Back-blowing sand grouting backfill structure and its construction method for tunnel collapse section

Abstract

The present invention relates to the technical field of tunnel excavation, and provides a back-blowing sand grouting backfill structure for a collapsed section of a tunnel and a construction method thereof. The structure comprises a closed wall for closing a gap on the upper portion of a tunnel face, the excavated side of the tunnel face is provided with back-pressure backfill soil, and a construction space is formed between the back-pressure backfill soil and the top of the excavated tunnel; the arch cavity is backfilled from bottom to top with a primary sand blowing layer, a concrete layer and a secondary sand blowing layer, the primary sand blowing layer is located in the lower region of the arch cavity, the concrete layer is located at the periphery of the arch contour line of the unexcavated tunnel, and the secondary sand blowing layer is located in the middle region of the arch cavity; the primary sand blowing layer plays the role of a cushion layer, the concrete layer mainly plays the role of strengthening the peripheral structure of the arch contour line of the unexcavated tunnel, and the secondary sand blowing layer plays the role of a buffer layer; the arch cavity is backfilled by the above structure, the stability of the backfill structure is ensured, and the secondary collapse of the tunnel is effectively controlled and avoided.

Description

Technical Field

[0001] The invention belongs to the technical field of tunnel excavation, and particularly relates to a tunnel collapse section backwash sand grouting backfill structure and a construction method thereof. Background Art

[0002] During tunnel excavation, there will be unstable sections with soft rock. This area has many types of unfavorable geology, large scale, complex geological structure, wide distribution of special rock and soil, and large engineering processing volume. It is very likely to encounter cave collapse during excavation, which will affect the construction of the project. If it is not handled properly, it is very likely to cause secondary collapse, which will directly affect the overall stability of the tunnel.

[0003] like Figure 1 As shown in the figure, when a tunnel is excavated, a gap 3 appears on the upper part of the face 2 of the excavated tunnel 1, and a large area of ​​block falls, and then a longitudinal crack occurs along the top of the tunnel toward the rear of the face 2; the original design of the surrounding rock level is level III, and the anchor spraying support method is adopted, and the excavation method is full section. The arch cavity 4 formed by the large-scale collapse is as high as 7 to 9 meters, and the lower part of the arch cavity 4 extends to the upper part of the unexcavated tunnel 5. The rock layer in front of the face changes to carbonaceous shale intercalated with carbonaceous phyllite, which is relatively broken due to the earthquake, and the carbonaceous phyllite is soft and has extremely low strength when it comes into contact with water. It was later found that there was a lot of surrounding rock fissure water seeping out of the rock surface, and the overall structure showed a trend of large deformation of soft rock. For the above-mentioned arch cavity 4, it is necessary to design a backfill structure to avoid secondary collapse of the tunnel. At the same time, when the excavation continues to move forward from the face 2 after backfilling, it is also necessary to further protect the unexcavated tunnel 5 below the arch cavity 4. Summary of the invention

[0004] The purpose of the present invention is to provide a back-blowing sand grouting backfilling structure for a collapsed section of a tunnel, so as to backfill the cavity of the arch and avoid secondary collapse of the tunnel.

[0005] In order to achieve the above-mentioned purpose, the present invention adopts the following technical scheme: a back-blowing sand grouting backfill structure for a collapsed section of a tunnel, comprising a closing wall for closing a gap on the upper part of a tunnel face, wherein the excavated side of the tunnel face is provided with back-pressure backfill soil, and a construction space is formed between the back-pressure backfill soil and the top of the excavated tunnel; the arch cavity is backfilled from bottom to top with a primary sand blowing layer, a concrete layer and a secondary sand blowing layer, wherein the primary sand blowing layer is located in the lower area of ​​the arch cavity, the concrete layer is located on the periphery of the arch contour line of the unexcavated tunnel, and the secondary sand blowing layer is located in the middle area of ​​the arch cavity.

[0006] Optionally, it also includes a sand blowing pipe 1 and a sand blowing pipe 2, wherein the sand outlet end of the sand blowing pipe 1 extends from the excavated tunnel through the closed wall to the lower area of ​​the arch cavity, and the sand blowing pipe 1 is used to form the primary sand blowing layer; the sand outlet end of the sand blowing pipe 2 extends from the excavated tunnel through the closed wall to the middle area of ​​the arch cavity, and the sand blowing pipe 2 is used to form the concrete layer and the secondary sand blowing layer.

