JP7461909B2 - Method for designing the longitudinal direction of a group of tunnel boxes and method for modifying the construction plan for a group of tunnel boxes - Google Patents

Description

The present invention relates to a method for designing the longitudinal direction of a group of tunnel boxes, and a method for modifying the construction plan for a group of tunnel boxes.

In the jacking method and shield method, a tunnel box group such as a jacking box group or a shield box group is constructed underground by connecting multiple jacking boxes together via ring joints (in a form in which the end of one jacking box is inserted into the end of the other jacking box, or in a form such as bolted joints) or by connecting multiple shield boxes together via ring joints (in a form such as bolted joints). Hereinafter, in this specification, the jacking box and the shield box are collectively referred to as the tunnel box, and the jacking box group and the shield box group are collectively referred to as the tunnel box group.
There are various types of longitudinal alignment for tunnel boxes, such as 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 (curved line), it is essential to properly evaluate various influences when designing the longitudinal direction.
For example, when considering the design of the longitudinal direction of a tunnel box group having a curved section using the jacking method, in the curved section using the jacking method, in order to ensure smooth advancement of the tunneling machine and the following tunneling box group, a construction method is generally used in which a copy cutter is extended from the side of the cutter head of the tunneling machine into the ground to perform over-excavation, and the tunneling machine excavates and the tunneling box group is advanced while filling the over-excavation section with a sliding material. In this case, since the tunneling machine is present in the sliding material filled in the over-excavation section, there is a risk that the tunneling machine will meander during the excavation process. If the curved shape in the longitudinal direction is a curved shape in a vertical plane, the tunneling machine excavating the curved section while rising in the sliding material of the over-excavation section will be subjected to the weight of the following tunneling box group in addition to its own weight, so the meandering of the tunneling machine will be even more noticeable.

In the thrusting method, adjacent thrust boxes are connected inside the starting shaft where the main thrust device is installed, so it is impossible to assemble the thrust box group inside the starting shaft so that it has a vertical cross-sectional linearity that takes into account the above-mentioned meandering during the thrusting process.
If the tunneling machine and the following group of tunneling boxes meander in the skid material filled in the overexcavation area, there is a risk that in some places, part of the tunneling machine or part of the tunneling boxes that make up the group of tunneling boxes may be restrained by the ground, and this restraint by the ground may cause the jack thrust to be insufficient, making it necessary to take emergency measures such as adding a center jack that was not originally planned.The additional jack thrust may then cause excessive external forces that were not anticipated in the design stage to act on each of the tunneling boxes that make up the group of tunneling boxes, making it necessary to re-examine the longitudinal cross-sectional forces of the tunneling boxes and, if necessary, to reinforce the tunneling boxes immediately.

In the design of the longitudinal direction of a group of tunnel boxes, a design method is generally used in which the group of tunnel boxes is modeled as a beam model in a computer, a ground spring is attached to this beam model to make a longitudinal beam model, and the longitudinal section force is verified based on the section force generated by loading a jack thrust on the longitudinal beam model. However, as mentioned above, even though the ground reaction force due to the ground spring does not act on the beam model (group of tunnel boxes) in the overexcavation section, the longitudinal section force of the group of tunnel boxes is calculated on the assumption that the ground spring acts, so it must be said that there is a problem with the accuracy of the design of the longitudinal direction of a group of tunnel boxes, especially those with curved sections.
In view of the above, there is a need for a method for designing the longitudinal direction of a tunnel box group that uses an appropriate longitudinal beam model that takes into account overexcavation sections to achieve highly accurate design in the longitudinal design of a tunnel box group that has at least curved sections, and for a method for revising the construction plan for the tunnel box group based on the design contents obtained by this design method.

Patent Document 1 proposes a method for determining whether or not to install a reaction wall at a sharp curve in a tunnel when constructing a tunnel in soft ground using the shield method or jacking method. Specifically, this method determines whether or not to install a reaction wall by comparing the ground reaction of the tunnel lining calculated by a structural analysis simulating a sharp curve with the strength of the original ground, and when it is determined that the ground reaction is greater than the original ground strength, this method increases the axial rigidity of the tunnel to reduce the ground reaction, making it unnecessary to install a reaction wall.

JP 2002-194989 A

The method for determining whether or not a reaction wall needs to be installed described in Patent Document 1 is said to be capable of providing a method for determining whether or not a reaction wall needs to be installed that corresponds to actual conditions. However, as mentioned above, it does not provide an appropriate longitudinal beam model that takes into account overexcavation in the longitudinal design of a group of tunnel boxes that has at least curved sections.

