Design method for longitudinal direction of tunnel box group

Abstract

To provide a method for designing a tunnel box group in the longitudinal direction, in the designing the tunnel box group in the longitudinal direction having at least a curved section, which enables a rational cross-sectional design of the tunnel boxes and calculation of the necessary jack thrust based on appropriate earth pressure.SOLUTION: A method for designing a tunnel box group in the longitudinal direction, which is formed by a plurality of tunnel boxes 21 and has at least a curved section, comprises at least an A step of creating an analytical model, and a B step of conducting an analysis and checking the stress level. In the step A, the analytical model is created as a longitudinal beam model for the tunnel box group 20. In setting the earth pressure in the curved section in the step B, consideration is given to the fact that the tunnel box 21 is displaced toward the outside of the curve due to the jack thrust, and when the tunnel box is displaced by a predetermined amount outward in the curved section, the earth pressure acting on the tunnel box 21 from inside the curved section is changed from static earth pressure to active earth pressure.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a method for designing a group of tunnel boxes in the longitudinal direction. [Background technology]

[0002] In the tunnel jacking method, a group of tunnel jacking boxes is constructed underground by connecting multiple tunnel jacking boxes via ring joints (either by inserting the end of one tunnel jacking box into the end of the other tunnel jacking box, or by bolting). Hereinafter, in this specification, a tunnel jacking box will be referred to as a tunnel box, and a group of tunnel jacking boxes will be referred to as a tunnel box group. There are various types of longitudinal alignments for tunnel boxes, including straight lines, circles, curved lines with multiple curvatures, and lines that combine straight and curved lines. However, for tunnel boxes that have at least a curved section in their longitudinal alignment, it is essential to properly evaluate the various influences when designing the longitudinal direction of the tunnel boxes. For example, in curved sections using the jacking method, a common construction method is to extend a copy cutter from the side of the tunneling machine's cutter head into the ground to perform over-excavation, and then fill the over-excavation area with lubricant while the tunneling machine excavates and the over-excavation box group is advanced. In such curved sections, the tunnel box is likely to be displaced toward the outside of the curve due to the jack thrust, and the formation of the above-mentioned over-excavation area makes the outward displacement in the curved section even more pronounced.

[0003] As for the thrust calculation method for curved construction, the Guidelines and Commentary for Sewerage Jacking Methods, Japan Sewage Works Association (hereinafter referred to as the Sewerage Guidelines), prescribes that the loads acting constantly on the tunnel box are earth overburden load and lateral pressure equivalent to static earth pressure, and that these loads must be taken into account when calculating thrust to calculate frictional resistance. In this curved section, the direction of thrust changes along the curve, so the tunnel box is subjected to a ground reaction from the outside of the curve. This ground reaction has a value equivalent to the component of the thrust acting on the tunnel box, and this results in a frictional force. For example, as the depth to which the tunnel boxes are constructed increases, they are subjected to heavy load conditions and high ground reaction conditions, and the constantly acting load and the frictional resistance caused by this load both increase, so the thrust required to propel the group of tunnel boxes increases.Furthermore, since the ground reaction and the resulting frictional resistance increase in proportion to the increase in the required thrust, when the thrust is calculated in accordance with the sewerage guidelines mentioned above, the required thrust will inevitably increase.

[0004] However, in curved sections, as mentioned above, the tunnel box generally displaces toward the outside of the curve due to the jack thrust, and therefore, in conventional design methods in which the static earth pressure, which is based on the assumption that the tunnel box is stationary, is applied as lateral pressure from the inside of the tunnel box, for example, it is difficult to say that the earth pressure acting on the actual tunnel box is accurately evaluated, and an excessive jack thrust is calculated due to the overestimation of the earth pressure. As mentioned above, in the design of tunnel boxes constructed at great depths, the required jack thrust is generally large, so it is desirable to take into account the behavior of the actual tunnel box, properly evaluate the earth pressure actually acting on the tunnel box, and rationally design the cross section of the tunnel box and calculate the required jack thrust based on the appropriate earth pressure.

[0005] Patent Document 1 proposes a curved jacking method for burying small-diameter pipes with low axial load-bearing capacity in a curved jacking manner. Specifically, this curved jacking method involves deflecting a leader from inside a starting shaft in a predetermined target direction, pushing the rear end of a temporary pipe connected to the rear of the leader to jack and bury the temporary pipes one after another, and after the temporary pipes have penetrated into the arrival shaft, connecting a buried pipe to the rearmost end of the temporary pipe in the starting shaft, and connecting a casing equipped with a friction coupler inside the buried pipe to the end of the temporary pipe, and then jacking or pulling the casing to advance the temporary pipe and buried pipe, replacing it with the buried pipe. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 5-214892 Summary of the Invention [Problem to be solved by the invention]

[0007] According to the curved jacking method described in Patent Document 1, the buried pipe body is not damaged by the jacking force, and the mechanism installed inside the buried pipe is a relatively simple device consisting of only a casing and friction couplers installed in several places, making it possible to easily perform curved jacking even for small-diameter pipes. However, as mentioned above, this method does not propose a rational design method that takes into account the displacement of the tunnel box group in the curved section.

