A method for enlarging tunnel excavation step

Abstract

The present invention provides a method for expanding the step distance of tunnel excavation, comprising the following steps: S1, excavating multiple peripheral sections along the tunnel section as the excavation of the tunnel face proceeds; S2, setting a support structure in the peripheral section, fixing a first steel arch frame to the surrounding rock by an anchor, and connecting adjacent first steel arch frames by longitudinal steel bars; S3, hanging a steel mesh on the plurality of first steel arch frames and spraying concrete; S4, performing initial support along the tunnel face according to the tunnel construction design, connecting the first steel arch frame and the corresponding second steel arch frame by a plurality of connectors; S5, performing secondary lining according to the tunnel construction design; the distance between the peripheral section close to the secondary lining and the secondary lining and the invert arch is less than the safe step distance, and the distance between two adjacent peripheral sections is less than the safe step distance, thereby expanding the excavation step distance, providing sufficient working space for the construction of each process, and ensuring that the deformation of the surrounding rock is basically completed; S6, repeating steps S1-S5 to perform construction until the tunnel is completed.

Description

Technical Field

[0001] The present invention relates to the technical field of tunnel engineering, and in particular to a method for enlarging the step distance of tunnel excavation. Background Art

[0002] The tunnel excavation step distance mainly refers to the distance between the tunnel face and the invert arch and secondary lining. In the New Austrian Tunneling Method (NATM) tunnel construction method, the safety of the tunnel construction process is controlled by setting a safe step distance. The safe step distances corresponding to common surrounding rock grades are: the distance between the invert arch of surrounding rock of grade 5 and above and the tunnel face shall not be greater than 40 meters, the distance between the invert arch of surrounding rock of grade 4 and the tunnel face shall not be greater than 50 meters, the distance between the invert arch of surrounding rock of grade 3 and the tunnel face shall not exceed 90 meters, the distance between the secondary lining of surrounding rock of grade 1 and 2 and the tunnel face shall not exceed 200 meters, the distance between the secondary lining of surrounding rock of grade 3 and the tunnel face shall not exceed 120 meters, the distance between the secondary lining of surrounding rock of grade 4 and the tunnel face shall not exceed 90 meters, and the distance between the secondary lining of surrounding rock of grade 5 and above and the tunnel face shall not exceed 70 meters.

[0003] As the face is excavated, the initial support stiffness is low, and sections without secondary lining are formed as "long beams." As bending moments increase, failure to adhere to safe stepover specifications can lead to tunnel collapse accidents, posing significant safety risks during tunnel construction. However, adhering to safe stepover specifications also presents operational challenges. From a spatial perspective, face excavation precedes secondary lining construction, with invert construction situated between the two. These three key tunnel construction processes require sufficient space for efficient and orderly execution. Controlling safe stepover significantly reduces this available space, creating spatial interference between the various processes, hindering construction organization and management and impacting progress. From a tunnel design safety perspective, the New Austrian Tunneling Method (NATM) design concept uses the surrounding rock deformation rate and deformation as dual control indicators, aiming to maximize the surrounding rock's self-supporting capacity within a controllable deformation range. The secondary lining primarily serves as a safety reserve, subject to minimal or no stress. When the safety step distance requirements are implemented, the surrounding rock of the secondary lining section may still be in a continuous deformation process, and the surrounding rock pressure it bears will be relatively large, which may cause the secondary lining to deform, crack and fall off, increase operation and maintenance costs and trip safety risks. Therefore, how to increase the excavation step distance while ensuring safe construction, ensure sufficient working space for each process, delay the timing of secondary lining construction, and ensure that the surrounding rock deformation is basically completed has become an urgent problem that needs to be solved. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for expanding the step distance of tunnel excavation, which solves the problems that as the face is excavated, the initial support stiffness is low, and a "long beam" is formed in the section without secondary lining. As the bending moment increases, if the safety step distance specifications are not implemented, tunnel collapse accidents may occur.

[0005] The embodiment of the present invention is achieved through the following technical solution: A method for expanding the step distance of tunnel excavation, comprising the following steps:

[0006] S1. As the excavation of the tunnel face proceeds, a plurality of peripheral sections are excavated along the tunnel section, wherein the plurality of peripheral sections are arranged at intervals;

[0007] S2. Setting a support structure in the external section, the support structure comprising at least five first steel arches, the first steel arches being fixed to the surrounding rock by anchors, and adjacent first steel arches being connected by longitudinal reinforcements;

[0008] S3. Hanging steel mesh on the first steel arches and spraying concrete;

[0009] S4. Performing initial support along the tunnel face according to the tunnel construction design, wherein the initial support comprises supporting the entire tunnel through a plurality of second steel arches, and connecting the first steel arches with corresponding second steel arches through a plurality of connectors;

[0010] S5. Carry out secondary lining according to the tunnel construction design, i.e., cast concrete or reinforced concrete lining is constructed inside the primary support, which together with the primary support forms a composite lining;

[0011] The distances between the external section close to the secondary lining and the secondary lining and the inverted arch are all less than the safe step distance, and the distance between two adjacent external sections is less than the safe step distance;

[0012] S6. Repeat steps S1-S5 to continue construction until the tunnel is completed.

