JP2016084605A - Construction method for underground structure, and pneumatic caisson used therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a construction method for underground structures of different forms built in a vertical direction, along with a pneumatic caisson used in the construction, which significantly reduce construction steps and costs.SOLUTION: A large caisson skeleton B1 for constructing a large structure by a pneumatic caisson method is installed at a shallow underground location. A small caisson skeleton S1 for constructing a small structure is assembled on a bottom slab 12 of the caisson skeleton B1. After installing the large caisson skeleton B1, the small caisson skeleton S1 is installed at a deeper underground location from the caisson skeleton B1. The structure is constructed using the skeletons B1, S1 as a foundation.SELECTED DRAWING: Figure 1

Description

  The present invention is suitable for constructing a large structure in a shallow part of the ground, constructing a small structure in a deep part of the ground, and constructing an underground structure having a different shape in the vertical direction as a whole. The present invention relates to a method for constructing an intermediate structure and a pneumatic caisson used therefor.

For example, underground structures such as substations that have large building facilities (structures) in shallow underground locations and small shafts (structures) for underground wires in deep locations In general, (1) Once the ground is excavated once with the construction of the earth retaining support, the building facility is built there, and then the deep shaft from there And (2) Excavating excessively by excavating the ground with the installation of the earth retaining so that all structures are enveloped or by sinking the caisson, From there, one of the methods of building a building facility in a shallow place and building a shaft in a deep place is adopted.
As described in Patent Document 1, for example, the caisson method is roughly classified into a pneumatic caisson method and an open caisson method according to the difference between the excavation method and the subsidence method. An airtight work room is installed in the ground, and compressed air corresponding to the pore water pressure of the ground is sent into it to prevent the ingress of groundwater. In the latter open caisson method, the structure built on the ground is gradually removed from the ground by excavating and transporting the inside of the cylindrical structure with the upper and lower surfaces opened by a cram shell or other excavating machine. This is a construction method.
As described in Patent Document 2, for example, the deep foundation work is a method in which an operator enters a hole and excavates manually by manpower construction.

JP 2004-44242 A Japanese Patent Laid-Open No. 10-152853

  However, when constructing a large structure in a shallow place in the ground, constructing a small structure in a deep place in the ground, and constructing a structure having a different shape in the vertical direction as a whole, In construction using two types of construction methods as in (1), there is a problem that the process from excavation of the ground to construction of the underground structure greatly increases, as in (2) above. There is a problem that excavation costs and other costs required for construction work are excessive in construction that performs large excavation that envelops all structures on the ground.

  The present invention solves the above-mentioned conventional problems, constructs a large structure in a shallow part of the ground, constructs a small structure in a deep part of the ground, and forms a shape vertically in the ground as a whole. When constructing different structures, it is possible to perform construction with one type of work and continuous construction, greatly reducing the process required for construction, and excavating along the shape of the structure in the vertical direction. It is possible to reduce the cost of excavation, and also to combine and divert various facilities used for construction, to reduce the cost required for various facilities, and to reduce the overall cost significantly. It is an object to provide a construction method and a pneumatic caisson used therefor.

In order to achieve the above object, the present invention constructs a large structure in a shallow part of the ground, constructs a small structure in a deep part of the ground, and has an underground structure whose shape differs in the vertical direction as a whole. In the construction method of the underground structure for constructing, a large caisson housing for forming the large structure is sunk in a shallow portion of the ground by a pneumatic caisson method, and the small caisson housing is The gist is to incorporate a small caisson housing for forming a structure, and to sink the small caisson housing from the large caisson housing in a deep place in the ground.
In this case, it is preferable that a small caisson housing is incorporated in the bottom plate of the large caisson housing before the large caisson housing is set in the ground.
Also, in this case, before the large caisson housing is submerged in the ground, a built-in portion for the small caisson housing is formed on the bottom plate of the large caisson housing, The small caisson housing may be incorporated into the bottom plate of the large caisson housing.

Further, the pneumatic caisson used in the underground structure construction method of the present invention is a large caisson housing for forming a large structure, and a large caisson housing that is detachably inserted into a bottom plate of the large caisson housing. And a small caisson housing for forming a small structure incorporated in the inside of the caisson housing.
In this case, it is preferable that the small caisson housing is integrated into the large caisson housing.
Further, in this case, the small caisson housing is separate from the large caisson housing, and has a built-in portion for the small caisson housing on the bottom plate of the large caisson housing, and the small caisson housing is the large caisson housing. You may make it integrate in a caisson housing by retrofitting.