The present invention aims to provide a method for designing the longitudinal direction of a group of tunnel boxes that has at least curved sections, in which an appropriate longitudinal beam model that takes into account overexcavation is used to realize highly accurate design, and a method for revising the construction plan for a group of tunnel boxes based on the design content of this design method and the amount of meandering during actual construction.

In order to achieve the above object, one aspect of the method for designing a tunnel group in a longitudinal direction according to the present invention comprises the steps of:
A method for designing a longitudinal section of a group of tunnel boxes formed by a plurality of tunnel boxes and having at least a curved section, while receiving a jack thrust from a jack of a tunneling machine or a tunnel excavator by a jacking method or a shield method, comprising the steps of:
A step A includes creating, in a computer, a curved beam model having equivalent rigidity for the group of tunnel boxes, or a curved beam model formed by connecting beam models of adjacent tunnel boxes with rotational springs, and attaching a ground spring to the curved beam model to create a longitudinal beam model (analysis model), in which the ground spring is a first nonlinear ground spring in which the ground reaction force is zero in the overexcavation portion and increases according to displacement in the area in contact with the ground;
The method is characterized by having a step B of calculating at least the longitudinal cross-sectional force of the tunnel box by setting and loading a jack thrust by the thrust jack on the longitudinal beam model.

According to this aspect, the tunnel box group having the curved section is modeled as a curved beam model having equivalent rigidity, and a ground spring is attached to this to form a longitudinal beam model, and 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 according to the displacement in the area in contact with the ground, and the longitudinal section force of the tunnel box is calculated based on the longitudinal beam model equipped with the ground spring in which the overexcavation section is properly modeled, so that the longitudinal design of the tunnel box group with high accuracy can be realized. Here, in the case where the tunnel box group has a curved section with a single circular longitudinal alignment, longitudinal beam models at various construction stages are created for each construction stage, such as a longitudinal beam model at the 10R stage where 10 tunnel box rings (1R) are advanced, a longitudinal beam model at the 20R stage where 20R are advanced, and a circular longitudinal beam model advanced all around, and the longitudinal section force of the tunnel box is calculated each time. Here, the cross-sectional forces calculated for each tunnel box that makes up the tunnel box group will differ from place to place, but at the design stage, the specifications for the tunnel box are determined based on the most severe cross-sectional force.
In addition, the jack thrust may be a jack thrust by a push jack of a push device in the jacking method, a jack thrust by a push jack of a push device in addition to a push jack, a jack thrust by a push jack equipped in a tunneling machine in both the jacking method and the shield method, etc. For example, in the jacking method using a tunneling machine equipped with a push jack, the jack thrust by the push jack is loaded on one end of the longitudinal beam model (starting shaft position), the jack thrust by the push jack equipped in the tunneling machine is loaded on the other end of the longitudinal beam model (tunnel position), and if a push device is interposed between the tunnel box groups, the jack thrust by the push jack is loaded on that position.

Also, there are various ways of attaching ground springs, such as attaching them to each tunnel box, attaching them to each 10R, etc. Furthermore, it is desirable for the ground properties of each location (each soil layer) to be appropriately reflected in the ground spring, and it is advisable to set the ground spring by evaluating the N value of each soil layer, the internal friction angle of the ground, adhesion (viscosity), etc.
In the ground spring applied in this embodiment, the ground reaction is set to zero in the overexcavation section because the tunnel box group is not in contact with the ground, and the ground reaction is set to increase (for example, increase linearly) according to the displacement in the area in contact with the ground, thereby realizing a safer and more accurate design than a longitudinal beam model equipped with a conventional ground spring that does not consider the overexcavation section. Also, the first nonlinear ground spring, in which the ground reaction 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 the ground reaction and the displacement changes at a certain displacement (two straight lines with different gradients are continuous).

In another aspect of the method for designing a tunnel group in the longitudinal direction according to the present invention,
The ground spring includes a normal ground spring in a normal direction of the arc in the curved section and a tangential ground spring in a tangential direction of 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.

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 with an upper limit value of the ground reaction force (normal ground reaction force) multiplied by the friction coefficient, which allows for even more accurate design of the longitudinal direction of the tunnel box group. 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 form a tangential ground spring that simulates friction behavior in which the tangential reaction force plateaus at a certain displacement.

In another aspect of the method for designing a tunnel group in the longitudinal direction according to the present invention,
The step B is characterized in that, in addition to the longitudinal section force, the ground reaction force and the required jack thrust are further calculated.

