Pneumatic caisson construction method, weight component for pneumatic caisson, and weight for pneumatic caisson

Abstract

To provide a pneumatic caisson construction method, a weight component, and weights that increase sinking force of a caisson.SOLUTION: In a pneumatic caisson construction method, a caisson 1 having a base slab 3 and a cutting edge 7 surrounding an excavation work chamber 9 in which excavation of the ground G is carried out, and cylindrical side walls 5 that are successively added onto the base slab 3, is lowered into the ground. The pneumatic caisson construction method comprises a lowering process in which the ground G is excavated in the excavation work chamber 9 and the caisson 1 is lowered. During the lowering process, temporary weights 30 are installed on the side walls 5.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pneumatic caisson construction method, a weight component for a pneumatic caisson, and a weight for a pneumatic caisson. [Background technology]

[0002] Conventionally, the pneumatic caisson method has been known as a construction method for constructing underground structures (see, for example, Patent Document 1 below). In the pneumatic caisson method, a bottom slab and cutting edge are provided to surround an excavation work chamber, and cylindrical side walls are successively added onto the bottom slab while being lowered into the ground. The excavation work chamber is an airtight space equipped with an airlock, and the interior of the excavation work chamber is filled with compressed air and pressurized to suppress external water pressure and excavate in a dry state. As soil is excavated below the bottom slab in the excavation work chamber, the caisson sinks due to the weight of the caisson and its equipment, and new side walls are added on top as the caisson sinks. This process is repeated to lower the caisson to the desired depth. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-316118 Summary of the Invention [Problem to be solved by the invention]

[0004] In such pneumatic caisson construction methods, it is necessary to obtain a settlement force greater than the resistance force from the ground, etc. If the settlement force is insufficient, it is possible to reduce the resistance force at the tip of the cutting edge by increasing the opening ratio of the cutting edge (the ratio of the excavation area of ​​the cutting edge to the total area of ​​the tip of the cutting edge). However, the larger the opening ratio, the more difficult it becomes to control the caisson's posture, and there is also concern about the impact on surrounding structures. Therefore, in order to address the insufficient settlement force of the caisson, it is considered more preferable to use a method that increases the settlement force. Therefore, an object of the present invention is to provide a pneumatic caisson construction method, weight component, and weight that increase the settlement force of the caisson. [Means for solving the problem]

[0005] The gist of the present invention lies in the following [1] to [7].

[0006] [1] A pneumatic caisson construction method for lowering a caisson into the ground, the caisson having a base plate and cutting edge surrounding a work chamber where the ground is excavated, and cylindrical side walls that are successively added onto the base plate, the method including a lowering step for excavating the ground in the work chamber and lowering the caisson, and temporary weights being installed on the upper end surfaces of the side walls during the lowering step.

[0007] [2] The pneumatic caisson construction method described in [1], wherein the weight has a plurality of weight parts arranged circumferentially around the entire circumference on the upper end surface and connected endlessly via a predetermined connecting device.

[0008] [3] A pneumatic caisson construction method according to [1] or [2], wherein the weight is installed on the upper end surface so as not to protrude horizontally from the upper end surface.

[0009] [4] The weight is installed in the space between the outer reinforcing bar and the inner reinforcing bar protruding upward from the upper end surface, [1] to [3]. A pneumatic caisson construction method according to any one of [1] to [3].

[0010] [5] A pneumatic caisson construction method according to any one of [1] to [4], comprising a weight installation process of installing the weight on the upper end surface before the subsidence process, the subsidence process, a weight removal process of removing the weight on the upper end surface after the subsidence process, and a side wall addition process of constructing a new lot of the side wall on top of the upper end surface after the weight removal process.

