Excavation Method for Small Clearance Three-arch Tunnel with Special-shaped Cross-section

Abstract

The present application relates to the field of tunnel construction, and in particular to a method for excavating a small-clearance triple-arch special-section tunnel, comprising the following steps: tunnel excavation: mechanical equipment excavates the rock mass multiple times according to a preset route; initial support: after excavation to a preset depth, initially spray a layer of concrete to seal the exposed rock surface; at least two rows of grouting pipes are pre-buried within a 120° range of the arch, and the end of the grouting pipe that is not inserted into the rock and soil is reserved for a set length to be exposed; spraying preparation: an extension rod is installed on the exposed part of the grouting pipe; a docking assembly is provided at one end of the extension rod, and the docking assembly is used to detachably connect the extension rod to the grouting pipe, and a marking portion is provided at the end of the other end; spraying begins: a spraying interval is formed between adjacent extension rods; concrete is sprayed on several spraying intervals one by one; the concrete thickness in the spraying interval is maintained not to exceed the marking portion. The present application has the effect of reducing the possibility of dangerous accidents in the tunnel.

Description

Technical Field

[0001] The present application relates to the field of tunnel construction, and in particular to a method for excavating a small-clearance triple-arch special-section tunnel. Background Art

[0002] At present, triple arch refers to a tunnel structure in which three tunnels are set up in parallel and the arc contours of the arches of adjacent tunnels intersect. It is commonly seen in urban rail transit construction. In the construction of triple arches, due to the different clear distances between the centers of the three tunnels, different construction methods will be used accordingly, mainly the double side wall pilot pit method and the step method.

[0003] When excavating a triple arch, double guide holes can be excavated on both sides first. After the double guide holes are excavated to a preset distance, the middle guide hole can be excavated to the same distance. After any guide hole is excavated to a certain depth, a layer of concrete must be sprayed in time to seal the exposed rock surface, and then anchor rods and nets are hung. After spraying concrete to a preset thickness, the above steps are repeated to continue excavation.

[0004] The inventor believes that when spraying concrete, tunnel construction workers hold the spray gun and operate it, and the spraying thickness is manually controlled by the construction workers, which may easily lead to different thicknesses of concrete in different areas, thereby easily causing dangerous accidents due to uneven stress on concrete in different areas of the tunnel. Summary of the invention

[0005] In order to reduce the possibility of dangerous accidents in the tunnel, the present application provides a method for excavating a small-clearance triple-arch special-section tunnel.

[0006] The present application provides a method for excavating a small-clearance triple-arch special-section tunnel using the following technical solution:

[0007] A method for excavating a small-clearance triple-arch special-section tunnel comprises the following steps:

[0008] Tunnel excavation: Mechanical equipment excavates the rock mass multiple times according to the preset route;

[0009] Initial support: When excavation reaches the preset depth, an initial layer of concrete is sprayed to seal the exposed rock surface;

[0010] At least two rows of grouting pipes are embedded within the 120° range of the arch, and the single-row grouting pipes are arranged parallel to each other and equidistantly distributed along the curvature of the arch; the end of the grouting pipe that is not inserted into the rock and soil is reserved for a set length to be exposed; when the initial support is closed into a ring, cement slurry is injected behind the initial support arch; the water-cement ratio of the cement slurry is 0.8-1.0; the grouting pressure is 0.1-0.3MPa;

[0011] Jetting preparation: Install an extension rod on the exposed part of the grouting pipe; one end of the extension rod is provided with a docking component for detachably connecting the extension rod to the grouting pipe, and the other end is provided with a marking part.

[0012] Start jetting: A jetting interval is formed between adjacent extension rods; spray concrete on several jetting intervals one by one; maintain the thickness of the concrete within the jetting interval not exceeding the marking part.

[0013] By adopting the above technical solution, after the grouting is completed, the extension rod is installed on the exposed end of the grouting pipe through the connecting component. Adjacent rows of extension rods can form multiple jetting intervals at the four corners. During excavation, the tunnel interior advances in a segmented manner, and the spraying of concrete is also completed synchronously in segments. Before spraying, adjust the height of the marking part according to the actual construction requirements; then, with the marking part as a reference, spray concrete on each of the multiple jetting intervals one by one. The spacing between adjacent grouting pipes can be adjusted according to the actual size of the tunnel, so as to adjust the actual size of the jetting interval; thereby reducing the situation where the thickness of the concrete in some areas is too thick or too thin during the spraying of concrete, and thus reducing the possibility of dangerous accidents caused by uneven stress of the concrete in different areas of the tunnel.

