Design method for tunnel crossing support structures

Abstract

To provide a method of designing the intersection supporting of a tunnel that is capable of setting an earth covering load in a structural analysis of a main pit supporting under a flow systematized on the basis of rational foundation.SOLUTION: A method of designing the intersection supporting of a tunnel comprises a process A of setting an earth covering load acting on a main pit 10 including an intersection on the basis of a loosening earth covering pressure of Terzaghi when a loosening height of Terzaghi can be calculated, and setting the earth covering load on the basis of drilling release force by the finite element method when the loosening height of Terzaghi cannot be calculated, a process B of applying the earth covering load set to main pit supporting models M1, M2 and executing a structural analysis, and calculating a load R for intersection supporting design when designing the intersection supporting 30 and a process C of executing the structural analysis of an intersection supporting model M3.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a design method for the intersection support work of tunnels.

Background Art

[0002] In recent mountain tunnel construction, when access to the portal side is difficult or when multiple headings are planned for the purpose of shortening the construction process, a method of constructing a connecting tunnel (or an advance pilot tunnel, a pilot tunnel) with a vertical linear shape intersecting the main tunnel in advance of the construction of the main tunnel is applied. At the intersection (branching part) of the main tunnel and the connecting tunnel that intersect each other, a portal-shaped intersection support work with a U-shaped or horseshoe-shaped front view is constructed. However, the construction of the intersection support work generally takes place in a narrow construction space and involves the lifting and assembly of construction members different from those of ordinary tunnels, so there are problems with workability and it is difficult to ensure construction safety at present. The conventional design method for the intersection support work of the above-mentioned tunnels is roughly as follows. That is, first, the main tunnel support work is considered. Among the axial forces (reaction forces) calculated in this consideration, the axial force (reaction force) at the position corresponding to the intersection is specified, and the intersection support work is considered using the specified axial force (reaction force). In the consideration of the main tunnel support work, the specifications of the main tunnel support work are determined, the ground reaction coefficient around the main tunnel support work is set, a main tunnel support work model that is a beam spring model (framework model) or a two-dimensional or three-dimensional FEM (Finite Element Method) model is created, the soil cover load (vertical load) acting on the main tunnel support work model is set, and a structural analysis is carried out by loading the set soil cover load onto the main tunnel support work model, whereby the main tunnel support work is designed. Among the axial forces (reaction forces) calculated in the structural analysis of the main tunnel support work, the axial force (reaction force) at the installation position of the intersection support work is specified and set as the load (vertical load) acting on the intersection support work. In the design of the intersection support work, an intersection support work model consisting of a beam spring model or the like is created, and a structural analysis is carried out by loading the axial force (reaction force) specified from the structural analysis of the main tunnel support work onto the intersection support work model, whereby the intersection support work is designed.

[0003] Incidentally, in the conventional design method for junction support structures described above, there are various methods for setting (calculating) the overburden load used in the structural analysis of the main tunnel support structure, which is the preceding step. Consequently, there is a problem in that the specifications of the designed junction support structure vary depending on the set overburden load. In other words, the method of setting the overburden load differs depending on the designer, and the specifications of the cross-section support structure, which are designed based on these different overburden load settings, will change, which can lead to problems with the reliability of the design results. Furthermore, there are issues regarding the rationality and efficiency of designers setting a single overburden load from among multiple methods for setting it each time a tunnel is designed, even when the rationale for its adoption may not be clear.

[0004] The above-mentioned methods for setting the overburden load include the Terzaghi method using loosening earth pressure, the method of evaluating the plastic region of the elastoplastic theoretical solution as loosening earth pressure, the method of evaluating the blast damage region as loosening earth pressure, and the method using excavation release force from FEM analysis. Terzaghi's method for calculating loosened soil pressure is based on soil strength parameters (internal friction angle, cohesion, etc.), making the evaluation of these strength parameters crucial. Furthermore, in the method of evaluating the plastic region of the elastoplastic theoretical solution as loosening earth pressure, the evaluation of the strength parameters is important because the plastic region is calculated based on the strength parameters of the ground (internal friction angle, cohesion, etc.). On the other hand, in the method of evaluating the blast damage area as loosened earth pressure, the blast damage area is evaluated as being within a 3m range from the tunnel wall. Furthermore, when the three methods for setting the overburden load described above are applied, the main tunnel support model on which the overburden load is applied is a beam spring model (framework model), whereas in the method using excavation release force by FEM analysis, the main tunnel support model becomes a literal FEM model, and the analysis results naturally differ from those of the frame structure analysis.

