Centering for covering work and method for placing covering concrete

Abstract

To provide an arch center for lining, and a lining concrete placing method, capable of suppressing cracks that may occur in the lining concrete, even when lining descending is performed when the lining concrete is weak and does not develop sufficient strength.SOLUTION: In an arch center 100 for lining applied when placing lining concrete C of a tunnel T, the arch center 100 for lining has a gantry 10 and an arch center form 20 supported by the gantry 10. The arch center form 20 includes a central crown portion, left and right arch portions of the crown portion, and side wall portions on left and right lower sides of the arch center form 20 on the sides of the arch portions. A prestressing force P1 is introduced to at least the crown portion of the arch center form 20, and the crown portion is pulled toward the inner hollow side of the tunnel T.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a centering for lining work and a method for placing lining concrete.

Background Art

[0002] In the construction of mountain tunnels, lining concrete is placed in the placement space between the centering form (formwork) of a centering for lining work (simply referred to as a centering), which is a steel formwork movable in the tunneling direction of the tunnel, and the ground. After the lining concrete develops a predetermined strength, the centering for lining work is moved, and the construction of placing the lining concrete in the same manner is sequentially repeated in some cases.

[0003] The centering for lining work includes a gantry (carriage) and a centering form supported by the gantry. Rails for the centering for lining work to move are generally laid on the roadbed of the tunnel, and the gantry is configured to move along the rails. After placing the lining concrete between the centering form and the ground, when the lining concrete develops a predetermined strength, the centering form is moved to the inner space side of the tunnel to perform so-called centering down for demolding, whereby the centering for lining work becomes movable.

[0004] By the way, in the method of sequentially constructing the lining concrete in the tunneling direction of the tunnel using the above-described centering for lining work, due to the balance with the entire process of tunnel construction, centering down is often performed at a stage where the placed lining concrete does not sufficiently develop strength according to the weak material order. And when centering down is performed at such a stage where the strength development is not sufficient, the lining concrete is displaced downward due to its own weight, and cracking occurs in the lining concrete due to this displacement, which has been a problem.

[0005] Although various factors can be considered as the causes of cracks in the overlaid concrete, when centering is carried out at a stage where the strength development is not sufficient, the downward displacement of the overlaid concrete due to its own weight becomes one of the main factors. Therefore, even when centering is carried out at a stage where the overlaid concrete does not sufficiently develop strength according to the weak material order for the purpose of shortening the construction period, a centering for the overlaid concrete and a placing method of the overlaid concrete that can suppress the cracks that may occur in the overlaid concrete are desired.

[0006] Here, Patent Document 1 proposes a centering method in which the outer periphery of a frame body capable of expanding or contracting in diameter is positioned inward along the inner periphery of an excavated tunnel, and overlaid concrete is placed in a closed space formed between the outer periphery of the frame body during diameter expansion and the inner periphery of the excavated tunnel. This centering is provided with pressure detection means for detecting the contact pressure to the overlaid concrete on the outer periphery of the end portion on the existing overlaid concrete side of the frame body.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] According to the centering described in Patent Document 1, by directly detecting and managing the contact pressure of the frame body to the existing overlaid concrete, it is possible to prevent excessive contact pressure from being applied to the overlaid concrete and to prevent the occurrence of cracks in the construction target part. However, the above-mentioned problem, that is, preventing the overlaid concrete from being displaced downward due to its own weight by centering and preventing cracks from occurring in the overlaid concrete due to this displacement, cannot be achieved.

[0009] The present invention has been made in view of the above problems, and even when centering down is performed at a stage where the strength development of the covering concrete is not sufficient according to the weak material order, it is possible to suppress cracks that may occur in the covering concrete. An object of the present invention is to provide a centering for covering work and a method for placing the covering concrete.

Means for Solving the Problems

[0010] To achieve the above object, one aspect of the centering for covering work according to the present invention is a centering for covering work applied when placing the covering concrete of a tunnel, the centering for covering work has a gantry and a centering form supported by the gantry, the centering form includes a central crown portion, left and right arch portions on both sides of the crown portion, and side wall portions on the sides of the arch portions and located at the lower left and right of the centering form, and prestress force is introduced into at least the crown portion of the centering form and is pulled toward the inner space side of the tunnel.