[0014] Optionally, the docking component includes an elastic docking part provided at the end of the grouting pipe and a buckle part provided at the end of the extension rod away from the marking part; a relief cavity is provided on the side of the elastic docking part away from the grouting pipe, and an anti-slip convex ring is protruded on the peripheral wall of the elastic docking part; the anti-slip convex ring has elasticity.

[0015] A docking inner cavity for the anti-slip convex ring to be inserted into is provided on the side of the buckle part away from the extension rod.

[0016] The inner wall of the relief cavity is arc-shaped, and the arc-shaped concave part of the relief cavity and the center of the anti-slip convex ring are in the same horizontal plane.

[0017] By adopting the above technical solution, when installing the extension rod on the grouting pipe, align the docking inner cavity with the elastic docking part, and apply an external force to force the anti-slip convex ring to be inserted into the inside of the docking inner cavity. When being inserted, the outer edge side of the anti-slip convex block is stressed, so as to force the inner wall of the relief cavity to deform towards the direction close to the axis of the extension rod, thereby realizing the anti-slip convex ring being inserted into the docking inner cavity, and thus improving the connection stability between the extension rod and the grouting pipe.

[0018] Optionally, a reset hole communicating with the docking inner cavity is penetrated through the peripheral wall of the buckle part; when the anti-slip convex ring and the docking inner cavity are in a buckled state, the center line of the reset hole and the center of the anti-slip convex ring are in the same horizontal plane.

[0019] By adopting the above technical solution, if the extension rod needs to be removed from the grouting pipe, an external rod-shaped object can be used to insert into the docking cavity from the reset hole to resist the protruding part of the anti-skid convex ring, thereby forcing the protruding part of the anti-skid convex ring to elastically recess into the avoidance cavity, thereby facilitating the anti-skid convex ring to detach from the docking cavity; in addition, when pouring concrete, part of the concrete can also enter the interior of the docking cavity from the reset hole, thereby increasing the stability of the connection between the anti-skid convex ring and the docking cavity.

[0020] Optionally, the step of starting the injection further includes the following steps:

[0021] Install waterproof layer: After the concrete is sprayed in the spraying area, install the waterproof layer on the side of the concrete away from the inner wall of the tunnel.

[0022] By adopting the above technical solution, the amount of water seeping from the rock and soil on the inner wall of the tunnel into the tunnel is reduced, thereby improving the waterproof performance of the tunnel.

[0023] Optionally, a plurality of positioning components are provided at one end of the extension rod away from the connecting component; the plurality of positioning components are equidistantly distributed on the circumference with the axis of the extension rod as the center; the marking portion is provided with a storage cavity for the plurality of positioning components to pass through; the marking portion is detachably connected to the plurality of positioning components; the end of the positioning component away from the extension rod is used to fix the side of the waterproof layer away from the injection area.

[0024] By adopting the above technical solution, before spraying concrete into the spraying interval, several positioning components are restricted by the marking part (storage cavity), and several positioning components are located in the area outside the adjacent spraying interval, thereby reducing the possibility of the positioning components interfering with the sprayed concrete; when the concrete is sprayed, the restricted state of several positioning components and the marking part is contacted, and the positioning components can be used to limit the waterproof layer, thereby improving the stability of the connection between the waterproof layer and the concrete layer.

[0025] Optionally, the positioning assembly includes a mounting base hinged to the end of the extension rod and a positioning plate hinged to the side of the mounting base away from the extension rod; a torsion spring is provided at the hinge between the positioning plate and the mounting base; a mounting hole is penetrated through the end of the positioning plate away from the mounting base, and the mounting hole is detachably connected to a fixing bolt that can penetrate the waterproof layer.

[0026] By adopting the above technical solution, when the positioning assembly is restricted in use by the marking part, several positioning plates force the torsion spring to be in a tightened state. When the positioning assembly is used to restrict the waterproof layer, the restriction state of the marking part and the positioning assembly is released, the positioning plate loses external force, and the torsion spring is reset, thereby driving the positioning plate to rotate in the direction close to the waterproof layer and fit on the waterproof layer, and finally the positioning plate and the waterproof layer are connected with fixing bolts passing through the positioning plate.