[0007] Optionally, the sand blasting pipe 2 includes an inclined pipe section and a vertical pipe section that are detachably connected, the inclined pipe section obliquely extends from the excavated tunnel to the lower area of ​​the arch cavity, and the vertical pipe section vertically extends from the lower area of ​​the arch cavity to the middle area of ​​the arch cavity.

[0008] Optionally, a reinforcement steel frame is provided on the inner wall of the excavated tunnel, and the reinforcement steel frame is connected to the existing anchor spraying support of the excavated tunnel.

[0009] Optionally, the counter-pressure backfill soil is divided into upper step backfill soil, middle step backfill soil and lower step backfill soil from top to bottom, the lengths of the upper step backfill soil, the middle step backfill soil and the lower step backfill soil gradually increase, and the upper step backfill soil is only the middle core soil.

[0010] Optionally, the rear section and the front section of the upper step excavation section below the arch cavity are both provided with an upper step arch frame, and the middle section is provided with a hanging arch, and the hanging arch includes a hanging anchor rod connected to the concrete layer and an arched steel formwork connected to the lower end of the hanging anchor rod.

[0011] Optionally, the hanging anchor rod includes an outer hollow rod and an inner hollow rod that are coaxially matched, the upper end of the outer hollow rod is provided with a wedge-shaped end cap, the upper end of the inner hollow rod is provided with a wedge-shaped end cap that matches the inner wall of the wedge-shaped end cap, the lower end of the inner hollow rod is provided with a fastening nut and a pad, the outer periphery of the outer hollow rod is plated with glass fiber, and the outer periphery of the outer hollow rod is also provided with a cement mortar roll.

[0012] Optionally, inner walls of the excavated tunnel and the unexcavated tunnel are provided with drainage pipes.

[0013] The present invention also aims to provide a construction method for a back-blowing sand grouting backfill structure of a collapsed section of a tunnel, so as to backfill the cavity of the arch and avoid secondary collapse of the tunnel.

[0014] In order to achieve the above object, the present invention adopts the following technical scheme: a construction method of a tunnel collapse section backwash sand grouting backfill structure, comprising the following steps:

[0015] A. Clean up the collapsed soil behind the face, install locking anchors and mortar anchors on the inner wall of the excavated tunnel, and reinforce the steel frame next to the existing anchor spraying support. Use locking anchors and mortar anchors to fix the reinforced steel frame;

[0016] B. Construct counter-pressure backfill soil adjacent to the working face and to its rear. The counter-pressure backfill soil is divided into upper step backfill soil, middle step backfill soil and lower step backfill soil from top to bottom. The lengths of the upper step backfill soil, middle step backfill soil and lower step backfill soil gradually increase, and the upper step backfill soil is only the core soil in the middle;

[0017] C. Construct a closed wall to close the gap on the upper part of the face. The sand blowing pipe 1 is an inclined pipe, and the sand blowing pipe 2 is composed of an inclined pipe section and a vertical pipe section. When closing the gap: pre-embed the sand blowing pipe 1 to extend it to the lower area of ​​the arch cavity, and pre-embed the sand blowing pipe 2 to extend it to the middle area of ​​the arch cavity;

[0018] D. Sand blowing backfill is carried out through the first sand blowing pipe to fill the lower area of ​​the arch cavity to form the first sand blowing layer; then concrete is pumped through the second sand blowing pipe, and the concrete covers the top of the first sand blowing layer to form a concrete layer, and the concrete layer is located on the periphery of the arch contour line of the unexcavated tunnel; after the initial setting of the concrete, sand blowing backfill is carried out through the second sand blowing pipe to fill the middle area of ​​the arch cavity to form the second sand blowing layer.

