Synchronous excavation method for three-arch tunnel main hole

Abstract

The present disclosure relates to the technical field of tunnel opening, and particularly relates to a three-arch tunnel main hole synchronous excavation method. The method first opens left and right side holes, and a position of a middle hole is reserved between the two side holes. The left and right side holes are excavated layer by layer from top to bottom. An initial support and a locking foot anchor are arranged on the periphery after each layer is excavated. The two side locking foot anchors are connected with a first transverse temporary support. The locking foot anchor forms a closed loop fixation of the initial support and the first transverse temporary support. A vertical support is arranged on a side of the left side hole and the right side hole close to the middle hole. A first top arch of the two side holes and a first inverted arch of a side wall and a tunnel bottom far away from the middle hole are poured and built. The first transverse temporary support of the left side hole and the right side hole is removed. The middle hole is excavated layer by layer from top to bottom. The first top arch and a second top arch of the two side holes form a three-arch top arch closure. The second temporary support is removed layer by layer. A side wall and a second inverted arch of the bottom of the middle hole which are common to the left side hole and the right side hole are arranged at the position of the vertical support of the two side holes.

Description

Technical Field

[0001] This disclosure relates to the field of tunnel excavation technology, and in particular to a method for simultaneous excavation of the main tunnel of a three-arch tunnel. Background Technology

[0002] With the development of my country's national economy, the railway is developing faster and faster, and the proportion of tunnels in railway projects is increasing. Due to the limitations of terrain, geology and track conditions, the construction of new railway branch lines or crossover lines is increasingly being carried out within tunnels, thus forming a series of arch tunnels. Some railway stations are even designed as underground tunnels with three arches.

[0003] Currently, twin-arch or triple-arch tunnels are mostly found in highway and subway tunnels, and the common method is to construct the central partition wall first, then excavate the left and right tunnels, and finally excavate the central tunnel. However, in railway tunnels, due to the greater depth and connection with ordinary tunnels, it is difficult to construct the central partition wall first. Moreover, after the central partition wall is constructed, it is easy to cause eccentric pressure on the central partition wall when excavating the left and right tunnels, leading to problems such as displacement or cracking of the central partition wall. Summary of the Invention

[0004] To solve, or at least partially solve, the aforementioned technical problems, this disclosure provides a method for simultaneous excavation of the main tunnel of a three-arch tunnel, comprising the following steps:

[0005] Step 1: Simultaneously excavate the left and right side tunnels, leaving space for the middle tunnel between the two side tunnels. The left and right side tunnels are excavated layer by layer from top to bottom. For each layer excavated, initial supports and anchor bolts are set around the perimeter. The anchor bolts are set on both sides of the guide tunnel, and a first transverse temporary support is connected between the anchor bolts on both sides. The anchor bolts make the initial support and the first transverse temporary support form a closed loop for fixation.

[0006] Step 2: Construct a first vertical temporary support on the side of the left and right tunnels near the central tunnel, and set a first vertical temporary support between the first horizontal temporary supports of the two guide tunnels;

[0007] Step 3: Construct the first arch of the two side tunnels, as well as the sidewall away from the central tunnel and the first invert arch at the bottom of the tunnel;

[0008] Step 4: Construct supporting columns. The supporting columns are set at the position of the first vertical support. The supporting columns are used to support the opposite side of the left and right openings after the first horizontal temporary support and the first vertical temporary support are removed. After the supporting columns reach the predetermined strength, the first horizontal temporary support and the first vertical temporary support of the left and right openings are removed, and the second lining of the first top arch, the side wall and the first invert arch is carried out.

[0009] Step 5: Excavate the central tunnel layer by layer from top to bottom. During the excavation of the top layer of the central tunnel, set up initial supports and second transverse temporary supports around the perimeter. The two ends of the second transverse temporary supports of each layer are connected to the anchor bolts of the corresponding layers of the two side tunnels. Then, pour the second top arch of the central tunnel. The first top arch of the two side tunnels supports the second top arch to form a three-way supply arch closure.

