A support method suitable for large deformation of mudstone tunnels

Abstract

The present invention discloses a construction support method suitable for large deformation of mudstone tunnels. The specific steps are as follows: Step 1: Select a corresponding reinforcement support structure based on tunnel survey data and deformation conditions after initial support; Step 2: Use the step method to excavate the tunnel, then carry out initial concrete spraying, lay steel mesh, erect arch frames and install locking anchor rods, drill radial anchor rods, and then spray concrete to the designed thickness; the above construction is carried out in sequence on the upper step part, the left part of the lower step, and the right part of the lower step; Step 3: According to the different deformation conditions of the surrounding rock, different arch frame support structures are installed inside the arch frame of the initial support structure; Step 4: Excavate the inverted arch part; Step 5: After performing different pretreatments on the tunnel according to the degree of intrusion, the secondary lining is cast. This solution improves the ability of the initial support to resist surrounding rock deformation and can safely and quickly handle this problem to ensure the lining thickness.

Description

Technical Field

[0001] The invention belongs to the technical field of preventing and controlling the deformation and intrusion of surrounding rocks in carbonaceous mudstone tunnels, and particularly relates to a support method suitable for large deformation mudstone tunnels. Background Art

[0002] As transportation systems continue to improve, new railways increasingly intersect existing roads. Tunnels are becoming increasingly popular due to their improved alignment, reduced land use, and reduced project investment. However, during construction, addressing the issue of surrounding rock deformation and intrusion in mudstone tunnels, ensuring tunnel construction safety, and ensuring lining thickness remain challenging challenges for the entire construction industry. This is particularly true in carbonaceous mudstone, which has poor self-stabilization and easily softens in contact with water, making it highly susceptible to collapse. Preventing this problem, ensuring construction safety, and minimizing project losses remain major challenges. Summary of the Invention

[0003] The purpose of the present invention is to solve the problems existing in the above-mentioned prior art and to provide a support method suitable for large deformation of mudstone tunnels. In the process of dealing with the problem of intrusion of surrounding rock deformation in carbonaceous mudstone tunnels, this solution reinforces the support structure so that the ability of the initial support to resist surrounding rock deformation is improved. If intrusion occurs, the problem can be handled safely and quickly to ensure the lining thickness.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: a construction support method suitable for large deformation of mudstone tunnels, the specific steps are as follows:

[0005] Step 1: Select the appropriate reinforcement support structure based on the tunnel investigation data and the deformation after initial support;

[0006] Step 2: Excavate the tunnel using the step method, followed by initial spraying of concrete, laying of steel mesh, erection of arch frames and installation of locking anchors, drilling of radial anchors, and re-spraying of concrete to the designed thickness; the above construction is carried out in sequence for the upper step, the left side of the lower step, and the right side of the lower step; first, mechanically excavate the upper step to establish the initial support structure of the upper step; second, mechanically excavate the left side of the lower step to establish the initial support structure of the left side of the lower step, and re-spray concrete to the designed thickness; third, mechanically excavate the right side of the lower step to establish the initial support structure on the right side of the lower step, and re-spray concrete to the designed thickness;

[0007] Step 3: According to the different deformation conditions of the surrounding rock, different arch support structures are set inside the arch of the initial support structure;

[0008] Step 4: excavate the invert arch of the tunnel section and construct the initial support structure of the invert arch, complete the invert arch shotcrete and apply the invert arch steel bar, and then complete the invert arch pouring and filling of the tunnel section;

[0009] Step 5: After the tunnel undergoes different pretreatments according to the degree of intrusion, the secondary lining is poured.

