Evaluation method of design load for tunnel widening construction and tunnel widening construction method

Abstract

To provide a tunnel widening construction method capable of reducing or omitting specifications of opening reinforcement material and an installation area around an opening, formed through cutout, and an evaluation method of design load for tunnel widening construction applied for a design step of the widening construction method.SOLUTION: An evaluation method of design load for tunnel widening construction which is provided with a cutout step and a widening step. In the cutout step, separated sections obtained by separating a widening section into multiple sections are cut out and, in the widening step, a whole of or a part of the separated sections is widened sequentially from a base end side to construct a widening part by repeating the cutout step and the widening step sequentially from the separated section at the base end side. The design load is determined by separating load acting on the cutout separated sections by half from a surrounding ground and distributing each of them for a perfect circle part or constructed widening parts in a separated section at the base end side and a separated section at the tip side sandwiching the cutout separated section when the separated sections are cut out.SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present invention relates to a method for evaluating design loads and a method for widening construction of a tunnel in tunnel widening construction.

Background Art

[0002] For example, when constructing a road tunnel in an urban area where soft ground is distributed, although the application of the excavation method is common, the excavation method has problems such as noise, vibration, and traffic restrictions during construction. In addition, since the underground space under roads in urban areas is crowded with buried objects such as multiple subways and utility tunnels, the installation depth of the tunnel to be newly constructed often tends to be deep, and the deepening of the installation depth directly leads to an increase in construction costs. Under such circumstances, the number of cases where the shield method is applied in the construction of road tunnels is increasing. By the way, in the construction of this road tunnel, an emergency exit and an emergency parking area are generally constructed by cutting (expanding) a tunnel with a circular cross-section (including a substantially circular cross-section with a horseshoe-shaped cross-section) in the ground. In this way, by cutting a part of the general part with a circular cross-section laterally, a widened part in a certain section is constructed in the tunnel axis direction (tunnel longitudinal direction). In the above-described tunnel widening construction, when constructing a widened part in a certain section in the true circular part of the existing tunnel, after removing and cutting the side walls of the true circular part in the certain section all at once, widening excavation is performed on the side ground, and a segment for the widened part is installed to construct a widened part in a certain section. In addition, in this widening excavation, an auxiliary method for retaining the ground is applied as necessary. For example, ground improvement such as chemical solution injection is performed on the widening excavation area, and soil retention by a pipe roof or the like is constructed.

[0003] Here, according to the "23rd Tunnel Library - Segment Design [Revised Edition] - From Allowable Stress Design Method to Limit State Design Method - Tunnel Engineering Committee Technical Subcommittee Segment Design Method Review Subcommittee", when openings are provided in sewer tunnels or utility tunnels, since the segment ring becomes non-circular in cross-section due to the openings, it is necessary to carry out opening reinforcement and make the reinforcement members around the opening bear the cross-sectional forces generated in the ring when it is circular. Here, the following are the main methods of opening reinforcement.

[0004] One method is to install beam members or column members made of steel in the secondary lining part around the opening. Another method is to provide a reinforcement structure made of steel or reinforced concrete outside the tunnel around the opening. Still another method is to incorporate beam members or column members, which are opening reinforcement materials, into the segment ring to endow the segment with the function of opening reinforcement. In this opening reinforcement, when the opening diameter is d, the opening reinforcement range is set to a range of 3d. Incidentally, the regulation of setting the opening reinforcement range to a range of 3d is described on page 2-16, "3-2 Reinforcement Range" of the "Interim Design Manual for Sewers - Shield Construction Edition - April 2023, Tokyo Metropolitan Sewerage Service Co., Ltd.", and this description is based on the "Experimental Research Report on the Direct Installation of Branch Pipes for Existing Sewer Ring Structures, 1983".

[0005] As described above, when constructing an emergency parking area, etc. by widening construction for an existing road tunnel, it is necessary to carry out widening construction over a wide range in the advancing direction of the shield tunnel. Therefore, in the conventional construction method of cutting open the existing tunnel all at once to provide an opening, since the range of opening reinforcement is proportional to the opening diameter (in the above example, a range of three times), it is necessary to install opening reinforcement materials over a wide range, which leads to a prolonged construction period and a soaring construction cost. In addition, since the ground is temporarily exposed, the above-mentioned auxiliary construction method for retaining the ground is required, but the specifications of the auxiliary construction method become extremely large and its range can also become extremely wide.

