Widening structure for existing tunnel, method for widening existing tunnel, and design method for curved pipe roof

Abstract

To provide a method for widening an existing tunnel, a widening structure for an existing tunnel, and a design method for a curved pipe roof, which can perform widening work while retaining earth with a curved pipe roof even when there is no existing tunnel or advance pilot tunnel to receive and support a tip of the curved pipe roof when constructing a widening section in a partial section of the existing tunnel.SOLUTION: A widening structure for an existing tunnel 100 comprises a plurality of arc-shaped curved pipe roofs 40 arranged from a side wall of a circular section 20 of the existing tunnel toward the surrounding natural ground, and a widening section 70 that is provided over a predetermined widening section below the curved pipe roofs 40 by cutting open a portion of the side wall. A base end 42 of the curved pipe roof 40 is fixed to the side wall of the existing tunnel above the spring line SL, and a tip end 44 of the curved pipe roof 40 is supported by the natural ground.SELECTED DRAWING: Figure 5C

Description

[Technical Field]

[0001] The present invention relates to an existing tunnel widening structure, an existing tunnel widening construction method, and a curved pipe roof design method. [Background technology]

[0002] For example, when constructing road tunnels in urban areas where soft ground is prevalent, the cut and cover method is generally used, but this method has inherent issues such as noise and vibration during construction and traffic restrictions. Furthermore, because the space under roads in urban areas is congested with buried objects such as multiple subways and utility tunnels, the installation depth of new tunnels tends to be deep, and deeper installation depth directly leads to increased construction costs. Against this background, the use of shield tunneling methods is increasing when constructing road tunnels. In road tunnel construction, emergency exits and emergency parking areas are generally constructed by cutting (widening) a tunnel with a circular cross section (including a roughly circular, horseshoe-shaped cross section) underground. In this way, by cutting open part of the general circular cross section to the side, a certain section of widening is constructed in the tunnel axis direction (longitudinal direction). In the above-mentioned tunnel widening construction, when constructing a certain section of a circular section of an existing tunnel, a construction method is applied in which the side walls of the certain section of the circular section are removed in one go and cut open, and then widening excavation is carried out on the side of the ground, and segments for the widening section are installed to construct the certain section of widening. Furthermore, when this widening excavation is carried out, auxiliary construction methods are applied to maintain the natural ground as necessary, for example, ground improvement such as chemical injection is carried out in the widening excavation area, and retaining earth is constructed using pipe roofs such as curved pipe roofs.

[0003] When excavating a curved pipe roof while retaining the ground above it, both ends of the curved pipe roof are generally supported by existing tunnels, etc. For example, when widening two rows of existing tunnels that have been constructed horizontally apart by connecting them, one construction method involves pushing the curved pipe roof from one existing tunnel toward the other, fixing both ends of the curved pipe roof to the two existing tunnels, and supporting both ends of the curved pipe roof by the two rows of existing tunnels. Curved pipe roofs include upward-curved pipe roofs that are convex upward and downward-curved pipe roofs that are convex downward. Sometimes only one type is constructed, and sometimes both types are constructed. Also, when constructing pilot tunnels in place of an existing tunnel, one possible construction method is to construct two rows of pilot tunnels in the ground at horizontal intervals in advance, and then, for example, push a curved pipe roof from one of the two rows of pilot tunnels to the other side, receive the tip of the curved pipe roof in the other pilot tunnel, fix both ends of the curved pipe roof to the two rows of pilot tunnels, and support both ends of the curved pipe roof with the two rows of pilot tunnels.

[0004] In this way, for example, when constructing a curved pipe roof in advance to retain soil in order to widen a section of an existing tunnel, the conventional method has been to fix and support both ends of the curved pipe roof to an existing tunnel or pilot tunnel, etc., so if there is no existing tunnel or pilot tunnel on the side that will receive the end of the curved pipe roof, it is not possible to plan the construction of the curved pipe roof itself. In view of the above, when constructing a widening section in a section of an existing tunnel, there is a need for a method of widening an existing tunnel and a widening structure for an existing tunnel that allows widening construction to be carried out while retaining soil with the curved pipe roof, even when there is no existing tunnel or pilot tunnel to accept and support the end of the curved pipe roof.

[0005] Here, Patent Document 1 proposes a construction method for underground structures. This construction method involves excavating parallel tunnels, and then excavating the opposing sides to form widened sections, by installing lining material on the natural ground of the tunnels and installing jacking pipes (roof materials) above and below the tunnels, and installing the lining material and jacking pipes so that the cross section closes into an elliptical shape in order to resist external forces acting on the lining material and jacking pipes mainly through axial force. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-124489 Summary of the Invention [Problem to be solved by the invention]

[0007] The construction method for underground structures described in Patent Document 1 also involves fixing and supporting both ends of the roof material (equivalent to a curved pipe roof) to two tunnels excavated in parallel, which also involves the above-mentioned problems.