[0027] Optionally, the inner wall of the storage cavity is provided with threads; the side of the mounting base away from the axis of the extension rod is threadedly connectable to the storage cavity.

[0028] By adopting the above technical solution, the marking part is threadedly connected to the mounting base through the threads in the storage cavity, thereby improving the convenience of disassembling the marking part.

[0029] Optionally, a chamfer is provided on the side of the positioning plate away from the mounting base.

[0030] By adopting the above technical solution, it is convenient to buckle a plurality of positioning plates into the storage cavity, thereby improving the convenience of restricting the positioning assembly.

[0031] Optionally, the marking part includes a fixing ring fixedly connected to the end of the extension rod and a sleeve threadedly connected to the extension rod. The storage cavity is formed through the sleeve and its axis is collinear with the axis of the sleeve; the side of the fixing ring close to the sleeve is flush with the side of the waterproof layer away from the inner wall of the tunnel.

[0032] By adopting the above technical solution, when it is necessary to disassemble the marking part to release the positioning assembly, it is only necessary to detach the sleeve from the extension rod. The fixing ring is flush with the outer wall of the waterproof layer, thereby reducing the distance between the cast concrete and the extension rod caused by removing the marking part, and further improving the waterproof effect inside the tunnel; when the positioning plate is driven by the torsion spring to rotate towards the outer wall of the waterproof layer, it can be rotated to a state flush with the outer wall of the waterproof layer, thereby improving the fitting effect between the positioning plate and the waterproof layer.

[0033] Optionally, the steps of installing the waterproof layer specifically further include the following steps:

[0034] Release the restriction of the positioning assembly: Remove the sleeve from the extension rod;

[0035] Rotate the end of the positioning plate away from the mounting base until it abuts against the waterproof layer;

[0036] Pass the fixing bolt through the mounting hole and connect it to the waterproof layer.

[0037] By adopting the above technical solution, the positioning plate is buckled onto the outer wall of the waterproof layer, and the self-weight of the waterproof layer can force the anti-slip convex ring and the docking inner cavity to be further locked. On the one hand, the stability of the installation of the waterproof layer is improved, and on the other hand, the stability of the connection between the extension rod and the grouting pipe is improved.

[0038] In summary, the present application includes at least one of the following beneficial technical effects:

[0039] 1. Two adjacent rows of extension rods can form multiple four-corner spraying intervals. When excavating, the tunnel is advanced in sections, and the spraying of concrete is also completed in sections. Before spraying, the height of the marking part is adjusted according to the actual construction needs; then, based on the marking part, concrete is sprayed one by one in multiple spraying intervals. The spacing between adjacent grouting pipes can be adjusted according to the actual size of the tunnel, so as to adjust the actual size of the spraying interval; thereby reducing the situation where some areas are too thick or too thin when spraying concrete;

[0040] 2. If the extension rod needs to be removed from the grouting pipe, an external rod-shaped object can be inserted into the docking inner cavity from the reset hole to resist the protruding part of the anti-skid convex ring, thereby forcing the protruding part of the anti-skid convex ring to elastically concave into the inside of the avoidance cavity, thereby facilitating the anti-skid convex ring to detach from the docking inner cavity;

[0041] 3. When the marking part needs to be removed to release the positioning assembly, it is only necessary to detach the sleeve from the extension rod, and the fixing ring is flush with the outer wall of the waterproof layer, thereby reducing the distance between the poured concrete and the extension rod caused by removing the marking part, and further improving the waterproof effect inside the tunnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a cross-sectional construction diagram of the triple arch in this application;

[0043] Figure 2 It is a flowchart of the steps of the method for excavating a small-clearance triple-arch special-section tunnel in the present application;

[0044] Figure 3 It is a schematic diagram of the overall structure after the triple arch injection is completed in this application;

[0045] Figure 4 is along Figure 3 Sectional view along line FF;

[0046] Figure 5 It is a schematic diagram of the overall structure of the triple arch waterproof layer installed in this application;

[0047] Figure 6 It is a partial structural schematic diagram of the positioning component in the present application in use.