According to the underground structure construction method of the present invention, a large structure is constructed in a shallow portion of the ground, a small structure is constructed in a deep portion of the ground, and the shape of the underground is different in the vertical direction as a whole. When constructing a structure, a large caisson housing for forming a large structure is submerged in a shallow part of the ground by a pneumatic caisson method, and a small structure is formed to form a small structure on this large caisson housing. The caisson housing is built in, and the small caisson housing is submerged from this large caisson housing in a deep location in the ground, enabling construction in one type of work and continuous construction, greatly reducing the process required for construction. It is possible to drill along the shape of the structure in the vertical direction, reducing drilling costs, and also using various facilities attached to the pneumatic caisson for construction. Diversion to, reducing the cost of various equipment can significantly reduce the cost as a whole, exhibit the present invention own particular effect that.
In addition, according to the pneumatic caisson of the present invention, there is an exceptional effect unique to the present invention that the construction method of the underground structure can be realized.

The figure which combines the construction method of the underground structure by the 1st Embodiment of this invention, and the pneumatic caisson used for this The figure which expands and shows the construction method of the underground structure and the main part of the pneumatic caisson The figure which shows together the construction method of the underground structure by the 2nd Embodiment of this invention, and the pneumatic caisson used for this

Next, embodiments for carrying out the present invention will be described with reference to the drawings.
FIG. 1 shows a first embodiment.
As shown in FIG. 1, this underground structure construction method constructs a large structure in a shallow part of the underground G, constructs a small structure in a deep part of the ground, and forms a shape in the vertical direction as a whole. In this method, a pneumatic caisson method is used, and a large caisson housing B1 for forming a large structure is submerged in a shallow portion of the underground G. Two large and small caisson housings that incorporate a small caisson housing S1 for forming a small structure into the caisson housing B1 and sink a small caisson housing S1 from the large caisson housing B1 into a deep portion of the ground G. The two-stage settling method of B1 and S1 is adopted.

FIG. 1 also shows a pneumatic caisson P1 used in this underground structure construction method, and FIG. 2 shows an enlarged main part thereof.
As shown in FIG. 1, this pneumatic caisson P1 is detachably inserted into a large caisson housing B1 for forming a large structure and a bottom slab 12 of the large caisson housing B1, and is installed in a large caisson housing B1. And a small caisson housing S1 for forming a small structure to be incorporated into the inside of the housing. In this case, the small caisson housing S1 is integrally incorporated in the large caisson housing B1.
Each of the large and small caisson housings B1 and S1 is different in size, and generally has a common configuration.
The large caisson housing B1 has a side wall 10 formed in the vertical direction, a blade edge 11 formed at the lower end of the side wall 10, and a bottom slab (ceiling slab) 12 formed on the lower side inside the side wall 11. A working chamber 13 is provided inside the blade edge 11 below. A part of the bottom plate 12 is provided with a hole into which the small caisson housing S1 can be removably inserted as an assembly portion 120 for incorporating the small caisson housing S1. In the caisson housing B1, a plurality of through holes 140 and 150 are formed at predetermined positions of the bottom plate 12, and communicated with the through holes 140 and 150 on the top surface of the bottom plate 12 to adjust the atmospheric pressure and earth and sand. A material shaft 14 used for unloading and a man shaft 15 used for raising and lowering workers are installed, and a plurality of rails 17 are attached to the ceiling slab in the underground work chamber 13, that is, the lower surface of the bottom plate 12. Excavating machines 18 used for excavating the ground below the caisson housing B1 are movably disposed on the rails 17, respectively, and a tower crane (not shown) used for constructing the caisson housing B1 on the ground. ), A skater crane (not shown) used to carry out the earth and sand is installed. Various facilities are located necessary to tick caisson method. In addition, a caisson continuous casing is appropriately stacked on the upper part of the caisson casing B1.
The small caisson S1 has a blade edge 111 formed in a hole formed as an assembly portion 120 of the small caisson housing S1 in the bottom plate 12 of the large caisson housing B1, and a side wall 110 is formed upward from the hole 120. Further, a bottom plate (ceiling slab) 112 is formed on the lower side of the inside of the side wall 110, and a work chamber 113 is provided in the blade edge 111 below the bottom plate 12. As a whole, the bottom plate 12 of the large caisson housing B1 ( Are inserted into the built-in portion 120) in a detachable manner. In addition, a caisson continuous casing is appropriately stacked on the upper part of the caisson casing S1. Further, as shown in FIG. 2, between the periphery of the small caisson housing S1, that is, between the outer surface of the side wall 110 of the caisson housing S1 and the inner peripheral surface of the hole 120 of the bottom plate 12 of the large caisson housing B1, In order to ensure airtightness, a water stop structure using the entrance 19 is provided around the upper hole 120 of the bottom slab 12 of the large caisson housing B1 so that the outer wall of the small caisson housing S1 can be tightly adhered. In this case, the entrance 19 is composed of an annular shield packing made of an elastic material (entrance packing) and an annular presser member made of a metal material that is put on the outer periphery of the shield packing. Grease 20 is injected and filled between the entrance 19 and the outer surface of the side wall 110 of the small caisson housing S1. Further, a plurality of lifting prevention pins are provided between the large caisson housing B1 and the small caisson housing S1 in order to resist the pressure of the small caisson housing S1 and prevent the caisson housing S1 from being lifted. A lifting prevention structure using 21 is employed. In this case, each lifting prevention pin 21 can be rotated only in a downward direction via a pin on the bottom plate side fixed to the inner peripheral surface of the hole 120 of the bottom plate 12 and a pin on the bottom plate side via a hinge pin and a rotation restricting member. And a pin on the small caisson housing side fixed to the side wall 110 of the small caisson housing S1. The caisson housing S1 communicates with a through hole 140 (only one is shown) penetratingly formed at a predetermined position of the bottom slab 112, and is used for pressure adjustment and sediment removal on the upper surface of the bottom slab 112. A shaft 114 and a man shaft (not shown) used for raising and lowering a worker are installed, and a plurality of rails 117 are attached to a ceiling slab in the work chamber 113 in the basement, that is, a bottom surface of the bottom plate 112 via a plurality of columns 116. In each of these rails 117, excavating machines 118 used for excavating the ground below the caisson housing S1 are movably disposed, and each part of the caisson housing S1 is necessary for the pneumatic caisson method. Various facilities are arranged.

