A reinforcement construction method for soft ground section of a long tunnel in phyllite geology

Abstract

The invention belongs to the technical field of tunnel construction, and specifically relates to a reinforcement construction method for a soft-ground section of a phyllite geological super-long tunnel; arch and pipe-roof guide pipe construction are carried out at a pre-constructed tunnel entrance; drilling construction is carried out in a plurality of pipe-roof guide pipes, and a piston ring is placed in each borehole, and a steel pipe is inserted into the center hole of the piston ring; grouting conduits are installed on the external ends of the plurality of steel pipes, and grouting is carried out in the plurality of steel pipes by connecting the grouting conduits through a grouting machine, so that the outflowing concrete pushes the piston ring to move outside the borehole and opens the openings on the steel pipe in turn, so that the concrete is pressurized and discharged into the rock stratum gaps along the inner side to the outer side of the openings in the steel pipe in turn, forming an initial pipe-roof support; after the tunnel is excavated to the bottom of the initial pipe-roof, a construction groove is excavated around the side of the tunnel, and the secondary pipe-roof support is continuously constructed in the construction groove toward the tunnel direction; the above steps are repeated until the tunnel is penetrated; and the strength of the pipe-roof advance support junction can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel construction, and in particular relates to a reinforcement construction method for a soft-ground section of a phyllite geological extra-long tunnel. Background Art

[0002] The reinforcement method during tunnel construction generally adopts pipe-roof advance support, which is a support method for tunnel construction. The pipe-roof is pushed into the stratum, and concrete grouting materials are injected into the stratum through the openings on the steel pipes of the pipe-roof to form a high-strength and high-rigidity pipe-roof support structure. The pipe-roof advance support has the following functions in tunnel construction: Enhance stratum rigidity: During the tunnel construction process, the pipe-roof can form a continuous support body of tens of meters in length with the stratum around the tunnel, effectively enhancing the stratum rigidity and avoiding large-scale deformation of the stratum around the tunnel. Reduce surface settlement: Through the bearing capacity of the pipe-roof, surface settlement can be effectively reduced and the impact on ground buildings can be reduced. Improve construction efficiency: Pipe-roof advance support can improve construction efficiency, reduce the construction period and engineering risks during tunnel construction, and save construction costs. Protect the environment: Compared with traditional tunnel support methods, pipe-roof advance support has the effect of reducing noise and dust pollution.

[0003] Since the steel pipes of the general pipe-roof advance support need to have a certain outward expansion angle based on the tunnel construction direction to ensure the support effect after the grouting solidifies, and in the grouting process, since the concrete grouting material has a certain viscosity, and the length of the steel pipes of the pipe-roof advance support is generally 10-45 meters, the pressure injected into the stratum gap by the openings close to the grouting port during grouting is relatively large, so the grouting range can be larger, and the openings on the side far from the grouting port need to overcome the resistance of the steel pipe to the concrete, and the resistance is greater the farther away from the grouting port. At the same time, the concrete in the steel pipe inclined upward also needs to overcome Gravity. Under the action of these two forces, the opening on the side of the steel pipe close to the grouting port injects concrete into the soil layer in a larger range and in a more sufficient amount, while the opening on the side of the steel pipe far from the grouting port injects concrete into the soil layer in a smaller range and in a smaller amount, resulting in the soil layer at the end of the pipe-roof advance support not forming a high strength. As a result, when it is used in the construction process of extra-long tunnels, when multiple pipe-roof advance supports are required to be carried out alternately with tunnel excavation, the position between the two pipe-roof advance supports will become a weak point in bearing capacity. This shortcoming is particularly obvious when constructing in geology with poor engineering geological properties and large deformation, such as phyllite.

[0004] Based on this, a reinforcement construction method for soft soil sections of extra-long tunnels in phyllite geology was proposed. Summary of the invention

[0005] In order to solve the above problems existing in the prior art, the present invention provides a reinforcement construction method for the soft ground section of a phyllite geological extra-long tunnel.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A reinforcement construction method for a soft-ground section of a phyllite geological extra-long tunnel comprises the following steps:

[0008] S1: Install the sleeve arch formwork at the pre-constructed tunnel entrance, embed a number of pipe shed guide pipes facing the tunnel direction and arranged obliquely on the sleeve arch formwork, and pour concrete in the sleeve arch formwork to form the sleeve arch;