According to this aspect, in addition to the longitudinal section force, the ground reaction force and the required jack thrust are calculated, so that the ground spring can be reviewed at any time based on the calculated ground reaction force, and the jack thrust of the push jack, etc. can be reviewed at any time based on the calculated required jack thrust. By performing analysis again based on the reviewed ground spring and jack thrust, the longitudinal tunnel box group can be designed with even higher accuracy, and the required jack thrust can be identified.

In another aspect of the method for designing a tunnel group in the longitudinal direction according to the present invention,
In the above-mentioned process A, the normal direction ground spring is modified to become a modified normal direction ground spring based on the amount of meandering of the tunnel box group that occurs during the actual construction, and the modified normal direction ground spring is installed in the beam model.

According to this aspect, the normal ground spring is modified to a modified normal ground spring based on the amount of meandering of the tunnel box group that occurs during the actual construction. This allows for analysis results that are in line with the actual construction based on an analysis model equipped with a more accurate normal ground spring (modified normal ground spring) that reflects the amount of meandering of the tunnel box group during the actual construction, and by comparing it with previous analysis results, it becomes possible to reinforce the tunnel box group, review the required jack thrust, etc. Here, the amount of meandering is measured using a position sensor such as a gyroscope equipped on the tunnel boring machine and each tunnel box that makes up the tunnel box group.

In another aspect of the method for designing a tunnel group in the longitudinal direction according to the present invention,
In the step A, the initially set friction coefficient is modified to a modified friction coefficient based on the friction coefficient identified in the actual construction, the tangential ground spring is modified to a modified tangential ground spring based on the modified friction coefficient, and the modified tangential ground spring is installed in the beam model.

According to this embodiment, the initially set friction coefficient is modified to a modified friction coefficient based on the friction coefficient identified in the actual construction, and the tangential ground spring is modified to a modified tangential ground spring based on the modified friction coefficient. This makes it possible to obtain an analytical model equipped with a more accurate tangential ground spring (modified tangential ground spring), and further, based on both the modified normal ground spring and modified tangential ground spring described above, analytical results that are in line with the actual construction can be obtained, and by comparing these with previous analytical results, it becomes possible to reinforce the tunnel box group, review the required jack thrust, etc.
Here, the method of determining the friction coefficient in the actual construction is, for example, to assume that the sum of the face pressure that the cutter head of the tunnel tunneling machine receives from the face and the peripheral friction force between the tunnel tunneling machine and the subsequent tunnel box group and the ground is the jack thrust, for example, from a thrust jack, to calculate the peripheral friction force by subtracting the face pressure from the determined jack thrust, and it becomes possible to determine the friction coefficient in the actual construction based on the calculated peripheral friction force.

In addition, one aspect of the method for correcting a construction plan for a tunnel box group according to the present invention is to
The method is characterized in that the need for correction of the specifications of the tunnel boxes, which are set based on the cross-sectional force in the longitudinal direction calculated by the longitudinal design method of the tunnel box group, the bearing capacity of the ground, which is set based on the ground reaction force, and the required jack thrust is determined based on the amount of meandering of the tunnel box group that occurred during construction, and when it is determined that correction is required for each, measures to reinforce the specifications of the tunnel boxes, measures to ensure the bearing capacity of the ground, and measures to increase thrust by adding a propulsion device are taken.

According to this aspect, based on the amount of meandering of the tunnel box group that occurred during the actual construction, it is determined whether or not the specifications of the tunnel box, the bearing capacity set based on the ground reaction, and the required jack thrust need to be revised. If necessary, measures can be taken to reinforce the specifications of the thrust box (reinforcement with reinforcing members, etc.), to ensure the bearing capacity of the ground (ground improvement, etc.), and to increase the thrust by adding thrust devices (such as inserting one or more thrust devices (push jacks) in the tunnel box group). This makes it possible to prevent problems such as inability to carry out construction or delays in construction due to insufficient thrust or insufficient bearing capacity, even if the tunnel boring machine or the tunnel box group meanders in various ways in the sliding material of the overexcavation section.

The longitudinal design method for a tunnel box group and the method for modifying a construction plan for a tunnel box group of the present invention provide a longitudinal design method for a tunnel box group that uses an appropriate longitudinal beam model that takes into account overexcavation in the longitudinal design of a tunnel box group that has at least a curved section, thereby enabling highly accurate design, and a method for modifying a construction plan for a tunnel box group based on the design content of this design method and the amount of meandering during construction.

