A construction method for weathered siltstone tunnel in a broken shallow buried section

Abstract

The present invention provides a construction method for exiting and penetrating a weathered siltstone tunnel in a broken shallow buried section. According to the on-site topography and geology, surface steel flower pipes are adopted at the surface position of the tunnel vault in the weak surrounding rock for grouting reinforcement as a whole. At the small pile entrance section, n rows of steel pipes with built-in reinforced steel cages are adopted as an advance pipe rack, which penetrates above the heading face of the large pile exit section and is combined with a double-layer advance small guide pipe as an advance support. The tunnel body adopts a system anchor rod + double-row lock-foot anchor rod to reinforce the steel arch frame to improve the overall stability of the support. When penetrating, the support is closed into a ring in time by using a three-step advance construction to improve the overall force of the support. The technical problem that the weathered siltstone tunnel may have large tunnel settlement or even roof collapse and large safety risks during the penetrating construction in the broken shallow buried section is solved. The method enables the excavation of the broken shallow buried section to be carried out by the drilling and blasting method. Compared with the existing technology that usually adopts the manual combined with mechanical excavation method in the broken shallow buried section of the tunnel, the construction efficiency of the tunnel penetration is improved.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel penetration construction, in particular to a tunnel penetration construction method for a weathered silty mudstone tunnel in a broken shallow buried section. Background Art

[0002] Currently, conventional construction methods for tunneling through weathered silty mudstone involve excavation and support, using a combination of the three-step method and the double-sidewall pilot tunnel method, while ensuring both tunneling progress and support strength. Excavation primarily relies on manual excavation to minimize disturbance to the surrounding rock to ensure safety, and the sole support method is a "single-layer advance small guide tube + system anchor" system. Because weathered silty mudstone further loses strength when exposed to water after excavation, the fractured shallow buried section of the tunnel cannot be properly integrated with the surrounding rock due to rock fragmentation, resulting in a loss of self-stabilization and increased load on the upper section. These conventional support methods cannot guarantee construction safety during the tunneling process, and excavation typically requires only weak blasting or manual excavation, resulting in a prolonged tunneling construction period. Summary of the Invention

[0003] The present invention aims to provide a construction method for exiting and penetrating a weathered siltstone tunnel in a broken shallow buried section, so as to solve the technical problem that the existing technology cannot ensure tunnel penetration under unfavorable conditions such as penetration of a weathered siltstone tunnel in a broken shallow buried section, and cannot ensure tunnel penetration under safe, stable and efficient conditions.

[0004] In order to achieve the above object, the technical solution adopted by the present invention is:

[0005] A construction method for tunneling through a weathered silty mudstone tunnel in a broken shallow buried section comprises the following steps:

[0006] S1, single hole advance: During tunnel construction, excavation is carried out inwards from both ends of the tunnel using a step construction method to form a small pile entrance section and a large pile exit section. The section between the small pile entrance section and the large pile exit section is the section to be penetrated. When the excavation of the small pile entrance section and the large pile exit section has made the section to be penetrated reach a preset length, excavation on the large pile exit section is stopped, and the tunnel is advanced from the small pile entrance section using the single hole three-step method;

[0007] S2, grouting reinforcement of the vault surface with steel flower pipes: During the tunneling process, surface steel flower pipes are installed on the tunnel vault surface to reinforce the tunnel vault surface with grouting;

[0008] S3, constructing the nth row of advanced pipe sheds: The advanced pipe sheds are used to provide advanced support for the current tunnel face at the entrance to the tunnel. The advanced pipe sheds include steel pipes and a reinforcement steel cage built into the steel pipes. The pipe walls of the steel pipes are provided with slurry outlet holes. The construction of the advanced pipe sheds includes the following steps:

[0009] S31, driving one end of the steel pipe into the rock and soil of the current tunnel face, and gradually tilting the steel pipe upward toward the large pile exit section;

