Inverted arch construction structure of tunnel penetrating karst stratum

Abstract

According to the inverted arch construction structure of the tunnel penetrating through the karst stratum, upper and lower reinforcing steel bars of an inverted arch are bent at a side wall and are accurately positioned by using a reinforcing steel bar positioning fixture, and a control steel wire is arranged on the side wall in a pulling manner to ensure that the bending and stretching lengths are consistent. Marked lines are marked on the side wall and the inverted arch primary support sprayed concrete to control the position of a drainage blind pipe, a steel wire mesh is arranged on the side wall in a pulling mode to control the height and flatness of the top face of an inverted arch backfill layer, and a novel n-shaped steel bar positioning clamp is used for fixing a middle-buried water stop belt. The main construction steps are as follows: spraying concrete to an inverted arch primary support; marking a side wall and nailing steel nails; mounting and positioning reinforcing steel bars; mounting a steel bar positioning fixture; inverted arch steel bars are installed; installing a drainage blind pipe; a middle-buried water stop belt is installed; inverted arch concrete is poured; pulling a steel wire mesh; constructing an inverted arch backfilling layer; and circularly constructing. The utility model ensures the quality, improves the waterproofness, and has technical and economic benefits.

Description

Technical Field

[0001] The utility model relates to the technical field of construction engineering, in particular to an inverted arch construction structure for a tunnel passing through a karst stratum, which is mainly applicable to the inverted arch construction of a tunnel, especially the inverted arch construction of a tunnel in karst geology. Background Technique

[0002] The inverted arch is one of the main components of the tunnel structure and is the foundation of the tunnel structure. Setting an inverted arch during tunnel construction can form a closed structural system for the support structure, improve the overall mechanical performance, and control the development of the convergence displacement of the tunnel and the plastic deformation of the surrounding rock mass. During the use of the tunnel, the inverted arch can effectively transfer the stratum pressure above the tunnel to the ground through the tunnel side wall structure or the road surface load, and can also effectively resist the reaction force transmitted from the lower stratum of the tunnel.

[0003] In the current industry situation, the importance of the inverted arch is often not enough, especially for tunnels in karst geology. The following problems often exist during the inverted arch construction process:

[0004] (1) The lengths of the inverted arch steel bars are uneven, the lengths of the inverted arch steel bars extending from the tunnel side wall are different, and at the same time, the spacing of the inverted arch steel bars is uneven;

[0005] (2) The undulation of the inverted arch filling concrete is large, the top elevation is inconsistent, and it is uneven, making it difficult to reach a unified flat line.

[0006] (3) The circumferential drainage blind pipe and the longitudinal drainage blind pipe are seriously offset, affecting the connection between the drainage blind pipes.

[0007] (4) The waterproof performance of the waterstop structure at the end form of the inverted arch is poor. When removing the formwork, the fixed structure for installing the waterstop needs to be removed, resulting in poor waterproof performance of the later structure.

[0008] Under the long-term erosion of karst water in the later stage, the above problems will cause settlement of the tunnel inverted arch, disconnection between the inverted arch and the secondary lining, and serious water seepage, affecting the stability and safety of the overall tunnel structure.

[0009] The purpose of the utility model is to ensure that the spacing of the inverted arch steel bars of the tunnel is uniform, the height of the inverted arch steel bars extending from the tunnel side wall is flush, improve the flatness of the inverted arch filling concrete and the installation accuracy of the drainage blind pipes, facilitate the installation and removal of the waterstop, improve the waterproof performance of the inverted arch structure, and urgently need to invent a simple and effective inverted arch and construction method for a tunnel passing through a karst stratum. Content of the Utility Model

[0010] To achieve the above technical purposes, the utility model adopts the following technical solutions:

[0011] The utility model relates to an inverted arch construction structure for a tunnel passing through a karst stratum, which includes tunnel side walls, the highest steel bar control wire, the lowest steel bar control wire, the circumferential drainage blind pipe marking, the highest steel bar, the lowest steel bar, the longitudinal drainage blind pipe, the positioning steel bar rod, the horizontal steel bar, the steel bar positioning fixture, and the inverted arch primary support shotcrete;