[0010] As a preferred solution, the specific steps of step 2 are as follows:

[0011] Step 21: First, mechanically excavate the upper step and establish the initial support structure at the upper step. During the installation of the arch frame of the initial support structure, the two rows of first arch frames are connected with longitudinal steel bars at intervals of 1 meter along their circumference; double rows of locking anchor pipes are installed 30 cm above the arch feet on both sides of the first arch frame, with an angle of 30°, and grouting is performed for reinforcement. Finally, radial anchor rods are drilled and concrete is sprayed to the designed thickness;

[0012] Step 22: Mechanically excavate the left side of the lower step and establish the initial support structure on the left side of the lower step. When installing the arch wall steel frame, use longitudinal 32# channel steel for support to increase the bearing area of ​​the arch wall steel frame footing. Install double rows of lower step locking anchor pipes 30 cm above the arch feet on both sides of the arch wall steel frame, with an angle of 30°. After the arch wall steel frame is stable, use a small grouting pipe to grout and spray concrete to the designed thickness.

[0013] Step 23: Mechanically excavate the right side of the lower step and build the initial support structure on the right side of the lower step. When installing the arch wall steel frame, use longitudinal 32# channel steel for support to increase the bearing area of ​​the arch wall steel frame footing. Install double rows of lower step locking anchor pipes 30 cm above the arch feet on both sides of the arch wall steel frame. The installation angle is 30°. After the arch wall steel frame is stable, use a small grouting tube for grouting, and spray concrete to the designed thickness.

[0014] As a preferred solution, in step five, for the portion of the 0-8 cm intrusion, a jackhammer is used to remove the surface sprayed concrete to ensure that the thickness of the secondary lining meets the requirements, and then the steel bars are installed and the concrete is poured, and finally the secondary lining is poured; for the portion of the 8-25 cm intrusion, an arch replacement process is performed, and the concrete in the intrusion portion is chiseled out by a crushing head, the intruding I-beam and connecting steel bars are cut off, and the I20B I-beam is installed and sprayed with concrete, and finally the secondary lining is poured.

[0015] As a preferred solution, the arch replacement method is as follows: two groups of φ42 small grouting tubes are used to anchor and reinforce the I-beam frames of the non-limiting first arch frame and / or second arch frame, and then the I-beam frames that violate the limit are removed one by one.

[0016] As a preferred solution, in step 21, the grouting reinforcement is performed by radial grouting reinforcement around the φ42 grouting small pipe. The length of a single grouting small pipe is 4.5m, the circumferential spacing is 1m, the longitudinal spacing is 1.2m, the pipe wall is staggered and drilled in a plum blossom shape, and is firmly welded to the I-beam frames of the first and second arch frames, acting as an anchor for the I-beam frames.

[0017] As a preferred option, the drilling position deviation of the grouting reinforcement construction drilling holes shall not exceed 10mm, and the hole depth deviation shall be ≤50mm, so that the rock surface is perpendicular to the drilling direction.

[0018] As a preferred solution, in step three, when the normal deformation of the surrounding rock is within 5 cm, a first horizontal brace and two first diagonal braces are provided inside the first arch frame, and the two first diagonal braces are symmetrically installed. The two ends of the first horizontal brace are fixedly connected to the middle positions on both sides of the first arch frame, one end of the first diagonal brace is connected to the first horizontal brace, and the other end is connected obliquely upward to the first I-beam frame, and the connection position of the first diagonal brace and the first horizontal brace does not exceed the midpoint of the first horizontal brace.

[0019] As a preferred solution, the first diagonal brace and the first transverse brace form an angle of 45°.

[0020] As a preferred solution, in step three, when the surrounding rock is deformed normally by 5-10 cm, a second arch frame is placed in the tunnel, and a PVC board with the same shape as the outer edge of the second arch frame is arranged between the outer annular surface of the second arch frame and the inner wall of the tunnel. A through hole is formed on the PVC board along its length, and the second arch frame and the PVC board are connected at the through hole by iron wire. Longitudinal connecting ribs are arranged between multiple second arch frames and fixedly connected as one.

[0021] As a preferred solution, the cross-sectional dimensions of the I-beam frames of the first and second arch frames are allowed to have a deviation of ±20 mm and a distortion of 20 mm.

