JP7813624B2 - Method for constructing underground structure and underground structure - Google Patents

Description

The present invention relates to a method for constructing an underground structure and an underground structure.

Deep foundations are generally constructed by excavating the ground while repeatedly connecting the left, right, and top and bottom edges of the liner plate to a specified depth, constructing an earth-retaining wall inside the shaft, then erecting rebar inside the wall, and then pouring concrete. The rebar erected inside the earth-retaining wall generally includes main rebars and hoops, and various techniques have been proposed for erecting these rebars.

For example, Patent Document 1 describes a technique in which support columns with support structures set at predetermined intervals are installed vertically along the wall surface inside a cylindrical pile hole to temporarily hold hoop reinforcement, and the hoop reinforcement is tied together using a hanging scaffold that can be moved up and down, concrete is poured using a floating scaffold, and reinforcing bars are connected using a mechanical joint method to form longitudinal main reinforcement.

Patent Document 2 also describes a technique in which scaffolding for assembling reinforcing bars is formed inside an excavated shaft, hoop bars are divided into multiple stages and temporarily assembled into a ring using assembly equipment on the ground around the shaft, the temporarily assembled multiple stages of hoop bars are then carried into the shaft one by one, and main bars are then inserted into the shaft and the main bars and hoops are connected using the scaffolding.

Furthermore, Patent Document 3 describes a technology in which a tower-shaped temporary platform is constructed above ground at the entrance of a deep foundation shaft, multiple chain wheel winches that can be operated synchronously are arranged to suspend and support a support ring, the vertical bars that make up the rebar cage are attached to the support ring one by one, ties are welded around the vertical bars, and the section that has secured the rigidity of the rebar cage is then successively lowered into the deep foundation shaft together with the support ring by operating the chain wheel winch.

Japanese Patent Application Laid-Open No. 2002-038475 Japanese Patent Application Laid-Open No. 2003-313860 Japanese Patent Application Publication No. 09-177070

However, the above-mentioned conventional rebar installation techniques pose several challenges. First, the method of assembling rebar inside a shaft, as described in Patent Document 1, allows for high construction precision because the concrete cover thickness outside the rebar can be checked while assembly is in progress, but requires scaffolding for assembly, making it less workable, and requires a lot of work inside the shaft, making it less safe. The method of assembling a certain amount of rebar above ground and then joining it inside the shaft, as described in Patent Document 2, improves construction efficiency and safety, but requires large hoisting machinery. Furthermore, while it reduces the amount of work inside the shaft, it still exists. The method of continuously feeding rebar while assembling it at the shaft entrance, as described in Patent Document 3, further improves construction efficiency and safety, but requires large-scale equipment, and since assembly work is done from outside the shaft, it is difficult to check the concrete cover thickness.

The present invention therefore aims to provide a method for constructing an underground structure and an underground structure that allows for the reinforcing bar installation process to be carried out using simple equipment with improved workability, safety, and quality.

