A tunnel front support structure and construction method

Abstract

The application discloses a tunnel front supporting structure and a construction method, which comprise a steel arch, advanced connecting steel bars and an advanced steel mesh. The steel arch comprises front and rear steel arches arranged side by side. The front steel arch is arranged close to a working face, and the rear steel arch is arranged at intervals from the front steel arch. The advanced connecting steel bars are arranged along the steel arch and extend obliquely upward at the front end into a front region near the working face. The front end of the advanced connecting steel bars is supported by a tunnel base of the working face, the middle part is supported by the front steel arch, and the rear end is connected with the rear steel arch. The advanced steel mesh is arranged at the top of the front region and is supported by the advanced connecting steel bars. The surfaces of the advanced steel mesh and the advanced connecting steel bars are sprayed with an advanced supporting concrete layer. The tunnel front supporting structure and the construction method can fill the front region at the working face and effectively prevent further expansion of overbreak.

Description

Technical Field

[0001] This invention relates to the field of tunnel engineering technology, and in particular provides a tunnel front support structure and construction method. Background Technology

[0002] When encountering heavily weathered or extremely fractured surrounding rock, even with smooth blasting, over-excavation and excessive longitudinal advance are common. Conventional initial support methods only involve shotcreting concrete between the steel arch frames, leaving the tunnel walls in the leading edge area (i.e., the arch area between the first steel arch frame and the tunnel face) exposed. With each subsequent blast, the collapse continues to develop. Under the combined effects of the blast vibration and shock waves from the next cycle, airflow escapes through the damping holes in the surrounding boreholes, forming airflow within the remaining cavity between the first steel arch frame and the surrounding rock at the arch level. This exacerbates gravity-induced rockfall in the leading edge area and continuously increases the arch span of the longitudinal arch in the next cycle. This cycle repeats, with over-excavation increasing with each subsequent blast. This phenomenon is frequently observed in gravity-induced rockfall formations such as embedded structures, slip zones, loose layers, low-strength layers, and water-rich layers.

[0003] Patent application "A Pre-grouted Small Pipe Grouting Structure and Its Construction Method" (CN109139048A) discloses a pre-grouted small pipe grouting structure and its construction method. The pre-grouted small pipe can ensure the rapid closure of the initial support. The grout stop wall and the initial support are an integral load-bearing structure, closely attached to the working face, which has a certain effect on increasing the stability of the working face. However, this technology is only applicable to situations where the design scheme includes pre-grouted small pipe early support, and it limits the connection between the front edge area and the grout stop wall. When there is no grout stop wall in the design scheme, the front edge area is usually not treated. When there are no pre-grouted small pipes or other advanced support measures in the design scheme, the steel arch frame is usually not drilled in advance, and the timeliness of support in the front edge area when encountering soft and broken strata is limited. In cases of severe over-excavation, the shotcrete is not easy to adhere, and there is serious voiding behind the initial support. In addition, the inner steel mesh is not easy to fix and is prone to falling off and injuring people. Summary of the Invention

[0004] Based on this, the present invention provides a tunnel front support structure and construction method, which effectively provides advance support for the front area generated by tunnel blasting excavation without using a grout stop wall, and improves the safety of the support, effectively avoiding the technical problem of over-excavation continuously expanding during the further blasting excavation of gravity-type ground-fallen strata tunnels.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a tunnel front support structure, comprising a steel arch frame, pre-connecting reinforcing bars, and a pre-reinforcing mesh; the steel arch frame includes a front steel arch frame and a rear steel arch frame arranged side by side, the front steel arch frame being arranged close to the tunnel face, and the rear steel arch frame being arranged at intervals from the front steel arch frame; the pre-connecting reinforcing bars are arranged along the steel arch frame and extend obliquely upwards into the front support area near the tunnel face, the front end of the pre-connecting reinforcing bars being supported by the tunnel matrix at the tunnel face, the middle being supported by the front steel arch frame, and the rear end being supported and connected to the rear steel arch frame; the pre-reinforcing mesh is disposed in the front support area and supported by the pre-connecting reinforcing bars, the pre-reinforcing mesh being configured in a sheet-like and / or rolled form for supporting the tunnel matrix in the front support area; the surfaces of the pre-reinforcing mesh and the pre-connecting reinforcing bars are sprayed with a pre-support concrete layer.