[0011] [6] A weight part for a pneumatic caisson for constructing a temporary weight to be installed on a caisson in a pneumatic caisson construction method in which a caisson having a base plate and cutting edge surrounding a working chamber where ground excavation is carried out, and cylindrical side walls that are successively added onto the base plate, is lowered into the ground, the weight part for a pneumatic caisson having a shape in plan view that does not protrude horizontally from the upper end surface of the side wall when installed on the upper end surface with its longitudinal direction facing circumferentially of the side wall, and is provided with bolt grooves at both ends in the longitudinal direction through which bolts are inserted for connecting to other weight parts installed adjacent to each other in the circumferential direction on the upper end surface.

[0012] [7] A weight for a pneumatic caisson comprising a plurality of weight parts for a pneumatic caisson as described in [6] connected via bolts, wherein the positional relationship between the weight parts for a pneumatic caisson connected by the bolts can be adjusted by the play of the bolts within the bolt grooves. [Effects of the Invention]

[0013] According to the present invention, a pneumatic caisson construction method, weight parts, and weights that increase the sinking force of a caisson can be provided. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view showing a caisson to which the pneumatic caisson construction method of this embodiment is applied. [Figure 2]1(a) is a plan view of the upper end of the side wall in the sinking process, and FIG. 1(b) is an enlarged cross-sectional view of the IIb-IIb cross section thereof. [Figure 3] FIG. 2 is a perspective view showing one weight part. [Figure 4] 4(a), (b) and (c) are a plan view, a front view and a bottom view of one weight component, respectively. [Figure 5] 4(a) and 4(b) are cross-sectional views taken along the line VV in FIG. 4(a). [Figure 6] This is an enlarged plan view showing the vicinity of the air pipe or concrete pouring pipe on the upper end surface on which the temporary weight is placed. [Figure 7] 7(a) is an enlarged plan view showing the vicinity of the connecting portion between adjacent weight components, FIG. 7(b) is a cross-sectional view taken along line VIIb-VIIb thereof, and FIG. 7(c) is an exploded view of the connector. [Figure 8] 10(a) and 10(b) are plan views each showing an example of the positional relationship between weight components connected by a connecting bolt. [Figure 9] FIG. 10 is a vertical cross-sectional view showing an example of the upper end portion of the side wall in the sinking process. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the pneumatic caisson construction method, weight component, and weight according to the present invention will be described in detail with reference to the drawings.

[0016] FIG. 1 is a cross-sectional view showing an example of a caisson 1 to which the pneumatic caisson construction method of this embodiment is applied. The caisson 1 of this embodiment has a relatively small diameter of about 6 to 8 m, and such small-diameter caissons are sometimes called "slim caissons." The pneumatic caisson construction method using slim caissons does not require large heavy machinery and produces little vibration or noise. Furthermore, safe and speedy construction is possible using automatic excavators, which also reduces the amount of manual work required by caisson divers.

[0017] The caisson 1 comprises a reinforced concrete base 3 and cylindrical reinforced concrete side walls 5 that are successively added on top of the base 3. The base 3 has a cutting edge 7 that points downward at its periphery. The excavation chamber 9, surrounded by the base 3 and the cutting edge 7, is an airtight, pressurized space for excavating the ground G. Air is pumped into the excavation chamber 9 from the outside, applying air pressure to prevent groundwater from seeping into the excavation chamber 9. The air from the outside is pumped into the excavation chamber 9 through an air pipe 10 (Figure 2(a)) that is embedded in the side walls 5 in advance. An excavator 11 is installed in the excavation chamber 9, and the excavator 11 excavates the ground G below the base slab 3.

[0018] A shaft 13 is provided as one of the caisson equipment in the center of the space surrounded by the side walls 5. The shaft 13 extends vertically upward from the upper surface of the bottom slab 3 and is connected to the excavation work chamber 9 via an airlock (not shown). The shaft 13 is used for accessing the excavation work chamber 9, discharging excavated soil from the excavation work chamber 9, etc.