[0006] From the above, regarding a method for widening a tunnel in which a part of the side wall of an existing tunnel is cut open to construct a widened portion, a method for widening a tunnel capable of reducing the specifications and installation range of an opening reinforcing material around an opening formed by the cutting or omitting the opening reinforcing material, and a method for evaluating the design load in the widening construction of a tunnel, which is applied at the design stage of this tunnel widening construction method, are desired.

[0007] Here, Patent Document 1 proposes a reinforcing structure for a subterranean structure for reinforcing a subterranean structure provided to secure a space serving as a work area when constructing a large cross-section tunnel in a part of an existing tunnel. This reinforcing structure is composed of a ring-shaped structure constructed circumferentially outside the planned construction area of the large cross-section tunnel and front and rear gusset walls constructed at each of both ends of a cylindrical body composed of the ring-shaped structure and through which the existing tunnel passes. One end and the other end of a tension member extending in the axial direction of the existing tunnel are installed at predetermined positions in a range joined to the front gusset wall and in a range facing the natural ground in the existing lining of the existing tunnel.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0009] According to the reinforcing structure of the subterranean structure described in Patent Document 1, since a part of the lateral earth pressure acting on the front gusset wall is borne by using a tension member, it is stated that the structural safety of the front gusset wall can be ensured even when a situation occurs in which the rigidity decreases, such as when a shield opening is formed in the front gusset wall. However, Patent Document 1 does not disclose means for solving the above problems, that is, regarding a method for widening a tunnel, reducing the specifications and installation range of an opening reinforcing material around an opening formed by cutting, or omitting the opening reinforcing material.

[0010] The present invention relates to a method for widening a tunnel, in which a part of the side wall of an existing tunnel is cut open to construct a widened portion, and it is possible to reduce the specifications and installation range of an opening reinforcing material around the opening formed by the cutting, or to omit the opening reinforcing material. An object of the present invention is to provide a method for widening a tunnel and a method for evaluating a design load in widening construction of a tunnel, which is applied at the design stage of this method for widening a tunnel.

Means for Solving the Problems

[0011] To achieve the above object, one aspect of the method for evaluating a design load in widening construction of a tunnel according to the present invention is as follows. In the widening construction of a tunnel, a part of the side wall is cut open from the circular part of an existing tunnel, and the widened portion in a predetermined widening section is constructed in order from the base end side where the construction starts to the tip end side where the construction ends. The widening construction of the tunnel includes a cutting step and a widening step. In the cutting step, the divided sections obtained by dividing the widening section into a plurality of sections are cut open. In the widening step, all or a part of the divided sections are widened in order from the base end side. In the widening section, the method for evaluating a design load in widening construction of a tunnel, in which the cutting step and the widening step are repeated in order from the divided section on the base end side to construct the widened portion, is characterized in that when the divided section is cut open, half of the load acting from the surrounding ground on the cut divided section is distributed to the circular part or the constructed widened portion existing in the base end side divided section and the tip end side divided section sandwiching the cut divided section, and this is used as the design load.

[0012] ​According to this aspect, in the cutting process of the widening construction, the construction is to cut the widening section for each of a plurality of divided sections (by removing the segments of the circular part to form an opening), and in the widening process of the widening construction, the construction is to widen all or part of the divided sections in order from the base end side (by installing segments in the widened part). In the so-called sequential partial excavation construction, by repeating the cutting process and the widening process in order from the divided section on the base end side to construct the widened part, the widening excavation range is limited to a certain range rather than the entire range of the widening section. By sequentially performing the cutting and widening construction within a certain range, the opening diameter of the divided section can be made significantly smaller compared to the case where the entire area of the widening section is used as the opening diameter. As a result, it is possible to reduce the specifications and installation range of the beam members and column members (both are support members) for suppressing the deformation in the opening formed by cutting the side wall of the circular part and the surrounding area, and furthermore, it becomes possible to omit the beam members and column members. Furthermore, when an auxiliary construction method is required for maintaining the ground, the specifications of this auxiliary construction method can be significantly reduced.