[0010] Step 6: Remove the second temporary support layer by layer and excavate to expose the support column. At the position of the support column of the two side holes, construct the partition wall of the middle hole, which is shared with the left hole and the right hole, as well as the second inverted arch at the bottom. The partition wall is set along the length of the tunnel and wraps around the support column.

[0011] Optionally, in step one and / or step five, the left-side tunnel, the right-side tunnel, and the middle tunnel are divided into a first pilot tunnel, a second pilot tunnel, a third pilot tunnel, and an inverted arch for excavation; the next pilot tunnel is excavated in a manner that lags behind the previous pilot tunnel.

[0012] Optionally, in step one, the space between the left and right holes for the middle hole is reserved to be greater than 15 meters.

[0013] Optionally, in step one, the second pilot tunnel is excavated after the first pilot tunnel is excavated to a depth of 10 to 15 meters, and the third pilot tunnel is excavated after the second pilot tunnel is excavated to a depth of 5 to 10 meters.

[0014] Optionally, in step one, after the initial support is constructed, a thick layer of concrete is initially sprayed, and system anchors, steel mesh, and an initial support steel frame are installed. The two ends of the initial support steel frame are connected to the connecting segment of the first transverse temporary support at the position of the locking anchor to form a closed loop.

[0015] Optionally, in step three, after pouring the first top arch, the side walls, and the first invert arch at the bottom of the tunnel, a waterproof layer is laid at the bottom of the walls and a drainage pipe is buried.

[0016] Optionally, in step three, when pouring the first invert arch, a steel reinforcement connector for the invert arch to be connected to the second invert arch is reserved on the side near the central hole.

[0017] Optionally, in step three, when pouring the first arch, a rebar connector for the second arch is reserved on the side near the central opening for connection with the second arch.

[0018] Optionally, in step five, the length of the initial support to be dismantled in sections is less than 12 meters.

[0019] Optionally, in step five, core soil is reserved during the excavation of the central tunnel.

[0020] Compared with existing technologies, the beneficial effects of this disclosure are as follows: This disclosure adopts a construction sequence of first excavating the sides and then the middle, and simultaneously constructing the partition walls and side tunnels. That is, the side tunnels are excavated first, and the middle tunnel is excavated after the left and right side tunnels are lined within a certain range. During the excavation of the three tunnels, they are divided into several units from top to bottom. The initial support, anchor bolts, and first transverse temporary supports are constructed in a timely manner during the step-by-step excavation to form a closed loop of the pilot tunnel. Together with the surrounding rock, they form a load-bearing system, cooperate in deformation bearing, and make full use of the self-supporting capacity of the surrounding rock. This makes the excavation of the three-arch tunnel more convenient, and the stress distribution of the tunnel body is more even. Each tunnel can be closed into a loop in a timely manner during construction, thereby achieving a safe and reliable support effect. Attached Figure Description

[0021] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0022] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the structure in which the anchor bolt, the initial support, and the first transverse temporary support form a closed loop for fixation as disclosed in this disclosure.

[0024] Figure 2 A schematic diagram of the structure for setting up the first horizontal temporary support and the first vertical temporary support for the excavation of the left and right tunnels in this disclosure;

[0025] Figure 3 A structural diagram showing the top arch, side walls, inverted arch, and supporting columns of this disclosure;

[0026] Figure 4 This is a structural diagram showing the removal of the first horizontal temporary support and vertical temporary support for the openings on both sides of the site disclosed in this publication.

[0027] Figure 5 This is a schematic diagram of the structure that forms a triple arch, has a central opening, and is equipped with a second transverse temporary support.