[0008] The present invention aims to provide a method for widening an existing tunnel, a widening structure for an existing tunnel, and a design method for a curved pipe roof, which enable widening work to be carried out while retaining soil with the curved pipe roof when constructing a widening section in a section of an existing tunnel, even when there is no existing tunnel or advance pilot tunnel to accept and support the tip of the curved pipe roof. [Means for solving the problem]

[0009] In order to achieve the above object, one aspect of the widening structure for an existing tunnel according to the present invention is as follows: A plurality of arc-shaped curved pipe roofs are arranged from the side wall of the circular portion of the existing tunnel toward the surrounding natural ground; A widened portion is provided below the curved pipe roof by cutting open a portion of the side wall over a predetermined widened section, The base end of the curved pipe roof is fixed to the side wall of the existing tunnel above the spring line, The tip of the curved pipe roof is characterized in that it is supported on the natural ground or improved ground.

[0010] According to this embodiment, the base end (one end) of the curved pipe roof is fixed above the spring line on the side wall of the existing tunnel, and the tip of the curved pipe roof (the tip in the thrust direction, the other end) is supported by the natural ground or improved ground, thereby eliminating the need for an existing tunnel or advance pilot tunnel to accept the tip of the curved pipe roof, and resulting in a widening structure in which the curved pipe roof acts as a retaining wall and a widened section is formed in a section of the existing tunnel.

[0011] Here, if the surrounding ground is hard, the tip (tip area in the direction of pushing) of the curved pipe roof pushed into the ground from the existing tunnel will be directly supported by the hard ground (ground); if the groundwater level in the surrounding ground is high or the ground is soft, ground improvement methods such as chemical injection methods and freezing methods are carried out in the construction area of ​​the widening section and the surrounding ground to construct improved ground, and the tip of the pushed curved pipe roof will be supported by the improved ground.

[0012] Furthermore, in this specification, the "tip of the curved pipe roof" refers to a part or the front part of the embedded portion in a structure in which the side of an existing tunnel has been cut open and the ground excavated, and the tip region of the curved pipe roof in the driving direction is embedded in the ground (or improved ground) below from the widening excavation region below the curved pipe roof. For example, even in the embedded region of the curved pipe roof, the ground or improved ground near the widening excavation region is loose and does not have the inherent rigidity of the ground or improved ground, so the forward range in the driving direction beyond this loosened region (which may include the loosened region) may be defined as the "tip of the curved pipe roof" where the curved pipe roof is supported by the ground or improved ground.

[0013] Another aspect of the widening structure for an existing tunnel according to the present invention is as follows: The length of the curved pipe roof is set to a length below the area loosened by excavation, which is below the active collapse line extending diagonally upward from the excavation range required for installing the segments in the widening section.

[0014] According to this aspect, the length of the curved pipe roof is set to a length below the active collapse line extending diagonally upward from the excavation range required for installing segments in the widening section, and below the area loosened by excavation.This allows the tip of the curved pipe roof to be stably supported by the natural ground or improved ground, and the length of the curved pipe roof can be set rationally.

[0015] In addition, one aspect of the method for widening an existing tunnel according to the present invention is as follows: A method for widening an existing tunnel, in which a part of the side wall is cut open from the circular part of the existing tunnel, and the widening part of a predetermined widening section is constructed in sequence from the base end where construction starts to the tip end where construction ends, The method includes an auxiliary process, a preceding widening excavation process, a widening section construction process, and a subsequent widening excavation process, The auxiliary process involves constructing a plurality of arc-shaped curved pipe roofs from the side wall toward the surrounding natural ground, fixing the base ends of the curved pipe roofs above the spring line on the side wall of the existing tunnel, and supporting the tips of the curved pipe roofs on the natural ground or improved ground. The preceding widening excavation process widens and excavates the area of ​​two rings of the segment at the base end side of the widening section to construct a widening excavation area, The widening portion construction step constructs a widening portion within the range of one ring of the base end side segment in the widening excavation area, The subsequent widening excavation process constructs a new widening excavation area within the range of one ring of the segment at the tip side of the widening excavation area, The widening section is constructed in the predetermined widening section by repeating the widening section construction process and the subsequent widening excavation process.

[0016] According to this aspect, in the auxiliary process, multiple arc-shaped curved pipe roofs are constructed from the side wall toward the surrounding ground, the base ends of the curved pipe roofs are fixed above the spring line on the side wall of the existing tunnel, and the tips of the curved pipe roofs are supported by the ground or improved ground.This makes it possible to eliminate the need for an existing tunnel or advance pilot tunnel to accept the tips of the curved pipe roofs, while retaining soil with the curved pipe roofs and constructing widening sections in some sections of the existing tunnel.