[0012] The inverted arch steel bars are laid on the inverted arch primary support shotcrete at a designed spacing. The inverted arch steel bars include the upper layer steel bars of the inverted arch and the lower layer steel bars of the inverted arch. The inverted arch steel bars are bent upwards at the tunnel side walls. The upper layer steel bars of the inverted arch are bent into the lowest steel bars, and the lower layer steel bars of the inverted arch are bent into the highest steel bars. The inverted arch steel bars are accurately positioned through the steel bar positioning fixtures, and the upper layer steel bars of the inverted arch and the lower layer steel bars of the inverted arch are respectively embedded into the steel bar positioning slots;

[0013] The highest steel bar control wire and the lowest steel bar control wire are arranged on the tunnel side walls at a designed height. The highest steel bar control wire is used to control the top height of the highest steel bar, and the lowest steel bar control wire is used to control the top height of the lowest steel bar;

[0014] Positioning steel bar rods are also driven into the inverted arch primary support shotcrete, and horizontal steel bars are also implanted into the tunnel side walls. The horizontal steel bars are welded and fixed to the positioning steel bar rods. Steel bar positioning fixtures are welded to the horizontal steel bars, and the highest steel bar and the lowest steel bar are embedded into multiple steel bar positioning slots on the steel bar positioning fixtures. The spacing between the highest steel bar and the lowest steel bar is accurately positioned through the steel bar positioning fixtures;

[0015] Circumferential drainage blind pipe markings are drawn on the tunnel side walls and the inverted arch primary support shotcrete at a designed position, and a longitudinal drainage blind pipe is installed between the positioning steel bar rod and the lowest steel bar.

[0016] Furthermore, it also includes a control wire mesh for the top surface of the backfill layer concrete, an inverted arch, an inverted arch backfill layer, an inverted arch central water channel, a left strip, a right strip, a central dividing rib, a narrow and long clip, a wide and short clip, a fixing plate, a screw hole, an equal - angle steel, a screw, a lower - layer inverted arch end formwork, an upper - layer inverted arch end formwork, a middle - buried water stop belt, and a several - shaped steel bar positioning clamp;

[0017] When the concrete of the inverted arch is poured, a combined structure of a lower - layer inverted arch end formwork and an upper - layer inverted arch end formwork is adopted;

[0018] The middle - buried water stop belt is fixed through a several - shaped steel bar positioning clamp, and the left strip of the middle - buried water stop belt is embedded into the narrow and long clip;

[0019] The central dividing rib is embedded into the wide and short clip. The fixing plate is connected to the equal - angle steel through screws. The equal - angle steel is located between the lower - layer inverted arch end formwork and the upper - layer inverted arch end formwork. The right strip of the middle - buried water stop belt is embedded into the gap between the lower - layer inverted arch end formwork and the upper - layer inverted arch end formwork;

[0020] A control wire mesh for the top surface of the backfill layer concrete is stretched on the tunnel side walls, which is used to control the top height and flatness of the inverted arch backfill layer.

[0021] Further, a plurality of steel bar positioning slots are uniformly arranged on the steel bar positioning fixture. Three steel bar positioning fixtures are longitudinally arranged on the shotcrete of the invert primary support, and one steel bar positioning fixture is arranged on each side tunnel wall. For the steel bar positioning fixture on the shotcrete of the invert primary support, the upper steel bar positioning slot penetrates into the upper layer of the invert steel bars, and the lower steel bar positioning slot penetrates into the lower layer of the invert steel bars. For the steel bar positioning fixture at the tunnel wall, the highest steel bar penetrates into the outer steel bar positioning slot, and the lowest steel bar penetrates into the inner steel bar positioning slot.

[0022] Further, both the highest steel bar control wire and the lowest steel bar control wire are nailed to the tunnel wall with steel nails.

[0023] Further, the embedded waterstop is composed of a left strip, a right strip, and a central dividing rib. The several-shaped steel bar positioning clamp is composed of a narrow and long clip, a wide and short clip, a fixing plate, and screw holes.

