JP2023068272A - Construction method of steel shell element - Google Patents

Abstract

To provide a construction method for eliminating work load for production and improving strength and workability for steel shell elements to be used.SOLUTION: A construction method is to construct an outer shell structural body 1 with a variable section in a tunnel direction by gradually changing extension length of a projected member 23 of a convex joint 24 for a joint part between adjacent steel shell elements 2, 3, wherein a part of an improvement body 8 is excavated as inserting a consecutive steel shell element 3 upon its insertion after replacing a space, in which a temporal steel pipe 6 is placed, with the improvement body 8 by injecting the improvement body 8 as pulling out the temporal steel pipe 6 attached on the inserted steel shell element 2 after the temporal steel pipe 6 is attached on the inserted steel shell element 2 to enlarge a section in a direction of an adjacent steel shell element 3 side.SELECTED DRAWING: Figure 6

Description

According to the present invention, a steel shell element having a rectangular hollow cross section is successively penetrated while connecting the already penetrated steel shell element and a joint to each other. Steel shell elements for constructing a variable cross-section tunnel in which the cross-sectional area is gradually changed in the tunnel direction in the outer shell precedent tunnel constructed by removing the internal earth and sand of this outer shell structure after construction. Concerning the construction method.

In recent years, as shown in FIG. 10, jointed steel shell elements 50, 50, . 52, and after filling concrete 51 into each of the steel shell elements 50, 50, . . This tunnel construction method is called the outer shell precedent tunnel construction method, and has the advantage of having little impact on the surrounding ground, so it is often applied to underpass construction of roads and railways.

The applicant of the present application further applied this method for constructing tunnels leading to the outer shell, and proposed a method for constructing a variable cross-section tunnel in which the cross-sectional area is gradually changed in the direction of the tunnel in Patent Document 1 below. Specifically, as the joint portion, between the adjacent steel shell elements, a concave joint provided at the tip of a projecting member projecting from the steel shell element on one side toward the steel shell element on the other side, and a concave joint on the other side A structure is adopted in which a convex joint provided at the tip of an overhang member projecting from one steel shell element toward the steel shell element on one side is fitted, and at the joint portion of the adjacent steel shell element, the concave This is a method of constructing an outer shell structure with a variable cross section in the tunnel direction by gradually changing the overhang length of the overhang member of the joint.

JP 2018-168597 A

In addition, in the above Patent Document 1, in this method, since the length of protrusion of the joint is gradually changed, the separation width of the square hollow cross section becomes too large, and the separation width of the square hollow section becomes In order to solve the problem that it is necessary to remove the earth and sand manually before filling the concrete in the unexcavated part, on the joint installation surface of the square hollow cross section in the steel shell element, both sides or A stepped portion is formed by forming a section-defective portion on one side, and an overhanging member extending from the end of the non-cross-section-defective portion toward the adjacent steel shell element is provided, and the tip of the overhanging member is It has also been proposed that the concave joint is provided and that the overhang length of the overhang member is gradually changed and that the concave joint is located within the stepped portion.

According to this proposal, the separation width of the square hollow cross section between the adjacent steel shell elements can be minimized by locating the joint part inside the square hollow cross section instead of at a position laterally separated from the square hollow cross section. There is an advantage that it can be kept to a minimum, and labor can be saved in the subsequent earth and sand removal work. However, since the stepped portion resulting from the formation of the section-defective portion is formed by bending the upper and lower plates of the steel shell element, it takes time and effort to process the long upper and lower plates. In addition, when the projection length of the stepped portion is different for each part, it is troublesome to manufacture a plurality of upper plates and lower plates corresponding to different projection lengths. In addition, the steel shell element including the bent upper plate and the lower plate has a risk of a decrease in strength against external pressure. Furthermore, in the convex joint that protrudes toward the steel shell element provided with the concave joint, the larger the separation distance between the adjacent steel shell elements, the longer the protrusion length, and the greater the resistance during penetration. rice field.