[0017] In addition, with regard to a tunnel widening construction method in which the widening sections of a certain widening section are constructed sequentially from the base end to the tip end, the widening excavation area is constructed by widening and excavating a range of two rings of the segment at the base end of the widening section (preceding widening and excavation process), a widening section is constructed within the range of one ring of the segment at the base end of the widening and excavation area (widening section construction process), and a new widening and excavation area is constructed within the range of one ring of the segment at the tip end of the widening and excavation area (subsequent widening and excavation process).By repeating the widening and excavation construction process and the subsequent widening and excavation process in a specified widening section (so-called sequential partial excavation construction), the widening and excavation area is limited to a certain range within the widening section rather than the entire range, and by sequentially cutting and widening a certain range, the opening diameter of the divided section can be made significantly smaller than when the opening diameter is the entire widening section.This makes it possible to reduce the specifications of the beam and column members to suppress deformation of the cut opening and the surrounding area, and even to omit the beam and column members.

[0018] In this method of evaluating design loads assuming tunnel widening, the design load is determined by distributing half of the load acting on the cut-out divided section from the surrounding ground to the circular sections or the widened sections that exist in the base-end and tip-end divided sections that sandwich the cut-out divided section when the divided section is cut open. This allows the design of the circular section of an existing tunnel (for example, when reinforcing a circular section) to be based on the total load of the load acting directly on each divided section and the load distributed from the cut-out divided section, thereby achieving a reinforcement design for the existing tunnel when widening is performed with high structural reliability. Furthermore, if widening is planned from the beginning of the design of the existing tunnel, the circular section of the existing tunnel can be designed based on the total load described above. If widening is planned after the construction of the existing tunnel, the total load described above can be applied when designing the structure of the circular section and its opening reinforcement member.

[0019] Here, the width of two rings of the segment is set as the divided section, and after cutting open the divided section of two ring width, the base end divided section is set to the width of one ring of the segment, a segment is installed in the widened section, and the widened section is constructed.After that, by cutting open the width of one ring of the segment further towards the tip end of the tip end divided section, a new width of two rings of the segment is cut open, and similarly, the widened section can be constructed in the base end divided section (one ring width of the segment).

[0020] In another aspect of the widening construction method for an existing tunnel according to the present invention, The auxiliary step is characterized in that, prior to the construction of the curved pipe roof, ground improvement is carried out at least in the widening excavation area.

[0021] According to this embodiment, the auxiliary process includes carrying out ground improvement work in at least the widening excavation area prior to the construction of the curved pipe roof. Therefore, even if the ground around the existing tunnel is soft or the groundwater level is high, improved ground can be formed using ground improvement methods such as chemical injection methods and freezing methods, and the widening section can be constructed with high construction safety while preventing ground collapse and groundwater seepage, etc., and the specifications of the curved pipe roof can be reduced as much as possible due to the reduction in earth pressure and soil-water pressure acting on the curved pipe roof.

[0022] Further, one aspect of the curved pipe roof design method according to the present invention is to A curved pipe roof is disposed from the side wall of the circular portion of an existing tunnel toward the surrounding natural ground, and below the curved pipe roof, an expanded excavation area is provided in which the natural ground is excavated from a part of the side wall that has been cut open, and the base end of the curved pipe roof is fixed to the side wall of the existing tunnel above the spring line, and the tip of the curved pipe roof is supported by the natural ground or improved ground, and a design method for a curved pipe roof is provided for the natural ground, In a computer, the curved pipe roof extending laterally in a cross section perpendicular to the axial direction of the existing tunnel and the surrounding natural ground including the widening excavation area below the curved pipe roof are modeled, and an analysis is performed using a three-dimensional finite element method to identify the area below the curved pipe roof that has been loosened due to excavation; Regarding the ground springs of the natural ground or improved ground that resist earth pressure or soil-water pressure attached to the curved pipe roof, in the widening excavation area located above the active collapse line extending diagonally upward from the underside of the existing tunnel, the ground springs are cut, The stiffness of the ground spring in the loosened region is set to 1 / 2 of the stiffness of the ground spring of the actual ground or the improved ground, Below the loosened area, the stiffness of the ground spring is set to the stiffness of the actual ground or the improved ground, The method is characterized in that the ground springs are installed in each region of the modeled curved pipe roof, and the curved pipe roof is designed by loading earth pressure or soil-water pressure and checking the stress level of the curved pipe roof.

[0023] According to this embodiment, an analysis using a three-dimensional finite element method is performed to identify the area of ​​loosening due to excavation below the curved pipe roof, and then with regard to the ground springs of the ground or improved ground that resist earth pressure or soil-water pressure and are attached to the curved pipe roof, the ground springs are cut in the widening excavation area, the rigidity of the ground springs in the loosened area is set to half the rigidity of the actual ground spring, and the rigidity of the ground springs below the loosened area is set to the rigidity of the actual ground spring, and by installing ground springs corresponding to each area of ​​the modeled curved pipe roof and performing a stress check of the curved pipe roof to design the curved pipe roof, a rational design of a curved pipe roof whose one end (tip) is supported by the ground or improved ground can be realized. [Effects of the Invention]