[0008] The object of the present invention is to provide a method for designing the longitudinal direction of a group of tunnel boxes that has at least a curved section, which allows for an appropriate evaluation of the earth pressure that actually acts on the tunnel box, and enables rational design of the cross section of the tunnel box and calculation of the required jack thrust based on the appropriate earth pressure. [Means for solving the problem]

[0009] In order to achieve the above object, one aspect of the method for designing a tunnel group in the longitudinal direction according to the present invention is to: A method for designing the longitudinal direction of a group of tunnel boxes formed by a plurality of tunnel boxes and having at least a curved section, while receiving jack thrust from a jacking jack of a propulsion device or a tunneling machine by a jacking method, comprising the steps of: The method includes a step A of creating at least an analytical model on a computer, and a step B of performing an analysis and checking the stress level, In the step A, For the group of tunnel boxes, a curved beam model having equivalent rigidity or a curved beam model formed by connecting the beam models of adjacent tunnel boxes with rotational springs is created, and a ground spring is attached to the curved beam model to create an analytical model as a longitudinal beam model; In the step B, When setting the earth pressure in the curved section, it is taken into consideration that the tunnel box will be displaced toward the outside of the curve due to the jack thrust, and when the tunnel box is displaced outward a predetermined amount in the curved section, the earth pressure acting on the tunnel box from the inside of the curved section is changed from static earth pressure to active earth pressure.

[0010] According to this aspect, the tunnel box group is modeled as a curved beam model, and a ground spring is attached to the curved beam model to create an analytical model as a longitudinal beam model.When setting the earth pressure in the curved section for this analytical model, it is taken into consideration that the tunnel box will displace toward the outside of the curve, and when it displaces a predetermined amount toward the outside in the curved section, the earth pressure acting on the tunnel box from the inside of the curved section is changed from static earth pressure to active earth pressure, thereby allowing the earth pressure actually acting on the tunnel box to be properly evaluated, and a rational cross-sectional design of the tunnel box and calculation of the required jack thrust can be made based on the appropriate earth pressure. Here, "changing the earth pressure from static earth pressure to active earth pressure when a predetermined amount of displacement has occurred" means that even in the design of curved sections, if the amount of displacement is less than the predetermined amount, using active earth pressure as the earth pressure will lead to an underestimation of the earth pressure, so conventional static earth pressure is applied, and when the amount of displacement exceeds the predetermined amount, the earth pressure is changed from static earth pressure to active earth pressure. This "predetermined amount" can be set in a variety of ways depending on various standards, past construction records, depth, and ground type (sandy soil or clayey soil, hard soil or soft soil, etc.).

[0011] When a group of tunnel boxes has a single circular longitudinal alignment in the curved section, longitudinal beam models are created for each construction stage, such as a longitudinal beam model at the 10R stage when 10 tunnel boxes (1R) are pushed through, a longitudinal beam model at the 20R stage when 20R boxes are pushed through, and a circular longitudinal beam model when the entire circumference is pushed through, and the longitudinal cross-sectional forces of the tunnel box are calculated each time. Furthermore, the calculated cross-sectional forces of each tunnel box that makes up the group of tunnel boxes will differ from location to location, but at the design stage, the specifications of the tunnel box are determined based on the most severe cross-sectional force.

[0012] Examples of jack thrust include the jack thrust from the main jack of the main thrust device in the jacking method, the jack thrust from the center jack of the center thrust device in addition to the main jack, and the jack thrust from the thrust jack equipped in the tunnel machine. For example, in the jacking method using a tunneling machine equipped with a thrust jack, the jack thrust from the main jack is applied to one end of the longitudinal beam model (the starting shaft position), and the jack thrust from the thrust jack equipped in the tunnel machine is applied to the other end of the longitudinal beam model (the tunneling machine position), and if a center thrust device is interposed between the tunnel boxes, the jack thrust from the center thrust jack is applied to that position.