[1] A method for constructing an underground structure, comprising: an initial excavation step of excavating the ground to form a vertical shaft; an earth retaining member installation step of installing earth retaining members along the wall surface of the vertical shaft; an initial reinforcing bar installation step of lowering reinforcing bars into the interior of the vertical shaft while fixing the horizontal position using a fixing jig attached to the earth retaining members; a final excavation step of further excavating the ground to excavate the vertical shaft in the vertical direction; a final reinforcing bar installation step of lowering reinforcing bars into the interior of the vertical shaft excavated in the final excavation step while fixing the horizontal position using the fixing jig; and a concrete pouring step of pouring concrete into the interior of the vertical shaft containing the reinforcing bars.
[2] A method for constructing an underground structure as described in [1], further comprising at least one intermediate excavation step between the first excavation step and the final excavation step, in which the ground is excavated and the shaft is dug vertically, and an intermediate reinforcing bar erection step, in which the reinforcing bar is lowered into the shaft dug in the intermediate excavation step while fixing its horizontal position using the fixing jig.
[3] A method for constructing an underground structure described in [1] or [2], wherein the retaining member has a corrugated cross section in the height direction.
[4] A method for constructing an underground structure described in any one of [1] to [3], further comprising a grouting step of applying grout between the wall surface of the shaft and the retaining member by either spraying or filling, or both.
[5] A method for constructing an underground structure described in any one of [1] to [4], wherein the reinforcing bars are arranged vertically and include at least a first main reinforcing bar and a second main reinforcing bar, each of which is composed of multiple reinforcing bars connected longitudinally, and when the tips of the first main reinforcing bar and the second main reinforcing bar reach the bottom of the excavated shaft in the final reinforcing bar installation process, the connection position of the first main reinforcing bar and the connection position of the second main reinforcing bar are located at different heights.
[6] A method for constructing an underground structure described in [5], which includes a step of connecting a new reinforcing bar to the upper end of an already installed reinforcing bar among the plurality of reinforcing bars, and then suspending the already installed reinforcing bar and the new reinforcing bar together.
[7] A method for constructing an underground structure described in any one of [1] to [6], wherein the reinforcing bars include main reinforcing bars arranged vertically, and further includes a fixing process, after the first reinforcing bar installation process, of engaging the protruding portion of the main reinforcing bars with the fixing jig to fix the height position of the main reinforcing bars.
[8] An underground structure comprising: retaining members installed along the wall surface of a vertical shaft formed by excavating the ground; fixing jigs attached to the retaining members; reinforcing bars arranged to engage with the fixing jigs; and concrete poured inside the vertical shaft containing the reinforcing bars.
[9] An underground structure described in [8], wherein the reinforcing bars include main reinforcing bars extending vertically, and the fixing jig has a structure capable of engaging the protruding portions of the main reinforcing bars.
[10] An underground structure as described in [9], wherein the fixing jig has a notch that allows the main reinforcing bars to be inserted and removed.
[11] An underground structure as described in [9], wherein the fixing jig has a curved portion that moves toward and away from the main reinforcing bars by rotating in a horizontal plane.

With the above configuration, the rebar installation process is carried out by sequentially lowering the rebar in parallel with the process of excavating the shaft in stages. This eliminates the need for scaffolding within the shaft for installing the rebar, improving workability and safety. Furthermore, because the horizontal position of the rebar is fixed by a fixture attached to the retaining wall, the concrete cover thickness outside the rebar can be reliably set without having to work inside the shaft. Because the rebar only needs to be lowered in stages, machinery such as cranes used for lowering it can be made smaller. In this way, the present invention makes it possible to carry out a rebar installation process using simple equipment with improved workability, safety, and quality.

1 is a diagram showing the steps of a method for constructing a deep foundation, which is an underground structure according to one embodiment of the present invention. 1 is a diagram showing the steps of a method for constructing a deep foundation, which is an underground structure according to one embodiment of the present invention. 1 is a diagram showing the steps of a method for constructing a deep foundation, which is an underground structure according to one embodiment of the present invention. 1 is a diagram showing the steps of a method for constructing a deep foundation, which is an underground structure according to one embodiment of the present invention. 1 is a diagram showing the steps of a method for constructing a deep foundation, which is an underground structure according to one embodiment of the present invention. 1 is a diagram showing the steps of a method for constructing a deep foundation, which is an underground structure according to one embodiment of the present invention. 1 is a diagram showing the steps of a method for constructing a deep foundation, which is an underground structure according to one embodiment of the present invention. 1 is a diagram showing the steps of a method for constructing a deep foundation, which is an underground structure according to one embodiment of the present invention. 1 is a diagram showing the steps of a method for constructing a deep foundation, which is an underground structure according to one embodiment of the present invention. FIG. 10 is a diagram showing a modified example of a construction method for an underground structure according to one embodiment of the present invention. FIG. 10 is a diagram showing a modified example of a construction method for an underground structure according to one embodiment of the present invention. FIG. 10 is a diagram showing a modified example of a construction method for an underground structure according to one embodiment of the present invention. 10A and 10B are diagrams illustrating an example of a method for fixing the height position of a reinforcing bar in one embodiment of the present invention. FIG. 14 is a diagram showing a first example of a fixture that can be used in the example shown in FIG. 13. FIG. 14 is a diagram showing a second example of a fixture that can be used in the example shown in FIG. 13. FIG. 14 is a diagram showing a third example of a fixture that can be used in the example shown in FIG. 13.

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that in this specification and drawings, components that have substantially the same functional configuration will be assigned the same reference numerals, and redundant explanations will be omitted.