[0024] According to the present invention's widening structure for an existing tunnel, the widening construction method for an existing tunnel, and the design method for a curved pipe roof, when constructing a widening section in a section of an existing tunnel, even if there is no existing tunnel or pilot tunnel to accept and support the tip of the curved pipe roof, the widening construction can be carried out while retaining soil with the curved pipe roof. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a side view of a tunnel illustrating an example of a tunnel widening construction method according to an embodiment. [Figure 2A] This is a process diagram of an example of a tunnel widening construction method according to an embodiment, and is a cross-sectional view perpendicular to the tunnel axis direction. [Figure 2B] FIG. 2B is a cross-sectional view of the tunnel in FIG. 2A cut at a midpoint. [Figure 3A]This is a process diagram of an example of a tunnel widening construction method according to an embodiment, and is a cross-sectional view perpendicular to the tunnel axis direction. [Figure 3B] FIG. 3B is a cross-sectional view of the tunnel in FIG. 3A cut at a midpoint. [Figure 4A] This is a process diagram of an example of a tunnel widening construction method according to an embodiment, and is a cross-sectional view perpendicular to the tunnel axis direction. [Figure 4B] FIG. 4B is a cross-sectional view of the tunnel in FIG. 4A cut at a midpoint. [Figure 5A] This is a process diagram of an example of a tunnel widening construction method according to an embodiment, and is a cross-sectional view perpendicular to the tunnel axis direction. [Figure 5B] FIG. 5B is a cross-sectional view of the tunnel in FIG. 5A cut at a midpoint. [Figure 5C] This is a cross-sectional view of an example of an existing tunnel widening structure according to an embodiment. [Figure 6] FIG. 10 is a diagram showing an example of an analytical model used in a three-dimensional FEM analysis for setting a load to be distributed to a distal end divided section and a proximal end divided section in a design load evaluation method. [Figure 7] FIG. 7 is a diagram showing an example of the analytical model shown in FIG. 6, in which the tunnel is cut into upper and lower parts along its center line. [Figure 8] 10 is a graph showing the analysis results. [Figure 9] FIG. 10 is an explanatory diagram showing the load after distribution between the tip-end divided section and the base-end divided section for each construction stage in the design load evaluation method. [Figure 10A] 10 is a diagram simulating an example of the results of a three-dimensional FEM analysis for identifying a loosened region in the curved pipe roof design method according to the embodiment. FIG. [Figure 10B] FIG. 10 is a diagram showing an example of an analytical model for stress inspection in the curved pipe roof design method according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention relates to a tunnel widening method, a tunnel widening structure, and a curved pipe roof design method, and is described below with reference to the accompanying drawings. In this specification and the drawings, substantially identical components are designated by the same reference numerals, and redundant description may be omitted.

[0027] [Existing tunnel widening construction method and existing tunnel widening structure, and curved pipe roof design method according to the embodiment] An example of an existing tunnel widening construction method, an existing tunnel widening structure, and a curved pipe roof design method according to an embodiment will be described with reference to Figures 1 to 10. Here, Figure 1 is a side view of a tunnel for explaining an example of a tunnel widening construction method according to an embodiment. Also, Figures 2A to 5A are process diagrams of an example of a tunnel widening construction method according to an embodiment, and are cross-sectional views perpendicular to the tunnel axis direction, and Figures 2B to 5B are cross-sectional views of the corresponding tunnels in Figures 2A to 5A cut at midpoints, respectively.

[0028] The existing tunnel shown in Fig. 1 has a circular portion 20 made up of multiple steel segment rings 10 and two circular portions on the left and right of it made up of multiple RC (Reinforced Concrete) segment rings 10', and a widening portion is constructed in a partial section of the circular portion 20 made up of the steel segment rings 10. For example, if the circular portion 20 is a road tunnel, the widening portion is used for an emergency exit or emergency parking lane provided in a partial section of the road tunnel.

[0029] The steel segment ring 10 is formed by assembling multiple steel segments (A segment, B segment, and K segment) in its circumferential direction. In the illustrated example, of the 31 rings from segment ring R3 to segment ring R33, the section corresponding to the central 21 rings is planned as the widening section, and the width t of the segment ring 10 in the tunnel axis direction is, for example, 1500 mm.

[0030] In the conventional construction method of cutting open the widening section equivalent to these 21 rings in one go, based on the description in the "Sewerage Temporary Design Manual - Shield Construction Edition - April 2023, Tokyo Metropolitan Sewerage Service Co., Ltd.", as shown in Figure 1, the affected area due to the cutting will be a 63-ring area, including the sections equivalent to 21 rings on each side of the widening section, and the specifications for the opening reinforcement material around the opening formed by the cutting will be extremely large, and the installation area will also be wide.

[0031] In contrast, according to the widening construction method of the embodiment described below, the area affected by the cutting of the circular section 20 is a 25-ring section, including sections equivalent to two rings on each side of the widening section, which significantly reduces the specifications and installation range of the opening reinforcement material around the opening formed by the cutting, and in some cases makes it possible to omit the opening reinforcement material.

[0032] 2A and 2B, a shoring 30 is installed to support the top and bottom of the opening formed in the widening section of the circular section 20. The shoring 30 includes vertically extending support columns and support beams (longitudinal beams) that extend in the axial direction of the tunnel at the top and bottom ends of the support columns. A stage 35 is also installed inside the circular section 20, allowing heavy machinery and other equipment to move and operate.