[0013] On the premise of such a tunnel widening construction, in the evaluation method of the design load of this aspect, when the divided section is cut, for the circular part or the already constructed widened part existing in the base end side divided section and the tip side divided section on the base end side and the tip side sandwiching the cut divided section, by distributing half of the load acting from the surrounding ground to the cut divided section to each as the design load, in the design of the circular part which is the existing tunnel (for example, the design when reinforcing the circular part), based on the total load composed of the load directly acting on its own section of each divided section and the load distributed from the cut divided section, a reinforcement design of the existing tunnel during the widening construction with high structural reliability can be realized. In addition, when the widening construction has been planned from the initial design of the existing tunnel, the design of the circular part of the existing tunnel can be carried out based on the above-mentioned total load. When the widening construction is planned after the construction of the existing tunnel, when designing the structure combining the circular part and its opening reinforcement members, the above-mentioned total load can be applied.

[0014] Here, as an example of the divided section, the width of 2 rings or 4 rings of the segment can be set. After cutting open the divided section with a width of 2 rings or 4 rings, the base-end side divided section is set to a width of 1 ring or 2 rings of the segment, and segments are installed in the widened part to perform the construction of the widened part. Then, by cutting open a width of 1 ring or 2 rings of the segment further on the tip side of the tip-side divided section, a width of 2 rings or 4 rings of the segment is newly cut open, and similarly, construction for installing a widened part can be performed on the base-end side divided section (width of 1 ring or 2 rings of the segment).

[0015] In addition, another aspect of the method for evaluating the design load in the tunnel widening construction according to the present invention is the divided section is in the range of 2 rings of the segment, when the load acting on 1 ring of the segment constituting the circular part is set to 100%, the design load after distribution of the circular part of the tip-side divided section after the load is distributed converges to 200% or approximately 200%.

[0016] According to this aspect, when the divided section is in the range of 2 rings of the segment and the load acting on 1 ring of the segment is set to 100%, the design load after distribution of the circular part of the tip-side divided section after the load is distributed converges to 200% or approximately 200%, thereby covering the prediction that the load increases cumulatively and setting the design load of the circular part of the tip-side divided section to a constant value (here, 200%).

[0017] In the construction method of mass excavation described in the above-mentioned "Temporary Sewer Design Manual", usually a load of 150% acts on the front and rear rings. However, regarding sequential partial excavation, due to the characteristics of the construction method, the load of the section cut in the previous process is redistributed in the newly cut section, and the load accumulates. That is, in the construction method of sequentially cutting and widening the construction for each of the above-mentioned divided sections, it is expected that the load distributed to the tip-side divided section, etc. of the divided section to be cut will increase cumulatively. However, according to the verification analysis by the present inventors, when the load acting on one ring of the segment is set to 100%, it is specified that the design load after distribution of the circular part of the tip-side divided section after the load is distributed converges to at most 200%. Based on the results of this verification analysis, the above numerical value is defined. Here, "substantially 200%" means that in the verification analysis, a load value of about 190% is calculated. Therefore, in this specification, for example, from 180% to less than 200% is regarded as substantially 200%.

[0018] Moreover, another aspect of the method for evaluating the design load in the tunnel widening construction according to the present invention is characterized in that the design load after distribution of the widened part of the base-end side divided section after the load is distributed converges to 100% or substantially 100%.

[0019] According to this aspect, when the divided section is within the range of two rings of the segment and the load acting on one ring of the segment is set to 100%, the design load after distribution of the circular part of the base-end side divided section after the load is distributed converges to 100% or substantially 100%. Thus, contrary to the expectation that the load increases cumulatively, the design load of the circular part of the base-end side divided section can be set to a constant value (here, 100%).

[0020] That is, in the construction method of sequentially cutting and constructing the widened portions for each of the above-described divided sections, it is expected that the load distributed to the base-end side divided section, etc. of the divided section to be cut will increase cumulatively. However, according to the verification analysis by the present inventors, when the load acting on one ring of the segment is set to 100%, it has been specified that the design load after distribution of the circular portion of the base-end side divided section after the load is distributed converges to at most 100%. The above numerical values are defined based on the results of this verification analysis. Here, "substantially 100%" means that in the verification analysis, a load value of about 90% is calculated. Therefore, in this specification, for example, 80% to less than 100% is regarded as substantially 100%.