[0013] Furthermore, the excavation of the peripheral section is implemented by adjusting the excavation profile of the tunnel face.

[0014] Furthermore, in step S2, the anchoring piece is a hollow grouting anchor rod, and the hollow grouting anchor rod is continuously arranged along the first steel arch frame.

[0015] Furthermore, in step S3, the sprayed concrete is steel fiber concrete.

[0016] Furthermore, in step S4, the connecting member includes two steel plates, which are respectively arranged on both sides of the first steel arch frame and the second steel arch frame, and the two steel plates are locked by screws and nuts.

[0017] Furthermore, an installation groove is excavated at a position corresponding to the peripheral section on the tunnel floor, a connecting bracket is arranged in the installation groove, and both ends of the connecting bracket are respectively connected to the arch feet of the second steel arch frame.

[0018] Furthermore, the connecting bracket includes two channel steels, the ends of the two channel steels that are away from each other are welded with a fork joint, and the ends of the two channel steels that are close to each other are socketed with each other, and the socket joint is fixed by bolts.

[0019] Furthermore, two adjacent connecting brackets are connected by a plurality of cross-arranged connecting steel bars.

[0020] The technical solutions of the embodiments of the present invention have at least the following advantages and beneficial effects:

[0021] The present invention provides a method for expanding the step distance of tunnel excavation. As the excavation operation of the tunnel face proceeds, an external section is excavated, and a support structure is set in the external section. The support structure in the external section is combined with the initial support originally designed for tunnel construction to form a reinforced support section in the initial support section, thereby solving the problem that the bending moment of the "long beam" is large and collapse accidents are prone to occur. The method increases the allowable distance between the tunnel face and the secondary lining and the invert arch, delays the timing of secondary lining application, provides sufficient working space for the construction of each process, is beneficial to construction organization and management, and improves tunnel excavation efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 A construction flow chart of a method for enlarging tunnel excavation step distance provided by the present invention;

[0024] Figure 2 Schematic diagram of the positional relationship between the tunnel face, secondary lining, and peripheral sections in an embodiment of the present invention;

[0025] Figure 3 Schematic diagram of the positional relationship between the first steel arch frame, the second steel arch frame and the connecting bracket in an embodiment of the present invention;

[0026] Figure 4 Schematic diagram of the structure of the steel arches and connecting brackets in the peripheral section in an embodiment of the present invention;

[0027] Figure 5 This is a schematic structural diagram of a portion of the steel arch frame and the connecting bracket in the external section in an embodiment of the present invention;

[0028] Figure 6 This is a schematic structural diagram of the connecting brackets connected as a whole in an embodiment of the present invention;

[0029] Figure 7 Schematic diagram of the structure of a fork joint in an embodiment of the present invention;

[0030] Wherein the longitudinal reinforcement, anchors, steel mesh, connectors are conventional structural members, not shown in the drawings;

[0031] 11. First steel arch frame; 21. Second steel arch frame; 30. Connecting bracket; 31. Fork joint; 311. Clamp; 312. Sleeve; 321. Through hole; 41. Connecting plate; 42. Connecting steel bar; 50. External section; 60. Initial support; 70. Installation groove; 80. Secondary lining. DETAILED DESCRIPTION

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0033] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort shall fall within the scope of protection of the present invention.

[0034] like Figure 1-7 As shown, the present invention provides a method for expanding the tunnel excavation pitch, comprising the following steps:

[0035] S1. As the excavation of the tunnel face proceeds, a plurality of peripheral sections 50 are excavated along the tunnel section, with the plurality of peripheral sections 50 being arranged at intervals;

[0036] S2. A support structure is provided in the external section 50. The support structure includes at least five first steel arches 11. The first steel arches 11 are fixed to the surrounding rock through anchors. Adjacent first steel arches 11 are connected by longitudinal steel bars.