[0011] According to this aspect, since prestress force is introduced into at least the crown portion of the centering form and it is pulled toward the inner space side of the tunnel, the linear shape in the circumferential direction of the centering form is approximately made in advance to the displacement line when the self-weight of the covering concrete acts. By placing and supporting the covering concrete on the centering form deformed in this way in advance, even if centering down is performed at a stage where the strength development of the covering concrete is not sufficient according to the weak material order, downward displacement due to the self-weight of the covering concrete does not occur or hardly occurs. Therefore, cracks caused by this downward displacement can be suppressed. As a result, it becomes possible to shorten the construction period of tunnel construction while suppressing cracks that may occur in the covering concrete.

[0012] According to this aspect, at the stage when the covering concrete is placed, since the centering form already forms a displacement line that deforms due to the self-weight of the covering concrete, such displacement of the centering form will be suppressed or restrained, and the placed covering concrete can gradually harden and develop strength without being affected by the displacement of the centering form. As a result, at the stage of a weak material order that allows centering down, when the centering form is centered down, the covering concrete has not been affected by the displacement of the centering form during the previous strength development stage, and cracking of the covering concrete can be suppressed.

[0013] Here, "at least prestress force is introduced into the crown part" means that in addition to introducing prestress force only into the crown part of the centering form, it includes forms in which prestress force is introduced into the crown part and the arch part, forms in which prestress force is introduced into the crown part and the side wall part, and forms in which prestress force is introduced into the crown part, the arch part, and the side wall part.

[0014] In any form, by pulling downward (vertically downward or obliquely downward) the crown part where the displacement due to the self-weight of the covering concrete is the largest, it becomes easier to form a displacement line that deforms due to the self-weight of the covering concrete with respect to the centering form. Also, by pulling the crown part downward, conversely, the arch part can deform so as to bulge toward the ground side. For example, by pulling the arch part toward the inner space side of the tunnel, excessive bulging of the arch part toward the ground side can be suppressed. Suppression of such excessive bulging of the arch part toward the ground side can also be achieved not only by directly pulling the arch part but also by pulling the side wall part adjacent to the arch part.

[0015] Moreover, another aspect of the centering for covering according to the present invention is characterized in that the crown part and the side wall part of the centering form are connected by prestress force introduction means, and both the crown part and the side wall part are being pulled.

[0016] According to this aspect, the crown portion and the side wall portion are connected by prestress force introduction means, and both the crown portion and the side wall portion are pulled by a common prestress force introduction means, so that with as few prestress force introduction means as possible, it is possible to achieve both suppression of downward displacement of the crown portion and suppression of protrusion of the arch portion toward the ground side.

[0017] Further, another aspect of the centering form for the lining according to the present invention is Prestress force introduction means are provided on both the crown portion and the arch portion of the centering form, and the prestress force introduction means is configured to receive the reaction force of the prestress force on the gantry, When the gantry floats due to the prestress force, a counterweight is attached to the gantry to suppress the floating, or the legs of the gantry grip the rails on which the gantry moves to suppress the floating.

[0018] According to this aspect, the prestress force introduction means provided on both the crown portion and the arch portion are respectively attached to the gantry and receive the reaction force of the prestress force, so that it becomes possible to easily receive the reaction force of the prestress force with a heavy gantry. On the other hand, when the prestress force is large and the gantry floats due to the prestress force, a form in which a counterweight is attached to the gantry or a form in which the legs of the gantry grip the rails on which the gantry moves is applied, so that the floating of the gantry due to the prestress force can be effectively suppressed.

[0019] Further, another aspect of the centering form for the lining according to the present invention is The crown portion and the arch portion of the centering form are connected by prestress force introduction means, and the arch portion and the gantry are connected by separate prestress force introduction means to receive the reaction force of the prestress force on the gantry. When the gantry floats due to the prestress force, a counterweight is attached to the gantry to suppress the floating, or the legs of the gantry grip the rails on which the gantry moves so as to suppress the floating.