[0022] Beneficial effects

[0023] The present invention improves the support method, not only improving the safety and stability of mudstone tunnel construction, but also speeding up the construction progress, effectively solving the instability caused by sudden deformation of the surrounding rock. By reinforcing the support structure, the ability of the initial support to resist the deformation of the surrounding rock is improved. If an intrusion problem occurs, the problem can be handled safely and quickly to ensure the lining thickness. The stability of the support structure and the safety of mudstone tunnel construction are improved, effectively preventing the surrounding rock from deforming too much and squeezing the arch frame, reducing the secondary consumption of the arch frame, and the second arch frame and PVC plastic sheet can be reused, effectively reducing construction costs. This construction method can complete the construction of mudstone tunnel projects safely, quickly and efficiently, not only improving the safety and stability of mudstone tunnel construction, but also speeding up the construction progress, effectively solving the instability caused by sudden deformation of the surrounding rock. It avoids secondary rework and has good social and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 Schematic diagram of the support structure of a mudstone large deformation tunnel according to the present invention;

[0026] Figure 2 This is the structural diagram of the first arch;

[0027] Figure 3 This is the structural diagram of the second arch;

[0028] Markings in the figure: 11, upper step locking anchor pipe, 12, upper step external sprayed concrete layer, 31, lower step locking anchor pipe, 32, lower step external sprayed concrete layer, 40, inverted arch initial support structure, 50, radial anchor rod, 60, grouting small pipe, 100, first arch frame, 101, first horizontal brace, 102, first diagonal brace, 103, first I-beam frame, 200, second arch frame, 201, PVC board, 202, second I-beam frame, 203, second horizontal brace, 204, second diagonal brace, 205, third diagonal brace;

[0029] Ⅰ, the upper step part, Ⅱ-1, the left part of the lower step, Ⅱ-2, the right part of the lower step, Ⅲ, the inverted arch part Ⅲ, Ⅳ, the inverted arch part Ⅳ, Ⅴ, the inverted arch part Ⅴ. DETAILED DESCRIPTION

[0030] The present invention is described in detail below by way of exemplary embodiments. However, it should be understood that elements, structures, and features in one embodiment may also be beneficially combined in other embodiments without further description.

[0031] It should be noted that: unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by persons having ordinary skills in the field to which the invention belongs. The words "one", "an" or "the" and the like used in the patent application specification and claims of the present invention do not express a quantitative limitation, but rather indicate the presence of at least one. Words such as "include" or "comprise" indicate that the elements or objects appearing before "include" or "comprises" include the elements or objects listed after "include" or "comprises" and their equivalents, but do not exclude other elements or objects with the same function.

[0032] This embodiment provides a construction support method suitable for large deformation mudstone tunnels. The specific steps are as follows:

[0033] Step 1: Select the appropriate reinforcement support structure based on the tunnel survey data and the deformation after initial support. Specifically, the geological conditions in front of the tunnel face are grasped through the advanced geological prediction system, and the appropriate reinforcement support structure is adopted after the initial support according to the deformation situation.

[0034] Step 2: Excavate the tunnel using the bench method, followed by initial shotcreting, laying steel mesh, erecting arch supports and installing anchor bolts, drilling 50 radial anchors, and then re-shotcreting to the designed thickness. A temporary cross brace is installed at the bottom, and the above construction is repeated for the upper bench, the left side of the lower bench, and the right side of the lower bench. First, mechanically excavate the upper bench to establish the initial support structure for the upper bench. Next, mechanically excavate the left side of the lower bench to establish the initial support structure for the left side of the lower bench and re-shotcrete to the designed thickness. Finally, mechanically excavate the right side of the lower bench to establish the initial support structure for the right side of the lower bench and re-shotcrete to the designed thickness. Tunnel construction should adhere to the principles of "weak blasting, short advances, strong support, early closure, and frequent measurement." The next bench should be excavated when the shotcrete of the previous bench reaches at least 70% of the designed strength.