[0009] S2: drilling holes in several pipe-roof guide pipes, and placing a piston ring in each drilled hole, inserting a steel pipe into the center hole of the piston ring, so that the outer wall and the inner wall of the piston ring are slidably fitted with the pipe-roof guide pipe and the steel pipe respectively;

[0010] S3: Grouting conduits are installed on the outer ends of the plurality of steel pipes, and grouting is performed in the plurality of steel pipes by connecting the grouting conduits with a grouting machine, so that the flowing concrete pushes the piston ring to move outside the borehole and sequentially opens the openings on the steel pipes, so that the concrete is sequentially pressurized and discharged from the steel pipes along the inner side to the outer side of the openings into the rock stratum gaps, thereby forming an initial pipe support;

[0011] S4: Excavate the tunnel. After excavating to the bottom of the initial pipe shed, excavate a construction trench around the side of the tunnel, and continue to construct the secondary pipe shed support in the construction trench toward the tunnel;

[0012] S5: Repeat the steps in S4 until the tunnel is penetrated.

[0013] Furthermore, the piston ring is composed of a plurality of single-layer rings coaxially fitted and buckled with each other, and the piston ring is adapted to different numbers of single-layer rings according to different grouting pressures.

[0014] Furthermore, the inner side surface and the outer side surface of the piston ring are both provided with a plurality of layers of annular teeth.

[0015] Furthermore, in S2, before the piston ring is placed in the borehole, the borehole is first cleaned.

[0016] Furthermore, in S3, each opening of the steel pipe is provided with a sliding cover plate, and when the piston ring moves toward the outside of the borehole, the cover plates on the moving path are slid open in sequence.

[0017] Furthermore, in S3, the plurality of steel pipes are divided into two groups according to intervals, and the two groups of steel pipes are grouting-initiated in sequence from bottom to top.

[0018] Furthermore, in S3, before installing grouting conduits on the plurality of steel pipes, a steel cage is arranged inside the steel pipes.

[0019] Furthermore, in S4, the soil in the tunnel is excavated by a core soil excavation method, and initial support construction is performed.

[0020] Furthermore, in S4, after the secondary pipe-roof support construction is completed, a steel cage is tied in the construction trench, and a casting formwork is made, and then concrete is poured to form a supporting arch column in the construction trench.

[0021] Furthermore, after the S5 is completed, secondary lining construction is carried out.

[0022] The beneficial effects of the present invention are:

[0023] (1) The piston ring is placed at the farthest end of the borehole, and then a steel pipe is placed into the borehole through a pipe-roof guide pipe, so that the steel pipe is inserted into the center hole of the piston ring. Then, a grouting conduit is connected to the steel pipe, and the grouting conduit is used to connect to a grouting machine. Concrete is injected into the steel pipe through the grouting machine. In the initial state, the cover plate is closed to the openings, and only the farthest opening is in an open state and concrete flows out. Under the continuous pressure of the grouting machine, the concrete is injected into the soil layer at this position. Then, when the grouting pressure is greater than the friction resistance between the piston ring, the steel pipe and the side wall of the borehole, the pressurized concrete will push the piston ring to move from the farthest end of the grouting port to the nearest end. When moving to the next opening, the moving piston ring changes the opening on the moving path from a closed state to an open state. The farthest opening can only push the piston ring to move after the predetermined grouting pressure is completed and then continue to be pressurized. By first grouting the soil layer at the farthest opening position and maintaining the pressure, the grouting amount and the support strength at this position can be guaranteed;

[0024] (2) By excavating a construction trench on the tunnel side wall at the junction, on the one hand, it is convenient to construct the next section of pipe-roof advance support. On the other hand, after the construction of the next section of pipe-roof advance support is completed, steel bars can be tied and poured at the construction trench to form supporting arch columns, thereby increasing the bearing capacity of the soil layer above and preventing tunnel collapse. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to facilitate understanding by those skilled in the art, the present invention is further described below with reference to the accompanying drawings.

[0026] Figure 1 It is a schematic diagram of the internal structure of the tunnel side of the present invention;

[0027] Figure 2 It is a schematic diagram of the internal structure of the tunnel front of the present invention;

[0028] Figure 3 It is a schematic diagram of the side structure of the piston ring and the steel pipe of the present invention;

[0029] Figure 4for Figure 3 A local enlarged schematic diagram of point A in the middle.

