Support structure and construction method for large deformation tunnel of soft rock tunnel in fold area

Abstract

The present invention provides a support structure and construction method for a large-deformation soft rock tunnel in a folded area. A grid arch frame with multiple steel bodies forming a ring-shaped structure is provided inside the grid arch frame. An outer layer of steel mesh is provided between the steel arch frame and the grid arch frame. An inner layer of steel mesh is provided on the inner wall of the steel arch frame. A lower step arch frame is provided at the bottom opening of the steel arch frame. The lower step arch frame and the steel arch frame form a closed loop. The design adopts a support structure of shotcrete + double-layer arch frame + steel mesh + radial grouting + large steel pipe locking feet. After the excavation surface is initially stabilized by initial shotcrete spraying, the double-layer arch frame is installed to form a pressure-yielding support structure. At the same time, radial grouting is used to consolidate the loose surrounding rock of the tunnel body. Finally, the mesh is hung and concrete is sprayed to the designed thickness to form a support system.

Description

Technical Field

[0001] The present invention relates to the field of steel arch construction, and in particular to a large-deformation tunnel support structure for a soft rock tunnel in a fold zone and a construction method thereof. Background Art

[0002] With the rapid development of highway engineering in my country, the geological context facing construction projects has become increasingly complex. Tunnels, as construction projects that excavate through geological rock strata, are significantly affected by geological factors such as strata and structure. In recent years, the large deformation of soft rock tunnels through folded areas has been a hot topic in tunnel construction research. Through research on tectonic stresses and surrounding rock properties in folded areas, the use of support structures such as double-layer steel arches and yielding anchors, based on the principle of combining support with high-in-situ stress relief, has been proposed. This has achieved good results in engineering practice. However, as the tunnel progresses deeper into increasingly complex geological environments, the soft surrounding rock of the tunnel is easily loosened and prone to collapse due to stress concentration. Traditional support methods such as mesh spraying and mixing are less effective in resolving this problem. Furthermore, due to stress concentration in the surrounding rock at the front end of the tunnel face, cracks in the surrounding rock are tightly closed, limiting advance grouting. As a result, the loose surrounding rock, after excavation, becomes gravelly and pours along the gaps between the primary support arches, causing continuous non-convergence of tunnel deformation. Using traditional arch support structures makes it difficult to achieve the design expectations. During the excavation of a tunnel in the core area of folded, highly weathered andesite rock, non-convergence of tunnel deformation and collapse of loose surrounding rock on site were still observed even with traditional support systems such as double-layer arches and yield anchors. This demonstrates that in the study of deformation treatment of soft rock tunnels in the core area of folded rock, the technical difficulties of supporting loose surrounding rock under conditions of tectonic stress concentration are particularly prominent. Therefore, in view of the above situation, it is urgent to design a support system that can solve the problems of structural stress concentration and large deformation of the tunnel body in loose surrounding rock to solve the above problems. Summary of the Invention

[0003] The main purpose of the present invention is to provide a large deformation tunnel support structure and construction method for soft rock tunnels in fold areas, so as to solve the problem that the weak surrounding rock of the tunnel is easily loosened and the vault collapses after being affected by stress concentration. The traditional support method of hanging mesh spraying and mixing is less effective in solving such problems. At the same time, since the surrounding rock at the front end of the tunnel face is affected by stress concentration, the surrounding rock cracks are tightly closed, resulting in limited advance grouting, causing the loose surrounding rock to gravel after excavation and pour out along the gaps between the initial support arch frames, which continuously causes the problem of non-convergence of tunnel deformation.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: a large deformation tunnel support structure for soft rock tunnels in a fold area, a grid arch frame with a ring structure composed of multiple steel bodies, a steel arch frame with a ring structure composed of multiple steel bodies is arranged on the inner side of the grid arch frame, an outer layer of steel mesh is arranged between the steel arch frame and the grid arch frame, an inner layer of steel mesh is arranged on the inner wall of the steel arch frame, a lower step arch frame is arranged at the opening position at the bottom of the steel arch frame, and the lower step arch frame and the steel arch frame form a closed loop.

