Carbonaceous phyllite soft stratum tunnel structure and excavation method thereof

Abstract

The invention relates to a carbonaceous phyllite soft stratum tunnel structure which comprises a tunnel body, the tunnel body is provided with an upper step, a middle step, a lower step and an inverted arch, the upper step, the middle step, the lower step and the inverted arch are sequentially arranged from top to bottom, and the cross section of the tunnel body is in an arch shape. A mounting groove is formed in the side wall, located at the middle step, of the tunnel body, the tunnel body is provided with a supporting frame mounted in the mounting groove, the supporting frame is provided with a plurality of first grouting anchor rods, and the first grouting anchor rods are distributed in the extending direction of the tunnel body; the first grouting anchor rod penetrates through the supporting frame and is anchored to the tunnel body, and the first grouting anchor rod extends downwards to the position, located on the lower step, of the tunnel body. The method has the effect of reducing the possibility of collapse in the excavation process.

Description

Technical Field

[0001] The present application relates to the technical field of tunnel construction, and in particular to a tunnel structure in a soft carbonaceous phyllite formation and an excavation method thereof. Background Art

[0002] With the rapid development of highway construction in recent years, it is inevitable to encounter tunnel projects with special geology and topography, especially tunnel projects with phyllite geology. The tunnel area is a tectonic erosion low mountain landform, and the overall terrain of the area is undulating, so there are many cases of shallow burial and bias pressure when the tunnel enters the cave.

[0003] The main components of the weak phyllite surrounding rock are quartz, chlorite and sericite. It is lumpy when the water content is high and scaly when the water content is low. The foliation is extremely developed, and the joint surfaces are smooth and shiny. The rock mass is broken and soft, the surrounding rock has poor self-stabilization ability, soft texture, and the original rock softens when it comes into contact with water and has expansibility.

[0004] Soft rock tunnels generally use the three-bench seven-step excavation method. When excavating the side of the lower step, the initial support of the upper and middle steps is not closed with the initial support of the lower step. At this time, the excavation position is at a high distance from the top of the tunnel, which can easily cause the side wall of the tunnel to deform during the excavation process and cause landslides. Summary of the invention

[0005] In order to reduce the possibility of collapse during excavation, the present application provides a tunnel structure in a soft carbonaceous phyllite formation.

[0006] The present application provides a carbonaceous phyllite soft stratum tunnel structure and an excavation method thereof, which adopts the following technical solutions: A tunnel structure in a soft carbonaceous phyllite formation comprises a tunnel body, wherein the tunnel body is provided with an upper step, a middle step, a lower step and an inverted arch, wherein the upper step, the middle step, the lower step and the inverted arch are arranged in sequence from top to bottom, wherein the cross section of the tunnel body is arched, wherein a mounting groove is provided on the side wall of the tunnel body at the middle step, wherein the tunnel body is provided with a support frame installed in the mounting groove, wherein the support frame is provided with a plurality of first grouting anchor rods, wherein the plurality of first grouting anchor rods are distributed along the extension direction of the tunnel body, wherein the first grouting anchor rods are passed through the support frame and anchored to the tunnel body, wherein the first grouting anchor rods extend downward to the position of the tunnel body at the lower step.

[0007] By adopting the above technical scheme, after excavating the middle step, firstly, an installation groove is excavated on the side wall of the tunnel body at the middle step, and a support frame is installed in the installation groove, and then concrete is sprayed on the side wall at the middle step for initial support, and then a first grouting anchor is penetrated downward from the bottom of the support frame, and grouting is injected into the tunnel body through the first grouting anchor. After the slurry solidifies in the tunnel, the softness of the tunnel side wall is reduced, thereby reducing the possibility of deformation of the tunnel side wall at the lower step when excavating the lower step, thereby reducing the possibility of collapse.

[0008] Optionally, the upper step, the middle step and the lower step are all provided with supporting structures for supporting the tunnel body, the supporting structure located at the middle step is connected to the support frame, a support rod is provided at the middle step, both ends of the support rod are respectively connected to the support frames on both sides, the support rod is in an arc shape, and the arc-shaped opening of the support rod faces upward.