[0019] E. Excavate forward from the backfill soil of the upper step, first break the closed wall, then dismantle the inclined pipe sections of the sand blowing pipe 1 and sand blowing pipe 2, and dig out the quicksand of the initial sand blowing layer and the soil of the upper step; during the excavation process, timely construct the upper step arch frame for the rear section and the front section of the upper step excavation section of the unexcavated tunnel;

[0020] F. Construct a hanging arch in the middle section of the upper step excavation section of the unexcavated tunnel: first, drill holes in the concrete layer, then install hanging anchors and perform grouting, then connect the arch steel formwork with the hanging anchors, and reserve a through hole in the arch steel formwork for the lower end of the vertical pipe section of the second sand blowing pipe to extend out, and finally install a plugging plate and pour concrete to form a hanging arch;

[0021] G. Excavate forward from the backfill soil of the middle step and the lower step. During the excavation process, permanent initial support is promptly applied to the inner wall of the middle step and the inner wall of the lower step of the unexcavated tunnel; then the invert of the unexcavated tunnel is constructed, so that the initial support of the unexcavated tunnel forms a ring as a whole;

[0022] H. Sand is blown back from the lower end of the vertical pipe section of the second sand blowing pipe to fill the middle and upper area of ​​the arch cavity to form three sand blowing layers. Finally, cement slurry is pumped from the lower end of the vertical pipe section of the second sand blowing pipe to fill the upper area of ​​the arch cavity to form a cement slurry layer.

[0023] Compared with the prior art, when encountering a landslide section, the present application first constructs counter-pressure backfill soil on the heading face to control the collapse and deformation trend of the heading face and the inner wall of the tunnel. The counter-pressure backfill soil is arranged at intervals with the top of the excavated tunnel to form a construction space, which is convenient for personnel to use the counter-pressure backfill soil to construct a closed wall above it to block the gap. The lower area of ​​the arch cavity, that is, the upper area of ​​the unexcavated tunnel, is first filled to form a primary sand blowing layer. The primary sand blowing layer plays the role of a cushion layer, which is convenient for backfilling a concrete layer above it. The concrete layer mainly plays the role of strengthening the peripheral structure of the arch contour line of the unexcavated tunnel, so that the arch of the unexcavated tunnel is stable and collapse and deformation are avoided when the unexcavated tunnel is excavated. The secondary sand blowing layer plays the role of a buffer layer to avoid stones falling from the arch cavity from damaging the concrete layer. The arch cavity is backfilled by the above structure to ensure the stability of the backfill structure and effectively control and avoid secondary collapse of the tunnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the formation of the arch cavity;

[0025] Figure 2 Schematic diagram of construction backfill, steel frame reinforcement, closed wall, sand blowing pipe 1 and sand blowing pipe 2;

[0026] Figure 3 Schematic diagram of backfilling the primary sand blowing layer, concrete layer and secondary sand blowing layer;

[0027] Figure 4 for Figure 3 The main view;

[0028] Figure 5 A schematic diagram of the upper step for excavating the tunnel to be excavated;

[0029] Figure 6 This is a schematic diagram of backfilling three sand blowing layers and cement slurry layers;

[0030] Figure 7 for Figure 6 The main view;

[0031] Figure 8 This is a schematic diagram of a hanging arch;

[0032] Fig. 9 Schematic diagram of hanging anchor rod.

[0033] Reference numerals:

[0034] 1. Excavated tunnel; 2. Heading face; 3. Gap; 4. Arch cavity; 5. Unexcavated tunnel; 6. Closed wall; 7. Backfill under counterpressure; 8. First sand blowing layer; 9. Concrete layer; 10. Second sand blowing layer; 11. Sand blowing pipe one; 12. Sand blowing pipe two; 13. Reinforced steel frame; 15. Suspension arch; 16. Suspension anchor rod; 161. External hollow rod; 162. Wedge-shaped end; 163. Internal hollow rod; 164. Wedge-shaped end; 165. Fastening nut; 166. Pad; 167. Cement mortar roll; 17. Arch steel formwork; 18. Third sand blowing layer; 19. Cement slurry layer. DETAILED DESCRIPTION

[0035] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It is to be understood that the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The specific embodiments described herein are only used to explain the present invention, rather than to limit the present invention. Based on the described embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art belong to the scope of protection of the present invention.

[0036] like Figures 1 to 9 As shown, the present invention provides a back-blowing sand grouting backfill structure for a collapsed section of a tunnel, comprising a closing wall 6 for closing a gap 3 on the upper part of a tunnel face 2, a back-pressure backfill soil 7 is provided on the excavated side of the tunnel face 2, and a construction space is formed between the back-pressure backfill soil 7 and the top of the excavated tunnel 1; the arch cavity 4 is backfilled from bottom to top with a primary sand blowing layer 8, a concrete layer 9 and a secondary sand blowing layer 10, the primary sand blowing layer 8 is located in the lower area of ​​the arch cavity 4, the concrete layer 9 is located on the periphery of the arch contour line of the unexcavated tunnel 5, and the secondary sand blowing layer 10 is located in the middle area of ​​the arch cavity 4.