(Construction method for underground structures)
A method for constructing a caisson foundation, an underground structure, according to one embodiment of the present invention will be described below with reference to Figures 1 to 9. First, Figure 1 illustrates the first stage (first excavation step) of the excavation process, in which the ground is excavated to form a vertical shaft 1; the process of installing a liner plate 2, which is an earth-retaining member, along the wall of the vertical shaft 1; and the process of applying grout 3 between the wall of the vertical shaft 1 and the liner plate 2. This process is followed by the process of installing main reinforcing bars 4A inside the vertical shaft 1 (first reinforcing bar installation step). The main reinforcing bars 4A are vertically arranged along the inner periphery of the vertical shaft 1. During this installation step, the main reinforcing bars 4A are lowered into the vertical shaft 1 from the entrance 1A of the vertical shaft 1 while their horizontal positions are fixed using a fixing jig 5 attached to the liner plate 2. Although omitted for simplicity, the main reinforcing bars 4A located at the rear of the figure are also fixed in their horizontal positions using a fixing jig attached to the liner plate 2 at the rear.

In this embodiment, the main reinforcing bars 4A include main reinforcing bars 41A (first main reinforcing bars) whose tips reach the excavated bottom surface 1B of the shaft 1 as shown in Figure 1, and main reinforcing bars 42A (second main reinforcing bars) whose tips are fixed at a height position before reaching the excavated bottom surface 1B. The advantages of making the main reinforcing bars 4A different heights during the erection process, and an example of the structure of the fixing jig 5 for fixing the height position of the main reinforcing bars 42A before their tips reach the excavated bottom surface 1B, will be described later.

Next, the second stage (intermediate excavation stage) of the excavation process is carried out, in which the ground is excavated and the shaft 1 is dug vertically, as shown in Figure 2. Then, sprayed grout 31 is applied to the wall of the excavated shaft 1 as shown in Figure 3. A liner plate 2 is installed along the wall of the excavated shaft 1 as shown in Figure 4. Furthermore, filled grout 32 is applied between the sprayed grout 31 and the liner plate 2 as shown in Figure 5. This type of application method for the liner plate 2 and grout 3 is also described in JP 2020-105806 A, and adopting this application method enables economical design and improved workability. However, the application method for the liner plate and grout according to embodiments of the present invention is not limited to this example. For example, the sprayed grout 31 may be omitted and only the filled grout 32 may be applied. Alternatively, the grout 3 may be omitted and concrete may be poured through holes in the liner plate 2 to fill the gap between the wall of the shaft 1 and the liner plate 2. The same applies to excavation other than the second stage, and an appropriate grout 3 application method can be selected depending on ground conditions, etc. In a multi-stage excavation process, the grout 3 may be applied all at once after only the liner plate 2 is installed, or the grout 3 application method may be different for each stage of excavation.

Next, as shown in Figures 6 and 7, the process of erecting main rebars (intermediate rebar erection process) is carried out inside the excavated shaft 1. First, as shown in Figure 6, new main rebars 4B (main rebars 41B, 42B) are connected to the top of main rebars 4A (main rebars 41A, 42A) using couplers 61, 62, and the connected main rebars 4A, 4B are lowered as shown in Figure 7. Here again, the tip of main rebar 41A is allowed to reach the excavated bottom surface 1B of the shaft 1, while the tip of main rebar 42A is fixed at a fixed height without reaching the excavated bottom surface 1B. Note that while couplers are used to connect the rebars used for the main rebar in this embodiment, in other embodiments, the rebars may be connected using mechanical joints other than those called couplers, lap joints, gas pressure welding joints, or welded joints; the connection method is not particularly limited.

In the example shown in Figure 6 above, new main rebars 4B are connected to the upper ends of the already installed main rebars 4A using couplers 61, 62, etc., and then the main rebars 4A, 4B are lowered together. As another example, the main rebars 4A may be lowered first, and then new main rebars 4B may be connected to the main rebars 4A using couplers 61, 62, etc. In this case, couplers 61, 62 may be attached to the upper ends of the main rebars 4A on the ground beforehand, and then the main rebars 4A may be lowered, or couplers 61, 62 may be attached to the upper ends of the main rebars 4A when connecting the main rebars 4B inside the shaft 1. As another example, new main rebars 4B may be connected to the lower ends of the main rebars 4A using couplers 61, 62, etc. In this case, instead of lowering the main reinforcing bar 4A, couplers 61 and 62 can be attached to the lower end of the main reinforcing bar 4A in advance, and then the main reinforcing bar 4B can be lowered and connected to the lower end of the main reinforcing bar 4A via couplers 61 and 62.

