A construction method for soft surrounding rock tunnel excavation support

Abstract

The application discloses a construction method for tunnel excavation and support in soft surrounding rock, which comprises the following steps: excavating the upper part of the upper portion to form an arch portion, forming a protective soil body at the middle position below the arch portion, and arranging an upper support along the wall surface of the arch portion; removing the protective soil body to form an upper pilot tunnel together with the arch portion, excavating the middle portion to form a middle pilot tunnel leading to the upper pilot tunnel, and arranging a middle support along the wall surface of the middle pilot tunnel; excavating the lower portion to form a tunnel bottom pilot tunnel leading to the middle pilot tunnel, arranging an inverted arch support in the tunnel bottom pilot tunnel, thereby completing the excavation and support of a tunnel unit; returning to the step of excavating the upper part of the upper portion to form an arch portion, forming a protective soil body at the middle position below the arch portion, and arranging an upper support along the wall surface of the arch portion until the excavation and support of each tunnel unit are completed, thereby completing the excavation and support of the whole tunnel. The construction method can effectively prevent the tunnel support from invading the secondary lining range.

Description

Technical Field

[0001] This invention relates to the field of tunnel construction technology, specifically to a construction method for tunnel excavation and support in weak surrounding rock. Background Technology

[0002] With the rapid development of tunnel engineering in my country, more and more tunnels are being built in complex areas. In particular, during the construction of tunnels in weak and fractured surrounding rock, factors such as poor geological conditions, non-standard construction operations, and unreasonable construction technology or organization can easily cause the initial support arch to sink, the sidewalls to converge, and the arch frame to deform and intrude into the secondary lining range, seriously threatening the safety of tunnel construction and affecting the subsequent construction of the secondary lining. In order to ensure the thickness of the secondary lining, it is necessary to remove and replace the arch frame in the encroaching section, thereby increasing the construction difficulty and affecting the project progress. Summary of the Invention

[0003] The main objective of this invention is to propose a construction method for the excavation and support of tunnels in weak surrounding rock, which aims to solve the problem that the initial support is prone to encroaching on the secondary lining area during the construction of tunnels in weak surrounding rock.

[0004] To achieve the above objectives, this invention proposes a construction method for excavation and support of tunnels in weak surrounding rock. The tunnel has multiple tunnel units connected sequentially along its extension direction, and each tunnel unit is sequentially divided into an upper part, a middle part, and a lower part in the vertical direction. The construction method for excavation and support of tunnels in weak surrounding rock includes the following steps:

[0005] Excavation is carried out above the upper part to form an arch, and a protective soil body is formed at the middle position below the arch. Upper support is provided along the wall of the arch.

[0006] Remove the protective soil to form an upper guide tunnel together with the arch, excavate the middle section to form a middle guide tunnel that connects to the upper guide tunnel, and set a middle support along the wall of the middle guide tunnel.

[0007] The lower part is excavated to form a tunnel bottom pilot tunnel that connects to the middle pilot tunnel. An inverted arch support is installed in the tunnel bottom pilot tunnel to complete the excavation and support of one tunnel unit.

[0008] Return to the steps of "excavating above the upper part to form an arch, forming a protective soil at the middle position below the arch, and setting upper support along the wall of the arch" until each tunnel unit has been excavated and supported, thereby completing the excavation and support of the entire tunnel.

[0009] Optionally, the step of "excavating above the upper part to form an arch, forming a protective soil mass at the middle position below the arch, and setting up an upper support along the wall of the arch" includes:

[0010] Excavation is carried out in the upper part according to the preset arch outline to form the arch and the protective soil.

[0011] Concrete is sprayed onto the walls of the arch to form an upper surrounding rock protective layer;

[0012] Based on the shape of the arch, an upper anchor mesh protection structure and an upper support steel frame are sequentially installed on the outside of the upper surrounding rock protection layer to form an arch support structure.

[0013] Concrete is sprayed on the outside of the arch support structure to connect the upper anchor mesh protection structure and the upper support steel frame, thereby forming the upper support.

[0014] Optionally, in the direction away from the tunnel, the locking foot guide pipe in the upper support steel frame is inclined from top to bottom, and the free end of the locking foot guide pipe in the upper support steel frame can extend into the upper surrounding rock.

[0015] Optionally, the length of the protective soil along the tunnel extension direction is L, wherein 0.5m≤L≤1m.