[0037] Compared with the prior art, when encountering a landslide section, the present application first constructs a counter-pressure backfill soil 7 on the face 2 to control the collapse and deformation trend of the face 2 and the inner wall of the tunnel. The counter-pressure backfill soil 7 is arranged at intervals with the top of the excavated tunnel 1 to form a construction space, which is convenient for personnel to use the counter-pressure backfill soil 7 to construct a closed wall 6 above it to block the gap 3. First, the lower area of ​​the arch cavity 4, that is, the upper area of ​​the unexcavated tunnel 5, is filled to form a primary sand blowing layer 8. The primary sand blowing layer 8 plays the role of a cushion layer, which is convenient for backfilling a concrete layer 9 above it. The concrete layer 9 mainly plays the role of strengthening the peripheral structure of the arch contour line of the unexcavated tunnel 5, so that the arch of the unexcavated tunnel 5 is stable and collapse and deformation are avoided when the unexcavated tunnel 5 is excavated. The secondary sand blowing layer 10 plays the role of a buffer layer to prevent stones from falling from the arch cavity 4 from causing damage to the concrete layer 9; the arch cavity 4 is backfilled by the above structure, the stability of the backfill structure is ensured, and the secondary collapse of the tunnel is effectively controlled and avoided.

[0038] In some embodiments, Figure 2 and Figure 3 As shown, it also includes a sand blowing pipe 11 and a sand blowing pipe 2 12. One or more of the sand blowing pipe 11 and the sand blowing pipe 2 12 can be arranged according to the actual construction. The sand outlet end of the sand blowing pipe 11 extends from the excavated tunnel 1 through the closed wall 6 to the lower area of ​​the arch cavity 4. The sand blowing pipe 11 is used to form the primary sand blowing layer 8; the sand outlet end of the sand blowing pipe 2 12 extends from the excavated tunnel 1 through the closed wall 6 to the middle area of ​​the arch cavity 4. The sand blowing pipe 2 12 is used to form the concrete layer 9 and the secondary sand blowing layer 10. The sand blowing pipe 1 11 is an inclined pipe, and the sand blowing pipe 2 12 is composed of an inclined pipe section and a vertical pipe section. When constructing the closed wall 6, the sand blowing pipe 1 11 is pre-buried to extend to the lower area of ​​the arch cavity 4, and the sand blowing pipe 2 12 is pre-buried to extend to the middle area of ​​the arch cavity 4.

[0039] In some embodiments, Figure 2 , Figure 3 , Figure 5 and Figure 6 As shown, the inner wall of the excavated tunnel 1 is provided with a reinforcement steel frame 13, and the reinforcement steel frame 13 is connected to the existing anchor spraying support of the excavated tunnel 1. The original support type of the excavated tunnel 1 is level III anchor spraying support. When a landslide section is found, the reinforcement steel frame 13 should also be constructed adjacent to the existing anchor spraying support during the construction of the backfill 7, so as to further ensure the control of the collapse and deformation trend of the face 2 and the inner wall of the tunnel, and provide a stable support structure to resist the subsequent possible secondary landslide.

[0040] In some embodiments, Figure 2 , Figure 3 and Figure 4 As shown, the backfill soil 7 is divided into upper step backfill soil, middle step backfill soil and lower step backfill soil from top to bottom, and the lengths of the upper step backfill soil, middle step backfill soil and lower step backfill soil gradually increase, and the upper step backfill soil is only the core soil in the middle. The excavated tunnel 1 is backfilled step by step to facilitate construction.