Therefore, the main object of the present invention is to provide a method of constructing a steel shell element that saves labor in manufacturing the steel shell element to be used and has improved strength, and furthermore, to provide a method for constructing a steel shell element that is used when the convex joint and the overhang member are penetrated. To provide a construction method of a steel shell element with reduced resistance.

In order to solve the above problem, as the present invention according to claim 1, the steel shell element having a rectangular hollow cross section is repeatedly penetrated into the ground while connecting the steel shell element and the joint part that have been penetrated one by one. After constructing an outer shell structure with a closed cross section using the steel shell elements, when constructing an outer shell precedent tunnel by removing the internal earth and sand of this outer shell structure,
The joint portion includes a concave joint provided at the tip of an overhang member projecting from one side steel shell element toward the other side steel shell element between adjacent steel shell elements, and a steel shell element on the other side. It is a structure in which a convex joint provided at the tip of an overhang member that protrudes from the steel shell element on one side is fitted,
Construction of steel shell elements for constructing an outer shell structure with a variable cross section in the tunnel direction by gradually changing the overhang length of the overhang member of the concave joint at the joint of the adjacent steel shell elements a method,
A temporary steel pipe that expands the cross section to the adjacent steel shell element side is attached to the steel shell element that is penetrated first,
replacing the space in which the temporary steel pipe was arranged with the improved body by injecting the improved body while pulling out the temporary steel pipe attached to the penetrated steel shell element,
There is provided a method for constructing a steel shell element, characterized in that when the steel shell element is penetrated in the next order, the improved body is partially excavated while the steel shell element is penetrated.

In the invention according to claim 1, in the steel shell element construction method for constructing an outer shell structure having a variable cross section in the tunnel direction, the steel shell element to be penetrated first has a cross section on the side of the adjacent steel shell element. The space in which the temporary steel pipe was placed is replaced with the improved body by injecting the improved body while pulling out the temporary steel pipe attached to the steel shell element that has been penetrated. After that, when penetrating the next steel shell element, it is penetrated while excavating a part of the improved body. Therefore, since the temporary steel pipe that enlarges the cross section is attached to the adjacent steel shell element side, the side plate of the rectangular hollow cross section can be formed of a flat plate perpendicular to the upper plate and the lower plate. Compared with the steel shell element described in Document 1, the steel shell element used can save labor in manufacturing and can improve the strength of the steel shell element itself.

As the present invention according to claim 2, the temporary steel pipe is provided in a range including a position where the joint portion changes as the overhang length of the overhang member changes. A method of constructing a steel shell element is provided.

In the invention according to claim 2, the temporary steel pipe is provided in a range including a position where the joint portion changes as the overhang length of the overhang member changes. That is, the position of the joint portion changes within the range where the temporary steel pipe is provided. As a result, after the temporary steel pipe is pulled out, the joint portion is positioned in the region replaced with the improved body, so the improved body is reliably interposed between the adjacent steel shell elements, and the joint portions are securely connected to each other. Can be connected.

As a third aspect of the present invention, there is provided a method for constructing a steel shell element according to any one of the first and second aspects, wherein the temporary steel pipe is formed with a constant cross-sectional shape in the tunnel direction.

In the third aspect of the invention, since the temporary steel pipe is formed with a constant cross-sectional shape in the tunnel direction, the temporary steel pipe can be easily pulled out.

As a fourth aspect of the present invention, there is provided a method for constructing a steel shell element according to any one of the first to third aspects, wherein the improved body is made of mortar or improved soil.

In the invention according to claim 4, the area replaced with the improved body after drawing out of the temporary steel pipe can be excavated relatively easily by an excavator, and the connection between the joint portions is facilitated. As a body, low strength mortar or improved body is used. As a result, the resistance when the convex joint and the projecting member are penetrated can be reduced, and the workability can be improved.