[0009] By adopting the above technical solution, when the detection instrument detects that the deformation inside the tunnel body is large, a support rod can be set at the middle step, and the two ends of the support rod are respectively connected to the support frames on both sides, so that the support structure, support frame and support rod located at the middle step are closed into a ring, thereby improving the support performance of the tunnel body and reducing the deformation of the surrounding rock of the side wall of the tunnel body.

[0010] Optionally, the support rod is a telescopic adjustable rod, and both ends of the support rod are detachably connected to the support frames on both sides respectively. Both ends of the support rod are slidably connected with a first connecting block in a horizontal direction, and are connected to the support frame through the first connecting block.

[0011] By adopting the above technical solution, the support rod is provided with a telescopic adjustment rod, so that the length of the support rod can be adjusted, thereby facilitating the carrying of the support rod into the tunnel, and a first connecting block is slidably connected at both ends of the support rod to facilitate fine-tuning the length of the support rod, and then the two ends of the support rod are respectively connected to the support frames on both sides.

[0012] Optionally, a support rod is provided at the opening of the support frame, and a first mounting block is detachably connected to the support rod, the first mounting block is provided with a positioning rod, the first connecting block is provided with a positioning hole for connection of the positioning rod, an elastic ring is provided on the positioning rod, a tightening hole for tightening the elastic ring is provided at one end of the positioning hole away from the positioning rod, the positioning rod is provided with a first guide surface for forcing the elastic ring to expand outward to tighten the inner wall of the tightening hole, and the positioning rod is provided with a driving rod for driving the elastic ring to approach the first guide surface.

[0013] By adopting the above technical solution, when installing the support rod, the positioning rod of the first mounting block is clamped on the positioning hole of the first connecting block to position the first connecting block, and then the elastic ring is driven by the driving rod to approach the first guide surface. The first guide surface forces the elastic ring to expand outward and tighten the tightening hole to position the first connecting block.

[0014] Optionally, the diameter of the first guide surface gradually increases in the direction approaching the positioning rod, the inner ring surface of the elastic ring is adapted to the first guide surface, the driving rod is provided with a pressure block, the pressure block abuts against the side of the elastic ring away from the positioning rod, and the first mounting block is provided with a first elastic member for forcing the driving rod to slide.

[0015] By adopting the above technical solution, under normal conditions, the first elastic member can be driven to force the driving rod to slide, thereby driving the elastic ring to slide in a direction close to the first guide surface through the pressure block. When the elastic ring slides along the first guide surface in a direction close to the guide block, the first guide surface stretches the inner side surface of the elastic ring, thereby forcing the elastic ring to deform, so that the outer diameter of the elastic ring becomes larger and is tightened to the tightening hole to fix the first connecting block.

[0016] Optionally, the supporting structure includes second grouting anchor rods, the upper portion of the supporting frame is arranged on the first connecting portion, and part of the second grouting anchor rods is passed through the second connecting portion and anchored to the tunnel body.

[0017] By adopting the above technical solution, when supporting the tunnel body located at the middle step, the second grouting anchor is passed through the first connecting portion on the support frame, and then the support structure is installed, so that the support frame and the support structure are connected as one, thereby improving the integrity and improving the supporting performance of the tunnel body.

[0018] Optionally, the upper and lower ends of the support frame are respectively connected to the supporting structures on the middle step and the lower step.

[0019] By adopting the above technical solution, the supporting structures of the middle step and the lower step are connected through the support frame, thereby improving the integrity between the supporting structures and improving the supporting performance of the tunnel body.

[0020] A method for excavating a tunnel in a soft carbonaceous phyllite stratum comprises the following steps: S1: Pre-support the upper part of the tunnel face by inserting the upper part of the advance small guide tube into the upper part of the tunnel face and then grouting to achieve pre-support; S2: excavating the upper step, excavating the tunnel face along the tunnel excavation contour line according to the upper step excavation cycle footage, and building a support structure for the upper step and pouring a concrete layer while excavating; S3: excavating the middle step, excavating along the excavation contour line of the tunnel according to the excavation cycle footage of the middle step, after the excavation is completed, digging two installation grooves on both sides of the middle step, the length direction of the installation groove is parallel to the length direction of the tunnel, installing a support frame in the installation groove, and then installing the first grouting anchor rod on the support frame, the first grouting anchor rod is passed through the support frame and anchored in the surrounding rock, the first grouting anchor rod is inclined downward to extend to the height corresponding to the lower step, and grouting is injected into the tunnel body through the first grouting anchor rod, and then the support structure is built and the concrete layer is poured; S5: excavating the lower step and the inverted arch pit according to the excavation cycle footage of the lower step, and at the same time, the lower step and the inverted arch are initially supported until the support structure of each step and the inverted arch are closed into a ring; S6: Repeat the above steps until the tunnel is opened.