[0041] In some embodiments, Figure 5 and Figure 8As shown, the rear section and the front section of the upper step excavation section below the arch cavity 4 are both provided with an upper step arch frame 14, and the middle section is provided with a hanging arch 15, and the hanging arch 15 includes a hanging anchor rod 16 connected to the concrete layer 9 and an arch steel formwork 17 connected to the lower end of the hanging anchor rod 16. Considering that the use of multiple steps to excavate the unexcavated tunnel 5 at the same time will cause great disturbance to the surrounding rock, the long step method is used to first excavate the upper step of the unexcavated tunnel 5, and the rear section and the front section of the upper step excavation section are connected to the surrounding rock, so it is convenient to construct the upper step arch frame 14, and the middle section of the upper step excavation section is not connected to the surrounding rock and is in an overhead state. At this time, it is necessary to construct the hanging arch 15 below the concrete layer 9 to serve as the initial support of the upper step, specifically, the hanging anchor rod 16 is driven below the concrete layer 9, and then the arch steel formwork 17 is installed, and finally the hanging arch 15 is cast.

[0042] In some embodiments, Fig. 9 As shown, the overall construction of the hanging arch 15 requires sufficient stability, so anchor rods that can provide sufficient anchoring force are required. The hanging anchor rod 16 includes a coaxial outer hollow rod 161 and an inner hollow rod 163. The upper end of the outer hollow rod 161 is provided with a wedge-shaped end head 162, and the upper end of the inner hollow rod 163 is provided with a wedge-shaped end head 164 that cooperates with the inner wall of the wedge-shaped end head 162. The lower end of the inner hollow rod 163 is provided with a fastening nut 165 and a pad 166. The outer periphery of the outer hollow rod 161 is plated with glass fiber, and the outer periphery of the outer hollow rod 161 is also provided with a cement mortar roll 167. A hole is drilled on the concrete layer 9, and the hanging anchor rod 16 is placed into the hole. The fastening nut 165 is tightened, and the outer hollow rod 161 remains stationary in the hole. The lower end of the inner hollow rod 163 is pulled out, and the wedge-shaped end 164 slides relative to the inner wall of the wedge-shaped end 162. The wedge-shaped end 162 expands and is tightly connected to the inner wall of the hole. Subsequently, high-pressure grouting is performed through the lower end of the inner hollow rod 163, and cement slurry flows out from the wedge-shaped end 164 to fill the entire hole. The cement mortar roll 167 expands and is tightly connected to the inner wall of the hole when it encounters moisture in the cement slurry. The pad 166 cooperates with the grouting plug to seal the hole. Finally, the fixing of the hanging anchor rod 16 is completed, and then the arch steel formwork 17 can be installed.

[0043] In some embodiments, drainage pipes are provided on the inner walls of the excavated tunnel 1 and the unexcavated tunnel 5. The longitudinal, transverse and circumferential drainage pipes are connected to the longitudinal drainage pipe at the tunnel arch foot through a tee, the longitudinal drainage pipe at the arch foot is connected to the transverse water diversion pipe at the bottom of the tunnel through a tee, and the transverse water diversion pipe is connected to the central drainage ditch of the tunnel to discharge the tunnel seepage in time.

[0044] A construction method for a tunnel collapse section backwash sand grouting backfill structure comprises the following steps:

[0045] A. Clean up the collapsed soil behind the face 2, and install locking anchors and mortar anchors on the inner wall of the excavated tunnel 1, close to the existing anchor spraying support to reinforce the steel frame 13, and use the locking anchors and mortar anchors to fix the reinforced steel frame 13;

[0046] B. Construct counter-pressure backfill soil 7 behind the face 2. The collapsed slag behind the face 2 can be used as the counter-pressure backfill soil 7. The counter-pressure backfill soil 7 is divided into upper step backfill soil, middle step backfill soil and lower step backfill soil from top to bottom. The lengths of the upper step backfill soil, the middle step backfill soil and the lower step backfill soil gradually increase, and the upper step backfill soil is only the core soil in the middle. According to the three-step construction method, the upper, middle and lower steps are backfilled. The step lengths are: 1-2m for the upper step, 2-5m for the middle step, and 4-8m for the lower step. The total backfill length is at least 1.5d md = tunnel diameter. Step A and step B can be constructed at the same time. The two together constitute a support system to control the collapse and deformation trend of the face 2 and the inner wall of the tunnel, and reconstruct the overall cross-sectional stress structure behind the face 2.

