A two-step fast-closed tunnel support structure with an invert and its construction method

Abstract

The present invention provides a two-step fast-closed tunnel support structure with an inverted arch and a construction method thereof. The support structure includes a first layer of initial support, a second layer of initial support, a waterproof layer, and a secondary lining from the outside to the inside. The first layer of initial support includes a first layer of initial upper step support and a first layer of initial lower step support, and the second layer of initial support includes a second layer of initial upper step support and a second layer of lower step support. The construction method includes the following steps: installing an upper step advance support and an upper step advance reinforcement anchor rod; excavating an upper step tunnel body; installing a first layer of initial upper step support; excavating a lower step tunnel body; installing a first layer of initial lower step support; installing a long anchor rod of a lower step side wall and a long anchor rod of a tunnel bottom; installing a second layer of initial lower step support; installing a long anchor rod of an upper step side wall and a long anchor rod of a vault top; installing a second layer of initial upper step support; and performing invert casting and secondary lining casting. The present invention can reduce the safety risk in the construction process, and is both safe and fast.

Description

Technical Field

[0001] The invention relates to the technical field of tunnel construction, and in particular to a two-step fast-enclosed tunnel supporting structure with an invert and a construction method thereof. Background Art

[0002] Tunnels are engineering structures built underground and are widely used in transportation, mining, water conservancy, national defense and other fields. At present, tunnels are usually constructed using the New Austrian Tunneling Method. The support structure is a composite lining structure, which includes the arch, invert and side walls along the tunnel circumference, and the primary support on the outside, the secondary lining on the inside and the waterproof layer between the primary support and the secondary lining along the tunnel radial direction.

[0003] With the rapid development of tunnels and underground engineering in southwest my country, the number of mountain railway tunnels and extra-long tunnels has gradually increased, and the construction sections of tunnels crossing high ground stress and weak surrounding rock have also increased accordingly. Since high ground stress and soft rock large deformation tunnels are extremely difficult to control during construction, deformation and landslide disasters are easily found during construction, and some difficult problems will also arise in the design and later maintenance of tunnel structures. There are generally two ways to build tunnels in deep-buried squeezing soft rocks: "hard over hard" and "soft over hard". "Hard over hard" means setting up strong rigid support immediately after excavation to resist the strong ground squeezing force; "soft over hard" means setting up flexible support first after excavation, allowing the ground to deform to a certain extent, and then setting up rigid support after releasing ground stress. For these two support concepts, the corresponding technical means are: "rigid support" corresponding to strong surrounding rock pre-reinforcement, initial support heavy steel frame and early secondary lining, and "flexible support" corresponding to the use of retractable steel frame, pressure anchor rods, and stress release of advanced pilot holes. Obviously, the latter conforms to the principle of New Austrian Tunneling Method. However, the "rigid" and "flexible" mentioned here are two relative concepts. "Rigid" is intended to resist the stratum pressure after excavation unloading to the maximum extent, and "flexible" is intended to reasonably release the deformation of the surrounding rock and reduce the force acting on the support structure. However, the premise of "flexibility" is to ensure that the support structure does not fail. Once it fails, deformation and landslide disasters will occur. The support structure in the prior art adopts a method of directly and closely adhering to the surface of the tunnel passage to establish a rigid initial support. Under the high stress in the rock formation outside the tunnel passage, the concrete in the initial support often cracks and peels off, and the steel arch frame twists and deforms; the deformation of the steel arch frame will occupy the space for the next secondary lining, making it impossible to continue the secondary lining, so that the existing rigid initial support has to be dismantled and a new rigid initial support has to be rebuilt. This not only greatly increases the project cost and construction risk, but also greatly prolongs the construction period. Summary of the invention

[0004] The first object of the present invention is to provide a two-step fast-enclosed tunnel supporting structure with an invert.

[0005] The second object of the present invention is to provide a construction method for a two-step fast-enclosed tunnel support structure with an invert.

[0006] In order to achieve the above-mentioned first purpose, the present invention provides a two-step fast-closed tunnel support structure with an inverted arch, which includes a top arch, a bottom inverted arch and two side walls along the tunnel circumferential direction, and includes an outer first layer of initial support, an inner secondary lining and a waterproof layer arranged between the first layer of initial support and the secondary lining along the tunnel radial direction, wherein the waterproof layer includes a geotextile and a waterproof board; the first layer of initial support includes a first layer of initial upper step support and a first layer of initial lower step support; the first layer of initial upper step support includes a first upper step steel arch frame, a first layer of initial lower step support It includes a first lower step steel arch frame, and the first upper step steel arch frame and the first lower step steel arch frame are connected end to end to form a closed ring; the support structure also includes a second layer of initial support arranged between the first layer of initial support and the waterproof layer, and the second layer of initial support is arranged along the radial direction of the tunnel; the second layer of initial support includes a second layer of initial upper step support and a second layer of initial lower step support, the second layer of initial upper step support includes a second upper step steel arch frame, the second layer of initial lower step support includes a second lower step steel arch frame, and the second upper step steel arch frame and the second lower step steel arch frame are connected end to end to form a closed ring.