[0005] Therefore, in designing tunnel intersection support structures, when determining the loads applied to the intersection support structure model from the structural analysis of the main tunnel support structure, a design method for tunnel intersection support structures is desired that allows the overburden load during the structural analysis of the main tunnel support structure to be set under a systematic flow based on rational grounds.

[0006] Here, Patent Document 1 proposes a shield tunnel structure in which an opening such as a branch tunnel is formed on the inner circumferential surface of the main tunnel excavated by a shield tunneling machine. Specifically, a pair of reinforcing column members are provided on both the front and rear outer sides in the axial direction of the main tunnel at the exit of the branch tunnel, and upper and lower reinforcing beam members are provided at both the upper and lower ends of this pair of reinforcing column members so as to straddle them. The reinforcing column members are made up of segments, and the reinforcing beam members are set in reinforcing material assembly parts that are provided in advance on the segments.

[0007] On the other hand, Patent Document 2 proposes a lining structure for the intersection of a main tunnel and a connecting tunnel. Specifically, it comprises a support member installed at the intersection and having an opening that connects the main tunnel and the connecting tunnel; a lining plate provided at the intersection at a distance from the inner wall of the main tunnel, with its end supported between the bottom of the main tunnel and the upper part of the support member; and mortar poured between the lining plate and the inner wall of the main tunnel, between the support member and the inner wall of the main tunnel, and between the support member and the inner wall of the connecting tunnel. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2003-253992 [Patent Document 2] Japanese Patent Publication No. 2011-32684 [Overview of the project] [Problems that the invention aims to solve]

[0009] Although Patent Documents 1 and 2 contain descriptions of the structure and lining structure of shield tunnels, as mentioned above, they do not propose a systematic method for setting the overburden load based on rational grounds in the design of tunnel crossing support structures.

[0010] The present invention aims to provide a design method for tunnel intersection support structures, which enables the determination of the load applied to the intersection support structure model from the structural analysis of the main tunnel support structure, by setting the overburden load during the structural analysis of the main tunnel support structure under a systematic flow based on rational grounds. [Means for solving the problem]

[0011] To achieve the above objective, one aspect of the design method for tunnel crossing support structures according to the present invention is: A design method for tunnel crossing supports, wherein the main tunnel and connecting tunnel intersect at an intersection, and the main tunnel support structure and the crossing support structure are modeled and designed separately. Step A involves setting the overburden load acting on the main tunnel, including the aforementioned intersection, by setting the overburden load based on the Terzaghi loosening earth pressure if the Terzaghi loosening height can be calculated, and setting the overburden load based on the excavation release force by the finite element method if the Terzaghi loosening height cannot be calculated. Step B involves applying the set soil cover load to the main tunnel support model of the main tunnel support structure including the intersection and performing a structural analysis to determine the reaction force at the position corresponding to the intersection in the main tunnel support model, and using this reaction force as the design load for the intersection support structure when designing the intersection support structure. The method is characterized by having step C, which involves applying the design load for the intersection support structure to the intersection support structure model and performing a structural analysis to set the structural specifications for the intersection support structure.

[0012] According to this embodiment, when setting the overburden load acting on the main tunnel including the intersection, if the ground is soft rock for which Terzaghi loosening height can be calculated, the overburden load is set based on Terzaghi loosening earth pressure. If the ground is hard rock (including medium-hard rock) for which Terzaghi loosening height cannot be calculated, the overburden load is set based on the excavation release force by the finite element method. This allows the overburden load to be set under a systematized flow based on rational grounds. As a result, the reliability of the design results of the shoring at the intersection is further increased, leading to the efficient and rational design of the shoring at the intersection.