[0021] Optionally, in step S3, before digging the installation groove, a row of second grouting anchor rods are inserted into the side wall of the middle step above the installation groove, and grouting is performed on the side wall above the installation groove through the second grouting anchor rods, thereby facilitating digging the installation groove below the second grouting anchor rods.

[0022] By adopting the above technical solution, before excavating the installation groove, firstly, a second grouting anchor is inserted above the position where the installation groove needs to be excavated and grouting is performed to reduce the softness of the tunnel side wall, thereby facilitating the excavation of the installation groove.

[0023] In summary, the present invention has the following beneficial effects: 1. After the middle step is excavated, first, an installation groove is excavated on the side wall of the tunnel body at the middle step, and a support frame is installed in the installation groove. Then, concrete is sprayed on the side wall at the middle step for initial support. Then, a first grouting anchor is inserted downward from the bottom of the support frame. Grouting is injected into the tunnel body through the first grouting anchor. After the grout solidifies in the tunnel, the softness of the tunnel side wall is reduced, thereby reducing the possibility of deformation of the tunnel side wall at the lower step when the lower step is excavated, thereby reducing the possibility of collapse; 2. When the detection instrument detects that the deformation inside the tunnel body is large, a support rod can be set at the middle step, and the two ends of the support rod are respectively connected to the support frames on both sides, so that the support structure, support frame and support rod at the middle step are closed into a ring, thereby improving the support performance of the tunnel body and reducing the deformation of the surrounding rock of the side wall of the tunnel body. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of this embodiment; Figure 2 is a schematic diagram of the structure of the tunnel body in this embodiment; Figure 3 is a schematic structural diagram of the telescopic rod in this embodiment; Figure 4 is a schematic diagram of the connection between the support frame and the telescopic rod in this embodiment; Figure 5 is a schematic diagram of the structure of the fixed block in this embodiment; Figure 6 is a schematic diagram of the connection between the first connecting block and the first mounting block in this embodiment; Figure 7 yes Figure 6 The enlarged schematic diagram of point A in the middle; Figure 8 Schematic diagram of the structure of the elastic ring in this embodiment.

[0025] In the figure, 1, tunnel body; 11, upper step; 12, middle step; 13, lower step; 14, inverted arch; 15, mounting groove; 2, support rod; 21, telescopic rod; 211, first sliding groove; 22, second connecting block; 221, sliding rod; 222, threaded rod; 23, first connecting block; 231, positioning rod; 232, sinking groove; 233, guide block; 234, first guide surface; 235, slider; 236, second spring; 237, sliding hole; 23 8. Drive rod; 2381. Pressure block; 239. Pressing sheet; 2391. First spring; 24. Elastic ring; 241. Second guide surface; 242. Second sliding groove; 243. First deformation groove; 244. Second deformation groove; 3. Support frame; 31. First connecting part; 311. Third penetration hole; 32. T-shaped block; 33. Fixing block; 331. T-shaped groove; 34. First mounting block; 341. Positioning hole; 342. Tightening hole; 4. Support structure;. DETAILED DESCRIPTION

[0026] The following is combined with Figure 1-8 This application is described in further detail.

[0027] The present application embodiment discloses a tunnel structure in a carbonaceous phyllite soft stratum, referring to Figure 1 and Figure 2 , including a tunnel body 1, the tunnel body 1 is provided with an upper step 11, a middle step 12, a lower step 13 and an inverted arch 14, the upper step 11, the middle step 12, the lower step 13 and the inverted arch 14 are arranged in sequence from top to bottom, the cross-section of the tunnel body 1 is an arch, and the upper step 11, the middle step 12 and the lower step 13 are all provided with a supporting structure 4 to support the side wall of the tunnel body 1.