[0028] Figure 6 This is one of the structural diagrams of the completed section of this disclosure;

[0029] Figure 7 The second structural diagram showing the completion of this publicly disclosed segment;

[0030] Among them, 2-left side tunnel; 21-first top arch; 22-side wall; 3-right side tunnel; 4-middle tunnel; 41-second top arch; 42-second lateral temporary support; 43-second invert arch; 5-initial support; 6-first lateral temporary support; 7-foot anchor; 9-first vertical temporary support; 10-first invert arch; A-first pilot tunnel; B-second pilot tunnel; C-third pilot tunnel; D-invert arch; E-core soil; 100-support column; 200-partition wall. Detailed Implementation

[0031] To better understand the above-mentioned objectives, features, and advantages of this disclosure, the solutions disclosed herein will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0032] Numerous specific details are set forth in the following description in order to provide a full understanding of this disclosure, but this disclosure may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some, and not all, of the embodiments of this disclosure.

[0033] Currently, triple-arch tunnels are mostly found in highway and subway tunnels, and the method of constructing the central partition wall first, then excavating the left and right tunnels, and finally excavating the central tunnel is commonly used. However, in railway tunnels, due to the greater depth of the tunnel and its connection with ordinary tunnels, it is difficult to construct the central partition wall first. Moreover, after the central partition wall is constructed, it is easy to cause eccentric pressure on the central partition wall when excavating the left and right tunnels, leading to problems such as displacement or cracking of the central partition wall.

[0034] Based on this, this disclosure provides a method for simultaneous excavation of the main tunnel of a three-arch tunnel. The method involves excavating the two sides first, followed by the central tunnel. During excavation, initial support, anchor bolts, and the first lateral temporary support are promptly implemented to form a closed loop of the pilot tunnel. This loop, together with the surrounding rock, forms a load-bearing system, coordinating deformation and bearing capacity. This fully utilizes the self-supporting capacity of the surrounding rock, making the excavation of the three-arch tunnel more convenient and resulting in a more even stress distribution in the tunnel structure. Each tunnel can be closed into a loop in a timely manner during construction, thus achieving a safe and reliable support effect. This successfully solves the technical challenges of constructing three-arch tunnels. By adopting this new construction method, not only is the construction progress accelerated, but the safety and quality of tunnel construction are also guaranteed, achieving significant economic and social benefits.

[0035] The following detailed explanation uses specific examples to illustrate the method for simultaneous excavation of the main tunnel of the three-arch tunnel:

[0036] This disclosure applies to the construction of multi-arch tunnels in Class III and Class IV surrounding rock; other multi-arch tunnels can refer to this method for construction. The three-arch tunnel construction technique for the transition section of a high-speed railway underground station adopts a construction sequence of first the sides and then the center, with the partition walls and side tunnels constructed simultaneously. The bench excavation method is used, and each tunnel is preferably excavated using the three-bench method, resulting in a fast and efficient overall construction process.

[0037] Specific reference Figures 1 to 7 As shown, this disclosure provides a method for simultaneous excavation of the main tunnel of a three-arch tunnel. This technology is based on the fundamental principles of the New Austrian Tunneling Method (NATM). Tunnel construction should adhere to the guiding principles of "weak blasting, short advances, strong support, early closure, and frequent measurements," and includes the following steps:

[0038] Step one discloses the overall excavation sequence and the specific supporting closed-loop structure. This disclosure involves simultaneously excavating the left side tunnel 2 and the right side tunnel 3, a so-called synchronous asymmetrical construction. Preferably, one side tunnel can be excavated slightly later than the other to ensure excavation stability. For example, the right tunnel can be constructed only after the left tunnel has been constructed a certain distance later. Symmetrical construction of the two side tunnels is strictly prohibited. Preferably, the left side tunnel 2 and the right side tunnel 3 are staggered by more than 15 meters. After the top pilot tunnel of one of the left side tunnel 2 and the right side tunnel 3 forms a closed loop, the other side tunnel is excavated. During construction, the blasting vibration velocity should be controlled to reduce the impact of blasting vibration on the initial support of the left tunnel, and a space for the middle tunnel 4 should be reserved between the two side tunnels.

