Hole entering construction method for unfavorable surrounding rock structure

Abstract

The invention discloses a tunnel entering construction method for an unfavorable surrounding rock structure, and belongs to the technical field of diversion tunnel construction. Comprising the following steps: S0, earlier-stage treatment; the method comprises the following steps: S1, reinforcing support of a hole slope; s2, forepoling within the range of a hole and a spandrel; s3, excavating a hole body; and S4, concrete lining. According to the method, under the condition that the tunnel face slope reveals an unfavorable surrounding rock structure, the upper slope of the tunnel opening is reinforced and supported, the anchor bar piles are utilized to carry out advanced support in the tunnel face and arch shoulder range, the tunnel opening is layered up and down, and the upper layer is excavated according to the two sides behind the pilot tunnel, and safe cut-through is achieved on the premise that the overall stability of the slope and the tunnel body is improved.

Description

Technical Field

[0001] The invention relates to the technical field of diversion tunnel construction, and in particular to a tunnel construction method at an unfavorable surrounding rock structure. Background Art

[0002] In the construction of diversion tunnels, the excavation and support of the tunnel face slopes must be completed before entering the tunnel. According to the size of the section, the support is basically based on the design, and a single threaded steel bar with a length of 3m~6m and a diameter of 22mm~28mm is used for slope support and lock construction; the advance support is usually carried out with a single anchor rod or pipe shed; then, the small hole is formed in one go, and the large hole is divided into upper and lower layers, and the upper layer adopts the pilot hole and then the expansion technology.

[0003] However, when the cavern is large and there is a broken rock vein zone within the cave face, safety cannot be guaranteed; cave face collapse is common, which not only prolongs the construction period but also increases costs. Summary of the invention

[0004] The purpose of the present invention is to solve the problem in the prior art that safety cannot be guaranteed when a broken rock vein zone exists within the tunnel face, and to propose a tunnel construction method at an unfavorable surrounding rock structure.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions: A method for entering a hole in an unfavorable surrounding rock structure comprises the following steps: S0, preliminary processing; S1. Strengthen the support of the tunnel entrance slope; S2, advance support within the opening and spandrel area; S3, tunnel excavation; S4. Concrete lining.

[0006] In some embodiments, in step S0, if collapse occurs and part of the locking anchor rod is pulled out, then: Demolition of collapsed rock mass; After leveling the bottom, add locking anchor rods to the collapsed part.

[0007] In some embodiments, in step S1, four rows of anchor bars are arranged on the upper slope of the tunnel opening for reinforced support; The arrangement length of each row of reinforcing support anchor bars extends to both sides of the tunnel axis: 3 to 6 meters beyond the excavation section.

[0008] In some embodiments, in step S1, the spacing of the reinforcing support anchor tendons is 2.0 m, and they are arranged in a plum blossom shape; The anchor bar bundles near the crushing zone are arranged perpendicular to the crushing zone.

[0009] In some embodiments, in step S1, the interlayer spacing between rows of reinforcing support anchor bundles gradually increases as the distance from the opening increases.

[0010] In some embodiments, in step S2: Arrange two rows of advanced support anchor bars directly above the tunnel face; Two rows of advance support anchor bars are arranged within 3 to 5 m between the tunnel top and the spandrel.

[0011] Among them, the layout position of the advance support anchor reinforcement bundle corresponds to the excavation contour.

[0012] In some embodiments, the spacing between the two rows of advance support anchor tendons directly above the tunnel face is 1.0~2.0m, arranged in a plum blossom shape, and angled outward at 5°; The spacing between the two rows of advance support anchor bars between the tunnel top and the spandrel is 1.0~2.0m, arranged in a plum blossom shape.

[0013] In some embodiments, the specifications of the advance support anchor bar bundle are: 3 to 5 steel bars welded together, a single steel bar has a diameter of 20 to 32 mm, and a length of 10 to 15 meters.

[0014] In some embodiments, in steps S1 and S2: Cement slurry is used to grout the anchor beam holes to form anchor piles; Due to the presence of crack combinations and broken zones on the slope, the grouting volume of a single hole is generally large; to ensure the quality of grouting, an automatic flow recorder is installed during the grouting process to track and record the grouting volume.

