Improved method for excavating a large cross-section mountain ridge tunnel

Abstract

This invention provides an improved construction method for excavating ultra-large cross-section mountain tunnels, comprising the following steps: S1, conducting advanced geological prediction for the tunnel; S2, excavating the tunnel using an improved construction method based on the single-sidewall pilot tunnel method or the double-sidewall pilot tunnel method; S3, erecting a steel frame; S4, dismantling the central partition wall and temporary invert arch; S5, constructing secondary lining; wherein, when using the double-sidewall pilot tunnel improved construction method, the first step is to excavate the upper left pilot tunnel; the second step is to excavate the middle left pilot tunnel; the third step is to excavate the upper right pilot tunnel; the fourth step is to excavate the middle right pilot tunnel; the fifth step is to excavate the lower left pilot tunnel; the sixth step is to excavate the lower right pilot tunnel; the seventh step is to excavate the upper central pilot tunnel; the eighth step is to excavate the middle central pilot tunnel; and the ninth step is to excavate the lower central pilot tunnel; when using the single-sidewall pilot tunnel improved construction method, the upper left pilot tunnel, the middle left pilot tunnel, the upper right pilot tunnel, the middle right pilot tunnel, the lower left pilot tunnel, and the lower right pilot tunnel are excavated sequentially. It effectively reduces the distribution of plastic failure areas, decreases the degree of plastic deformation, and further ensures construction safety.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology, and in particular to an improved construction method for excavating ultra-large cross-section mountain tunnels. Background Technology

[0002] my country is a mountainous and hilly country, and the convenience of transportation directly affects the construction and development of regional economies. Therefore, the construction of transportation infrastructure has become a key factor influencing national economic development. Highway tunnels, as an important part of transportation construction, play an increasingly important role in my country's transportation construction and economic development due to their excellent throughput and safety, as well as their advantages in shortening routes, traversing complex geological formations, and reducing vegetation damage caused by conventional roadbed excavation. Since the beginning of the 21st century, in order to meet the needs of rapid economic development and improve transportation capacity, the scale of highway tunnel construction across the country has been continuously expanding. Among these developments, highway tunnels have gradually evolved from the initial two-lane to three-lane and four-lane tunnels. However, theoretical research on ultra-large cross-section highway tunnels is still relatively scarce, and the design and construction of ultra-large cross-section bifurcated tunnels are mostly still in the exploratory and experimental stage.

[0003] In current construction of large-span bifurcated tunnels, for cases with poor surrounding rock conditions, the traditional improved double-sided wall pilot tunnel method or the improved single-sided wall pilot tunnel method is generally used for excavation. The traditional double-sided wall pilot tunnel method uses two central diaphragms to divide the entire tunnel cross-section into three smaller sections (left, middle, and right). The left and right pilot tunnels are constructed first, followed by the middle section. After the initial support arch is formed, the temporary supports of the two pilot tunnels are removed, forming the full cross-section. The traditional single-sided wall pilot tunnel method uses one central diaphragm to divide the entire tunnel cross-section into two smaller sections, further dividing the cross-section into upper and lower bench sections. After the initial support arch is formed, the temporary supports of the two pilot tunnels are removed, forming the full cross-section.

[0004] These two construction methods are highly instructive for the construction of shallow-buried tunnels in weak surrounding rock, and are currently the most common development methods implemented in shallow-buried or weak surrounding rock sections. However, with the increasing number of large-section and ultra-large-section tunnel constructions, these methods have certain shortcomings in controlling the plastic failure zone, posing certain safety hazards. Summary of the Invention

[0005] Based on this, the purpose of this invention is to provide an improved construction method for excavating ultra-large cross-section mountain tunnels, which effectively reduces the distribution of plastic failure areas, decreases the degree of plastic deformation, and further ensures construction safety. To achieve the above objective, the technical solution of this invention is as follows:

[0006] An improved construction method for excavating ultra-large cross-section mountain tunnels includes the following steps:

[0007] S1, perform advanced geological prediction for the tunnel; if the advanced geological prediction for the tunnel meets the preset requirements, proceed to step S2; if the advanced geological prediction for the tunnel does not meet the preset requirements, perform advanced support until it meets the preset requirements.

[0008] S2, the tunnel excavation is carried out using either the improved construction method of single-side wall pilot tunnel or the improved construction method of double-side wall pilot tunnel.