In this underground structure construction method, as shown in FIG. 1, before sinking the large caisson housing B1 into the ground, the small caisson housing S1 is incorporated into the bottom plate 12 of the large caisson housing B1. Using each of these large and small caisson housings B1 and S1, a step for setting the large caisson housing B1 and a step for setting the small caisson housing S1 are sequentially performed. A large structure is constructed in a shallow part of the ground, and a small structure is constructed in a deep part of the ground. The procedure will be specifically described below.
In the step of depositing the large caisson housing B1, the large caisson housing B1 for forming a large structure is deposited in a shallow portion of the ground by a pneumatic caisson method.
In this case, first, the caisson housing B1 made of reinforced concrete is constructed on the ground, and compressed air is sent into the airtight working chamber 13 below the caisson housing B1 to prevent water from entering, while in the working chamber 113 of the small caisson housing S1. While excavating the ground by each of the excavating machines 18 in the work chamber 13 including the excavating machine 118, the large caisson frame B1 is caused by its own weight (and, if necessary, the caisson frame B1 is promoted to sink) There is a case where load water is loaded on the bottom plate 12 of the frame B1 or a caisson frame is pressed into the ground by using a press-in jack and an anchor material. A caisson continuous frame is placed on top of this caisson frame B1 (according to this, material shafts 14, 114, man shafts are installed) 5 is extended upward) and bottom landing large caissons skeleton B1 to a predetermined depth. In the process of excavating the ground by sending compressed air into the work chamber 13 below the caisson housing B1, the inner peripheral surface of the hole 120 of the bottom slab 12 of the large caisson housing B1 and the side wall 110 of the small caisson housing S1. Airtightness between the outer surface and the outer surface is ensured by the combined use of the entrance 19 and the grease 20 (see FIG. 2), and for the lifting pressure of the small caisson housing S1, there is a space between the bottom plate 12 and the small caisson housing S1. The plurality of anti-lifting pins 21 (see FIG. 2) resist (restrain the upward movement of the small caisson housing S1), and the caisson housing S1 is prevented from lifting. Further, the sinking of the small caisson housing S1 is resisted by the traveling rail 117 and the column 116 (see FIG. 2) of the excavating machine 118 in the work chamber 113 below the caisson housing S1. After the large caisson housing B1 (and the caisson continuous housing) is set, the work chamber 13 of the caisson housing B1 is filled with the embedded concrete 22, and the work chamber 13 is filled. In this filling, low-strength concrete may be placed directly under the small caisson housing S1.
After the large caisson housing B1 is set (bottomed) and filled, the process proceeds to a step for setting the small caisson housing S1. In this step, the small caisson housing S1 incorporated in the bottom slab 12 of the large caisson housing B1 is sunk from the bottom slab 12 of the large caisson housing B1 at a deep depth in the ground by the pneumatic caisson method. In this case, similarly to the step of laying the large caisson housing B1, the ground is removed by the excavating machines 118 in the work chamber 113 while supplying compressed air to the work chamber 113 below the small caisson housing S1 to prevent water from entering. The small caisson housing S1 is self-weighted (and, if necessary, load water is loaded on the bottom slab 112 of the caisson housing S1, or a press-fit jack is attached to the bottom slab 112 of the caisson housing S1. The anchor material may be used to press-fit the caisson housing S1 into the ground), and the caisson housing S1 may be overlaid on the caisson housing S1 with appropriate press-sedimentation by a predetermined stroke on the ground. Along with this, the material shaft and the man shaft are extended upward, and the small caisson housing S1 is grounded to a predetermined depth. In the settling process of the small caisson housing S1, the anti-lifting pin 21 (see FIG. 2) between the bottom plate 12 and the small caisson housing S1 allows the small caisson housing S1 to move downward. There is no obstacle to sedimentation of the housing S1. After the caisson housing S1 is laid down, the working chamber 113 is filled with buried concrete, and the working chamber 113 is buried. In this way, the small caisson housing S1 is sunk in connection with the large caisson housing B1.
Based on these caisson housings B1 and S1 (and caisson connection housings), a large structure is constructed at a shallow location in the ground, a small structure is constructed at a deep location in the ground, and the vertical direction as a whole. Build underground structures with different shapes.