[0039] Furthermore, the left tunnel 2 and right tunnel 3 are excavated layer by layer from top to bottom. At each excavation layer, initial supports 5 and anchor bolts 7 are installed around the perimeter. The anchor bolts 7 are located on both sides of the pilot tunnel, and a first transverse temporary support 6 connects the two anchor bolts 7. The anchor bolts 7 fix the initial support 5 and the first transverse temporary support 6, forming a load-bearing system together with the surrounding rock, coordinating deformation and load bearing. After excavation, some deformation of the surrounding rock is allowed, thereby releasing some ground stress and fully utilizing the self-supporting capacity of the surrounding rock. When constructing the initial support 5, attention should be paid to its installation method and stability. After the initial support 5 is constructed, a thick initial shotcrete layer is applied, preferably 4cm thick, and system anchor bolts, steel mesh, and the initial support steel frame are installed. The two ends of the initial support steel frame are connected to the first transverse temporary support 6 at the anchor bolt 7 positions to form a closed loop for fixation.

[0040] In a preferred embodiment, the left tunnel 2, right tunnel 3, and middle tunnel 4 are divided into a first pilot tunnel A, a second pilot tunnel B, a third pilot tunnel C, and an invert section D for weak blasting excavation. The excavation of each pilot tunnel is delayed by the previous one to prevent the risk of tunnel collapse caused by simultaneous excavation. The delay distance is preferably 10-15 meters. For example, the first pilot tunnel A is excavated for 10 meters and then closed into a ring to form a load-bearing system with the surrounding rock. After coordinated deformation and load bearing, the second pilot tunnel B is opened, and the third pilot tunnel is excavated 5 to 10 meters later. Preferably, after excavating the invert section D, a waterproof layer is promptly laid at the bottom of the tunnel wall, drainage pipes are buried, and the tunnel floor is filled, with provisions for the steel reinforcement connector of the middle tunnel invert section. Under this delayed construction scheme, the first pilot tunnel A, second pilot tunnel B, third pilot tunnel C, and invert section D form a stepped structure inside the tunnel to prevent the risk of tunnel collapse. Furthermore, a monitoring and measurement system is established during the excavation process, implementing information management and providing timely guidance for construction based on feedback information to ensure safety and stability.

[0041] Step two is the specific disclosure of the first vertical temporary support 9. After step one is completed, the first vertical temporary support 9 needs to be installed on the side of the left tunnel 2 and the right tunnel 3 near the middle tunnel 4. The function of the first vertical temporary support 9 is to better support the overall structure of the tunnel, and at the same time reserve the construction position for the common sidewall of the middle tunnel 4, the left tunnel 2, and the right tunnel 3. For example, the first vertical temporary support 9 is set between the first horizontal temporary supports 6 of the two pilot tunnels. The first vertical temporary support 9 is supported on the bottom surface of the first horizontal temporary support 6 of the first pilot tunnel A and the top surface of the first horizontal temporary support 6 of the second pilot tunnel B. The first vertical temporary support 9 in the third pilot tunnel C below is also set in the same way. Optionally, the first vertical temporary support 9 can also be set separately from the first horizontal temporary support 6. The first vertical temporary support 9 can be supported between multiple first horizontal temporary supports 6 in the tunnel extension direction by means of I-beams, steel frames, etc. The purpose is to leave space for the shared sidewalls of the prefabricated central tunnel 4, left tunnel 2 and right tunnel 3. The prefabricated sidewalls can be directly placed between two vertical supports for splicing. The tunnel slab splicing process is an existing technology and will not be described in detail.