[0006] In some preferred technical solutions, an advanced support guide tube is also included. The front end of the advanced support guide tube extends obliquely upward into the hole on the working face, and the rear end is supported by a reserved hole in the front steel arch. The advanced connecting steel bar is at the same height as the advanced support guide tube, and the advanced steel mesh is supported by the advanced connecting steel bar and the advanced support guide tube.

[0007] Furthermore, the advanced support conduit and the advanced connecting steel bars are spaced apart, the spacing between the advanced support conduits is greater than the spacing between the advanced connecting steel bars, and multiple advanced connecting steel bars are provided between adjacent advanced support conduits.

[0008] Furthermore, the advanced connecting steel bar includes an overlapping first steel bar segment and a second steel bar segment. The length of the first steel bar segment is greater than the length of the second steel bar segment and the front ends are aligned. The overlapping section of the first steel bar segment and the second steel bar segment is located in the leading edge area and is supported by the front steel arch and the tunnel matrix of the tunnel face. The individual segment of the first steel bar is located between the front steel arch and the rear steel arch and is supported by the rear steel arch.

[0009] Furthermore, the advanced steel mesh includes advanced steel mesh sheets that cover the leading edge area and extend along the arch frame, with advanced connecting steel bars supporting the advanced steel mesh sheets.

[0010] In some preferred technical solutions, the advanced steel mesh further includes an advanced steel mesh roll, which fills the leading edge area and extends along the arch frame. The outer side of the advanced steel mesh roll contacts the tunnel foundation support in the leading edge area, and the inner side is supported by advanced connecting steel bars.

[0011] Furthermore, the advanced steel mesh rolls include multiple rolls arranged in parallel, with the outer advanced steel mesh rolls contacting the tunnel foundation support in the leading edge area, and the inner advanced steel mesh rolls supported by advanced connecting steel bars.

[0012] To achieve the above objectives, in a second aspect, the present invention provides a construction method for a tunnel front support structure, comprising the following steps:

[0013] S100. After completing the excavation of one ring of the tunnel, remove the slag and locate the roof and sides;

[0014] S200. Construct steel arch frames, with the front steel arch frame close to the working face and the rear steel arch frame spaced apart from the front steel arch frame. Reinforce the front and rear steel arch frames with connecting steel bars and steel mesh overlap.

[0015] S300. An advanced connecting steel bar is arranged along the steel arch frame. The front end of the advanced connecting steel bar extends obliquely upward into the front edge area and is supported by the front steel arch frame and the tunnel base of the tunnel face. The middle and rear ends are supported by the front steel arch frame and the rear steel arch frame, respectively.

[0016] S400. Drill holes at the working face, and pass the advanced support guide pipe through the reserved hole in the steel arch frame and insert the front end into the hole at the working face;

[0017] S500. Insert advanced steel mesh and advanced steel mesh rolls supported by advanced connecting steel bars and / or advanced support conduits on the outside of the advanced support in the front area.

[0018] S600. The front area and the initial support are simultaneously wet-sprayed with advanced support concrete layer to cover the advanced support;

[0019] S700. Proceed to the next ring excavation. After the leading edge area is fully exposed, press the advanced support guide pipe or advanced connecting steel bar into the outside of the last steel arch frame of the next ring.

[0020] S800. The connecting steel bars between the first steel arch frame of the previous ring and the last steel arch frame of the next ring are reinforced with steel mesh on the inside and wet sprayed concrete layer.