[0007] It can be seen from the above scheme that through the coordination of the first initial support and the second layer of initial support, the stress distribution around the tunnel can be effectively improved and the development of the surrounding rock crushing range can be reduced. It can effectively solve the limitations of the mechanized construction method of tunnels caused by adverse geological conditions such as high ground stress and large deformation of soft rocks, greatly reduce the safety risks in the tunnel construction process, and is safe, fast, economical and reasonable.

[0008] A further solution is that the first upper step steel arch frame includes a first side wall steel arch frame, a first top steel arch frame, and a second side wall steel arch frame connected in sequence; the first lower step steel arch frame includes a third side wall steel arch frame, a fourth side wall steel arch frame, a first bottom steel arch frame, a fifth side wall steel arch frame, and a sixth side wall steel arch frame connected in sequence; the first end of the third side wall steel arch frame is connected to the first side wall steel arch frame, the second end of the third side wall steel arch frame extends downward, and the fourth side wall steel arch frame is connected to the side of the first end of the third side wall steel arch frame; the first end of the sixth side wall steel arch frame is connected to the second side wall steel arch frame, the second end of the sixth side wall steel arch frame extends downward, and the fifth side wall steel arch frame is connected to the side of the first end of the sixth side wall steel arch frame.

[0009] A further solution is that the second upper step steel arch frame includes a first side wall steel support, a first top steel support, and a second side wall steel support connected in sequence; the second lower step steel arch frame includes a third side wall steel support, a first bottom steel support, and a fourth side wall steel support connected in sequence; the first side wall steel support is connected to the third side wall support, and the second side wall steel support is connected to the fourth side wall steel support.

[0010] It can be seen from the above scheme that by splitting the first upper step steel arch frame, the first lower step steel arch frame, the second upper step steel arch frame and the second lower step steel arch frame into multiple steel arch frames, mechanized construction transportation and storage are greatly facilitated.

[0011] A further solution is that a reserved deformation space is provided between the first layer of initial support and the second layer of initial support, and two reserved deformation spaces are provided between the second layer of initial support and the waterproof layer, and the reserved deformation amount of one reserved deformation space is greater than the reserved deformation amount of the second reserved deformation space.

[0012] It can be seen from the above scheme that by setting one reserved deformation space and two reserved deformation spaces, a retreat space is provided for the deformation of the surrounding rock, thereby ensuring the realization of the maximum allowable deformation of the surrounding rock in terms of space.

[0013] A further solution is that the first layer of initial upper step support also includes an arch anchor assembly, which includes a plurality of combined hollow anchors with exhaust devices, and the plurality of combined hollow anchors are arranged on the arch along the circumferential and longitudinal directions of the tunnel.

[0014] A further solution is that the support structure also includes a reinforcing anchor rod assembly, which includes a plurality of long arch anchor rods, a plurality of long upper step side wall anchor rods, a plurality of long lower step side wall anchor rods, and a plurality of long tunnel bottom anchor rods; the plurality of long arch anchor rods are arranged on the arch top along the circumferential and longitudinal directions of the tunnel, the plurality of long upper step side wall anchor rods are arranged on both side walls of the upper step of the tunnel along the circumferential and longitudinal directions of the tunnel, the plurality of long lower step side wall anchor rods are arranged on both side walls of the lower step of the tunnel along the circumferential and longitudinal directions of the tunnel, and the plurality of long tunnel bottom anchor rods are arranged on the bottom of the tunnel along the circumferential and longitudinal directions of the tunnel.

[0015] It can be seen from the above scheme that by arranging multiple anchor rods of different specifications in the tunnel ring direction, the deformation of the surrounding rock in the tunnel ring direction can be limited and constrained, the strength of the surrounding rock in the anchoring area can be increased, and tunnel collapse can be prevented.

[0016] In order to achieve the above-mentioned second purpose, the present invention provides a construction method for a two-step fast-closed tunnel support structure with an invert, which includes the following steps: installing upper step advance support and upper step advance reinforcement anchor rods; excavating the tunnel body of the upper step; installing the first layer of initial upper step support and spraying concrete; excavating the tunnel body of the lower step; installing the first layer of initial lower step support and spraying concrete; installing long anchor rods on the side walls of the lower step and long anchor rods on the tunnel bottom; installing the second layer of initial lower step support and spraying concrete, and backfilling the tunnel bottom; installing long anchor rods on the side walls of the upper step and long anchor rods on the arch top; installing the second layer of initial upper step support and spraying concrete; casting the invert and casting the invert filling; and casting the secondary lining.