[0030] Legend: 1. Piston ring; 2. Ring gear; 3. Steel pipe; 31. Opening; 32. Cover plate; 33. Slide groove; 4. Arch; 5. Pipe rack guide pipe; 6. Construction groove. DETAILED DESCRIPTION

[0031] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0032] like Figure 1-4 As shown, a reinforcement construction method for a soft-ground section of a phyllite geological extra-long tunnel of the present invention comprises the following steps:

[0033] S1: Install the arch 4 template at the pre-constructed tunnel entrance, embed a number of pipe shed guide pipes 5 facing the tunnel direction and inclined on the arch 4 template, and pour concrete in the arch 4 template to form the arch 4;

[0034] S2: drilling holes in a plurality of pipe-roof guide pipes 5, and placing a piston ring 1 in each drilled hole, inserting a steel pipe 3 into the center hole of the piston ring 1, so that the outer wall and the inner wall of the piston ring 1 are slidably fitted with the pipe-roof guide pipe 5 and the steel pipe 3 respectively;

[0035] S3: Grouting conduits are installed on the outer ends of the plurality of steel pipes 3, and grouting is performed in the plurality of steel pipes 3 by connecting the grouting conduits with a grouting machine, so that the flowing concrete pushes the piston ring 1 to move outside the borehole and sequentially opens the openings 31 on the steel pipes 3, so that the concrete is sequentially pressurized and discharged from the steel pipes 3 along the inner side to the outer side of the openings 31 into the rock stratum gap, thereby forming an initial pipe support;

[0036] S4: excavate the tunnel, and after excavating to the bottom of the initial pipe shed, excavate a construction trench 6 around the side of the tunnel, and continue to construct the secondary pipe shed support in the construction trench 6 towards the tunnel direction;

[0037] S5: Repeat the steps in S4 until the tunnel is penetrated.

[0038] Since the steel pipe 3 of the general pipe-roof advance support needs to have a certain outward expansion angle based on the tunnel construction direction to ensure the support effect after the grouting solidifies, and in the grouting process, since the concrete grouting material has a certain viscosity, and the length of the steel pipe 3 of the pipe-roof advance support is generally 10-45 meters, the pressure that can be injected into the stratum gap by the opening 31 close to the grouting port during grouting is relatively large, so the grouting range can be larger, and the opening 31 on the side far away from the grouting port needs to overcome the resistance of the steel pipe 3 to the concrete, and the resistance is greater the farther away from the grouting port. At the same time, the concrete in the steel pipe 3 inclined upward also needs to overcome the pressure of the steel pipe 3. Under the action of these two forces, the opening 31 of the steel pipe 3 close to the grouting port injects a larger range of concrete into the soil layer, and the amount is more sufficient, while the opening 31 of the steel pipe 3 far from the grouting port injects a smaller range of concrete into the soil layer, and the amount is also less, resulting in the soil layer at the end of the pipe-roof advance support not forming a high strength. As a result, when it is used in the construction process of a super-long tunnel, when multiple pipe-roof advance supports and tunnel excavation are required to be carried out alternately, the position between the two pipe-roof advance supports will become a weak point in bearing capacity. This shortcoming is particularly obvious when constructing in geology with poor engineering geological properties and large deformation, such as phyllite.

[0039] In order to prevent too little concrete slurry from being injected into the soil layer around the opening at the end of the steel pipe 3, a piston ring 1 is placed in the borehole through S2. In order to facilitate the placement of the piston ring 1 in the borehole and ensure the fit between the piston ring 1 and the side wall of the borehole and the steel pipe 3, the material of the piston ring 1 is preferably made of elastic material such as rubber. The piston ring 1 is placed at the farthest end of the borehole, and then the steel pipe 3 is placed into the borehole through the pipe rack guide pipe 5, so that the steel pipe 3 is inserted into the center hole of the piston ring 1, and then a grouting catheter is connected to the steel pipe 3. The grouting catheter is used to connect to a grouting machine, and concrete is injected into the steel pipe 3 through the grouting machine, so that the concrete flows out of the borehole through the opening 31 and is squeezed into the gap in the soil layer under the pressure force. In order to ensure that the soil layer on the side of the borehole away from the grouting port is close to the soil layer on the side close to the grouting port The soil layers on the sides are subjected to the same pressure, so several openings on the steel pipe 3 are closed in the initial state, and only the opening 31 at the farthest end is always in the open state. After the grouting starts, only the opening 31 at the farthest end has concrete flowing out and the concrete is injected into the soil layer at this position under the continuous pressure of the grouting machine. Then, when the grouting pressure is greater than the friction resistance between the piston ring 1, the steel pipe 3 and the side wall of the borehole, the pressurized concrete will push the piston ring 1 to move from the farthest end to the nearest end of the grouting port. When moving to the next opening 31, the moving piston ring 1 changes the opening 31 from the closed state to the open state. At this time, the opening 31 at the farthest end to the opening 31 at the nearest end can be named as the first opening 31, the second opening 31, the third opening 31, and so on. After the piston ring 1 passes through the second opening 31, concrete is injected into the nearest soil layer through the first opening 31 and the second opening 31, and continues to push the piston ring 1 to move under the action of pressure, and continues to open the third opening 31 until the piston ring 1 changes all the openings 31 from a closed state to an open state.