[0042] Step three details the pouring of the top arch, side walls, and invert arch. After the left and right tunnels have been constructed for a certain distance, based on the monitoring and measurement structural analysis, and after the initial support has stabilized, the lining of the left and right tunnels will be carried out. Simultaneously, the partition walls will be constructed, and the first top arch 21 of both tunnels, the side wall 22 on the side away from the central tunnel 4, and the first invert arch 10 at the bottom of the tunnel will be poured. After pouring the first top arch 21, side wall 22, and the first invert arch 10 at the bottom of the tunnel, the waterproof layer at the bottom of the walls can be laid and drainage pipes can be buried. When pouring the first invert arch 10 and the first top arch 21, a steel reinforcement connector for the invert arch 43 will be reserved on the side near the central tunnel 4. It should be noted that in the technical solution of this disclosure, since the side tunnels are excavated first, the partition wall 200 shared by the side tunnels and the central tunnel 4 will be constructed later. The first vertical temporary support 9 also serves a positioning function. When the first vertical temporary supports 9 of the side tunnels are excavated during the subsequent excavation of the central tunnel, the workers can more clearly and intuitively perceive the construction progress and excavation range, facilitating the excavation of the central tunnel. Furthermore, when constructing the first vertical temporary support 9, a certain amount of excavation can continue on the side of the left and right side tunnels closest to the central tunnel. This will create a hollow area when excavating the sides of the central tunnel, directly exposing the first vertical temporary support 9 and avoiding damage to it.

[0043] Step four is a specific disclosure of the timing for dismantling the first transverse temporary support. After step three is completed, a support column 100 is constructed. The support column 100 is set at the position of the first vertical temporary support 9. The support column 100 is used to support the opposite side of the left tunnel 2 and the right tunnel 3 after the first transverse temporary support 6 and the first vertical temporary support 9 are dismantled. Specifically, the position of the first vertical temporary support 9 can be configured in accordance with the above-mentioned scheme of staggering the first vertical temporary support 9 and the first transverse support 6, or it can be set side by side with the first vertical temporary support 9 in the extension direction of the tunnel. For example, if the two are not staggered, the support column 100 is set at the interval between the two first transverse temporary supports 6 in the extension direction of the tunnel. Generally, the interval between the two first transverse temporary supports 6 is 1 meter. If the two are staggered, the support column 100 can be set directly next to each other along the extension direction of the tunnel. The purpose is that the support column 100 can support the top and bottom of the side (between the top arch end and the invert arch end). Once the supporting column 100 reaches the predetermined strength, the first temporary transverse supports 6 of the left tunnel 2 and right tunnel 3 can be removed, providing better support during the simultaneous construction of the three arches, and the secondary lining of the first top arch 21, side walls 22, and first invert arch 10 can then be carried out. It should be noted that the length of each temporary transverse support removed should not exceed the length of each lining section constructed.

[0044] Step five is the specific disclosure of the excavation of the central tunnel 4 in this disclosure. The central tunnel 4 is excavated layer by layer from top to bottom. Preferably, a core soil E is reserved during the excavation of the central tunnel 4 to prevent stress concentration from causing tunnel collapse. During the excavation of the top layer of the central tunnel 4, initial supports 5 and second transverse temporary supports 42 are set around the perimeter. The two ends of the second transverse temporary supports 6 of each layer are connected to the anchor bolts 7 of the corresponding layers of the two side tunnels. The method and sequence of the lower pilot tunnel are the same as those of the left side tunnel 2 and the right side tunnel 3. After the invert arch of the central tunnel 4 is excavated for a certain distance, the initial supports 5 in the common area of ​​the two side tunnels and the central tunnel are removed in sections along the extension length of the tunnel. Preferably, the length of the initial supports 5 removed in sections of the left side tunnel 2 and the right side tunnel 3 is less than 12 meters. The second top arch 41 of the central tunnel 4 is poured, so that the first top arch 21 of the two side tunnels supports the second top arch 41 to form a three-way sealed top arch. Because the support of the left and right side tunnels is stable, and support columns 100 are set in both the left and right side tunnels, the first top arch 21 of the two side tunnels can support the second top arch 41.