[0017] It can be seen from the above scheme that this construction method adopts the method of double-layer support and long and short anchor groups. At the same time, combined with the advantages of tunnel mechanized construction equipment, it adopts a two-step belt arch rapid construction method to decompose the deformation of the large deformation tunnel into each construction link, and adopts a step-by-step control and rapid closure method to effectively control the total deformation of the surrounding rock, reduce the safety risks during tunnel construction, and achieve the purpose of safe, rapid, and economical tunnel construction.

[0018] A further solution is that the construction method also includes: judging whether the tunnel is opened, if not, while installing the long anchor rods of the upper step side walls and the long anchor rods of the arch, successively installing the upper step advance support and the upper step advance reinforcement anchor rods along the longitudinal direction of the tunnel, excavating the tunnel body of the upper step, installing the first layer of initial upper step support and spraying concrete, excavating the tunnel body of the lower step, installing the first layer of initial lower step support and spraying concrete, installing the long anchor rods of the lower step side walls and the long anchor rods of the tunnel bottom, installing the second layer of initial lower step support and spraying concrete and backfilling the tunnel bottom, forming a short step rapid closed loop to promote construction.

[0019] A further solution is that the upper step advance support includes multiple small advance grouting ducts, and the multiple small advance grouting ducts are arranged along the circumferential and longitudinal directions of the tunnel.

[0020] A further solution is that the upper step advance reinforcement anchor rods include a plurality of longitudinal anchor rods, and the plurality of longitudinal anchor rods are arranged on the working face of the upper step of the tunnel along the longitudinal direction of the tunnel. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic diagram of the cross section of the support structure according to the embodiment of the present invention.

[0022] Figure 2 It is a schematic cross-sectional view of the first layer of initial support and the second layer of initial support in an embodiment of the present invention.

[0023] Figure 3 It is a flow chart of the construction method of an embodiment of the present invention.

[0024] Figure 4 It is a schematic cross-sectional view of the support structure when executing step one, step two and step three of the construction method according to an embodiment of the present invention.

[0025] Figure 5 It is a schematic cross-sectional view of the support structure when executing step four, step five and step six of the construction method according to an embodiment of the present invention.

[0026] Figure 6 It is a schematic cross-sectional view of the support structure when executing step seven of the construction method according to an embodiment of the present invention.

[0027] Figure 7 It is a schematic cross-sectional view of the support structure when executing step eight of the construction method according to an embodiment of the present invention.

[0028] Figure 8 It is a schematic cross-sectional view of the support structure when executing step nine of the construction method according to an embodiment of the present invention.

[0029] Fig. 9 It is a schematic cross-sectional view of the support structure when executing step ten of the construction method according to an embodiment of the present invention.

[0030] Fig.10 It is a schematic cross-sectional view of the support structure when executing step eleven of the construction method according to an embodiment of the present invention.

[0031] The present invention is further described below in conjunction with the accompanying drawings and embodiments. DETAILED DESCRIPTION

[0032] See also Figures 1 to 2 , Figure 1 is a schematic cross-sectional view of a support structure according to an embodiment of the present invention, Figure 2 It is a cross-sectional schematic diagram of the first layer of initial support 1 and the second layer of initial support of an embodiment of the present invention. The support structure of this embodiment includes a top vault, a bottom invert and two side walls along the tunnel circumferential direction; along the tunnel radial direction, it includes an outer first layer of initial support 1, an inner secondary lining 3 and a waterproof layer arranged between the first layer of initial support 1 and the secondary lining 3, and the waterproof layer includes a geotextile and a waterproof board. The first layer of initial support 1 includes a first layer of initial upper step support and a first layer of initial lower step support. The first initial upper step support and the first layer of initial lower step support are divided up and down by the step dividing line of the tunnel. The first layer of initial upper step support includes a first upper step steel arch frame arranged above the step dividing line; the first layer of initial lower step support includes a first lower step steel arch frame arranged below the step dividing line. The first upper step steel arch frame and the first lower step steel arch frame are connected end to end to form a closed ring.

[0033] The support structure also includes a second layer of initial support arranged between the first layer of initial support 1 and the waterproof layer, and the second layer of initial support is arranged along the radial direction of the tunnel. The second layer of initial support includes a second layer of initial upper step support and a second layer of initial lower step support, and the second layer of initial upper step support includes a second upper step steel arch frame arranged above the step boundary line, and the second layer of initial lower step support includes a second lower step steel arch frame arranged below the step boundary line, and the second upper step steel arch frame and the second lower step steel arch frame are connected end to end to form a closed ring.