[0015] In some embodiments, in step S3: After the tunnel face reinforcement construction is completed and has a certain strength, the remaining tunnel sections can be excavated; In order to ensure safety during the excavation process and reduce potential safety hazards, the tunnel excavation is carried out according to the construction process of "pilot tunnel first and then expansion excavation"; initial support is carried out crosswise during the pilot tunnel excavation process; the tunnel excavation adopts the excavation technology of upper and lower layers and upper left and right partitions.

[0016] In some embodiments, in step S3: During the concrete lining stage, based on the tunnel lining structure diagram, the area between the tunnel face and the side wall is backfilled with concrete to connect them into a whole, so as to further ensure the stability of the slope.

[0017] Compared with the prior art, the present invention provides a method for entering a hole in an unfavorable surrounding rock structure, which has the following beneficial effects.

[0018] 1. The present invention, when the tunnel face slope reveals an unfavorable surrounding rock structure, reinforces the support of the upper slope of the tunnel entrance, and uses anchor piles to perform advance support in the tunnel face and spandrel range.

[0019] 2. The present invention strengthens the extension of the anchor piles to both sides and beyond the excavation section, thereby forming a larger range of reinforcement and further ensuring the construction safety of the project.

[0020] 3. The present invention is divided into upper and lower layers according to the tunnel opening, and the upper layer is excavated according to the excavation technology on both sides of the pilot tunnel, so as to safely penetrate the tunnel while improving the overall stability of the slope and the tunnel body.

[0021] 4. The present invention can safely and smoothly complete the construction of large tunnels within the cross-section range of unfavorable surrounding rock structures, and the slope collapse is controlled; it is worthy of reference and utilization in the construction of other caverns.

[0022] Other advantages, objectives and features of the present invention will be described in part in the following description; and in part, will be apparent to those skilled in the art based on an examination of the following; or, may be taught from the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the plan layout of the diversion tunnel and inlet slope area.

[0024] Figure 2 This is a cross-sectional view of the diversion tunnel.

[0025] Figure 3 This is a photo of the fault and collapse of the cave face slope.

[0026] Figure 4 This is the second photo of the fault and collapse of the cave face slope.

[0027] Figure 5 Schematic diagram of the arrangement of anchor bars for strengthening the support of the tunnel entrance slope.

[0028] Figure 6 These are photos of the hole face processing process.

[0029] Figure 7 This is a photo taken of the excavation through the right side of the upper layer of the diversion tunnel.

[0030] Figure 8 This is a photo taken after the diversion tunnel excavation was completed.

[0031] Fig. 9 This is a photo of the diversion tunnel outlet face and left and right side walls after casting.

[0032] In the figure: 1. Diversion tunnel; 2. Exit slope; 3. Left side slope of the open channel section outside the diversion tunnel; 4. Diversion tunnel section; 5. Excavation slope on the right side of the open channel at the diversion tunnel outlet; 6. Open channel section for water diversion; 7. Layout of advanced anchor piles outside the tunnel top; 8. Upper tunnel guide tunnel; 9. First layer of the lower tunnel on the right; 10. Lower part of the lower tunnel on the right; 11. First layer of the lower tunnel on the left; 12. Lower part of the lower tunnel on the left. DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0034] Reference Figure 1-9 A method for entering a hole in an unfavorable surrounding rock structure comprises the following steps: S0, preliminary processing (perform corresponding operations according to the on-site conditions); S1. Strengthen the support of the tunnel entrance slope; S2, advance support within the opening and spandrel area; S3, tunnel excavation; S4. Concrete lining.

[0035] Wherein, in step S0: According to the engineering design, the tunnel face locking support and the upper slope system anchor support are carried out.

[0036] If the hole face collapses and some of the locking anchors are pulled out, then: Demolition of collapsed rock mass; After leveling the bottom, add locking anchor rods to the collapsed part.

[0037] Among them, the anchor rod length is arranged according to the initial locking length to avoid the previous locking anchor rod hole.

[0038] In step S1: four rows of anchor bars are arranged on the upper slope of the tunnel opening for reinforced support.

[0039] Among them, the arrangement length of each row of reinforced support anchor bundles is extended to both sides of the tunnel axis: excavation section width / 2+3~6 meters; that is, extended to both sides of the excavation section: 3~6 meters beyond the excavation section.

[0040] For example, in a certain project, the width of the excavation section is 17 meters and the width on one side is 8.5 meters; the length of each row of reinforced support anchor bars extends 13 meters on both sides of the tunnel axis; that is, it exceeds the excavation section by 4.5 meters.