[0048] Explanation of the reference numerals in the accompanying drawings: 1. Grouting pipe; 2. Extension rod; 3. Docking assembly; 31. Elastic docking part; 32. Buckle part; 33. Avoidance cavity; 34. Anti-slip convex ring; 35. Docking inner cavity; 36. Reset hole; 4. Marking part; 41. Storage cavity; 42. Fixing ring; 43. Sleeve; 5. Positioning assembly; 51. Mounting base; 52. Positioning plate; 53. Torsion spring; 54. Fixing bolt; 55. Mounting hole; 6. Spraying section; 7. Waterproof layer. DETAILED DESCRIPTION

[0049] In order to make the purpose, technical solutions and advantages of this application more clear, the following Figures 1-6 It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0050] The embodiment of the present application discloses a method for excavating a small-clearance triple-arch special-section tunnel.

[0051] Reference Figure 1 and Figure 2 A method for excavating a small-clearance triple-arch special-section tunnel comprises the following steps:

[0052] S100: Tunnel excavation.

[0053] Specifically, mechanical equipment excavates the rock multiple times along preset routes.

[0054] S200: Initial support.

[0055] Reference Figure 1 and Figure 3 Specifically, step S200 includes the following steps:

[0056] S210: After excavation to the preset depth, a layer of concrete is sprayed to seal the exposed rock surface;

[0057] S220: at least two rows of grouting pipes 1 are embedded within a 120° range of the arch, and the single rows of grouting pipes 1 are arranged parallel to each other and equidistantly distributed along the arc of the arch; the end of the grouting pipe 1 that is not inserted into the rock soil is left exposed by a set length;

[0058] When the initial support is closed into a ring, cement slurry is injected behind the initial support arch; the water-cement ratio of the cement slurry is 0.8-1.0; the grouting pressure is 0.1-0.3MPa;

[0059] S300: Injection preparation.

[0060] Specifically, step S300 includes the following steps:

[0061] S310: Install the extension rod 2 on the exposed part of the grouting pipe 1.

[0062] Reference Figure 3 and Figure 4 A docking assembly 3 is provided at one end of the extension rod 2, and the docking assembly 3 is used to detachably connect the extension rod 2 to the grouting pipe 1. A marking portion 4 and a plurality of positioning assemblies 5 are provided at the other end. The marking portion 4 can be sleeved on the outer edge side of the plurality of positioning assemblies 5 to achieve storage restriction of the plurality of positioning assemblies 5.

[0063] A plurality of positioning components 5 are equidistantly distributed in a circle with the axis of the extension rod 2 as the center; the marking portion 4 is provided with a storage cavity 41 for the plurality of positioning components 5 to pass through; the marking portion 4 is detachably connected to the plurality of positioning components 5; the end of the positioning component 5 away from the extension rod 2 is used to fix the side of the waterproof layer 7 away from the injection zone 6.

[0064] Before spraying concrete in the spraying interval 6 , the plurality of positioning components 5 are restricted by the marking portion 4 (the receiving cavity 41 ), and the plurality of positioning components 5 are located in an area outside the adjacent spraying interval 6 , thereby reducing the possibility that the positioning components 5 interfere with the spraying concrete.

[0065] The docking assembly 3 includes an elastic docking portion 31 and a buckle portion 32; wherein the elastic docking portion 31 is fixedly connected to one end of the grouting pipe 1 protruding outside the rock and soil, and the buckle portion 32 is fixedly connected to one end of the extension rod 2 away from the marking portion 4.

[0066] An avoidance cavity 33 is provided on the side of the elastic docking portion 31 away from the grouting pipe 1 . The inner wall of the avoidance cavity 33 is arranged in an arc shape, and the avoidance cavity 33 is connected to the grouting port of the grouting pipe 1 , so as to facilitate grouting into the grouting pipe 1 through the avoidance cavity 33 .

[0067] An anti-skid convex ring 34 is protruding from the peripheral wall of the elastic docking portion 31; the anti-skid convex ring 34 is integrally formed with the elastic docking portion 31 and is elastic; a docking inner cavity 35 for the anti-skid convex ring 34 to be buckled into is provided on the side of the buckle portion 32 away from the extension rod 2; the arc-shaped inner concave part of the avoidance cavity 33 and the center of the anti-skid convex ring 34 are in the same horizontal plane.