[0040] In this sequential grouting process, the farthest opening 31 can push the piston ring 1 to move after continuing to pressurize only after the predetermined grouting pressure is achieved. After the second opening 31 is opened, the original grouting pressure will be injected into the soil layer from the second opening 31 on the one hand, and on the other hand, the grouting pressure will also maintain the grouting pressure at the first opening 31 to prevent the concrete from flowing back under the action of gravity after grouting at the first opening 31. Finally, continued pressurization will also push the piston ring 1 to move to the third opening 31. Similarly, when concrete is injected into the soil layer at this position through the third opening 31, the first opening 31 and the second opening 31 will also maintain the original grouting pressure to the soil layer under the action of the grouting pressure. Therefore, it is greatly different from the prior art that, in the prior art, during grouting, the entire steel pipe 3 must be filled before concrete can be injected into the soil layer, so the grouting pressure of the opening 31 at the far end of the steel pipe 3 is insufficient. In the present embodiment, since the farthest end is grouted first, the grouting position will not move beyond the grouting port until the grouting pressure is reached, and the grouting pressure of the farthest opening 31 can be maintained all the time.

[0041] Since the piston ring 1 moves toward the grouting port, and since the pressure near the grouting port and at the low end is high, and the pressure far away from the grouting port and at the high end is low, the grouting pressure applied to the opening 31 in the grouting state is always at the maximum state. For example, after the piston ring 1 moves to the second opening 31, the grouting pressure of the second opening 31 is greater than that of the first opening 31. After the piston ring 1 moves to the third opening 31, the grouting pressure of the third opening 31 is greater than that of the second opening 31 and the first opening 31. Grouting is continued in the steel pipe 3 until the piston ring 1 moves to the vicinity of the grouting port and stops, and then the grouting pressure is maintained for a period of time and then stopped, thereby completing the grouting construction of the borehole.

[0042] When carrying out pipe-roof advance support construction for extra-long tunnels, it is necessary to advance through multiple sections of pipe-roofs in sequence, and the junction of two sections of pipe-roof supports may not be able to form a good bearing capacity. In addition, since phyllite will soften when it comes into contact with water, in relatively humid geographical locations or weather conditions, it is necessary to form a better support effect for the junction of the pipe-roof supports at both ends. Therefore, it is necessary to excavate the soil underneath after completing a pipe-roof advance support, and continue the construction of the next section of pipe-roof advance support after clearing the soil in the tunnel. The shape of each section of the pipe-roof advance support after completion is similar to a trumpet, and multiple trumpets are connected to each other, with the larger side being nested on the smaller side to form a more stable structure. Therefore, after the construction of the pipe-roof advance support at one end is completed and the soil in the tunnel is excavated, it is necessary to simultaneously excavate a construction trench 6 on the tunnel side wall at the junction. On the one hand, it is convenient for the construction of the next section of the pipe-roof advance support. On the other hand, after the construction of the next section of the pipe-roof advance support is completed, steel bars can be tied and poured to form a supporting arch column in the construction trench 6, thereby increasing the bearing capacity of this position for the soil layer above and preventing tunnel collapse.

[0043] Since all the openings 31 are grouted simultaneously in the prior art, a grout-stop valve needs to be provided between the pipe-roof guide pipe 5 and the steel pipe 3 and at the outermost position to prevent concrete from flowing out from between the pipe-roof guide pipe 5 and the steel pipe 3 during grouting. In the present embodiment, since a piston ring 1 is provided between the steel pipe 3 and the pipe-roof guide pipe 5, a grout-stop valve does not need to be provided. Instead, only a blocking plate or other blocking device needs to be provided to prevent the piston ring 1 from directly sliding out after moving to the nearest end.

