure 6 Sectional view at AA in the middle;

[0040] Figure 8 for Figure 6 Cross-section at the middle BB;

[0041] Fig. 9 for Figure 6 Sectional view at CC;

[0042] Fig.10 It is a schematic plan view of the variable length combined jacking pipe of the present invention in a state of increasing length;

[0043] Fig.11 for Fig.10 Sectional view at DD in the middle;

[0044] Fig.12 for Fig.10 Sectional view at EE in the middle;

[0045] Fig.13 for Fig.10 Cross-section at FF;

[0046] Fig.14 When the variable length combined jacking pipe of the present invention is connected to the steel box extension section Figure 6 Cross-section at the middle BB;

[0047] Fig.15 When the variable length combined jacking pipe of the present invention is connected to the steel box extension section Figure 6 Sectional view at CC;

[0048] Fig.16When the variable length combined jacking pipe of the present invention is connected to the steel box extension section Fig.10 Cross-section at FF;

[0049] In the above drawings:

[0050] 1. Pipe 1;

[0051] 2. Guide tube 2; 2-1. Fixed joint guide tube; 2-2. Flexible joint guide tube; 2-3. Double-side opening guide tube;

[0052] 3. Combined pipe jacking machine; 3-1. First pipe jacking machine; 3-2. Second pipe jacking machine; 3-3. Third pipe jacking machine;

[0053] 4. Steel box; 4-1. Steel box extension section;

[0054] 5. Length-invariant composite structure;

[0055] 6. Variable length combination structure;

[0056] 7-1, second transition section steel pipe; 7-2, first transition section steel pipe; 7-2-1, inner side steel plate; DETAILED DESCRIPTION

[0057] The present invention is further described in detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0058] It should be noted that, in the description of the present invention, the terms "lateral", "longitudinal", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc. indicating orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0059] like Figure 5 As shown, an embodiment of the present invention provides a bell-mouth tunnel pipe curtain structure, wherein the portion of the pipe curtain prefabricated structure located at the tunnel vault and the invert is composed of a plurality of groups of variable-length combined jacking pipes as described in any one of the above items, and the portion located at the tunnel arch wall is composed of an existing fixed-length combined pipe body, such as the combined pipe body used in the double-guide pipe pipe curtain prefabrication method mentioned in the background technology.

[0060] In the above embodiment, when the tunnel profile is a curve, in order to facilitate construction, all or part of the tunnel profile can be divided into broken line segments similar to the curve shape, and variable length combined jacking pipes are arranged in the broken line segments. Figure 5As shown, in the vault and inverted arch area of ​​the horseshoe-shaped cross-section, the curve is replaced by a broken line segment, and the broken line area is the variable-length combined structure 6, and the shape of the arch wall position is still a curve, and this area is the constant-length combined structure 5; Figure 5 The length of the broken line segment in the pipe curtain prefabricated structure in (a) is L1, at which time the length of the variable length combined top pipe is the shortest. Figure 5 In the prefabricated structure of the pipe curtain in (b), the length of the broken line segment is L2. At this time, the length of the variable-length combined top pipe is in the longest state. By adjusting the length of the variable-length combined top pipe, the length of the broken line segment can be increased from L1 to L2, and can be selected between L1 and L2 according to actual needs.

[0061] Specifically, the variable length combined jacking pipe includes a steel box 4, a flexible joint guide tube 2-2 and a fixed joint guide tube 2-1, one end of the flexible joint guide tube 2-2 and the fixed joint guide tube 2-1 are respectively connected to the first transition section steel tube 7-2 and the second transition section steel tube 7-1, and the first transition section steel tube 7-2 and the second transition section steel tube 7-1 are respectively provided with a first receiving groove and a second receiving groove on the side close to each other, and an opening is provided on the flexible joint guide tube 2-2, one end of the steel box 4 passes through the opening and is slidably connected to the flexible joint guide tube 2-2, and the other end thereof is fixedly connected to the fixed joint guide tube 2-1. Through the sliding between the steel box 4 and the flexible joint guide tube 2-2, when the distance between the flexible joint guide tube 2-2 and the fixed joint guide tube 2-1 changes, the length of the part of the steel box 4 extending into the flexible joint guide tube 2-2 changes accordingly, thereby ensuring the connection between the steel box 4, the flexible joint guide tube 2-2 and the fixed joint guide tube 2-1.