[0037] S3, hanging steel mesh on the first steel arches 11 and spraying concrete;

[0038] S4. Providing initial support 60 along the tunnel face according to the tunnel construction design. The initial support 60 supports the entire tunnel through a plurality of second steel arches 21 , and a plurality of connectors connect the first steel arches 11 and the corresponding second steel arches 21 ;

[0039] S5. Carry out secondary lining 80 according to the tunnel construction design, i.e., cast concrete or reinforced concrete lining is applied inside the primary support 60, which together with the primary support 60 forms a composite lining;

[0040] The distances between the external section 50 close to the secondary lining 80 and the secondary lining 80 and the inverted arch are all less than the safe step distance, and the distance between two adjacent external sections 50 is less than the safe step distance;

[0041] S6. Repeat steps S1-S5 to continue construction until the tunnel is completed.

[0042] In addition to the above steps, conventional tunnel excavation construction can be carried out according to the tunnel design. It should be noted that the excavation of the external section 50 is generally carried out together with the excavation of the tunnel face.

[0043] The excavation of the external section 50 is along the tunnel cross section, and a accommodating cavity is formed in the interval for constructing the first steel arch frame 11. In fact, it is equivalent to over-excavating a part based on the original designed excavation outline, erecting a row of first steel arch frames 11, and the initial support 60 of the original tunnel excavation design is constructed as usual. Generally speaking, the model of the first steel arch frame 11 is larger than the second steel arch frame 21. After the first steel arch frame 11 is erected, the steel mesh is hung and concrete is sprayed to further improve stability; the excavation position of the external section 50 is mainly selected according to the safe step distance, ensuring that the distance between the external section 50 close to the secondary lining 80 and the secondary lining 80 and the inverted arch is less than the safe step distance, and the distance between two adjacent external sections 50 is less than the safe step distance. At the same time, the connection with the initial support 60 also needs to be considered. Taking the fifth-level surrounding rock as an example, the safe step distance is set to be less than 40 meters between the heading face and the inverted arch, and less than 40 meters between the heading face and the secondary lining 80. 70 meters, the designed steel arch spacing is 80 centimeters, and 5 steel arch frames are set in the external section 50, then the excavation width of the external section 50 is 4 meters. Of course, the actual excavation width will be slightly wider to facilitate construction operations; regarding the selection of the position of the external section 50, it can be set within the allowable range based on the results of advanced geological prediction, geological survey, etc. For example, if the surrounding rock state near the current tunnel face is good and there is a trend of improvement in the excavation direction, then the setting distance value of the external section 50 can be taken as the extreme value, that is, the distance between the external section 50 and the invert is 40 meters, and the distance between the external section 50 and the secondary lining 80 is 70 meters, whichever is reached first. If the surrounding rock state near the tunnel face is poor and there is a trend of deterioration, then the setting distance value of the external section 50 can be appropriately reduced, that is, the distance between the external section 50 and the invert is 30 meters, and the distance between the external section 50 and the secondary lining 80 is 55 meters, whichever is reached first.

[0044] It should also be noted that the addition of the external section 50 and the addition of the support structure will inevitably increase the construction cost, such as the cost of earth and stone formed by the excavation of the external section 50, the cost of steel arch frames, steel mesh, etc. However, it is understandable that the external section 50 is set at intervals, and the number of steel arch frames erected is generally 5-8. The increase in cost is acceptable compared to the impact of conventional construction on project progress, construction organization and management, etc. To make a simple understanding, if the current excavation step has reached the limit of the safe step, then the excavation of the heading face needs to be stopped to wait for the construction of the invert arch and the secondary lining 80, which will directly affect the excavation progress and will also cause idle work. Therefore, the way of strengthening the support of the external section 50 can be generally understood as "losing sesame seeds and picking up watermelons."

[0045] Through the implementation of this solution, the tunnel face does not need to be shut down due to the inability to keep up with the construction of the invert arch and the secondary lining 80. The excavation step is expanded, and the construction environment of the invert arch and the secondary lining 80 is better, which is conducive to construction organization and thus forms a virtuous circle.

[0046] As a preferred solution, this solution differs from the above solution in that eight steel arch frames are provided in the external section 50 .

[0047] As a preferred solution, the excavation of the peripheral section 50 is implemented by adjusting the excavation profile of the face, that is, during the face excavation operation, over-excavation is performed by conventional means such as adjusting the blasthole angle. The principle is the same as that of conventional tunnel excavation and will not be elaborated here. The peripheral section 50 is then excavated without having to excavate the peripheral section 50 separately, thereby reducing construction procedures and improving excavation efficiency.