[0010] S32, after grouting in the steel pipe, replenish slurry through the slurry outlet to the surrounding broken loose rock and soil;

[0011] S4: After continuing to advance the current tunnel face, concrete is first sprayed on the tunnel face after the advance and the steel arch frame is supported. Subsequently, holes are opened on the steel arch frame within a 120° circumferential range on both sides of the centerline of the steel arch frame, and double-layer advance small ducts are used for support. The double-layer advance small ducts include several pairs of grouting steel flower tubes. The pairs of grouting steel flower tubes are spaced along the length of the steel arch frame. A pair of grouting steel flower tubes are driven into the rock and soil of the corresponding tunnel face at two angles, and one end is fixed in the opening of the steel arch frame. The rock and soil of the tunnel face are grout-reinforced by the grouting steel flower tubes to complete the advance support.

[0012] S5: After advanced support, anchor bolts are laid out in a plum blossom pattern with a spacing of 100 × 100 cm on both sides of the centerline of the steel arch in a circumferential range of 180° on the steel arch frame to reinforce the surrounding rock. Double-row locking anchor bolts are installed at the arch waist and arch foot of the steel arch frame to embed into the surrounding rock. After the double-row locking anchor bolts are driven into the tunnel rock mass, they are welded to the steel arch frame using U-shaped connecting bars. Finally, cement rolls are used to fill and compact the gaps between the double-row locking anchor bolts and the tunnel rock mass.

[0013] S6, determine whether the distance between one end of the advance pipe shed near the large pile exit section and one end of the section to be penetrated near the large pile exit section exceeds 3 meters: if so, excavate the upper step and cooperate with the advance small pipe support until the section to be penetrated is penetrated, thereby realizing the penetration of the tunnel, and finally carry out the construction of secondary lining and lining invert arch to make the support closed in a ring; if not, enter step S2 again.

[0014] Furthermore, the preset length of the section to be penetrated is 28 meters. When the length of the advanced pipe shed used is 12 meters, the spacing between two adjacent rows of advanced pipe sheds is 2 sheds, and the lap length of the tail end of the previous row of advanced pipe sheds in the latter row is 2m, a total of 3 rows of advanced pipe sheds are constructed along the length direction of the tunnel to ensure that the distance between the end of the advanced pipe shed close to the large pile number exit section and the end of the section to be penetrated close to the large pile number exit section exceeds 3 meters.

[0015] Furthermore, one end of the steel pipe is a slurry inlet, and the other end of the steel pipe is a conical head. In step S31, the steel pipe is drilled through the conical head until the steel pipe is driven into the rock and soil of the current tunnel face. In step S32, grouting is injected into the steel pipe from the slurry inlet.

[0016] Furthermore, a reinforcement hoop is welded and fixed at the slurry inlet, and the reinforcement hoop is arranged around the slurry inlet.

[0017] Furthermore, the reinforcement steel cage includes a plurality of fixing rings and a plurality of threaded steel bars, wherein the plurality of fixing rings are arranged at intervals along the axial direction of the steel pipe, and the plurality of threaded steel bars are evenly arranged around the outer circumference of the fixing rings, and each threaded steel bar is fixedly connected to the plurality of fixing rings.

[0018] Furthermore, in step S2, the surface grouting from the entrance of the small pile number section to the top of the tunnel vault to be penetrated is completed, and 1.5m plum blossom-shaped grouting reinforcement holes are opened on the surface of the tunnel vault, and then surface steel pipes are driven into the corresponding grouting reinforcement holes for grouting reinforcement.

[0019] Furthermore, in step S4, one end of each pair of grouting steel flower tubes is respectively fixed in the openings of two adjacent steel arch frames, and the angles between the extension directions of the two grouting steel flower tubes in each pair and the horizontal plane are different.

[0020] Furthermore, the double-row locking foot anchor rods are respectively arranged on the front and rear sides of the steel arch frame at corresponding positions, and the double-row locking foot anchor rods have different inclination angles relative to the horizontal plane.