[0009] S3, Erect the steel frame;

[0010] S4, dismantle the central partition wall and temporary inverted arch;

[0011] S5, secondary lining construction;

[0012] In step S2, when using the improved double-sidewall pilot tunnel method for excavation, the tunnel cross-section is divided into three steps: an upper step, a middle step, and a lower step. The upper step contains the upper left pilot tunnel, the upper middle pilot tunnel, and the upper right pilot tunnel in sequence; the middle step contains the middle left pilot tunnel, the middle middle pilot tunnel, and the middle right pilot tunnel in sequence; and the lower step contains the lower left pilot tunnel, the lower middle pilot tunnel, and the lower right pilot tunnel in sequence. The specific excavation sequence is as follows:

[0013] S21, excavate the upper left pilot tunnel, after the upper left pilot tunnel is excavated, anchor spray support is applied to it, then the partition wall is constructed, and a temporary invert arch is constructed at the bottom of the upper left pilot tunnel.

[0014] S22, excavate the left central pilot tunnel, after the left central pilot tunnel is excavated, anchor spray support is applied to it, then the partition wall is constructed, and a temporary invert arch is constructed at the bottom of the left central pilot tunnel;

[0015] S23, excavate the upper right pilot tunnel, after the upper right pilot tunnel is excavated, anchor spray support is applied to it, and then a temporary invert arch is constructed at the bottom of the upper right pilot tunnel;

[0016] S24, excavate the right central pilot tunnel, after the right central pilot tunnel is excavated, anchor spray support is applied to it, and then a temporary invert arch is constructed at the bottom of the right central pilot tunnel.

[0017] S25, excavate the lower left pilot tunnel, after the lower left pilot tunnel is excavated, anchor spray support is applied to it, and then a temporary invert arch is constructed at the bottom of the lower left pilot tunnel;

[0018] S26, excavate the lower right pilot tunnel, after the lower right pilot tunnel is excavated, anchor spray support is applied to it, then the partition wall is constructed, and a temporary invert arch is constructed at the bottom of the lower right pilot tunnel.

[0019] S27, excavate the middle upper pilot tunnel, after the middle upper pilot tunnel is excavated, anchor spray support is applied to it, and then a temporary invert arch is constructed at the bottom of the middle upper pilot tunnel;

[0020] S28, excavate the central pilot tunnel, and after the central pilot tunnel is excavated, construct a temporary invert arch at its bottom;

[0021] S29, excavate the middle lower pilot tunnel, and after the middle lower pilot tunnel is excavated, construct a temporary inverted arch at its bottom;

[0022] When using the improved single-sidewall pilot tunnel method for excavation, the tunnel cross-section is divided into three steps: the upper step, the middle step, and the lower step. The upper step contains the upper left pilot tunnel and the upper right pilot tunnel in sequence; the middle step contains the middle left pilot tunnel and the middle right pilot tunnel in sequence; and the lower step contains the lower left pilot tunnel and the lower right pilot tunnel in sequence. The specific excavation sequence is as follows:

[0023] S21', excavate the upper left pilot tunnel, after the upper left pilot tunnel is excavated, anchor spray support is applied to it, then the partition wall is constructed, and a temporary invert arch is constructed at the bottom of the upper left pilot tunnel;

[0024] S22', excavate the left central pilot tunnel, after the left central pilot tunnel is excavated, anchor spray support is applied to it, then the partition wall is constructed, and a temporary invert arch is constructed at the bottom of the left central pilot tunnel;

[0025] S23', excavate the upper right pilot tunnel, after the upper right pilot tunnel is excavated, anchor spray support is applied to it, and a temporary invert arch is constructed at the bottom of the upper right pilot tunnel;

[0026] S24', excavate the right central pilot tunnel, after the right central pilot tunnel is excavated, anchor spray support is applied to it, and then a temporary invert arch is constructed at the bottom of the right central pilot tunnel;

[0027] S25' Excavate the lower left pilot tunnel. After the lower left pilot tunnel is excavated, anchor spray support is applied to it. Then, the partition wall is constructed, and a temporary invert arch is built at the bottom of the lower left pilot tunnel.

[0028] S26', excavate the lower right pilot tunnel. After the lower right pilot tunnel is excavated, anchor spray support is applied to it. Then, a temporary invert arch is constructed at the bottom of the lower right pilot tunnel.