[0024] Further, screw holes are drilled in the equal-angle steel. One is arranged on the upper and lower parts of the equal-angle steel respectively and is firmly embedded with the lower invert end formwork and the upper invert end formwork.

[0025] Further, a plurality of several-shaped steel bar positioning clamps are uniformly arranged at equal intervals along the length direction of the equal-angle steel. The left strip of the embedded waterstop is fixed by a plurality of several-shaped steel bar positioning clamps, and the left strip is buried by pouring the invert concrete on the left strip side.

[0026] Further, the top surface control wire mesh of the backfill layer concrete is also fixed with steel nails. One wire is arranged longitudinally along the tunnel wall for the top surface control wire mesh of the backfill layer concrete, and multiple wires are arranged transversely. The smoothness of the invert backfill layer is controlled by the wires.

[0027] The utility model has the following characteristics and beneficial effects:

[0028] 1) The utility model uses a steel bar positioning fixture to accurately control the spacing of the invert steel bars, and uses a wire pulled on the tunnel wall to control the protruding length of the invert steel bars at the tunnel wall, so that the elevation is kept consistent, ensuring the installation quality of the invert steel bars.

[0029] 2) The utility model draws circumferential drainage blind pipe markings on the tunnel wall and the shotcrete of the invert primary support, and uses positioning steel bar rods to position the longitudinal drainage blind pipes, ensuring that the installation positions of the circumferential drainage blind pipes and the longitudinal drainage blind pipes do not deviate, and realizing the precise installation and docking of the drainage blind pipes.

[0030] 3) The utility model uses a new type of several-shaped steel bar positioning clamp to fixedly install the embedded waterstop. After the upper and lower end formworks of the invert and the equal-angle steel are removed, the several-shaped steel bar positioning clamp is directly left in the invert without being removed, which can improve the waterproof performance.

[0031] 4) In the utility model, a control steel wire mesh for the top surface of the backfill layer concrete is stretched on the side wall of the tunnel to control the top surface height of the invert backfill layer and level it, ensuring that the top surface of the invert backfill layer is flat and there is no unevenness, thus improving the construction quality of the invert. Brief Description of the Drawings

[0032] Figure 1 It is the overall structure diagram of the accurate installation, positioning and alignment of the invert steel bars in the tunnel of the utility model;

[0033] Figure 2 It is the structure diagram of the steel bar positioning fixture of the utility model;

[0034] Figure 3 It is the structure diagram of accurately fixing the upper and lower layer steel bars on the invert by the steel bar positioning fixture on the sprayed concrete of the initial support of the invert in the utility model;

[0035] Figure 4 It is the structure diagram of accurately fixing the high and low steel bars extending from the invert by the steel bar positioning fixture at the side wall of the tunnel in the utility model;

[0036] Figure 5 It is the structure diagram of controlling the top surface height of the invert backfill layer by the control steel wire mesh for the top surface of the invert backfill layer concrete in the utility model;

[0037] Figure 6 It is the structure diagram of the embedded waterstop in the utility model;

[0038] Figure 7 It is the structure diagram of the several - type steel bar positioning clamp in the utility model;

[0039] Figure 8 It is the sectional view of fixing the embedded waterstop by the several - type steel bar positioning clamp in the utility model;

[0040] Figure 9 It is the construction drawing of segment formwork pouring for the invert and the invert backfill layer in the utility model;

[0041] Figure 10 It is the detailed structure diagram of fixing the embedded waterstop by the several - type steel bar positioning clamp in the utility model.