The intermediate excavation process and intermediate rebar installation process are repeated in the same manner, further excavating the ground and digging the shaft 1 vertically while installing the main rebars inside the excavated shaft 1. Figure 8 shows the final stage of the excavation process (final excavation process) in which the shaft 1 has reached the specified design depth and the final stage of the process of installing the main rebars inside the excavated shaft 1 (final rebar installation process) has been carried out. Note that Figures 8 and 9 are different examples from those shown up to Figure 7, so the positions of the couplers for each rebar do not necessarily match. As shown, in the final rebar installation process, the tips of all of the main rebars 41 and 42 reach the excavated bottom surface 1B of the shaft 1.

As described above, in this embodiment, the main reinforcing bars 41, 42 are each constructed by connecting multiple reinforcing bars longitudinally with couplers 61, 62. As shown in the examples of Figures 6 and 7, during excavation, the height positions of the couplers 61, 62 are aligned between the main reinforcing bars 41A, 41B constituting the main reinforcing bar 41 (first main reinforcing bar) and the main reinforcing bars 42A, 42B constituting the main reinforcing bar 42 (second main reinforcing bar), but the tip height positions of the main reinforcing bars are set to different heights. As a result, when the tips of the main reinforcing bars 41, 42 reach the bottom of the excavation 1B, as shown in Figure 8, the connection position of the main reinforcing bar 41 via the coupler 61 and the connection position of the main reinforcing bar 42 via the coupler 62 are located at different heights. This prevents the connection positions from being aligned for all main reinforcing bars, which could be a structural weakness, and improves the strength of the entire foundation, including the main reinforcing bars. In the illustrated example, two types of main rebars are placed with their connection positions located at different heights, but three or more types of main rebars may be placed with their connection positions located at different heights.

Finally, as shown in Figure 9, concrete 7 is poured inside the shaft 1, including the main reinforcing bars 41, 42, to complete the caisson foundation. Note that while the caisson foundation in the illustrated example has a solid structure in which concrete 7 is poured throughout the entire interior of the shaft 1, in other examples it may have a hollow structure in which the concrete is poured leaving a space inside. In addition to caisson foundations, underground structures with hollow structures can also be used as vertical shafts (as structures) or drainage wells. The hollow structure may also be used as a caisson foundation after earth and sand, such as surplus soil from excavating the natural ground, are poured into the internal space. Furthermore, there is no particular limit to the number of times the excavation process steps are repeated. For example, the excavation process may be repeated up to the second step, or more steps may be repeated.

In this embodiment, a liner plate 2 with a corrugated cross section in the height direction is used as an earth retaining member. The corrugated cross section of the liner plate 2 provides a shear-stop effect, similar to that of deformed reinforcing bars, between the grout 3 applied on the outside and the concrete 7 poured on the inside. Furthermore, because the liner plates 2 are connected to each other in the height and width directions using bolts or other means, they also function as reinforcement for the concrete 7 in the height direction (substitute for main reinforcing bars) and in the width direction (substitute for hoop reinforcing bars). Therefore, in this embodiment, the reinforcing bars of the deep foundation foundation include only main reinforcing bars 4A, 4B, and 4C arranged vertically, and do not include hoop reinforcing bars arranged circumferentially around the shaft 1, as in the illustrated example, or the number of hoop reinforcing bars is reduced compared to conventional designs. Such a deep foundation foundation design is also described, for example, in JP 2021-080628 A. In other embodiments of the present invention, hoop reinforcing bars can also be arranged, in which case the main reinforcing bars connected to the hoop reinforcing bars are lowered with their tips aligned. In this case, reinforcement of the coupler portion of the main rebar is considered separately. In addition to so-called liner plates, various other materials with similar functions can also be used as earth retaining members.

According to the underground structure construction method of this embodiment described above, the rebar installation process is carried out by sequentially lowering the main rebars 4A, 4B, and 4C from the entrance 1A of the shaft 1 in parallel with the process of excavating the shaft 1 in stages. This eliminates the need for scaffolding for installing the rebars inside the shaft 1, improving workability and safety. Furthermore, because the horizontal positions of the main rebars 4A, 4B, and 4C are fixed by fixing jigs 5 attached to the liner plate 2, the concrete cover thickness outside the main rebars 4A, 4B, and 4C can be reliably set without work inside the shaft 1. Furthermore, if hoops are omitted, the main rebars 4A, 4B, and 4C can be lowered one by one (one set at a time), eliminating the need for large cranes or other machinery for lowering. Even when hoops are installed, if the number of hoops is reduced compared to conventional methods, the machinery used for lowering the rebars, such as cranes, can be made smaller.