[0034] The first upper step steel arch frame includes a first side wall steel arch frame 11, a first top steel arch frame 12, and a second side wall steel arch frame 13 which are sequentially connected by a connecting steel frame, and the first side wall steel arch frame 11 and the second side wall steel arch frame 13 are symmetrically arranged on the left and right sides of the first top steel arch frame 12. The first lower step steel arch frame includes a third side wall steel arch frame 14, a fourth side wall steel arch frame 15, a first bottom steel arch frame 16, a fifth side wall steel arch frame 17, and a sixth side wall steel arch frame 18 which are sequentially connected by a connecting steel frame. The fourth side wall steel arch frame 15 and the fifth side wall steel arch frame 17 are symmetrically arranged on the left and right sides of the first bottom steel arch frame 16. The first end of the third side wall steel arch frame 14 is connected to the first side wall steel arch frame 11, the second end of the third side wall steel arch frame 14 extends downward, and the side of the first end of the third side wall steel arch frame 14 is connected to an end of the fourth side wall steel arch frame 15 away from the first bottom steel arch frame 16; the first end of the sixth side wall steel arch frame 18 is connected to the second side wall steel arch frame 13, the second end of the sixth side wall steel arch frame 18 extends downward, and the side of the first end of the sixth side wall steel arch frame 18 is connected to an end of the fifth side wall steel arch frame 17 away from the first bottom steel arch frame 16.

[0035] The second upper step steel arch frame includes a first side wall steel support, a first top steel support, and a second side wall steel support which are sequentially connected by a connecting steel frame, and the first side wall steel support and the second side wall steel support are symmetrically arranged on the left and right sides of the first top steel support. The second lower step steel arch frame includes a third side wall steel support 24, a first bottom steel support 25, and a fourth side wall steel support 26 which are sequentially connected by a connecting steel frame, and the third side wall steel support 24 and the fourth side wall steel support 26 are symmetrically arranged on the left and right sides of the first bottom steel support 25. The first side wall steel support is connected to the third side wall support by a connecting steel frame, and the second side wall steel support is connected to the fourth side wall steel support 26 by a connecting steel frame.

[0036] A reserved deformation space 4 is provided between the first layer of initial support 1 and the second layer of initial support, and two reserved deformation spaces 5 are provided between the second layer of initial support and the waterproof layer. The reserved deformation amount of the one reserved deformation space 4 is greater than the reserved deformation amount of the two reserved deformation spaces 5. In this embodiment, the reserved deformation amount of the one reserved deformation space 4 is preferably 30 cm, and the reserved deformation amount of the two reserved deformation spaces 5 is preferably 15 cm.

[0037] The first layer of initial upper step support also includes an arch anchor assembly, which includes a plurality of combined hollow anchors 6 with exhaust devices, and a plurality of combined hollow anchors 6 are arranged on the arch along the circumferential and longitudinal directions of the tunnel. The combined hollow anchors 6 are 3 meters long, and one combined hollow anchor 6 is applied at intervals of 1.2 meters in the circumferential direction, and one combined hollow anchor 6 is applied at intervals of 1.0 meters in the longitudinal direction.

[0038] The support structure also includes a reinforcement anchor assembly, which includes a plurality of arch long anchors 7, a plurality of side wall long anchors 8, and a plurality of tunnel bottom long anchors 9. The plurality of arch long anchors 7 are arranged on the arch along the circumferential and longitudinal directions of the tunnel. The plurality of side wall long anchors 8 are arranged on the side walls on both sides along the circumferential and longitudinal directions of the tunnel. The side walls on both sides include an upper step side wall and a lower step side wall respectively arranged on the upper and lower sides of the step boundary line. Correspondingly, the side wall long anchors 8 include an upper step side wall long anchor 8 and a lower step side wall long anchor 8. The upper step side wall long anchor 8 is arranged on the upper step side wall, and the lower step side wall long anchor 8 is arranged on the lower step side wall. The plurality of tunnel bottom long anchors 9 are arranged on the tunnel bottom along the circumferential and longitudinal directions of the tunnel. The arch long anchor 7 adopts a resin anchor with a diameter of 25 mm and a length of 6 m. A resin anchor is applied at intervals of 1.2 m in the circumferential direction, and a resin anchor is applied at intervals of 1.2 m in the longitudinal direction. The long anchor rods 8 of the side wall and the long anchor rods 9 of the tunnel bottom are self-propelled anchor rods with a diameter of 32 mm and a length of 8 m. A self-propelled anchor rod is installed at intervals of 1.2 m in the circumferential direction and at intervals of 1.0 m in the longitudinal direction.