[0041] The spacing between the reinforced support anchor bars is 2.0m and they are arranged in a plum blossom shape.

[0042] Accordingly, when there is a conflict with the locking anchor rod, the position should be adjusted appropriately.

[0043] In addition, the anchor tendons near the crushing zone are arranged perpendicular to the crushing zone.

[0044] It should be noted that the interlayer spacing (i.e., height difference) between each row of reinforcing support anchor bundles gradually increases with the distance from the opening; preferably, it is gradually increased and adjusted from 1.5m to 3.5m.

[0045] For example, in a certain project, the arrangement elevations of each row of reinforced anchor tendons are: The first row is EL2268, the second row is EL2269.5, the third row is EL2271.5, and the fourth row is EL2275.

[0046] That is, the layer spacing (height difference) of each row from bottom to top is: 1.5 meters, 2.0 meters, and 3.5 meters.

[0047] In step S2: Arrange two rows of advanced support anchor bars directly above the tunnel face; Two rows of advance support anchor bars are arranged within 3 to 5 m between the tunnel top and the spandrel.

[0048] like Figure 2 As shown, the layout position of the advance support anchor tendons corresponds to the excavation contour.

[0049] Among them, the spacing between the two rows of advance support anchor bundles just above the tunnel face is 1.0~2.0m, arranged in a plum blossom shape, with an angle of 5° outward; the spacing between the two rows of advance support anchor bundles between the tunnel top and the arch spandrel is 1.0~2.0m, arranged in a plum blossom shape.

[0050] In some embodiments, the specifications of the advance support anchor bar bundle are: 3 to 5 steel bars welded together, a single steel bar has a diameter of 20 to 32 mm, and a length of 10 to 15 meters.

[0051] Preferably, the specifications of the advance support anchor bar bundle are: 3φ28, L=12.

[0052] In addition, in steps S1 and S2: cement slurry is injected into the anchor bundle hole to form an anchor pile.

[0053] Due to the existence of certain crack combinations and broken zones in the slope, the grouting volume of a single hole is generally large; to ensure the quality of grouting, an automatic flow recorder is installed during the grouting process to track and record the grouting volume.

[0054] In some embodiments, after step S2: Hang steel mesh on the front side of the excavation and spray concrete.

[0055] Preferably, hang φ8@20×20 steel mesh and spray C20 concrete 15cm.

[0056] In some embodiments, in step S3: After the tunnel face reinforcement construction is completed and has a certain strength, the remaining tunnel sections will be excavated.

[0057] Among them, in order to ensure safety during the excavation process and reduce safety hazards, the tunnel excavation is carried out according to the construction process of "first pilot tunnel and then expansion".

[0058] The pilot tunnel is excavated according to 5×6m, and initial support is carried out crosswise during the excavation process; steel arch frames are erected, fixed anchor rods are driven, steel mesh is hung, and steel fiber concrete is sprayed.

[0059] Preferably, the spacing between the supporting steel arch frames is 50 cm, and fixed anchor rods with a spacing of 1 m, φ25, and L=6 m are installed; φ8@15×15 steel mesh is hung and C25 steel fiber concrete is sprayed with a thickness of 15 cm.

[0060] The pilot tunnel excavation is controlled at 1.5m per cycle, and the measures of "short advance, weak blasting and strong support" are adopted.

[0061] The tunnel excavation adopts the excavation technology of upper and lower layers and upper left and right divisions.

[0062] After the pilot tunnel is penetrated, the tunnel body is expanded and formed from the outside of the tunnel; the expansion and excavation construction is carried out separately on both sides, that is, after the expansion and support of one side is completed, the expansion and support of the other side is carried out; the exit lower branch tunnel is used as the main driving passage; when local landslides or cavities are formed during the tunnel body expansion and excavation construction, concrete backfilling or spraying of concrete is carried out in time.

[0063] In some embodiments, in step S4: During the concrete lining stage, based on the tunnel lining structure diagram, the area between the tunnel face and the side wall is backfilled with concrete to connect them into a whole, so as to further ensure the stability of the slope.

[0064] The construction method provided by the present invention can be safely and smoothly completed in the large-scale tunnel construction within the unfavorable surrounding rock structure section range, and the slope collapse is controlled; in this construction method, the advanced construction under the tunnel face and arch shoulder is successfully applied in the diversion tunnel, which is worthy of reference and utilization in the construction of other caverns.