[0021] In addition, another aspect of the method for evaluating the design load in the tunnel widening construction according to the present invention is characterized in that the upper line and the lower line of the adjacent divided sections are aligned.

[0022] According to this aspect, by aligning the upper line and the lower line of the adjacent divided sections, the design load after distribution of the circular portion of the tip-side divided section described above can be set to 200% or substantially 200%, and the design load after distribution of the circular portion of the base-end side divided section can be set to 100% or substantially 100%.

[0023] In addition, one aspect of the tunnel widening construction method according to the present invention is a tunnel widening construction method in which a part of the side wall is cut open from the circular portion of the existing tunnel, and the widened portion of a predetermined widened section is constructed in order from the base-end side where the construction starts to the tip-side where the construction ends, comprising a prior widening excavation step, a widened portion construction step, and a subsequent widening excavation step, wherein the prior widening excavation step constructs a widened excavation area by widening and excavating a range of two rings of segments at the base-end side of the widened section, the widened portion construction step constructs a widened portion in a range of one ring of segments at the base-end side of the widened excavation area, and the subsequent widening excavation step constructs a new widened excavation area in a range of one ring of segments at the tip-side of the widened excavation area. The method is characterized by repeating the widthening part construction process and the subsequent widthening excavation process to construct the widthening part in the predetermined widthening section.

[0024] According to this aspect, it relates to a tunnel widening construction method for sequentially constructing the widening part of a predetermined widening section from the base end side to the tip end side. An excavation area is constructed by widening excavation of a range of two rings of segments at the base end side of the widening section (prior widening excavation process), a widening part is constructed in a range of one ring of segments at the base end side of the widening excavation area (widthening part construction process), a new widening excavation area is constructed in a range of one ring of segments at the tip end side of the widening excavation area (subsequent widening excavation process), and by repeating the widthening part construction process and the subsequent widening excavation process in the predetermined widening section, the widening excavation range is limited to a certain range instead of the entire range of the widening section. By sequentially performing the opening and widening construction of the certain range, the opening diameter of the divided section can be made significantly smaller compared to the case where the entire area of the widening section is used as the opening diameter. The specifications of beam members and column members for suppressing deformation of the cut opening and the surrounding area can be reduced, and furthermore, it becomes possible to omit the beam members and column members.

Advantages of the Invention

[0025] According to the method for evaluating the design load and the tunnel widening construction method in the tunnel widening construction of the present invention, the specifications and installation range of the opening reinforcement material around the opening formed by the cutting can be reduced, or the opening reinforcement material can be omitted.

Brief Description of the Drawings

[0026]

Figure 1

Figure 2A

Figure 2B

Figure 3A

Figure 3B

Figure 4A

Figure 4B

Figure 5A

Figure 5B

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10A

Figure 10B

Figure 11A

Figure 11B

Mode for Carrying Out the Invention

[0027] Hereinafter, a method for evaluating design loads and a method for widening a tunnel in the tunnel widening construction according to the embodiment will be described with reference to the attached drawings. In the present specification and drawings, substantially the same components may be denoted by the same reference numerals, and redundant descriptions may be omitted.

[0028] [Method for Evaluating Design Loads and Method for Widening a Tunnel in Tunnel Widening Construction According to the Embodiment] With reference to FIGS. 1 to 11, an example of a method for evaluating design loads and a method for widening a tunnel in the tunnel widening construction according to the embodiment will be described. Here, FIG. 1 is a side view of a tunnel for explaining an example of a method for widening a tunnel and a method for evaluating design loads according to the embodiment. FIGS. 2A to 5A are process diagrams of an example of a method for widening a tunnel according to the embodiment in order, which are cross-sectional views orthogonal to the tunnel axis direction, and FIGS. 2B to 5B are cross-sectional views of the tunnel cut at an intermediate position in the corresponding FIGS. 2A to 5A, respectively.

[0029] The existing tunnel shown in FIG. 1 has a circular portion 20 composed of a plurality of steel segment rings 10 and circular portions composed of a plurality of RC (Reinforced Concrete) segment rings 10' on the left and right thereof, and a widened portion is constructed in a partial section of the circular portion 20 composed of the steel segment rings 10. For example, when the circular portion 20 is a road tunnel, the widened portion is provided for an emergency exit or an emergency parking area provided in a partial section of the road tunnel.