[0005] In the preferred embodiment, the outer wall of the grid arch is further provided with a plurality of vertically arranged steel flower tubes.

[0006] In the preferred embodiment, the exterior of the steel arch frame and the grid arch frame are further provided with a plurality of locking foot anchor pipes inclined downward.

[0007] In the preferred embodiment, the grid arch frame, the lower step arch frame and the steel arch frame are all assembled by connecting the rigid body through the first arch frame connector.

[0008] In the preferred embodiment, the structure of the first arch frame connecting head is: positioning claws are provided on both sides of the second fixed plate of the second steel body, the positioning claws pass through the second fixed plate and are connected to the rotating shaft, the first fixed plate of the first steel body is clamped on both sides on the positioning claws, and the first fixed plate and the second fixed plate are connected by multiple double-headed nuts.

[0009] In a preferred embodiment, sliding grooves are further provided on both sides of the second steel body, and a sliding head is provided at one end of the rotating shaft. The sliding head is arranged inside the sliding groove and is axially limited inside the sliding groove.

[0010] In a preferred embodiment, the lower surface of the slot of the positioning claw is flush with the surface of the second fixing plate;

[0011] The first fixing plate is further provided with a plurality of first angle fixing screws, which pass through the first fixing plate and abut against the surface of the second fixing plate;

[0012] One side of the first fixing plate is a wedge-shaped structure, which is clamped in the clamping groove of the positioning claw. One side of the wedge-shaped structure is provided with a limiting boss, which abuts against one side of the positioning claw for limiting position;

[0013] The bolt holes on the second fixing plate are all waist-shaped holes.

[0014] In the preferred embodiment, the lower step arch frame and the steel arch frame are connected by a second arch frame connector.

[0015] In the preferred embodiment, the structure of the second arch frame connector is as follows: a third fixing plate is provided on one side of the steel arch frame, and limit claws are provided on both sides of the third fixing plate, the limit claws pass through the third fixing plate, and a limit plate is provided at the tail end of the limit claws, and the fourth fixing plate at the end of the lower step arch frame is clamped on the limit claws, and the fourth fixing plate is connected to the third fixing plate by a plurality of stud bolts;

[0016] The bolt holes on the third fixing plate are all waist-shaped holes;

[0017] The fourth fixing plate is further provided with a plurality of second angle fixing screws, which pass through the fourth fixing plate and abut against the third fixing plate.

[0018] The method includes:

[0019] S1. After the steps on the tunnel are excavated, spray 2~5cm of shotcrete initially, install the grid arch frame and set two 6m long φ108*6m first lock anchor pipes at the arch foot, then install the outer steel mesh to complete the support of the upper steps;

[0020] S2. After the middle step of the tunnel is excavated, spray concrete with a thickness of 2 to 5 cm. Install the grid arch frame and set two 6m long φ108*6mm second lock anchor pipes at the arch foot. Then install the outer steel mesh to complete the middle step support.

[0021] S3. Determine whether the tunnel deformation has reached the reserved deformation amount based on the monitoring measurement data. When the tunnel deformation reaches the reserved deformation amount, radial φ42*4 mm steel tubes are arranged in a plum blossom pattern with a spacing of 1.2*1.2 m, and grouting is performed using cement slurry with a water-cement ratio of 1:1. The grouting range should not be less than the size of the loosening circle.

[0022] S4. After grouting, install the inner steel arch frame and inner steel mesh. Install a 4.5m long φ42*4mm third lock anchor pipe at the arch foot. Then spray the concrete layer layer by layer to the designed thickness. The thickness should cover the outer steel mesh to form the middle and upper step support system.

[0023] S5. When the deformation of the tunnel body does not reach the reserved deformation, the on-site process should be adjusted to install the steel arch frame, and real-time monitoring should be carried out to guide the timing of radial grouting;

[0024] S6. After the lower step and inverted arch are excavated, 2~5cm of shotcrete is sprayed initially. The grid arch frame, outer steel mesh, steel arch frame and inner steel mesh are installed in sequence. A 6m long φ108*6mm third lock foot anchor pipe is installed at the arch foot.