[0029] Furthermore, before excavation of the tunnel face, advanced geological forecasting needs to be carried out in accordance with the specifications. The forecasting methods are ground-penetrating radar, advanced drilling, or TSP.

[0030] Furthermore, the advanced support is reinforced by grouting using small guide pipes.

[0031] Furthermore, before the central partition wall is removed, the initial support must be closed into a ring and meet the design strength requirements.

[0032] Furthermore, the central partition wall can only be dismantled when the deformation measured by monitoring is stable. The distance between the dismantling point and the nearest central excavation face must not be less than 30m. During the dismantling process, the deformation of the initial support structure needs to be monitored more intensively.

[0033] Furthermore, during the construction process, regular deformation monitoring is conducted on the tunnel support structure, the ground, and nearby buildings. If abnormal deformation occurs, an early warning is issued to the construction personnel.

[0034] The beneficial effects of this invention are:

[0035] The improved construction method for excavating ultra-large cross-section mountain tunnels of the present invention is based on the improved construction method of double-side wall pilot tunnel and single-side wall pilot tunnel. The method is improved to reduce the distribution of plastic failure area and reduce the degree of plastic deformation, making it more suitable for the excavation of ultra-large cross-section tunnels and further ensuring construction safety. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the excavation sequence of an embodiment of the improved construction method for excavating ultra-large cross-section mountain tunnels according to the present invention.

[0037] Figure 2 This is a schematic diagram of the excavation sequence of another embodiment of the improved construction method for excavating ultra-large cross-section mountain tunnels according to the present invention.

[0038] Figure 3 This is a schematic diagram of the plastic yielding failure zone of the surrounding rock when using the improved construction method of traditional double-sidewall pilot tunnel;

[0039] Figure 4 This is a schematic diagram of the plastic yielding failure zone of the surrounding rock when using the improved double-sidewall pilot tunnel method of this invention.

[0040] Figure 5 This is a schematic diagram of the plastic yielding failure zone of the surrounding rock when using the improved construction method of traditional single-sidewall pilot tunnel;

[0041] Figure 6 This is a schematic diagram of the plastic yielding failure zone of the surrounding rock when using the improved single-sidewall pilot tunnel method of this invention.

[0042] in:

[0043] 1. Upper left pilot tunnel; 2. Middle left pilot tunnel; 3. Upper right pilot tunnel; 4. Middle right pilot tunnel; 5. Lower left pilot tunnel;

[0044] 6. Lower right pilot tunnel; 7. Upper central pilot tunnel; 8. Middle central pilot tunnel; 9. Lower central pilot tunnel. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of this invention clearer, the improved construction method for excavating ultra-large cross-section mountain tunnels according to this invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the following embodiments and features can be combined with each other. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of this invention.

[0046] Reference Figure 1 and Figure 2 An improved construction method for excavating ultra-large cross-section mountain tunnels according to an embodiment of the present invention includes the following steps:

[0047] S1, perform advanced geological prediction for the tunnel; if the advanced geological prediction for the tunnel meets the preset requirements, proceed to step S2; if the advanced geological prediction for the tunnel does not meet the preset requirements, perform advanced support until it meets the preset requirements.

[0048] S2, the tunnel excavation is carried out using either the improved construction method of single-side wall pilot tunnel or the improved construction method of double-side wall pilot tunnel.

[0049] S3, Erect the steel frame;

[0050] S4, dismantle the central partition wall and temporary inverted arch;

[0051] S5, secondary lining construction;

[0052] In step S2, when the double-side-wall pilot tunnel improved construction method is used for excavation, such as Figure 1 As shown, the tunnel cross-section is divided into three steps: the upper step, the middle step, and the lower step. The upper step contains the left upper pilot tunnel 1, the middle upper pilot tunnel 7, and the right upper pilot tunnel 3; the middle step contains the left middle pilot tunnel 2, the middle middle pilot tunnel 8, and the right middle pilot tunnel 4; and the lower step contains the left lower pilot tunnel 5, the middle lower pilot tunnel 9, and the right lower pilot tunnel 6. The specific excavation sequence is as follows:

[0053] S21, excavate the upper left pilot tunnel 1, after the upper left pilot tunnel 1 is excavated, anchor spray support is applied to it, then the partition wall is constructed, and a temporary invert arch is constructed at the bottom of the upper left pilot tunnel 1.