[0044] Due to the different hardness and density of different soil layers, as well as the different gap spaces in the soil layers, detection is required before construction. The grouting pressure is determined based on the detection results of the soil layers. The piston ring 1 is slidably set in the borehole, and the movement of the piston ring 1 is driven by the grouting pressure. At this time, if the required grouting pressure is small, and the friction between the piston ring 1 and the borehole side wall and the steel pipe 3 remains unchanged, the grouting pressure must be greater than the friction, so it is impossible to adapt to the grouting pressure. In order to avoid this problem, the piston ring 1 is composed of a number of single-layer rings that are coaxially fitted and buckled with each other. The piston ring 1 is adapted to different numbers of single-layer rings according to different grouting pressures;

[0045] That is, the single-layer ring is the smallest unit of the piston ring 1. During the construction process, the number of single-layer rings on the piston ring 1 is matched according to the required grouting pressure. When the required grouting pressure is large, more single-layer rings are used to fit and buckle each other. When the required grouting pressure is small, fewer single-layer rings are used to fit and buckle each other. When the number of single-layer rings is large, the friction generated is large, while when the number of single-layer rings is small, the friction generated is small. At the same time, the piston ring 1 is composed of multiple single-layer rings that fit and buckle each other, which can also facilitate the installation of the piston ring 1. The inner and outer sides of the piston ring 1 are both provided with several layers of annular teeth 2, and the annular teeth 2 are in contact with the steel pipe 3 and the side wall of the borehole. Since there may be protruding small stones on the inner side wall of the borehole, if the piston ring 1 abuts against the small stones, it may be difficult to move. Therefore, when the outer side wall of the piston ring 1 is provided with annular teeth 2, it can be deformed when encountering small stones, and then pass through the small stones. Although a certain amount of grout leakage will occur at this time, a small amount of grout leakage has no effect on the overall grouting construction.

[0046] In one embodiment, in step S2, before the piston ring 1 is placed in the borehole, the borehole is first cleaned; after drilling, most of the sand and soil can be discharged, but some sand and soil are not completely cleared out of the borehole. The remaining sand and soil can be blown out by filling the borehole with high-speed gas to prevent the sand in the hole from causing the piston ring 1 to get stuck.

[0047] When the piston ring 1 moves from the inside of the borehole to the outside of the borehole, each time it passes through an opening 31 on the steel pipe 3, the opening 31 will be changed from a closed state to an open state. Specifically, a sliding cover plate 32 is provided on each opening 31 of the steel pipe 3. When the piston ring 1 moves to the outside of the borehole, the cover plates 32 on the moving path are slid open in sequence. A sliding groove 33 for slidingly setting the cover plate 32 is provided on the inner wall of the steel pipe 3, and the cover plate 32 can only slide along the axial direction of the steel pipe 3 under the action of the piston ring 1. A handle that cooperates with the piston ring 1 is provided on the cover plate 32. When the piston ring 1 passes by, the piston ring 1 The annular teeth 2 first contact and push the handle on the cover plate 32, so that the cover plate 32 changes from a closed state to an open state, until the cover plate 32 slides to the maximum open state and cannot move, and then the piston ring 1 continues to move under the grouting pressure, so that the annular teeth 2 contact and deform with the handle and then slide over the handle, and then the opening 31 on the steel pipe 3 changes to an open state. Although the pressure inside the steel pipe 3 is relatively high during grouting, the cover plate 32 slides horizontally and is restricted by the slide groove 33, so the grouting pressure will squeeze the cover plate 32 on the slide groove 33 until the piston ring 1 pushes, which can avoid the exposure of concrete. After the cover plate 32 slides to the maximum open state, in addition to not continuing to move, it can also make the cover plate 32 slide and fall off directly after moving to the maximum open state, and then push the cover plate 32 out of the borehole during the movement of the piston ring 1 to prevent the structural strength of the borehole from being reduced or the borehole from being blocked.

[0048] In the above step S3, the plurality of steel pipes 3 are divided into two groups according to the intervals, and the two groups of steel pipes 3 are grouting sequentially from bottom to top; since the geology of some phyllite is relatively loose, if grouting is performed once, the concrete may be completely penetrated into the soil layer. After the concrete solidifies, it may be found that there are cavities in some parts of the soil layer. In this case, the amount of grouting is insufficient, which is difficult to be found in the one-time grouting;

[0049] Therefore, in order to solve this problem, the problem can be effectively solved by grouting in batches. A number of steel pipes 3 are arranged around the arch 4, and from one side to the other side, each steel pipe 3 and the borehole are named the first hole, the second hole, the third hole, and so on. Similarly, the first hole, the third hole, etc. and the second hole, the fourth hole are divided into two groups in sequence. One group is grouted first, and it is necessary to ensure that the grouting is from bottom to top. After the grouting is completed, the concrete is allowed to stand for a period of time to allow the concrete to gradually solidify, and then the second grouting of the other group of steel pipes 3 is carried out. At this time, the concrete in the borehole that has been grouted into the soil layer by the first grouting has reached a stable state. At this time, the second grouting can ensure that the newly injected concrete will not completely penetrate into the soil layer, but will be combined with the initially poured structure, thereby playing a better reinforcement role.