[0020] According to this aspect, the crown part and the arch part are connected by the prestress force introduction means, and the arch part is attached to the gantry by a separate prestress force introduction means to take the reaction force of the prestress force. Thus, it becomes possible to easily take the reaction force of the prestress force with a heavy gantry. On the other hand, when the prestress force is large and the gantry floats due to the prestress force, a form in which a counterweight is attached to the gantry or a form in which the legs of the gantry grip the rails on which the gantry moves is applied, so that the floating of the gantry due to the prestress force can be effectively suppressed.

[0021] Another aspect of the centering for the capping according to the present invention is Prestress force introduction means are provided in each of the crown part, the arch part, and the side wall part of the centering form, and the prestress force introduction means is configured to take the reaction force of the prestress force on the gantry. When the gantry floats due to the prestress force, a counterweight is attached to the gantry to suppress the floating, or the legs of the gantry grip the rails on which the gantry moves so as to suppress the floating.

[0022] According to this aspect, the prestress force introduction means provided in the crown part, the arch part, and the side wall part are respectively attached to the gantry, and by taking the reaction force of the prestress force, it becomes possible to easily take the reaction force of the prestress force with the heavy gantry. On the other hand, when the prestress force is large and the gantry floats due to the prestress force, a form in which a counterweight is attached to the gantry or a form in which the rail on which the gantry moves is gripped by the legs of the gantry is applied, so that the floating of the gantry due to the prestress force can be effectively suppressed.

[0023] Also, in another aspect of the centering form for capping according to the present invention, The magnitude of the prestress force is characterized in that it is a magnitude that imparts a displacement amount before placement to the crown part, which corresponds to the downward displacement amount of the crown part when the capping concrete is placed.

[0024] According to this aspect, since the magnitude of the prestress force is a magnitude corresponding to the downward displacement amount of the crown part when the capping concrete is placed, the displacement of the crown part of the centering form when the capping concrete is placed can be eliminated, and cracking of the capping concrete caused by the displacement of the crown part can be suppressed.

[0025] Also, another aspect of the centering form for capping according to the present invention is Characterized in that the prestress force is gradually load-released from during the placement of the capping concrete to the end of the placement by the prestress force introduction means.

[0026] According to this aspect, since the prestress force is gradually load-released from during the placement of the capping concrete to the end of the placement, the displacement amount of the centering form can be gradually changed during the strength development process of the capping concrete, and the displacement amount of the capping concrete that can change during the strength development process can be kept constant.

[0027] Another aspect of the centering form for lining according to the present invention is that the prestress force introducing means is made of PC steel material.

[0028] According to this aspect, since the prestress force introducing means is made of PC steel material, it becomes easy to install on a centering form, a gantry, etc., and it also becomes easy to manage the introduction of the prestress force. Here, the PC steel material includes PC steel bars, PC steel wires, etc.

[0029] Another aspect of the centering form for lining according to the present invention is that the prestress force introducing means is a jack.

[0030] According to this aspect, since the prestress force introducing means is a jack, it becomes easy to install on a centering form, a gantry, etc., and it also becomes easy to manage the introduction of the prestress force. Here, the jack includes a hydraulic jack, an air jack, an electric jack, etc.

[0031] Also, one aspect of the method for placing lining concrete according to the present invention is a method for placing lining concrete, which has a gantry and a centering form supported by the gantry, and the centering form includes a central crown portion, left and right arch portions of the crown portion, and side wall portions on the sides of the arch portions and at the lower left and right of the centering form, and uses the centering form for lining to place the lining concrete of the tunnel, before placing the lining concrete, introducing a prestress force into at least the crown portion of the centering form to pull it toward the inner space side of the tunnel, and applying a displacement amount before placement, which corresponds to the amount of downward displacement of the crown portion when the lining concrete is placed, to the crown portion, step A; and step B of placing the lining concrete between the natural ground and the centering form.