As the present invention according to claim 5, each of the steel shell elements has a basic cross-sectional dimension defined by a maximum width dimension and a maximum height dimension of a shape obtained by combining a rectangular hollow cross section and the temporary steel pipe in the tunnel direction. A method for constructing a steel shell element according to any one of claims 1 to 4 is provided.

In the fifth aspect of the invention, the cross-sectional shape of each steel shell element should basically match the excavation cross-sectional shape of the excavator, so the basic cross-sectional dimension of each steel shell element is constant in the tunnel direction. .

As the present invention according to claim 6, the procedure of penetrating while connecting the convex joint of the steel shell element in the next order to the concave joint of the steel shell element that has already been penetrated. A method of constructing a steel shell element is provided.

In the invention according to claim 6, when the steel shell element is penetrated, the concave joint portion of the steel shell element is penetrated without connecting, and when the next steel shell element is penetrated, the concave joint of the steel shell element whose convex joint has already been installed is inserted. It is intrusively installed in a state where it is connected to According to this procedure, the penetration accuracy and efficiency of the steel shell element are improved, and at the same time, it becomes easier to secure water stoppage.

According to a seventh aspect of the present invention, the excavator used for penetrating the steel shell element has a shape of the front excavation portion that matches the shape of the square hollow cross section of the steel shell element and the temporary steel pipe. and an auxiliary cutter for excavating the earth and sand portion corresponding to the joint portion is provided in the body portion, or the excavator performs over excavation in a range including the joint portion A method of constructing the described steel shell element is provided.

In the invention according to claim 7, the excavator used for penetrating the steel shell element has a shape of the front excavation portion that matches the shape of the combination of the square hollow cross section of the steel shell element and the temporary steel pipe. In addition, since the body is equipped with an auxiliary cutter for excavating the earth and sand portion corresponding to the joint portion, or the excavator is used to excavate the range that includes the joint portion, excavation It becomes easier to penetrate the steel shell element into the excavated part by machine.

As described in detail above, according to the present invention, the steel shell element used can save labor in manufacturing, improve the strength of the steel shell element, and reduce the resistance when the convex joint and the overhang member penetrate. By doing so, it becomes possible to provide a method for constructing a steel shell element that can improve workability.

FIG. 2 is a perspective view of a main part showing an outer shell structure 1 with a variable cross section. (A) is a plan view, (B) is a cross-sectional view on the arrival side, and (C) is a cross-sectional view on the departure side, showing the outer shell structure 1 . (A) to (C) are a cross-sectional view of the arrival side and a cross-sectional view of the departure side showing the construction procedure of the outer shell structure 1. FIG. FIG. 4 is a perspective view showing a construction procedure (Part 1) of the outer shell structure 1; FIG. 11 is a perspective view showing a construction procedure (Part 2) of the outer shell structure 1; FIG. 11 is a perspective view showing a construction procedure (part 3) of the outer shell structure 1; FIG. 11 is a perspective view showing a construction procedure (part 4) of the outer shell structure 1; Fig. 2(A) is a front view showing an excavator 45 to be used, and (B) is a cross-sectional view of an arrangement portion of an auxiliary cutter 46. Figs. 4 is a perspective view showing a connecting steel shell element 5 for equal width. FIG. FIG. 11 is a cross-sectional view showing an example of a tunnel 52 constructed by the shell-first tunnel construction method;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