[0035] More specifically, the above specific steps are as follows: Step 21: First, mechanically excavate the upper step portion and establish the initial support structure at the upper step. During the installation of the first arch frame 100, two rows of first arch frames 100 are connected with longitudinal steel bars at intervals of 1m along their circumference; double rows of locking foot anchor pipes are installed 30cm above the arch feet on both sides of the first arch frame 100, with an angle of 30°, and grouting reinforcement is performed. Finally, radial anchor rods 50 are drilled and concrete is sprayed to the designed thickness. After the I-beam frame of the first arch frame 100 is stabilized, radial grouting reinforcement is performed around the φ42 grouting small pipe 60. The grouting small pipe 60 is 4.5m long, with a circumferential spacing of 1m and a longitudinal spacing of 1.2m. The pipe wall is staggered and drilled in a plum blossom shape, and is firmly welded to the I-beam frame of the first arch frame 100, acting as an anchor for the I-beam frame. Finally, after drilling radial anchor rods 50, concrete is sprayed to the designed thickness, and a temporary cross brace (i.e., the first cross brace 101) is erected at the bottom. The drilling position deviation of the grouting reinforcement construction drilled holes is no more than 10 mm, and the hole depth deviation is ≤50 mm, so that the rock surface is perpendicular to the drilling direction.

[0036] Step 22: Mechanically excavate the left side of the lower step and establish the initial support structure on the left side of the lower step. When installing the arch wall steel frame, use longitudinal 32# channel steel for support to increase the bearing area of ​​the arch wall steel frame footing. Set double rows of lower step locking anchor pipes 31 30 cm above the arch feet on both sides of the arch wall steel frame, with an angle of 30°. After the arch wall steel frame is stable, use a small grouting pipe 60 to grout, and spray concrete to the designed thickness. 32 in the figure indicates the outer sprayed concrete layer of the lower step.

[0037] Step 23: Mechanically excavate the right side of the lower step and establish the initial support structure on the right side of the lower step. When installing the arch wall steel frame, use longitudinal 32# channel steel for support to increase the bearing area of ​​the arch wall steel frame footing. Install double rows of lower step locking anchor pipes 31 30 cm above the arch feet on both sides of the arch wall steel frame. The installation angle is 30°. After the arch wall steel frame is stable, use a small grouting pipe 60 to inject grout, and spray concrete to the designed thickness. The lower step concrete layer is indicated by 32 in the figure.

[0038] like Figure 1 As shown, Figure 1 Reference numeral 100 refers to the first bracket of the upper step, 101 is the first cross brace, 11 is the upper step foot locking anchor pipe, and 12 is the outer sprayed concrete layer of the upper step. In the figure, part I is the upper step, part II-1 is the left side of the lower step, and part II-2 is the right side of the lower step.

[0039] Step 3. Different support structures are set up inside the arch frame according to the deformation of the surrounding rock. If the deformation of the surrounding rock is small, that is, the normal deformation of the surrounding rock is within 5 cm, temporary cross braces and diagonal braces can be set up inside the arch frame. Specifically, when the normal deformation of the surrounding rock is within 5 cm, the first arch frame 100 includes a first I-beam frame 103, and a first cross brace 101 and two first diagonal braces 102 are set inside the first I-beam frame 103. The two first diagonal braces 102 are symmetrically installed, and the two ends of the first cross brace 101 are fixedly connected to the middle section of both sides of the first arch frame 100. One end of the first diagonal brace 102 is connected to the first cross brace 101, and the other end is connected obliquely upward to the first I-beam frame 103. The welding position of the first diagonal brace 102 and the first cross brace 101 does not exceed the midpoint of the first cross brace 101. The first diagonal brace 102 and the first cross brace 101 are firmly welded to each other at an angle of 45°.