As described above, in this underground structure construction method, a large caisson housing B1 for forming a large structure is set in a shallow portion of the ground by a pneumatic caisson method, and a large caisson housing B1 is formed. A small caisson housing S1 for forming a small structure is incorporated into the bottom slab 12 of the large caisson housing B1, and a small caisson housing S1 is installed from the bottom slab 12 of the large caisson housing B1. Because it is submerged in the deep part of the ground, it can be constructed with one type of construction and can be constructed continuously, the process required for construction can be greatly reduced, and the shape along the shape of the structure in the vertical direction Drilling is possible, and the drilling cost is reduced, and further, the caisson housing B1, the excavating machines 18, 118 under the S1, the caisson housing B1, the material shaft 14 inside the S1, The cost of the various facilities can be reduced by combining and diverting the various facilities used for the construction that are attached to the pneumatic caisson P1, such as the rotary shaft 15, the compressed air equipment on the ground, and various cranes. It can be greatly reduced.
Moreover, the construction method of the underground structure can be realized by the pneumatic caisson P1.

FIG. 3 shows a second embodiment.
As shown in FIG. 3, this underground structure construction method also constructs a large structure in a shallow part of the ground, constructs a small structure in a deep part of the ground, and has a shape in the vertical direction as a whole. In this method, a large caisson frame B2 for forming a large structure is submerged in a shallow portion of the ground by a pneumatic caisson method. Two large and small caisson housings B2 and S2 in which a small caisson housing S2 for forming a small structure is incorporated in the housing B2 and a small caisson housing S2 is sunk from the large caisson housing B2 to a deep portion in the ground. The two-stage settling method is adopted.