[0054] S22, excavate the left central pilot tunnel 2, after the excavation of the left central pilot tunnel 2 is completed, anchor spray support is applied to it, then the partition wall is constructed, and a temporary invert arch is constructed at the bottom of the left central pilot tunnel 2;

[0055] S23, excavate the upper right pilot tunnel 3, after the upper right pilot tunnel 3 is excavated, anchor spray support is applied to it, and then a temporary invert arch is constructed at the bottom of the upper right pilot tunnel 3.

[0056] S24, excavate the right central pilot tunnel 4, after the excavation of the right central pilot tunnel 4 is completed, anchor spray support is applied to it, and then a temporary invert arch is constructed at the bottom of the right central pilot tunnel 4.

[0057] S25, excavate the lower left pilot tunnel 5, after the lower left pilot tunnel 5 is excavated, anchor spray support is applied to it, and then a temporary invert arch is constructed at the bottom of the lower left pilot tunnel 5.

[0058] S26, excavate the lower right pilot tunnel 6, after the excavation of the lower right pilot tunnel 6 is completed, anchor spray support is applied to it, then the partition wall is constructed, and a temporary invert arch is constructed at the bottom of the lower right pilot tunnel 6.

[0059] S27, excavate the middle upper guide tunnel 7, after the middle upper guide tunnel 7 is excavated, anchor spray support is applied to it, and then a temporary invert arch is constructed at the bottom of the middle upper guide tunnel 7.

[0060] S28, excavate the central pilot tunnel 8, and after the central pilot tunnel 8 is excavated, construct a temporary inverted arch at its bottom;

[0061] S29, excavate the middle lower guide tunnel 9, and after the middle lower guide tunnel 9 is excavated, construct a temporary inverted arch at its bottom.

[0062] In this embodiment, the improved double-sided wall pilot tunnel excavation method is used for cavern development, and the excavation sequence is as follows: Figure 1 As shown, Figure 1 The diagram shows the step distribution and construction sequence. Specifically: Step 1: Excavate the upper left pilot tunnel 1; Step 2: Excavate the middle left pilot tunnel 2; Step 3: Excavate the upper right pilot tunnel 3; Step 4: Excavate the middle right pilot tunnel 4; Step 5: Excavate the lower left pilot tunnel 5; Step 6: Excavate the lower right pilot tunnel 6; Step 7: Excavate the upper central pilot tunnel 7; Step 8: Excavate the middle central pilot tunnel 8; Step 9: Excavate the lower central pilot tunnel 9. Anchor spraying support should be carried out promptly after each section is excavated.

[0063] When using the improved single-sidewall pilot tunnel method for excavation, such as Figure 2 As shown, the tunnel cross-section is divided into three steps: the upper step, the middle step, and the lower step. The upper step contains the upper left pilot tunnel 1 and the upper right pilot tunnel 3; the middle step contains the middle left pilot tunnel 2 and the middle right pilot tunnel 4; and the lower step contains the lower left pilot tunnel 5 and the lower right pilot tunnel 6. The specific excavation sequence is as follows:

[0064] S21', excavate the upper left pilot tunnel 1, after the upper left pilot tunnel 1 is excavated, anchor spray support is applied to it, then the partition wall is constructed, and a temporary invert arch is constructed at the bottom of the upper left pilot tunnel 1.

[0065] S22', excavate the left central pilot tunnel 2, after the excavation of the left central pilot tunnel 2 is completed, anchor spray support is applied to it, then the partition wall is constructed, and a temporary invert arch is constructed at the bottom of the left central pilot tunnel 2;

[0066] S23', excavate the upper right pilot tunnel 3, after the upper right pilot tunnel 3 is excavated, anchor spray support is applied to it, and a temporary invert arch is constructed at the bottom of the upper right pilot tunnel 3;

[0067] S24', excavate the right central pilot tunnel 4, after the right central pilot tunnel 4 is excavated, anchor spray support is applied to it, and then a temporary invert arch is constructed at the bottom of the right central pilot tunnel 4.

[0068] S25' Excavate the lower left pilot tunnel 5. After the lower left pilot tunnel 5 is excavated, anchor spray support is applied to it. Then, the partition wall is constructed, and a temporary invert arch is constructed at the bottom of the lower left pilot tunnel 5.

[0069] S26', excavate the lower right pilot tunnel 6. After the excavation of the lower right pilot tunnel 6 is completed, anchor spray support is applied to it. Then, a temporary invert arch is constructed at the bottom of the lower right pilot tunnel 6.