[0065] The following is an explanation using a specific project as an example.

[0066] The No. 1 diversion tunnel project of a hydropower station has a total length of more than 1,500 meters and is a double-bend tunnel in plane. The tunnel section is in the shape of a city gate tunnel, with an excavation section size of 17×21m (width×height); the longitudinal slope i=9.2‰, and a group of broken rock veins are developed on the exit slope, with a width of about 25~50cm, starting from the left top arch and extending to the right, extending about 20m in the direction of the tunnel depth; the rock mass on the upper part of the entire tunnel face is in block and sub-block structures.

[0067] like Figure 1 The figure shows the plan layout of the diversion tunnel and the inlet slope area.

[0068] 1 is a diversion tunnel with excavation dimensions of 17m×21m and dimensions of 15m×19m after lining; 2 is the exit slope, the width of the first level of the bridleway at the top of the tunnel entrance is 9m, and the width of the bridleways above it is 2m; 3 is the left side slope of the open channel section outside the diversion tunnel, and the excavation slope ratio is 1:0.5; 4 is the diversion tunnel section, where the tunnel entrance section intersects the tunnel axis at 55° and exits the tunnel obliquely; 5 is the excavation slope layout on the right side of the open channel at the diversion tunnel outlet, with a rock slope ratio of 1:0.3; 6 is the water diversion open channel section; the open channel structure is divided into two sections, and the end of the left side wall spreads downstream at an angle of 25°.

[0069] It should be noted that the "left and right sides" in the above description are distinguished in combination with the water flow direction, which is different from the left and right sides generally considered when viewing the drawings; technicians in the field are generally aware of this.

[0070] During the excavation of the tunnel face slope at the diversion tunnel exit, after completing the locking support of the tunnel face and the system anchor support of the upper slope, the tunnel face guide tunnel excavation was carried out at a depth of 1.0m; after the excavation was completed, the top of the tunnel face collapsed, causing some locking anchors to be pulled out.

[0071] The collapse revealed that there was a combination of developed fissures at the cave entrance, and the cut rock mass was in an unloading state. At the same time, there were two obvious cracks in the upper rock mass. The exposed surrounding rock was porphyritic biotite-potassium feldspar granite, which belonged to the weakly weathered lower section. The rock mass was fresh to weakly weathered, with a mainly mosaic to sub-block structure. The gently inclined structural surface in this section was relatively developed, and local block collapse was serious. According to the analysis of rock strata changes, within 5m of the rock plug section, there might be medium-inclined faults such as f25 or medium- and steep-inclined fissures outside the syncline slope close to the cave, which would be extremely unfavorable to the stability of the cave side walls.

[0072] To this end, on the basis of perfecting the lock construction, the tunnel face area has carried out enhanced support to enhance the stability of the upper slope; and advanced support anchor reinforcement bundles have been constructed on the tunnel face and the upper half of the tunnel body to speed up the excavation and support progress of the remaining sections of the tunnel body, shorten the construction time of each cycle, and improve overall stability.

[0073] First, the collapsed part needs to be dealt with; the collapsed rock mass needs to be deflated; after leveling the bottom, additional locking anchor rods need to be driven into the collapsed part; the anchor rod length is arranged according to the initial locking length, avoiding the first locking anchor rod hole.

[0074] Afterwards, reinforced support construction was carried out on the tunnel face; a scaffolding with a height of about 8m and a specification of 1.2×1.2×1.5m was erected, and four rows of anchor bundles were arranged for reinforced support to prevent the overall collapse of the upper rock mass during the later excavation and support period; the length of each row was extended by 13m on both sides of the tunnel axis, and a total of about 70 anchor bundles were arranged.

[0075] Among them, the specifications of the reinforced support anchor bundles are: 3φ28, L=15; the spacing between the anchor bundles is 2.0m, and they are arranged in a plum blossom shape; the exposed length is 10cm, and the anchor bundles near the broken zone are arranged perpendicular to the broken zone.

[0076] like Figure 5 The figure shows the schematic diagram of the arrangement of the reinforced support anchor bars.

[0077] The arrangement elevations are: first row: EL2268, second row: EL2269.5, third row: EL2271.5, fourth row: EL2275 (as the distance from the opening increases, the spacing between each row of reinforced support anchor bundles gradually increases).