[0039] The first layer of initial support 1 is composed of a shotcrete structure including a first layer upper step steel arch frame, a first layer lower step steel arch frame, a steel mesh, longitudinal connecting steel bars, connecting steel bars, and upper and lower step locking foot anchor pipes 10. The second layer of initial support is composed of a shotcrete structure including a second layer upper step steel arch frame, a second layer lower step steel arch frame, a steel mesh, longitudinal connecting steel bars, and connecting steel bars.

[0040] join Figures 3 to 10 The construction method of the two-step inverted rapid closed tunnel support structure of the present invention comprises the following steps:

[0041] In step S1, the upper step advance support and upper step advance reinforcement anchor are installed. First, a rock drill is used to drive an advance small conduit 20 with a diameter of 42 mm and a length of 4.5 m forward at a certain angle along the excavation outer contour line of the arch. The advance small conduit 20 is constructed as a loop connection according to the longitudinal 3m, and the two loops are longitudinally overlapped by 1.5m. The circumferential arrangement spacing of the advance small conduit 20 is 40cm. Then, grouting reinforcement is performed in the advance small conduit 20 with a certain pressure, and the grouting of the advance small conduit 20 needs to be full. Next, a rock drill is used to install an advance reinforcement anchor 30 on the upper step face. The advance reinforcement anchor 30 is preferably a glass fiber anchor, and the glass fiber anchor has a diameter of 22 mm and a length of 6 m. Multiple glass fiber anchors are divided into multiple horizontal rows and multiple vertical rows, each horizontal row is separated by 1.5 m, and each vertical row is separated by 1.5 m. For the convenience of operation, the horizontal auxiliary lines and the vertical auxiliary lines can be drawn on the upper step face according to the specifications of 1.5m horizontal spacing and 1.5m vertical spacing, and the horizontal auxiliary lines and the vertical auxiliary lines are staggered. Then, multiple intersections of the horizontal auxiliary lines and the vertical auxiliary lines are selected to construct the fiberglass anchor rods, so that the spacing between two adjacent fiberglass anchor rods is 3.0m in the horizontal direction and 3.0m in the vertical direction. The fiberglass anchor rods are connected and constructed in a cycle of 6m in the longitudinal direction.

[0042] Then, step S2 is executed to excavate the upper step of the tunnel. Specifically, a drilling trolley is used for drilling construction, and then a weak blasting method is used to excavate the upper step. During the excavation process, the arch is excavated first, and then the side wall is excavated. The advance per cycle does not exceed the spacing of 2 steel frames, that is, not more than 1.2m. After five excavations, a total of 6m is excavated. Before excavating the side wall, two locking foot anchor pipes 10 with a diameter of 42mm and a length of 4.5m are driven into the rock wall on both sides of the arch, and grouting is injected into the locking foot anchor pipes 10 to prevent the arch from shrinking or falling.

[0043] Then execute step S3, and install the first layer of initial upper step support closely following the upper step face. After excavating the upper step of the tunnel, the rock surface of the upper step is sprayed with concrete of 4 cm thickness in time. Then, a rock drilling trolley or anchor drilling machine is used to install a combined hollow anchor rod 6 with an exhaust device of 22 mm in diameter and 3 m in length on the arch of the tunnel and grout it fully. Two adjacent combined hollow anchor rods 6 are spaced 1.2 m in the circumferential direction and 1.0 m in the longitudinal direction. Then install the first layer of initial upper step steel arch frame. Before installing the first layer of initial upper step steel arch frame, first connect the first side wall steel arch frame 11, the first top steel arch frame 12, and the second side wall steel arch frame 13 in sequence. The first side wall steel arch frame 11 and the first top steel arch frame 12 are connected by a connecting steel frame, and the first top steel arch frame 12 and the second side wall steel arch frame 13 are connected by a connecting steel frame. Then install the first layer of initial upper step steel arch frame by a steel arch frame installation machine. Then install the steel frame mesh, and weld and fix the steel frame mesh, locking foot anchor pipe 10, etc. to the first layer of initial upper step steel arch frame, followed by re-spraying concrete, so that the total thickness of the initial spraying concrete and re-spraying concrete of the first layer of initial upper step support is 27 cm, and ensure that the whole is uniform and dense without voids at the back.

[0044] Then, step S4 is executed to excavate the lower step of the tunnel. First, a drilling trolley is used for drilling construction, and then the lower step is excavated by weak blasting. Each cycle is performed with a spacing of no more than 5 steel frames, that is, no more than 3m. After two excavations, a total of 6m is excavated to form a short step rapid construction with the upper step. When excavating the lower step, two locking foot anchor pipes 10 with a diameter of 42mm and a length of 4.5m are driven into the rock wall on both sides of the invert, and grouting is injected into the locking foot anchor pipes 10.