[0040] When the surrounding rock deformation is significant, i.e., 5-10 cm in normal deformation, a secondary arch frame (also known as a second arch frame 200) is placed inside the tunnel. Temporary horizontal and diagonal braces are installed within the second arch frame 200, and longitudinal connecting bars are installed between the second arch frames 200, leaving a certain distance from the tunnel inner wall. After the second arch frame 200 is installed, a PVC sheet of the same shape is placed on the outside. Before the secondary lining is completed, the second arch frame 200 is removed and placed inside the tunnel. A PVC sheet 201 of the same shape as the outer edge of the second arch frame 200 is placed between the outer ring surface of the second arch frame 200 and the tunnel inner wall. Through holes are formed along the length of the PVC sheet 201. The second arch frames 200 are connected to the PVC sheet 201 with wire at the through holes. Longitudinal connecting bars are installed between multiple second arch frames 200 to secure them together. The second arch frame 200 and the PVC sheet are reusable, reducing secondary consumption of the arch frame and effectively lowering construction costs.

[0041] In this solution, the second arch frame 200 can adopt the following structure: the second arch frame 200 includes a second I-beam frame 202, a second cross brace 203, two second diagonal braces 204 and two third diagonal braces 205, the two second diagonal braces 204 are symmetrically arranged, one end of the second diagonal brace 204 is fixedly connected to the midpoint of the second cross brace 203, and the other end extends obliquely upward and is connected to the second I-beam frame 202, one end of the third cross brace 205 is connected to the connection between the second cross brace 203 and the second I-beam frame 202, and the other end is connected to the connection between the second cross brace 203 and the second I-beam frame 202, the second cross brace 203, the second diagonal brace 204 and the third diagonal brace 205 form an acute triangle.

[0042] During the welding process, the welding points between the upper ends of the internal diagonal braces of the second arch frame 200 and the second arch frame 200 were determined based on the surveyed points of greatest deformation, ensuring that the second and third diagonal braces 204 and 205 formed an acute triangle with the second cross brace 203. After the second arch frame 200 was installed, a PVC sheet of the same shape was placed on the outside. The PVC sheet was perforated at the edges and secured to the steel frame with wire. Longitudinal connecting reinforcement was installed between rows of second arch frames 200, leaving a certain distance from the tunnel's inner wall. The second arch frames 200 were removed before the second lining was completed. Radial grouting reinforcement was implemented using φ42 grouting tubes 60, each 4.5m long, spaced 1m circumferentially and 1.2m longitudinally. Holes were drilled in the wall (post-processing) in a staggered pattern and welded securely to the steel frame, acting as anchors for the I-beams.

[0043] It should be noted that the two rows of arch frames are connected longitudinally with steel bars according to the design requirements, and the verticality and spacing meet the design requirements to form a longitudinal connection system; the arch frames must be tried out after processing to ensure there is no distortion or warping, and the joint connection requirements require that each frame can be interchangeable; the allowable deviation of the cross-sectional size is ±20mm, and the distortion is 20mm.

[0044] When the surrounding rock deformation reaches the convergence range and the safety of demolition is strictly verified, it can be demolished only. At the same time, attention should be paid to the timely follow-up of subsequent operations. If the stability conditions of the surrounding rock meet the design requirements, the temporary support can be removed at one time before the invert arch concrete is poured. The length of one removal is determined according to the casting length of the invert arch (generally 2 to 3 meters).

[0045] Step 4: excavate the inverted arch part III and construct the initial support structure 40 of the inverted arch; cast the inverted arch part IV and the side wall foundation at a distance from the excavated inverted arch part III; after the inverted arch concrete has initially set, cast the inverted arch part V and fill it with concrete to the designed height; and then lay the waterproof board.

[0046] The excavation length of each step should not be too long and can be adjusted appropriately according to the surrounding rock conditions, but it must meet the requirements of the specifications. The length of the upper step of the step method is 3-10m, and the length of the lower step is 15-25m. After the invert arch is excavated, the invert arch should be constructed in time to close it into a ring. In the initial support closure position of the V-level surrounding rock, the distance between the invert arch and the heading face shall not be greater than 35m.