[0028] Reference Figure 2The side wall of the tunnel body 1 at the middle step 12 is provided with an installation groove 15, and the tunnel body 1 is provided with a support frame 3 installed in the installation groove 15. When the tunnel is continuously excavated, several support frames 3 can be installed in sequence along the extension direction of the tunnel, and the support frames 3 can be assembled with each other. The support frame 3 is provided with several first grouting anchor rods, and the several first grouting anchor rods are distributed along the extension direction of the tunnel body 1. The bottom wall of the support frame 3 is provided with first penetration holes corresponding to the first grouting anchor rods one by one. The first grouting anchor rods are penetrated through the first penetration holes and anchored to the tunnel body 1. The first grouting anchor rods extend downward to the position of the tunnel body 1 at the lower step 13.

[0029] Reference Figure 2 The support structure 4 includes a second grouting anchor, a steel mesh and a steel arch. After the step is excavated, concrete needs to be sprayed on the side wall of the tunnel body 1 to form an initial support, and then the second grouting anchor is anchored on the side wall of the tunnel body 1 and grouting is injected into the tunnel body 1. Then the steel mesh is set up, the steel arch is installed, and finally the concrete layer is poured for support.

[0030] Referring to the figure, the upper and lower sides of the support frame 3 are both provided at the first connection part 31, the first connection part 31 is provided with a third penetration hole 311, part of the second grouting anchor rod is penetrated through the second connection part and anchored to the tunnel body 1, wherein the steel mesh of the support structure 4 of the step 12 and the lower step 13 is fixedly connected to the first connection parts 31 on the upper and lower sides respectively. The support frame 3 and the support structure 4 are connected as one, thereby improving the integrity and the supporting performance of the tunnel body 1.

[0031] Reference Figure 2 A support rod 2 is provided at the middle step 12, and the two ends of the support rod 2 are detachably connected to the support frames 3 on both sides, and the support rod 2 is in an arc shape, and the arc opening of the support rod 2 faces upward. When the deformation inside the tunnel body 1 is large, the support rod 2 can be provided at the middle step 12, and the two ends of the support rod 2 are respectively connected to the support frames 3 on both sides, so that the support structure 4, the support frame 3 and the support rod 2 at the middle step 12 are closed into a ring, thereby improving the support performance of the tunnel body 1 and reducing the deformation of the surrounding rock of the side wall of the tunnel body 1.

[0032] Reference Figure 2 and Figure 3 The support rod 2 is a telescopic adjustment rod, and includes two telescopic rods 21, one of which is provided with a first sliding groove 211 along its extension direction, and the other telescopic rod 21 is slidably connected to the first sliding groove 211. The telescopic rod 21 is provided with a plurality of second through holes, and the relative positions of the two telescopic rods 21 can be fixed by bolts through the second through holes. This makes the length of the support rod 2 adjustable, and thus facilitates carrying the support rod 2 into the tunnel.

[0033] Reference Figure 4 The end of the telescopic rod 21 away from the other telescopic rod 21 is hinged with a second connection block 22, and the second connection block 22 is provided with three sliding rods 221 and a threaded rod 222. The three sliding rods 221 and the threaded rod 222 are rectangularly distributed on the second connection block 22, one end of the sliding rod 221 is fixedly connected to the second connection block 22, and one end of the threaded rod 222 is rotatably connected to the second connection block 22. Both ends of the support rod 2 are slidably connected to the first connection block 23 in the direction away from the telescopic rod 21, and are connected to the support frame 3 through the first connection block 23.

[0034] Reference Figure 4 The first connecting block 23 is connected to the sliding rod 221 by sliding along the length direction of the sliding rod 221, and the threaded rod 222 is threadedly connected to the first connecting block 23. The threaded rod 222 is rotated to drive the first connecting block 23 to slide, so that the first connecting block 23 is close to the support frame 3, thereby facilitating the connection of the two ends of the support rod 2 with the support frames 3 on both sides.

[0035] Reference Figure 4 and Figure 5 A fixing block 33 is provided at the opening of the support frame 3, and a first mounting block 34 is detachably connected to the fixing block 33. The fixing block 33 protrudes from the side of the support frame 3 at the opening. A T-shaped slot 331 is provided on the upper surface of the fixing block 33 in the vertical direction. A T-shaped block 32 is fixedly connected to the side of the first mounting block 34. When the first mounting block 34 is installed, the T-shaped block 32 is slidably connected to the T-shaped slot 331 in the vertical direction to realize the installation of the first mounting block 34.