[0033] Following or prior to the installation of the above-mentioned shoring 30 and stage 35, ground improvement work such as chemical injection and freezing methods is carried out on the ground surrounding at least the widening section to create improved ground G. Note that if the surrounding ground is hard or has a relatively low groundwater level, the creation of improved ground G may be unnecessary.

[0034] After the improved ground G has been created, a curved pipe roof 40 for retaining soil above the widening excavation area is installed by pushing (pushing) it from the inside of the circular portion 20 into the improved ground G. Specifically, by adding curved steel pipes or the like, an arc-shaped curved pipe roof 40 of a predetermined length v is installed inside the improved ground G as shown in the illustrated example, and this is repeated over the widening section at intervals in the axial direction of the tunnel or so that the pipes abut each other, thereby retaining soil in the improved ground G above and making it possible to carry out widening excavation of the improved ground G below.

[0035] 2A, the base end 42 of the curved pipe roof 40 is fixed above the opening of the circular portion 20 and above the spring line SL of the circular portion 20. Meanwhile, the tip 44 of the curved pipe roof 40 in the advancing direction is supported by the improved ground G.

[0036] Here, in conventional construction methods in which a curved pipe roof is constructed in advance to retain soil in order to construct a widening section of an existing tunnel, it is common to fix and support both ends of the curved pipe roof to an existing tunnel or pilot tunnel, etc., which means that a separate existing tunnel or pilot tunnel is required on the side to receive the tip of the curved pipe roof.

[0037] In contrast, in the illustrated example widening construction method, even if there is no existing tunnel or pilot tunnel to accept and support the tip of the curved pipe roof, widening construction can be carried out while retaining soil with the curved pipe roof.In order to do this, the area extending over a certain section from the tip 44 of the curved pipe roof 40 (the sum of the loosened area J1 (length v2) and the non-loosened area J2 (length v3) in Figure 3A) is set as the embedment length into the ground (here, improved ground G), so that the tip side of the curved pipe roof 40 is supported by the ground, etc.

[0038] If the construction of improved ground G is not required, the tip of the curved pipe roof is embedded in the ground and supported by the ground. The method for setting the overall length v of this curved pipe roof 40, the length v2 of the loosened region J1, and the length v3 of the non-loosened region J2 will be explained in detail below (these are auxiliary steps).

[0039] In the illustrated widening construction method, the widening section is constructed sequentially by sequential partial excavation, in which cutting and widening construction (cutting and widening process) are repeated in order from the base ring R8 in the widening section shown in FIG. 1 to the tip ring R28. More specifically, the first two rings are cut open together as divided sections in the widening section, and widening excavation is performed in the divided sections. After that, widening section segments are installed in the widening area of ​​the base ring to construct the widening ring. Next, the tip ring of the widening excavation area is cut open and widening excavation is performed, thereby forming a new two-ring divided section. Then, widening rings are constructed in the divided sections while sequentially forming the divided sections in this way, and this is repeated up to ring R28 of the circular section 20, thereby constructing a widening section with multiple widening rings alongside (the widening section) rings R8 to R28 of the circular section 20.

[0040] To explain the above construction work in more detail, first, as shown in Figure 2B, two rings (2 x t width), ring R8 and ring R9, are designated as the target for removal (divided section) together, and as shown in Figures 3A and 3B, a backhoe U1 placed on stage 35 is used to widen and excavate the improved ground G1 to construct a widened excavation area, and concrete is then sprayed onto the flooring surface of the widened excavation area to construct a sprayed floor F.

[0041] Here, the widening excavation area can be set below the circular portion 20 in an area above the active collapse line L1, which extends diagonally upward from the excavation range required to install segments in the widening portion.This setting method makes it possible to form a stable excavation surface in the ground (improved ground G in the illustrated example).

[0042] Regarding the setting of the active collapse line, for example, as shown in Figure 3A, it can be set at 45° + φ / 2 (φ is the internal friction angle of the natural ground or improved ground) relative to the horizontal line (this is the preceding widening excavation process).

[0043] 4A and 4B, widening segments are installed in the widening excavation area of ​​the base-end ring R8 to construct the widening ring 60. Next, an aerial work platform U2 is placed on the stage 35, and a back filler material 50 such as liquefied treated soil is filled into the back area of ​​the widening ring 60 (the area below the curved pipe roof 40) through filling holes (not shown) provided in the widening ring 60.

[0044] At this stage, no widening rings are installed in the widening excavation area on the sides of the ring R9 on the tip side, and the widening excavation area is left below the curved pipe roof 40 (this is the widening portion construction process).

[0045] Next, as shown in Figures 5A and 5B, a new widening excavation area is constructed by widening excavation of the improved ground G2 on the side of ring R10 at the tip side of ring R9, and together with the widening excavation area on the side of ring R9 where no widening ring has yet been installed, a new widening excavation area in the divided section of the two rings is formed (follow-up widening excavation process).