[0019] In the pneumatic caisson method, the ground G is excavated in the excavation work chamber 9, and the caisson 1 is lowered by the weight of the caisson 1 and its equipment, and a new lot of side wall 5 is added to correspond to the depth to which it has sunk. This process is repeated until the caisson 1 is lowered to a pre-planned depth. After the caisson 1 reaches the planned depth, the excavator 11 inside the excavation work chamber 9 is removed, and the excavation work chamber 9 is filled with backfill concrete. This backfill concrete is sent into the excavation work chamber 9 from the ground through concrete pouring pipes 21 (Figure 2(a)) that have been embedded in the side wall 5 in advance. By filling the excavation work chamber 9 with backfill concrete, the caisson 1 is fixed to the ground G, and installation of the caisson 1 using the pneumatic caisson method is completed. The installed caisson 1 is used, for example, as a foundation.

[0020] Here, in order to sink the caisson 1 as described above, it is necessary to obtain a sinking force greater than the resistance force that resists the sinking of the caisson 1. The resistance forces mentioned above include the uplift pressure due to the compressed air in the excavation work chamber 9, the peripheral friction force caused by friction between the caisson 1 and the ground G, and the cutting edge resistance force acting from the ground G on the tip of the cutting edge 7. On the other hand, the sinking force mentioned above includes gravity due to the weight of the caisson 1 and caisson rigging (compressed air equipment, shaft 13, etc.).

[0021] For example, the deeper underground, the greater the surface friction force, so as the caisson 1 sinks, the resistance force increases, and there is a possibility that the settlement force will be insufficient. In particular, since the caisson 1 has a small diameter as mentioned above, its own weight relative to the surface friction force is relatively small, and the settlement force tends to be insufficient. If the settlement force is insufficient relative to the resistance force, it is possible to reduce the resistance force by increasing the opening ratio of the tip of the cutting edge 7 (the ratio of the excavation area of ​​the cutting edge to the total area of ​​the tip of the cutting edge 7). However, the larger the opening ratio, the more difficult it becomes to control the posture of the caisson 1, and there are also concerns about the impact on surrounding structures. Therefore, in order to address the insufficient settlement force of the caisson 1, it is considered more preferable to use a method that increases the settlement force.

[0022] One method for increasing the sinking force of the caisson 1 is to load weights into the space between the side wall 5 and the shaft 13. However, because the caisson 1 has a small diameter, the space between the side wall 5 and the shaft 13 is relatively narrow. Moreover, this space is occupied by the internal scaffolding 23 used to install the internal formwork 17 for pouring concrete into the side wall 5, making it difficult to secure space for installing weights. For this reason, water ballast W is introduced into the space between the side wall 5 and the shaft 13 instead of solid weights. However, because the caisson 1 has a small diameter, the amount of water ballast W that can be held is limited, and because water has a relatively low specific gravity, the water ballast W alone may not be enough to sufficiently increase the sinking force of the caisson 1.

[0023] Therefore, in the pneumatic caisson construction method of this embodiment, a temporary weight 30 (pneumatic caisson weight) is used, which is temporarily installed on the side wall 5 to increase the sinking force of the caisson 1. The temporary weight 30 is made of a material with a high specific gravity. The temporary weight 30 will be described below.

[0024] FIG. 2(a) is a plan view of the upper end of the side wall 5 during the subsidence process, and FIG. 2(b) is an enlarged cross-sectional view of the IIb-IIb section. As shown in FIG. 2, the upper end surface 5a of the side wall 5 of the caisson 1 is annular in plan view. The temporary weight 30 is annular in plan view with a diameter approximately equal to that of the upper end surface 5a. The temporary weight 30 is installed concentrically on the upper end surface 5a. The radial width of the temporary weight 30 is narrower than the radial width of the upper end surface 5a, and the temporary weight 30 installed on the upper end surface 5a does not protrude horizontally from the upper end surface 5a. More specifically, the temporary weight 30 can be installed so as not to protrude horizontally from the annular space 33 described below.