[0013] Ground springs can also be attached in various ways, such as attached to each tunnel box or every 10R. Furthermore, it is desirable that the ground properties of each location (each soil layer) are appropriately reflected in the ground spring, and it is advisable to set the ground spring after evaluating the N value of each soil layer, the internal friction angle of the ground, adhesion (viscosity), etc.

[0014] In another aspect of the method for designing a tunnel box group in the longitudinal direction according to the present invention, The predetermined amount of displacement: d is set under the condition of d>0.002H~0.005H when the tunnel box is in sandy soil, and under the condition of d>0.01H~0.02H when the tunnel box is in clayey soil, when the depth of the tunnel box in the curved section is H.

[0015] According to this aspect, the displacement of the tunnel box (predetermined displacement: d) when changing the earth pressure applied to the tunnel box in a curved section from static earth pressure to active earth pressure is set to d > 0.002H to 0.005H if the tunnel box is in sandy soil, and d > 0.01H to 0.02H if the tunnel box is in clayey soil, thereby enabling a change to static earth pressure under reliable conditions. In the design of a typical retaining wall, where H' is the height of the retaining wall and d' is the displacement when the retaining wall moves away from the soil behind it, the displacement required to generate active earth pressure is 0.002H' to 0.005H' or more for sandy soil and 0.01H' to 0.02H' or more for clayey soil. Therefore, the height of the retaining wall in this retaining wall design method is considered to be the depth (earth cover) of the tunnel box, and a threshold value for the displacement of the tunnel box when active earth pressure is applied is specified.

[0016] Another aspect of the design method for the longitudinal direction of a tunnel box group according to the present invention is as follows: In the step A, The ground spring is a first nonlinear ground spring in which the ground reaction force is zero in the overexcavation portion and the ground reaction force increases according to displacement in the area in contact with the ground, In the step B, The method is characterized in that the jack thrust by the propulsion jack is set and loaded on the longitudinal beam model, thereby calculating at least the longitudinal cross-sectional force of the tunnel box.

[0017] According to this aspect, a group of tunnel boxes having curved sections is modeled as a curved beam model or the like having equivalent rigidity, to which a ground spring is attached to create a longitudinal beam model.In this case, the ground spring is modeled as a first nonlinear ground spring in which the ground reaction force is zero in the overexcavation section and increases in accordance with displacement in the area where it abuts the ground.By doing so, the longitudinal cross-sectional force of the tunnel box can be calculated based on the longitudinal beam model equipped with a ground spring in which the overexcavation section is appropriately modeled, thereby making it possible to realize highly accurate longitudinal design of a group of tunnel boxes.

[0018] In the ground springs applied in this embodiment, the ground reaction force is set to zero in the overexcavation section because the tunnel box group is not in contact with the ground, and is set so that the ground reaction force increases (for example, increases linearly) in accordance with displacement in the area in contact with the ground, thereby achieving a safer and more accurate design than a longitudinal beam model equipped with conventional ground springs that does not take overexcavation sections into consideration. Also, the first nonlinear ground spring, in which the ground reaction force is zero in the overexcavation section, is a nonlinear ground spring with different properties from conventional general nonlinear ground springs, in which the linear gradient showing the relationship between ground reaction force and displacement changes at a certain displacement (two straight lines with different gradients are continuous).

[0019] In another aspect of the method for designing a tunnel box group in the longitudinal direction according to the present invention, The ground springs include normal ground springs in a normal direction to the arc in the curved section and tangential ground springs in a tangential direction to the arc, The normal ground spring is the first nonlinear ground spring, The tangential ground spring is characterized in that it is a second nonlinear ground spring whose upper limit value is a value obtained by multiplying the ground reaction force by a friction coefficient.

[0020] According to this aspect, the ground springs have a normal ground spring consisting of a first nonlinear ground spring that takes into account the overexcavation, and a tangential ground spring consisting of a second nonlinear ground spring whose upper limit is the ground reaction force (normal ground reaction force) multiplied by the friction coefficient, thereby enabling the design of the longitudinal direction of the tunnel group with even greater accuracy. For example, the normal friction coefficient μ is calculated from tan(φ / 2) (φ is the internal friction angle of the ground) or set to 1 / 3, etc., but by multiplying the maximum value of the normal ground reaction force by the friction coefficient μ, it is possible to create a tangential ground spring that simulates friction behavior in which the tangential reaction force plateaus at a certain displacement. [Effects of the Invention]