[0048] As a preferred solution, in step S2, hollow grouting anchor rods are used as anchor pieces, and the hollow grouting anchor rods are continuously arranged along the first steel arch frame 11. Taking the fifth-level surrounding rock as an example, a three-step excavation method is adopted, and a steel arch frame consists of 5 or 7 sections. After the excavation of the first step is completed, hollow grouting anchor rods are set at the arch foot as locking anchor rods. In addition, multiple system anchor rods are set along the arch frame, and corresponding anchor pieces are set after the excavation of the corresponding second and third steps is completed. The use of hollow grouting anchor rods can consolidate broken rock mass, improve rock mass, isolate groundwater and prevent corrosion of the rod body. Compared with solid anchor rods, better stiffness and shear strength can be obtained, further ensuring the stability of the external section 50.

[0049] As a preferred solution, in step S3, the sprayed concrete uses steel fiber concrete, a novel multiphase composite material formed by incorporating randomly distributed short steel fibers into ordinary concrete. These randomly distributed steel fibers effectively inhibit the expansion of microcracks within the concrete and the formation of macrocracks, significantly improving the concrete's tensile, flexural, impact, and fatigue resistance, resulting in good ductility. Spraying steel fiber concrete within the peripheral section 50 improves the integrity of the support structure within the peripheral section 50, thereby enhancing the support effectiveness.

[0050] As a preferred solution, in step S4, the connecting member includes two steel plates, which are locked together by screws and nuts. The two steel plates are respectively arranged on opposite sides of the first steel arch frame 11 and the second steel arch frame 21. Screw holes are provided at opposite positions of the two steel plates, through which screws are inserted and locked by nuts, thereby binding the first steel arch frame 11 and the second steel arch frame 21 together. Five connecting members are generally provided, namely, at the arch crown, arch waist, and arch foot. The steel plates can also be connected to the first steel arch frame 11 and the second steel arch frame 21 by welding.

[0051] It is understandable that the purpose of setting up the external section 50 is to solve the problem of forming a "long beam" in the section where the secondary lining 80 is not constructed, which increases the bending moment and has the risk of collapse. It is equivalent to providing support in the middle section of the "long beam", and the "long beam" becomes a "short beam", and its collapse risk is greatly reduced. In the above scheme, hollow grouting anchor rods, sprayed steel fiber concrete and the first steel arch frame 11 and the second steel arch frame 21 are connected. Through the support effects of each of them, the overall support effect is enhanced by superposition, and the excavation step distance is expanded while ensuring safety.

[0052] As a preferred solution, an installation groove 70 is excavated at a position corresponding to the external section 50 on the tunnel ground, and a connecting bracket 30 is arranged in the installation groove 70. The two ends of the connecting bracket 30 are respectively connected to the arch feet of the second steel arch frame 21. The excavation of the installation groove 70 can be carried out together with the excavation of the heading face. In order to cooperate with the installation of the connecting bracket 30, when excavating the external section 50, a small section of about 20 cm is dug downward at the arch foot. The corresponding excavation depth of the installation groove 70 is 20 cm. Then the first steel arch frame 11 and the second steel arch frame 21 corresponding to the first steel arch frame 11 are also extended by 20 cm and extend into the installation groove 70.

[0053] By providing the connecting bracket 30, the steel arch frame in the peripheral section 50 forms a closed loop, thereby enhancing the force-bearing capacity of the steel arch frame, especially the inward pressure of the rock wall, thereby further improving the support effect and ensuring the stability of the entire primary support section.

[0054] As a preferred solution, the connecting bracket 30 includes two channel steels, one end of the channel steel is welded with a fork joint 31, and the other end is socketed with another channel steel. The socket joint is connected by bolts, and the plug joint includes a socket head 312 matching the channel steel and a clamp head 311 matching the second steel arch frame 21.

[0055] The connecting bracket 30 is connected to the second steel arch frame 21 by abutting, and the fork joints 31 at one end of the two channel steels are respectively clamped at the two arch frame arch feet of the second steel, and the other ends of the two channel steels are connected to each other. In the specific implementation, the two channel steels are put together upside down, one right and the other upside down, and connected by bolts near the connecting sections of the two channel steels. Specifically, through holes 321 can be opened at relative positions on both side walls of the channel steel, and bolts can be inserted to lock them.

[0056] There will be a slight positional deviation in the installation of steel arch frames at different positions. This is due to factors such as differences in contour excavation and irregularities in the rock wall surface. Therefore, the distance between the arch feet of the first steel arch frames 11 at different positions will have a slight deviation, and the connecting bracket 30 is made according to the average distance. A plurality of continuous through holes 321 are set at the socket ends of the two channel steels to adjust the overall length after the two channel steels are connected to each other. During the specific construction process, on the one hand, a rough length adjustment is made by adjusting the connection position of the two channel steel sockets. On the other hand, a pad can be set in the clamp 311 of the fork joint 31 to ensure that the fork joint 31 is tightly pressed against the second steel arch frame 21.