[0047] C. Construct a closed wall 6 to close the gap 3 on the upper part of the tunnel face 2. The sand blowing pipe 1 11 is an inclined pipe, and the sand blowing pipe 2 12 is composed of an inclined pipe section and a vertical pipe section. When closing the gap 3: pre-embed the sand blowing pipe 1 1 to extend to the lower area of ​​the arch cavity 4, and pre-embed the sand blowing pipe 2 12 to extend to the middle area of ​​the arch cavity 4;

[0048] D. Use the sand blowing pipe 11 to blow sand backfill, fill the lower area of ​​the arch cavity 4 to form the initial sand blowing layer 8, ensure that the end of the sand blowing pipe 11 extends to the arch top position of the upper part of the unexcavated tunnel 5, use a jet machine to blow in coarse sand in time, and alternately inject clean water to drive the coarse sand to flow through the fluidity of water, so that the coarse sand can fill the lower area of ​​the arch cavity 4, that is, the upper area of ​​the unexcavated tunnel 5, and at the same time, the initial sand blowing layer 8 can be leveled;

[0049] Then, concrete is pumped by the second sand blowing pipe 12, and the concrete covers the first sand blowing layer 8 to form a concrete layer 9. The concrete layer 9 is located at the periphery of the arch contour line of the unexcavated tunnel 5. The height of the concrete layer 9 should be 2.0-2.5m. After the concrete pumping is completed, the next pumping is 2-3m. 3 The mortar is intended to clean the pumping pipe and the sand blowing pipe 12, and also to further level the concrete layer 9;

[0050] After the initial setting of the concrete, the sand blowing pipe 12 is used to blow sand back to fill the middle area of ​​the arch cavity 4 to form a secondary sand blowing layer 10. At the same time, clean water should be injected alternately to drive the coarse sand to flow through the fluidity of the water, so that the coarse sand covers the surface of the concrete layer 9, and the secondary sand blowing layer 10 can be leveled at the same time.

[0051] E. Excavate forward from the backfill soil of the upper step, first break the closed wall 6, then dismantle the inclined pipe sections of the sand blowing pipe 1 11 and the sand blowing pipe 2 12, and dig out the quicksand of the initial sand blowing layer 8 and the soil of the upper step; during the excavation process, the upper step arch frame 14 is timely constructed for the rear section and the front section of the upper step excavation section of the unexcavated tunnel 5, and anchor spraying support is also required before the construction of the upper step arch frame 14;

[0052] F. The middle section of the upper step excavation section of the unexcavated tunnel 5 is at a certain distance from the surrounding rock, and there is no foundation for installing an arch frame as an initial support, so a hanging arch 15 is constructed for the middle section of the upper step excavation section of the unexcavated tunnel 5: first, a hole is drilled in the concrete layer 9, and then a hanging anchor rod 16 is installed and grouting is performed, and then an arch steel template 17 is connected to the hanging anchor rod 16, and the arch steel template 17 reserves a through hole for the lower end of the vertical pipe section of the sand blowing pipe 12 to extend out, and finally a plugging plate is installed and concrete is poured to form the hanging arch 15, which reinforces the arch support structure of the middle section of the unexcavated tunnel 5;

[0053] G. Excavate forward from the backfill soil of the middle step and the backfill soil of the lower step. During the excavation process, permanent initial support is applied to the inner wall of the middle step and the inner wall of the lower step of the unexcavated tunnel 5 in time. The permanent initial support is composed of anchor spraying support and steel frame in the prior art. This is a conventional technical means for those skilled in the art and will not be described in detail here. Then construct the invert of the unexcavated tunnel 5 so that the initial support of the unexcavated tunnel 5 is formed into a ring as a whole, and then the invert filling can be carried out first;