[0021] According to the method for designing a tunnel box group in the longitudinal direction of the present invention, in the longitudinal design of a tunnel box group having at least a curved section, the earth pressure actually acting on the tunnel box can be properly evaluated, and a rational cross-sectional design of the tunnel box and calculation of the required jack thrust can be performed based on the appropriate earth pressure. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a flowchart showing an example of a design method for the longitudinal direction of a tunnel box group according to an embodiment. [Figure 2] This is a schematic diagram showing the state in which a group of tunnel boxes with a single circular longitudinal cross section are being advanced in a vertical plane using the jacking method. [Figure 3] This is a schematic diagram showing the state in which a tunnel tunneling machine is creating an overexcavation section in a curved section and advancing a group of tunnel boxes while filling the overexcavation section with lubricant. [Figure 4] FIG. 10 is a diagram showing the analysis results regarding the outward displacement of the propulsion box group in the curved section. [Figure 5] 1 is a diagram showing a conceptual diagram of loads in a curved section in a conventional design method and a design method according to an embodiment of the present invention. FIG. [Figure 6] FIG. 1 is a diagram illustrating the relationship between static earth pressure and active earth pressure. [Figure 7] FIG. 1 is a schematic diagram showing the concept of thrust calculation in a curved section, which is adopted in a conventional design method. [Figure 8] FIG. 2 is a schematic diagram illustrating the concept of thrust calculation in a curved section, which is employed in the design method of the embodiment. [Figure 9] FIG. 10 is a schematic diagram illustrating an example of a longitudinal beam model. [Figure 10A] FIG. 10 is a diagram illustrating the relationship between normal ground reaction force and normal displacement, which explains the spring characteristics of a normal ground spring. [Figure 10B] FIG. 10 is a diagram showing the relationship between tangential ground reaction force and tangential displacement, which explains the spring characteristics of a tangential ground spring. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, a method for designing a longitudinal section of a tunnel box group according to an embodiment will be described with reference to the accompanying drawings. In this specification and drawings, substantially identical components will be designated by the same reference numerals, and redundant explanations may be omitted.

[0024] [Method for designing a group of tunnel boxes in the longitudinal direction according to the embodiment] An example of a design method for the longitudinal section of a tunnel-box group according to an embodiment will be described with reference to Figures 1 to 11. Here, Figure 1 is a flowchart showing an example of a design method for the longitudinal section of a tunnel-box group according to an embodiment. Also, Figure 2 is a schematic diagram showing a state in which a tunnel-box group having a single circular longitudinal section is being advanced in a vertical plane using a jacking method, and Figure 3 is a schematic diagram showing a state in which a tunneling machine is advancing a tunnel-box group in a curved section while creating an overexcavation section and filling the overexcavation section with lubricant.

[0025] In the illustrated example of the design method for the longitudinal direction of a group of tunnel boxes, the longitudinal alignment of the group of tunnel boxes to be designed is a single circle in the vertical plane, and all sections are curved sections, but in addition to the illustrated example, the longitudinal alignment of the group of tunnel boxes to be designed can be a variety of longitudinal alignments, such as a longitudinal alignment with multiple curvatures in the vertical or horizontal plane, or a longitudinal alignment with a mixture of curved and straight sections, etc.

[0026] As shown in FIG. 1, the design method for the longitudinal direction of a tunnel box group according to this embodiment is a design method at the design stage before construction begins, and includes Process A and Process B.

[0027] Process A mainly comprises the process of setting input conditions and the process of creating an analysis model, while Process B comprises the process of carrying out the analysis and checking the stress level in the longitudinal direction of the tunnel body.

[0028] In setting the input conditions in Step A, the specifications of the tunnel box are set, the longitudinal alignment of the tunnel box group (its diameter if it is a single circle, or each curvature and its alignment if it has multiple curvatures), and the soil layers through which the tunnel box group passes are modeled. In modeling the soil layers, the properties (sand layer, clay layer, gravel layer, etc.), N value, unit volume weight of the ground, internal friction angle, adhesion force, etc. are set for each soil layer based on the results of the ground survey.

[0029] The example shown in Figure 2 is an example in which a group of tunnel boxes 20 (circumferential tunnel) having a vertical cross-sectional alignment of a single circle with a radius r in a vertical plane is constructed using the jacking method. As shown in Figure 2, when connecting and widening a main tunnel HT (for example, a main shield tunnel) that has already been constructed underground G with a ramp tunnel RT (for example, a ramp shield tunnel) located next to it, a vertical shaft T is constructed that extends vertically below the ramp tunnel RT. Note that this vertical shaft may also be configured to extend diagonally downward rather than vertically.