[0025] A large number of reinforcing bars 19a, 19b protrude upward from the upper end surface 5a of the side wall 5 to be joined to the reinforcing bars of the next lot of side wall 5. That is, when the side wall 5 is extended, the protruding reinforcing bars 19a, 19b are joined to the reinforcing bars 19a, 19b of the next lot using a predetermined joint structure. The reinforcing bars 19a are outer periphery reinforcing bars arranged on the outer periphery of the side wall 5, and the reinforcing bars 19b are inner periphery reinforcing bars arranged on the inner periphery of the side wall 5. Between the outer periphery reinforcing bars 19a and the inner periphery reinforcing bars 19b, which are present in large numbers in the circumferential direction, there exists an annular space 33 that forms an annular shape in a plan view, and an annular temporary weight 30 is installed so as to fit within this annular space 33.

[0026] The temporary weight 30 is configured by connecting multiple weight components 35 (weight components for pneumatic caissons) in a string-like pattern in the longitudinal direction in a plan view. That is, the temporary weight 30 has multiple weight components 35, which are arranged circumferentially within the annular space 33 on the upper end face 5a and connected in series via predetermined connectors 37. The weight components 35 are arranged around the entire circumference of the upper end face 5a and are connected endlessly using the same number of connectors 37 as the weight components 35. In the example of FIG. 2(a), the temporary weight 30 has 17 weight components 35 and forms a closed annular shape. The specific gravity of the weight components 35 is 7 or more.

[0027] The weight component 35 will now be described in detail. FIG. 3 is a perspective view of one weight component 35, and FIGS. 4(a), 4(b), and 4(c) are a plan view, a front view, and a bottom view, respectively, of one weight component 35. The weight component 35 is, for example, a metal ingot produced by casting, i.e., a cast iron block. The weight component 35 has dimensions of approximately 1 m in the longitudinal direction, approximately 0.5 m in the lateral direction, and approximately 1 m in height. The weight component 35 weighs approximately 3 t. The weight component 35 can stand on its own in the state shown in FIG. 3 on the upper end surface 5a of the flat side wall 5. Hereinafter, in the description of the weight component 35, terms such as "upper / lower" and "upper surface / lower surface (bottom surface)" are used to refer to the up / down direction in the freestanding state shown in FIG. 3. Furthermore, the longitudinal direction and the lateral direction of the weight component 35 in a plan view will be simply referred to as the "longitudinal direction" and the "lateral direction", respectively.

[0028] As shown in Figures 3 and 4, the weight component 35 as a whole is curved in a plan view to form a gentle arc with a curvature roughly equivalent to that of the upper end surface 5a of the side wall 5. That is, the outer peripheral surface 34 of the weight component 35, which is located radially outward from the arc, bulges along the arc shape, and the inner peripheral surface 36 opposite the outer peripheral surface 34 is recessed along the same arc shape. This shape makes it easy to form a temporary weight 30 that is annular in shape and has a diameter roughly equivalent to that of the upper end surface 5a when multiple weight components 35 are connected in the longitudinal direction. Because the width of the weight component 35 in the lateral direction is narrower than the width of the annular space 33 (Figure 2) above the upper end surface 5a, the weight component 35 can be installed so that its longitudinal direction faces the circumferential direction of the side wall 5 and fits within the annular space 33. It can be said that the weight component 35 has a shape in a plan view that does not protrude horizontally from the upper end surface 5a when placed on the upper end surface 5a with its longitudinal direction facing the circumferential direction of the side wall 5. More specifically, it can be said that the weight component 35 has a shape in a plan view that does not protrude horizontally from the annular space 33 when placed in the annular space 33 with its longitudinal direction facing the circumferential direction of the side wall 5.