[0036] Reference Figure 6 and Figure 7In order to fix the first connection block 23 and the first installation block 34, a positioning rod 231 is provided on the side of the first installation block 34 away from the T-shaped block 32, and the first connection block 23 is provided with a positioning hole 341 for the positioning rod 231 to connect, and a limiting member for limiting the first installation block 34 is provided on the positioning rod 231. The limiting member is an elastic ring 24, and a tightening hole 342 for tightening the elastic ring 24 is provided at one end of the positioning hole 341 away from the positioning rod 231. A recessed groove 232 is provided at one end of the positioning rod 231 away from the first mounting block 34, and the positioning rod 231 is provided with a guide block 233 located in the recessed groove 232. The guide block 233 is coaxially arranged with the positioning rod 231, and the outer annular surface of the guide block 233 is a first guide surface 234. The diameter of the first guide surface 234 gradually increases in the direction approaching the positioning rod 231, and the inner annular surface of the elastic ring 24 is a second guide surface 241 adapted to the first guide surface 234. The positioning rod 231 is provided with a driving rod 238 for driving the elastic ring 24 to move toward the first guide surface 234. The driving rod 238 can force the elastic ring 24 to move in the direction approaching the guide block 233, thereby expanding the elastic ring 24 outward through the first guide surface 234, so that the elastic ring 24 is deformed to be tightened in the tightening hole 342.

[0037] Reference Figure 6 and Figure 7 The guide block 233 is provided with a slider 235 located on the first guide surface 234 , and the elastic ring 24 is provided with a second sliding groove 242 located on the first guide surface 234 , and the slider 235 is slidably connected to the second sliding groove 242 .

[0038] Reference Figure 8 The end surface of the elastic ring 24 is provided with a plurality of first deformation grooves 243, which are distributed in a circumferential array around the axis of the elastic ring 24, and the first deformation grooves 243 penetrate to the inner annular surface of the elastic ring 24. The end surface of the elastic ring 24 is provided with a plurality of second deformation grooves 244, which are distributed in a circumferential array around the axis of the elastic ring 24, and the second deformation grooves 244 penetrate to the outer annular surface of the elastic ring 24. The first deformation grooves 243 and the second deformation grooves 244 are provided to facilitate the elastic ring 24 to be stretched outward.

[0039] Reference Figure 6 and Figure 7The end surface of the positioning rod 231 is coaxially penetrated with a sliding hole 237, one end of the first sliding hole 237 extends to the side of the first mounting block 34 away from the first connecting block 23, and the other end of the sliding hole 237 extends to the end surface of the guide block 233. The driving rod 238 is slidingly connected to the sliding hole 237, and one end of the driving rod 238 extends to the side of the first mounting block 34 away from the first connecting block 23. The end of the driving rod 238 close to the guide block 233 is fixedly connected with a pressing block 2381, and the pressing block 2381 abuts against the end surface of the elastic ring 24. The sliding driving rod 238 can force the elastic ring 24 to slide along the guide block 233 through the pressing block 2381, so that the elastic jacket is deformed to tighten the tightening hole 342.

[0040] Reference Figure 6 and Figure 7 The end of the driving rod 238 away from the first connecting block 23 is fixedly connected with a pressing piece 239, and the first mounting block 34 is provided with a first elastic member forcing the driving rod 238 to slide, and the first elastic member is a first spring 2391, and the first spring 2391 is coaxially sleeved on the driving rod 238, and one end of the first spring 2391 is fixedly connected to the pressing piece 239, and the other end of the first spring 2391 is fixedly connected to the first mounting block 34. By pressing the pressing piece 239, the driving rod 238 can be driven to slide, thereby contacting the first connecting block 23, and the first spring 2391 can force the driving rod 238 to slide, so as to force the elastic ring 24 to deform, thereby improving the installation stability of the first connecting block 23.

[0041] Reference Figure 6 and Figure 7 The positioning rod 231 is provided with a second spring 236 for forcing the elastic ring 24 to move away from the positioning rod 231 . The second spring 236 is located in the sink 232 . One end of the second spring 236 is fixedly connected to the positioning rod 231 , and the other end of the second spring 236 abuts against the elastic ring 24 .