[0016] Optionally, in the step of "excavating the middle section to form a middle guide tunnel that connects to the upper guide tunnel":

[0017] Excavation is carried out on the left side of the middle section until the excavation length meets the first preset value, thus obtaining the first pre-excavated guide tunnel;

[0018] Continue excavating based on the first pre-excavated pilot tunnel until the first preset advance value is met, and obtain the pilot tunnel on the left wall.

[0019] Excavation is carried out on the right side of the middle section until the first preset advance value is met to form the right wall guide tunnel, wherein the left wall guide tunnel and the right wall guide tunnel are connected.

[0020] Return to the step of "Continue excavating based on the first pre-excavated pilot tunnel until the excavation length meets the first preset advance value to obtain the left wall pilot tunnel" until the excavation of the central pilot tunnel of a single tunnel unit is completed.

[0021] Optionally, the first preset value is A1, and the first preset advance value is A2, wherein 3m≤A1-A2≤5m.

[0022] Optionally, in the step of "setting a central support along the wall of the central guide tunnel":

[0023] Concrete was sprayed onto the walls of the central pilot tunnel to form a central surrounding rock protective layer.

[0024] Based on the shape of the central pilot tunnel, a central anchor mesh protection structure and a central support steel frame are sequentially installed on the outside of the central surrounding rock protection layer to form a side wall support structure, wherein the upper end of the side wall support structure abuts against the lower end of the upper support.

[0025] Concrete is sprayed on the outside of the sidewall support structure to connect the central anchor mesh protection structure and the central support steel frame to obtain the central support.

[0026] Optionally, in the step of "excavating the lower part to form a tunnel bottom pilot tunnel that connects to the middle pilot tunnel":

[0027] Excavation is carried out on the lower left side until the excavation length meets the second preset value, thus obtaining the second pre-excavated guide pit;

[0028] Continue excavating based on the second pre-excavated pilot tunnel until the second preset advance value is met, and obtain the lower left pilot tunnel;

[0029] Excavation is carried out on the right side of the lower part until the second preset advance value is met to form the lower right guide pit;

[0030] Return to the step of "Continue excavating based on the second pre-excavated pilot tunnel until the second preset advance value is met to obtain the lower left pilot tunnel", until the excavation of the lower left pilot tunnel and the lower right pilot tunnel of a single tunnel unit is completed.

[0031] Optionally, the second preset value is B1, and the second preset advance length is B2, wherein 3m≤B1-B2≤5m.

[0032] Optionally, the ratio of earthwork volume of the upper, middle and lower parts in each tunnel unit is 4:1:2.

[0033] In the technical solution of this invention, the tunnel is divided into multiple tunnel units along its extension direction, and each tunnel unit is excavated and supported sequentially. Each tunnel unit has an upper part, a middle part, and a lower part distributed sequentially in a vertical direction. When excavating and supporting a single tunnel unit, firstly, the upper part is excavated to form an arch, and protective soil is formed at the middle position below the arch. Upper support is then installed along the wall of the arch. Next, the protective soil is moved... In addition to forming an upper pilot tunnel together with the arch, the middle section is excavated to form a middle pilot tunnel connecting to the upper pilot tunnel, and a middle support is installed along the wall of the middle pilot tunnel. Next, the lower section is excavated to form a tunnel bottom pilot tunnel connecting to the middle pilot tunnel, and an invert arch support is installed in the tunnel bottom pilot tunnel, thereby completing the excavation and support of one tunnel unit. Finally, the above construction steps are repeated multiple times until each tunnel unit has been excavated and supported, thereby completing the excavation and support of the entire tunnel. By gradually completing the excavation and support of the upper, middle, and lower sections of the tunnel unit from top to bottom, the area excavated in each construction is relatively small, which helps to ensure the stability of the excavation face. After completing the excavation and support of the upper section, the excavation and support of the middle and lower sections are completed in sequence, which improves construction safety and the stability of each part of the support, and effectively prevents the support of the tunnel unit from encroaching on the secondary lining area. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0035] Figure 1 This is a schematic flowchart of an embodiment of the construction method for tunnel excavation and support in weak surrounding rock provided by the present invention.

[0036] Figure 2 A schematic diagram of tunnel excavation and support in soft surrounding rock tunnels provided for the invention.