[0030] A starting platform T1 is installed below a vertical shaft T that has been constructed to a predetermined depth, and a main pushing device 30 equipped with a main pushing jack is installed on the starting platform T1. The tunnel excavator 10 and tunnel box body 21 are lowered from the ramp tunnel RT as needed, and the tunnel excavator 10 excavates into the ground. Multiple tunnel boxes 21 are placed one after the other behind it, and the tunnel box group 20 formed by the tunnel excavator 10 and multiple tunnel boxes 21 is advanced by the jack thrust of the main pushing jack 30.

[0031] The illustrated tunneling machine 10 has a front body 11 and a rear body 12, and a propulsion jack (not shown) is provided between the two (a jack that controls the direction of the tunneling machine in addition to propelling the tunneling machine itself). The shape of the tunneling machine 10 when viewed from the front is, for example, a horizontally long rectangle, and multiple cutter heads 13 are arranged on the front surface. Each cutter head 13 has a built-in copy cutter that can move in and out from the side, and when creating an overexcavation area, the copy cutter extends outward from each cutter head 13, and the copy cutter rotates in accordance with the rotation of the cutter head 13 to create the overexcavation area. At this time, the size of the overexcavation area can be adjusted as desired by adjusting the extension length of the copy cutter.

[0032] As described above, the tunnel box 21 connected to the rear of the tunneling machine 10, which is rectangular when viewed from the front, is made of a steel shell having the same shape as the tunneling machine 10 when viewed from the front.

[0033] Face pressure S acts from the front on the cutter head 13 of the tunneling machine 10. Furthermore, an inner friction force Fin due to the initial earth pressure acts on the inside of the curved section (radially inward), and an outer friction force Fout2 due to the curve reaction force acts on the outside of the curved section (radially outward) in addition to an outer friction force Fout1 due to the initial earth pressure. This outer friction force Fout2 due to the curve reaction force is a friction force caused by the ground reaction force R that accompanies curve construction. Note that the illustrated example is a group of tunnel boxes in the vertical direction, so each tunnel box also experiences its own weight, but this weight will not be taken into consideration here.

[0034] Here, the front tunnel excavator 10 and tunnel box group 20 are propelled forward by the jack thrust Fn acting from the head jack 30 in the shaft T, and the acting jack thrusts Fn-m1, Fn-m2, Fn-m3 gradually decrease toward the front of the tunnel box group 20. The ground reaction R associated with curved construction is a reaction force resulting from this jack thrust Fn, and therefore, as shown in Figure 2, it is greatest near the head jack 30 and tends to gradually decrease toward the tunnel excavator 10.

[0035] In this way, in the jacking method that follows a curved line in a vertical plane in the illustrated example, the tunnel excavator 10 and the group of tunnel boxes 20 are advanced by a jack thrust Fn (required thrust) that is greater than the sum of the face pressure S acting on the tunnel excavator 10, the inner friction force Fin acting on the tunnel excavator 10, and the outer friction forces Fout1 and Fout2 acting on the tunnel excavator 10.

[0036] If the jack thrust of the main jack 30 is insufficient, one or more intermediate jacks are arranged between the tunnel box groups 20 to make up for the insufficient jack thrust.

[0037] When setting the jack thrust of the main push jack 30 and the jack thrust of the main push jack 30 and the intermediate push jack provided as needed, the required jack thrust (required thrust) changes from time to time during the process of advancing the tunnel box group 20, so the required jack thrust is set according to each stage, such as the stage up to 10 tunnel box groups 20 (10R), the stage up to 20R, and the final stage when the tunnel boring machine 10 reaches the vertical shaft T.

[0038] As shown in Figure 3, a copy cutter 14 extends from the side of the cutter head 13 (here, for ease of explanation, the figure shows a form having only one cutter head 13), and as the cutter head 13 rotates and the tunnel tunneling machine 10 excavates in the excavation direction along the planned vertical section L1, an over-excavation section 25 of a predetermined width t1 is created on the side of the tunnel tunneling machine 10 and the subsequent tunnel box group 20, and a slip material 28 is filled into the over-excavation section 25 from the tunnel tunneling machine 10.

[0039] A rectangular frame-shaped overexcavation section 25 with width t1 is created around the tunneling machine 10, which is rectangular when viewed from the front. In the illustrated example, the width t1 of the overexcavation section 25 is set according to the radius r of the single circle, etc.

[0040] Figure 3 shows the state in which the tunnel boring machine 10 is excavating along the planned vertical alignment L1 and the tunnel box group 20 is being advanced, with the inner line L2 of the overexcavation section 25 on the radial inside of the single circle and the outer line L3 of the overexcavation section 25 on the radial outside. In other words, Figure 3 shows a state in which the tunnel boring machine 10 is not meandering. Furthermore, width t1 is the designed overexcavation amount under the input conditions.