[0021] Furthermore, step S300 includes:

[0022] The advanced connecting steel bar includes a first steel bar segment and a second steel bar segment that are lapped together. The length of the first steel bar segment is greater than the length of the second steel bar segment. The lapped section of the first steel bar segment and the second steel bar segment is located in the leading edge area and is supported by the front steel arch and the tunnel foundation at the working face. The individual segment of the first steel bar is located between the front steel arch and the rear steel arch and is supported by the rear steel arch. One end of the advanced connecting steel bar abuts against the upper flange of the second steel arch and the other end abuts against the working face. The advanced connecting steel bar is tied to the steel arch.

[0023] Furthermore, step S500 includes:

[0024] The advanced steel mesh roll is made by rolling steel mesh into a barrel shape, binding it with iron wire, installing it above the advanced connecting steel bars, and then cutting the iron wire until the advanced steel mesh roll is stretched out and fills the leading edge area.

[0025] Compared with existing technologies, the technical advantages of the tunnel front support structure and construction method provided by this invention are reflected in at least the following aspects:

[0026] (1) The front steel arch frame and the rear steel arch frame arranged in parallel near the working face support the advanced connecting steel bars. The front end of the advanced connecting steel bars extends into the front area and supports the advanced steel mesh, forming an advanced support structure. This provides effective support to the tunnel foundation outside the front area, reduces the impact of the superposition of the blasting vibration and shock wave of the next cycle on the tunnel foundation outside the front area, and thus avoids the further over-excavation problem caused by subsequent blasting excavation.

[0027] (2) The advanced steel mesh is set as a sheet structure and a roll structure. The roll structure is elastically stretched outside the tunnel base in the leading area and elastically contacts and supports the tunnel base. The above structure effectively fills the outer space of the leading area and effectively blocks the blasting vibration and shock wave of the next cycle. The elastic structure setting effectively avoids the use of rigid structure support to transmit blasting vibration and impact, and reduces the problem of tunnel base falling off caused by this.

[0028] (3) Pre-reserved holes were set on the steel arch frame. The front end of the advanced support guide pipe was supported by the tunnel foundation at the working face, and the rear end was supported by the pre-reserved holes of the steel arch frame. Together with the advanced connecting steel bars, they supported the steel mesh. Wet concrete was sprayed on the surface of the steel mesh, the advanced connecting steel bars and the advanced support guide pipe to form a solid integrated advanced support structure, which avoids the problem of the steel mesh falling off during use and during the next ring blasting vibration, thus improving construction safety.

[0029] (4) The tunnel front support structure provided does not require a grout stop wall structure. All required materials are easy to select and manufacture. The size of the advanced steel mesh roll is easy to adjust flexibly according to the space size of the front area and can be completed on site. It is highly flexible and convenient for on-site construction operations. Attached Figure Description

[0030] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. The accompanying drawings, which are included to provide a further understanding of the invention and constitute a part of this application, illustrate exemplary embodiments of the invention and, together with their descriptions, serve to explain the invention and do not constitute an undue limitation thereof.

[0031] Figure 1 This is a schematic diagram of the tunnel front support structure before the application of sprayed concrete, as provided by the present invention.

[0032] Figure 2 for Figure 1 A schematic diagram of the structure in the AA view direction.

[0033] Figure 3 for Figure 1 A schematic diagram of the structure supporting the advanced steel mesh at point C with the advanced connecting steel bars.

[0034] Figure 4 A schematic diagram of a structure in which pre-connected reinforcing bars are supported by a steel arch frame.

[0035] Figure 5 for Figure 1 A schematic diagram of the structure supporting the advanced steel mesh at point C with the advanced support guide pipe.

[0036] Figure 6 This is a schematic diagram showing the state after the advanced support guide tube is separated from the steel arch frame.

[0037] Figure 7 This is a schematic diagram of the tunnel front support structure after spraying concrete, as provided by the present invention.

[0038] Figure 8 The present invention provides a flowchart of a construction method for a tunnel front support structure.