[0037] Explanation of icon numbers:

[0038] label name label name 1 Tunnel Unit 12 Central 11 upper part 12a Central support 11a Protective soil 13 lower part 11b Upper support 13a Invert arch support

[0039] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0041] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0042] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the meaning of "and / or" throughout the text includes three parallel solutions; for example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0043] With the rapid development of tunnel engineering in my country, more and more tunnels are being built in complex areas. In particular, during the construction of tunnels in weak and fractured surrounding rock, factors such as poor geological conditions, non-standard construction operations, and unreasonable construction technology or organization can easily cause the initial support arch to sink, the sidewalls to converge, and the arch frame to deform and intrude into the secondary lining range, seriously threatening the safety of tunnel construction and affecting the subsequent construction of the secondary lining. In order to ensure the thickness of the secondary lining, it is necessary to remove and replace the arch frame in the encroaching section, thereby increasing the construction difficulty and affecting the project progress.

[0044] In view of this, the present invention proposes a construction method for tunnel excavation and support in weak surrounding rock, which makes the area of ​​each excavation relatively small, helps to ensure the stability of the excavation face, and after the upper excavation and support is completed, the middle and lower excavation and support are completed in sequence to improve construction safety and the stability of each part of the support, and effectively prevent the support of the tunnel unit from encroaching on the secondary lining range. Figure 1 This is a schematic flowchart of an embodiment of the construction method for tunnel excavation and support in weak surrounding rock provided by the present invention. Figure 2A schematic diagram of tunnel excavation and support in soft surrounding rock tunnels provided for the invention.

[0045] The construction method for tunnel excavation and support in weak surrounding rock includes the following steps:

[0046] Step S10: Excavate above the upper part 11 to form an arch, form a protective soil body 11a at the middle position below the arch, and set an upper support 11b along the wall of the arch.

[0047] Step S20: Remove the protective soil 11a to form an upper guide tunnel together with the arch, excavate the middle part 12 to form a middle guide tunnel that connects to the upper guide tunnel, and set a middle support 12a along the wall of the middle guide tunnel.

[0048] Step S30: Excavate the lower part 13 to form a tunnel bottom guide tunnel that connects to the middle guide tunnel, and set up an invert arch support 13a in the tunnel bottom guide tunnel to complete the excavation and support of one tunnel unit 1.

[0049] Step S40: Return to the steps of "excavating above the upper part 11 to form an arch, forming a protective soil body 11a at the middle position below the arch, and setting an upper support 11b along the wall of the arch" until each tunnel unit 1 has been excavated and supported, thereby completing the excavation and support of the entire tunnel.

[0050] In the technical solution of the present invention, the tunnel is divided into multiple tunnel units 1 along its extension direction, and each tunnel unit 1 is excavated and supported sequentially. Each tunnel unit 1 has an upper part 11, a middle part 12, and a lower part 13 distributed sequentially in the vertical direction. When excavating and supporting a single tunnel unit 1, firstly, the upper part 11 is excavated to form an arch, and a protective soil body 11a is formed at the middle position below the arch. An upper support 11b is then provided along the wall of the arch. Next, the protective soil body... 11a is removed to form an upper pilot tunnel together with the arch. The middle section 12 is excavated to form a middle pilot tunnel that connects to the upper pilot tunnel. A middle support 12a is installed along the wall of the middle pilot tunnel. Next, the lower section 13 is excavated to form a tunnel bottom pilot tunnel that connects to the middle pilot tunnel. An invert arch support 13a is installed in the tunnel bottom pilot tunnel, thereby completing the excavation and support of one tunnel unit 1. Finally, the above construction steps are repeated multiple times until each tunnel unit 1 has been excavated and supported, thereby completing the excavation and support of the entire tunnel. By progressively excavating and supporting the upper part 11, the middle part 12, and the lower part 13 of the tunnel unit 1 from top to bottom, the area excavated in each construction phase is relatively small, which helps to ensure the stability of the excavation face. After completing the excavation and support of the upper part 11, the excavation and support of the middle part 12 and the lower part 13 are completed in sequence to improve construction safety and the stability of each part of the support, effectively preventing the support of the tunnel unit 1 from encroaching on the secondary lining area.

[0051] It should be noted that the multiple tunnel units 1 include an initial tunnel unit 1. In front of the initial tunnel unit 1, pipe roofs are installed along the preset outline of the initial tunnel unit 1 to form an advanced support structure. In this way, a beam effect is formed to reinforce the unexcavated surrounding rock, thereby supporting the surrounding rock, controlling large deformations during tunnel excavation, and ensuring construction safety.