As shown in FIGS. 1 and 2, the present invention repeats the procedure of penetrating steel shell elements 3 and 4 having square hollow cross sections one by one while connecting joints to steel shell elements 2 that have already penetrated the ground. After constructing an outer shell structure 1 in which a large number of steel shell elements are closed in a shape such as a rectangular shape, a circular shape, or a polygonal shape when viewed in cross section, the inner earth and sand of the outer shell structure 1 are removed. When constructing the hull precedent tunnel by
The joint portion is located between the adjacent steel shell elements 2, 3 (2, 4) at the tip of the projecting member 23 projecting from the steel shell element 2 on one side toward the steel shell elements 3, 4 on the other side. A structure in which the provided concave joint 24 is fitted with a convex joint 34 provided at the tip of a projecting member 33 projecting from the steel shell elements 3 and 4 on the other side toward the steel shell element 2 on the one side. By gradually changing the extension length of the extension member 23 of the concave joint 24 at the joint portion of the adjacent steel shell elements 2 and 3, the outer shell structure 1 having a variable cross section in the tunnel direction is formed. It builds.

In the present invention, in particular, in the method of constructing a variable cross-section preceding tunnel in which the cross-sectional area of the shell structure 1 is gradually changed, as shown in FIG. , a temporary steel pipe 6 for enlarging the cross section is attached to the adjacent steel shell elements 3 and 4, and by injecting the improved body 8 while pulling out the temporary steel pipe 6 attached to the penetrated steel shell element 2, this temporary After the space in which the steel pipe 6 was arranged is replaced with the improved body 8, when the next steel shell element 3 is penetrated, a part of the improved body 8 is excavated and penetrated.

Since the method for constructing tunnels in front of the outer shell has the advantage of having little impact on the surrounding ground, it is often used as a construction method for constructing underpass tunnels without excavation in the ground beneath roads, railways, etc. It is what is done.

FIG. 1 is a perspective view of a main part showing a part of an outer shell structure 1 with a variable cross section. For example, as shown in FIG. 10, when the outer shell structure 52 is constructed in a rectangular shape by an upper plate 52A, a lower plate 52B and both side wall plates 52C, 52C, FIG. 3 shows a perspective view of a main part when the cross section is variable so that the width dimension of the outer shell structure 1 is gradually increased from the start side to the arrival side.

The illustrated outer shell structure 1 (upper plate or lower plate) is an example composed of three steel shell elements 2 to 4, as also shown in FIG. That is, the central steel shell element 2 is arranged in the middle, and the connecting steel shell elements 3 and 4 for widening are arranged on both sides thereof. These three steel shell elements 2 to 4 have the same basic cross-sectional dimension in the tunnel direction, which is defined by the maximum width dimension B and the maximum height dimension H of the shape combining the square hollow cross section and the temporary steel pipe 6. be done. That is, each of the steel shell elements 2 to 4 has a maximum width dimension of B and a maximum height dimension of H according to the cross-sectional dimension of the excavation part of the excavator to be used, and this basic cross-sectional dimension is in the tunnel direction. are the same throughout. In addition, in FIG. 2(A), square hollow portions of the steel shell elements 2 to 4 are indicated by thick broken lines.

First, as shown in detail in FIGS. 3(A) and 4, the central steel shell element 2 is an element having a square hollow cross section composed of an upper plate 20, a lower plate 21 and side plates 22, 22. Basic form. The side plate 22 is a flat plate extending in the tunnel direction, and is arranged perpendicular to the upper plate 20 and the lower plate 21 . Therefore, the steel shell element 2 can be manufactured easily, and a certain strength can be secured. Both sides of the upper plate 20 and the lower plate 21 are provided with projecting members 23, 23 extending outward from the side plate 22 and extending toward the adjacent steel shell elements 3, 4. Concave joints 24, 24 are provided at the tip along the longitudinal direction of the member.

As can be seen by comparing the start side cross section and the arrival side cross section in FIG. That is, the overhang length of the overhang member 23 is _L1 on the starting side, and _L2 on the arrival side. The difference in overhang length (L ₂ -L ₁ ) is the amount of widening. In addition, the extension length of the extension member 23 or the width dimension of the temporary steel pipe 6 is adjusted so that the position of the concave joint 24 in the width direction is positioned within the width of the temporary steel pipe 6 .