[0046] Thereafter, an expansion ring 60 is constructed in the expansion excavation area on the side of ring R9, and an expansion section construction process is carried out in which back filler material 50 is filled in. Then, the improved ground on the side of the next ring R11 is expanded and excavated, and so on. The expansion section construction process and the subsequent expansion excavation process are repeated, and an expansion section is constructed in which expansion rings 60 are placed next to each other throughout the expansion section.

[0047] 5C, this construction method constructs an existing tunnel widening structure 100, which has a plurality of arc-shaped curved pipe roofs 40 arranged from the side wall of the existing tunnel's circular section 20 toward the surrounding natural ground (here, improved ground G), and a widening section 70 formed by cutting open part of the side wall below the curved pipe roofs 40 and providing the widening section 70 over a predetermined widening interval. The curved pipe roofs 40 forming the widening structure 100 have their base ends 42 fixed above the spring line SL on the side wall of the existing tunnel 20, and their tips 44 supported by the natural ground (here, improved ground G).

[0048] According to this construction method, even if there is no existing tunnel or pilot tunnel to receive and support the tip 44 of the curved pipe roof 40, widening construction can be carried out while retaining soil with the curved pipe roof 40.

[0049] Furthermore, by limiting the widening excavation range to a certain range rather than the entire widening section, and sequentially cutting open a certain range and constructing the widening section, the opening diameter of the divided section can be made significantly smaller than if the opening diameter were the entire widening section.

[0050] For example, in the illustrated example, since the divided section is two rings, the affected area is 25 rings in total, consisting of the widening section, 21 ring, and the two rings on either side of it. Compared to the affected area of ​​63 rings when a conventional 21-ring widening section is cut open all at once, the specifications for the beam and column members used to suppress deformation of the cut-out opening and its surrounding area can be significantly reduced, the installation range can be significantly narrowed, and in some cases it may even be possible to omit the beam and column members.

[0051] Next, an example of a design load evaluation method will be described with reference to Figs. 6 to 9. Fig. 6 is a diagram showing an example of an analytical model used in a 3D FEM analysis for setting the load to be distributed to the tip-side divided section and the base-side divided section in the design load evaluation method. Fig. 7 is a diagram showing an example of an analytical model in which the tunnel is cut vertically along its centerline in the analytical model shown in Fig. 6, and Fig. 8 is a graph showing the analysis results. Fig. 9 is an explanatory diagram showing the load after distribution to the tip-side divided section and the base-side divided section for each construction stage in the design load evaluation method.

[0052] As shown in Figure 6, in a 3D FEM (Finite Element Method) analysis to set the distributed load, a ground model M0 is created in a computer, and within the ground model M0, a circular part model M1 of the existing tunnel with a diameter of 2D is further created at a depth H, and the range of 2H on both sides of the circular part model M1 is modeled as the affected area.

[0053] Furthermore, as shown in Figure 7, in the widening section of the circular section model M1, a support beam model M3 and a support column model M4 (both support models) are created, and on the side of the circular section model M1, a widening section model M2, which is constructed sequentially, is created step by step.

[0054] This sequential excavation analysis allows the distributed loads to be determined as shown in Figure 8, which are distributed to the widening excavation area (area A) in the divided section of the two rings shown in Figure 9, the divided section of the two rings at the base end (area B2), and the divided section of the two rings at the tip end (area B1).

[0055] In Figure 8, the horizontal load acting on the circular part from the surrounding ground is 468 kN / m 2 When this horizontal load acting on one ring of the circular section is taken as 100%, the horizontal load of the two rings that was initially acting on the widened excavation area of ​​Area A is 918kN / m in Area B1, which is at the tip of Area A, which is the widened excavation area. 2As a result, the analysis results showed that 196% (equivalent to approximately 200%) of the horizontal load acts.

[0056] On the other hand, in Figure 8, when the horizontal load acting on one ring of the circular section is set to 100%, the horizontal load of the two rings that was initially acting on the widening excavation area of ​​area A is 431 kN / m 2 As a result, the analysis results showed that 92% (equivalent to approximately 100%) of the horizontal load acts.

[0057] This will be explained with reference to Figure 9, which shows the incremental load for each analysis step. When 1, 2R (ring) is opened, 100% of the 200% horizontal load in area A is increased by 50% to each of the two rings in areas B1 and B2, and 150% of both rings becomes the design load of the segment rings that make up the circular portion.

[0058] Next, when an expansion ring is constructed on 1R (ring) using the above construction method and 3R (ring) is cut open to form openings on 2R and 3R (ring), the horizontal load of 150%, which is the design load of area B1 when 1R and 2R are opened, is redistributed to the new areas B1 and B2, so a horizontal load of 150% / 4 = 37.5% is redistributed to each ring. As a result, the horizontal load on 4R in area B1 is 150% + 37.5% = 187.5%, and the horizontal load on 5R is 100% + 37.5% = 137.5%, so the design load of the expansion ring already constructed on 1R in area B2 is 37.5%.