[0032] According to this aspect, by introducing prestress force into at least the crown part of the centering form and pulling it toward the inner space side of the tunnel, the circumferential linearity of the centering form is approximately made in advance to the displacement line when the self-weight of the lining concrete acts. By placing and supporting the lining concrete on the centering form that has been deformed in advance in this way, even if centering down is carried out when the lining concrete does not fully develop strength according to the weak material order, downward displacement due to the self-weight of the lining concrete does not occur or is difficult to occur. Therefore, cracking caused by this downward displacement can be suppressed. As a result, it becomes possible to shorten the construction period of the tunnel while suppressing cracking that may occur in the lining concrete.

[0033] Also, another aspect of the method for placing lining concrete according to the present invention is In the step B, the prestress force is adjusted so that the prestress force is gradually released from during the placement of the lining concrete until the placement is completed.

[0034] According to this aspect, since the prestress force is gradually released from during the placement of the lining concrete until the placement is completed, the displacement amount of the centering form is gradually changed during the process of strength development of the lining concrete, and it becomes possible to keep the displacement amount of the lining concrete that can change during the process of strength development constant.

Effect of the Invention

[0035] As can be understood from the above description, according to the centering for lining and the method for placing lining concrete of the present invention, even when centering down is carried out when the lining concrete does not fully develop strength according to the weak material order, cracking that may occur in the lining concrete can be suppressed.

Brief Description of the Drawings

[0036]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0037] Hereinafter, an example of the centering for covering work and the method of placing the covering concrete according to each embodiment will be described with reference to the accompanying drawings. In the present specification and drawings, substantially the same components may be denoted by the same reference numerals, and redundant description may be omitted.

[0038] [The centering for covering work according to the first embodiment and the method of placing the covering concrete according to the embodiment] First, referring to FIGS. 1 and 2, an example of a centering for lining work according to the first embodiment and an example of a method for placing lining concrete according to the embodiment will be described. Here, FIG. 1 is a front view of the centering for lining work according to the first embodiment, showing the bending moment acting on the centering form when lining concrete is placed, and also showing the displacements in the crown portion and the arch portion of the centering form. Further, FIG. 2 is a view showing a state in which prestress force is introduced into the prestress force introducing means in the centering for lining work according to the first embodiment.

[0039] The centering 100 for lining work has a portal gantry 10 and a centering form 20 supported by support members 25, 26, 27 extending in the vertical, horizontal, and diagonal directions from the gantry 10. The gantry 10 is a portal-type mobile gantry, and wheels 12 are provided at the lower ends of the left and right legs 11 (the legs 13 are formed by the legs 11 and the wheels 12), and the gantry 10 can move along rails R laid in the longitudinal direction of the tunnel T on the roadbed B of the tunnel T.

[0040] The centering form 20 is formed by a group of forms 21 arranged in the circumferential and longitudinal directions of the tunnel T. The centering form 20 has a length of about 10 m in the longitudinal direction of the tunnel T, for example, and a gable form (not shown) is provided at the longitudinal end of the tunnel T in the centering form 20.

[0041] The centering form 20 can be formally divided into mainly three regions: a central crown portion, left and right arch portions on both sides of the crown portion, and side wall portions on the sides of the arch portions and located at the lower left and right of the centering form 20.

[0042] Inside the horseshoe-shaped or circular hole walls created in the ground G by blasting, mechanical excavation, etc., such as those shown in the illustrated example, before the centering 100 for lining reaches, reinforcing bars for lining (not shown) are arranged in both the circumferential and longitudinal directions of the tunnel T. Then, when the centering 100 for lining reaches as shown in FIG. 1, a placement space S is formed between the centering form 20 and the hole wall for placing the lining concrete. Here, when shotcrete is constructed on the inner peripheral surface of the hole wall, the placement space S is formed between the centering form 20 and the shotcrete.

[0043] A plurality of inspection openings (not shown) are provided in the centering form 20. This inspection opening is an opening through which the tip of a placement hose (not shown) extending in the tunnel T passes and faces the placement space S for placing concrete in the placement space S. Additionally, it is an opening for inserting a vibrator into the placement space S, and further, it is an opening for checking the placement status of the concrete.