[0068] When installing the extension rod 2 onto the grouting pipe 1, align the docking inner cavity 35 with the elastic docking portion 31, and apply external force to force the anti-skid convex ring 34 to buckle into the interior of the docking inner cavity 35. When buckled in, the outer edge side of the anti-skid convex ring 34 is subjected to force, thereby forcing the inner wall of the avoidance cavity 33 to deform in the direction close to the axis of the extension rod 2, thereby achieving the buckling of the anti-skid convex ring 34 into the docking inner cavity 35, thereby improving the stability of the connection between the extension rod 2 and the grouting pipe 1.

[0069] A reset hole 36 connected to the docking cavity 35 is formed through the peripheral wall of the buckle portion 32 ; when the anti-skid convex ring 34 and the docking cavity 35 are in the buckled state, the center line of the reset hole 36 and the center of the anti-skid convex ring 34 are in the same horizontal plane.

[0070] If the extension rod 2 needs to be removed from the grouting pipe 1, an external rod-shaped object can be inserted into the docking cavity 35 from the reset hole 36 to resist the protruding part of the anti-slip convex ring 34, thereby forcing the protruding part of the anti-slip convex ring 34 to elastically recess into the avoidance cavity 33, thereby facilitating the anti-slip convex ring 34 to detach from the docking cavity 35.

[0071] ReferenceFigure 4 and Figure 5 The positioning assembly 5 includes a mounting base 51, a positioning plate 52, a torsion spring 53 and a fixing bolt 54. Among them, the mounting base 51 is fixedly connected to the end of the extension rod 2 away from the grouting pipe 1. The positioning plate 52 is hinged to the side of the mounting base 51 away from the extension rod 2. The torsion spring 53 is sleeved at the hinge of the positioning plate 52 and the mounting base 51 to achieve elastic hinge between the positioning plate 52 and the mounting base 51. An installation hole 55 is formed through the end of the positioning plate 52 away from the mounting base 51, and the fixing bolt 54 is threadedly connected to the installation hole 55.

[0072] When the positioning assembly 5 is restricted in its use state by the marking part 4, several positioning plates 52 force the torsion spring 53 to be in a tightened state. When the positioning assembly 5 is used to restrict the waterproof layer 7, the restriction state between the marking part 4 and the positioning assembly 5 is released. The positioning plate 52 loses the external force, and the torsion spring 53 resets, thereby driving the positioning plate 52 to rotate towards the waterproof layer 7 and fit on the waterproof layer 7. Finally, the fixing bolt 54 passes through the positioning plate 52 and the waterproof layer 7 for connection.

[0073] Refer to Figure 4 and Figure 6 The inner wall of the storage cavity 41 is provided with threads. The side of the mounting base 51 away from the axis of the extension rod 2 can be threadedly connected to the threads on the inner wall of the storage cavity 41. The side of the positioning plate 52 away from the mounting base 51 is provided with a chamfer.

[0074] Based on the above structure, during installation, the construction personnel can threadedly connect the marking part 4 to the mounting base 51 through the threads in the storage cavity 41, thereby improving the convenience of disassembling the marking part 4. In addition, the provided chamfer also facilitates buckling multiple positioning plates 52 into the storage cavity 41, thereby improving the convenience of restricting the positioning assembly 5.

[0075] The marking part 4 includes a fixing ring 42 fixedly connected to the end of the extension rod 2 and a sleeve 43 threadedly connected to the extension rod 2. The storage cavity 41 is formed on the sleeve 43 and its axis is collinear with the axis of the sleeve 43. The side of the fixing ring 42 close to the sleeve 43 is flush with the side of the waterproof layer 7 away from the tunnel inner wall.

[0076] When it is necessary to disassemble the marking part 4 to release the positioning assembly 5, only the sleeve 43 needs to be detached from the extension rod 2. The fixing ring 42 is flush with the outer wall of the waterproof layer 7, thereby reducing the distance between the cast concrete and the extension rod 2 caused by removing the marking part 4 and further improving the waterproof effect inside the tunnel. When the positioning plate 52 is driven by the torsion spring 53 to rotate towards the outer wall of the waterproof layer 7, it can complete the rotation to a state flush with the outer wall of the waterproof layer 7, thereby improving the fitting effect between the positioning plate 52 and the waterproof layer 7.

[0077] Refer to Figure 1 andFigure 3 S400: Start spraying.