[0042] This embodiment also discloses a method for excavating a tunnel in a soft carbonaceous phyllite formation, comprising the following steps: S1: Pre-support the upper part of the tunnel face by inserting the upper part of the advance small guide tube into the upper part of the tunnel face and then performing grouting to achieve pre-support.

[0043] S2: excavating the upper step, excavating the heading face along the tunnel excavation contour line according to the upper step excavation cycle footage, and performing initial support on the upper step while excavating, until the upper step of a predetermined length is formed, and then supporting the structure and pouring the concrete layer.

[0044] S3: excavate the middle step, and excavate along the excavation contour line of the tunnel according to the middle step excavation cycle footage. After the excavation is completed, a row of second grouting anchors are inserted into the side wall of the middle step above the installation groove, and grouting is performed to the side wall above the installation groove through the second grouting anchors. Then, the installation groove is excavated below the second grouting anchors. Two installation grooves are excavated on both sides of the middle step. The length direction of the installation groove is parallel to the length direction of the tunnel. A support frame is installed in the installation groove, and then the first grouting anchor is installed on the support frame. The first grouting anchor is penetrated through the support frame and anchored in the surrounding rock. The first grouting anchor is inclined downward to extend to a height corresponding to the lower step, and grouting is performed into the tunnel body 1 through the first grouting anchor. Then, the support structure is built and the concrete layer is poured.

[0045] S5: excavate the lower step and the inverted arch pit according to the lower step excavation cycle footage, and carry out initial support for the lower step and the inverted arch at the same time, then build a support structure on the lower step and pour a concrete layer until the initial support structure of each step and the inverted arch are closed into a ring; S6: Repeat the above steps until the tunnel is opened.

[0046] The implementation principle of a carbonaceous phyllite soft stratum tunnel structure in the embodiment of the present application is as follows: first, after excavating the middle step 12, first, excavate the installation groove 15 on the side wall of the tunnel body 1 located at the middle step 12, and install the support frame 3 in the installation groove 15, then spray concrete on the side wall at the middle step 12 for initial support, then penetrate the first grouting anchor rod downward from the bottom of the support frame 3, and inject grout into the tunnel body 1 through the first grouting anchor rod. After the grout solidifies in the tunnel, the softness of the tunnel side wall is reduced, thereby reducing the possibility of deformation of the tunnel side wall at the lower step 13 when excavating the lower step 13, thereby reducing the possibility of collapse; When a large deformation inside the tunnel body 1 is detected by the detection instrument, a support rod 2 can be set at the middle step 12, and the two ends of the support rod 2 are respectively connected to the support frames 3 on both sides, so that the support structure 4, support frame 3 and support rod 2 located at the middle step 12 are closed into a ring, thereby improving the support performance of the tunnel body 1 and reducing the deformation of the surrounding rock of the side wall of the tunnel body 1.

[0047] The above are all preferred embodiments of the present application, and the protection scope of the present application is not limited thereto. Therefore, any equivalent changes made according to the structure, shape, and principle of the present application should be included in the protection scope of the present application.

Claims

1. A tunnel structure in a soft carbonaceous phyllite formation, characterized by: The invention comprises a tunnel body (1), wherein the tunnel body (1) is provided with an upper step (11), a middle step (12), a lower step (13) and an inverted arch (14), wherein the upper step (11), the middle step (12), the lower step (13) and the inverted arch (14) are arranged in sequence from top to bottom, wherein the cross section of the tunnel body (1) is arched, wherein a mounting groove (15) is provided on a side wall of the tunnel body (1) at the middle step (12), wherein the tunnel body (1) is provided with a support frame (3) mounted in the mounting groove (15), wherein the support frame (3) is provided with a plurality of first grouting anchor rods, wherein the plurality of first grouting anchor rods are distributed along the extension direction of the tunnel body (1), wherein the first grouting anchor rods are passed through the support frame (3) and anchored to the tunnel body (1), and wherein the first grouting anchor rods extend downward to the position of the tunnel body (1) at the lower step (13).

2. A carbonaceous phyllite soft stratum tunnel structure according to claim 1, characterized in that: The upper step (11), the middle step (12) and the lower step (13) are all provided with supporting structures (4) for supporting the tunnel body (1); the supporting structure (4) located at the middle step (12) is connected to the supporting frame (3); a supporting rod (2) is provided at the middle step (12); both ends of the supporting rod (2) are respectively connected to the supporting frames (3) on both sides; the supporting rod (2) is in an arc shape, and the arc-shaped opening of the supporting rod (2) faces upward.