[0044] In the method of sequentially constructing the lining concrete C in the advancing direction of the tunnel T using the centering for lining, considering the overall process of tunnel construction, centering down is often carried out when the placed lining concrete C has not fully developed strength according to the weak material order. And when centering down is carried out at such a stage where the strength development is not sufficient, the lining concrete C is displaced downward due to its own weight, and the problem is that cracks occur in the lining concrete due to this displacement.

[0045] For example, as shown in FIG. 1, when the lining concrete C is placed in the placement opening S, a bending moment M is generated in the centering form 20 due to the self-weight load of the lining concrete C, and at the same time, displacements occur at each part due to the self-weight of the lining concrete C. Generally, the maximum bending moment occurs at the crown part of the centering form 20, and similarly, the maximum downward displacement δ1 occurs.

[0046] As shown in Fig. 1, the bending moment M may result in a moment distribution that, for example, reverses in the arch portion of the centering form 20 and then converges to zero bending moment toward the lower end of the side wall portion. Then, a maximum downward displacement δ1 occurs at the crown portion, and a displacement δ2 (<δ1) toward the ground may occur in the arch portion. However, the displacement δ2 in this arch portion is less than the displacement δ2 because the centering form 20 that attempts to be displaced by the placed lining concrete C is pushed back toward the inner space side of the tunnel T, so the actual displacement is less than the displacement δ2.

[0047] In any case, due to the occurrence of the maximum downward displacement δ1 at the crown portion of the centering form 20, cracks C1 may occur on the inner space side of the crown portion of the lining concrete C. Also, in the arch portion of the centering form 20, cracks C2 may occur on the ground side of the arch portion of the lining concrete C due to the displacement toward the ground.

[0048] Even when the centering down is executed at a stage where the placed lining concrete C does not sufficiently develop strength according to the weak material order, since the lining concrete C according to the weak material order is also displaced by the displacement of the centering form 20 after placement, the possibility of cracks C1 and C2 occurring due to this displacement increases.

[0049] Therefore, in the centering 100 for lining, before placing the lining concrete C, prestress force is introduced into at least the crown portion of the centering form 20 to put the crown portion of the centering form 20 in a state of being pulled toward the inner space side of the tunnel T, and a displacement corresponding to the maximum downward displacement δ1 is given to the crown portion in advance. Then, by placing the lining concrete C thereon, the displacement of the centering form 20 after placing the lining concrete C is suppressed, and the cracks that may occur due to the displacement of the lining concrete C following the displacement of the centering form 20 are suppressed or prevented.

[0050] As shown in Fig. 1, in the centering form 100 for lining, the crown part and the left and right side wall parts of the centering form 20 are connected by PC steel materials 30 (an example of prestress force introduction means) such as PC steel bars and PC steel wires.

[0051] Then, as shown in Fig. 2, by introducing the prestress force P1 into the PC steel material 30, both the crown part and the side wall part of the centering form 20 are put in a tension state, and a displacement of about the assumed downward displacement δ1 is given to the crown part of the centering form 20 in advance. That is, the magnitude of the prestress force P1 is the magnitude of imparting the displacement amount before placement to the crown part, which corresponds to the downward displacement δ1 of the crown part when the lining concrete C is placed.

[0052] Also, due to the introduction of this prestress force P1, the arch part adjacent to the side wall part of the centering form 20 is pulled by the load Q1 toward the inner space side of the tunnel T, and this tensile load Q1 makes it possible to suppress the excessive displacement δ2 toward the natural ground side shown in Fig. 1.

[0053] Here, although not shown in the figure, in addition to PC steel materials, a hydraulic jack (an example of a jack) or the like may be applied as the prestress force introduction means. When applying a hydraulic jack, at the crown part of the centering form 20, a hydraulic jack for pulling the centering form 20 toward the inner space side of the tunnel T is mounted on the gantry 10, and further, a separate hydraulic jack is attached to the side of the leg 11 of the gantry 10, and by pulling the side wall part of the centering form 20 with the separate hydraulic jack in the same manner as in Fig. 2, it becomes possible to introduce the prestress force P1 into the centering form 20 in the same manner as the PC steel material.