[0039] Explanation of reference numerals in the attached diagram:

[0040] 1-Front steel arch frame; 11-Reserved hole; 2-Rear steel arch frame; 3-Advanced connecting steel bars; 31-First steel bar segment; 32-Second steel bar segment; 4-Advanced steel bar mesh; 5-Advanced steel bar mesh roll; 6-Advanced support guide pipe; 7-Advanced support concrete layer; 8-Excavation outline; 9-Front edge area; 10-Working face. Detailed Implementation

[0041] In gravity-induced detachment strata such as inlaid structures, slip zones, loose, low-strength, and water-rich formations, even with smooth blasting, over-excavation and excessive longitudinal advance are common. Conventional initial support methods only involve shotcreting concrete between the steel arch frames, leaving the tunnel walls in the arch area between the first steel arch frame and the tunnel face exposed. With each subsequent blast, the cavities continue to develop and deteriorate. Under the combined effects of the blast vibrations and shock waves from the next cycle, airflow emerges through the damping holes in the surrounding boreholes, creating airflow within the remaining void between the first steel arch frame and the surrounding rock at the arch level. This exacerbates gravity-induced detachment of the surrounding rock in the leading area and continuously increases the arch span of the longitudinal arch in the next cycle. This cycle repeats itself, with over-excavation increasing with each subsequent blast. Current methods are only applicable when the design includes pre-support with small guide pipes, and they limit the connection between the frontal area and the grout stop wall. When the design does not include a grout stop wall, the frontal area is usually left untreated. When the design does not include pre-support measures such as small guide pipes, the steel arch frame is usually not pre-drilled, limiting the timeliness of support in the frontal area when encountering weak and fractured strata. Furthermore, in cases of severe over-excavation, shotcrete does not adhere well, resulting in significant voids behind the initial support. Additionally, the inner steel mesh is difficult to fix and is prone to falling off and causing injury.

[0042] To address this, the present invention provides a tunnel front support structure and construction method, comprising a steel arch frame, pre-connecting reinforcing bars, and pre-reinforcing bar mesh. The steel arch frame includes a front steel arch frame and a rear steel arch frame arranged side-by-side. The pre-connecting reinforcing bars are arranged along the steel arch frame and extend obliquely upwards into the front support area near the tunnel face. The front end of the pre-connecting reinforcing bars is supported by the tunnel matrix at the tunnel face, the middle is supported by the front steel arch frame, and the rear end is supported and connected to the rear steel arch frame. The pre-reinforcing bar mesh is placed on top of the front support area and supported by the pre-connecting reinforcing bars. The surfaces of the pre-reinforcing bar mesh and the pre-connecting reinforcing bars are sprayed with a pre-support concrete layer. This tunnel front support structure and construction method can fill the front support area at the tunnel face, provide effective support and protection for the tunnel matrix in the front support area, prevent gravity-induced rockfall caused by the next blasting cycle, and thus avoid further expansion of over-excavation in the front support area.

[0043] The specific embodiments of the present invention will now be described in detail 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 them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use.

[0044] like Figure 1 and Figure 2 As shown, the present invention provides a tunnel front support structure, including a steel arch frame, advance connecting steel bars 3, and advance steel mesh; the steel arch frame includes a front steel arch frame 1 and a rear steel arch frame 2 arranged side by side, the front steel arch frame 1 being arranged close to the tunnel face 10, and the rear steel arch frame 2 being arranged at intervals from the front steel arch frame 1; the advance connecting steel bars 3 are arranged along the steel arch frame and extend obliquely upwards into the front area 9 near the tunnel face 10, the front end of the advance connecting steel bars 3 is supported by the tunnel matrix of the tunnel face 10, the middle is supported by the front steel arch frame 1, and the rear end is supported and connected to the rear steel arch frame 2; the advance steel mesh is set at the top of the front area 9 and supported by the advance connecting steel bars 3; as shown Figure 7 As shown, the surfaces of the advanced steel mesh and the advanced connecting steel bars 3 are sprayed with an advanced support concrete layer 7.