[0021] Furthermore, the U-shaped connecting rib includes a first fixing portion, a second fixing portion and a connecting portion fixedly connecting the same end of the first fixing portion and the second fixing portion, which are arranged opposite to each other. The first fixing portion, the second fixing portion and the connecting portion are arranged to form a receiving cavity. The U-shaped connecting rib is sleeved on the steel arch frame through the receiving cavity. The top surface of the steel arch frame is welded and fixed to the inner side surface of the connecting portion. The double-row locking foot anchor rods are respectively arranged on the opposite sides of the U-shaped connecting rib, and are respectively welded and fixed to the outer side surfaces of the first fixing portion and the second fixing portion.

[0022] Furthermore, during the through-construction process, monitoring and measurement measures are used to assist. By continuously monitoring the settlement of the arch surrounding rock at the left measuring point, the middle measuring point and the right measuring point of the arch, the peripheral displacement and settlement observations are carried out on the convergence measuring lines around the upper step, the middle step and the lower step, so as to provide timely guidance for on-site support construction.

[0023] Due to the adoption of the above technical solution, the present invention has the following beneficial effects:

[0024] The present invention provides a construction method for a weathered siltstone tunnel to pass through a broken shallow buried section. The construction tunnel is siltstone with a broken shallow buried section above. According to the on-site topography and geology, the method adopts surface steel flower pipes for grouting reinforcement as a whole at the surface position of the tunnel vault in the weak surrounding rock. At the small pile entrance section, n rows of steel pipes with built-in reinforced steel cages are adopted as advance pipe racks to pass through the top of the heading face of the large pile exit section and are combined with double-layer advance small guide pipes as advance support. The tunnel body adopts system anchor rods + double-row locking foot anchor rods to reinforce the steel arch frame to improve the overall stability of the support. When penetrating, the three-step advance construction is used to timely close the support into a ring to improve the overall stress of the support. The weathered siltstone mudstone tunnel exit and penetration construction method of the present invention uses the "multi-layer overlapped advanced large pipe shed (with built-in steel cage to increase strength) + double-layer advanced small guide pipe + surface grouting above the penetration section" measures to further enhance the integrity and self-stabilization ability of the tunnel rock mass, and solve the technical difficulties that the weathered siltstone mudstone tunnel exit and penetration construction in the broken shallow buried section may have large tunnel settlement or even roof collapse and high safety risks, so that its excavation can be carried out by weak blasting using the drilling and blasting method. Compared with the existing technology of using manual combined with mechanical excavation, the construction efficiency of the tunnel penetration is improved, and the construction method is easy to operate, the materials are easy to obtain, and it is safe and economical, ensuring that the tunnel is smoothly penetrated under safe, stable and efficient conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart of a construction method for exiting and penetrating a weathered silty mudstone tunnel in a broken shallow buried section according to a preferred embodiment of the present invention;

[0026] Figure 2 Schematic diagram of the construction state of a weathered siltstone tunnel in a preferred embodiment of the present invention during construction of a method for exiting and penetrating a broken shallow buried section;

[0027] Figure 3 Schematic diagram of the structure for opening grouting reinforcement holes on the surface of the vault;

[0028] Figure 4 This is a structural diagram of an advanced pipe rack according to a preferred embodiment of the present invention;

[0029] Figure 5 This is a schematic structural diagram of a reinforced steel cage according to a preferred embodiment of the present invention;

[0030] Figure 6 for Figure 5 Schematic diagram of the cross-sectional structure;

[0031] Figure 7 This is a structural diagram of a double-layer advanced small catheter support according to a preferred embodiment of the present invention;

[0032] Figure 8This is a schematic diagram of the cross-sectional structure of a weathered siltstone tunnel during construction of a method for exiting and penetrating the broken shallow buried section according to a preferred embodiment of the present invention;

[0033] Figure 9 This is a schematic structural diagram of the connection between the double-row locking foot anchor rods and the steel arch frame in a preferred embodiment of the present invention;

[0034] Figure 10 for Figure 9 A magnified view of the middle part of the structure;

[0035] Figure 11 Schematic diagram of the locations of the monitoring points of the monitoring and measurement measures adopted in the preferred embodiment of the present invention.