[0054] For example, in order to reduce the deformation of the centering form due to the self-weight of the covering concrete C, there is also a measure to increase the rigidity of the centering itself by increasing the cross-sectional size of the steel material used for the centering. However, such an increase in the rigidity of the centering will increase the manufacturing cost of the centering. On the other hand, according to the centering 100 for covering work, by introducing prestress force into the desired location of the centering form 20 using the PC steel material 30, the displacement of the centering form 20 due to the self-weight of the covering concrete C can be suppressed. Therefore, it is possible to suppress the cracks that may occur in the covering concrete C without increasing the manufacturing cost of the centering. In particular, even when the centering down is executed at a stage where the covering concrete C does not sufficiently develop strength according to the weak material order, since the downward displacement due to the self-weight of the covering concrete C does not occur or hardly occurs, the cracks caused by this downward displacement can be suppressed. Therefore, it is possible to shorten the construction period of the tunnel construction while suppressing the cracks that may occur in the covering concrete C.

[0055] Here, an example of the placing method of the covering concrete according to the embodiment will be outlined. This placing method is a method of placing the covering concrete C in the placing space S using the centering 100 for covering work shown in FIGS. 1 and 2.

[0056] Before placing the covering concrete C, by introducing the prestress force P1 into at least the crown portion of the centering form 20, the crown portion is pulled toward the inner space side of the tunnel T, and the pre-placement displacement amount corresponding to the downward displacement amount δ1 of the crown portion when the covering concrete C is placed is imparted to the crown portion (Step A).

[0057] Next, the covering concrete C is placed in the placing space S between the natural ground G and the centering form 20 (Step B).

[0058] In this step B, it is preferable to adjust the prestress force so that the prestress force is gradually released from during the placement of the covering concrete to the end of the placement, so that the displacement amount of the centering form 20 gradually changes during the strength development process of the covering concrete C, and the displacement amount of the covering concrete C that can change during the strength development process can be kept constant.

[0059] [Centering for Covering According to the Second Embodiment] Next, with reference to FIG. 3, an example of the centering for covering according to the second embodiment will be described. Here, FIG. 3 is a front view of the centering for covering according to the second embodiment, and shows a state in which the prestress force is introduced into the prestress force introducing means.

[0060] The centering for covering 100A has PC steel materials 31 and 32 provided on both the crown part and the arch part of the centering form 20, and the PC steel materials 31 and 32 are configured to take the reaction forces of the prestress forces P2 and P3 on the gantry 10. Although not shown, an example of the PC steel materials 31 and 32 is fixed to the gantry 10 with a truss structure extending in the longitudinal direction of the centering for covering 100A, and the vertical members of this truss structure are used as the PC steel materials 31 and 32, so that they are attached to the gantry 10.

[0061] Furthermore, as a countermeasure when the gantry 10 floats due to the buoyancy F caused by the reaction force of the upward prestress force P2, a counterweight 40 with a weight W is attached to the gantry 10.

[0062] In this way, by taking the reaction forces of the prestress forces P2 and P3 against the heavy gantry 10, it becomes possible to easily and stably take the reaction forces of the prestress forces P2 and P3. On the other hand, as a countermeasure against the upward prestress force P2 being large and the gantry 10 floating due to the prestress force P2, a counterweight 40 is attached to the gantry 10, so that the floating of the gantry 10 due to the upward prestress force P2 can be effectively suppressed.

[0063] [Centering for Covering Work According to the Third Embodiment] Next, with reference to FIG. 4, an example of the centering for covering work according to the second embodiment will be described. Here, FIG. 4 is a front view of the centering for covering work according to the third embodiment, and shows a state in which prestress force is introduced into the prestress force introducing means.

[0064] The centering 100B for covering work is different from the centering 100A for covering work in that the leg portion 13 of the gantry 10 grips the rail R on which the gantry 10 moves via the gripping member 50, instead of attaching the counterweight 40 to the gantry 10.