[0062] like Figure 5-Figure 16 As shown, an embodiment of the present invention further provides a construction method for the above-mentioned bell-mouth tunnel pipe curtain structure, taking the case where the cross-sectional dimensions required by the dark excavation structure gradually increase along the longitudinal direction of advancement as an example, comprising the following steps:

[0063] S1. Push the pilot pipe 1 into the stratum until it penetrates through. The distance between two adjacent pilot pipes 1 varies with the cross-sectional dimensions of the underground excavation structure.

[0064] Before construction, construction preparations need to be made: according to design requirements, set the jacking path of the pilot pipe 1, and in sections where a gradual change is required in the underground engineering section, set multiple groups of variable-length combined jacking pipes according to the gradient amplitude, and each group of variable-length combined jacking pipes is located on a straight line.

[0065] For the part of the pipe curtain prefabricated structure located at the tunnel vault and invert, multiple groups of variable length combined jacking pipes are used, and its construction includes the following steps:

[0066] S2. Carry out the jacking of the first set of variable length combined jacking pipes:

[0067] S2.1. Connect one end of the first transition section steel pipe 7-2 and the second transition section steel pipe 7-1 to two adjacent pilot pipes 1 respectively, and arrange a combined pipe jacking machine 3 between the first transition section steel pipe 7-2 and the second transition section steel pipe 7-1, and extend both ends of the combined pipe jacking machine 3 into the first receiving groove and the second receiving groove respectively; the combined pipe jacking machine 3 comprises a first pipe jacking machine 3-1 and at least one second pipe jacking machine 3-2, and the first pipe jacking machine 3-1 and the second pipe jacking machine 3-2 are arranged side by side along the transverse direction of the steel box;

[0068] S2.2, one end of the movable joint guide tube 2-2 and the fixed joint guide tube 2-1 are connected to the other ends of the first transition section steel pipe 7-2 and the second transition section steel pipe 7-1 respectively, and the steel box 4 is connected to a plurality of pipe jacking machines respectively;

[0069] After connection, the initial state of the variable length combined jacking structure is as follows: Figure 6 As shown, at this time, the length of the broken line segment is L1, that is, the wheelbase of the two pilot pipes 1 is L1; most of the first pipe jacking machine 3-1 is located in the first receiving groove, and the part of one end of the steel box 4 located in the flexible joint guide pipe 2-2 is in the longest state;

[0070] S2.3, multiple pipe jacking machines start to work, pushing the first group of variable-length combined pipe jacking along the path of the pilot pipe 1, the pilot pipe 1, the first transition section steel pipe 7-2 and the second transition section steel pipe 7-1 are gradually pushed out, and as the spacing between the two pilot pipes 1 changes, one end of the steel box 4 slides in the flexible joint guide pipe 2-2, and drives one end of the combined pipe jacking machine 3 to move in the first receiving groove;

[0071] The state of the variable length combined jacking pipe structure during the advancement process is as follows: Fig.10 As shown, at this time, the length of the broken line segment is L2, that is, the wheelbase of the two pilot pipes 1 is L2; ​​the first pipe jacking machine 3-1 moves out of the first receiving groove, and the part where one end of the steel box 4 is located in the flexible joint guide pipe 2-2 is in the shortest state;

[0072] S3, repeat S2, and complete the jacking of other variable length combination jacking pipes in sequence until it is finished. When jacking other variable length combination jacking pipes, two adjacent groups of variable length combination jacking pipes share a double-side opening guide pipe 2-3, that is, the double-side opening guide pipe 2-3 is used to replace the fixed joint guide pipe 2-1 and the movable joint guide pipe 2-2, and the two steel boxes 4 on both sides of the double-side opening guide pipe 2-3, one of the steel boxes 4 extends into the opening on one side of the double-side opening guide pipe 2-3 and is slidably connected to it, and the other steel box 4 is fixedly connected to the other side of the double-side opening guide pipe 2-3.