[0036] Description of main component symbols

[0037] 1. Surface steel flower pipe; 2. Advance pipe shed; 3. Double-layer advance small guide tube; 4. Small pile entrance section; 5. Large pile exit section; 6. Section to be penetrated; 7. Soil; 11. Tunnel vault surface; 12. Grouting reinforcement hole; 21. Steel pipe; 22. Reinforcement hoop; 23. Grouting hole; 24. Conical head; 25. Reserved grouting section; 26. Reinforcement steel cage; 27. Threaded steel bar; 28. Retaining ring; 31. Grouting steel flower pipe; 32. Steel arch frame; 34. Secondary lining; 41. System Anchor rod; 42. Double-row locking anchor rod; 43. Lining invert arch; 421. Cement roll; 422. Welding connection; 423. U-shaped connecting reinforcement; 4231. First fixing part; 4232. Second fixing part; 4233. Connecting part; 4234. Accommodation cavity; 424. Tunnel rock mass; 81. Left measuring point of arch crown; 82. Middle measuring point of arch crown; 83. Right measuring point of arch crown; 84. Convergence measuring line around upper step; 85. Convergence measuring line around middle step; 86. Convergence measuring line around lower step. DETAILED DESCRIPTION

[0038] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0039] It should be noted that when a component is referred to as being "fixed to" another component, it may be directly on the other component or there may also be a central component. When a component is considered to be "connected to" another component, it may be directly connected to the other component or there may also be a central component. When a component is considered to be "set on" another component, it may be directly set on the other component or there may also be a central component. The terms "vertical", "horizontal", "left", "right" and similar expressions used herein are for illustrative purposes only.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0041] Please also see Figures 1 to 11 A preferred embodiment of the present invention provides a method for constructing a weathered silty mudstone tunnel through a broken shallow buried section, comprising the following steps:

[0042] S1, single hole advance: During tunnel construction, excavation is carried out inward from both ends of the tunnel in a step-by-step manner to form a small-pile entrance section 4 and a large-pile exit section 5. The section 6 to be penetrated is located between the small-pile entrance section 4 and the large-pile exit section 5. When the excavation of the small-pile entrance section 4 and the large-pile exit section 5 makes the section 6 to be penetrated reach a preset length, excavation on the side of the large-pile exit section 5 is stopped, and the single-hole three-step method is adopted to enter the tunnel from the small-pile entrance section 4 to excavate the soil 7 of the section 6 to be penetrated, thereby achieving tunnel penetration.

[0043] Preferably, in this embodiment, the position of the through hole is ensured to be located 22 m inward from the hole opening of the large pile exit section 5 .

[0044] S2, grouting reinforcement of the vault surface steel pipe: During the tunnel entry process, a surface steel pipe 1 is installed on the tunnel vault surface 11 to perform grouting reinforcement on the tunnel vault surface 11.

[0045] In step S2, grouting is performed from the opening of the small pile entrance section 4 to the tunnel vault surface 11 above the tunnel vault section 6 to be penetrated. Specifically, grouting reinforcement holes 12 are opened on the tunnel vault surface 11 in a plum blossom shape with a spacing of a = 1.5m, and then the surface steel pipe 1 is driven into the corresponding grouting reinforcement hole 12 for grouting reinforcement.