[0057] When the external section 50 needs to be constructed into an inverted arch, the connecting bracket 30 can be removed and reused. Generally speaking, setting two external sections 50 between the tunnel face and the secondary lining 80 can meet the space requirements of each construction process. Only two sets of connecting brackets 30 need to be made to meet the recycling of tunnel construction, which can save costs and reduce inventory space.

[0058] As a preferred solution, two adjacent connecting brackets 30 are connected by cross-arranged connecting steel bars 42, and two groups of cross-arranged steel bars are arranged between each two connecting brackets 30, and each group of steel bars is connected to adjacent channel steels. Specifically, each connecting bracket 30 is composed of two channel steels, and two connecting heads are arranged at intervals on each channel steel. The connecting head includes two symmetrically arranged connecting plates 41, and the two connecting plates 41 are locked on the channel steel by bolts. The two ends of the steel bars are respectively connected to the connecting heads of the two adjacent channel steels to form a cross structure, thereby connecting the connecting brackets 30 as a whole. It should be understood that the first steel arches 11 are connected by longitudinal steel bars, and the second steel arches 21 of the original design initial support 60 are also connected by longitudinal steel bars. The connecting bracket 30 abuts the second steel arch 21 and is connected by cross-arranged connecting steel bars 42. In this way, the support structure in the external section 50 and the installation groove 70 forms a closed whole, which greatly improves the support effect of the external section 50 on the surrounding rock, thereby ensuring the stability of the entire initial support section after the excavation step is expanded.

[0059] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for enlarging the step distance of tunnel excavation, characterized in that: The following steps are involved: S1, as the excavation of the tunnel face proceeds, a plurality of peripheral sections (50) are excavated along the tunnel section, wherein the plurality of peripheral sections (50) are arranged at intervals; S2. A support structure is provided in the external section (50), wherein the support structure comprises at least five first steel arch frames (11), wherein the first steel arch frames (11) are fixed to the surrounding rock through anchors, and adjacent first steel arch frames (11) are connected through longitudinal steel bars; S3, hanging steel mesh on the first steel arches (11) and spraying concrete; S4, performing initial support (60) along the tunnel face according to the tunnel construction design, wherein the initial support (60) supports the entire tunnel through a plurality of second steel arch frames (21), and the first steel arch frames (11) and the corresponding second steel arch frames (21) are connected by a plurality of connecting members; S5. Perform secondary lining (80) according to the tunnel construction design, i.e., cast concrete or reinforced concrete lining is applied inside the primary support (60), and together with the primary support (60), a composite lining is formed; The distances between the peripheral section (50) close to the secondary lining (80) and the secondary lining (80) and the inverted arch are all less than the safe step distance, and the distance between two adjacent peripheral sections (50) is less than the safe step distance; S6. Repeat steps S1-S5 until the tunnel is completed. The excavation of the peripheral section (50) is carried out by adjusting the excavation profile of the tunnel face, that is, during the tunnel face excavation operation, over-excavation is carried out by adjusting the blasthole angle.

2. A method for enlarging tunnel excavation pitch according to claim 1, characterized in that: In step S2, the anchoring piece adopts a hollow grouting anchor rod, and the hollow grouting anchor rod is continuously arranged along the first steel arch frame (11).

3. The method for enlarging the tunnel excavation pitch according to claim 1, characterized in that: In step S3, steel fiber concrete is used as the sprayed concrete.

4. The method for enlarging the tunnel excavation pitch according to claim 1, characterized in that: In step S4, the connecting member comprises two steel plates, the two steel plates are respectively arranged on both sides of the first steel arch frame (11) and the second steel arch frame (21), and the two steel plates are locked by means of screws and nuts.

5. The method for enlarging the tunnel excavation pitch according to claim 1, characterized in that: An installation groove (70) is excavated at a position corresponding to the peripheral section (50) on the tunnel floor, a connecting bracket (30) is arranged in the installation groove (70), and both ends of the connecting bracket (30) are respectively connected to the arch feet of the second steel arch frame (21).

6. A method for enlarging tunnel excavation pitch according to claim 5, characterized in that: The connecting bracket (30) comprises two channel steels, with a fork joint (31) welded to one end of the two channel steels that are away from each other, and the other ends of the two channel steels that are close to each other being sleeved together, and the sleeve joint is fixed by bolts.

7. The method for enlarging the tunnel excavation pitch according to claim 6, characterized in that: Two adjacent connecting brackets (30) are connected via a plurality of cross-arranged connecting steel bars (42).

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