[0070] In this embodiment, the improved single-sidewall pilot tunnel excavation method is used for cavern development, and the excavation sequence is as follows: Figure 2 As shown, Figure 2 The diagram shows the step distribution and construction sequence. Specifically: Step 1: Excavate the upper left pilot tunnel 1; Step 2: Excavate the middle left pilot tunnel 2; Step 3: Excavate the upper right pilot tunnel 3; Step 4: Excavate the middle right pilot tunnel 4; Step 5: Excavate the lower left pilot tunnel 5; Step 6: Excavate the lower right pilot tunnel 6. Anchor spraying support should be carried out promptly after each section is excavated.

[0071] For both of the above implementation methods, advanced geological prediction needs to be carried out before excavation at the working face, in accordance with the specifications. The prediction method should be at least one of the following: ground-penetrating radar, advanced drilling, and TSP. Advanced geological prediction is a supplementary exploration following the geological survey of the surrounding rock ahead.

[0072] TSP stands for Tunnel Seismic Prediction Ahead, which is an elastic wave reflection method.

[0073] Ideally, pre-support should be reinforced with grouting using small guide pipes.

[0074] During the excavation process, anchor spraying support should be carried out promptly after each section is excavated. Before the central diaphragm is removed, the initial support must be closed into a ring and meet the design strength requirements.

[0075] The central diaphragm wall is preferably arc-shaped. When using the improved double-sidewall pilot tunnel method for excavation, the three central diaphragm walls on the left are connected sequentially to form an arc-shaped structure with openings facing the same direction. Similarly, the three central diaphragm walls on the right are also connected sequentially to form an arc-shaped structure with openings facing the same direction, but the opening directions of the three central diaphragm walls on the left are opposite to those of the three central diaphragm walls on the right. When using the improved single-sidewall pilot tunnel method for excavation, the three central diaphragm walls are connected sequentially to form an arc-shaped structure with openings facing the same direction. Alternatively, one central diaphragm wall can have an opening direction opposite to the other two. For example, the opening direction of the middle central diaphragm wall can be opposite to the other two, which can improve support strength and save materials. The central diaphragm walls can be connected sequentially according to actual conditions. The central diaphragm walls can also be connected to a temporary invert arch, which can further improve the stability of the support.

[0076] The central diaphragm can only be dismantled when the deformation measured by monitoring is stable. The distance between the dismantling work point and the nearest central excavation face must not be less than 30m. During the dismantling process, it is necessary to intensify the monitoring of the deformation of the initial support structure. In other words, the frequency of detecting the deformation of the initial support structure needs to be increased.

[0077] Preferably, during the construction process, the tunnel support structure, ground, and nearby buildings are regularly monitored for deformation. If abnormal deformation occurs, an early warning is issued to the construction personnel.

[0078] Other technical requirements are mainly as follows:

[0079] (1) Before excavation of the working face, it is necessary to carry out advanced geological forecasting in accordance with the specifications. The forecasting methods generally include ground-penetrating radar, advanced drilling, TSP, etc.

[0080] (2) For sections with poor surrounding rock and design requirements, it is necessary to carry out advance support on the rock mass in front of the tunnel face before excavation. Small pipes can generally be used.

[0081] (3) The spacing, depth and angle of the drill holes must be strictly controlled during blasting operations. The allowable deviation of the spacing and depth of the cut holes and the hole openings is 5cm, and the allowable deviation of the spacing of the peripheral holes is 5cm.

[0082] (4) Before the removal of the central partition wall, the initial support must be closed into a ring and meet the design strength requirements; deformation stability must be monitored and measured; and the distance between the removal work point and the nearest central excavation face must not be less than 30m. During the removal process, the deformation of the initial support structure needs to be monitored more intensively.

[0083] (5) During the construction process, it is necessary to conduct regular deformation monitoring of the development support structure, ground and buildings near the ground surface in accordance with the specifications, and issue early warnings for abnormal deformation.

[0084] The Midas GTS numerical simulation software was used to calculate and compare the two construction methods, and the results showed that the plastic yielding failure zone of the surrounding rock was as follows: Figure 3 and Figure 4 As shown. Among them, Figure 3 This is a schematic diagram of the plastic yielding failure zone of the surrounding rock when using the improved construction method of traditional double-sidewall pilot tunnel; Figure 4 This is a schematic diagram of the plastic yielding failure zone of the surrounding rock when using the improved double-sidewall pilot tunnel method of this invention.