[0013] The inventors have conducted structural analysis on several past design examples, setting different soil cover loads than those used in the design, and have verified the results by comparing the structural analysis results for each soil cover load with the actual measurement results (stress measurement results, calculated stresses based on displacement measurement results, etc.). In design cases where the ground is hard, it was confirmed that the cohesion and friction angle of the ground are large, making it impossible to calculate the Terzaghi loosening height. Therefore, methods for setting the overburden load were investigated using the blast damage area method, the elastoplastic theory solution method, and the two-dimensional FEM analysis method. As a result, it was verified that the blast damage area method and the elastoplastic theory solution method underestimate the sectional forces calculated by structural analysis, while the two-dimensional FEM analysis method reproduces the sectional forces calculated by structural analysis with relatively good accuracy. Based on these verification results, if the ground is hard (hard rock or moderately hard rock) and the Terzaghi loosening height cannot be calculated, the overburden load will be set based on the excavation release force obtained by the finite element method (for example, the two-dimensional finite element method). On the other hand, in design examples where the ground is soft, it has been confirmed that both the method using blast damage zones and the method using two-dimensional FEM analysis underestimate the axial force and bending moment calculated by structural analysis. It has been verified that the method using Terzaghi's loosening earth pressure and the method using elastoplastic theory reproduce the sectional forces calculated by structural analysis with relatively good accuracy. However, the method using elastoplastic theory has design constraints, such as the prerequisites of isotropy and isobaric conditions and a single layer of ground. Based on these verification results, if the ground is soft (soft rock) and the Terzaghi loosening height can be calculated, the overburden load will be set based on the Terzaghi loosening earth pressure.

[0014] Furthermore, in another aspect of the design method for tunnel crossing support structures according to the present invention, The aforementioned intersection support structure model is characterized by being a model that incorporates both steel support structures and shotcrete.

[0015] According to this embodiment, when the shoring at an intersection includes both steel shoring and sprayed concrete, the shoring model at the intersection is a model that incorporates both the steel shoring and the sprayed concrete. This results in a design method that reflects the actual structure of the shoring at the intersection and can reproduce the measurement results with greater accuracy. Intersection shoring is generally formed by applying sprayed concrete (filling concrete) to the drilled borehole walls and then erecting steel shoring, such as H-beams, inside the sprayed concrete. However, according to the inventors' verification of several past design examples, sprayed concrete is generally not considered when creating models for intersection shoring. The reason for this is presumably based on a conservative structural design, but since sprayed concrete applied to a predetermined thickness has a certain degree of rigidity, designs that do not consider sprayed concrete lead to the setting of oversized steel shoring. Therefore, as a result of modeling the intersection support work including the sprayed concrete actually under construction and performing structural analysis, it has been verified that the structural analysis results using the intersection support work model that models both the sprayed concrete and the steel support work reproduce the measurement results with relatively high accuracy, making it possible to set the steel support work with excessive specifications to appropriate specifications. This leads to an improvement in the workability of the intersection support work, which is generally constructed in a narrow construction space, as described above.

[0016] In addition, another aspect of the design method for the intersection support work of a tunnel according to the present invention is When the Terzaghi loosening height can be calculated in the step A, in the step B, the main pit support work model is used as a framework model, a radial ground spring for the main pit support work is installed on the framework model, and a circumferential ground spring for the main pit support work is not installed.

[0017] According to this aspect, when the Terzaghi loosening height can be calculated, by installing a radial ground spring on the main pit support work model, which is a framework model, and not installing a circumferential ground spring (shear spring), the measurement results can be reproduced with higher accuracy. This result is also based on the verification results by the inventors.

[0018] In addition, another aspect of the design method for the intersection support work of a tunnel according to the present invention is When the Terzaghi loosening height can be calculated in the step A, a horizontal load is applied to the framework model in addition to the overburden load.

[0019] According to this aspect, when the Terzaghi loosening height can be calculated, by applying a horizontal load to the main pit support work model, which is a framework model, in addition to the overburden load, the measurement results can be reproduced with higher accuracy. This result is also based on the verification results by the inventors.