1 is a flowchart (design flowchart in the design stage) showing an example of a design method in the longitudinal direction of a tunnel box group according to the first embodiment. This is a schematic diagram showing the state in which a group of tunnel boxes having a single circular longitudinal section in a vertical plane are being advanced using the jacking method. FIG. 1 is a schematic diagram showing the state in which a tunnel tunneling machine advances a group of tunnel boxes in a curved section while constructing an overexcavation area and filling the overexcavation area with lubricant. FIG. 13 is a schematic diagram illustrating the external forces acting on one tunnel box during the propulsion process. FIG. 13 is a schematic diagram illustrating an example of a longitudinal beam model. FIG. 13 is a diagram showing the relationship between normal ground reaction force and normal displacement, which explains the spring characteristics of a normal ground spring. FIG. 13 is a diagram showing the tangential ground reaction force-tangential displacement relationship, which explains the spring characteristics of a tangential ground spring. FIG. 13 shows a flowchart showing an example of a method for designing the longitudinal direction of a tunnel box group according to the second embodiment (design flowchart at the construction stage), and a flowchart showing an example of a method for revising the construction plan for the tunnel box group according to the embodiment (design flowchart at the construction stage). This is a schematic diagram illustrating a state in which the tunnel boring machine and the group of tunnel boxes as a whole are uniformly meandering radially inward in the curved section (single circle). FIG. 9 is a diagram showing the relationship between normal ground reaction force and normal displacement, explaining the spring characteristics of a modified normal ground spring based on the amount of meandering in the meandering state of FIG. 8 . This is a schematic diagram illustrating a state in which the tunnel boring machine and the group of tunnel boxes as a whole are uniformly meandering radially outward in the curved section (single circle). FIG. 11 is a diagram showing the relationship between normal ground reaction force and normal displacement, explaining the spring characteristics of a modified normal ground spring based on the amount of meandering in the meandering state of FIG. 10. FIG. 1 is a schematic diagram illustrating the state in which the tunnel boring machine and the group of tunnel boxes snake radially inward and outward in a curved section (single circle).

Below, a method for designing the longitudinal direction of a group of tunnel boxes according to an embodiment and a method for modifying the construction plan for a group of tunnel boxes will be explained with reference to the attached drawings. Note that in this specification and the drawings, substantially identical components may be designated by the same reference numerals to avoid redundant explanations.

[Design method for the longitudinal direction of a tunnel box group according to the first embodiment]
First, an example of a design method for the longitudinal direction of a tunnel box group according to the first embodiment will be described with reference to Figs. 1 to 6. Here, Fig. 1 is a flowchart (design flowchart in the design stage) showing an example of a design method for the longitudinal direction of a tunnel box group according to the first embodiment. Fig. 2 is a schematic diagram showing a state in which a tunnel box group having a single circular longitudinal line shape in a vertical plane is advanced by a jacking method, and Fig. 3 is a schematic diagram showing a state in which a tunneling machine advances a tunnel box group while constructing an over-excavation section in a curved section and filling the over-excavation section with a slipper. Fig. 4 is a schematic diagram explaining an external force acting on one tunnel box in the advancement process, and Fig. 5 is a schematic diagram explaining an example of a longitudinal beam model. Furthermore, Fig. 6A is a diagram showing a normal ground reaction force-normal displacement relationship explaining the spring characteristics of a normal ground spring, and Fig. 6B is a diagram showing a tangential ground reaction force-tangential displacement relationship explaining the spring characteristics of a tangential ground spring.

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

As shown in Figure 1, the design method for the longitudinal direction of a group of tunnel boxes according to this embodiment is a design method used in the design stage before construction begins, and includes Process A and Process B.

Process A mainly comprises the process of setting input conditions and creating an analysis model, while Process B comprises the process of carrying out the analysis and inspecting the longitudinal stress of the tunnel body.

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

The example shown in Figure 2 is an example of constructing a group of tunnel boxes 20 (circumferential tunnel) having a vertical cross section of a single circle with radius r in a vertical plane using the thrusting method. As shown in Figure 2, when connecting and widening a main line tunnel HT (e.g., a main line shield tunnel) that has already been constructed underground G with a ramp tunnel RT (e.g., a ramp shield tunnel) located to the side of it underground, a vertical shaft T is constructed that extends vertically below the ramp tunnel RT. Note that this vertical shaft may extend diagonally downward instead of vertically.