[0073] When the second group of variable-length combined jacking pipes is being pushed in, the flexible joint guide pipe 2-2 of the first group of variable-length combined jacking pipes is pushed out by the corresponding double-sided open guide pipe 2-3 in the second group, and the steel box 4 of the first group of variable-length combined jacking pipes extends into the opening of the corresponding double-sided open guide pipe 2-3 in the second group.

[0074] For the part of the pipe curtain prefabrication structure located in the tunnel arch wall, the existing fixed-length combined pipe body is used, which can be constructed by the existing double-guide pipe curtain prefabrication method, and will not be elaborated here. Finally, the combined pipe body structures of each section on the tunnel section are completed in sequence, and the adjacent combined pipe body structures are connected, and the concrete in the combined pipe body is poured to finally form a prefabricated lining structure.

[0075] In addition, when the cross-sectional dimensions required for the underground excavation structure gradually decrease along the longitudinal direction of advancement, the initial state of the variable length combined jacking pipe structure should be as follows: Fig.10 As shown in the figure, the state of the variable length combined jacking pipe structure during the advancement process is as follows Figure 6 As shown, during the advancement of the variable-length combined jacking structure, the spacing between adjacent leading pipes 1 gradually decreases, and the distance between the first transition section steel pipe 7-2 and the second transition section steel pipe 7-1 connected thereto also decreases accordingly, so that the first jacking machine 3-1 gradually enters the first receiving groove, and the portion of one end of the steel box 4 located in the flexible joint guide pipe 2-2 increases accordingly.

[0076] Preferably, in a construction method of a bell-mouth tunnel pipe curtain structure, after the length of the broken line segment reaches L2, the variable length combined jacking pipe needs to continue to be pushed in, and the length of the broken line segment needs to be increased. At this time, when one end of the steel box 4 slides outward to the opening, the lateral length of the steel box 4 can no longer meet the needs, and a steel box extension section 4-1 can be connected to one end of the steel box 4 to increase the lateral length of the steel box 4. Specifically,

[0077] S2.4. When one end of the steel box 4 slides outward to the opening, the one end of the steel box 4 is connected to the steel box extension section 4-1.

[0078] Furthermore, in a construction method of a bell-mouth tunnel pipe curtain structure, S2.4 specifically includes:

[0079] S2.4.1. A notch is pre-opened on the first transition section steel pipe 7-2, and an inner steel plate 7-2-1 is detachably connected to the notch; the stratum where the first transition section steel pipe 7-2 is located is reinforced, and after the reinforcement is completed, the inner steel plate 7-2-1 is removed from the notch to expose the notch, and the third pipe jacking machine 3-3 is placed into the first transition section steel pipe 7-2 through the notch, and then the inner steel plate 7-2-1 is installed to seal the notch;

[0080] S2.4.2. With the advancement of the variable length combined jacking pipe, the third jacking machine 3-3 is gradually pulled out from the first transition section steel pipe 7-2, and then the steel box extension section 4-1 is connected to one end of the steel box 4, and the steel box extension section 4-1 is connected to the third jacking machine 3-3.

[0081] If the transverse length of the steel box 4 still does not meet the requirement after the steel box extension section 4-1 is installed, the operation of S2.4 can be repeated to continue to add the steel box extension section 4-1 and the third jacking machine 3-3, so that the transverse length of the variable-length combined pipe body is further extended, thereby meeting the lining pre-construction requirements of a larger section.

[0082] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes. They can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the embodiments shown and described herein.