Effects of the Invention

[0020] According to the design method for tunnel intersection support structures of the present invention, in designing tunnel intersection support structures, when determining the loads applied to the intersection support structure model from the structural analysis of the main tunnel support structure, the overburden load during the structural analysis of the main tunnel support structure can be set under a systematic flow based on rational grounds. [Brief explanation of the drawing]

[0021] [Figure 1] This is a schematic diagram illustrating an example of a configuration in which the main tunnel and the connecting tunnel intersect. [Figure 2] This is a view from the direction of arrow II in Figure 1. [Figure 3] This is a view from the direction of arrow III in Figure 1. [Figure 4] This is a flowchart illustrating an example of a design method for tunnel crossing support structures according to the embodiment. [Figure 5] This is a model diagram of an example of a main tunnel support structure model, which is a framework model. [Figure 6] This is a model diagram of an example of a two-dimensional FEM model of a main tunnel support structure. [Figure 7] This is a model diagram of an example of a crossing support structure model. [Figure 8A] This figure shows both the structural analysis results and measurement results when the method of determining the overburden load using the blast damage area was applied in a design example where the ground is hard. [Figure 8B] This figure shows both the structural analysis results and measurement results when a method based on elastoplastic theory is applied as the method for setting the soil cover load in a design example where the ground is hard. [Figure 8C] This figure shows both the structural analysis results and measurement results when a two-dimensional FEM analysis method was applied as a method for setting the soil cover load in a design example where the ground is hard. [Figure 9A] This figure shows both the structural analysis results and measurement results when Terzaghi's method of determining soil cover load was applied as a design example where the ground is soft. [Figure 9B]This figure shows both the structural analysis results and measurement results when the method of determining the overburden load was applied using the blast damage area method in a design example where the ground is soft. [Figure 9C] This figure shows both the structural analysis results and measurement results when a method based on elastoplastic theory is applied as the method for setting the overburden load in a design example where the ground is soft. [Figure 9D] This figure shows both the structural analysis results and measurement results when a two-dimensional FEM analysis method was applied as a method for setting the overburden load in a design example where the ground is soft. [Figure 10A] This figure shows both the structural analysis results and measurement results when circumferential ground springs (shear springs) are installed for the main tunnel support model in a design example where the ground is soft. [Figure 10B] This figure shows both the structural analysis results and measurement results for a design example where the ground is soft, and circumferential ground springs (shear springs) are not installed for the main tunnel support model. [Figure 11A] This figure shows both the structural analysis results and measurement results when a horizontal load is applied to the main tunnel support model in a design example where the ground is soft. [Figure 11B] This figure shows both the structural analysis results and measurement results for a design example where the ground is soft, specifically when no horizontal load is applied to the main tunnel support model. [Figure 12A] This figure shows both the structural analysis results and measurement results when using a cross-section support model that does not consider shotcrete in a design example where the ground is hard. [Figure 12B] This figure shows both the structural analysis results and measurement results when using a cross-section support model that does not consider shotcrete in a design example where the ground is soft. [Figure 12C] This figure shows both the structural analysis results and measurement results when using a cross-section support model that takes into account shotcrete in a design example where the ground is hard. [Figure 12D]This figure shows both the structural analysis results and measurement results when using a cross-section support model that takes into account shotcrete in a design example where the ground is soft. [Modes for carrying out the invention]

[0022] The design method for tunnel crossing support structures according to the embodiment will be described below with reference to the attached drawings. In this specification and the drawings, substantially identical components may be denoted by the same reference numerals to avoid redundant explanations.

[0023] [Design method for tunnel crossing support structure according to the embodiment] Referring to Figures 1 to 12, an example of a design method for tunnel intersection support structures according to the embodiment will be described. Here, Figure 1 is a schematic diagram showing an example of a configuration in which the main tunnel and the connecting tunnel intersect, and Figures 2 and 3 are views in direction II and direction III of Figure 1, respectively. Figure 4 is a flowchart of an example of a design method for tunnel intersection support structures according to the embodiment. Furthermore, Figure 5 is a model diagram of an example of a main tunnel support structure model which is a framework model, Figure 6 is a model diagram of an example of a main tunnel support structure model which is a two-dimensional FEM model, and Figure 7 is a model diagram of an example of an intersection support structure model.