[0041] According to structural analysis by the present inventors, it has been determined that a group of tunnel boxes in a curved section will displace toward the outside of the curve. For example, FIG. 4 shows the results of a finite element method (FEM) analysis performed by the present inventors to calculate the amount of displacement in the ground of the circular tunnel box group shown in FIG. 2. As such, in curved sections, the group of tunnel boxes will displace toward the outside of the curve, and it is essential to properly evaluate the earth pressure acting on the tunnel boxes by taking this displacement into consideration. Below, we will explain the methods for evaluating earth pressure in the conventional design method and the design method of this embodiment, as well as the differences in the jack thrust calculation results due to the differences in the earth pressure evaluation methods.

[0042] First, with reference to FIG. 5, the difference between the conventional design method and the design method of this embodiment in terms of the concept of load acting on the tunnel box in the curved section will be described.

[0043] The upper part of Figure 5 shows a conceptual diagram of loads in a conventional design method, and the lower part shows a conceptual diagram of loads in an embodiment. In the conventional design method, an inner earth pressure Qin acts on the inner side of the tunnel box, and an outer earth pressure Qout and a ground reaction force R act on the outer side. Furthermore, an overburden pressure Qup acts above the tunnel box, and a base reaction force Qdn acts below the tunnel box.

[0044] The method for evaluating the ground reaction force R is to balance the forces acting from the inside and outside of the tunnel box (forces acting from the left and right), and all of the thrust force components become the ground reaction force R.

[0045] In conventional design methods, the static earth pressure is applied to both the internal earth pressure Qin and the external earth pressure Qout. However, as explained with reference to Figure 4, the tunnel box displaces outward in curved sections. Therefore, it is difficult to say that the method of setting earth pressure, which assumes a stationary tunnel box and applies static earth pressure to the inside of the tunnel box, or the design method based on this method, properly evaluates the earth pressure acting on an actual tunnel box. In other words, the conventional design method does not take into account the decrease in internal earth pressure caused by the outward displacement of the tunnel box.

[0046] Therefore, in the design method according to the embodiment, the outward displacement of the tunnel body in the curved section is taken into consideration, and when the amount of outward displacement reaches a predetermined amount or more, the earth pressure acting on the inside of the tunnel body is changed from static earth pressure to active earth pressure.

[0047] FIG. 6 illustrates the relationship between earth pressure at rest and active earth pressure. Earth pressure varies depending on the direction of displacement of the structure relative to the ground, and the magnitude of the generated earth pressure also changes depending on the magnitude of the displacement. The magnitude of earth pressure has the relationship passive earth pressure > active earth pressure at rest. The displacement required to generate active earth pressure is d, and the depth of the tunnel box in the curved section is H. If the tunnel box is in sandy soil, the condition d > 0.002H to 0.005H is satisfied. If the tunnel box is in clayey soil, the condition d > 0.01H to 0.02H is satisfied. This substitutes the design method used in conventional retaining wall design, where the height of the retaining wall is defined as H' and the displacement of the retaining wall is defined as d', and the design method for stability calculations of the retaining wall is used. In this embodiment, the height of the retaining wall, H', is interpreted as the depth of the tunnel box, H, and the displacement of the retaining wall, d', is interpreted as the outward displacement of the tunnel box, d, in the curved section.

[0048] Returning to Figure 5, in the design method of the embodiment, the decrease in the inner earth pressure caused by the outward displacement of the tunnel box is taken into consideration, and if the amount of displacement is equal to or greater than a predetermined amount, the earth pressure is changed from the static earth pressure to the active earth pressure, and if the amount of displacement is less than the predetermined amount, the static earth pressure is applied as is. As a result, the decrease in the inner earth pressure (decrease ΔQ) also causes the outer ground reaction R' to decrease by ΔQ from the initial ground reaction R.

[0049] 7 and 8 are schematic diagrams showing the concept of thrust calculation in curved sections adopted in the conventional design method and the design method of the embodiment, respectively.

[0050] As described above, when the outward displacement of the tunnel body in the curved section is equal to or greater than a predetermined amount, the reduction in the internal earth pressure ΔQ reduces the thrust force Fn' of the main push jack by 2×μ×ΔQ compared to the thrust force Fn in the conventional design method (more specifically, a reduction of 2×μ×ΔQ / (cosθ-μsinθ)).

[0051] In this way, by properly evaluating the earth pressure that actually acts on the tunnel box, it becomes possible to calculate the required jack thrust based on the appropriate earth pressure, and at the same time, rational cross-sectional design of the tunnel box can be carried out based on the appropriate earth pressure.