[0045] Then, step S5 is executed, and the first layer of initial lower step support is installed immediately after the lower step face. After the lower step of the tunnel is excavated, the rock surface of the lower step is sprayed with concrete of 4 cm in thickness in time. Then, a drilling rig or an anchor drill is used to install the long anchor rod 9 at the bottom of the tunnel and inject M20 cement slurry. The long anchor rod 9 of the tunnel preferably adopts a self-propelled anchor rod with a diameter of 32 mm and a length of 8 m, and a self-propelled anchor rod is installed at intervals of 1.2 m in the circumferential direction, and a self-propelled anchor rod is installed at intervals of 1.0 m in the longitudinal direction. Then, a drilling rig or an anchor drill is used to drill a guide hole on the bottom of the tunnel and grouting is performed through the orifice pipe 40 inserted into the guide hole. The depth of the guide hole is 3 m, and a guide hole is drilled at intervals of 1.5 m in the circumferential direction, and a guide hole is drilled at intervals of 2.5 m in the longitudinal direction. Subsequently, a steel arch frame installation machine is used to install the first layer of initial lower step support, so that the first layer of initial lower step support and the first layer of initial upper step support form a closed loop. Before installing the first layer of initial lower step support, first connect the third side wall steel arch frame 14, the fourth side wall steel arch frame 15, the first bottom steel arch frame 16, the fifth side wall steel arch frame 17, and the sixth side wall steel arch frame 18 through the connecting steel frame in sequence. Then install the steel frame mesh, and weld and fix the steel frame mesh, the locking foot anchor pipe 10, etc. to the first layer of initial upper step steel arch frame, and then spray concrete, so that the total thickness of the first layer of initial lower step concrete and the spray concrete is 27cm, and ensure that the whole is uniform and dense, and there is no void behind.

[0046] In step S6, the long anchor rods 8 of the side wall of the lower step and the long anchor rods 9 of the tunnel bottom are installed. Multiple long anchor rods 8 of the side wall are installed on the side walls of the lower step along the circumferential direction and longitudinal direction of the tunnel, and multiple long anchor rods 9 of the tunnel bottom are installed along the circumferential direction and longitudinal direction of the tunnel. The long anchor rods 8 of the side wall of the lower step and the long anchor rods 9 of the tunnel bottom are self-propelled anchor rods with a diameter of 32 mm and a length of 8 m. One self-propelled anchor rod is installed at intervals of 1.2 m in the circumferential direction, and one self-propelled anchor rod is installed at intervals of 1.0 m in the longitudinal direction.

[0047] Then, step S7 is executed to install the second layer of initial step-down support and sprayed concrete, and backfill the tunnel bottom. Before installing the second layer of initial step-down support, the third side wall steel support 24, the first bottom steel support 25, and the fourth side wall steel support 26 are connected in sequence by connecting the steel frame. After the first layer of initial support is initially stable, the second layer of initial step-down support is installed by the steel arch installation machine. Then, the steel mesh is installed, and the steel frame mesh is welded and fixed to the second layer of initial step-down steel arch, and concrete is sprayed, so that the thickness of the second layer of initial step-down support after spraying concrete is 25cm, and it is ensured that the whole is uniform and dense, and there is no void behind, that is, the concrete should completely fill the gap between the second layer of initial step-down support and the first layer of step-down support. Before the spraying concrete construction, after the second layer of initial support step-down steel arch is installed, the joints on both sides of the external leakage section are reserved and protective measures are taken before spraying concrete, that is, the joints are reserved at the third side wall steel arch 14 and the sixth side wall steel arch 18, and the reserved joints are taken Protective measures are taken before spraying concrete. After the second layer of initial support is installed, tunnel slag is used to backfill and compact the tunnel bottom.

[0048] Then, step S8 is executed to determine whether the tunnel is opened. If yes, only steps S9 to S12 are executed; if not, while steps S9 to S12 are executed for the previous construction section, steps S1 to S7 are executed for the next construction section, so as to form a short step and quickly close the loop according to a longitudinal cycle of 6m to advance the construction. The previous construction section and the next construction section are two adjacent construction sections. For the convenience of explanation, the previous construction section is named the first construction section, and the next construction section is named the second construction section.