[0042] Wherein: 1. Tunnel side wall; 2. Highest steel bar control wire; 3. Lowest steel bar control wire; 4. Circumferential drainage blind pipe marking; 5. Highest steel bar; 6. Lowest steel bar; 7. Longitudinal drainage blind pipe; 8. Positioning steel bar rod; 9. Horizontal steel bar; 10. Steel bar positioning fixture; 11. Inverted arch primary shotcrete; 12. Inverted arch steel bars; 12-1. Upper layer steel bars of the inverted arch; 12-2. Lower layer steel bars of the inverted arch; 13. Steel bar positioning slot; 14. Steel nail; 15. Control wire mesh for the top surface of the backfill layer concrete; 16. Inverted arch; 17. Inverted arch backfill layer; 18. Central ditch of the inverted arch; 19. Left belt; 20. Right belt; 21. Central dividing rib; 22. Narrow and long clip; 23. Wide and short clip; 24. Fixed plate; 25. Screw hole; 26. Equal-angle steel; 27. Screw; 28. Lower layer end form of the inverted arch; 29. Upper layer end form of the inverted arch; 30. Embedded waterstop; 31. Type-J steel bar positioning clip. Detailed implementation method

[0043] The composition of the tunnel inverted arch structure, the connection method between the inverted arch steel arch and the steel arch inside the side wall, the diameter and spacing of the inverted arch steel bars, the installation quality requirements of the drainage blind pipes, the material of the embedded waterstop, the material of the type-J steel bar positioning clip, the detailed structure of the inverted arch end form, the formwork support method for the central ditch of the inverted arch, the quality requirements for steel bar welding, the formwork support technology for the inverted arch arc formwork, the concrete pouring process, etc. are not elaborated in this utility model. The implementation method of the structure involved in this utility model is mainly described.

[0044] Embodiment 1

[0045] As Figure 1-4 shown in the overall structure diagram of the precise installation, positioning and alignment of the tunnel inverted arch steel bars, including tunnel side wall 1, highest steel bar control wire 2, lowest steel bar control wire 3, circumferential drainage blind pipe marking 4, highest steel bar 5, lowest steel bar 6, longitudinal drainage blind pipe 7, positioning steel bar rod 8, horizontal steel bar 9, steel bar positioning fixture 10, inverted arch primary shotcrete 11, inverted arch steel bars 12, upper layer steel bars 12-1 of the inverted arch, lower layer steel bars 12-2 of the inverted arch, steel bar positioning slot 13, steel nail 14, etc. The inverted arch steel bars 12 are laid on the inverted arch primary shotcrete 11 at the designed spacing. The inverted arch steel bars 12 include upper layer steel bars 12-1 of the inverted arch and lower layer steel bars 12-2 of the inverted arch. The inverted arch steel bars 12 are bent upwards at the tunnel side wall 1. The upper layer steel bars 12-1 of the inverted arch are bent into the lowest steel bar 6, and the lower layer steel bars 12-2 of the inverted arch are bent into the highest steel bar 5. Three steel bar positioning fixtures 10 are longitudinally arranged on the inverted arch primary shotcrete 11, and one steel bar positioning fixture 10 is respectively arranged on both sides of the tunnel side wall 1. The inverted arch steel bars 12 are accurately positioned through the steel bar positioning fixtures 10. A plurality of steel bar positioning slots 13 are evenly arranged on the steel bar positioning fixtures 10. The upper steel bar positioning slot 13 on the steel bar positioning fixture 10 on the inverted arch primary shotcrete 11 penetrates into the upper layer steel bars 12-1 of the inverted arch, and the lower steel bar positioning slot 13 penetrates into the lower layer steel bars 12-2 of the inverted arch.

[0046] Preferably, positioning steel bars 8 are driven into the shotcrete 11 of the invert primary support, horizontal steel bars 9 are implanted into the tunnel side wall 1, and the horizontal steel bars 9 are welded to the positioning steel bars 8; steel bar positioning clamps 10 are welded onto the horizontal steel bars 9, and the highest steel bar 5 is inserted into the outer steel bar positioning slot 13 of the steel bar positioning clamp 10 at the tunnel side wall 1, and the lowest steel bar 6 is inserted into the inner steel bar positioning slot 13; the spacing between the highest steel bar 5 and the lowest steel bar 6 is accurately positioned by the steel bar positioning clamp 10.