[0052] Returning to Fig. 1, after setting the input conditions, an analytical model is created. Specifically, as shown in Fig. 9, the tunnel box group 20 is modeled in a computer as a curved beam model BM having equivalent rigidity. In this modeling, although not shown in the figure, a curved beam model may be created in which the beam models of adjacent tunnel boxes 21 are connected by rotational springs.

[0053] A longitudinal beam model M is created by attaching ground springs JM to the curved beam model BM. The ground springs JM may be attached to each tunnel box position in the curved beam model BM, or may be attached every 10R, for example.

[0054] The ground spring JM has a normal ground spring JM1 in the normal direction of the circumferential tunnel of radius r, and a tangential ground spring JM2 in the tangential direction, and both ground springs are simulated by, for example, connector elements. Furthermore, although not shown, restraint springs are attached to one end BM1 (or its vicinity) of the curved beam model BM where the jack thrust P from the main jack is applied, and to the other end BM2 (or its vicinity) of the curved beam model BM that has reached the shaft.

[0055] In modeling the normal-direction ground spring JM1, the overexcavation area 25 shown in Fig. 3 is appropriately taken into consideration. That is, as is clear from Fig. 3, the overexcavation area 25 is filled with sliding material 28, and the tunnel box group 20 does not receive a ground reaction force from the ground G. Therefore, if the tunneling machine 10 or the tunnel box group 20 is within the range of the designed overexcavation amount t1, setting the magnitude of the ground reaction force to zero is a conservative design, and it can be said that this model accurately reflects the actual situation.

[0056] 10A, when modeling the normal ground spring JM1, the ground reaction force R is set to zero in the range of overexcavation amount t1 set on the radial outside and inside of the circumferential tunnel, and when the tunneling machine 10 and tunnel box group 20 snake in the excavation direction in the overexcavation section 25 and come into contact with the ground, the ground reaction force is modeled to increase proportionally in the area where it comes into contact with the ground according to the amount of displacement in the normal direction of the tunnel box group 20. In this case, because the rate at which the ground reaction force increases in response to displacement differs for each soil layer, it is preferable to model the normal ground spring JM1 for each soil layer.

[0057] As shown in Figure 10A, the normal ground spring JM1 (first nonlinear ground spring), in which the ground reaction force is zero in the overexcavation section 25, is a nonlinear ground spring with different properties from conventional general nonlinear ground springs, in that the linear gradient showing the relationship between ground reaction force and displacement changes at a certain displacement (two straight lines with different gradients become continuous).

[0058] On the other hand, as shown in Figure 10B, the tangential ground spring JM2 is modeled as a second nonlinear ground spring in which the tangential ground reaction force increases as the tangential displacement increases, and the value obtained by multiplying the normal ground reaction force R by the friction coefficient μ is set as the upper limit (and lower limit) of the tangential ground reaction force. For example, by multiplying the maximum value of the normal ground reaction force R by the friction coefficient μ, it is possible to form a tangential ground spring JM2 that simulates frictional behavior in which the tangential reaction force plateaus at a certain displacement.

[0059] The friction coefficient μ is calculated, for example, from tan(φ / 2) (φ is the internal friction angle of the ground), and it is preferable to calculate the friction coefficient μ by applying the internal friction angle φ of each soil layer and model the tangential ground spring JM2 for each soil layer.

[0060] In this way, a curved beam model BM is created in the computer for each construction stage, and a longitudinal beam model M (analysis model) is created by attaching ground springs JM having a first nonlinear ground spring, normal ground spring JM1, and a second nonlinear ground spring, tangential ground spring JM2, to multiple positions on the curved beam model BM (this is Process A, including setting the input conditions and creating the analysis model).

[0061] As shown in Fig. 9, a jack thrust Fn is set by a thrust jack such as a push jack 30 and loaded onto the longitudinal beam model M, thereby calculating the longitudinal section forces of each tunnel box 21 constituting the tunnel box group 20 and the ground reaction R in the longitudinal direction of the tunnel box group 20. These section forces include bending moment, shear force, and axial force (longitudinal compression force and tension force). In the illustrated model in which all sections are curved, the calculated ground reaction R gradually changes in the longitudinal direction, as shown in Fig. 9.

[0062] For example, in the initial stage, as explained with reference to Figure 2, the jack thrust of the main jack 30 is analyzed assuming a jack thrust capable of propelling the tunnel excavator 10 and the tunnel box group 20, and if the axial force contained in the longitudinal cross-sectional force at the position of the leading tunnel excavator 10 is a compressive force equivalent to or greater than the face pressure S, it is determined that the set jack thrust is too large, and the analysis is repeated while changing the jack thrust until the compressive force becomes equivalent to the face pressure S, and the required jack thrust is set.