[0045] The provided tunnel front support structure uses front and rear steel arches arranged side-by-side near the tunnel face to support the advanced connecting steel bars. The front ends of the advanced connecting steel bars extend into the front area and support the advanced steel mesh, forming an advanced support structure. This structure effectively supports the tunnel foundation surrounding the front area, reducing the impact of the superposition of blasting vibrations and shock waves from the next cycle on the tunnel foundation surrounding the front area. This avoids further over-excavation problems caused by subsequent blasting excavation. The provided tunnel front support structure does not require a grout stop wall structure, and the selection and fabrication of various required materials are convenient, facilitating on-site construction operations.

[0046] like Figure 3 and Figure 4 As shown, further, the advanced connecting steel bar 3 includes a first steel bar segment 31 and a second steel bar segment 32 that overlap. Specifically, the advanced connecting steel bar is embedded between two steel arch frames. The advanced connecting steel bar is tied with two steel bars. The length of the first steel bar segment 31 is greater than the length of the second steel bar segment 32 and their front ends are aligned. The overlap section of the first steel bar segment 31 and the second steel bar segment 32 is set in the front edge area 9 and supported by the tunnel matrix of the front steel arch frame 1 and the tunnel face 10. The first steel bar segment is set between the front steel arch frame 1 and the rear steel arch frame 2 and supported by the rear steel arch frame 2. The rear end of the first steel bar segment abuts against the upper flange of the rear steel arch frame, and the front ends of the first steel bar segment and the second steel bar segment abut against the tunnel face. The advanced connecting steel bar is tied to the steel arch frame.

[0047] This structure, in which the first and second steel reinforcement segments overlap to form an advanced connecting reinforcement, uses the overlapping form of the first and second steel reinforcement segments in the frontal area. This structure provides stable support for the steel mesh in the frontal area, forming a robust frontal support structure. When the rear end requires less support, the first steel reinforcement segment is used for independent support. This not only meets the support needs of the frontal support but also saves on steel reinforcement, reduces the weight of the entire frontal support structure, and thus reduces the load on the steel arch frame. The structure is simple and easy to fabricate on site.

[0048] like Figure 5 and Figure 6 As shown, in some preferred embodiments, an advanced support conduit 6 is also included. The front end of the advanced support conduit 6 extends obliquely upward into the hole in the working face 10, and the rear end is supported through the reserved hole 11 of the front steel arch frame 1. The advanced connecting steel bars 3 are at the same height as the advanced support conduit 6, and the advanced steel mesh is supported by the advanced connecting steel bars 3 and the advanced support conduit 6. The advanced support conduit 6 and the advanced connecting steel bars 3 are spaced apart, and the spacing between the advanced support conduits 6 is greater than the spacing between the advanced connecting steel bars 3. Multiple advanced connecting steel bars 3 are provided between adjacent advanced support conduits 6.

[0049] This preferred structure features pre-drilled holes in the steel arch frame. The front end of the advanced support guide pipe is supported by the tunnel foundation at the tunnel face, and the rear end is supported by the pre-drilled holes in the steel arch frame. Together with the advanced connecting steel bars, they support the steel mesh. Wet concrete is sprayed onto the surfaces of the steel mesh, the advanced connecting steel bars, and the advanced support guide pipe to form a robust, integrated advanced support structure. This prevents the steel mesh from falling off during use or during the next blasting vibration, thus improving construction safety.

[0050] like Figure 3 and Figure 5As shown, in the above embodiments, preferably, the advanced reinforcing mesh includes advanced reinforcing mesh sheets 4, which cover the leading edge region and extend along the steel arch frame, with advanced connecting reinforcing bars 3 supporting the advanced reinforcing mesh sheets 4. Further, the advanced reinforcing mesh also includes advanced reinforcing mesh rolls 5, which fill the leading edge region 9 and extend along the steel arch frame. The outer side of the advanced reinforcing mesh roll 5 contacts the tunnel foundation support of the leading edge region 9, and the inner side is supported by the advanced connecting reinforcing bars 3. Moreover, multiple advanced reinforcing mesh rolls 5 are arranged in parallel, with the outermost rolls contacting the tunnel foundation support of the leading edge region 9 and the innermost rolls supported by the advanced connecting reinforcing bars 3.