A starting platform R is installed below a vertical shaft T that has been constructed to a specified depth, and a push device 30 equipped with a push jack is installed on the starting platform R. The tunnel excavator 10 and tunnel box body 21 are hung down from the ramp tunnel RT as required, and the tunnel excavator 10 is caused to excavate into the ground. Multiple tunnel box bodies 21 are sequentially placed behind it, and the tunnel box group 20 formed by the tunnel excavator 10 and multiple tunnel box bodies 21 is advanced by the jack thrust of the push jack 30.

The illustrated tunneling machine 10 has a front body 11 and a rear body 12, and between them is a propulsion jack (not shown) (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 side. Each cutter head 13 has a built-in copy cutter that can move freely 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.

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

A face pressure S acts from the front on the cutter head 13 of the tunneling machine 10. In addition, because the tunneling machine 10 is propelled in a vertical plane as shown in the example shown, an axial component force W1 of its own weight acts on the tunneling machine 10, and an axial component force W2 of its own weight acts on each tunnel box 21.

The tunnel box group 20 is subjected to a peripheral resistance force F1 between itself and the surrounding ground G as it is advanced, and also to a frictional resistance force F2 due to a ground reaction force Q associated with curved construction. Here, the forward tunnel excavator 10 and the tunnel box group 20 are advanced by a jack thrust force P1 acting from the base jack 30 in the shaft T, so the jack thrust forces P2, P3, and P4 acting thereon gradually decrease toward the front of the tunnel box group 20. The ground reaction force Q associated with curved construction is a reaction force resulting from this jack thrust force P, so as shown in FIG. 2, it is maximum near the base jack 30 and tends to gradually decrease toward the tunnel excavator 10.

In this way, in the illustrated example, in the jacking method along a curved line in a vertical plane, the tunnel excavator 10 and the group of tunnel boxes 20 are advanced by a jack thrust P equal to or greater than the sum of the face pressure S acting on the tunnel excavator 10, the axial component force W1 of its own weight acting on the tunnel excavator 10, the axial component force W2 of its own weight acting on each tunnel box 21, the peripheral resistance force F1 between the tunnel excavator 10 and the surrounding ground G, and the frictional resistance force F2 caused by the ground reaction force Q associated with curved construction. Note that, for example, in construction in a horizontal plane, the axial component force W1 of its own weight acting on the tunnel excavator 10 and the axial component force W2 of its own weight acting on each tunnel box 21 are not necessary when calculating the jack thrust of the main jack 30.

If the jack thrust of the main jack 30 is insufficient, one or more intermediate jacks are placed between the tunnel box groups 20 to compensate for the insufficient jack thrust.

When setting the jack thrust of the main jack 30 and the main jack 30 and the intermediate jack provided as necessary, the required jack thrust changes from time to time during the advancement of 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 group 20 (10R), the stage up to 20R, and the final stage when the tunnel boring machine 10 reaches the shaft T.

As shown in FIG. 3, the copy cutter 14 protrudes from the side of the cutter head 13 (here, for ease of explanation, the drawing shows a form having only one cutter head 13), and as the cutter head 13 rotates while the tunnel excavator 10 excavates in the excavation direction along the planned vertical alignment L1, a predefined width t1 overexcavation section 25 is created on the side of the tunnel excavator 10 and the following group of tunnel boxes 20, and the tunnel excavator 10 fills the overexcavation section 25 with a slippery material 28. A rectangular frame-shaped overexcavation section 25 with width t1 is created around the tunnel excavator 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.

Figure 3 shows the state in which the tunnel tunneling machine 10 is excavating along the planned vertical alignment L1 and the group of tunnel boxes 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 the state in which the tunnel tunneling machine 10 is not meandering. Furthermore, width t1 is the designed overexcavation amount under the input conditions.

As shown in FIG. 4, focusing on one tunnel box 21n (the nth tunnel box from the tunnel excavator 10 side) that constitutes the tunnel box group 20, balance of forces in the axial direction (longitudinal direction) and balance of forces perpendicular to the axis are established.

The balance of axial forces is (load Pn transmitted to adjacent steel shell) = (axial component of load (jack thrust) transmitted from adjacent steel shell Pn-1v) - (circumferential resistance F1n) - (friction resistance due to ground reaction F2n) - (axial component of steel shell's own weight W2v).

On the other hand, the balance of forces perpendicular to the axis is (subgrade reaction force Q (restraining outward deformation)) = (perpendicular force component Pn-1h of the load (jack thrust) transmitted from the adjacent steel shell).