[0025] S7. Then spray the concrete layer by layer to the designed thickness, which should cover the outer steel mesh and the lower step arch;

[0026] S8. Install the steel arch frame closed support ring structure at the inverted arch simultaneously, and backfill the inverted arch;

[0027] S9. The arch frame is connected in the tunnel after segmented processing. Each segment of the arch frame is connected by a connector. The arch wall and the arch top are assembled through the first arch frame connector, and the inverted arch and the arch foot are connected through the second arch frame connector.

[0028] The present invention provides a large deformation tunnel body support structure and construction method for soft rock tunnels in fold areas. The present invention targets the soft surrounding rock characteristics of tunnel bodies in the core area of folds, and takes into account the limited advance grouting. The loose surrounding rock after excavation is subjected to grouting consolidation treatment by using a double-layer arch frame pressure-releasing mechanism, directly solving the problem of loose surrounding rock gravel collapse after tectonic stress concentration and squeezing. At the same time, a self-stabilizing circle of consolidated surrounding rock is formed within the loose circle of the tunnel body, thereby partially differentiating the supporting pressure of the tunnel body. Compared with traditional support structures that directly enhance the stiffness and density of the support structure, the present invention has the advantages of strong targeting, high practicality, economy and convenience. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The present invention will be further described below with reference to the accompanying drawings and examples:

[0030] Figure 1 It is a schematic diagram of the overall construction of the present invention;

[0031] Figure 2 It is a multi-layer schematic diagram of the support structure of the present invention;

[0032] Figure 3 This is a schematic diagram of the concrete layer wrapping of the present invention;

[0033] Figure 4 This is a schematic diagram of the step excavation construction of the present invention;

[0034] Figure 5 This is a construction diagram after step excavation in the present invention;

[0035] Figure 6 This is a construction diagram of the present invention after the lower step and inverted arch are excavated;

[0036] Figure 7 It is a schematic diagram of the sprayed concrete construction of the present invention;

[0037] Figure 8 This is a main structural diagram of the first arch connector of the present invention;

[0038] Figure 9 This is a main structural diagram of the first arch connector of the present invention after angle adjustment;

[0039] Figure 10 This is a side structural diagram of the first arch connector of the present invention;

[0040] Figure 11 This is a side view of the first angle fixing screw locking angle structure of the first arch connector of the present invention;

[0041] Figure 12 This is a disassembled structural diagram of the first arch connector of the present invention;

[0042] Figure 13 This is a cross-sectional structural diagram of the first arch connector of the present invention;

[0043] Figure 14 This is a main structural diagram of the second arch connector of the present invention;

[0044] Figure 15 This is a side view of the second arch connector installation structure of the present invention;

[0045] Figure 16 This is a diagram of the angle adjustment structure of the second arch connector of the present invention;

[0046] Figure 17 This is a disassembled structural diagram of the second arch support connector of the present invention.

[0047] In the figure: grille arch 1; first steel body 101; second steel body 102; first fixing plate 103; second fixing plate 104; sliding groove 105; steel flower tube 2; first arch connector 3; positioning claw 301; rotating shaft 302; first angle fixing screw 303; sliding head 304; outer steel mesh 4; steel arch 5; third fixing plate 501; inner steel mesh 6; first locking foot anchor pipe 7; second locking foot anchor pipe 8; third locking foot anchor pipe 9; second arch connector 10; limiting claw 1001; limiting plate 1002; lower step arch 11; fourth fixing plate 1101; second angle fixing screw 1102; concrete layer 12; sprayed concrete 13. DETAILED DESCRIPTION