[0051] The advanced steel mesh is configured as sheet-like or rolled structures, with the rolled structures elastically extending outside the tunnel matrix in the leading edge area, providing elastic contact and support with the tunnel matrix. This structure effectively fills the surrounding space of the leading edge area, effectively blocking the blasting vibrations and shock waves of the next cycle. The elastic structure effectively avoids the use of rigid structures to support and transmit blasting vibrations and impacts, reducing the risk of tunnel matrix detachment. Furthermore, the size of the advanced steel mesh rolls can be flexibly adjusted according to the space available in the leading edge area and can be fabricated on-site, offering high flexibility and facilitating on-site construction.

[0052] like Figure 8 As shown, based on the above embodiments, the present invention provides a construction method for a tunnel front support structure, including the following steps:

[0053] S100. After completing the excavation of one ring of the tunnel, remove the slag and locate the roof and sides;

[0054] S200. In specific implementation, when the over-excavation depth in the current area is >20cm, support is provided at the over-excavation location; steel arch frames are erected, with the front steel arch frame 1 close to the working face 10 and the rear steel arch frame 2 spaced apart from the front steel arch frame 1, and connecting steel reinforcement and steel mesh overlap are carried out between the front steel arch frame 1 and the rear steel arch frame 2.

[0055] S300. The advanced connecting steel bars 3 are arranged along the steel arch frame. The front end of the advanced connecting steel bars 3 extends obliquely upward into the front edge area 9 and is supported by the tunnel matrix of the front steel arch frame 1 and the tunnel face 10. The middle and rear ends are supported by the front steel arch frame 1 and the rear steel arch frame 2 respectively.

[0056] Preferably, the advanced connecting steel bar 3 includes a first steel bar segment 31 and a second steel bar segment 32 that are lapped together. The length of the first steel bar segment 31 is greater than the length of the second steel bar segment 32. The lapped section of the first steel bar segment 31 and the second steel bar segment 32 is located in the leading edge area and is supported by the tunnel matrix of the front steel arch frame 1 and the tunnel face 10. The individual segment of the first steel bar is located between the front steel arch frame 1 and the rear steel arch frame 2 and is supported by the rear steel arch frame 2. One end of the advanced connecting steel bar 3 abuts against the upper flange of the second steel arch frame, and the other end abuts against the tunnel face 10. The advanced connecting steel bar 3 is tied to the steel arch frame.

[0057] S400. Drill holes in the working face 10, and the advanced support guide tube 6 passes through the reserved hole in the steel arch frame and its front end enters the hole in the working face 10;

[0058] S500. An advanced steel mesh 4 and an advanced steel mesh roll 5, supported by advanced connecting steel bars 3 and / or advanced support conduit 6, are inserted on the outside of the advanced support in the leading area 9.

[0059] Preferably, the advanced steel mesh roll 5 is made by rolling steel mesh into a barrel shape, binding it with iron wire, installing it above the advanced connecting steel bar 3, and then cutting the iron wire until the advanced steel mesh roll 5 is stretched out and fills the front edge area 9.

[0060] When the over-excavation depth in the leading area is greater than 30cm, an outer pre-excavation steel mesh should be added outside the steel arch frame, and a pre-excavation steel mesh roll should be inserted into the leading area. The pre-excavation steel mesh roll is made by rolling the pre-excavation steel mesh into a barrel shape, binding it with iron wire, and cutting the iron wire after it is in place, until the pre-excavation steel mesh roll fills the leading area; when the over-excavation depth in the leading area is 20-30cm, it is not necessary to insert the pre-excavation steel mesh roll.