Returning to FIG. 1, after setting the input conditions, an analysis model is created. Specifically, as shown in FIG. 5, the tunnel box group 20 is modeled in a computer as a curved beam model BM having equivalent rigidity. When 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.

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.

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. In addition, although not shown, restraining springs are attached to one end BM1 (or its vicinity) of the curved beam model BM where the jack thrust P from the thrust jack is loaded, and to the other end BM2 (or its vicinity) of the curved beam model BM that has reached the shaft.

When modeling the normal ground spring JM1, the overexcavation portion 25 shown in Figure 3 is appropriately taken into consideration. That is, in the conventional method of setting the normal ground spring, the overexcavation portion is not taken into consideration, but as is clear from Figure 3, the overexcavation portion 25 is filled with slippery 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 safe design, and it can be said that this modeling correctly reflects the actual situation.

As shown in FIG. 6A, when modeling the normal ground spring JM1, the ground reaction force Q 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 to the normal displacement of the tunnel box group 20 in the area where it comes into contact with the ground. At this time, since the rate at which the ground reaction force increases in response to the displacement differs for each soil layer, it is preferable to model the normal ground spring JM1 for each soil layer.

As shown in FIG. 6A, 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 nonlinear ground springs in that the linear gradient showing the relationship between the ground reaction force and the displacement changes at a certain displacement (two straight lines with different gradients are continuous).

On the other hand, as shown in FIG. 6B, 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 upper limit (and lower limit) of the tangential ground reaction force is the normal ground reaction force Q multiplied by the friction coefficient μ. For example, by multiplying the maximum value of the normal ground reaction force Q by the friction coefficient μ, a tangential ground spring JM2 can be formed that simulates frictional behavior in which the tangential reaction force plateaus at a certain displacement.

The friction coefficient μ is calculated, for example, from tan(φ/2) (φ is the internal friction angle of the soil), 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 soil spring JM2 for each soil layer.

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 normal ground spring JM1, which is a first nonlinear ground spring, and a tangential ground spring JM2, which is a second nonlinear ground spring, to multiple positions on the curved beam model BM (this concludes Process A, including setting the input conditions and creating the analysis model).

As shown in Figure 5, a jack thrust P by a driving jack such as a thrust jack 30 is set and loaded on the longitudinal beam model M to calculate the longitudinal section force of each tunnel box 21 constituting the tunnel box group 20 and the ground reaction force Q in the longitudinal direction of the tunnel box group 20. This section force includes bending moment, shear force, and axial force (longitudinal compression force and tension force). In the illustrated model in which the entire section is a curved section, the calculated ground reaction force Q gradually changes in the longitudinal direction as shown in Figure 5.

For example, in the initial stage, as explained with reference to Figure 2, the analysis is performed assuming that the jack thrust of the main jack 30 is a jack thrust capable of propelling the tunnel excavator 10 and the group of tunnel boxes 20. If the axial force contained in the longitudinal section 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 large, and the analysis is repeated while changing the jack thrust until the compressive force is equivalent to the face pressure S, and the required jack thrust is set.

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. 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.

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

The stress check identifies the originally set tunnel box specifications (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 set again, and the tunnel box specifications 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 re-created and the analysis is performed again, and a stress check is performed to determine specifications that satisfy the bearing capacity of both the tunnel box and the ground (this is Process B, including the analysis and stress check).

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, an analysis is performed using a longitudinal beam model M equipped with a ground spring JM including a normal ground spring JM1 that takes into account the overexcavation section 25, thereby enabling highly accurate design of the longitudinal direction of the tunnel box group.

[Method of designing the longitudinal direction of a tunnel box group according to the second embodiment and method of correcting the construction plan of a tunnel box group according to the embodiment]
Next, an example of a design method for the longitudinal direction of the tunnel box group according to the second embodiment and an example of a method for correcting the construction plan of the tunnel box group according to the embodiment will be described with reference to Fig. 7 to Fig. 12. Here, Fig. 7 shows a flowchart (design flowchart in the construction stage) showing an example of a design method for the longitudinal direction of the tunnel box group according to the second embodiment and a flowchart (design flowchart in the construction stage) showing an example of a method for correcting the construction plan of the tunnel box group according to the embodiment. Fig. 8 is a schematic diagram explaining a state in which the tunnel excavator and the tunnel box group are uniformly meandering inward in the radial direction of the curved section (single circle) as a whole, and Fig. 9 is a diagram showing the relationship between normal ground reaction and normal displacement, which explains the spring characteristics of the corrected normal ground spring based on the meander amount in the meandering state of Fig. 8. Fig. 10 is a schematic diagram explaining the state in which the tunnel excavator and the group of tunnel boxes are uniformly meandering radially outward of the curved section (single circle) as a whole, and Fig. 11 is a diagram showing the normal ground reaction force-normal displacement relationship explaining the spring characteristics of the corrected normal ground spring based on the amount of meandering in the meandering state of Fig. 10. Furthermore, Fig. 12 is a schematic diagram explaining the state in which the tunnel excavator and the group of tunnel boxes are meandering radially inward and outward of the curved section (single circle).