As shown in FIGS. 3(A) and 4, both side plates 22, 22 of the central steel shell element 2 are fitted with temporary steel pipes 6 that expand the cross section toward the adjacent steel shell elements 3, 4. It is The temporary steel pipe 6 is a steel pipe having a substantially rectangular cross section and extending in the tunnel direction, and is fixed to the outer surface of the side plate 22 by a plurality of bolts 7 .

In the central steel shell element 2, the temporary steel pipes 6 are provided between overhang members 23, 23 extending to the sides of the upper plate 20 and the lower plate 21, and concave joints 24, 24 provided at the ends thereof, respectively. is provided. That is, the height dimension _H6 of the temporary steel pipe 6 is smaller than the height dimension H of the rectangular hollow section by the thickness of the concave joints 24,24. The temporary steel pipe 6 is formed with a constant cross-sectional shape in the tunnel direction.

A plurality of bolts 7 are used to fix the temporary steel pipe 6 to the central steel shell element 2 . For fixing by the bolts 7, a through hole is provided in the side plate 22 of the central steel shell element 2, and a through hole is provided in the corresponding position of the temporary steel pipe 6, and a nut is fixed inside. A bolt 7 is inserted through the through hole from the inside of the rectangular hollow section and screwed into the nut. As a result, after the central steel shell element 2 is inserted and installed, a worker can enter the inside of the rectangular hollow section to remove the bolts 7 .

The central steel shell element 2 has concave joints 24, 24, . The excavator used for penetrating installation of the steel shell element 2 has a shape in which the square hollow cross section and the temporary steel pipe 6 are combined, and the ratio between the maximum width dimension B and the maximum height dimension H is approximately 2:1. Therefore, as shown in FIG. 8, an excavator 45 having a structure in which square cross-section cutters are arranged side by side is used. The concave joints 24 protrude slightly outward in the vertical direction from the square hollow cross section, and gradually move outward in the width direction as the excavation progresses. Preferably, the excavator 45 is provided with auxiliary cutters 46, 46 on the top and bottom, respectively, for excavating the . It should be noted that the excavator 45 may be used to excavate the area including the recessed joint 24 without the auxiliary cutter 46 . The propulsion method of the excavator 45 may be a main pushing method or a traction method.

Next, as shown in detail in FIGS. An element having a square hollow cross section constituted by side plates 32, 32 is used as a basic form. The side plate 32 is a flat plate extending in the tunnel direction, and is arranged perpendicular to the upper plate 30 and the lower plate 31 . Therefore, the steel shell element 3 can be manufactured easily, and a certain strength can be secured. Projecting members 33, 33 extending outward from the side plate 32 are provided on one side of the upper plate 30 and the lower plate 31 (on the side of the central steel shell element 2). A convex joint 34 is provided along the direction. On the opposite side of the convex joint 34, projecting members 35, 35 are provided in which the upper plate 30 and the lower plate 31 extend outward from the side plate 32. A recessed joint 36 is provided along.

As can be seen by comparing the starting side cross section and the reaching side cross section in FIG. That is, the overhang length of the overhang member 35 is _L1 on the start side, and _L2 on the arrival side. The difference in overhang length (L ₂ -L ₁ ) is the amount of widening. In addition, the extension length of the extension member 35 or the width dimension of the temporary steel pipe 6 is adjusted so that the position of the concave joint 36 in the width direction is positioned within the width of the temporary steel pipe 6 . On the other hand, on the convex joint 34 side, the overhang length _L3 of the overhang member 33 that supports the convex joint 34 is constant in the tunnel direction.

As shown in FIGS. 3(C) and 7, adjacent steel shell elements (width-expanding connecting steel shell elements 3 A temporary steel pipe 6 that enlarges the cross section is attached to the side of the next steel shell element that is connected to and penetrated. On the other hand, the temporary steel pipe 6 is not provided on the side plate 32 on which the convex joint 34 is provided. Since the temporary steel pipe 6 has the same structure as that used in the central steel shell element 2, the explanation thereof is omitted.