[0061] S600. The advanced support concrete layer 7 is wet-sprayed simultaneously in the leading area and the initial support to cover the advanced support. The advanced support guide pipe or advanced connecting steel bar of the advanced support structure is covered by the sprayed concrete in the leading area.

[0062] S700. Proceed to the next ring excavation. After the leading edge area is fully exposed, press the advanced support guide pipe 6 or the advanced connecting steel bar 3 into the outside of the last steel arch frame of the next ring.

[0063] S800. The connecting steel bars between the first steel arch frame of the previous ring and the last steel arch frame of the next ring are reinforced with steel mesh on the inside and wet sprayed concrete layer.

[0064] Based on the above embodiments, the tunnel front support structure and construction method provided by the present invention support the advanced connecting steel bars through parallel front and rear steel arches between the foremost steel arch and the tunnel face. The front end of the advanced connecting steel bars extends into the front area and supports the advanced steel mesh. Wet concrete is sprayed onto the surface of the steel mesh, the advanced connecting steel bars, and the advanced support guide pipe to form a solid integrated advanced support structure. This provides effective support for the tunnel foundation outside the front area, preventing the steel mesh from falling off during use and during the next blasting vibration, thus improving construction safety. This advanced support structure reduces the impact of the superposition of blasting vibration and shock waves from the next cycle on the tunnel foundation outside the front area, thereby avoiding further over-excavation problems caused by subsequent blasting excavation.

[0065] Furthermore, during implementation, the advanced steel mesh is set as a sheet structure or a roll structure. The choice of whether to use a roll structure steel mesh depends on the over-excavation depth in the leading area. The roll structure elastically extends outside the tunnel base in the leading area and elastically contacts and supports the tunnel base. The above structure effectively fills the outer space of the leading area and effectively blocks the blasting vibration and shock wave of the next cycle. The elastic structure setting effectively avoids the use of rigid structure support to transmit blasting vibration and impact, reducing the problem of tunnel base falling off as a result.

[0066] The provided tunnel front support structure does not require a grout stop wall structure, nor does it require connection between the front area and the grout stop wall. The selection and fabrication of various required materials are convenient, and the size of the advanced steel mesh rolls can be flexibly adjusted according to the space size of the front area and fabricated on-site, which facilitates on-site construction operations.

[0067] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. The above drawings and specific embodiments are for illustrative purposes only, and this invention is not limited thereto. Minor modifications to this invention within the inventive spirit and scope defined by the claims of this invention all fall within the protection scope of this invention.

Claims

1. A tunnel front support structure, characterized in that: Includes steel arch frame, advanced connecting steel bars (3) and advanced steel mesh; The steel arch frame includes a front steel arch frame (1) and a rear steel arch frame (2) arranged side by side. The front steel arch frame (1) is arranged close to the working face (10), and the rear steel arch frame (2) is arranged at intervals from the front steel arch frame (1). The advanced connecting steel bar (3) is arranged along the steel arch frame and its front end extends obliquely upward into the front edge area (9) near the working face (10). The front end of the advanced connecting steel bar (3) is supported by the tunnel matrix of the working face (10), the middle is supported by the front steel arch frame (1), and the rear end is supported and connected to the rear steel arch frame (2). The advanced steel mesh is set in the front edge area (9) and supported by the advanced connecting steel bar (3). The advanced steel mesh is set in sheet form and / or roll form to support the tunnel matrix in the front edge area. The surface of the advanced steel mesh and the advanced connecting steel bars (3) is sprayed with an advanced support concrete layer (7); the advanced steel mesh includes an advanced steel mesh roll (5), which is filled in the front edge area (9) and extends along the steel arch frame. The outer side of the advanced steel mesh roll (5) is in contact with the tunnel matrix support of the front edge area (9), and the inner side is supported by the advanced connecting steel bars (3). The advanced steel mesh roll (5) includes multiple rolls arranged in parallel. The outer advanced steel mesh roll (5) is in contact with the tunnel matrix support of the leading edge area (9), and the inner advanced steel mesh roll (5) is supported by advanced connecting steel bars (3).