Figures 10 to 12 are diagrams showing modified examples of a construction method for underground structures according to one embodiment of the present invention. As a method for ultimately positioning the connection positions of the first main reinforcing bars and the second main reinforcing bars at different heights, the examples shown in Figures 1 to 7 explain a method in which the connection positions during excavation are aligned at the same height, the tip heights of the main reinforcing bars are made different, and the tip of the main reinforcing bar with the deeper tip reaches the bottom of the excavation. However, as explained below, other methods are also applicable. Note that Figures 10 to 12 below correspond to the stage shown in Figure 1 in the above example.

For example, as shown in the example in Figure 10, the tip height positions of the main rebars 41A, 42A may be staggered, and the height position of the main rebar 41A with the deeper tip position may be fixed so that it does not reach the bottom surface 1B of the excavation. Alternatively, as shown in the example in Figure 11, the tip height positions of the main rebars 41A, 42A may be aligned at a point in the middle of excavation so that both reach the bottom surface 1B of the excavation. In this case, the connecting positions of the main rebars 41, 42 will be at different heights at a point in the middle of excavation. Also, as shown in the example in Figure 12, the tip height positions of the main rebars 41A, 42A may be aligned, and the height positions may be fixed so that neither tip of the main rebars 41A, 42A reaches the bottom surface 1B of the excavation.

(Method of fixing rebar)
FIG. 13 is a diagram showing an example of a method for fixing the height position of rebars in one embodiment of the present invention. For simplicity, only a pair of rebars located within the radial cross section of the shaft 1 and the fixing jigs for securing these rebars are shown. In the illustrated example, the first stage of the excavation process for the shaft 1 has been completed, as in the example shown in FIG. 1 , and the main rebars have been installed. In this example, the main rebar 4A is shorter than the example shown in FIG. 1 , and the main rebar 4B has already been connected to its upper part via a coupler 6A. Furthermore, although no other rebars have yet been connected to the upper end of the main rebar 4B, the coupler 6B has already been attached. Here, the couplers 6A and 6B are cylindrical members with threaded holes (internal threads) that thread onto the threaded portions (external threads) formed at the respective ends of the main rebars 4A and 4B. The couplers 6A and 6B attached to the main rebars 4A and 4B form protrusions with larger outer diameters than the main rebars 4A and 4B. In the illustrated example, the height positions of the main reinforcing bars 4A, 4B are fixed by positioning the fixing jig 5 to match the length of the main reinforcing bars 4A, 4B and engaging the protruding couplers 6A, 6B with the fixing jig 5. Therefore, thereafter, the height positions of the main reinforcing bars 4A, 4B can be maintained during the second stage of excavation of the shaft 1, and the main reinforcing bars 4A, 4B can be lowered after excavation is completed.

Figure 14 shows a first example of a fixing jig that can be used in the example shown in Figure 13. In the example shown, the fixing jig 5A is generally plate-shaped with one fork, and an attachment hole 51 for the liner plate 2 is formed at the base of the fork, and a notch 52 with parallel opposing sides is formed in the fork. As shown in Figure 14(a), with a coupler 6A attached to the upper end of a main reinforcing bar 4A, the main reinforcing bar 4A can be inserted into the notch 52 of the fixing jig 5A and the coupler 6A can be placed on the top surface of the fixing jig 5A on both sides of the notch 52 to engage the coupler 6A and fix the height position of the main reinforcing bar 4A. To allow for the insertion of the main rebar 4A (and main rebar 4B) and the engagement of the coupler 6A (and coupler 6B), the inner dimension of the notch 52 is larger than the outer diameter of the main rebar 4A (and main rebar 4B) and smaller than the outer diameter of the coupler 6A (and coupler 6B).

As shown in Figure 14(b), the main rebar 4B is attached to the coupler 6A from above to connect the main rebars 4A and 4B. Then, as shown in Figure 14(c), the coupler 6B is attached to the upper end of the main rebar 4B. The horizontal position of the main rebars 4A and 4B is then shifted away from the fixing jig 5A, i.e., toward the center of the shaft 1 (not shown). This disengages the coupler 6A from the notch 52, releasing it from the fixing jig 5A. In this state, the main rebars 4A and 4B are lowered, as shown in Figure 14(d), and the main rebar 4B is then inserted into the notch 52. The height position of the main rebars 4A and 4B after lowering can be fixed by engaging the coupler 6B with the fixing jig 5A.