[0047] Preferably, the highest steel bar control wire 2 and the lowest steel bar control wire 3 are set at the designed height on the tunnel side wall 1. The highest steel bar control wire 2 is used to control the top surface height of the highest steel bar 5, and the lowest steel bar control wire 3 is used to control the top surface height of the lowest steel bar 6. Both the highest steel bar control wire 2 and the lowest steel bar control wire 3 are nailed to the tunnel side wall 1 by steel nails 14.

[0048] Preferably, circumferential drainage blind pipe markings 4 are drawn at the designed positions on the tunnel side wall 1 and the shotcrete 11 of the invert primary support, and a longitudinal drainage blind pipe 7 is installed between the positioning steel bar 8 and the lowest steel bar 6.

[0049] As Figure 6 shown in the structure diagram of the embedded waterstop, which includes the left strip 19, the right strip 20, and the central dividing rib 21. The embedded waterstop 30 is mainly composed of three parts: the left strip 19, the right strip 20, and the central dividing rib 21.

[0050] As Figure 7 shown in the structure diagram of the several-shaped steel bar positioning clamp, which includes the narrow and long clip 22, the wide and short clip 23, the fixing plate 24, and the screw hole 25. The several-shaped steel bar positioning clamp 31 is mainly composed of parts such as the narrow and long clip 22, the wide and short clip 23, the fixing plate 24, and the screw hole 25.

[0051] As Figure 8 、 10 shown in the structure diagram of the several-shaped steel bar positioning clamp for fixing the embedded waterstop, which includes the invert 16, the left strip 19, the right strip 20, the central dividing rib 21, the narrow and long clip 22, the wide and short clip 23, the fixing plate 24, the screw hole 25, the equal-angle steel 26, the screw 27, the lower invert end form 28, the upper invert end form 29, the embedded waterstop 30, the several-shaped steel bar positioning clamp 31, etc. When pouring the concrete of the invert 16, a combined structure of the lower invert end form 28 and the upper invert end form 29 is adopted, and the embedded waterstop 30 is fixed by the several-shaped steel bar positioning clamp 31.

[0052] The left strip 19 of the center-embedded waterstop 30 is embedded in the narrow and long clip 22, the central dividing rib 21 is embedded in the wide and short clip 23, the fixing plate 24 is connected to the equal-angle steel 26 by screws 27, and screw holes 25 are drilled in the equal-angle steel 26; the equal-angle steel 26 is located between the lower invert end form 28 and the upper invert end form 29, and one equal-angle steel 26 is provided respectively above and below, and is firmly embedded with the lower invert end form 28 and the upper invert end form 29. The right strip 20 of the center-embedded waterstop 30 is embedded in the gap between the lower invert end form 28 and the upper invert end form 29.

[0053] Preferably, a plurality of U-shaped steel bar positioning clips 31 are arranged at equal intervals along the length direction of the equal-angle steel 26. The left strip 19 of the center-embedded waterstop 30 is fixed by the plurality of U-shaped steel bar positioning clips 31, and the left strip 19 is embedded by pouring the concrete of the invert 16 on the side of the left strip 19.

[0054] As Figure 5 、 9 As shown in the structure diagram of the top surface control wire mesh of the invert backfill layer for controlling the top surface height of the invert backfill layer, including the tunnel side wall 1, steel nails 14, the top surface control wire mesh 15 of the backfill layer concrete, the invert 16, the invert backfill layer 17, etc. The top surface control wire mesh 15 of the backfill layer concrete is pulled on the tunnel side wall 1 to control the top surface height and flatness of the invert backfill layer 17. The top surface control wire mesh 15 of the backfill layer concrete is fixed by steel nails 14. One wire is arranged longitudinally along the tunnel side wall 1 for the top surface control wire mesh 15 of the backfill layer concrete, and multiple wires are arranged transversely. The flatness of the invert backfill layer 17 is controlled by the wires.