[0045] Step six is ​​a specific disclosure of the construction method of the partition wall 200 and the second inverted arch 43 at the bottom of the central tunnel 4. The lining construction of the central tunnel 4 requires attention to the following: After the upper step of the central tunnel 4 has been excavated for a certain distance, based on the monitoring and measurement structure analysis, after the initial support of the upper step has stabilized, the temporary initial supports 5 of the left and right side tunnels are dismantled in sections, and the arch lining of the central tunnel is constructed first. The second temporary support 42 is dismantled layer by layer. The dismantling length of each section of the second transverse temporary support 42 should not exceed the construction length of each lining section. The second temporary support (42) is dismantled layer by layer, and the support columns 100 are excavated to both sides. At the position of the support columns 100 of the two side tunnels, the partition wall 200 shared by the left tunnel 2 and the right tunnel 3 of the central tunnel 4 and the second inverted arch 43 at the bottom are constructed. The partition wall 200 is set along the entire length of the tunnel and wraps around the support columns 100. This is a specific disclosure of the partition wall 200 setting method of this disclosure, the contents of which are as follows:

[0046] In one embodiment, the partition wall 200 of this disclosure is a partition wall integrally cast using a template, and its interior includes supporting columns 100, which together form a supporting function.

[0047] In another embodiment, the partition wall 200 of this disclosure is a prefabricated wall, which is divided into a first wall and a second wall. The first and second walls are provided with receiving grooves for the supporting column 100. Specifically, after the first wall and the second cavity are spliced ​​together, the shape of the two receiving grooves is configured to match the shape of the supporting column 100. For example, the supporting column 100 is a cuboid, a cylinder, etc., so the spliced ​​receiving groove matches the shape of the supporting column 100.

[0048] In terms of specific construction, during the installation of the partition wall 200, the first wall can be installed first in portions of the left side tunnel 2 and the right side tunnel 3 (installing one side first), which also provides better support. When further removing the temporary supports in the central tunnel, the excavation can be expanded outwards towards the two side tunnels. After the support column 100 and the first wall are visible, the shape is adjusted and the second wall is installed. In this embodiment, the collapse problem of simultaneous excavation of the three arches can be effectively avoided, and the tunnel excavation speed can be effectively improved.

[0049] This disclosure simplifies the construction process of a three-arch tunnel through the aforementioned technical solution, significantly improving construction efficiency and saving construction costs. Furthermore, by continuously optimizing construction organization, the construction period is shortened. Therefore, while ensuring tunnel construction safety, economic benefits are also considered. The construction of a three-arch tunnel in the transition section of a high-speed railway underground station reduces manpower output and improves construction efficiency through optimized construction organization, saving labor for society. The reasonable excavation sequence reduces surface subsidence and effectively protects the environment. The synchronous excavation technology of the main tunnel of the three-arch tunnel in the transition section of a high-speed railway underground station provides a reliable decision-making basis and technical indicators for future mountain tunnels in similar situations. This novel technology will promote the advancement of underground engineering construction technology, resulting in significant social and environmental benefits. Good results have been achieved in tunnel construction safety, construction quality, and construction progress, ensuring excavation safety and tunnel construction quality, accelerating the construction process, and creating good economic and social benefits for the enterprise.