Figure 15 shows a second example of a fixing jig that can be used in the example shown in Figure 13. In the illustrated example, the fixing jig 5B is plate-shaped and has an attachment portion and a curved portion. The attachment portion has an attachment hole 51 for connecting to the liner plate 2, and a C-shaped inner edge 53 is formed on the inside of the curved portion. As shown in Figure 15(a), with a coupler 6A attached to the upper end of a main reinforcing bar 4A, the inner edge 53 of the fixing jig 5B is aligned with the main reinforcing bar 4A, and the coupler 6A is placed on the top surface of the fixing jig 5B outside the inner edge 53 to lock the coupler 6A and fix the height position of the main reinforcing bar 4A. To stably lock the coupler 6A, it is preferable that the inner edge 53 has a planar shape with a radius of curvature that is greater than the radius of curvature of the outer surface of the main reinforcing bar 4A (and main reinforcing bar 4B) and smaller than the radius of curvature of the outer surface of the coupler 6A (and coupler 6B).

As shown in Figure 15(b), the main rebar 4B is attached to the coupler 6A from above to connect the main rebars 4A and 4B. Then, as shown in Figure 15(c), the fixing jig 5B is rotated in the horizontal plane around the mounting hole 51 to move it away from the main rebar 4A. This moves the coupler 6A away from the inner edge 53 of the fixing jig 5B, releasing the coupler 6A from its engagement with the fixing jig 5B. In this state, the main rebars 4A and 4B are lowered as shown in Figure 15(d), and the fixing jig 5B is again rotated in the horizontal plane around the mounting hole 51 to move it closer to the main rebar 4B, this time aligning the inner edge 53 with the main rebar 4B. The height positions of the main rebars 4A and 4B after lowering can be fixed by engaging the coupler 6B with the fixing jig 5B. This type of fixing jig 5B can fix and release the vertical position without moving the horizontal position of the main reinforcing bars 4A, 4B, so it can also be used, for example, when hoops are placed in addition to the main reinforcing bars 4A, 4B and the main reinforcing bars 4A, 4B are lowered while still connected to the hoops.

Figure 16 shows a third example of a fixing jig that can be used in the example shown in Figure 13. In the illustrated example, the fixing jig 5C is an annular member fixed to the shaft entrance 1A (not shown) of the shaft 1 using flat bars or angles. Multiple notches 54 are formed on the inner periphery of the fixing jig 5C. Similar to the notches in the example described above with reference to Figure 14, these notches 54 are portions into which main rebars can be inserted. The inner periphery of the fixing jig 5C is formed with notches 54 spaced at intervals corresponding to the spacing of the main rebars circumferentially around the shaft 1. By inserting the main rebars into each notch 54 and engaging the couplers, the height position of the main rebars can be fixed, as in the examples of Figures 14 and 15 above. Furthermore, by removing the main rebars from the notches 54 and releasing the couplers, the main rebars can be further lowered. This type of fixing jig 5C can be used, for example, even in cases where it is difficult to attach the fixing jig to a liner plate.

In the example described above, the height positions of the main reinforcing bars 4A and 4B are fixed by engaging the couplers 6A and 6B with the fixing jigs 5A, 5B, and 5C. However, in other examples, a sleeve-shaped member may be pressed against the middle of the main reinforcing bars 4A and 4B, or another member may be welded to form a protrusion, which can then be engaged with the fixing jigs 5A, 5B, and 5C. The fixing jigs 5A and 5B may be attached to multiple tiers of the liner plate 2, including the top tier, using the mounting holes 51, as in the example shown in Figure 13, or they may be attached to just the top tier.

Note that embodiments of the present invention are not limited to the example described above in which the height position of the main rebar is fixed by engaging the protruding portion of the main rebar with the fixing jig; a separate clamp or other means may be used to fix the height position of the main rebar. Furthermore, fixing jigs capable of fixing the horizontal and vertical positions of the main rebar, such as fixing jigs 5A, 5B, and 5C described above, may be used in combination with fixing jigs that fix only the horizontal position of the main rebar. A fixing jig that fixes the height position of the main rebar may be placed in only one location, for example, on the topmost level of each main rebar. Note that while multiple fixing jigs are placed in the height direction in the example described above, if the horizontal position is fixed with at least one fixing jig, two-point support can be achieved by, for example, abutting the tip of the main rebar against the bottom of the excavation at the end of excavation, thereby stabilizing the horizontal position of the main rebar.