[0024] The tunnel intersection support structure targeted by the design method of this embodiment is a support structure constructed at the intersection of the main tunnel 10, which is a mountain tunnel constructed within the ground G, and a connecting tunnel 20 (pilot tunnel) that intersects the main tunnel 10. The connecting tunnel 20, which is constructed prior to the main tunnel 10, generally has a smaller cross-section than the main tunnel 10 and is constructed in advance for various purposes, such as obtaining the physical properties of the ground G during the construction (excavation) of the main tunnel 10, and transporting materials and equipment during the construction of the main tunnel 10. Then, the starting tunnel for construction of the main tunnel 10 is constructed using the connecting tunnel 20, and construction of the main tunnel 10 is carried out starting from the starting tunnel.

[0025] As shown in Figures 2 and 3, the main tunnel 10 has a main tunnel support structure 11 including a main tunnel steel support structure 12 and a main tunnel shotcrete 13, and a main tunnel lining concrete 14 that is constructed inside the main tunnel support structure 11. Here, the cross-sectional shape of the main tunnel 10 in the illustrated example is horseshoe-shaped, but various other cross-sectional shapes such as circular, elliptical, and rectangular can also be applied.

[0026] The cross-section support structure 30, constructed at the intersection of the main tunnel 10 and the connecting tunnel 20, consists of a steel support structure 31 and shotcrete 32 surrounding it. Inside the steel support structure 31, the connecting tunnel lining concrete 22, which constitutes the connecting tunnel 20, is constructed. In the construction of the connecting tunnel 20, the connecting support structure, including shotcrete and steel support structures, is constructed on the drilled tunnel wall, and the connecting tunnel lining concrete 22 is constructed inside it. In this example, the cross-sectional shape of the cross-section support structure 30 is also horseshoe-shaped, and the cross-sectional shape of the connecting tunnel 20 constructed inside it is circular. In addition to the horseshoe shape shown in the example, the cross-sectional shape of the cross-section support structure 30 may also be U-shaped, etc., but all cross-sectional shapes of cross-section support structures are included in portal support structures.

[0027] Next, with reference to Figure 4, we will explain in detail the design method for the shoring at the intersection.

[0028] The general design method for the support structure at the intersection is as follows: First, the axial force (reaction force) acting at the intersection is identified by performing a structural analysis of the main tunnel support structure including the intersection; and then, the identified reaction force is used in the structural analysis of the support structure at the intersection.

[0029] In the examination of the main tunnel support structure, first, the hardness of the ground G in which the main tunnel 10 and connecting tunnels 20, including the crossing support structure 30, are constructed is determined, and it is determined whether the target ground is soft rock or moderately hard rock (an example of hard rock) (Step S10).

[0030] If the determination of the hardness of the ground G determines that it is soft rock, the structural analysis is performed via the right-hand route of the flow to identify the axial force (reaction force) acting at the intersection. On the other hand, if the determination of the ground G is medium-hard rock (a type of hard rock), the structural analysis is performed via the left-hand route of the flow to identify the axial force (reaction force) acting at the intersection.

[0031] In this design method, if the ground G is determined to be soft rock, the Terzaghi loosening height can be calculated, and the overburden load is set based on the Terzaghi loosening earth pressure. If the ground G is determined to be moderately hard rock, the Terzaghi loosening height cannot be calculated, and the overburden load is set based on the excavation release force using the finite element method.

[0032] First, we will explain the case where the ground G is determined to be soft rock. First, the specifications of the main tunnel support structure 11 are determined. Here, the specifications of the main tunnel support structure 11 include ν (Poisson's ratio), E (Young's modulus), A (cross-sectional area), and I (second moment of area) according to the specifications of the main tunnel steel support structure 12, and also include ν, E, A, etc. according to the specifications of the main tunnel shotcrete 13 (Step S12).