[0050] It should be noted that, in this document, relational terms such as "first arch" and "second arch" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0051] The above description is merely a specific embodiment of this disclosure, enabling those skilled in the art to understand or implement it. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for simultaneous excavation of the main tunnel of a three-arch tunnel, characterized in that, Includes the following steps, Step 1: Simultaneously open the left side hole (2) and the right side hole (3), and reserve the position of the middle hole (4) between the two side holes. The left side hole (2) and the right side hole (3) are excavated layer by layer from top to bottom. Each layer is excavated and a primary support (5) and a locking anchor (7) are set around the perimeter. The locking anchor (7) is set on both sides of the guide pit, and a first transverse temporary support (6) is connected between the two sides of the locking anchor (7). The locking anchor (7) makes the primary support (5) and the first transverse temporary support (6) form a closed loop and fix them. Step 2: On the side of the left tunnel (2) and the right tunnel (3) near the middle tunnel (4), a first vertical temporary support (9) is constructed. The first vertical temporary support (9) is provided between the first horizontal temporary supports (6) of the two pilot tunnels. The first vertical temporary support (9) is staggered from the first horizontal temporary support (6). The first vertical temporary support (9) is supported between multiple first horizontal temporary supports (6) in the tunnel extension direction. Step 3: Construct the first arch (21) of the two side tunnels, the sidewall (22) on the side away from the central tunnel (4), and the first invert arch (10) at the bottom of the tunnel. Step 4: Construct support columns (100). The support columns (100) are set at the position of the first vertical temporary support (9). The support columns (100) are used to support the opposite side of the left hole (2) and the right hole (3) after the first horizontal temporary support (6) and the first vertical temporary support (9) are removed. After the support columns (100) reach the predetermined strength, the first horizontal temporary support (6) and the first vertical temporary support (9) of the left hole (2) and the right hole (3) are removed, and the second lining of the first top arch (21), the side wall (22) and the first inverted arch (10) is carried out. Step 5: Excavate the central tunnel (4) layer by layer from top to bottom. During the excavation of the top layer of the central tunnel (4), set up initial supports (5) and second transverse temporary supports (42) around the perimeter. The two ends of the second transverse temporary supports (42) of each layer are connected to the anchor rods (7) of each layer of the two side tunnels. The second arch (41) of the central tunnel (4) is poured. The first arch (21) of the two side tunnels supports the second arch (41) to form a triple arch arch closure. Step 6: Remove the second transverse temporary support (42) layer by layer and excavate to expose the support column (100). At the position of the support column (100) of the two side holes, construct the partition wall (200) of the middle hole (4) shared with the left hole (2) and the right hole (3) and the second invert arch (43) at the bottom. The partition wall (200) is set along the tunnel direction and wraps around the support column (100).

2. The method for simultaneous excavation of the main tunnel of a three-arch tunnel according to claim 1, characterized in that, In step one and / or step five, the left side tunnel (2), the right side tunnel (3) and the middle tunnel (4) are divided into a first pilot tunnel (A), a second pilot tunnel (B), a third pilot tunnel (C) and an inverted arch (D) for excavation; the next pilot tunnel is excavated in a manner that the next pilot tunnel lags behind the previous pilot tunnel.

3. The method for simultaneous excavation of the main tunnel of a three-arch tunnel according to claim 1, characterized in that, In step one, the space between the left hole (2) and the right hole (3) is reserved for the middle hole (4) by more than 15 meters.

4. The method for simultaneous excavation of the main tunnel of a three-arch tunnel according to claim 2, characterized in that, In step one, after the first pilot tunnel (A) is excavated to a depth of 10 to 15 meters, the second pilot tunnel (B) is excavated. After the second pilot tunnel (B) is excavated to a depth of 5 to 10 meters, the third pilot tunnel (C) is excavated.

5. The method for simultaneous excavation of the main tunnel of a three-arch tunnel according to claim 1, characterized in that, In step one, after the initial support (5) is constructed, thick concrete is sprayed and system anchors, steel mesh and initial support steel frame are installed. The two ends of the initial support steel frame form a closed loop with the first transverse temporary support (6) at the position of the locking foot anchor (7).

6. The method for simultaneous excavation of the main tunnel of a three-arch tunnel according to claim 1, characterized in that, In step three, after pouring the first top arch (21), the side wall (22) and the first invert arch (10) at the bottom of the tunnel, a waterproof layer is laid at the bottom of the wall and a drainage pipe is buried.

7. The method for simultaneous excavation of the main tunnel of a three-arch tunnel according to claim 1, characterized in that, In step three, when pouring the first invert arch (10), a steel reinforcement connector for the invert arch (43) is reserved on the side near the central hole (4) to be connected to the second invert arch (43).

8. The method for simultaneous excavation of the main tunnel of a three-arch tunnel according to claim 1, characterized in that, In step three, when pouring the first arch (21), a top arch steel bar connector is reserved on the side near the central hole (4) to connect with the second arch (41).

9. The method for simultaneous excavation of the main tunnel of a three-arch tunnel according to claim 1, characterized in that, In step five, core soil (E) is reserved during the excavation of the central tunnel (4).

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