The above describes in detail preferred embodiments of the present invention with reference to the accompanying drawings, but the present invention is not limited to such examples. It is clear that a person with ordinary skill in the technical field to which the present invention pertains can conceive of various modifications or alterations within the scope of the technical ideas set forth in the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

1... shaft, 1A... mine entrance, 1B... excavation bottom, 2... liner plate, 3... grout, 31... sprayed grout, 32... filled grout, 4A, 4B, 4C, 41, 41A, 41B, 42, 42A, 42B... main reinforcing bars, 5, 5A, 5B, 5C... fixing jig, 51... mounting hole, 52, 54... notch, 53... inner edge, 61, 62, 6A, 6B... coupler, 7... concrete.

Claims (9)

a first excavation step of excavating the ground to form a vertical shaft;
a first earth retaining member installation step of installing a first earth retaining member along a wall surface of the vertical shaft excavated in the first excavation step ;
A first reinforcing bar erection process in which reinforcing bars arranged vertically inside the vertical shaft are lowered while fixing the horizontal position using a fixing jig attached to the first retaining member;
at least one second excavation step of further excavating the ground to excavate the shaft in a vertical direction;
At least one second earth retaining member installation step of installing a second earth retaining member along a wall surface of the shaft excavated in the second excavation step;
At least one second reinforcing bar erection step of lowering the reinforcing bar into the shaft excavated in the second excavation step while fixing the horizontal position using the fixing jig;
a concrete pouring step of pouring concrete into the shaft containing the reinforcing bar ,
A method for constructing an underground structure , wherein the reinforcing bars include a first reinforcing bar and a second reinforcing bar that are placed near the first earth retaining member or the second earth retaining member and connected in the longitudinal direction . 2. The method for constructing an underground structure as described in claim 1, wherein the second reinforcing bar erection process includes a process of connecting the second reinforcing bar to the upper end of the first reinforcing bar that has already been erected, and then suspending the first reinforcing bar and the second reinforcing bar together. 3. The method for constructing an underground structure according to claim 1, wherein the first and second retaining members have a wave-shaped cross section in the height direction. A method for constructing an underground structure as described in any one of claims 1 to 3, further comprising a grouting step of applying grout between the wall surface of the shaft and at least the second retaining member by either spraying or filling, or both. The reinforcing bars include at least a first main reinforcing bar and a second main reinforcing bar, and the first main reinforcing bar and the second main reinforcing bar are respectively configured by the first reinforcing bar and the second reinforcing bar connected in a longitudinal direction;
A method for constructing an underground structure described in any one of claims 1 to 4 , wherein when the tips of the first main reinforcing bar and the second main reinforcing bar reach the bottom of the excavated shaft in the final second reinforcing bar installation process, the connection position of the first main reinforcing bar and the connection position of the second main reinforcing bar are located at different heights. At least the end or middle portion of the first reinforcing bar is formed with a protruding portion having an outer diameter larger than that of other portions,
A method for constructing an underground structure as described in any one of claims 1 to 5 , further comprising a fixing step of engaging the protrusion with the fixing jig to fix the height position of the first reinforcing bar after the first reinforcing bar erection step. an earth retaining member installed along the wall surface of a vertical shaft formed by excavating the ground;
A fixing jig attached to the retaining member;
A reinforcing bar arranged vertically and disposed so as to engage with the fixing jig;
and concrete poured inside the shaft containing the reinforcing bar ,
The reinforcing bars include a first reinforcing bar and a second reinforcing bar connected in a longitudinal direction;
At least the first reinforcing bar has a protruding portion having an outer diameter larger than that of other portions,
The fixing jig is an underground structure having a structure capable of engaging the protrusion . 8. The underground structure according to claim 7 , wherein the structure capable of locking the protrusion has a notch into which the portion of the reinforcing bar other than the protrusion can be inserted and removed. The underground structure according to claim 7 , wherein the structure capable of locking the protrusion has a curved portion that moves toward and away from the reinforcing bar by rotating in a horizontal plane.