FIG. 3 also shows the pneumatic caisson P2 used in this underground structure construction method.
As shown in FIG. 3, this pneumatic caisson P2 is detachably inserted into a large caisson housing B2 for forming a large structure and a bottom slab 12 of the large caisson housing B2, and is installed in a large caisson housing B2. A small caisson housing S2 for forming a small structure to be incorporated in the inside of the housing. In this case, the small caisson housing S2 and the large caisson housing B2 are separate, and the bottom plate 12 of the large caisson housing B2 is provided. The small caisson housing S2 is incorporated into the bottom plate 12 of the large caisson housing B2 by retrofitting.
The large and small caisson housings B2 and S2 have almost the same configuration except for the size.
Since the large caisson housing B2 as a whole has a configuration substantially the same as that of the first embodiment (large caisson housing B1), the same reference numerals are given to portions common to the first embodiment. Therefore, the duplicate description will be omitted. Further, illustration of the material shaft 14, the man shaft 15 and the like is omitted. This large caisson housing B2 is the first in that, instead of incorporating the small caisson housing S2 (as an initial aspect) into the bottom plate 12, only the assembly portion 120 for the small caisson housing S2 is formed. Different from the first embodiment. In this case, a hole into which the small caisson housing S2 can be removably inserted is drilled as a built-in portion 120 for incorporating the small caisson housing S2 into a part of the bottom plate 12, and the hole 120 is blocked by the temporary bottom plate 121. Is done. The temporary bottom plate 121 is formed by casting concrete into the hole 120 of the bottom plate 12, and a plurality of support works 23 are installed between the bottom plate 12 and the temporary bottom plate 121 in order to resist lifting pressure on the temporary bottom plate 121. The In this case, the temporary bottom plate 23 is formed in a range from the lower side opening of the hole 120 of the bottom plate 12 to the vicinity of the middle portion between the lower side opening and the upper side opening. It is installed and fixed between the peripheral surface and the outer peripheral side edge of the upper surface of the temporary bottom plate 121, and the temporary bottom plate 121 is pressed from above by each supporting work 23. Further, on the bottom plate 12 of the large caisson housing B2, the side wall 110 of the small caisson housing S2 is formed around the mounting portion 120 of the small caisson housing S2 when the small caisson housing S2 is assembled into the mounting portion 120. A water stop structure using the entrance 19 is provided so that the outer surface can be airtightly adhered. The entrance 19 is as described in the first embodiment. Further, the grease 20 is also used when the small caisson housing S2 is assembled. In addition, a caisson continuous casing is appropriately stacked on the upper part of the caisson casing B2.
Similarly to the first embodiment, the small caisson S2 has a blade edge 111 formed in a hole formed as an embedded portion 120 of the small caisson housing S2 in the bottom plate 12 of the large caisson housing B2. A side wall 110 is formed from the upper side to the upper side, a bottom plate (ceiling slab) 112 is formed on the lower side of the side wall 110, and a working chamber 113 is provided in the lower blade edge 111. The large caisson housing B2 is removably inserted into the bottom plate 12 (the built-in portion 120). In addition, a caisson continuous casing is appropriately stacked on the upper part of the caisson casing S2. The caisson housing S2 communicates with an opening 140 (only one shown) penetratingly formed at a predetermined position of the bottom slab 112, and a material shaft used for pressure adjustment and sediment transport on the upper surface of the bottom slab 112. 114, a man shaft (not shown) used for raising and lowering a worker is installed, and a plurality of rails 17 are attached to the lower surface of the ceiling slab in the underground working chamber 113, that is, the bottom slab 112. Various equipment necessary for the pneumatic caisson method is arranged in each part of the caisson housing S2, such as an excavating machine 118 used for excavating the ground below the caisson housing S2 to be able to travel.