As an excavator used for penetrating installation of the connecting steel shell element 3 for widening, an excavator similar to the excavator 45 used for the central steel shell element 2 can be used. However, in the width-expanding connecting steel shell element 3, since the concave joint 36 protruding outward in the vertical direction from the square hollow section is provided only on one side, the auxiliary cutter is provided only on the side where the concave joint 36 is provided. 46 can be provided. Further, on the convex joint 34 side, an auxiliary cutter projecting laterally from the body may be provided in order to excavate the overhanging members 33, 33 projecting laterally beyond the rectangular hollow section.

The next steel shell element to be connected and inserted into the width-expanding connecting steel shell element 3 should be exactly the same element as the width-expanding connecting steel shell element 3 if it is desired to further widen the width. Use to connect and penetrate. Since the extension member 35 for supporting the concave joint 36 of the width-expansion connecting steel shell element 3 gradually projects in the width direction, the width can be further increased by the increase in the extension length.

If the width need not be further increased, the connecting steel shell element 5 for equal width shown in FIG. The equal-width connecting steel shell element 5 differs from the widening connecting steel shell element 3 only in that the length _L1 of the projection of the overhanging member 35 of the concave joint 36 is constant over the tunnel direction. , otherwise the same steel shell element.

On the other hand, the steel shell element 4 located on the opposite side of the central steel shell element 2 is arranged such that the widening connecting steel shell element 3 and the equal width connecting steel shell element 5 are aligned with the center line of the central steel shell element 2. Since the structure is line symmetric across the straddle, the description is omitted.

Next, a method for constructing the steel shell element will be described with reference to FIGS. 3 and 4 to 7. FIG.

First, as shown in FIGS. 3(A) and 4, the central steel shell element 2 having temporary steel pipes 6 attached to both sides thereof is installed by penetrating into the ground.

Next, as shown in FIGS. 3(B) and 5, all the bolts 7 for fixing one temporary steel pipe 6 among the temporary steel pipes 6, 6 attached to the penetrated central steel shell element 2 are removed. After the temporary steel pipe 6 and the central steel shell element 2 are separated from each other, the improved body 8 is injected while the temporary steel pipe 6 is pulled out, so that the space in which the temporary steel pipe 6 is arranged becomes the improved body 8. Replace. The improved body 8 is filled in the space outside the side plate 22 of the central steel shell element 2 after the temporary steel pipe 6 is pulled out to form a solid solidified body. As the improvement body 8, it is preferable to use low-strength mortar or improved soil. By replacing it with low-strength mortar or improved soil, it is possible to reduce the penetration resistance of the convex joint and the overhang member, and improve the workability.

As shown in FIG. 5, the overhang member 23 that supports the concave joint 24 of the central steel shell element 2 gradually increases in length from the starting side to the reaching side. protrudes greatly from the tip of the concave joint 24 on the starting side, and the amount of protrusion gradually decreases toward the reaching side.

Thereafter, as shown in FIG. 6, the next widening connecting steel shell element 3 is penetrated. During this penetration, an excavator provided at the tip of the connecting steel shell element 3 for widening penetrates while excavating a portion of the improved body 8, that is, the portion of the improved body 8 projecting outward from the concave joint 24. As shown in FIG.

As a result, in a state in which the width-expanding connecting steel shell element 3 is inserted and installed, as shown in FIGS. In the meantime, the improved material 8 is filled.

Thereafter, the connecting steel shell element 4 for widening on the opposite side is penetrated and installed in the same manner, and the steel shell elements adjacent to these steel shell elements 3 and 4 are also penetrated and installed in the same manner.

[Other form examples]
(1) In the above embodiment, the cross section is variable in the width direction, but it is also possible to make the cross section variable in the height direction. That is, in the variable cross-section tunnel according to the present invention, only the width direction or only the height direction of the tunnel may be changed, or both the width direction and the height direction of the tunnel may be changed.