[0050] Since the length of the steel pipe 3 inserted into the borehole of the general pipe-roof advance support is relatively long, the length of the steel pipe 3 will cause the steel pipe 3 to deform, and the accumulated error after deformation will increase the grouting, causing the steel pipe 3 to deflect downward. Therefore, in order to solve this problem, in the above S3, before installing the grouting conduit on the plurality of steel pipes 3, a steel cage is arranged in the steel pipe 3;

[0051] After grouting the soil layer, the steel pipe 3 is combined with the soil layer, and the steel cage arranged in the hollow structure inside the steel pipe 3 is also combined with the steel pipe 3 as a whole. At this time, the structural strength of the steel pipe 3 is higher and the supporting effect is stronger.

[0052] In one embodiment, after the above S5 is completed, secondary lining construction is carried out.

[0053] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief 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 reinforcement construction method for soft ground section of a phyllite geological extra-long tunnel, characterized by: The following steps are involved: S1: Install the sleeve arch formwork at the pre-constructed tunnel entrance, embed a number of pipe shed guide pipes facing the tunnel direction and arranged obliquely on the sleeve arch formwork, and pour concrete in the sleeve arch formwork to form the sleeve arch; S2: drilling holes in several pipe-roof guide pipes, and placing a piston ring in each drilled hole, inserting a steel pipe into the center hole of the piston ring, so that the outer wall and the inner wall of the piston ring are slidably fitted with the pipe-roof guide pipe and the steel pipe respectively; S3: Grouting conduits are installed on the outer ends of the plurality of steel pipes, and grouting is performed in the plurality of steel pipes by connecting the grouting conduits with a grouting machine, so that the flowing concrete pushes the piston ring to move outside the borehole and sequentially opens the openings on the steel pipes, so that the concrete is sequentially pressurized and discharged from the steel pipes along the inner side to the outer side of the openings into the rock stratum gaps, thereby forming an initial pipe support; S4: Excavate the tunnel. After excavating to the bottom of the initial pipe shed, excavate a construction trench around the side of the tunnel, and continue to construct the secondary pipe shed support in the construction trench toward the tunnel; S5: Repeat the steps in S4 until the tunnel is penetrated; The piston ring is composed of a plurality of single-layer rings coaxially fitted and buckled with each other, and the piston ring is adapted to different numbers of single-layer rings according to different grouting pressures; The inner side and outer side of the piston ring are both provided with several layers of annular teeth.

2. The soft-ground reinforcement construction method for a long tunnel in phyllite geology according to claim 1 is characterized by: In S2, before the piston ring is placed in the borehole, the borehole is cleaned.

3. The soft ground reinforcement construction method for a long tunnel in phyllite geology according to claim 2 is characterized by: In S3, each opening of the steel pipe is provided with a sliding cover plate, and the piston ring slides and opens the cover plates on the moving path in sequence when moving toward the outside of the borehole.

4. The soft-ground reinforcement construction method for a long phyllite tunnel according to claim 1, characterized in that: In S3, the plurality of steel pipes are divided into two groups according to intervals, and the two groups of steel pipes are grouting-initiated in sequence from bottom to top.

5. The soft-ground reinforcement construction method for a long phyllite tunnel according to claim 1, characterized in that: In S3, before installing grouting conduits on the plurality of steel pipes, a steel cage is arranged inside the steel pipes.

6. The soft-ground reinforcement construction method for a long phyllite tunnel according to claim 1, characterized in that: In S4, the soil in the tunnel is excavated by a core soil excavation method, and initial support construction is performed.

7. The soft-ground reinforcement construction method for a long tunnel in phyllite geology according to claim 6, characterized in that: In S4, after the secondary pipe-roof support construction is completed, a steel cage is tied in the construction trench, a casting formwork is made, and then concrete is poured to form a supporting arch column in the construction trench.

8. The soft-ground reinforcement construction method for a long phyllite tunnel according to claim 7, characterized in that: After the S5 is completed, the secondary lining construction is carried out.

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