[0055] Embodiment 2

[0056] The invert of the tunnel passing through the karst stratum and the construction method include the following steps:

[0057] (1) Spraying concrete for the primary support of the tunnel invert

[0058] Excavate the base surface of the tunnel invert, clean up sundries, mud, accumulated water, etc. at the bottom of the tunnel, spray concrete on the bottom of the tunnel according to the design requirements to form the primary support sprayed concrete 11 of the invert. Erect a steel arch frame on the primary support sprayed concrete 11 of the invert. The steel arch frame of the invert must be aligned and connected with the steel arch frame inside the side wall, and a connecting plate is used between the two to form a closed loop.

[0059] (2) Marking and nailing steel nails on the side wall

[0060] Measure and set out the lines according to the designed spacing and position, drive steel nails 14 at the measurement and setting-out points, pull the highest steel bar control wire 2 and the lowest steel bar control wire 3 through the steel nails 14, and draw the circumferential drainage blind pipe marking lines 4 on the tunnel side wall 1 and the primary support sprayed concrete 11 of the invert according to the setting-out points.

[0061] (3) Installing the positioning steel bar rod

[0062] Install the positioning steel bars 8 on the shotcrete 11 of the invert primary support according to the measured lofting points. At the same time, implant the horizontal steel bars 9 into the tunnel side wall 1, and weld the horizontal steel bars 9 to the positioning steel bars 8.

[0063] (4) Install the steel bar positioning fixtures

[0064] Install and fix three steel bar positioning fixtures 10 on the shotcrete 11 of the invert primary support according to the positions measured and set out. At the same time, weld one steel bar positioning fixture 10 on the horizontal steel bars 9 on both sides of the tunnel side wall 1.

[0065] (5) Install the invert steel bars

[0066] Pass the upper layer of invert steel bars 12-1 through the upper steel bar positioning slots 13 of the three steel bar positioning fixtures 10 on the shotcrete 11 of the invert primary support in sequence. Then, bend it upward at the tunnel side wall 1 to form the lowest steel bar 6. The lowest steel bar 6 passes through the inner steel bar positioning slot 13 of one steel bar positioning fixture 10 on the horizontal steel bar 9 and is kept at the same height as the lowest steel bar control wire 3. Pass the lower layer of invert steel bars 12-2 through the lower steel bar positioning slots 13 of the three steel bar positioning fixtures 10 on the shotcrete 11 of the invert primary support in sequence. Then, bend it upward at the tunnel side wall 1 to form the highest steel bar 5. The highest steel bar 5 passes through the outer steel bar positioning slot 13 of one steel bar positioning fixture 10 on the horizontal steel bar 9 and is kept at the same height as the highest steel bar control wire 2.

[0067] (6) Install the drainage blind pipes

[0068] Install the circumferential drainage blind pipes according to the circumferential drainage blind pipe markings 4 marked on the tunnel side wall 1 and the shotcrete 11 of the invert primary support. At the same time, install the longitudinal drainage blind pipe 7 between the positioning steel bars 8 and the lowest steel bar 6, and effectively connect the longitudinal drainage blind pipe 7 with the circumferential drainage blind pipes.

[0069] (7) Install the embedded waterstop

[0070] Install the lower layer of invert end form 28 and the upper layer of invert end form 29 on the shotcrete 11 of the invert primary support. Embed the left belt 19 of the embedded waterstop 30 into the narrow long clip 22 of the channel-shaped steel bar positioning clamp 31, and embed the central dividing rib 21 into the wide short clip 23. Connect the fixing plate 24 of the channel-shaped steel bar positioning clamp 31 with the equal-angle steel 26 through the screw 27. Then, extend the right belt 20 of the embedded waterstop 30 into the gap between the lower layer of invert end form 28 and the upper layer of invert end form 29, and fasten the equal-angle steel 26 to the gap between the lower layer of invert end form 28 and the upper layer of invert end form 29.

[0071] (8) Pour the invert concrete

[0072] Use a new type of self-propelled invert trestle to support the arc formwork of the invert, pump and pour the invert concrete 16. The top surface of the concrete is leveled based on the elevation line of the top surface of the invert concrete 16 marked on the tunnel sidewall 1. Vibration is compacted near the embedded waterstop 30. The invert concrete 16 embeds the left belt 19 and the central dividing rib 21.