[0048] Example 1

[0049] like Figures 1 to 17 As shown, a large deformation tunnel support structure for soft rock tunnels in a folded area is provided. A grid arch 1 with a ring-shaped structure is formed by multiple steel bodies. A steel arch 5 with a ring-shaped structure is provided inside the grid arch 1. An outer layer of steel mesh 4 is provided between the steel arch 5 and the grid arch 1. An inner layer of steel mesh 6 is provided on the inner wall of the steel arch 5. A lower step arch 11 is provided at the bottom opening of the steel arch 5. The lower step arch 11 forms a closed loop with the steel arch 5. The outer wall of the grid arch 1 is also provided with multiple vertically arranged steel flower pipes 2. The exterior of the steel arch 5 and the grid arch 1 is also provided with multiple locking foot anchor pipes inclined downward. The grid arch 1, the lower step arch 11 and the steel arch 5 are assembled by connecting the rigid bodies via a first arch connector 3. Two 6m long φ108*6mm locking foot anchor pipes are respectively set at the arch feet of the upper and middle steps of the grid arch frame 1, and two 4.5m long φ42*4mm locking foot anchor pipes are respectively set at the arch feet of the lower step. The outer steel mesh 4 is installed to the inner side of the grid arch frame 1 and is installed according to the process during the step-by-step construction; φ42*4 mm steel flower pipes 2 are arranged in a plum blossom shape with a spacing of 1.2*1.2 m along the circumference of the tunnel body, and cement slurry with a water-cement ratio of 1:1 is used for grouting, and the grouting pressure is 0.5~1 MPa.

[0050] Two 4.5m long φ42*4mm locking foot anchor pipes are set at the arch foot of the steel arch frame 5, and the inner steel mesh 6 is installed to the inner side of the grid steel arch frame 5. It is installed according to the process in the step-by-step construction; the sprayed concrete 13 includes an overall support system to form a concrete layer 12 structure, such as Figure 3 The structure shown is sprayed layer by layer during construction, beginning with an initial 2-5 cm spray after tunnel excavation. After the outer layer of steel mesh 4 is installed, spraying is repeated layer by layer to the designed thickness. The arches are fabricated in sections and then connected within the tunnel. Each arch section is connected using connectors: the first arch connector 3 is located at the arch wall and vault, while the second arch connector 10 is located at the invert and arch foot. These connections are all made using traditional methods.

[0051] In order to solve the problem of large deformation of the tunnel body caused by the closed cracks in the surrounding rock in front of the face and limited advance support under the condition of tectonic stress concentration, and the extremely broken and loose surrounding rock in the excavated section collapsing, the outer layer of low-rigidity grid arch frame and large locking foot anchor pipe are used to make the surrounding rock deform and unload under certain support resistance conditions when excavating the upper and middle steps. At the same time, when the surrounding rock unloads and cracks open, grouting steel flower pipes are used to consolidate the loose circle of the tunnel body, consolidate the loose surrounding rock to prevent it from collapsing, and construct a surrounding rock self-stabilizing circle to reduce the support resistance. Combined with the inner layer of high-rigidity steel arch frame, the main support structure is formed. Finally, after the mesh is hung and the anchor is sprayed, a complete support system is formed after the inverted arch frame is installed in a closed loop.

[0052] Example 2

[0053] like Figures 8 to 13 As shown, in the preferred embodiment, the structure of the first arch frame connector 3 is as follows: positioning claws 301 are provided on both sides of the second fixing plate 104 of the second steel body 102, the positioning claws 301 pass through the second fixing plate 104 and are connected to the rotating shaft 302, the first fixing plate 103 of the first steel body 101 is clamped on both sides of the positioning claws 301, and the first fixing plate 103 and the second fixing plate 104 are connected by a plurality of stud nuts. The grille arch 1, the lower step arch 11 and the steel arch 5 are all assembled by connecting the rigid bodies through the first arch frame connector 3. The first arch frame connector 3 is mainly connected by the first fixing plate 103 and the second fixing plate 104 through a plurality of stud nuts and is simply positioned by the positioning claws 301, and then the grille arch 1, the lower step arch 11 and the steel arch 5 are assembled, and the assembly efficiency is high.

[0054] In the preferred embodiment, sliding grooves 105 are further provided on both sides of the second steel body 102, and a sliding head 304 is provided at one end of the rotating shaft 302. The sliding head 304 is arranged inside the sliding groove 105 and is axially limited inside the sliding groove 105. The positioning claw 301 rotates through the rotating shaft 302, and the sliding head 304 at the end of the rotating shaft 302 slides up and down or rotates inside the sliding groove 105, which can make the sliding head 304 rotate at multiple angles, thereby changing the connection angle between the second steel body 102 and the second steel body 102, such as Figure 9 The structure shown is adaptable to different arc structures.