[0054] H. The secondary sand blowing layer 10 can be made of fine sand. The secondary sand blowing layer 10 only fills the middle area of ​​the arch cavity 4. If too much is backfilled at one time, its weight is too large and may still cause a certain pressure effect on the concrete layer 9. Therefore, the secondary sand blowing layer 10 only plays a certain buffering role. After the initial support of the unexcavated tunnel 5 is completed and the overall ring is formed and the structure is stable, the lower end of the vertical pipe section of the sand blowing pipe 2 12 is used for sand blowing backfilling. Figure 6 and Figure 7As shown, the middle and upper regions of the arch cavity 4 are filled to form a three-time sand blowing layer 18. The three-time sand blowing layer 18 may be coarse sand, and then cement slurry is pumped. The cement slurry may be a slurry of phosphoric acid, water glass and cement. The cement slurry gradually penetrates from the upper region of the arch cavity 4 into the gaps between the coarse sand of the three-time sand blowing layer 18, so that the three-time sand blowing layer 18 constitutes a cement mortar layer with more stable structural performance. At the same time, the cement slurry also penetrates into the rock stratum cracks outside the arch cavity 4, further improving the overall stability of the arch cavity 4. Finally, the cement slurry fills the upper part of the arch cavity 4 to form a cement slurry layer 19; at this time, the arch cavity 4 is completely filled, and the secondary sand blowing layer 10, the cement mortar layer, and the cement slurry layer 19 play a role in filling and limiting the deformation of the surrounding rock, thereby preventing the surrounding rock deformation from directly affecting the concrete layer 9 and the initial support of the unexcavated tunnel 5. Finally, the secondary lining of the unexcavated tunnel 5 is completed, and the tunnel construction is completed, which completely solves the problem of the tunnel collapse section, avoids the secondary collapse during tunnel excavation, and ensures the stability of the formed tunnel.

[0055] It should be noted that when backfilling the three sand blowing layers 18 and cement slurry layers 19, because the vertical pipe section of the sand blowing pipe 12 only extends to the middle of the arch cavity 4, an additional inner pipe can be driven upward from the lower end of the vertical pipe section of the sand blowing pipe 12 to the upper part of the arch cavity 4 for sand blowing and pumping cement slurry.

[0056] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A tunnel collapse section backwash sand grouting backfill structure, characterized in that: The invention comprises a closing wall (6) for closing a notch (3) at the top of a tunnel face (2); a counter-pressure backfill soil (7) is provided on the excavated side of the tunnel face (2); a construction space is formed between the counter-pressure backfill soil (7) and the top of the excavated tunnel (1); the arch cavity (4) is backfilled from bottom to top with a primary sand blowing layer (8), a concrete layer (9) and a secondary sand blowing layer (10); the primary sand blowing layer (8) is located in the lower area of ​​the arch cavity (4); the concrete layer (9) is located at the periphery of the arch contour line of the unexcavated tunnel (5); and the secondary sand blowing layer (10) is located in the middle area of ​​the arch cavity (4); The counter-pressure backfill soil (7) is divided into upper step backfill soil, middle step backfill soil and lower step backfill soil from top to bottom, the lengths of the upper step backfill soil, the middle step backfill soil and the lower step backfill soil gradually increase, and the upper step backfill soil is only the middle core soil; The rear section and the front section of the upper step excavation section below the arch cavity (4) are both provided with an upper step arch frame (14), and the middle section is provided with a hanging arch (15), and the hanging arch (15) comprises a hanging anchor rod (16) connected to the concrete layer (9) and an arched steel formwork (17) connected to the lower end of the hanging anchor rod (16); The hanging anchor rod (16) comprises an outer hollow rod (161) and an inner hollow rod (163) which are coaxially matched. The upper end of the outer hollow rod (161) is provided with a wedge-shaped end head (162), and the upper end of the inner hollow rod (163) is provided with a wedge-shaped end head (164) which matches with the inner wall of the wedge-shaped end head (162). The lower end of the inner hollow rod (163) is provided with a fastening nut (165) and a pad (166). The outer periphery of the outer hollow rod (161) is plated with glass fiber, and the outer periphery of the outer hollow rod (161) is also provided with a cement mortar roll (167).

2. The tunnel collapse section backwash sand grouting backfill structure according to claim 1 is characterized by: The invention also comprises a first sand blowing pipe (11) and a second sand blowing pipe (12), wherein the sand discharge end of the first sand blowing pipe (11) extends from the excavated tunnel (1) through the closed wall (6) to the lower area of ​​the arch cavity (4), and the first sand blowing pipe (11) is used to form the primary sand blowing layer (8); the sand discharge end of the second sand blowing pipe (12) extends from the excavated tunnel (1) through the closed wall (6) to the middle area of ​​the arch cavity (4), and the second sand blowing pipe (12) is used to form the concrete layer (9) and the secondary sand blowing layer (10).

3. The tunnel collapse section backwash sand grouting backfill structure according to claim 2 is characterized by: The second sand blasting pipe (12) comprises an oblique pipe section and a vertical pipe section which are detachably connected, wherein the oblique pipe section extends obliquely from the excavated tunnel (1) to the lower area of ​​the arch cavity (4), and the vertical pipe section extends vertically from the lower area of ​​the arch cavity (4) to the middle area of ​​the arch cavity (4).