[0052] Specifically, step S10 includes:

[0053] Step S101: Excavate and advance the upper part 11 according to the preset arch outline to form the arch and the protective soil 11a;

[0054] Step S102: Spray concrete on the wall of the arch to form the upper 11 surrounding rock protection layer;

[0055] Step S103: According to the shape of the arch, on the outside of the upper 11 surrounding rock protection layer, the upper 11 anchor net protection structure and the upper support steel frame are set in sequence to form the arch support structure.

[0056] Step S104: Spray concrete on the outside of the arch support structure to connect the upper 11 anchor net protection structure and the upper support steel frame, thereby forming the upper support 11b.

[0057] During the construction of the upper part 11, excavation is first carried out according to the preset arch outline to form the arch and the protective soil 11a. By reserving the protective soil 11a, support can be provided for the unexcavated soil layers behind, ensuring the safety of the arch construction. In the event of mudslides or water inrushes in the tunnel unit 1, the protective soil 11a acts as a barrier, providing reaction time for construction personnel, effectively reducing casualties and improving tunnel construction safety. Then, concrete is sprayed onto the walls of the arch to form a surrounding rock protection layer for the upper part 11, thus sealing the arch. After the excavation of the exposed surrounding rock, according to the shape of the arch, an upper anchor mesh protection structure and an upper support steel frame are sequentially installed on the outside of the upper 11 surrounding rock protection layer to form an arch support structure to support the upper 11 surrounding rock and ensure the structural stability of the arch. Finally, concrete is sprayed on the outside of the arch support structure to connect the upper 11 anchor mesh protection structure and the upper support steel frame, thereby forming the upper support 11b. In this way, the support of the tunnel unit 1 is more reliable and stable, effectively preventing the arch support structure from encroaching on the secondary lining area.

[0058] Furthermore, in the direction away from the tunnel, the locking guide pipe in the upper support steel frame is inclined from top to bottom, and the free end of the locking guide pipe in the upper support steel frame can extend into the surrounding rock of the upper 11. The locking guide pipe's downward inclination and the ability of its free end to extend into the surrounding rock of the upper 11 form a support structure to support the upper support steel frame, ensuring that the upper 11 support steel frame is securely installed on the arch to support the surrounding rock at the arch and guarantee the stability of the arch structure.

[0059] Furthermore, the length of the protective soil mass 11a along the tunnel extension direction is L, where 0.5m ≤ L ≤ 1m. By reserving the protective soil mass 11a, it serves two purposes: firstly, it provides support for the unexcavated soil layers following, ensuring the safety of the arch construction; secondly, it acts as a barrier in the event of mudslides or water inrushes in tunnel unit 1, providing construction personnel with reaction time to increase escape opportunities and reduce casualties. Thus, by limiting the length of the protective soil mass 11a, the cyclic advance length of the arch is controlled, ensuring the quality of arch excavation and support, as well as construction safety.

[0060] Specifically, step S20 includes:

[0061] Step S201: Excavate on the left side of the middle part 12 until the excavation length meets the first preset value to obtain the first pre-excavated guide pit;

[0062] Step S202: Continue excavating based on the first pre-excavated guide pit until the first preset advance value is met, and obtain the left wall guide pit;

[0063] Step S203: Excavation is carried out on the right side of the middle part 12 until the first preset advance value is met to form the right wall guide tunnel, wherein the left wall guide tunnel and the right wall guide tunnel are connected.

[0064] Step S204: Return to the step of "Continue to excavate based on the first pre-excavated guide pit until the excavation length meets the first preset advance value and the left wall guide pit is obtained" until the excavation of the middle guide pit of a single tunnel unit 1 is completed.

[0065] Before excavating the central pilot tunnel, the protective soil 11a reserved after the arch excavation is removed. Then, excavation is carried out from the left side of the central section 12 to obtain the first pre-excavated pilot tunnel, and the length of the first pre-excavated pilot tunnel meets the first preset value. Then, according to the first preset advance value, excavation continues on the basis of the first pre-excavated pilot tunnel to obtain the left wall pilot tunnel. Next, according to the first preset advance value, excavation is carried out on the right side of the central section 12 to form the right wall pilot tunnel that communicates with the left wall pilot tunnel. In this way, the other steps except for the first pre-excavated pilot tunnel excavation step are repeated in sequence until the central pilot tunnel excavation of a single tunnel unit 1 is completed.

[0066] Specifically, the first preset value is A1, and the first preset advance value is A2, where 3m ≤ A1 - A2 ≤ 5m. Thus, during the formation of the central pilot tunnel, the left and right wall pilot tunnels are staggered by 3m to 5m to prevent simultaneous removal of soil layers on both sides, which could cause collapse and thus ensure the safety of the central pilot tunnel excavation.