[0085] Depend on Figure 3 and Figure 4The comparison shows that the darker areas are normal areas, while other areas have undergone plastic deformation, with lighter colors indicating a higher degree of deformation. It is evident that the improved method significantly reduces both the area and degree of plastic deformation compared to the traditional method, resulting in a more dispersed distribution of the plastic deformation areas.

[0086] in, Figure 5 This is a schematic diagram of the plastic yielding failure zone of the surrounding rock when using the improved construction method of traditional single-sidewall pilot tunnel; Figure 6 This is a schematic diagram of the plastic yielding failure zone of the surrounding rock when using the improved single-sidewall pilot tunnel method of this invention.

[0087] Depend on Figure 5 and Figure 6 The comparison shows that the darker areas are normal areas, while other areas have undergone plastic deformation, with lighter colors indicating a higher degree of deformation. It is evident that the improved method significantly reduces both the area and degree of plastic deformation compared to the traditional method, resulting in a more dispersed distribution of the plastic deformation areas.

[0088] The improved construction method has a significant effect on reducing the distribution of plastic deformation and damage areas in the tunnel face and surrounding soil and rock, and on reducing the degree of plastic deformation. The improved construction method can greatly improve the safety and stability of the tunnel face construction for large-section tunnels, and further ensure construction safety.

[0089] The improved construction methods for excavating ultra-large cross-section mountain tunnels in the above embodiments further decompose the composition of the tunnel chambers, resulting in regular and uniformly distributed chamber shapes. This effectively controls settlement and the distribution of the tunnel's plastic zone, improving construction safety. It is particularly suitable for the excavation of large and ultra-large cross-section tunnels, whether for highways or mountainous areas.

[0090] The above-described embodiments are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and all equivalent implementations or changes made without departing from the spirit of the present invention should be included within the protection scope of the present invention.