[0078] Afterwards, the construction of advance support anchor reinforcement bundles is carried out.

[0079] The scope of advance support is: 1) Two rows of 3φ28, L=12.0m, 1.0~2.0m spacing, plum blossom-shaped advance support anchor beams are arranged directly above the tunnel face, with an angle of 5° outward; the position is adjusted appropriately when there is a conflict with the locking anchor rod; 2) Two rows of 3φ28, L=12.0m, 1.0~2.0m spacing, plum blossom-shaped anchor beams are arranged within 3m between the tunnel top and the arch spandrel; 3) The arc-shaped layout is carried out around the excavation contour, and the distance between each advance support anchor pile and the excavation contour is kept consistent.

[0080] In addition, cement grout is used in all anchor bar bundle holes; That is, reinforce the support anchor bundle and advance the support anchor bundle by grouting in the hole to form anchor piles.

[0081] It should be noted that due to the presence of certain crack combinations and broken zones in the slope, the grouting volume of a single hole is generally large; to ensure the quality of grouting, an automatic flow recorder is installed during the grouting process to track and record the grouting volume.

[0082] Afterwards, hang a φ8@20×20 steel mesh on the front of the excavation of the tunnel face and spray 15cm of C20 concrete; then, carry out excavation and lining.

[0083] It should be noted that: after the tunnel face reinforcement construction is completed and has a certain strength, the remaining tunnel sections will be excavated; the tunnel body excavation adopts the excavation technology of upper and lower layers and upper left and right partitions.

[0084] Specifically, in order to ensure safety during the excavation process and reduce potential safety hazards, the tunnel excavation is carried out according to the construction process of "pilot tunnel first and then expansion"; the pilot tunnel is excavated according to 5×6m, and initial support is carried out crosswise during the excavation process; the steel arch frames are supported with a spacing of 50cm, and fixed anchor rods with a spacing of 1m, φ25, and L=6m are driven, and φ8@15×15 steel mesh is hung and C25 steel fiber concrete is sprayed with a thickness of 15cm. System support for this part is no longer constructed.

[0085] Each cycle of pilot tunnel excavation is controlled at 1.5m, and the measures of "short advance, weak blasting, strong support" are adopted. After penetration, the tunnel body is expanded and excavated from the outside. The two sides are separated during the expansion and excavation construction, that is, the expansion and support of one side is completed before the expansion and support of the other side. The exit lower branch tunnel is used as the main driving channel. If local collapse or cavity formation occurs during the tunnel body expansion and excavation construction, concrete backfilling construction or spraying concrete should be carried out in time.

[0086] like Figure 2 As shown; 7 is the layout of the anchor piles for advanced support (the original lock anchor is not shown, it is a conventional double-layer anchor with a diameter of 25mm, a length of 5m, and a spacing of 50cm); 8 is the upper half tunnel pilot tunnel, with a size of 5m×5.5m. After the excavation is completed, the right side excavation support is carried out first, and then the left side excavation support is carried out. The single excavation depth is controlled at 1.5m. 9 is the first layer of the lower half of the right side tunnel, and the excavation depth is controlled within 2m; 10 is the lower part of the lower half of the right side tunnel; the steel arch frame is connected in order, and the single excavation length is controlled within 5m; 11 is the first layer of the lower half of the left tunnel, and the excavation depth is controlled within 2m; 12 is the lower part of the lower half of the left side tunnel; the steel arch leg is constructed, and the single excavation length is controlled within 5m.

[0087] During construction, attention should be paid to controlling the sliding of the inclined layers of the side walls and the falling off along the structural surface to complete the cavern excavation smoothly and safely.

[0088] Finally, in the concrete lining stage: according to the tunnel lining structure diagram, the area between the tunnel face and the side wall is backfilled with concrete to connect them into a whole to further ensure the stability of the slope.

[0089] The present invention can safely and smoothly complete the construction of a large tunnel within the cross-section range of an unfavorable surrounding rock structure, and the collapse of the slope is controlled; it has been successfully applied in a diversion tunnel, and can be used as a reference in the support of the tunnel face of various engineering cavern structures and the construction of tunnel entry locks.