2. The tunnel front support structure according to claim 1, characterized in that: It also includes an advanced support conduit (6), the front end of which extends obliquely upward into the hole of the working face (10), and the rear end is supported by the preset hole (11) of the front steel arch frame (1). The advanced connecting steel bar (3) is at the same height as the advanced support conduit (6), and the advanced steel mesh is supported by the advanced connecting steel bar (3) and the advanced support conduit (6).

3. The tunnel front support structure according to claim 2, characterized in that: The advanced support conduit (6) and the advanced connecting steel bars (3) are spaced apart. The spacing between the advanced support conduits (6) is greater than the spacing between the advanced connecting steel bars (3). Multiple advanced connecting steel bars (3) are provided between adjacent advanced support conduits (6).

4. The tunnel front support structure according to claim 1, 2, or 3, characterized in that: The advanced connecting steel bar (3) includes a first steel bar segment (31) and a second steel bar segment (32) that overlap. The overlap of the first steel bar segment (31) and the second steel bar segment (32) is set in the front edge area (9) and supported by the tunnel matrix of the front steel arch frame (1) and the tunnel face (10).

5. The tunnel front support structure according to claim 1, characterized in that: The advanced steel mesh includes an advanced steel mesh sheet (4), which covers the leading edge area and extends along the steel arch frame, and the advanced connecting steel bars (3) support the advanced steel mesh sheet (4).

6. A construction method for implementing the tunnel front support structure as described in claim 1, characterized in that, Including the following steps: S100. After completing the excavation of one ring of the tunnel, remove the slag and locate the roof and sides; S200. Construct steel arch frames, with the front steel arch frame (1) close to the working face (10) and the rear steel arch frame (2) spaced apart from the front steel arch frame (1). Reinforcing bars are used to reinforce the front steel arch frame (1) and the rear steel arch frame (2), and steel mesh is overlapped between them. S300. Arrange the advanced connecting steel bars (3) along the steel arch frame. The front end of the advanced connecting steel bars (3) extends obliquely upward into the front edge area (9) and is supported by the tunnel matrix of the front steel arch frame (1) and the tunnel face (10). The middle and rear ends are supported by the front steel arch frame (1) and the rear steel arch frame (2) respectively. S400. Drill holes in the working face (10), and advance support guide (6) passes through the reserved hole of the steel arch frame and the front end passes into the hole in the working face (10); S500. An advanced steel mesh (4) and an advanced steel mesh roll (5) supported by advanced connecting steel bars (3) and / or advanced support conduit (6) are placed on the outside of the advanced support in the leading area (9). S600. The front area and the initial support are simultaneously wet-sprayed with advanced support concrete layer (7) to cover the advanced support. S700. After the next ring is excavated and the front area is fully exposed, the advanced support guide pipe (6) or the advanced connecting steel bar (3) is pressed into the outside of the last steel arch frame of the next ring. S800. The connecting steel bars between the first steel arch frame of the previous ring and the last steel arch frame of the next ring are reinforced with steel mesh on the inside and wet sprayed concrete layer.

7. The construction method of the tunnel front support structure according to claim 6, characterized in that, Step S300 includes: the overlapping section of the first steel bar segment (31) and the second steel bar segment (32) of the advanced connecting steel bar (3) is set in the front edge area and supported by the tunnel matrix of the front steel arch (1) and the tunnel face (10); the individual segment of the first steel bar segment is set between the front steel arch (1) and the rear steel arch (2) and supported by the rear steel arch (2).

8. The construction method of the tunnel front support structure according to claim 6 or 7, characterized in that, Step S500 includes: the advanced steel mesh roll (5) is made by rolling steel mesh into a barrel shape, binding it with iron wire, installing it above the advanced connecting steel bar (3), and then cutting the iron wire until the advanced steel mesh roll (5) is stretched out and fills the front edge area (9).

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