[0047] Step 5: After pre-treatment of the tunnel based on the degree of intrusion, the secondary lining is poured. Specifically, for intrusions between 0 and 8 cm, a jackhammer is used to remove the surface sprayed concrete to ensure the secondary lining meets the required thickness. Rebar installation and concrete pouring are then performed, and the secondary lining is poured. For intrusions between 8 and 25 cm, arch replacement is performed. This involves anchoring and reinforcing the non-intrusive first and second arch frames (100 and 200 mm) using two sets of 60 φ42 grouting tubes. The intruding I-beams are then removed one by one. The concrete in the intruding area is chiseled out with a crushing head, and the intruding I-beams and connecting rebar are manually cut out. Any areas that are still under-excavated are cleared manually with a jackhammer to the structural section. I20B I-beams are promptly installed and sprayed with concrete, and the secondary lining is poured.

[0048] During installation of the arch steel frame, two rows of steel frames must be connected with Φ22 longitudinal reinforcement every 1m along the perimeter, ensuring a seamless connection with the enclosing concrete. Longitudinal connecting reinforcement between the steel frames should be promptly installed and securely connected. The locking foot pipes must be securely welded to the steel frames, and temporary cross braces should be connected to the steel frames to ensure a timely closure of the loop.

[0049] In this solution, the cross-sectional dimensions of the I-beam frames of the first arch frame 100 and the second arch frame 200 have an allowable deviation of ±20 mm and a torsion of 20 mm.

[0050] In this embodiment, when the step method is used for construction in a Grade V surrounding rock area, the excavation and support advance per cycle of the upper step shall not be greater than the spacing between 1 steel frame, and the excavation and support advance per cycle of the side wall shall not be greater than the spacing between 2 steel frames. The steel frame locking feet must be completed before the invert arch is excavated, and the advance per cycle of the invert arch excavation shall not be greater than 3m.