The design method for the longitudinal direction of the tunnel box group in the second embodiment is based on steps A and B shown in Figure 1, but involves modifying the ground spring based on the ground conditions identified during the actual construction and the amount of meandering of the tunnel boring machine 10 and the tunnel box group 20, and performing analysis to determine whether or not the bearing capacity of the tunnel boring machine and the tunnel box group 20 during construction and the surrounding ground is necessary based on the initial design. If measures are required for the tunnel box group 20 or the ground, countermeasures are proposed, which leads to a method of revising the construction plan.

As shown in Figure 7, to set the construction conditions, the actual ground conditions are acquired during construction, and the amount of meandering determined by position sensors such as gyros installed inside the tunnel boring machine 10 and the tunnel box group 20 is acquired. The ground conditions at the design stage are then reviewed based on the acquired ground conditions.

As part of the calibration, the friction coefficient of each soil layer is corrected. For example, the peripheral friction force acting on the periphery of the tunnel box group 20 is calculated from the measured face pressure and the actual jack thrust from the jack, and the actual friction coefficient of the ground is identified from this peripheral friction force, and the friction coefficient at the design stage is corrected. At this time, in a tunnel box group 20 that is long in the excavation direction, for example, the soil layers passed through may differ at each location, such as the 10R in front, the next 10R following that, and the next 10R following that, so a calibration may be performed to set a unique friction coefficient for each 10R, for example.

In the actual construction, as shown in Figure 8, the tunneling machine 10 and the tunnel box group 20 may meander overall by a meander amount t2 toward the inside of the circumferential tunnel (the excavation direction axis of the tunneling machine 10 and the tunnel box group 20 relative to the planned vertical alignment L1 is L4, and the line of the initial overexcavation section 25 is the overexcavation section 25A of the inner line L5 and the outer line L6), or, as shown in Figure 10, they may meander overall by a meander amount t2 toward the outside of the circumferential tunnel (the excavation direction axis of the tunneling machine 10 and the tunnel box group 20 relative to the planned vertical alignment L1 is L7, and the line of the initial overexcavation section 25 is the overexcavation section 25B of the inner line L8 and the outer line L9).

As shown in Figure 8, if the overall meandering inward is by an amount t2, a corrected normal direction ground spring is modeled based on this amount t2, as shown in Figure 9. Specifically, the amount of inner overexcavation is set to t1+t2, and the amount of outer overexcavation is set to t1-t2 (the original graph is shifted by t2 in the - direction on the X-axis), and a ground reaction-displacement graph is created.

On the other hand, as shown in Figure 10, if the overall meandering outward is by an amount t2, a corrected normal direction ground spring is modeled based on this amount t2, as shown in Figure 11. Specifically, the amount of outer overexcavation is set to t1+t2, and the amount of inner overexcavation is set to t1-t2 (the original graph is shifted by t2 in the + direction on the X-axis), and a ground reaction-displacement graph is created.

Also, as shown in Figure 12, when the excavation direction axis of the tunnel boring machine 10 and the tunnel box group 20 meanders in different ways at different locations toward the inside and outside of the circumferential tunnel, such as L10, relative to the planned vertical alignment L1, a unique meander amount t is identified for each tunnel box position, and the corrected normal direction ground spring is set based on this meander amount t.

On the other hand, for the tangential ground spring, the friction coefficient of the ground is corrected by calibration, so the tangential ground spring is modified based on this corrected friction coefficient to create a modified tangential ground spring.

Based on the amount of meandering that occurs, the amount of subsequent design overexcavation will be changed in order to modify the longitudinal alignment of the tunnel box group (above, in step A', a longitudinal beam model with corrected ground springs is created based on the amount of meandering during actual construction, etc., in contrast to step A).

Next, an analysis is carried out using the modified longitudinal beam model, and stress checks are performed (Step B').