Claims

1. An improved construction method for excavating ultra-large cross-section mountain tunnels, characterized in that, Includes the following steps: S1, conduct advanced geological prediction for tunnels; If the tunnel's advanced geological prediction meets the preset requirements, proceed to step S2; if the tunnel's advanced geological prediction does not meet the preset requirements, carry out advanced support until it meets the preset requirements. S2, the tunnel excavation is carried out using either the improved construction method of single-side wall pilot tunnel or the improved construction method of double-side wall pilot tunnel. S3, Erect the steel frame; S4, dismantle the central partition wall and temporary inverted arch; S5, secondary lining construction; In step S2, when the double-side-wall pilot tunnel improved construction method is used for excavation, the tunnel cross-section is divided into three steps: the upper step, the middle step, and the lower step. The upper step is successively distributed with the upper left pilot tunnel (1), the upper middle pilot tunnel (7), and the upper right pilot tunnel (3); the middle step is successively distributed with the middle left pilot tunnel (2), the middle middle pilot tunnel (8), and the middle right pilot tunnel (4); the lower step is successively distributed with the lower left pilot tunnel (5), the lower middle pilot tunnel (9), and the lower right pilot tunnel (6). The specific excavation sequence is as follows: S21, excavate the upper left pilot tunnel (1), after the upper left pilot tunnel (1) is excavated, anchor spray support is applied to it, then the partition wall is constructed, and a temporary inverted arch is constructed at the bottom of the upper left pilot tunnel (1). S22, excavate the left middle guide tunnel (2), after the left middle guide tunnel (2) is excavated, anchor spray support is applied to it, then the middle partition is constructed, and a temporary inverted arch is constructed at the bottom of the left middle guide tunnel (2); S23, excavate the upper right pilot tunnel (3), after the upper right pilot tunnel (3) is excavated, anchor spray support is applied to it, and then a temporary invert arch is constructed at the bottom of the upper right pilot tunnel (3); S24, excavate the right middle guide tunnel (4), after the right middle guide tunnel (4) is excavated, anchor spray support is applied to it, and then a temporary invert arch is constructed at the bottom of the right middle guide tunnel (4); S25, excavate the lower left pilot tunnel (5), after the lower left pilot tunnel (5) is excavated, anchor spray support is applied to it, and then a temporary inverted arch is constructed at the bottom of the lower left pilot tunnel (5); S26, excavate the lower right pilot tunnel (6), after the lower right pilot tunnel (6) is excavated, anchor spray support is applied to it, then the partition wall is constructed, and a temporary invert arch is constructed at the bottom of the lower right pilot tunnel (6). S27, excavate the middle upper guide tunnel (7), after the middle upper guide tunnel (7) is excavated, anchor spray support is applied to it, and then a temporary invert arch is constructed at the bottom of the middle upper guide tunnel (7); S28, excavate the central pilot tunnel (8), and after the central pilot tunnel (8) is excavated, construct a temporary inverted arch at its bottom; S29, excavate the middle lower guide tunnel (9), and after the middle lower guide tunnel (9) is excavated, construct a temporary inverted arch at its bottom; When using the improved single-sidewall pilot tunnel method for excavation, the tunnel cross-section is divided into three steps: the upper step, the middle step, and the lower step. The upper step has the upper left pilot tunnel (1) and the upper right pilot tunnel (3) distributed sequentially; the middle step has the middle left pilot tunnel (2) and the middle right pilot tunnel (4) distributed sequentially; and the lower step has the lower left pilot tunnel (5) and the lower right pilot tunnel (6) distributed sequentially. The specific excavation sequence is as follows: S21', excavate the upper left pilot tunnel (1), after the upper left pilot tunnel (1) is excavated, anchor spray support is applied to it, then the partition wall is constructed, and a temporary inverted arch is constructed at the bottom of the upper left pilot tunnel (1); S22', excavate the left middle guide tunnel (2), after the left middle guide tunnel (2) is excavated, anchor spray support is applied to it, then the middle partition wall is constructed, and a temporary inverted arch is constructed at the bottom of the left middle guide tunnel (2); S23', excavate the upper right pilot tunnel (3), after the upper right pilot tunnel (3) is excavated, anchor spray support is applied to it, and a temporary inverted arch is constructed at the bottom of the upper right pilot tunnel (3); S24', excavate the right middle guide tunnel (4), after the right middle guide tunnel (4) is excavated, anchor spray support is applied to it, and then a temporary invert arch is constructed at the bottom of the right middle guide tunnel (4); S25' Excavate the lower left pilot tunnel (5). After the lower left pilot tunnel (5) is excavated, it is anchored and sprayed for support. Then, the partition wall is constructed, and a temporary inverted arch is constructed at the bottom of the lower left pilot tunnel (5). S26', excavate the lower right pilot tunnel (6), after the lower right pilot tunnel (6) is excavated, anchor spray support is applied to it, and then a temporary invert arch is constructed at the bottom of the lower right pilot tunnel (6). When using the double-sided wall pilot tunnel improved construction method for excavation, the central diaphragm is arc-shaped. Among the three central diaphragms on the left, the opening direction of the middle central diaphragm is opposite to that of the other two. Among the three central diaphragms on the right, the opening direction of the middle central diaphragm is opposite to that of the other two. The opening direction of the three central diaphragms on the left is opposite to that of the three central diaphragms on the right. When using the improved single-sidewall pilot tunnel method for excavation, the central diaphragm is arc-shaped, and among the three central diaphragms, the opening direction of the middle diaphragm is opposite to that of the other two.

2. The improved construction method for excavating ultra-large cross-section mountain tunnels according to claim 1, characterized in that: Before excavation of the tunnel face, advanced geological forecasting needs to be carried out in accordance with the specifications. The forecasting methods are ground-penetrating radar, advanced drilling, or TSP.

3. The improved construction method for excavating ultra-large cross-section mountain tunnels according to claim 1, characterized in that: The aforementioned advanced support is achieved by grouting reinforcement using small guide pipes.

4. The improved construction method for excavating ultra-large cross-section mountain tunnels according to claim 1, characterized in that: Before the central partition wall is removed, the initial support must be closed into a ring and meet the design strength requirements.

5. The improved construction method for excavating ultra-large cross-section mountain tunnels according to claim 4, characterized in that: The central partition wall can only be dismantled when the deformation measured by monitoring is stable. The distance between the dismantling point and the nearest central excavation face must not be less than 30m. During the dismantling process, the deformation of the initial support structure needs to be monitored more intensively.

6. The improved construction method for excavating ultra-large cross-section mountain tunnels according to any one of claims 1-5, characterized in that: During construction, regular deformation monitoring is conducted on the tunnel support structure, the ground, and nearby buildings. If abnormal deformation occurs, an early warning is issued to the construction personnel.

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