[0030] The steel segment ring 10 is formed by assembling a plurality of steel segments (A segment, B segment, and K segment) in the circumferential direction. In the illustrated example, among the 31 rings from segment ring R3 to segment ring R33, the section corresponding to the 21 rings in the center thereof is planned as the widened section, and the width t of the steel segment ring 10 in the tunnel axis direction is, for example, 1500 mm.

[0031] In the conventional construction method of cutting open the widened section corresponding to this 21-ring all at once, based on the description in the aforementioned "Sewer Temporary Design Manual - Shield Construction Edition - April 2023, Tokyo Sewerage Service Co., Ltd.", as shown in Figure 1, the affected range due to the cutting is a 63-ring section including the sections corresponding to 21 rings on each side of the widened section. The specifications of the opening reinforcement materials around the opening formed by the cutting are extremely large, and the installation range is also extensive.

[0032] In contrast, according to the widened construction method and the method for evaluating the design load according to the embodiment described below, the affected range due to the cutting of the circular part 20 is a 25-ring section including the sections corresponding to 2 rings on each side of the widened section. The specifications and installation range of the opening reinforcement materials around the opening formed by the cutting can be significantly reduced, and in some cases, it is also possible to omit the opening reinforcement materials.

[0033] To explain the widened construction method according to the embodiment, first, as shown in Figures 2A and 2B, a support work 30 for supporting the upper and lower parts of the opening formed in the widened section of the circular part 20 is installed. The support work 30 includes support columns extending vertically and support beams (longitudinal beams) extending in the axial direction of the tunnel at the upper and lower ends of the support columns. Also, inside the circular part 20, a stage 35 for the movement and driving of heavy machinery and other equipment to perform operations is installed.

[0034] Subsequent to or prior to the installation of the above-mentioned support work 30 and stage 35, at least in the surrounding ground of the widened section, ground improvement construction such as the chemical solution injection method or the freezing method is carried out to create the improved ground G. Note that if the surrounding ground is hard or the groundwater level is relatively low, the creation of the improved ground G can be made unnecessary.

[0035] After constructing the improved ground G, a pipe roof 40 for retaining soil at the upper part of the widened excavation area is installed while being pushed out from the inside of the circular part 20 into the inside of the improved ground G. Specifically, while adding curved steel pipes or the like, an arc-shaped pipe roof 40 of a predetermined length is installed inside the improved ground G as shown in the illustrated example, and this is repeatedly carried out at intervals in the axial direction of the tunnel over the widened section, thereby retaining the improved ground G above it and enabling the widened excavation of the improved ground G below it.

[0036] In the widened construction method of the illustrated example, the widened part is sequentially constructed by successive partial excavation in which cutting construction (cutting process) and widened construction (widening process) are repeatedly carried out in order from the base-end side ring R8 to the tip-end side ring R28 in the widened section shown in FIG. 1. More specifically, the first two rings are cut open in one go as a divided section in the widened section, widened excavation is carried out in the divided section, and then widened rings are constructed by installing widened part segments in the widened area of one ring on the base-end side. Next, one ring at the tip-end side of the widened excavation area is cut open and widened excavation is carried out to form a new divided section of two rings. Then, widened rings are constructed in the divided section while sequentially forming such divided sections, and this is repeatedly carried out up to ring R28 of the circular part 20, thereby constructing a widened part in which a plurality of widened rings are provided side by side (widened section) on the side of rings R8 to R28 of the circular part 20.

[0037] Explaining the above construction details in more detail, first, as shown in FIG. 2B, two rings (width of 2×t) of ring R8 and ring R9 are taken as a removal target (divided section) in one go, and as shown in FIGS. 3A and 3B, the improved ground G1 is widened and excavated by the backhoe U1 placed on the stage 35 to construct a widened excavation area, and a sprayed floor F is constructed by spraying concrete onto the floor surface of the widened excavation area (preceding widened excavation process).