[0049] In step S9, the long anchor rods 8 of the side walls of the upper step and the long anchor rods 7 of the vault are installed. Multiple long anchor rods 8 of the side walls of the upper step are installed on the side walls on both sides along the circumferential direction and longitudinal direction of the tunnel, and multiple long anchor rods 7 of the vault are installed on the vault along the circumferential direction and longitudinal direction of the tunnel. The long anchor rods of the side walls of the upper step are self-propelled anchor rods with a diameter of 32 mm and a length of 8 m. One self-propelled anchor rod is installed at intervals of 1.2 m in the circumferential direction, and one self-propelled anchor rod is installed at intervals of 1.0 m in the longitudinal direction. The long anchor rods of the vault are resin anchor rods with a diameter of 25 mm and a length of 6 m. One resin anchor rod is installed at intervals of 1.2 m in the circumferential direction, and one resin anchor rod is installed at intervals of 1.2 m in the longitudinal direction.

[0050] In order to further improve the integrity of the broken surrounding rock, the whole tunnel uses a rock drilling rig or anchor drilling rig to drill guide holes in the arch and side wall surrounding rock and inject grout through the orifice pipe 40 inserted into the guide hole. The depth of the guide hole is 3m, so that the grouting reinforcement is within 3m of the excavation contour line. The guide holes are spaced 1.5m apart in the circumferential direction and 2.5m apart in the longitudinal direction.

[0051] Then execute step S10, install the second layer of initial upper step support on the first construction section and spray concrete. Install the second layer of initial upper step support after the upper step of the second construction section is excavated 15 to 20m, and after the deformation of the first layer of initial support converges to 1 / 2 of the reserved deformation or the deformation does not reach 1 / 2 of the reserved deformation but has stabilized. A reserved deformation space is reserved between the second layer of initial upper step support and the first layer of initial upper step support, and the reserved deformation of the reserved deformation space is preferably 30cm. The second layer of initial support is arranged along the radial direction of the tunnel, and the second layer of initial support includes a second upper step steel arch frame. The second upper step steel arch frame includes a first side wall steel support 21, a first top steel support 22, and a second side wall steel support 23 connected in sequence. Before installing the second layer of initial support, first connect the first side wall steel support 21, the first top steel support 22, and the second side wall steel support 23 in sequence, and then install the second upper step steel arch frame through the steel arch frame installation machine, so that the second upper step steel arch frame and the second lower step steel arch frame form a closed ring. Then install the steel mesh and weld the steel mesh to the second layer of upper step steel arch frame firmly, and then spray concrete, so that the total thickness of the second layer of upper steps after spraying concrete is 25cm, and ensure that the whole is uniform and dense, and there is no void behind, that is, the concrete should completely fill the gap between the second layer of initial upper step support and the first layer of upper step support.

[0052] Then, step S11 is executed to cast the inverted arch and cast the inverted arch filling. After the second layer of initial support of the first construction section has supported a certain distance, and the convergence deformation data of the second layer of initial support in the closed loop section is evaluated to be stable, the inverted arch filling casting construction is carried out. First, the inverted arch formwork is installed, double-layer steel bars are placed, and C35 concrete is used for inverted arch casting. After the inverted arch casting is basically solidified, the inverted arch filling formwork is installed, and C20 concrete is used for filling casting.

[0053] Then execute step S12 to cast the secondary lining. Before casting the secondary lining, first lay a waterproof layer on the second layer of initial upper support, and the waterproof layer includes a geotextile and a waterproof board. Two reserved deformation spaces should be reserved between the waterproof layer and the second layer of initial support, or two reserved deformation spaces should be reserved between the second lining and the second layer of initial support, and the waterproof layer is contained in the two reserved deformation spaces. The reserved deformation amount of the two reserved deformation spaces is less than the reserved deformation amount of the one reserved deformation space. In this embodiment, the two reserved deformation amounts are 15cm. Then install the secondary lining formwork and put in double-layer steel bars, and then use C35 concrete to cast the secondary lining concrete, so that the total thickness of the secondary lining reaches 60cm. After the secondary lining is cast for a distance, after the deformation of the secondary lining is stable, the ditch cable trough formwork on both sides can be installed and the casting construction of the ditch cable trough can be carried out.