[0073] (9) Stretch the control steel wire mesh for the top surface of the backfill layer concrete

[0074] Nail the steel nails 14 according to the measurement layout points, and stretch the control steel wire mesh 15 for the top surface of the backfill layer concrete through the steel nails 14. One steel wire is arranged longitudinally along the tunnel sidewall 1 for the control steel wire mesh 15 of the top surface of the backfill layer concrete, and multiple steel wires are arranged transversely.

[0075] (10) Construction of the invert backfill layer

[0076] After the invert concrete 16 has finally set, clean the top surface of the invert 16, sprinkle water for wetting, support the bottom formwork and end formwork of the invert backfill layer 17, support the formwork of the central drain 18 of the invert at the central position of the invert 16, and carry out the concrete pouring of the invert backfill layer 17. The pouring is carried out in layers, and the thickness of each layer does not exceed 50 cm. Manually use an inserted vibrator for vibration, and use the control steel wire mesh 15 for the top surface of the backfill layer concrete to control the top surface height of the invert backfill layer 17 and level it.

[0077] (11) Circular construction

[0078] Carry out the tunnel invert construction in cycles according to the above procedures. The invert backfill layer 17 lags behind the invert 16 by one segment, and the length of each segment is about 30 - 50 m. The embedded waterstop 30 is set in the expansion joint at the junction of adjacent segments for waterproofing.

Claims

1. A tunnel invert construction structure passing through a karst stratum, characterized in that: It comprises a tunnel side wall (1), a highest steel bar control wire (2), a lowest steel bar control wire (3), a circumferential drainage blind pipe marking line (4), a highest steel bar (5), a lowest steel bar (6), a longitudinal drainage blind pipe (7), a positioning steel bar rod (8), a horizontal steel bar (9), a steel bar positioning fixture (10), and an inverted arch primary support shotcrete (11); An inverted arch steel bar (12) is laid on the inverted arch primary support shotcrete (11) at a designed interval, the inverted arch steel bar (12) comprising an inverted arch steel bar upper layer bar (12-1) and an inverted arch steel bar lower layer bar (12-2), the inverted arch steel bar (12) is bent upward at the tunnel side wall (1), the inverted arch steel bar upper layer bar (12-1) is bent to form the lowest steel bar (6), and the inverted arch steel bar lower layer bar (12-2) is bent to form the highest steel bar (5); the inverted arch steel bar (12) is accurately positioned by a steel bar positioning fixture (10), and the inverted arch steel bar upper layer bar (12-1) and the inverted arch steel bar lower layer bar (12-2) are respectively embedded in the steel bar positioning slot (13); The tunnel side wall (1) is provided with a highest reinforcement control wire (2) and a lowest reinforcement control wire (3) at a designed height, wherein the highest reinforcement control wire (2) is used to control the top surface height of the highest reinforcement (5), and the lowest reinforcement control wire (3) is used to control the top surface height of the lowest reinforcement (6); A positioning steel bar (8) is also driven into the primary support shotcrete (11) of the inverted arch, and a horizontal steel bar (9) is also implanted into the tunnel side wall (1), and the horizontal steel bar (9) is welded and fixed to the positioning steel bar (8); a steel bar positioning fixture (10) is welded to the horizontal steel bar (9), and a plurality of steel bar positioning slots (13) on the steel bar positioning fixture (10) are embedded with the highest steel bar (5) and the lowest steel bar (6), and the spacing between the highest steel bar (5) and the lowest steel bar (6) is accurately positioned by the steel bar positioning fixture (10); Circumferential drainage blind pipe marking lines (4) are drawn on the tunnel side walls (1) and the initial support concrete spraying (11) of the inverted arch according to the designed positions, and a longitudinal drainage blind pipe (7) is installed between the positioning steel bar (8) and the lowest steel bar (6).