[0046] S3, constructing the nth row of advanced pipe sheds 2: The advanced pipe shed 2 is used to provide advanced support for the current tunnel face at the entrance. The advanced pipe shed 2 includes a steel pipe 21 and a reinforcement steel cage 26 built into the steel pipe 21. The wall of the steel pipe 21 is provided with a slurry outlet hole 23. The construction of the advanced pipe shed 2 includes the following steps:

[0047] S31, driving one end of the steel pipe 21 into the rock and soil of the current tunnel face, and gradually tilting the steel pipe 21 upward toward the large pile exit section 5;

[0048] S32, after grouting in the steel pipe 21, slurry is added to the surrounding broken loose rock and soil through the slurry outlet 23, which plays a role in reinforcing the surrounding rock and strengthening the integrity of the surrounding rock.

[0049] In this embodiment, the length of the advanced pipe rack 2 used is 12 meters, the spacing between two adjacent rows of advanced pipe racks 2 is 2 racks, and the lap length of the tail end of the previous row of advanced pipe racks 2 of the next row of advanced pipe racks 2 is 2m, that is, the overlapping part of the previous row of advanced pipe racks 2 of the next row of advanced pipe racks 2 has a projection length of 2 meters on the horizontal plane.

[0050] One end of the steel pipe 21 is a grouting port (not shown), and a predetermined length of the steel pipe 21 is reserved inward from the grouting port as a reserved grouting stop section 25. The other end of the steel pipe 21 is a conical head 24. In step S31, the steel pipe 21 is drilled through the conical head 24 until it is driven into the rock and soil of the current tunnel face. In step S32, grouting is injected into the steel pipe 21 from the grouting port. In addition, a reinforcement hoop 22 is welded and fixed to the grouting port. The reinforcement hoop 22 is arranged around the grouting port to prevent deformation of the grouting port during the grouting process.

[0051] The reinforcement cage 26 includes a plurality of fixing rings 28 and a plurality of threaded steel bars 27. The fixing rings 28 are spaced apart along the axial direction of the steel pipe 21. The threaded steel bars 27 are evenly arranged around the outer circumference of the fixing rings 28. Each threaded steel bar 27 is fixedly connected to a plurality of fixing rings 28. The provision of the reinforcement bars 26 can greatly enhance the strength of the advanced pipe rack 2.

[0052] S4, after continuing to advance the current tunnel face, first spray concrete on the tunnel face after the advance and support the steel arch frame 32, then open holes on the steel arch frame 32 within a 120° range on both sides of the center line of the arch top of the steel arch frame 32 and use double-layer advanced small pipes 3 for support. The double-layer advanced small pipes 3 include several pairs of grouting steel flower pipes 31, and the several pairs of grouting steel flower pipes 31 are spaced apart along the length direction of the steel arch frame 32. A pair of grouting steel flower pipes 31 are driven into the rock and soil of the corresponding tunnel face at two angles, and one end is fixed to the opening of the steel arch frame 32. The rock and soil of the tunnel face are grouting reinforced by the grouting steel flower pipes 31 to complete the advanced support.

[0053] In this embodiment, specifically, the double-layer advance small duct 3 is arranged within a circumferential range of 120° on both sides of the center line of the arch of the steel arch frame 32, and one end of each pair of grouting steel flower pipes 31 is respectively fixed in the openings of two adjacent steel arch frames 32, and the extension directions of the two grouting steel flower pipes 31 in each pair have different angles with the horizontal plane, among which the angle α1 between the grouting steel flower pipe 31 near the small pile number inlet section 4 and the horizontal plane is greater than the angle α2 between the grouting steel flower pipe 31 near the large pile number outlet section 5 and the horizontal plane.

[0054] S5, after the advance support, on the steel arch frame 32, system anchor rods 41 are arranged in a plum blossom pattern with a spacing of 100×100 cm within a circumferential range of 180° on both sides of the center line of the arch crown of the steel arch frame 32 to reinforce the surrounding rock. Double-row locking foot anchor rods 42 are set at the arch waist and arch foot of the steel arch frame 32 to embed into the surrounding rock. After the double-row locking foot anchor rods 42 are driven into the tunnel rock mass 424, they are welded to the steel arch frame 32 using U-shaped connecting bars 423. Finally, cement rolls 421 are used to fill and densely fill the gaps between the double-row locking foot anchor rods 42 and the tunnel rock mass 423.