As a result of the stress assessment, it is verified whether the problem can be addressed by simply modifying the vertical alignment. If this verification determines that the problem can be addressed by simply modifying the vertical alignment, the vertical alignment is modified and the designed amount of overexcavation is changed. Thereafter, the tunnel boring machine 10 is caused to excavate along the modified vertical alignment, and the tunnel box group 20 is advanced.

On the other hand, if it is determined that the problem cannot be solved by simply correcting the longitudinal alignment, various countermeasures are proposed. Specifically, the tunnel body is reinforced. Here, reinforcement refers to reinforcing part or all of the inside of the tunnel body, and examples of such measures include installing reinforcing ribs or reinforcing columns in areas that require reinforcement, or pouring concrete.

Reinforcement measures to ensure the bearing capacity of the ground include ground improvement measures such as chemical injection and creation of frozen soil.

Measures to increase thrust include installing more center thrust jacks and strengthening the main thrust jacks inside the shaft.

In this way, the analytical model is modified based on the ground conditions acquired during the actual construction and the amount of meandering that occurred during the actual construction, the modified analytical model is used to perform analysis, the necessity for proposed countermeasures is determined, and various countermeasures are taken if necessary, thereby revising the construction plan. This is the method for revising the construction plan for a group of tunnel boxes according to the embodiment.

Note that the configurations described in the above embodiments may be combined with other components, and the present invention is not limited to the configurations shown here. In this regard, changes can be made without departing from the spirit of the present invention, and can be determined appropriately according to the application form.

10: tunneling machine 11: front body 12: rear body 13: cutter head 20: tunnel box group 21: tunnel box 25, 25A, 25B: overexcavation section 28: skid 30: push device (pushing jack)
G: Ground (underground)
P: Jack thrust S: Face pressure (tip resistance)
W1: Axial force component of the tunneling machine's own weight W2: Axial force component of the tunnel box group weight F1: Surface friction force F2: Frictional resistance force due to ground reaction in curved section Q: Ground reaction force M: Longitudinal beam model BM: Beam model including curved line JM: Ground spring JM1: Normal ground spring (first nonlinear ground spring)
JM2: Tangential soil spring (second nonlinear soil spring)

Claims (6)

A method for designing a longitudinal section of a group of tunnel boxes formed by a plurality of tunnel boxes and having at least a curved section, while receiving a jack thrust from a jack of a tunneling machine or a tunnel excavator by a jacking method or a shield method, comprising the steps of:
A step A includes creating, in a computer, a curved beam model having equivalent rigidity for the group of tunnel boxes, or a curved beam model formed by connecting beam models of adjacent tunnel boxes with rotational springs, and attaching a ground spring to the curved beam model to create a longitudinal beam model, in which the ground spring is a first nonlinear ground spring in which the ground reaction force is zero in the overexcavation portion and increases according to displacement in the area in contact with the ground;
and a step B of calculating at least the longitudinal cross-sectional force of the tunnel box by setting and loading a jack thrust by the driving jack on the longitudinal beam model. The ground spring includes a normal ground spring in a normal direction of the arc in the curved section and a tangential ground spring in a tangential direction of the arc,
The normal ground spring is the first nonlinear ground spring;
The longitudinal design method for a group of tunnel boxes as described in claim 1, 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. The method for designing a group of tunnel boxes in the longitudinal direction according to claim 1 or 2, characterized in that in step B, in addition to the longitudinal section forces, ground reaction forces and required jack thrusts are further calculated. The design method for the longitudinal direction of a group of tunnel boxes according to claim 2 or claim 3 dependent on claim 2, characterized in that in step A, the normal ground spring is modified to a modified normal ground spring based on the amount of meandering of the group of tunnel boxes that occurs during construction, and the modified normal ground spring is installed in the beam model. The design method for the longitudinal direction of a group of tunnel boxes according to claim 2, claim 3 or claim 4 dependent on claim 2, characterized in that in step A, the initially set friction coefficient is modified to a modified friction coefficient based on a friction coefficient identified in the actual construction, the tangential ground spring is modified to a modified tangential ground spring based on the modified friction coefficient, and the modified tangential ground spring is installed in the beam model. A method for modifying a construction plan for a group of tunnel boxes, which is characterized by determining whether or not each of the specifications of the tunnel boxes, which are set based on the longitudinal section force calculated by the longitudinal design method for a group of tunnel boxes described in any one of claims 1 to 5, needs to be modified based on the amount of meandering of the group of tunnel boxes that occurred during construction, and taking measures to reinforce the specifications of the tunnel boxes, ensure the bearing capacity of the ground, and increase the thrust by adding a propulsion device, when it is determined that each of them needs to be modified.

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