[0067] Specifically, step S20 also includes:

[0068] Step S205: Shot concrete on the wall of the central pilot tunnel to form a central surrounding rock protection layer;

[0069] Step S206: According to the shape of the central pilot tunnel, a central anchor mesh protection structure and a central support steel frame are sequentially installed on the outside of the central surrounding rock protection layer to form a side wall support structure, wherein the upper end of the side wall support structure abuts against the lower end of the upper support 11b.

[0070] Step S207: Spray concrete on the outside of the side wall support structure to connect the central anchor mesh protection structure and the central support steel frame to obtain the central support 12a.

[0071] After the central pilot tunnel of tunnel unit 1 is excavated, concrete is sprayed onto the walls of the central pilot tunnel to form a central surrounding rock protection layer. This seals the exposed surrounding rock after the central pilot tunnel is excavated. Then, according to the shape of the central pilot tunnel, a central anchor mesh protection structure and a central support steel frame are sequentially installed on the outside of the central surrounding rock protection layer to form a sidewall support structure, thereby supporting the central surrounding rock and ensuring the structural stability of the central section 12. Finally, concrete is sprayed onto the outside of the sidewall support structure to connect the central anchor mesh protection structure and the central support steel frame to obtain the central support 12a. This makes the support of tunnel unit 1 more reliable and stable, effectively preventing the sidewall support structure from encroaching on the secondary lining area. The upper end of the sidewall support structure abuts against the lower end of the upper support 11b, thus supporting the upper support 11b through the sidewall support structure and improving the support stability of the upper support 11b.

[0072] Specifically, step S30 includes:

[0073] Step S301: Excavate on the left side of the lower part 13 until the excavation length meets the second preset value to obtain the second pre-excavated guide pit;

[0074] Step S302: Continue excavating based on the second pre-excavated guide pit until the second preset advance value is met, and obtain the lower left guide pit;

[0075] Step S303: Excavate and advance on the right side of the lower part 13 until the second preset advance value is met to form the lower right guide pit;

[0076] Step S304: Return to the step of "Continue excavating based on the second pre-excavated guide pit until the second preset advance value is met to obtain the lower left guide pit", until the excavation of the lower left guide pit and the lower right guide pit of a single tunnel unit 1 is completed.

[0077] First, excavation begins from the left side of the lower part 13 to obtain the second pre-excavated guide tunnel, and the length of the second pre-excavated guide tunnel meets the second preset value. Then, based on the second preset advance value, excavation continues on the basis of the second pre-excavated guide tunnel to obtain the lower left guide tunnel. Next, based on the second preset advance value, excavation proceeds on the right side of the lower part 13 to form the lower right guide tunnel. In this way, the above steps are repeated in sequence until the excavation of the lower left guide tunnel and the lower right guide tunnel of a single tunnel unit 1 is completed.

[0078] It should be noted that after the excavation of the lower left pilot tunnel and the lower right pilot tunnel is completed, the soil layer between the lower left pilot tunnel and the lower right pilot tunnel is removed to form an inverted arch pilot tunnel. The inverted arch pilot tunnel is connected to the lower left pilot tunnel and the lower right pilot tunnel to jointly form the tunnel bottom pilot tunnel. An inverted arch support 13a is installed in the tunnel bottom pilot tunnel. In this way, the excavation and support of one tunnel unit 1 are completed.

[0079] Specifically, the second preset value is B1, and the second preset advance length is B2, where 3m ≤ B1 - B2 ≤ 5m. Thus, during the excavation of the lower left and lower right pilot tunnels, they are staggered by 3m to 5m to prevent simultaneous removal of soil layers on both sides, which could cause collapse and thus ensure the safety of the excavation work.

[0080] Specifically, the earthwork volume ratio of the upper part 11, the middle part 12, and the lower part 13 in each tunnel unit 1 is 4:1:2. Thus, dividing the upper part 11, the middle part 12, and the lower part 13 according to the 4:1:2 earthwork volume ensures that each part has sufficient working space and a relatively fast construction speed.