[0055] In a preferred embodiment, the lower surface of the slot of the positioning claw 301 is flush with the surface of the second fixing plate 104 , so that the second fixing plate 104 can be easily inserted into the slot of the positioning claw 301 .

[0056] The first fixing plate 103 is further provided with a plurality of first angle fixing screws 303 , which pass through the first fixing plate 103 and abut against the surface of the second fixing plate 104 ; the first angle fixing screws 303 facilitate fixing the connection angle between the second steel body 102 and the second steel body 102 .

[0057] One side of the first fixing plate 103 is a wedge-shaped structure, which is stuck in the slot of the positioning claw 301. A limiting boss is provided on one side of the wedge-shaped structure, which rests on one side of the positioning claw 301 for limiting; it can locate and simply fix the position of the first fixing plate 103.

[0058] The bolt holes on the second fixing plate 104 are all waist-shaped holes, which can be locked at multiple angles.

[0059] Example 3

[0060] like Figures 14-17 As shown, in the preferred embodiment, the lower step arch frame 11 and the steel arch frame 5 are connected by a second arch frame connector 10. The structure of the second arch frame connector 10 is as follows: a third fixing plate 501 is provided on one side of the steel arch frame 5, and limiting claws 1001 are provided on both sides of the third fixing plate 501. The limiting claws 1001 pass through the third fixing plate 501, and a limiting plate 1002 is provided at the tail end of the limiting claw 1001. The fourth fixing plate 1101 at the end of the lower step arch frame 11 is clamped on the limiting claw 1001, and the fourth fixing plate 1101 is connected to the third fixing plate 501 by a plurality of stud bolts; the second arch frame connector 10 can connect the steel arch frame 5 and the lower step arch frame 11, and the angle between the lower step arch frame 11 and the steel arch frame 5 can be adjusted through the second arch frame connector 10, and the limiting claws 1001 are used to limit the position of the fourth fixing plate 1101 of the lower step arch frame 11.

[0061] The bolt holes on the third fixing plate 501 are all waist-shaped holes; the waist-shaped holes can be locked at multiple angles.

[0062] The fourth fixing plate 1101 is also provided with a plurality of second angle fixing screws 1102, which pass through the fourth fixing plate 1101 and rest on the third fixing plate 501; the second angle fixing screws 1102 facilitate fixing the connection angle between the lower step arch frame 11 and the steel arch frame 5.

[0063] Example 4

[0064] Further illustrate with reference to Example 1, Figure 1-17In the structure shown, after the steps on the tunnel are excavated, 2~5cm shotcrete 13 is initially sprayed, the grid arch frame 1 is installed, and two 6m long φ108*6m first locking foot anchor pipes 7 are set at the arch foot, and then the outer steel mesh 4 is installed to complete the support of the upper steps; the effective effect of the present invention is: using the low-rigidity grid arch frame 1 to support the surrounding rock, so that the surrounding rock squeezes the grid arch frame 1 and deforms to release stress, forming an initial unloading system, and at the same time using high-strength locking foot anchor pipes to enhance the overall stability of the grid arch frame 1 to avoid arch instability.

[0065] After the middle step of the tunnel is excavated, 2~5cm shotcrete 13 is initially sprayed, the grid arch frame 1 is installed and two 6m long φ108*6mm second lock foot anchor pipes 8 are set at the arch foot, and then the outer steel mesh 4 is installed to complete the middle step support.

[0066] Determine whether the tunnel deformation has reached the reserved deformation amount based on the monitoring measurement data. When the tunnel deformation reaches the reserved deformation amount, arrange two radial φ42*4 mm steel tubes in a plum blossom shape with a spacing of 1.2*1.2 m, and use cement slurry with a water-cement ratio of 1:1 for grouting. The grouting range should not be less than the size of the loose circle.