(2) In the above embodiment, an example of the outer shell structure 1 in which the cross-sectional dimension gradually increases from the starting side to the reaching side is shown. It is also possible to make the outer shell structure 1 so as to allow

(3) In the above embodiment, by gradually changing the extension length of the extension member 23 of the concave joint 24 at the joint portion of the adjacent steel shell elements 2 and 3, the outer shell having a variable cross section in the tunnel direction can be obtained. Although the structure is constructed, if the relationship between the concave joint 24 and the convex joint 34 is reversed, the protruding length of the convex joint 34 of the steel shell element that has already been penetrated is gradually changed and the penetration is made. The overhang length of the concave joint 24 of the steel shell element 3 may be kept constant. As shown in this embodiment, the relationship between the convex joint and the concave joint is such that the following steel shell element 3 is connected while the convex joint 34 is connected to the concave joint 24 of the steel shell element 2 that has already penetrated. Penetration is preferable.

DESCRIPTION OF SYMBOLS 1... Outer shell structure 2... Center part steel shell element 3.4... Connection steel shell element for widening 5... Steel shell element for equal width 6... Temporary steel pipe 7... Bolt 8... Improved body 24 36... concave joint, 34... convex joint, 23, 33, 35... projecting member, 45... excavator, 46... auxiliary cutter

Claims (7)

After constructing an outer shell structure with a closed cross-section of the steel shell elements in the ground by repeating the procedure of penetrating the steel shell elements with square hollow cross sections sequentially while connecting the steel shell elements that have already been penetrated and the joint parts. , When constructing the outer shell preceding tunnel by removing the internal earth and sand of this outer shell structure,
The joint portion includes a concave joint provided at the tip of an overhang member projecting from one side steel shell element toward the other side steel shell element between adjacent steel shell elements, and a steel shell element on the other side. It is a structure in which a convex joint provided at the tip of an overhang member that protrudes from the steel shell element on one side is fitted,
Construction of steel shell elements for constructing an outer shell structure with a variable cross section in the tunnel direction by gradually changing the overhang length of the overhang member of the concave joint at the joint of the adjacent steel shell elements a method,
A temporary steel pipe that expands the cross section to the adjacent steel shell element side is attached to the steel shell element that is penetrated first,
replacing the space in which the temporary steel pipe was arranged with the improved body by injecting the improved body while pulling out the temporary steel pipe attached to the steel shell element that has been penetrated,
A method for constructing a steel shell element, characterized in that, when penetrating the next steel shell element, the improved body is partially excavated while penetrating. 2. The method of constructing a steel shell element according to claim 1, wherein the temporary steel pipe is provided in a range including a position where the joint portion changes as the length of the overhang of the overhang member changes. 3. The method for constructing a steel shell element according to claim 1, wherein the temporary steel pipe is formed with a constant cross-sectional shape in the tunnel direction. The method for constructing a steel shell element according to any one of claims 1 to 3, wherein the improved body is made of mortar or improved soil. Each of said steel shell elements has a basic cross-sectional dimension defined by a maximum width dimension and a maximum height dimension of a shape obtained by combining a square hollow cross section and said temporary steel pipe, and is constant in the tunnel direction. A method of constructing a steel shell element according to . The method for constructing a steel shell element according to any one of claims 1 to 5, wherein the step of inserting the steel shell element while connecting the convex joint of the next steel shell element to the concave joint of the steel shell element that has already been penetrated. The excavator used for penetrating the steel shell element has a shape of the front excavation part that matches the shape of the square hollow cross section of the steel shell element and the temporary steel pipe, and the joint part is attached to the body part. The steel shell element construction method according to any one of claims 1 to 6, wherein an auxiliary cutter is provided for excavating the earth and sand portion corresponding to the above, or the excavator performs over excavation in a range including the joint portion.

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