[0078] Specifically, when step S400 is executed, a spraying interval 6 is formed based on the adjacent extension rods 2; the construction workers spray concrete on several spraying intervals 6 one by one; the thickness of the concrete within the spraying interval 6 is maintained so as not to exceed the side of the fixed ring 42 close to the sleeve 43.

[0079] S500: Install the waterproof layer 7.

[0080] Specifically, after the concrete spraying within the spraying interval 6 is completed, the waterproof layer 7 is installed on the side of the concrete away from the tunnel inner wall.

[0081] Refer to Figure 4 and Figure 5 , step S500 includes the following steps:

[0082] S510: Remove the restriction of the positioning component 5: Remove the sleeve 43 from the extension rod 2;

[0083] Specifically, separate the sleeve 43 from the fixed ring 42 (during installation, the sleeve 43 and the fixed ring 42 are adjacent and in contact), and multiple positioning components 5 are detached from the inside of the sleeve 43. The positioning plate 52 loses the external force, and the torsion spring 53 resets, forcing the positioning plate 52 to rotate away from the axis of the extension rod 2 until it abuts against the surface of the waterproof layer 7.

[0084] S520: Rotate the end of the positioning plate 52 away from the mounting base 51 until it abuts against the waterproof layer 7.

[0085] Specifically, the construction workers adjust the excess impurities on the surface of the waterproof layer 7 according to the actual situation on site, forcing the positioning plate 52 to achieve further contact with the waterproof layer 7, thereby improving the stable effect of the positioning plate 52 in fixing the waterproof layer 7.

[0086] Refer to Figure 5 and Figure 6 , as a further optimized option, the positioning plate 52 includes a top - contact section and a pressing section connected side by side; the end of the top - contact section away from the pressing section is hinged to the mounting base 51; there is an angle greater than 150 degrees between the top - contact section and the pressing section, and an arc surface is provided on the side wall of the end of the pressing section away from the top - contact section, and the surface of the waterproof layer 7 can abut against this arc surface to increase the contact area between the positioning plate 52 and the waterproof layer 7.

[0087] S530: Pass the fixing bolt 54 through the mounting hole 55 to connect with the waterproof layer 7.

[0088] The implementation principle of a method for excavating a small clear distance triple-arch tunnel with a special-shaped cross-section in this application is as follows: After grouting is completed, the extension rod 2 is installed on the exposed end of the grouting pipe 1 through the connecting component. The extension rods 2 in adjacent two rows can form a plurality of spraying intervals 6 at the four corners. During excavation, the tunnel interior is advanced in a segmented manner, and the spraying of concrete is also completed synchronously in segments. Before spraying, the height of the marking part 4 is adjusted according to the actual construction requirements; then, with the marking part 4 as the reference, concrete is sprayed one by one in the plurality of spraying intervals 6. The spacing between adjacent grouting pipes 1 can be adjusted according to the actual size of the tunnel, so as to adjust the actual size of the spraying interval 6; thereby reducing the situation that some areas are too thick or too thin when spraying concrete, and thus reducing the possibility of dangerous accidents caused by uneven concrete stress in different areas of the tunnel.

[0089] The above are all the preferred embodiments of this application. The protection scope of this application is not limited thereby. Any feature disclosed in this specification (including the abstract and drawings), unless specifically described, can be replaced by other equivalent or similar-purpose alternative features. That is, unless specifically described, each feature is only an example in a series of equivalent or similar features.

Claims

1. A method for excavating a small clear distance triple-arch tunnel with a special-shaped cross-section, characterized in that, The following steps are involved: Tunnel excavation: Mechanical equipment excavates the rock mass multiple times according to the preset route; Initial support: When excavation reaches the preset depth, an initial layer of concrete is sprayed to seal the exposed rock surface; At least two rows of grouting pipes (1) are pre-buried within a 120° range of the arch, and the single row of grouting pipes (1) are arranged parallel to each other and are equidistantly distributed along the curvature of the arch; the end of the grouting pipe (1) that is not inserted into the rock soil is reserved for a set length to be exposed; when the initial support is closed into a ring, cement slurry is injected behind the initial support arch; the water-cement ratio of the cement slurry is 0.8-1.0; and the grouting pressure is 0.1-0.3MPa; Preparation for spraying: an extension rod (2) is installed on the exposed part of the grouting pipe (1); a docking assembly (3) is provided at one end of the extension rod (2), the docking assembly (3) is used to detachably connect the extension rod (2) to the grouting pipe (1), and a marking portion (4) is provided at the end of the other end; Starting spraying: forming a spraying section (6) between adjacent extension rods (2); spraying concrete in a plurality of spraying sections (6) one by one; maintaining the thickness of the concrete in the spraying section (6) not exceeding the marking portion (4); Installing a waterproof layer (7): After the concrete is sprayed in the spraying section (6), a waterproof layer (7) is installed on the side of the concrete away from the inner wall of the tunnel; A plurality of positioning components (5) are arranged at one end of the extension rod (2) away from the connection component; the plurality of positioning components (5) are equidistantly distributed on the circumference with the axis of the extension rod (2) as the center; the marking portion (4) is provided with a storage cavity (41) through which the plurality of positioning components (5) can pass; the marking portion (4) is detachably connected to the plurality of positioning components (5); the end of the positioning component (5) away from the extension rod (2) is used to fix the side of the waterproof layer (7) away from the injection zone (6).