[0067] After grouting, the inner steel arch frame 5 and the inner steel mesh 6 are installed. A 4.5m long φ42*4mm third lock foot anchor pipe 9 is set at the arch foot of the arch frame, and the sprayed concrete layer 12 is sprayed layer by layer to the designed thickness. The thickness should cover the outer steel mesh 4 to form the middle and upper step support system;

[0068] When the deformation of the tunnel body does not reach the reserved deformation amount, the on-site process should be adjusted to install the steel arch frame 5, and real-time monitoring should be carried out to guide the timing of radial grouting. When the deformation of the tunnel body does not reach the reserved deformation amount, the on-site process should be adjusted to install the steel arch frame 5, and real-time monitoring should be carried out to guide the timing of radial grouting. The effective effect of the present invention is to utilize the gaps opened by the surrounding rock cracks after the tunnel body is unloaded to perform radial grouting reinforcement on the annular loose zone of the tunnel body, thereby preventing the extremely broken surrounding rock in the stress concentration area from loosening and collapsing, and at the same time improving the self-stability of the surrounding rock zone to reduce the tunnel body support resistance.

[0069] After the lower step and inverted arch are excavated, 2~5cm shotcrete 13 is initially sprayed, and the grid arch frame 1, outer steel mesh 4, steel arch frame 5 and inner steel mesh 6 are installed in sequence, and a 6m long φ108*6mm third lock foot anchor pipe 9 is set at the arch foot.

[0070] Then spray the concrete layer by layer to the designed thickness, which should cover the outer steel mesh 4 and the lower step arch 11.

[0071] The steel arch frame 5 is installed synchronously at the inverted arch to close the supporting annular structure and the inverted arch is backfilled. The effective effect of the present invention is: the φ108*6mm locking foot anchor pipe is used to improve the structural stability of the grid arch frame 1 in front of the arch frame closed loop, and to provide sufficient construction opportunities for the inverted arch excavation and arch frame closed loop.

[0072] The arch frame is connected in the hole after segmented processing. The arch frames are connected by connectors. The arch wall and arch top are assembled by the first arch frame connector 3, and the inverted arch and arch foot are connected by the second arch frame connector 10.

[0073] The above embodiments are merely preferred technical solutions of the present invention and should not be construed as limiting the present invention. The scope of protection of the present invention shall be the technical solutions set forth in the claims, including equivalent alternatives to the technical features of the technical solutions set forth in the claims. In other words, equivalent alternatives and improvements within this scope are also within the scope of protection of the present invention.

Claims

1. A large deformation tunnel support structure for soft rock tunnels in folded areas, characterized by: A grid arch frame (1) having a ring structure formed by multiple steel bodies, a steel arch frame (5) having a ring structure formed by multiple steel bodies is provided on the inner side of the grid arch frame (1), an outer steel mesh (4) is provided between the steel arch frame (5) and the grid arch frame (1), an inner steel mesh (6) is provided on the inner wall of the steel arch frame (5), a lower step arch frame (11) is provided at the bottom opening of the steel arch frame (5), and the lower step arch frame (11) and the steel arch frame (5) form a closed loop; The grid arch frame (1), the lower step arch frame (11) and the steel arch frame (5) are all assembled by connecting the rigid body through the first arch frame connector (3); The structure of the first arch connector (3) is as follows: positioning claws (301) are provided on both sides of the second fixing plate (104) of the second steel body (102), the positioning claws (301) pass through the second fixing plate (104) and are connected to the rotating shaft (302), the first fixing plate (103) of the first steel body (101) is clamped on both sides of the positioning claws (301), and the first fixing plate (103) and the second fixing plate (104) are connected by a plurality of stud nuts; The lower step arch frame (11) and the steel arch frame (5) are connected via a second arch frame connector (10); The structure of the second arch frame connector (10) is as follows: a third fixing plate (501) is provided on one side of the steel arch frame (5), limiting claws (1001) are provided on both sides of the third fixing plate (501), the limiting claws (1001) pass through the third fixing plate (501), and a limiting plate (1002) is provided at the tail end of the limiting claw (1001), a fourth fixing plate (1101) at the end of the lower step arch frame (11) is clamped on the limiting claw (1001), and the fourth fixing plate (1101) and the third fixing plate (501) are connected by a plurality of stud bolts; The bolt holes on the third fixing plate (501) are all waist-shaped holes; A plurality of second-angle fixing screws (1102) are further provided on the fourth fixing plate (1101), and the second-angle fixing screws (1102) pass through the fourth fixing plate (1101) and abut against the third fixing plate (501).