In this underground structure construction method, before the large caisson housing B2 is submerged in the ground, the built-in portion 120 for the small caisson housing S2 is formed on the bottom plate 12 of the large caisson housing B2, After the large caisson housing B2 is set (bottomed) and filled, the small caisson housing S2 is incorporated into the bottom plate 120 of the large caisson housing B2, and each of these large and small caisson housings B2, S2 is used. The large caisson housing B2 and the small caisson housing S2 are sequentially installed, and based on these caisson housings B2 and S2, a large structure is constructed in a shallow portion of the ground. Build a small structure in a deep location. The procedure will be specifically described below.
In the step of depositing the large caisson housing B2, the large caisson housing B2 for forming a large structure is deposited in a shallow portion of the ground by a pneumatic caisson method.
In this case, first, the reinforced concrete caisson housing B2 is constructed on the ground, and compressed air is sent into the airtight working chamber 13 below the caisson housing B2 to prevent water from entering, while the excavating machines 18 in the working chamber 13 use each excavating machine 18. While excavating the ground, the large caisson housing B2 is loaded by its own weight (and, if necessary, load water is loaded on the bottom slab 12 of the caisson housing B2 or used for press-fitting. The caisson housing may be press-fitted into the ground using a jack and anchor material, and the caisson housing will be placed on top of the caisson housing B2 as needed. The material shaft and the man shaft are extended upwards accordingly, and the large caisson housing B2 is grounded to a predetermined depth. In the process of excavation of the ground by sending compressed air to the work chamber 13 below the caisson housing B2, the pressure between the bottom plate 12 and the temporary bottom plate 121 is raised against the lifting pressure of the temporary bottom plate 121 of the bottom plate 12. The plurality of supporters 23 are pressed and resisted, and the temporary bottom plate 121 is prevented from being lifted. After the large caisson housing B2 (and the caisson continuous housing) is set up, the work chamber 13 is filled with the embedded concrete 22, and the work chamber 13 is filled. In this filling, low-strength concrete may be placed directly under the temporary bottom plate 121.
After the large caisson housing B2 is set (bottomed) and filled, the process proceeds to the setting step for the small caisson housing S2. In this step, as described above, the small caisson housing S2 is incorporated into the assembly portion (hole) 120 of the bottom plate 12 of the large caisson housing B2, and the bottom plate 12 of the large caisson housing B2 is formed by the pneumatic caisson method. A small caisson housing S2 is placed deep in the ground. In this case, as in the step of sinking the large caisson housing B2, the ground is removed by the excavating machines 118 in the work chamber 113 while sending compressed air to the work chamber 113 below the small caisson housing S2 to prevent water from entering. The caisson housing S2 is self-weighted (and, if necessary, to load the caisson housing S2 on the bottom slab 112 of the caisson housing S2, or to load the load water or press-fit jacks and anchors. The caisson housing S2 may be press-fitted into the ground using a material.) The caisson housing S2 is placed on the caisson housing S2 by appropriately press-settling the caisson housing S2 by a predetermined stroke. (Accordingly, the material shaft and the man shaft are extended upward), and the small caisson housing S2 is grounded to a predetermined depth. After the caisson housing S2 is laid down, the working chamber 113 is filled with buried concrete, and the working chamber 113 is buried. In this way, the small caisson housing S2 is sunk in connection with the large caisson housing B2.
Based on these caisson housings B2 and S2 (and caisson connection housings), a large structure is constructed at a shallow location in the ground, a small structure is constructed at a deep location in the ground, and the vertical direction as a whole. Build underground structures with different shapes.

  Even if it does in this way, there can exist an effect similar to 1st Embodiment.

P1, P2 Pneumatic caisson B1, B2 Large caisson housing S1, S2 Small caisson housing 10, 110 Side wall 11, 111 Blade 12, 12, 112 Bottom plate (ceiling slab)
120 assembly part (hole)
121 Temporary bottom plate 13, 113 Work chamber 140 Through hole 14, 114 Material shaft 150 Through hole 15 Man shaft 16, 116 Post 17, 117 Rail 18, 118 Excavating machine 19 Entrance 20 Grease 21 Lifting prevention pin 22 Filled concrete 23 Support construction

Claims (6)

In the construction method of an underground structure that constructs a large structure in a shallow part of the ground, constructs a small structure in a deep part of the ground, and constructs an underground structure having a different shape in the vertical direction as a whole.
By pneumatic caisson method
A large caisson housing for forming the large structure is set in a shallow place in the ground,
Incorporating a small caisson housing for forming the small structure into the large caisson housing, and sinking the small caisson housing from the large caisson housing to a deep location in the ground.
The construction method of the underground structure characterized by this.   The method for constructing an underground structure according to claim 1, wherein a small caisson housing is incorporated into a bottom plate of the large caisson housing before the large caisson housing is submerged in the ground.   Before the large caisson housing is submerged in the ground, a built-in portion for the small caisson housing is formed on the bottom plate of the large caisson housing, and after the large caisson housing is settled, the large caisson housing is formed. The method for constructing an underground structure according to claim 1, wherein the small caisson housing is incorporated in a bottom plate of the housing. A large caisson housing for forming a large structure, and a small caisson for forming a small structure that is removably attached to a bottom plate of the large caisson housing and incorporated into the large caisson housing. The body,
Comprising
The pneumatic caisson used for the construction method of the underground structure of Claim 1 characterized by the above-mentioned.   5. The pneumatic caisson according to claim 4, wherein the small caisson housing is integrated into the large caisson housing.   The small caisson housing is separated from the large caisson housing, and has a built-in portion for the small caisson housing on the bottom plate of the large caisson housing. The small caisson housing is attached to the large caisson housing by retrofitting. The pneumatic caisson according to claim 4, which is incorporated.

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