3. A carbonaceous phyllite soft stratum tunnel structure according to claim 2, characterized in that: The support rod (2) is a telescopic adjustable rod, and the two ends of the support rod (2) are detachably connected to the support frames (3) on both sides respectively. The two ends of the support rod (2) are slidably connected to the first connection blocks (23) in the horizontal direction, and are connected to the support frames (3) via the first connection blocks (23).

4. The carbonaceous phyllite soft stratum tunnel structure according to claim 3, characterized in that: A fixing block (33) is provided at the opening of the support frame (3); a first mounting block (34) is detachably connected to the fixing rod; the first mounting block (34) is provided with a positioning rod (231); the first connecting block (23) is provided with a positioning hole (341) for connection with the positioning rod (231); an elastic ring (24) is provided on the positioning rod (231); an end of the positioning hole (341) away from the positioning rod (231) is provided with a tightening hole (342) for tightening the elastic ring (24); the positioning rod (231) is provided with a first guide surface (234) for forcing the elastic ring (24) to be stretched outwards to tighten the inner wall of the tightening hole (342); and the positioning rod (231) is provided with a driving rod (238) for driving the elastic ring (24) to approach the first guide surface (234).

5. The carbonaceous phyllite soft stratum tunnel structure according to claim 4, characterized in that: The diameter of the first guide surface (234) gradually increases in a direction approaching the positioning rod (231); the inner ring surface of the elastic ring (24) is adapted to the first guide surface (234); the driving rod (238) is provided with a pressure block (2381); the pressure block (2381) abuts against a side of the elastic ring (24) away from the positioning rod (231); and the first mounting block (34) is provided with a first elastic member for forcing the driving rod (238) to slide.

6. The carbonaceous phyllite soft stratum tunnel structure according to claim 2, characterized in that: The support structure (4) comprises a second grouting anchor rod, the upper portion of the support frame (3) is arranged on the first connection portion (31), and part of the second grouting anchor rod is passed through the second connection portion and anchored to the tunnel body (1).

7. The carbonaceous phyllite soft stratum tunnel structure according to claim 6, characterized in that: The upper and lower ends of the support frame (3) are respectively connected to the support structures (4) on the middle step (12) and the lower step (13).

8. A method for tunnel excavation in soft carbonaceous phyllite strata according to claim 6, characterized in that: The following steps are included: S1: Pre-support the upper part of the tunnel face by inserting the upper part of the advance small guide tube into the upper part of the tunnel face and then grouting to achieve pre-support; S2: excavating the upper step (11), excavating the tunnel face along the tunnel excavation contour line according to the excavation cycle footage of the upper step (11), and performing initial support on the upper step (11) during the excavation, and then constructing a support structure (4) and pouring a concrete layer; S3: excavating the middle step (12), excavating along the excavation contour line of the tunnel according to the excavation cycle footage of the middle step (12), after the excavation is completed, digging two installation grooves (15) on both sides of the middle step (12), the length direction of the installation grooves (15) is parallel to the length direction of the tunnel, installing a support frame (3) in the installation grooves (15), then installing a first grouting anchor rod on the support frame (3), the first grouting anchor rod is passed through the support frame (3) and anchored in the surrounding rock, the first grouting anchor rod is inclined downward to extend to a height corresponding to the lower step (13), and grouting is performed into the tunnel body (1) through the first grouting anchor rod, and then a support structure (4) is built and a concrete layer is poured; S5: excavating the pits of the lower step (13) and the invert (14) according to the excavation cycle footage of the lower step (13), and simultaneously constructing the support structure (4) and pouring the concrete layer on the lower step (13) and the invert (14) until the support structure (4) of each step and the invert (14) are closed into a ring; S6: Repeat the above steps until the tunnel is opened.

9. A method for excavating a tunnel structure in a soft carbonaceous phyllite stratum according to claim 8, characterized in that: In step S3, before excavating the installation groove (15), a row of second grouting anchor rods are inserted into the side wall of the middle step (12) above the installation groove (15), and grouting is performed on the side wall above the installation groove (15) through the second grouting anchor rods, thereby facilitating the excavation of the installation groove (15) below the second grouting anchor rods.

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