2. The large deformation tunnel support structure for soft rock tunnels in folded areas according to claim 1 is characterized by: The outer wall of the grid arch (1) is also provided with a plurality of vertically arranged steel flower tubes (2).

3. The large deformation tunnel support structure for soft rock tunnels in folded areas according to claim 1 is characterized by: The steel arch frame (5) and the grid arch frame (1) are also provided with a plurality of locking foot anchor pipes arranged obliquely downward on the outside.

4. The large deformation tunnel support structure for soft rock tunnels in folded areas according to claim 1 is characterized by: Sliding grooves (105) are further provided on both sides of the second steel body (102). A sliding head (304) is provided at one end of the rotating shaft (302). The sliding head (304) is arranged inside the sliding groove (105). The sliding head (304) is axially limited inside the sliding groove (105).

5. The large deformation tunnel support structure for soft rock tunnels in folded areas according to claim 1 is characterized by: The lower surface of the slot of the positioning claw (301) is flush with the surface of the second fixing plate (104); A plurality of first-angle fixing screws (303) are further provided on the first fixing plate (103), and the first-angle fixing screws (303) pass through the first fixing plate (103) and abut against the surface of the second fixing plate (104); One side of the first fixing plate (103) is a wedge-shaped structure, which is clamped in the clamping groove of the positioning claw (301), and one side of the wedge-shaped structure is provided with a limiting boss, which abuts against one side of the positioning claw (301) to limit the position; The bolt holes on the second fixing plate (104) are all waist-shaped holes.

6. The construction method of a large deformation tunnel support structure for a soft rock tunnel in a fold area according to any one of claims 1 to 5, characterized in that: The method includes: S1. After the steps on the tunnel are excavated, 2~5cm shotcrete (13) is initially sprayed, the grid arch frame (1) is installed, and two 6m long φ108*6m first lock foot anchor pipes (7) are set at the arch foot, and then the outer steel mesh (4) is installed to complete the upper step support; S2. After the middle step of the tunnel is excavated, 2~5cm of shotcrete (13) is sprayed initially, the grid arch (1) is installed, and two 6m long φ108*6mm second lock foot anchor pipes (8) are set at the arch foot, and then the outer steel mesh (4) is installed to complete the middle step support; S3. Determine whether the deformation of the tunnel body has reached the reserved deformation amount based on the monitoring measurement data. When the tunnel body has deformed to the reserved deformation amount, arrange radial φ42*4 mm steel flower pipes (2) in a plum blossom shape with a spacing of 1.2*1.2 m, and use cement slurry with a water-cement ratio of 1:1 for grouting. The grouting range should not be less than the size of the loose circle. S4. After grouting, the inner steel arch frame (5) and the inner steel mesh (6) are installed. A 4.5m long φ42*4mm third lock foot anchor pipe (9) is set at the arch foot of the arch frame, and the sprayed concrete layer (12) is sprayed layer by layer to the designed thickness. The thickness should cover the outer steel mesh (4) to form the middle and upper step support system; S5. When the deformation of the tunnel body does not reach the reserved deformation, the on-site process should be adjusted to install the steel arch frame (5), and real-time monitoring should be carried out to guide the timing of radial grouting; S6. After the lower steps and inverted arch are excavated, 2~5cm of shotcrete (13) are initially sprayed, and the grid arch frame (1), outer steel mesh (4), steel arch frame (5) and inner steel mesh (6) are installed in sequence, and a 6m long φ108*6mm third lock foot anchor pipe (9) is installed at the arch foot; S7, then spray the shotcrete layer by layer to the designed thickness, which should cover the outer steel mesh (4) and the lower step arch (11); S8, synchronously installing the steel arch frame (5) at the inverted arch to close the supporting annular structure, and backfilling the inverted arch; S9, the arch frame is connected in the hole after segmented processing, and the arch frames of each segment are connected by a connector. The arch wall and the arch top are assembled by the first arch frame connector (3), and the inverted arch and the arch foot are connected by the second arch frame connector (10).

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