[0055] Specifically, the system anchor rods 41 are arranged within a 180° circumferential range on both sides of the centerline of the steel arch, and one end of the system anchor rods 41 is welded to the steel arch 32. The double-row locking foot anchor rods 42 are respectively arranged at the front and rear sides of the steel arch 32 at corresponding positions, and the double-row locking foot anchor rods 32 are inclined at different angles relative to the horizontal plane. The U-shaped connecting rib 423 includes a first fixing portion 4231 and a second fixing portion 4232 that are relatively arranged, and a connecting portion 4233 that is fixedly connected to the same end of the first fixing portion 4231 and the second fixing portion 4232. The first fixing portion 4231, the second fixing portion 4232 and the connecting portion 4233 are arranged to form a receiving cavity 4234. The U-shaped connecting rib 423 is sleeved on the steel arch frame 32 through the receiving cavity 4233. The top surface of the steel arch frame 32 is welded and fixed to the inner side surface of the connecting portion 4233. The double-row locking foot anchor rods 42 are respectively arranged on the opposite sides of the U-shaped connecting rib 423 and are respectively welded and fixed to the outer side surfaces of the first fixing portion 4231 and the second fixing portion 4232.

[0056] S6, judge whether the distance L between the end of the advance pipe roof 2 close to the large pile exit section 5 and the end of the section to be penetrated 6 close to the large pile exit section 5 exceeds 3 meters, that is, whether the end of the projected length of the advance pipe roof 2 is 3 meters longer than the surface to be penetrated: if so, excavate the upper step and cooperate with the advance small pipe support until the section to be penetrated 6 is penetrated, thereby realizing the penetration of the tunnel, and finally carry out the construction of the secondary lining 34 and the lining arch 43 to make the support closed in a ring; if not, enter step S2 again.

[0057] Specifically, the surface to be penetrated is the top surface of the section to be penetrated 6. In this embodiment, the preset length of the surface to be penetrated of the section to be penetrated 6 is approximately 28 meters. When the length of the used advance pipe shed 2 is 12 meters, the spacing between two adjacent rows of advance pipe sheds 2 is 2 frames, and the overlap length between the tail end of the rear row of advance pipe sheds 2 and the tail end of the front row of advance pipe sheds 2 is 2m, a total of 3 rows of advance pipe sheds 2 are constructed along the length direction of the tunnel, which can make the projection length of the advance pipe shed 2 along the longitudinal section of the tunnel exceed the length of the section to be penetrated 6 by more than 3 meters, so that the advance pipe shed 2 passes through the arch of the section to be penetrated 6 to pass through above the heading face of the large pile number exit section.

[0058] In this embodiment, monitoring and measurement measures are also used during the through-construction process. By continuously monitoring the settlement of the arch surrounding rock at the left measuring point 81, the middle measuring point 82 and the right measuring point 83 of the arch, the peripheral displacement and settlement observations are carried out on the upper step perimeter convergence measuring line 84, the middle step perimeter convergence measuring line 85 and the lower step perimeter convergence measuring line 86, so as to timely guide the on-site support construction.