[0051] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with the present profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A construction support method suitable for large deformation of mudstone tunnels, characterized by: The specific steps are as follows: Step 1: Select the appropriate reinforcement support structure based on the tunnel investigation data and the deformation after initial support; Step 2: Excavate the tunnel using the bench method, followed by initial shotcreting, laying steel mesh, erecting arch supports and installing anchor bolts, drilling radial anchor bolts, and then re-shotcreting to the designed thickness. This construction is repeated for the upper bench, the left side of the lower bench, and the right side of the lower bench. First, mechanically excavate the upper step and build the initial support structure of the upper step; During the installation of the arch frame of the initial support structure, the first arch frame is installed, and two rows of the first arch frames are connected with longitudinal steel bars at intervals of 1m along the circumference; double rows of locking anchor pipes are installed 30cm above the arch feet on both sides of the first arch frame, with an angle of 30°, and grouting is performed for reinforcement. Finally, radial anchor rods are drilled and concrete is sprayed to the designed thickness. Secondly, mechanically excavate the left side of the lower step and build the initial support structure on the left side of the lower step. When installing the arch wall steel frame, use longitudinal 32# channel steel for support to increase the bearing area of ​​the arch wall steel frame footing. Install double rows of lower step locking anchor pipes 30 cm above the arch feet on both sides of the arch wall steel frame, with an angle of 30°. After the arch wall steel frame is stable, use a small grouting pipe to grout, and spray concrete to the designed thickness. Next, mechanically excavate the right side of the lower step and build the initial support structure on the right side of the lower step. When installing the arch wall steel frame, use longitudinal 32# channel steel for support to increase the bearing area of ​​the arch wall steel frame footing. Install double rows of lower step locking anchor pipes 30 cm above the arch feet on both sides of the arch wall steel frame, with an angle of 30°. After the arch wall steel frame is stable, use a small grouting pipe to grout, and spray concrete to the designed thickness. Step 3: According to the different deformation conditions of the surrounding rock, different arch support structures are set inside the arch of the initial support structure; When the normal deformation of the surrounding rock is less than 5 cm, the first arch frame includes a first I-beam frame, a first cross brace and two first diagonal braces are provided inside the first I-beam frame, the two first diagonal braces are symmetrically installed, the two ends of the first cross brace are fixedly connected to the middle sections of both sides of the first arch frame, one end of the first diagonal brace is connected to the first cross brace, and the other end is connected obliquely upward to the first I-beam frame, and the connection position of the first diagonal brace and the first cross brace does not exceed the midpoint of the first cross brace; When the normal deformation of the surrounding rock is 5-10cm, a second arch frame is placed in the tunnel, and temporary horizontal braces and diagonal braces are set inside the second arch frame. Longitudinal connecting bars are set between the second arch frames, and a certain distance is reserved from the inner wall of the tunnel. After the second arch frame is installed, a PVC board of the same shape is placed on the outside. The second arch frame is removed before the second lining. A PVC board of the same shape as the outer edge of the second arch frame is set between the outer ring surface of the second arch frame and the inner wall of the tunnel. A through hole is formed on the PVC board along its length. The second arch frame and the PVC board are connected at the through hole by iron wire. Longitudinal connecting bars are set between multiple second arch frames to fix them together. The second arch frame and the PVC board can be used for repeated use. The second arch frame includes a second I-beam frame, a second transverse brace, two second diagonal braces and two third diagonal braces, the two second diagonal braces are symmetrically arranged, one end of the second diagonal brace is fixedly connected to the midpoint of the second transverse brace, and the other end extends obliquely upward and is connected to the second I-beam frame, one end of the third transverse brace is connected to the connection between the second transverse brace and the second I-beam frame, and the other end is connected to the connection between the second transverse brace and the second I-beam frame, and the second transverse brace, the second diagonal brace and the third diagonal brace form an acute triangle; Step 4: excavate the invert arch of the tunnel section and construct the initial support structure of the invert arch, complete the invert arch shotcrete and apply the invert arch steel bar, and then complete the invert arch pouring and filling of the tunnel section; Step 5. After different pretreatments are carried out on the tunnel according to the degree of intrusion, the secondary lining is poured. For the intrusion part with a depth of 0-8 cm, a jackhammer is used to remove the surface sprayed concrete to ensure that the thickness of the secondary lining meets the requirements. Then the steel bars are installed and the concrete is poured. Finally, the secondary lining is poured. For the intrusion part with a depth of 8-25 cm, the arch is replaced. The concrete in the intrusion part is chiseled out with a crushing head, the intruding I-beam and connecting steel bars are cut off, and the I20B I-beam is installed and sprayed with concrete. Finally, the secondary lining is poured.

2. A construction support method suitable for large deformation of mudstone tunnels according to claim 1, characterized in that: The arch replacement method is specifically as follows: two groups of φ42 small grouting tubes are used to anchor and reinforce the I-beam frames of the non-limiting first arch frame and / or second arch frame, and then the limiting I-beam frames are removed one by one.

3. A construction support method suitable for large deformation of mudstone tunnels according to claim 1, characterized in that: The grouting reinforcement adopts radial grouting reinforcement around the φ42 grouting small pipe. The length of a single grouting small pipe is 4.5m, the circumferential spacing is 1m, the longitudinal spacing is 1.2m, the pipe wall is staggered and drilled in a plum blossom shape, and is firmly welded to the I-beam frames of the first and second arch frames, which acts as an anchor for the I-beam frames.

4. A construction support method suitable for large deformation of mudstone tunnels according to claim 3, characterized in that: The drilling position deviation of the grouting reinforcement construction drilling holes shall not exceed 10mm, and the hole depth deviation shall be ≤50mm, so that the rock surface is perpendicular to the drilling direction.

5. The construction support method for large deformation mudstone tunnels according to claim 1, characterized in that: The first diagonal brace and the first transverse brace form an angle of 45°.

6. The construction support method for large deformation mudstone tunnels according to claim 1, characterized in that: The allowable deviation of the cross-sectional dimensions of the I-beam frames of the first and second arch frames is ±20mm, and the distortion is 20mm.

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