[0063] On the other hand, if the analysis shows that the axial force at the position of the tunneling machine 10 is smaller than the compressive force equivalent to the face pressure S, it is determined that the set jack thrust is insufficient, and the jack thrust is increased and analysis is performed, and the required jack thrust is set by repeating the above analysis until the axial force becomes the compressive force equivalent to the face pressure S.

[0064] Through analysis, the longitudinal cross-sectional force of the tunnel box, ground reaction force, and required jack thrust are calculated, and various stress level checks are carried out based on the calculated cross-sectional force, etc.

[0065] The stress check identifies the originally set specifications of the tunnel box (strength, bearing capacity), the bearing capacity of the ground, and the required jack thrust. If the tunnel box or the ground does not have sufficient bearing capacity, the input conditions are returned to and the specifications of the tunnel box are changed, the longitudinal alignment is reviewed, and ground improvement measures to increase the bearing capacity of the ground are considered. The analysis model is then recreated and the analysis is carried out again, and a stress check is carried out to determine specifications that satisfy the bearing capacity of both the tunnel box and the ground (the above, including the implementation of the analysis and the stress check, is Process B).

[0066] According to the illustrated method for designing the longitudinal direction of a tunnel box group, when designing the longitudinal direction of a tunnel box group 20 having at least a curved section, analysis is performed using a longitudinal beam model M equipped with ground springs JM including normal ground springs JM1 that take into account the overexcavation section 25, thereby enabling highly accurate design of the longitudinal direction of the tunnel box group.

[0067] 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]

[0068] 10: Excavation machine 11: Front body 12: Rear body 13: Cutter head 20: Tunnel Box Group 21: Tunnel box 25: Extra excavation section 28: Sliding material 30: Main push device (main push jack) G: Ground (underground) Fn: Jack thrust (main push jack thrust, main push thrust) S: Face pressure (tip resistance force) Fin, Fin': Inner friction force due to initial earth pressure (inner friction force) Fout1,Fout1': Outer friction force due to initial earth pressure (outer friction force) Fout2, Fout2': Outer friction force due to curve reaction force (outer friction force) R: Ground reaction (curve reaction) M: Longitudinal beam model BM: Beam model with curves JM: Ground spring JM1: Normal ground spring (first nonlinear ground spring) JM2: Tangential soil spring (second nonlinear soil spring)

Claims

1. A method for designing the longitudinal direction of a group of tunnel boxes formed by a plurality of tunnel boxes and having at least a curved section, while receiving jack thrust from a jacking jack of a propulsion device or a tunneling machine by a jacking method, comprising the steps of: The method includes a step A of creating at least an analytical model in a computer, and a step B of performing an analysis and checking the stress level, In the step A, For the group of tunnel boxes, a curved beam model having equivalent rigidity or a curved beam model formed by connecting the beam models of adjacent tunnel boxes with rotational springs is created, and a ground spring is attached to the curved beam model to create an analytical model as a longitudinal beam model; In the step B, A design method for the longitudinal direction of a group of tunnel boxes, characterized in that when setting the earth pressure in the curved section, it is taken into consideration that the tunnel box will be displaced toward the outside of the curve due to the jack thrust, and when the tunnel box is displaced outward by a predetermined amount in the curved section, the earth pressure acting on the tunnel box from the inside of the curved section is changed from static earth pressure to active earth pressure.

2. 2. The method for designing a tunnel box group in the longitudinal direction according to claim 1, wherein the predetermined amount of displacement: d is set under the condition of d>0.002H to 0.005H when the tunnel box is in sandy soil, and under the condition of d>0.01H to 0.02H when the tunnel box is in clayey soil, when the depth of the tunnel box in the curved section is H.

3. In the step A, The ground spring is a first nonlinear ground spring in which the ground reaction force is zero in the overexcavation portion and the ground reaction force increases according to displacement in the area in contact with the ground, In the step B, 3. A method for designing a tunnel box group in the longitudinal direction according to claim 1 or 2, characterized in that a jack thrust by the propulsion jack is set and loaded on the longitudinal beam model, thereby calculating at least the cross-sectional force of the tunnel box in the longitudinal direction.

4. The ground springs include normal ground springs in a normal direction to the arc in the curved section and tangential ground springs in a tangential direction to the arc, The normal ground spring is the first nonlinear ground spring, The longitudinal design method for a group of tunnel boxes according to claim 3, characterized in that the tangential ground spring is a second nonlinear ground spring whose upper limit value is the ground reaction force multiplied by a friction coefficient.

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