[0033] In the right-hand route, where the overburden load is set based on Terzaghi's loosening earth pressure, the main tunnel support model M1 is created in the computer as a framework model (beam spring model), as shown in Figure 5.

[0034] Next, the ground reaction coefficient around the main tunnel support structure 11 is set. Here, the ground springs attached to the main tunnel support structure model can be radial ground springs and circumferential ground springs (shear springs), but here only the radial ground spring M1a is installed, and the circumferential ground spring is not installed (step S16).

[0035] Next, since the ground G has been determined to be soft rock, the Terzaghi loosening height can be calculated, and as shown in Figure 5, the overburden load Q is set based on the Terzaghi loosening earth pressure.

[0036] Furthermore, horizontal loads P1 and P2, which are earth pressure or soil water pressure, are applied to the main tunnel support model M1 (step S16, this completes process A). Note that, depending on the shape of the main tunnel support model M1, if the horizontal load acts from only one side (left or right), only the horizontal load on one side (for example, horizontal load P1) is applied.

[0037] A structural analysis is performed on the main tunnel support model M1 by applying the overburden load Q and horizontal loads P1 and P2 based on Terzaghi's loosening earth pressure.

[0038] This structural analysis calculates the axial force N acting on the intersecting support structure in the main tunnel support model M1, as shown in Figure 5 (Step S18, Process B).

[0039] On the other hand, if the ground G is determined to be moderately hard rock (a type of hard rock), the specifications of the main tunnel support structure 11 are determined in the same way as in step S12 (step S20). Here, in the route on the left side of Figure 4, the main tunnel support structure model is created as a two-dimensional FEM model M2 as shown in Figure 6, and the specifications of the main tunnel support structure 11 are determined (step S20).

[0040] Next, since the Terzaghi loosening height cannot be calculated based on the determination that the ground G is moderately soft rock, the overburden load is set based on the excavation release force using the finite element method (step S22), and a structural analysis is performed on a computer (step S18). This structural analysis identifies the design loads for the crossing support structure acting on the crossing support structure model.

[0041] In this way, after determining the hardness of the ground G, the structural analysis of the main tunnel support structure is performed using different routes, and in each route, the design loads for the crossing support structure acting on it are identified.

[0042] Next, we move on to examining the intersection support structure 30 (gate-type support structure). First, we determine the specifications of the intersection support structure 30. Here, since the intersection support structure 30 has a steel support structure 31 and shotcrete 32 as shown in Figure 3, we create the intersection support structure model M3 by attaching radial ground springs M3c to a stacked beam model of a steel support structure model M3a and a shotcrete model M3b, which model both, as shown in Figure 7 (step S24).

[0043] Next, the ground reaction coefficient is set (step S26), and the specified design load R for the crossing support structure is set (step S28), as shown in Figure 7. Specifically, as shown in Figure 5, the vertical load (design load for crossing support structure): R acting on the crossing support structure model is set as R = Nsinθ, taking into account the angle θ of the axial force N acting at the calculated crossing support structure location.

[0044] The structural analysis is performed by applying the set design load R for the intersection support structure to the intersection support structure model M3 (step S30).

[0045] According to the illustrated design method for the shoring at the intersection, when setting the overburden load acting on the main tunnel 10 including the intersection, if the Terzaghi loosening height can be calculated, the overburden load is set based on the Terzaghi loosening earth pressure. If the Terzaghi loosening height cannot be calculated, the overburden load is set based on the excavation release force by the finite element method. This allows the overburden load to be set under a systematized flow based on rational grounds. As a result, the design results will not vary depending on the designer, the reliability of the design results for the shoring at the intersection 30 will be further enhanced, and it will lead to an efficient and rational design for the shoring at the intersection 30.

[0046] Next, referring to Figures 8 to 12, we will explain the basis for setting the overburden load based on the determination of the hardness or softness of the ground G, the basis for not installing circumferential ground springs on the main tunnel support model when the ground is soft, the basis for applying a horizontal load to the main tunnel support model when the ground is soft, and the basis for considering shotcrete in the crossing support model.