4. The tunnel collapse section backwash sand grouting backfill structure according to claim 1 is characterized by: The inner wall of the excavated tunnel (1) is provided with a reinforcement steel frame (13), and the reinforcement steel frame (13) is connected to the existing anchor spraying support of the excavated tunnel (1).

5. The tunnel collapse section backwash sand grouting backfill structure according to claim 1 is characterized by: Drainage pipes are provided on the inner walls of the excavated tunnel (1) and the unexcavated tunnel (5).

6. A construction method for a tunnel collapse section backwash sand grouting backfill structure, applied to the tunnel collapse section backwash sand grouting backfill structure according to claim 3, characterized in that: The steps include: A. Cleaning the collapsed soil behind the tunnel face (2), installing locking anchor rods and mortar anchor rods on the inner wall of the excavated tunnel (1), and constructing a reinforcement steel frame (13) adjacent to the existing anchor spraying support, and fixing the reinforcement steel frame (13) with the locking anchor rods and mortar anchor rods; B. constructing counter-pressure backfill soil (7) adjacent to the tunnel face (2) and to the rear thereof, wherein the counter-pressure backfill soil (7) is divided into upper step backfill soil, middle step backfill soil and lower step backfill soil from top to bottom, wherein the lengths of the upper step backfill soil, the middle step backfill soil and the lower step backfill soil gradually increase, and the upper step backfill soil is only the core soil in the middle; C. Constructing a closed wall (6) to close the gap (3) at the top of the tunnel face (2); the first sand blasting pipe (11) is an inclined pipe, and the second sand blasting pipe (12) is composed of an inclined pipe section and a vertical pipe section. When closing the gap (3): pre-bury the first sand blasting pipe (11) to extend to the lower area of ​​the arch cavity (4), and pre-bury the second sand blasting pipe (12) to extend to the middle area of ​​the arch cavity (4); D. Sand blowing backfill is performed by using the first sand blowing pipe (11) to fill the lower area of ​​the arch cavity (4) to form a primary sand blowing layer (8); concrete is then pumped by using the second sand blowing pipe (12), and the concrete covers the upper part of the primary sand blowing layer (8) to form a concrete layer (9), and the concrete layer (9) is located at the periphery of the arch contour line of the unexcavated tunnel (5); after the concrete is initially set, sand blowing backfill is performed by using the second sand blowing pipe (12) to fill the middle area of ​​the arch cavity (4) to form a secondary sand blowing layer (10).

7. The construction method of the tunnel collapse section backwash sand grouting backfill structure according to claim 6 is characterized by: After step D, the method further includes the following steps: E. Excavate forward from the backfill soil of the upper step, first break the closed wall (6), then dismantle the inclined pipe sections of the sand blowing pipe 1 (11) and the sand blowing pipe 2 (12), and dig out the quicksand of the initial sand blowing layer (8) and the soil of the upper step; during the excavation process, promptly construct an upper step arch frame (14) on the rear section and the front section of the upper step excavation section of the unexcavated tunnel (5); F. constructing a hanging arch (15) in the middle section of the upper step excavation section of the unexcavated tunnel (5): firstly, drilling holes in the concrete layer (9), then installing hanging anchor rods (16) and performing grouting, then connecting the arch steel formwork (17) with the hanging anchor rods (16), and leaving a through hole in the arch steel formwork (17) for the lower end of the vertical pipe section of the second sand blowing pipe (12) to protrude, and finally installing a plugging plate and pouring concrete to form the hanging arch (15); G. Excavate forward from the backfill soil of the middle step and the backfill soil of the lower step, and in the process of excavation, apply permanent initial support to the inner wall of the middle step and the inner wall of the lower step of the unexcavated tunnel (5) in time; then construct the invert of the unexcavated tunnel (5), so that the initial support of the unexcavated tunnel (5) forms a ring as a whole; H. Sand is blown back from the lower end of the vertical pipe section of the second sand blowing pipe (12) to fill the middle and upper area of ​​the arch cavity (4) to form a third sand blowing layer (18). Finally, cement slurry is pumped from the lower end of the vertical pipe section of the second sand blowing pipe (12) to fill the upper area of ​​the arch cavity (4) to form a cement slurry layer (19).

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