Claims

1. A variable length combined jacking pipe, characterized in that: It includes a steel box, a movable joint guide tube and a fixed joint guide tube, one end of the movable joint guide tube and the fixed joint guide tube are respectively connected to a first transition section steel tube and a second transition section steel tube, the first transition section steel tube and the second transition section steel tube are respectively provided with a first accommodating groove and a second accommodating groove on the side close to each other, the movable joint guide tube is provided with an opening, one end of the steel box passes through the opening and is slidably connected to the movable joint guide tube, and the other end is fixedly connected to the fixed joint guide tube.

2. A variable length combined jacking pipe as claimed in claim 1, characterized in that: One end of the steel box is connected with an extension section.

3. A variable length combined jacking pipe as claimed in claim 1, characterized in that: The cross section of the first transition section steel pipe is C-shaped.

4. A bell-mouth tunnel pipe curtain structure, characterized in that: The part of the pipe-roof prefabricated structure located at the tunnel vault and the invert is composed of a plurality of groups of variable-length combined jacking pipes as described in any one of claims 1-3.

5. A construction method for a bell-mouth tunnel pipe-roof structure as claimed in claim 4, characterized in that: The following steps are involved: S1. Pushing a pilot pipe into the stratum until it penetrates, the distance between two adjacent pilot pipes varies with the cross-sectional dimensions of the dark excavation structure; S2, carrying out the jacking of the first group of variable length combined jacking pipes: S2.

1. Connect one end of the first transition section steel pipe and the second transition section steel pipe to two adjacent pilot pipes respectively, and arrange a combined pipe jacking machine between the first transition section steel pipe and the second transition section steel pipe, with both ends of the combined pipe jacking machine extending into the first receiving tank and the second receiving tank respectively; S2.2, connecting one end of the movable joint guide tube and the fixed joint guide tube to the other end of the first transition section steel pipe and the second transition section steel pipe respectively, and connecting the steel box to the plurality of pipe jacking machines respectively; S2.3, the plurality of pipe jacking machines start to work, and push the first group of variable-length combined pipe jacking machines along the path of the pilot pipe, and the pilot pipe, the first transition section steel pipe and the second transition section steel pipe are gradually pushed out, and as the spacing between the two pilot pipes changes, one end of the steel box slides in the flexible joint guide pipe, and drives one end of the combined pipe jacking machine to move in the first receiving groove; S3, repeat S2, and complete the jacking of other variable-length combined jacking pipes in sequence until the end.

6. The construction method of a bell-mouth tunnel pipe-roof structure according to claim 5, characterized in that: The combined pipe jacking machine comprises a first pipe jacking machine and at least one second pipe jacking machine, and the first pipe jacking machine and the second pipe jacking machine are arranged in parallel along the transverse direction of the steel box.

7. The construction method of a bell-mouth tunnel pipe-roof structure according to claim 5, characterized in that: Two adjacent groups of the variable-length combined jacking pipes share a double-side opening guide pipe, one side of the double-side opening guide pipe is provided with the opening, and the other side is fixedly connected to the corresponding steel box.

8. The construction method of a bell-mouth tunnel pipe-roof structure according to claim 5, characterized in that: S2 also includes: S2.

4. When one end of the steel box slides outward to the opening, a steel box extension section is connected to the one end of the steel box.

9. The construction method of a bell-mouth tunnel pipe-roof structure according to claim 8, characterized in that: S2.4 specifically includes: S2.4.

1. Reinforce the stratum where the first transition section steel pipe is located, and open a notch on the first transition section steel pipe, place the third pipe jacking machine into the first transition section steel pipe through the notch, and then seal the notch; S2.4.

2. As the variable-length combined jacking pipe is advanced, the third jacking machine is gradually pulled out of the first transition section steel pipe, and then the steel box extension section is connected to one end of the steel box, and the steel box extension section is connected to the third jacking machine.

10. The construction method of a bell-mouth tunnel pipe-roof structure according to claim 9, characterized in that: The notch is detachably connected with an inner steel plate.

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