[0038] Next, as shown in FIGS. 4A and 4B, an expansion ring 60 is constructed by installing a segment for expansion in the widened excavation area of the base-end side ring R8. Next, an aerial work platform U2 is placed on the stage 35, and a backfill material 50 such as fluidized treated soil is filled into the back area of the expansion ring 60 (the area below the pipe roof 40) through a filling hole (not shown) provided in the expansion ring 60.

[0039] At this stage, no expansion ring is installed in the widened excavation area on the side of the tip-end side ring R9, and the widened excavation area is left below the pipe roof 40 (the above is the expansion part construction process).

[0040] Next, as shown in FIGS. 5A and 5B, the improved ground G2 on the side of the ring R10 at the tip-end side of the ring R9 is widened and excavated to construct a new widened excavation area, which is combined with the widened excavation area on the side of the ring R9 where the expansion ring is not yet installed, to form a widened excavation area in a new two-ring divided section (the subsequent widened excavation process).

[0041] Thereafter, an expansion part construction process of constructing an expansion ring 60 and filling the backfill material 50 is performed on the widened excavation area on the side of the ring R9, and the widened excavation area on the side of the next ring R11 is widened and excavated. In this way, the expansion part construction process and the subsequent widened excavation process are repeated to construct an expansion part in which the expansion rings 60 are arranged side by side with each other over the expansion section.

[0042] According to this construction method, the excavation range for widening is limited to a certain range rather than the entire range of the widening section. By sequentially performing the excavation of a certain range and the construction of the widened part, the opening diameter of the divided section can be significantly reduced compared to the case where the entire widening section is used as the opening diameter. For example, in the illustrated example, since the divided section is 2 rings, the 21 rings of the widening section and the 2 rings on both its left and right sides, a total of 25 rings, become the affected range. Compared with the affected range of 63 rings when the conventional 21-ring widening section is excavated all at once, the specifications of the beam members and column members for suppressing the deformation of the excavated opening and the surrounding area can be significantly reduced, the installation range can be significantly narrowed, and in some cases, the beam members and column members can be omitted.

[0043] Next, with reference to FIGS. 6 to 9, an example of the method for evaluating the design load according to the embodiment will be described. Here, FIG. 6 is a diagram showing an example of an analysis model used in a three-dimensional FEM analysis for setting the loads distributed to the tip-side divided section and the base-end side divided section in the method for evaluating the design load according to the embodiment. FIG. 7 is a diagram showing an example of an analysis model obtained by cutting the tunnel vertically along its center line in the analysis model shown in FIG. 6, and FIG. 8 is a graph showing the analysis results. Further, FIG. 9 is an explanatory diagram showing the loads after distribution to the tip-side divided section and the base-end side divided section at each construction stage in the method for evaluating the design load according to the embodiment.

[0044] As shown in FIG. 6, in the three-dimensional FEM (Finite Element Method) analysis for setting the loads after distribution, in the ground model M0, a circular part model M1 of an existing tunnel with a diameter of 2D is created at a position with a depth of H, and the range of 2H on both the left and right sides of the circular part model M1 is modeled as the affected range.

[0045] Also, as shown in FIG. 7, in the widening section of the circular part model M1, a support beam model M3 and a support column model M4 (both are support work models) are created, and on the side of the circular part model M1, the widening part model M2 to be sequentially constructed is created step by step.

[0046] Through this sequential excavation analysis, the distribution loads assigned to the widened excavation area (Area A) in the two-ring division section shown in Fig. 9, the two-ring division section (Area B2) on the proximal side, and the two-ring division section (Area B1) on the distal side are determined as shown in Fig. 8.

[0047] In Fig. 8, the horizontal load acting from the surrounding ground on the circular part is calculated as 468 kN / m. 2 When this horizontal load acting on one ring of the circular part is taken as 100%, the horizontal load for two rings initially acting on the widened excavation area of Area A is 918 kN / m on Area B1, which is on the distal side of Area A, the widened excavation area. 2 As a result, an analysis result is obtained where a horizontal load of 196% (equivalent to approximately 200%) acts.

[0048] On the other hand, in Fig. 8, when the horizontal load acting on one ring of the circular part is taken as 100% as described above, the horizontal load for two rings initially acting on the widened excavation area of Area A is 431 kN / m on Area B2, which is on the proximal side of Area A, the widened excavation area. 2 As a result, an analysis result is obtained where a horizontal load of 92% (equivalent to approximately 100%) acts.