[0059] The present invention provides a construction method for a weathered siltstone tunnel to pass through a broken shallow buried section. The construction tunnel is siltstone with a broken shallow buried section above. According to the on-site topography and geology, the method adopts a surface steel flower pipe 1 at the surface position of the tunnel vault in the weak surrounding rock for grouting reinforcement as a whole. At the small pile entrance section 4, n rows of steel pipes with built-in reinforced steel cages 26 are adopted as an advance pipe shed 2 to pass through the top of the large pile exit section 5 and are combined with a double-layer advance small guide pipe 3 as an advance support. The tunnel body adopts a system anchor rod 41 + a double row of locking foot anchor rods 42 to strengthen the steel arch frame 32 to improve the overall stability of the support. When penetrating, the three-step advance construction is used to timely close the support into a ring to improve the overall stress of the support. The weathered siltstone mudstone tunnel exit and penetration construction method of the present invention uses the "multi-layer overlapped advanced large pipe shed (with built-in steel cage to increase strength) + double-layer advanced small guide pipe + surface grouting above the penetration section" measures to further enhance the integrity and self-stabilization ability of the tunnel rock mass, and solve the technical difficulties that the weathered siltstone mudstone tunnel may have large tunnel settlement or even roof collapse and high safety risks in the penetration construction of the broken shallow buried section, so that the excavation of the broken shallow buried section can still be carried out by the weak blasting method of drilling and blasting. Compared with the existing technology of using manual combined with mechanical excavation, the construction efficiency of the tunnel penetration is improved, and the construction method is easy to operate, the materials are easy to obtain, and it is safe and economical, ensuring that the tunnel is smoothly penetrated under safe, stable and efficient conditions.

[0060] The above description is a detailed description of the preferred embodiments of the present invention, but the embodiments are not intended to limit the scope of the patent application of the present invention. Any equivalent changes or modifications completed under the technical spirit suggested by the present invention should fall within the patent scope covered by the present invention.

Claims

1. A construction method for a weathered silty mudstone tunnel in a broken shallow buried section, characterized in that: The following steps are involved: S1, single hole advance: During tunnel construction, excavation is carried out inwards from both ends of the tunnel using a step construction method to form a small pile entrance section and a large pile exit section. The section between the small pile entrance section and the large pile exit section is the section to be penetrated. When the excavation of the small pile entrance section and the large pile exit section has made the section to be penetrated reach a preset length, excavation on the large pile exit section is stopped, and the tunnel is advanced from the small pile entrance section using the single hole three-step method; S2, grouting reinforcement of the vault surface with steel flower pipes: During the tunneling process, surface steel flower pipes are installed on the tunnel vault surface to reinforce the tunnel vault surface with grouting; S3, constructing the nth row of advanced pipe sheds: the advanced pipe sheds are used to provide advanced support for the current tunnel face at the entrance to the tunnel. The advanced pipe sheds include steel pipes and a reinforced steel cage built into the steel pipes. The pipe walls of the steel pipes are provided with slurry outlet holes. During the construction of the advanced pipe sheds, The following steps are involved: S31, driving one end of the steel pipe into the rock and soil of the current tunnel face, and gradually tilting the steel pipe upward toward the large pile exit section; S32, after grouting in the steel pipe, replenish slurry through the slurry outlet to the surrounding broken loose rock and soil; S4: After continuing to advance the current tunnel face, concrete is first sprayed on the tunnel face after the advance and the steel arch frame is supported. Subsequently, holes are opened on the steel arch frame within a 120° circumferential range on both sides of the centerline of the steel arch frame, and double-layer advance small ducts are used for support. The double-layer advance small ducts include several pairs of grouting steel flower tubes. The pairs of grouting steel flower tubes are spaced along the length of the steel arch frame. A pair of grouting steel flower tubes are driven into the rock and soil of the corresponding tunnel face at two angles, and one end is fixed in the opening of the steel arch frame. The rock and soil of the tunnel face are grout-reinforced by the grouting steel flower tubes to complete the advance support. S5: After advanced support, anchor bolts are laid out in a plum blossom pattern with a spacing of 100 × 100 cm on both sides of the centerline of the steel arch in a circumferential range of 180° on the steel arch frame to reinforce the surrounding rock. Double-row locking anchor bolts are installed at the arch waist and arch foot of the steel arch frame to embed into the surrounding rock. After the double-row locking anchor bolts are driven into the tunnel rock mass, they are welded to the steel arch frame using U-shaped connecting bars. Finally, cement rolls are used to fill and compact the gaps between the double-row locking anchor bolts and the tunnel rock mass. S6, determine whether the distance between one end of the advance pipe shed near the large pile exit section and one end of the section to be penetrated near the large pile exit section exceeds 3 meters: if so, excavate the upper step and cooperate with the advance small pipe support until the section to be penetrated is penetrated, thereby realizing the penetration of the tunnel, and finally carry out the construction of secondary lining and lining invert arch to make the support closed in a ring; if not, enter step S2 again.