[0047] First, with reference to Figures 8A to 8C and 9A to 9D, the basis for setting the overburden load based on the determination of the hardness or softness of the ground G will be explained. Here, Figures 8A to 8C show the structural analysis results and measurement results for design examples where the ground is hard, and the overburden load is set using the blast damage area method, the elastoplastic theoretical solution method, and the two-dimensional FEM analysis method, respectively. Similarly, Figures 9A to 9D show the structural analysis results and measurement results for design examples where the ground is soft, and the overburden load is set using Terzaghi's loosened earth pressure method, the blast damage area method, the elastoplastic theoretical solution method, and the two-dimensional FEM analysis method, respectively. Hereafter, in Figures 8A to 8C relating to design examples where the ground is hard, the analysis values ​​and measurement values ​​are shown as values ​​normalized to a standard magnitude.

[0048] In the following figures, solid lines represent the main tunnel support structure model, dotted lines represent generated stresses (axial force and bending moment), and dashed lines represent measurement results in the actual tunnel (measured cross-sectional forces, etc.).

[0049] First, referring to Figures 8A to 8C, it can be seen that the analysis results shown in Figures 8A and 8B show a large discrepancy with the measured results for both axial force and bending moment, while the analysis results shown in Figure 8C reproduce the measured results with greater accuracy.

[0050] Based on these verification results, if the target ground is moderately soft rock and the Terzaghi loosening height cannot be calculated, the overburden load will be set based on the excavation release force using the finite element method.

[0051] On the other hand, referring to Figures 9A to 9D, it can be seen that the analysis results shown in Figures 9B and 9D deviate significantly from the measured results for both axial force and bending moment, while the analysis results shown in Figures 9A and 9C reproduce the measured results with greater accuracy. Among these, the method using the elastoplastic theory solution shown in Figure 9C has design constraints, such as the prerequisites of isotropy and isobaric and being a single-layer ground. Therefore, considering a general design without constraints, if the target ground is soft rock and the Terzaghi loosening height can be calculated, the overburden load will be set based on the Terzaghi loosening earth pressure.

[0052] Next, with reference to Figures 10A and 10B, we will explain the rationale for not installing circumferential ground springs (shear springs) in the main tunnel support model. Here, Figures 10A and 10B show the structural analysis results and measurement results for the main tunnel support model with and without circumferential ground springs (shear springs), respectively, in a design example where the ground is soft.

[0053] Referring to Figures 10A and 10B, it can be seen that the analysis results shown in Figure 10B reproduce the measurement results more accurately. When circumferential ground springs are considered, the sectional forces below the shoulder of the main tunnel support model become smaller, but the measurement results show that axial forces and bending moments occur below the shoulder as well, so the results are closer to the measurement results when circumferential ground springs are not considered.

[0054] Based on these verification results, in the design of the main tunnel support structure, we will not install circumferential ground springs (shear springs) in the main tunnel support structure model, which is a framework model, but will only install radial ground springs.

[0055] Next, with reference to Figures 11A and 11B, the rationale for applying a horizontal load to the main tunnel support model will be explained. Here, Figures 11A and 11B show the structural analysis results and measurement results for the main tunnel support model with and without a horizontal load, respectively, in a design example where the ground is soft.

[0056] Referring to Figures 11A and 11B, it can be seen that the analysis results shown in Figure 11A reproduce the measurement results with greater accuracy. By applying a horizontal load, the load acting on the main tunnel support model becomes closer to isotropic and equibaric, resulting in a tendency for axial force to prevail and bending moment to decrease compared to the case without horizontal load.

[0057] Based on these verification results, in the design of the main tunnel support structure, horizontal loads such as earth pressure and soil water pressure will be applied to the main tunnel support structure model, which is a framework model.

[0058] Next, with reference to Figures 12A to 12D, the rationale for considering shotcrete in the creation of the intersection support model will be explained. Here, Figures 12A and 12B show both the structural analysis results and measurement results when using an intersection support model that does not consider shotcrete, in design examples where the ground is hard and soft, respectively. On the other hand, Figures 12C and 12D show both the structural analysis results and measurement results when using an intersection support model that considers shotcrete, in design examples where the ground is hard and soft, respectively. Hereafter, in Figures 12A and 12C relating to the design example where the ground is hard, the analysis values ​​and measurement values ​​are shown as values ​​normalized to a standard size.