[0049] Explaining this with reference to Fig. 9, which shows the incremental load for each analysis step, when the 1,2R (ring) opening occurs, 50% of the 100% of the horizontal load of 200% in Area A is incremented by 50% to each of the two rings in Area B1 and Area B2, and for each ring, 150% becomes the design load of the segment ring that constitutes the circular part.

[0050] Next, when a widened ring is constructed on the 1R (ring) and the 3R (ring) is cut open to form an opening in the 2,3R (ring) by the above construction method, since a horizontal load of 150% which is the design load of the B1 region at the time of the 1,2R opening is redistributed to the new B1 region and B2 region, a horizontal load of 150% / 4 = 37.5% is redistributed to each ring. As a result, the horizontal load of the 4R in the B1 region becomes 150% + 37.5% = 187.5%, the horizontal load of the 5R becomes 100% + 37.5% = 137.5%, and the design load of the widened ring already constructed in the 1R of the B2 region becomes 37.5%.

[0051] Next, when the 4R (ring) is cut open to form an opening in the 3,4R (ring), since a horizontal load of 187.5% which is the design load of the B1 region at the time of the 2,3R opening is redistributed to the new B1 region and B2 region, a horizontal load of 187.5% / 4 = 46.95% is redistributed to each ring. As a result, the horizontal load of the 5R in the B1 region becomes 137.5% + 46.95% = 184.4%, which is less than 187.5% which is the maximum horizontal load in the B1 region at the previous construction step.

[0052] On the other hand, the design load of the widened ring constructed in the 1R of the B2 region becomes 37.5% + 46.95% = 84.4%, which is less than 100% which is the horizontal load initially acting on the 1R.

[0053] That is, in the sequential partial excavation of the illustrated example, when the horizontal load acting on one ring is set to 100%, as the design load of the B1 region (the design load of the existing tunnel, or the design load for the existing tunnel and the opening reinforcement member) on the tip side where the horizontal load of the A region is distributed, at most 200% is the maximum as in the analysis result shown in Fig. 8, and as the design load of the B2 region (the design load of the widened ring) on the base end side where the horizontal load of the A region is distributed, at most 100% is the maximum as in the analysis result shown in Fig. 8.

[0054] From the above, in the method for evaluating the design load in the tunnel widening construction according to the embodiment, on the premise of implementing the tunnel widening construction method according to the embodiment, when the divided section is opened, for the circular part or the already widened part existing in the base end side divided section and the tip side divided section sandwiching the opened divided section, half of the load acting from the surrounding ground on the opened divided section is distributed to each as the design load. And when the load acting on one ring of the segments constituting the circular part is set to 100%, the design load after distribution of the circular part of the tip side divided section after the load is distributed converges to 200% or approximately 200%, and the design load after distribution of the widened part of the base end side divided section after the load is distributed converges to 100% or approximately 100%.

[0055] By the method for evaluating the design load in the illustrated example, it is possible to realize the reinforcement design of the existing tunnel during the widening construction with high structural reliability.

[0056] Next, with reference to FIGS. 10 and 11, a method for designing the improved ground on the side and bottom of the divided section will be described. Here, FIG. 10A is a diagram for explaining the method for designing the improved ground on the side of the divided section, and FIG. 10B is a view taken along the line B - B of FIG. 10A. On the other hand, FIG. 11A is a diagram for explaining the method for designing the improved ground at the bottom of the divided section, and FIG. 11B is a view taken along the line B - B of FIG. 11A.

[0057] As shown in FIGS. 10A and 10B, in the circular part, the water pressure Pw and the active earth pressure Pa act on the improved ground Gs on the side of the two - ring widened ring 60 which is the divided section forming the widened part 70. The improved ground Gs with strength and thickness capable of resisting the total value of these, that is, the soil - water pressure, is designed by the shear resistance S of the improved ground Gs. This is a study of the punching shear resistance against the soil - water pressure.

[0058] On the other hand, as shown in FIGS. 11A and 11B, in the circular part, the hydraulic pressure Pw acts on the improved ground Gs at the bottom of the two-ring widened ring 60, which is the divided section forming the widened section 70. The improved ground Gs with strength and thickness capable of resisting the hydraulic pressure Pw is designed based on the soil mass weight W and shear resistance S of the improved ground Gs. This is the study of the swelling of the ground against the uplift pressure.