[0059] Next, when 4R (ring) is cut open to form an opening at 3,4R (ring), the horizontal load of 187.5%, which was the design load for area B1 when 2,3R was opened, is redistributed to the new areas B1 and B2, so a horizontal load of 187.5% / 4 = 46.95% is redistributed to each ring. As a result, the horizontal load at 5R in area B1 is 137.5% + 46.95% = 184.4%, which is less than the maximum horizontal load of 187.5% in area B1 during the previous construction step.

[0060] On the other hand, the design load of the widening ring installed on 1R in area B2 is 37.5% + 46.95% = 84.4%, which is less than 100% of the horizontal load originally acting on 1R.

[0061] In other words, in the illustrated example of sequential partial excavation, if the horizontal load acting on ring 1 is 100%, the design load of area B1 (design load of the existing tunnel, or design load for the existing tunnel and opening reinforcement member) at the tip end where the horizontal load of area A is distributed will be at most 200%, as in the analysis results shown in Figure 8, and the design load of area B2 (design load of the widening ring) at the base end where the horizontal load of area A is distributed will be at most 100%, as in the analysis results shown in Figure 8.

[0062] Based on the above, in the design load evaluation method, assuming the implementation of the tunnel widening construction method according to the embodiment, when a divided section is cut open, half of the load acting on the cut-open divided section from the surrounding ground is distributed to each of the circular sections or widened sections that exist in the base-end divided section and the tip-end divided section, which are located on the base and tip sides of the cut-open divided section, to determine the design load. When the load acting on one ring of the segment that constitutes the circular section is taken as 100%, the design load after distribution of the circular section of the tip-end divided section after the load is distributed is set to 200% or approximately 200%, and the design load after distribution of the widened section of the base-end divided section after the load is distributed is set to 100% or approximately 100%.

[0063] The design load evaluation method shown in the figure allows for the realization of a reinforcement design for existing tunnels when widening construction work is carried out with high structural reliability.

[0064] Next, an example of a curved pipe roof design method according to the embodiment will be described with reference to Fig. 7 and Figs. 10A and 10B. Fig. 10A is a diagram simulating an example of the results of a 3D FEM analysis for identifying loosened areas in the curved pipe roof design method according to the embodiment. Fig. 10B is a diagram showing an example of an analytical model used in stress inspection in the curved pipe roof design method according to the embodiment.

[0065] As shown in Figure 7, by performing a three-dimensional finite element analysis on a ground model M0 including a widening section model M2 (modeling the widening excavation area), the loosened area due to the widening excavation is identified, as shown in the analysis results in Figure 10A.

[0066] More specifically, a linear elastic analysis was performed as a ground stability analysis (3D excavation analysis), and the local safety factor of the ground during construction of the widening section was evaluated, confirming the stability of the ground (loosening range: local safety factor 1.0 or less). The length (circumferential length) of the loosened area identified in this analysis was 3.5 m.

[0067] Furthermore, this analysis revealed that the loosening range was up to 0.5 m outside the curved pipe roof, and even when taking into account the safety factor Fs: 1.5, it was determined that the loosening range was within the ground improvement range (chemical injection ground range), confirming that the ground would not be loosened.

[0068] After determining the length of the loosened area (circumferential length) through this analysis, a stress check is carried out on the curved pipe roof, whose base end is fixed and whose tip is supported by the ground, as shown in Figure 10B. The appropriateness of the specifications and length of the curved pipe roof is verified, and a curved pipe roof with specifications and length that satisfy the allowable stress is designed.

[0069] Specifically, with regard to the ground springs of the ground (improved ground in the illustrated example) that resist the earth pressure or soil-water pressure attached to the curved pipe roof, the ground springs are cut in the widening excavation area above the active collapse line, which is extended diagonally upward from the excavation area required to install the segments in the widening section. Furthermore, the stiffness of the ground springs in the identified loosened area (a circumferentially long range in this example, 3.5 m) is set to half the stiffness of the ground springs of the actual improved ground. Furthermore, below the loosened area, the stiffness of the ground springs is set to the stiffness of the actual improved ground.

[0070] The penetration length of a curved pipe roof into the non-slack region below the loosened region can be set to approximately 1.5 m to 3 m. For example, in an earth retaining wall, the minimum penetration length of the parent pile horizontal sheet piles into the ground is sometimes set to approximately 1.5 m, and the minimum penetration length of a water-impermeable earth retaining wall (e.g., steel sheet piles) is sometimes set to approximately 3.0 m. Considering that a curved pipe roof is a parent pile structure, the penetration length may be set to 1.5 m or more, and considering that the curved pipe roof is located in improved ground, the penetration length may be set to 3.0 m or more as a water-impermeable earth retaining wall. Therefore, the penetration length of a curved pipe roof into the non-slack region can be set to approximately 1.5 m to 3.0 m.