2. The excavation method for a small clear distance triple-arch tunnel with a special-shaped cross-section according to claim 1, characterized in that: The docking assembly (3) comprises an elastic docking portion (31) arranged on the end of the grouting pipe (1) and a buckle portion (32) arranged on the end of the extension rod (2) away from the marking portion (4); a relief cavity (33) is provided on the side of the elastic docking portion (31) away from the grouting pipe (1); an anti-skid convex ring (34) is protruding from the peripheral wall of the elastic docking portion (31); the anti-skid convex ring (34) is elastic; The buckle portion (32) is provided with a docking inner cavity (35) on a side away from the extension rod (2) into which the anti-slip convex ring (34) can be buckled; The inner wall of the avoidance cavity (33) is arranged in an arc shape, and the arc-shaped inner concave part of the avoidance cavity (33) and the center of the anti-slip convex ring (34) are located in the same horizontal plane.

3. The excavation method for a small clear distance triple-arch tunnel with a special-shaped cross-section according to claim 2, wherein: A reset hole (36) communicating with the docking inner cavity (35) is formed through the peripheral wall of the buckle portion (32); when the anti-skid convex ring (34) and the docking inner cavity (35) are in a buckled state, the center line of the reset hole (36) and the center of the circle of the anti-skid convex ring (34) are in the same horizontal plane.

4. The excavation method for a small clear distance triple-arch tunnel with a special-shaped cross-section according to claim 1, characterized in that: The positioning component (5) includes a mounting base (51) hinged to the end of the extension rod (2) and a positioning plate (52) hinged to the side of the mounting base (51) away from the extension rod (2); a torsion spring (53) is provided at the hinge between the positioning plate (52) and the mounting base (51); an installation hole (55) is penetrated and opened at the end of the positioning plate (52) away from the mounting base (51), and a fixing bolt (54) that can penetrate into the waterproof layer (7) is detachably connected to the installation hole (55).

5. The excavation method for a small clear distance triple-arch tunnel with a special-shaped cross-section according to claim 4, characterized in that: The inner wall of the storage cavity (41) is provided with threads; the side of the mounting base (51) away from the axis of the extension rod (2) can be threadedly connected to the storage cavity (41).

6. The excavation method for a small clear distance triple-arch tunnel with a special-shaped cross-section according to claim 4, characterized in that: A chamfer is provided on the side of the positioning plate (52) away from the mounting base (51).

7. The excavation method for a small clear distance triple-arch tunnel with a special-shaped cross-section according to claim 6, characterized in that: The marking part (4) includes a fixing ring (42) fixedly connected to the end of the extension rod (2) and a sleeve (43) threadedly connected to the extension rod (2). The storage cavity (41) is penetrated and opened on the sleeve (43) and the axis is collinear with the axis of the sleeve (43); the side of the fixing ring (42) close to the sleeve (43) is flush with the side of the waterproof layer (7) away from the tunnel inner wall.

8. The excavation method for a small clear distance triple-arch tunnel with a special-shaped cross-section according to claim 7, characterized in that, The steps of installing the waterproof layer (7) specifically further include the following steps: Release the restriction of the positioning component (5): Remove the sleeve (43) from the extension rod (2); Rotate the end of the positioning plate (52) away from the mounting base (51) until it abuts against the waterproof layer (7); Pass the fixing bolt (54) through the installation hole (55) and connect it to the waterproof layer (7).

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