2. The weathered siltstone tunnel construction method according to claim 1, wherein: The preset length of the section to be penetrated is 28 meters. When the length of the advanced pipe shed used is 12 meters, the spacing between two adjacent rows of advanced pipe sheds is 2 sheds, and the lap length of the tail end of the previous row of advanced pipe sheds in the latter row is 2m, a total of 3 rows of advanced pipe sheds are constructed along the length direction of the tunnel to ensure that the distance between the end of the advanced pipe shed close to the large pile exit section and the end of the section to be penetrated close to the large pile exit section exceeds 3 meters.

3. The construction method for weathered siltstone tunnel in a broken shallow buried section according to claim 1 is characterized in that: One end of the steel pipe is a slurry inlet, and the other end of the steel pipe is a conical head. In step S31, the steel pipe is drilled through the conical head until the steel pipe is driven into the rock and soil of the current tunnel face. In step S32, grouting is injected into the steel pipe from the slurry inlet.

4. The weathered siltstone tunnel construction method according to claim 3, wherein: A reinforcement hoop is welded and fixed at the slurry inlet, and the reinforcement hoop is arranged around the slurry inlet.

5. The weathered siltstone tunnel construction method according to claim 1, wherein: The reinforcement steel cage includes a plurality of fixing rings and a plurality of threaded steel bars. The plurality of fixing rings are arranged at intervals along the axial direction of the steel pipe. The plurality of threaded steel bars are evenly arranged around the outer circumference of the fixing rings. Each threaded steel bar is fixedly connected to the plurality of fixing rings.

6. The weathered siltstone tunnel construction method according to claim 1, wherein: In step S2, the surface grouting from the entrance of the small pile section to the top of the tunnel vault to be penetrated is completed, and 1.5m plum blossom-shaped grouting reinforcement holes are opened on the surface of the tunnel vault. Then, surface steel pipes are driven into the corresponding grouting reinforcement holes for grouting reinforcement.

7. The weathered siltstone tunnel construction method of claim 1, wherein: In step S4, one end of each pair of grouting steel flower tubes is respectively fixed in the openings of two adjacent steel arch frames, and the angles between the extension directions of the two grouting steel flower tubes in each pair and the horizontal plane are different.

8. The weathered siltstone tunnel construction method according to claim 1, wherein: The double-row locking foot anchor rods are respectively arranged on the front and rear sides of the steel arch frame at corresponding positions, and the double-row locking foot anchor rods have different inclination angles relative to the horizontal plane.

9. The construction method for weathered silty mudstone tunnel in a broken shallow buried section according to claim 8, characterized in that: The U-shaped connecting rib includes a first fixing portion, a second fixing portion and a connecting portion fixedly connecting the same end of the first fixing portion and the second fixing portion, which are arranged opposite to each other. The first fixing portion, the second fixing portion and the connecting portion are arranged to form a receiving cavity. The U-shaped connecting rib is sleeved on the steel arch frame through the receiving cavity. The top surface of the steel arch frame is welded and fixed to the inner side surface of the connecting portion; the double-row locking foot anchor rods are respectively arranged on the opposite sides of the U-shaped connecting rib, and are respectively welded and fixed to the outer side surfaces of the first fixing portion and the second fixing portion.

10. The weathered siltstone tunnel construction method of claim 1, wherein: During the through-construction process, monitoring and measurement measures are used to assist. By continuously monitoring the settlement of the arch surrounding rock at the left measuring point, the middle measuring point and the right measuring point of the arch, the peripheral displacement and settlement observations are carried out on the convergence measuring lines around the upper step, the middle step and the lower step, so as to provide timely guidance for on-site support construction.

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