[0059] In any design, the range where the improved ground Gs is punched out or swells is limited to the width of the two-ring divided section, and since the shear resistance S at both ends can be expected for each divided section, for example, compared with the case of considering the punching out or swelling of the improved ground over the entire area of 21 rings, it becomes possible to reduce the thickness of the improved ground, contributing to the reduction of construction costs and ensuring the separation from the public-private boundary due to the narrowing of the improved ground range.

[0060] In addition, other embodiments in which other components are combined with the configurations described in the above embodiments may be possible, and the present invention is not limited to the configurations shown here at all. In this regard, it can be changed without departing from the spirit of the present invention, and can be appropriately determined according to the application form.

Explanation of Reference Numerals

[0061] 10, 10': Segment ring 20: Existing tunnel (circular part) 30: Support 35: Stage 40: Pipe roof 50: Backfill material 60: Widened ring 70: Widened section G: Improved ground G1, G2: Improved ground U1: Backhoe U2: Aerial work platform F: Spraying floor M0: Ground model M1: Circular part model (existing tunnel model) M2: Widened section model M3: Support Beam Model (Support Structure Model) M4: Support Column Model (Support Structure Model) M5: Pipe Roof Model

Claims

1. A method for evaluating the design load in the widening construction of a tunnel, wherein a part of the side wall is cut open from the circular part of an existing tunnel, and the widened part of a predetermined widening section is constructed in order from the base end side where the construction starts to the tip end side where the construction ends. The tunnel widening construction comprises a cutting open step and a widening step. The cutting open step cuts open divided sections into which the widening section is divided into a plurality. The widening step widens all or part of the divided sections in order from the base end side thereof. In the widening section, the cutting open step and the widening step are repeated in order from the divided section on the base end side to construct the widened part. In the method for evaluating the design load in the widening construction of a tunnel, when the divided section is cut open, half of the load acting from the surrounding ground on the cut divided section is distributed to the base end side divided section and the tip end side divided section existing on the base end side and the tip end side sandwiching the cut divided section, with respect to the circular part or the already constructed widened part, and this is taken as the design load. A method for evaluating the design load in the widening construction of a tunnel, characterized in that when the divided section is cut open, half of the load acting from the surrounding ground on the cut divided section is distributed to the base end side divided section and the tip end side divided section existing on the base end side and the tip end side sandwiching the cut divided section, with respect to the circular part or the already constructed widened part, and this is taken as the design load.

2. The divided section is in the range of two rings of segments. When the load acting on one ring of the segments constituting the circular part is taken as 100%, The method for evaluating the design load in the widening construction of a tunnel according to Claim 1, characterized in that the design load after distribution of the circular part of the tip end side divided section after the load is distributed converges to 200% or approximately 200%.

3. The method for evaluating the design load in the widening construction of a tunnel according to Claim 2, characterized in that the design load after distribution of the widened part of the base end side divided section after the load is distributed converges to 100% or approximately 100%.

4. The method for evaluating the design load in the widening construction of a tunnel according to any one of Claims 1 to 3, characterized in that the upper line and the lower line of adjacent divided sections are aligned.

5. A method for widening a tunnel, wherein a part of the side wall is cut open from the circular part of an existing tunnel, and the widened part of a predetermined widening section is constructed in order from the base end side where the construction starts to the tip end side where the construction ends. The method comprises a prior widening excavation step, a widened part construction step, and a subsequent widening excavation step. The prior widening excavation step excavates and widens a range of two rings of segments at the base end side of the widening section to construct a widened excavation area. The prior widening excavation step excavates and widens a range of two rings of segments at the base end side of the widening section to construct a widened excavation area. In the widening part construction process, a widening part is constructed within the range of one ring of the segment on the proximal end side in the widening excavation area, In the subsequent widening excavation process, a new widening excavation area is constructed within the range of one ring of the segment on the distal end side in the widening excavation area, A tunnel widening construction method, characterized in that the widening part construction process and the subsequent widening excavation process are repeated to construct the widening part in the predetermined widening section.

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