[0059] Referring to Figures 12A and 12B, in both cases of hard and soft ground, the stress values ​​obtained from the analysis when shotcrete is not considered in the crossing support model show a large discrepancy, approximately two to three times the measured values. In contrast, referring to Figures 12C and 12D, it can be seen that in both cases of hard and soft ground, the stress values ​​obtained from the analysis when shotcrete is considered in the crossing support model accurately reproduce the measured values.

[0060] This verification result indicates that when the shoring at an intersection includes both sprayed concrete and steel shoring, both components support the load as structural members.

[0061] Here, the sprayed concrete that constitutes the crossing support model that forms the basis of the results shown in Figures 12C and 12D is hardened sprayed concrete, and the results shown in Figures 12C and 12D are the results when the bending stiffness of the sprayed concrete is taken into consideration. Although not shown in the illustrations, the inventors have also conducted verification in the case of hardened sprayed concrete without considering its bending stiffness, and the analysis results are closer to the measured values ​​than those in Figures 12A and 12B, but less close to the measured values ​​than those in Figures 12C and 12D.

[0062] Incidentally, sprayed concrete is generally unreinforced concrete, but in terms of design, it is not common to expect bending rigidity from sprayed concrete, which is unreinforced concrete.

[0063] Based on the above, in modeling the cross-section support structure equipped with sprayed concrete and steel support, the elastic modulus of the sprayed concrete after hardening will be taken into consideration, and it will be modeled as a rod member without bending rigidity.

[0064] Furthermore, other embodiments may be used in which other components are combined with the configurations listed in the above embodiments, and the present invention is not limited in any way to the configurations shown herein. In this regard, modifications can be made without departing from the spirit of the present invention, and can be appropriately determined according to the application form. [Explanation of symbols]

[0065] 10: Main pit 11:Main shaft support 12: Main shaft steel shoring 13: Main tunnel sprayed concrete 14: Main tunnel lining concrete 20: Connecting tunnel 21: Support structure for connecting tunnels 22: Concrete lining for connecting tunnels 30: Shoring at intersections 31: Steel shoring 32: Sprayed concrete G: Ground (Soil) M1: Main tunnel support structure model (beam spring model) M1a: Radial ground spring M2: Main tunnel support structure model (2D FEM model) M3: Cross-section support structure model M3a: Steel support structure model M3b: Sprayed concrete model M3c: Radial ground spring Q: Soil cover load P1, P2: Horizontal load N: Axial force R: Reaction force (load used for designing shoring at intersections)

Claims

1. A design method for tunnel crossing supports, wherein the main tunnel and connecting tunnel intersect at an intersection, and the main tunnel support structure and the crossing support structure are modeled and designed separately. Step A involves setting the overburden load acting on the main tunnel including the aforementioned intersection, setting the overburden load based on the terzaghi loosening earth pressure if the terzaghi loosening height can be calculated, and setting the overburden load based on the excavation release force by the finite element method if the terzaghi loosening height cannot be calculated. Step B involves applying the set soil cover load to the main tunnel support model of the main tunnel support structure including the intersection and performing a structural analysis, determining the reaction force at the position corresponding to the intersection in the main tunnel support model, and using this reaction force as the design load for the intersection support structure when designing the intersection support structure. The process includes step C, which involves applying the design load for the intersection support structure to the intersection support structure model and performing a structural analysis to set the structural specifications for the intersection support structure. A method for designing tunnel crossing support, characterized in that, if the terzaghi loosening height can be calculated in step A, in step B the main tunnel support model is used as a framework model, radial ground springs for the main tunnel support are installed on the framework model, and circumferential ground springs for the main tunnel support are not installed.

2. The design method for tunnel crossing support according to claim 1, characterized in that, if the terzaghi loosening height can be calculated in step A, a horizontal load is applied to the frame model in addition to the soil cover load.

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