[0071] From the above, in this example, the root length of the curved pipe roof can be set to approximately 5.0 m to 6.5 m, which is the sum of the circumferential length of the identified loosened area of ​​the curved pipe roof: 3.5 m and the root length into the non-loosened area: 1.5 m to 3.0 m.

[0072] The above-mentioned ground springs are installed in each area of ​​the modeled curved pipe roof, and earth pressure or soil-water pressure is applied to perform a stress check on the curved pipe roof.By repeating this process until the specifications and length satisfy the allowable stress, a curved pipe roof is designed whose tip is supported by the ground (in this case, improved ground).

[0073] According to the illustrated curved pipe roof design method, it is possible to realize a rational design of a curved pipe roof 40 whose one end (tip) is supported by the natural ground or improved ground.

[0074] It should be noted that the present invention is not limited to the configurations shown here, and other embodiments may be possible in which other components are combined with the configurations described in the above embodiments. In this regard, the present invention can be modified within the scope of the present invention, and can be appropriately determined depending on the application form. [Explanation of symbols]

[0075] 10,10': Segment ring 20: Existing tunnel (circular section) 30: Shoring 35: Stage 40: Curved pipe roof 42: Proximal end 44: Tip 50: Back filler 60: Widening ring 70: Widened section 100: Widening structure (widening structure of existing tunnel) G: Improved ground G1, G2: Improved ground SL: Spring Line U1: Backhoe U2: Aerial work platform L1: Active collapse line L2: Loosening area line J1: Loosening area J2: Non-loose region F: Sprayed floor M0: Ground model M1: Circular section model (existing tunnel model) M2: Widening section model M3: Support beam model (support model) M4: Support model (support model) M5: Curved pipe roof model

Claims

1. A plurality of arc-shaped curved pipe roofs are arranged from the side wall of the circular portion of the existing tunnel toward the surrounding natural ground; A widened portion is provided below the curved pipe roof by cutting open a portion of the side wall over a predetermined widened section, The base end of the curved pipe roof is fixed to the side wall of the existing tunnel above the spring line, An expansion structure for an existing tunnel, characterized in that the tip of the curved pipe roof is supported on the natural ground or improved ground.

2. The widening structure for an existing tunnel as described in claim 1, characterized in that the length of the curved pipe roof is set to a length below the active collapse line extending diagonally upward from the excavation range required for installing segments in the widening section, and below the area loosened by excavation.

3. A method for widening an existing tunnel, in which a part of the side wall is cut open from the circular part of the existing tunnel, and the widening part of a predetermined widening section is constructed in sequence from the base end where construction starts to the tip end where construction ends, The method includes an auxiliary process, a preceding widening excavation process, a widening section construction process, and a subsequent widening excavation process, The auxiliary process involves constructing a plurality of arc-shaped curved pipe roofs from the side wall toward the surrounding natural ground, fixing the base ends of the curved pipe roofs above the spring line on the side wall of the existing tunnel, and supporting the tips of the curved pipe roofs on the natural ground or improved ground. The preceding widening excavation process widens and excavates the area of ​​two rings of the segment at the base end side of the widening section to construct a widening excavation area, The widening portion construction step constructs a widening portion within a range of one ring of the base end side segment in the widening excavation area, The subsequent widening excavation process constructs a new widening excavation area within the range of one ring of the segment at the tip side of the widening excavation area, A method for widening an existing tunnel, characterized in that the widening section construction process and the subsequent widening excavation process are repeated to construct the widening section in the specified widening section.

4. 4. The method for widening an existing tunnel according to claim 3, wherein the auxiliary step includes carrying out ground improvement work in at least the widening excavation area prior to the construction of the curved pipe roof.

5. A curved pipe roof is disposed from the side wall of the circular portion of an existing tunnel toward the surrounding natural ground, and below the curved pipe roof, an expanded excavation area is provided in which the natural ground is excavated from a part of the side wall that has been cut open, and the base end of the curved pipe roof is fixed to the side wall of the existing tunnel above the spring line, and the tip of the curved pipe roof is supported by the natural ground or improved ground, and a design method for a curved pipe roof is provided for the natural ground, In a computer, the curved pipe roof extending laterally in a cross section perpendicular to the axial direction of the existing tunnel and the surrounding natural ground including the widening excavation area below the curved pipe roof are modeled, and an analysis is performed using a three-dimensional finite element method to identify the area below the curved pipe roof that has been loosened due to excavation, Regarding the ground springs of the natural ground or improved ground that resist earth pressure or soil-water pressure attached to the curved pipe roof, in the widening excavation area located above the active collapse line extending diagonally upward from the underside of the existing tunnel, the ground springs are cut, The stiffness of the ground spring in the loosened region is set to 1 / 2 of the stiffness of the ground spring of the actual ground or the improved ground, Below the loosened area, the stiffness of the ground spring is set to the stiffness of the actual ground or the improved ground, A method for designing a curved pipe roof, characterized in that the ground springs are installed in each area of ​​a modeled curved pipe roof, earth pressure or soil-water pressure is applied, and a stress check of the curved pipe roof is performed to design the curved pipe roof.

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