[0081] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A construction method for excavation and support of tunnels in weak surrounding rock, wherein the tunnel has multiple tunnel units connected sequentially along its extension direction, and each tunnel unit is sequentially divided into an upper part, a middle part, and a lower part in the vertical direction, characterized in that... The construction method for tunnel excavation and support in weak surrounding rock includes the following steps: Excavation is carried out above the upper part to form an arch, and a protective soil body is formed at the middle position below the arch. Upper support is provided along the wall of the arch. Remove the protective soil to form an upper guide tunnel together with the arch, excavate the middle section to form a middle guide tunnel that connects to the upper guide tunnel, and set a middle support along the wall of the middle guide tunnel. The lower part is excavated to form a tunnel bottom pilot tunnel that connects to the middle pilot tunnel. An inverted arch support is installed in the tunnel bottom pilot tunnel to complete the excavation and support of one tunnel unit. Return to the steps of "excavating above the upper part to form an arch, forming a protective soil at the middle position below the arch, and setting upper support along the wall of the arch" until each tunnel unit has been excavated and supported, thereby completing the excavation and support of the entire tunnel. The steps of "excavating above the upper part to form an arch, forming a protective soil mass at the middle position below the arch, and setting up upper support along the wall of the arch" include: Excavation is carried out in the upper part according to the preset arch outline to form the arch and the protective soil. Concrete is sprayed onto the walls of the arch to form an upper surrounding rock protective layer; Based on the shape of the arch, an upper anchor mesh protection structure and an upper support steel frame are sequentially installed on the outside of the upper surrounding rock protection layer to form an arch support structure. Concrete is sprayed on the outside of the arch support structure to connect the upper anchor mesh protection structure and the upper support steel frame, thereby forming the upper support. In the step of "excavating the middle section to form a middle guide tunnel that connects to the upper guide tunnel": Excavation is carried out on the left side of the middle section until the excavation length meets the first preset value, thus obtaining the first pre-excavated guide tunnel; Continue excavating based on the first pre-excavated pilot tunnel until the first preset advance value is met, and obtain the pilot tunnel on the left wall. Excavation is carried out on the right side of the middle section until the first preset advance value is met to form the right wall guide tunnel, wherein the left wall guide tunnel and the right wall guide tunnel are connected. Return to the step of "Continue excavating based on the first pre-excavated pilot tunnel until the excavation length meets the first preset advance value and the left wall pilot tunnel is obtained" until the excavation of the middle pilot tunnel of a single tunnel unit is completed; In the step of "setting up a central support along the wall of the central guide tunnel": Concrete was sprayed onto the walls of the central pilot tunnel to form a central surrounding rock protective layer. Based on the shape of the central pilot tunnel, a central anchor mesh protection structure and a central support steel frame are sequentially installed on the outside of the central surrounding rock protection layer to form a side wall support structure, wherein the upper end of the side wall support structure abuts against the lower end of the upper support. Concrete is sprayed on the outside of the sidewall support structure to connect the central anchor mesh protection structure and the central support steel frame to obtain the central support. In the step of "excavating the lower part to form a tunnel bottom pilot tunnel that connects to the middle pilot tunnel": Excavation is carried out on the lower left side until the excavation length meets the second preset value, thus obtaining the second pre-excavated guide pit; Continue excavating based on the second pre-excavated pilot tunnel until the second preset advance value is met, and obtain the lower left pilot tunnel; Excavation is carried out on the right side of the lower part until the second preset advance value is met to form the lower right guide pit; Return to the step of "Continue excavating based on the second pre-excavated pilot tunnel until the second preset advance value is met to obtain the lower left pilot tunnel", until the excavation of the lower left pilot tunnel and the lower right pilot tunnel of a single tunnel unit is completed; The ratio of earthwork volume in the upper, middle and lower parts of each tunnel unit is 4:1:

2.

2. The construction method for tunnel excavation and support in weak surrounding rock as described in claim 1, characterized in that, In the direction away from the tunnel, the locking foot guide pipe in the upper support steel frame is inclined from top to bottom, and the free end of the locking foot guide pipe in the upper support steel frame can extend into the upper surrounding rock.

3. The construction method for tunnel excavation and support in weak surrounding rock as described in claim 1, characterized in that, The length of the protective soil along the tunnel extension direction is L, where 0.5m≤L≤1m.

4. The construction method for tunnel excavation and support in weak surrounding rock as described in claim 1, characterized in that, The first preset value is A1, and the first preset advance value is A2, wherein 3m≤A1-A2≤5m.

5. The construction method for tunnel excavation and support in weak surrounding rock as described in claim 1, characterized in that, The second preset value is B1, and the second preset advance length is B2, wherein 3m≤B1-B2≤5m.

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