[0090] In the present invention, when the tunnel face slope reveals an unfavorable surrounding rock structure, the upper slope of the tunnel entrance is reinforced and supported, and anchor piles are used to perform advance support in the tunnel face and spandrel range, so that the slope collapse is controlled; the reinforced support anchor piles are extended to both sides and exceed the excavation section to form a larger range of reinforcement, further ensuring the construction safety of the project; the anchor bundles near the broken zone are arranged perpendicular to the broken zone to ensure the effect; multi-layer anchor piles are used under the tunnel face and spandrel for advance support to ensure the stability of the upper rock layer, which has good reinforcement Effect: The anchor piles use 3 to 5 anchor bars arranged in a plum blossom shape, combined with cement grouting, and the grouting volume is tracked and recorded to ensure the grouting quality and pile forming effect; the excavation surface of the tunnel face is hung with steel mesh and sprayed with concrete to form a closure; then the tunnel entrance is divided into upper and lower layers, and the upper layer is constructed according to the construction process of "pilot tunnel first and then expansion", which ensures safe penetration under the premise of improving the overall stability of the slope and tunnel body; adopt "short advance, weak blasting, and strong support" measures to reduce safety hazards; the tunnel face and the side wall are connected as a whole with concrete to further ensure the stability of the slope.

[0091] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

[0092] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0093] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A method for entering a hole in an unfavorable surrounding rock structure, characterized in that: The following steps are involved: S0, preliminary processing; S1. Strengthen the support of the upper slope of the tunnel entrance; S2, advance support within the opening and spandrel area; S3, tunnel excavation; S4. Concrete lining.

2. The method for entering a hole in an unfavorable surrounding rock structure according to claim 1 is characterized in that: In step S0, if collapse occurs and some of the locking anchors are pulled out, then: Demolition of collapsed rock mass; After leveling the bottom, add locking anchor rods to the collapsed part.

3. The method for entering a hole in an unfavorable surrounding rock structure according to claim 1 is characterized in that: In step S1, four rows of anchor bars are arranged on the upper slope of the tunnel entrance for reinforced support; The arrangement length of each row of reinforcing support anchor bars extends to both sides of the tunnel axis: 3 to 6 meters beyond the excavation section.

4. The method for entering a hole in an unfavorable surrounding rock structure according to claim 1 is characterized in that: In step S1, the spacing of the reinforcement anchor tendons is 2.0 m, and they are arranged in a plum blossom shape; The anchor bar bundles near the crushing zone are arranged perpendicular to the crushing zone.

5. The method for entering a hole in an unfavorable surrounding rock structure according to claim 3 is characterized in that: In step S1, the interlayer spacing between rows of reinforcing support anchor tendons gradually increases as the distance from the opening increases.

6. The method for entering a hole in an unfavorable surrounding rock structure according to claim 1 is characterized in that: In step S2: Arrange two rows of advanced support anchor bars directly above the tunnel face; Two rows of advance support anchor bars are arranged within 3-5m between the cave roof and the spandrel; Among them, the layout position of the advance support anchor reinforcement bundle corresponds to the excavation contour.

7. The method for entering a hole in an unfavorable surrounding rock structure according to claim 6 is characterized in that: The specifications of the advanced support anchor bar bundle are: 3 to 5 steel bars welded together, the diameter of a single steel bar is 20 to 32 mm, and the length is 10 to 15 meters.

8. The method for entering a hole in an unfavorable surrounding rock structure according to claim 1 is characterized in that: In steps S1 and S2: Cement slurry is used to grout the anchor beam holes to form anchor piles; Due to the presence of crack combinations and broken zones on the slope, the grouting volume of a single hole is generally large; to ensure the quality of grouting, an automatic flow recorder is installed during the grouting process to track and record the grouting volume.

9. The method for entering a hole in an unfavorable surrounding rock structure according to claim 1, characterized in that: In step S3: after the tunnel face reinforcement construction is completed and has a certain strength, the remaining tunnel sections are excavated; In order to ensure safety during the excavation process and reduce potential safety hazards, the tunnel excavation is carried out according to the construction process of "first excavating the pilot tunnel and then expanding it"; initial support is carried out crosswise during the excavation of the pilot tunnel; the tunnel excavation adopts the excavation technology of upper and lower layers and upper left and right partitions.

10. The method for entering a hole in an unfavorable surrounding rock structure according to claim 1, characterized in that: In step S3: During the concrete lining stage, based on the tunnel lining structure diagram, the area between the tunnel face and the side wall is backfilled with concrete to connect them into a whole, so as to further ensure the stability of the slope.

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