Claims

1. A two-step fast-closed tunnel support structure with an inverted arch, which includes a top arch, a bottom inverted arch and two side walls along the tunnel circumferential direction, and includes an outer first layer of primary support, an inner secondary lining and a waterproof layer arranged between the first layer of primary support and the secondary lining along the tunnel radial direction, wherein the waterproof layer includes a geotextile and a waterproof board, and is characterized in that: The first layer of initial support includes a first layer of initial upper step support, a first layer of initial lower step support and an arch anchor assembly; the first layer of initial upper step support includes a first upper step steel arch frame, the first layer of initial lower step support includes a first lower step steel arch frame, the first upper step steel arch frame and the first lower step steel arch frame are connected end to end to form a closed ring, and the arch anchor assembly includes a plurality of combined hollow anchors with exhaust devices, and the plurality of combined hollow anchors are arranged on the arch along the circumferential and longitudinal directions of the tunnel; The support structure also includes a second layer of initial support arranged between the first layer of initial support and the waterproof layer, the second layer of initial support being arranged along the radial direction of the tunnel; the second layer of initial support includes a second layer of initial upper step support and a second layer of initial lower step support, the second layer of initial upper step support includes a second upper step steel arch frame, the second layer of initial lower step support includes a second lower step steel arch frame, and the second upper step steel arch frame and the second lower step steel arch frame are connected end to end to form a closed ring; The support structure also includes a reinforcing anchor rod assembly, which includes a plurality of arch long anchor rods, a plurality of upper step side wall long anchor rods, a plurality of lower step side wall long anchor rods, and a plurality of tunnel bottom long anchor rods; the plurality of arch long anchor rods are arranged on the arch top along the circumferential and longitudinal directions of the tunnel, the plurality of upper step side wall long anchor rods are arranged on both side walls of the upper step of the tunnel along the circumferential and longitudinal directions of the tunnel, the plurality of lower step side wall long anchor rods are arranged on both side walls of the lower step of the tunnel along the circumferential and longitudinal directions of the tunnel, and the plurality of tunnel bottom long anchor rods are arranged on the tunnel bottom along the circumferential and longitudinal directions of the tunnel.

2. The support structure according to claim 1, characterized in that: The first upper step steel arch frame includes a first side wall steel arch frame, a first top steel arch frame, and a second side wall steel arch frame connected in sequence; the first lower step steel arch frame includes a third side wall steel arch frame, a fourth side wall steel arch frame, a first bottom steel arch frame, a fifth side wall steel arch frame, and a sixth side wall steel arch frame connected in sequence; the first end of the third side wall steel arch frame is connected to the first side wall steel arch frame, the second end of the third side wall steel arch frame extends downward, and the fourth side wall steel arch frame is connected to the side of the first end of the third side wall steel arch frame; the first end of the sixth side wall steel arch frame is connected to the second side wall steel arch frame, the second end of the sixth side wall steel arch frame extends downward, and the fifth side wall steel arch frame is connected to the side of the first end of the sixth side wall steel arch frame.

3. The support structure according to claim 1, characterized in that: The second upper step steel arch frame includes a first side wall steel support, a first top steel support, and a second side wall steel support connected in sequence; the second lower step steel arch frame includes a third side wall steel support, a first bottom steel support, and a fourth side wall steel support connected in sequence; the first side wall steel support is connected to the third side wall support, and the second side wall steel support is connected to the fourth side wall steel support.

4. The support structure according to any one of claims 1 to 3, characterized in that: A reserved deformation space is provided between the first layer of initial support and the second layer of initial support, and two reserved deformation spaces are provided between the second layer of initial support and the waterproof layer. The reserved deformation amount of the one reserved deformation space is greater than the reserved deformation amount of the two reserved deformation spaces.

5. A construction method for a two-step fast-enclosed tunnel support structure with an invert, characterized in that: The following steps are involved: Install upper step advance support and upper step advance reinforcement anchors; Excavate the upper step of the tunnel; Install the first layer of initial step supports and spray concrete; Excavation of the lower step of the tunnel; Install the first layer of initial lower step supports and spray concrete; Install long anchor rods on the lower step side wall and long anchor rods on the tunnel bottom; Install the second layer of initial lower step support and shotcrete, and backfill the tunnel bottom; Install the long anchor rods on the upper step side walls and the long anchor rods on the arch top; Install the second level initial step supports and spray concrete; Carry out invert pouring and invert filling pouring; Carry out secondary lining pouring; The construction method also includes: judging whether the tunnel is opened, if not, while installing the long anchor rods of the upper step side walls and the long anchor rods of the arch, successively carrying out the steps of installing the upper step advance support and the upper step advance reinforcement anchor rods, the step of excavating the tunnel upper step body, the step of installing the first layer of initial upper step support and spraying concrete, the step of excavating the tunnel lower step body, the step of installing the first layer of initial lower step support and spraying concrete, the step of installing the long anchor rods of the lower step side walls and the long anchor rods of the tunnel bottom, the step of installing the second layer of initial lower step support and spraying concrete and backfilling the tunnel bottom, so as to form a short step rapid closed loop to promote construction.

6. The construction method according to claim 5, characterized in that: The upper step advance support comprises a plurality of small advance grouting conduits, and the plurality of small advance grouting conduits are arranged along the circumferential direction and the longitudinal direction of the tunnel.

7. The construction method according to claim 5, characterized in that: The upper step advance reinforcement anchor rods include a plurality of longitudinal anchor rods, and the plurality of longitudinal anchor rods are arranged on the working face of the upper step of the tunnel along the longitudinal direction of the tunnel.

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