[0065] By gripping the rail R by the leg portion 13 of the gantry 10 via the gripping member 50, it is also possible to effectively suppress the lifting of the gantry 10 due to the prestress force P2.

[0066] [Centering for Covering Work According to the Fourth Embodiment] Next, with reference to FIG. 5, an example of the centering for covering work according to the third embodiment will be described. Here, FIG. 5 is a front view of the centering for covering work according to the third embodiment, and shows a state in which prestress force is introduced into the prestress force introducing means.

[0067] The centering 100C for covering work is configured such that the crown portion and the arch portion of the centering form 20 are connected by the PC steel material 33, and the arch portion and the gantry 10 are connected by a separate PC steel material 34, so that the reaction force of the prestress force P5 introduced into the PC steel material 34 is taken by the gantry 10.

[0068] The magnitude of the prestress force P4 is such that it corresponds to the downward displacement δ1 of the crown portion when the covering concrete C is placed, and is the magnitude for imparting the displacement amount before placement to the crown portion. Further, the prestress forces P4 and P5 act directly on the arch portion, and the arch portion of the centering form 20 is pulled by the load Q1 toward the inner space side of the tunnel T, so that it becomes possible to suppress the excessive displacement δ2 toward the natural ground side shown in FIG. 1.

[0069] Even in the centering device 100C for formwork installation, as a countermeasure against the gantry 10 floating due to the buoyancy force F caused by the reaction force of the upward prestress force P5, a counterweight 40 with a weight W is attached to the gantry 10. Here, instead of the counterweight 40, a countermeasure against floating may be taken in which the leg portion 13 of the gantry 10 grips the rail R via the gripping member 50 shown in FIG. 4.

[0070] Even with the centering device 100C for formwork installation, by taking the reaction force of the prestress force P5 against the heavy gantry 10, it becomes possible to easily and stably take the reaction force of the prestress force P5.

[0071] [Centering Device for Formwork Installation According to the Fifth Embodiment] Next, with reference to FIG. 6, an example of the centering device for formwork installation according to the fourth embodiment will be described. Here, FIG. 6 is a front view of the centering device for formwork installation according to the fourth embodiment, and shows a state in which the prestress force is introduced into the prestress force introducing means.

[0072] In the centering device 100D for formwork installation, PC steel materials 35, 36, and 37 are provided in the crown portion, arch portion, and side wall portion of the centering form 20, respectively. By connecting each PC steel material 35, 36, and 37 to the gantry 10, the reaction forces of the prestress forces P6, P7, and P8 introduced into the PC steel material 33 are taken by the gantry 10.

[0073] The magnitude of the prestress force P6 is such that it corresponds to the downward displacement δ1 of the crown portion when the formwork concrete C is placed, and is the magnitude for imparting the displacement amount before placement to the crown portion. Further, due to the prestress force P7 acting directly on the arch portion and the prestress force P8 acting on the side wall portion, the arch portion of the centering form 20 is pulled by the load Q1 toward the inner space side of the tunnel T, so that it becomes possible to suppress the excessive displacement δ2 toward the natural ground side shown in FIG. 1.

[0074] Even in the case of the centering device 100D for concreting, as a countermeasure against the gantry 10 floating due to the buoyancy force F caused by the reaction forces of the upward prestress forces P6 and P8, a counterweight 40 with a weight W is attached to the gantry 10. Here, instead of the counterweight 40, a countermeasure against floating may be taken in which the leg portion 13 of the gantry 10 grips the rail R via the gripping member 50 shown in FIG. 4.

[0075] Even with the centering device 100D for concreting, by taking the reaction forces of the prestress forces P6, P7, and P8 against the heavy gantry 10, it becomes possible to easily and stably take the reaction forces of the prestress forces P6, P7, and P8.

[0076] Other embodiments in which other components are combined with the configurations and the like described in the above embodiments may also be possible, and the present invention is not limited to the configurations shown here at all. In this regard, it can be changed without departing from the gist of the present invention and can be appropriately determined according to the application form.