2. The invert construction structure for a tunnel through a karst stratum as claimed in claim 1, characterized in that: The invention also comprises a backfill layer concrete top surface control steel wire mesh (15), an inverted arch (16), an inverted arch backfill layer (17), an inverted arch central ditch (18), a left belt (19), a right belt (20), a central dividing rib (21), a narrow and long clip (22), a wide and short clip (23), a fixing plate (24), a screw hole (25), an equilateral angle steel (26), a screw (27), a lower inverted arch end mold (28), an upper inverted arch end mold (29), a buried water stop strip (30), and several types of steel bar positioning cards (31); When pouring concrete for the inverted arch (16), a combined structure of a lower inverted arch end form (28) and an upper inverted arch end form (29) is adopted; The embedded water stop strip (30) is fixed by several types of steel bar positioning clips (31), and the left strip (19) of the embedded water stop strip (30) is embedded in the narrow and long clamping piece (22); The central partition rib (21) is embedded in the wide and short clip (23), the fixing plate (24) is connected to the equilateral angle steel (26) through screws (27), the equilateral angle steel (26) is located between the lower inverted arch end mold (28) and the upper inverted arch end mold (29), and the right belt (20) of the embedded water stop belt (30) is embedded in the gap between the lower inverted arch end mold (28) and the upper inverted arch end mold (29); The tunnel side wall (1) is provided with a backfill layer concrete top surface control steel wire mesh (15) for controlling the top surface height and flatness of the invert backfill layer (17).

3. The invert construction structure of a tunnel passing through a karst stratum as claimed in claim 2, characterized in that: A plurality of steel bar positioning slots (13) are evenly arranged on the steel bar positioning fixture (10); three steel bar positioning fixtures (10) are longitudinally arranged on the inverted arch primary support sprayed concrete (11); and one steel bar positioning fixture (10) is respectively arranged on the tunnel side walls (1) on both sides; the upper steel bar positioning slot (13) of the steel bar positioning fixture (10) on the inverted arch primary support sprayed concrete (11) penetrates the upper steel bar (12-1) of the inverted arch steel bar, and the lower steel bar positioning slot (13) penetrates the lower steel bar (12-2) of the inverted arch steel bar; the highest steel bar (5) is penetrated into the outer steel bar positioning slot (13) of the steel bar positioning fixture (10) at the tunnel side wall (1), and the lowest steel bar (6) is penetrated into the inner steel bar positioning slot (13).

4. The invert construction structure for a tunnel passing through a karst stratum as claimed in claim 3, characterized in that: The highest reinforcement control steel wire (2) and the lowest reinforcement control steel wire (3) are both nailed to the tunnel side wall (1) via steel nails (14).

5. The invert construction structure for a tunnel passing through a karst stratum as claimed in claim 4, characterized in that: The buried water stop strip (30) is composed of three parts: a left strip (19), a right strip (20), and a central dividing rib (21); the several types of steel bar positioning clips (31) are composed of a narrow and long clip (22), a wide and short clip (23), a fixing plate (24), and a screw hole (25).

6. The invert construction structure for a tunnel passing through a karst stratum as claimed in claim 5, characterized in that: The equilateral angle steel (26) is drilled with a screw hole (25). The equilateral angle steel (26) is provided with one screw hole at the top and one screw hole at the bottom, and is firmly embedded with the lower inverted arch end mold (28) and the upper inverted arch end mold (29).

7. The invert construction structure for a tunnel passing through a karst stratum as claimed in claim 6, characterized in that: A plurality of the several types of steel bar positioning clips (31) are evenly spaced along the length direction of the equilateral angle steel (26), and the left belt (19) of the buried water stop belt (30) is fixed by the plurality of the several types of steel bar positioning clips (31), and the left belt (19) is buried by pouring the concrete of the inverted arch (16) on the side of the left belt (19).

8. The invert construction structure for a tunnel passing through a karst stratum as claimed in claim 7, characterized in that: The backfill layer concrete top surface control steel wire mesh (15) is also fixed by steel nails (14). The backfill layer concrete top surface control steel wire mesh (15) is provided with one steel wire each along the longitudinal direction of the tunnel side wall (1) and multiple steel wires along the transverse direction, and the flatness of the invert backfill layer (17) is controlled by the steel wires.

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