Explanation of Reference Numerals

[0077] 10: Gantry 11: Leg 12: Wheel 13: Leg Portion 20: Centering Form 21: Form 25, 26, 27: Support Member 30, 31, 32, 33, 34, 35, 36, 37: Prestress Force Introduction Means (PC Steel Material) 40: Counterweight 50: Gripping Member 100, 100A, 100B, 100C, 100D: Centering Device for Concreting T: Tunnel G: Natural Ground S: Placing Space B: Roadbed R: Rail C: Concreting C1, C2: Crack M: Bending Moment

Claims

1. A centering form for lining used when placing lining concrete for a tunnel, comprising: the centering form for lining has a gantry and a centering form supported by the gantry; the centering form includes a central crown portion, left and right arch portions on both sides of the crown portion, and side wall portions on the sides of the arch portions and located at the lower left and right of the centering form; A centering form for lining, characterized in that prestress force is introduced into at least the crown portion of the centering form and is pulled toward the inner space side of the tunnel.

2. The centering form for lining according to claim 1, characterized in that the crown portion and the side wall portion of the centering form are connected by a prestress force introducing means, and both the crown portion and the side wall portion are pulled.

3. Prestress force introducing means are provided on both the crown portion and the arch portion of the centering form, and the prestress force introducing means is configured to take the reaction force of the prestress force on the gantry. When the gantry floats due to the prestress force, a counterweight is attached to the gantry to suppress the floating, or the legs of the gantry grip the rails on which the gantry moves to suppress the floating. The centering form for lining according to claim 1, characterized in that it is configured as described above.

4. The crown portion and the arch portion of the centering form are connected by a prestress force introducing means, and the arch portion and the gantry are connected by a separate prestress force introducing means to take the reaction force of the prestress force on the gantry. When the gantry floats due to the prestress force, a counterweight is attached to the gantry to suppress the floating, or the legs of the gantry grip the rails on which the gantry moves to suppress the floating. The centering form for lining according to claim 1, characterized in that it is configured as described above.

5. Prestress force introducing means are provided on each of the crown portion, the arch portion, and the side wall portion of the centering form, and the prestress force introducing means is configured to take the reaction force of the prestress force on the gantry. ​ ​ When the gantry floats due to the prestress force, a counterweight is attached to the gantry to suppress the floating, or the legs of the gantry grip the rails on which the gantry moves so as to suppress the floating. The centering device for lining according to claim 1, characterized in that it is configured as described above.

6. The magnitude of the prestress force is such that it corresponds to the amount of downward displacement of the crown portion when the lining concrete is placed, and is the magnitude that imparts the displacement amount before placement to the crown portion. The centering device for lining according to any one of claims 1 to 5, characterized in that it is configured as described above.

7. By the prestress force introducing means, the prestress force is gradually released from during the placement of the lining concrete until the placement is completed. The centering device for lining according to any one of claims 2 to 5 and any one of claims 6 dependent on any one of claims 2 to 5, characterized in that it is configured as described above.

8. The prestress force introducing means is a PC steel material. The centering device for lining according to any one of claims 2 to 5 and any one of claims 6 and 7 dependent on any one of claims 2 to 5, characterized in that it is configured as described above.

9. The prestress force introducing means is a jack. The centering device for lining according to any one of claims 2 to 5 and any one of claims 6 and 7 dependent on any one of claims 2 to 5, characterized in that it is configured as described above.

10. A method for placing lining concrete, using a centering device for lining having a gantry and a centering form supported by the gantry, the centering form including a central crown portion, left and right arch portions of the crown portion, and side wall portions on the sides of the arch portions and located at the lower left and right of the centering form, the method comprising: Before placing the lining concrete, introducing a prestress force into at least the crown portion of the centering form to pull it toward the inner space side of the tunnel, and imparting a displacement amount before placement corresponding to the amount of downward displacement of the crown portion when the lining concrete is placed to the crown portion. Step A; A method for placing lining concrete, characterized by having a step B of placing the lining concrete between the natural ground and the centering form.

11. The method for placing the covering concrete according to claim 10, characterized in that, in the step B, the prestress force is adjusted so that the prestress force is gradually released from during the placing of the covering concrete to the end of the placing.

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