[0029] A hanging hole 41, which is a recess for passing a wire or hook of a lifting device (e.g., a crane), is formed in the center of the upper surface 39 of the weight component 35. A hanging bolt 43 extending in the short direction passes through the hanging hole 41. By hanging a wire or hook on the hanging bolt 43, the weight component 35 can be lifted and moved by the lifting device. Details of the vicinity of the hanging hole 41 will be described. FIGS. 5(a) and 5(b) are VV cross-sectional views of FIG. 4(a) and show the vicinity of the hanging hole 41. A pair of bolt mounting portions 40 and 42 are formed on the upper surface 39 so as to sandwich the hanging hole 41 in the short direction. The bolt mounting portion 40 is a recess formed in the corner between the upper surface 39 and the outer peripheral surface 34 and accommodates the head of the hanging bolt 43. Similarly, the bolt mounting portion 42 is a recess formed in the corner between the upper surface 39 and the inner peripheral surface 36 and accommodates a nut 44 for fastening the hanging bolt 43.

[0030] Near the hanging hole 41, two sheath tubes 46, 46 extending in the same straight line in the short direction are embedded at a position slightly lower than the top surface 39. Both ends of one sheath tube 46 are exposed to the hanging hole 41 and the bolt attachment portion 40, respectively. Similarly, both ends of the other sheath tube 46 are exposed to the hanging hole 41 and the bolt attachment portion 42, respectively. The sheath tube 46 is made of a high-strength material that is resistant to wear, different from the material (cast iron) of the other portions of the weight component 35, and is embedded in the above position by insert casting when the weight component 35 is manufactured.

[0031] The hollow portions of these sheath tubes 46 form bolt holes 48 for the suspension bolt 43, and the suspension bolt 43 is inserted from the bolt mounting portion 40 to the bolt mounting portion 42 so as to pass through the bolt holes 48. The center portion of this suspension bolt 43 crosses the inside of the suspension hole 41 and is exposed within the suspension hole 41, so that a wire or the like of the lifting device as described above can be hung on this center portion.

[0032] Because the weight component 35 is lifted by hanging a wire or the like around the hanging bolt 43, repeated use of the weight component 35 will cause the hanging bolt 43 to wear out due to contact with the wire or the like. In this case, the weight component 35 can be continued to be used by replacing the hanging bolt 43. Furthermore, the inner surfaces of the bolt holes 48, 48 may be worn or chipped due to contact with the hanging bolt 43. To prevent this wear, the bolt holes 48, 48 are formed by hollow portions of the sheath tubes 46, 46. Furthermore, by using a material for the sheath tube 46 that is more wear-resistant and resistant to damage such as chipping than cast iron, wear of the bolt holes 48, 48 and the possibility of damage are reduced.

[0033] As shown in Figures 3 and 4, one of the longitudinal end faces of the weight component 35 is a convex end face 45, and the other is a concave end face 47. The convex end face 45 and the concave end face 47 are generally cylindrical with approximately the same curvature. Connector attachment portions 49, 51 for attaching a connector 37 (Figure 2) are formed at both longitudinal ends of the upper surface 39. One end of the connector 37 is hooked to the connector attachment portion 49 on the convex end face 45 side, and the other end of the connector 37 is hooked to the connector attachment portion 51 on the concave end face 47 side, thereby connecting multiple weight components 35 adjacent to each other in the longitudinal direction by the connector 37. Details of this connecting structure will be described later.

[0034] A truncated cone-shaped tenon 53 protruding upward from the upper surface 39 is formed in a position on the upper surface 39 between the connector attachment portion 49 and the hanging hole 41. Correspondingly, a truncated cone-shaped mortise 57 that is slightly larger than the tenon 53 is formed in the lower surface 55 of the weight component 35 at a position directly below the tenon 53. With such tenon 53 and mortise 57, when multiple weight components 35 are stacked vertically, the tenon 53 and mortise 57 fit together, thereby positioning the weight components 35 relative to one another and preventing misalignment.

[0035] As described above, the air flue pipe 10 and the concrete pouring pipe 21 ( FIG. 2( a) ) are embedded in the side wall 5, and the air flue pipe 10 and the concrete pouring pipe 21 are pulled upward from the annular space 33 on the upper end surface 5 a. Correspondingly, two piping grooves 59 extending in the vertical direction and having an arc-shaped cross section are formed on the outer peripheral surface 34 of the weight component 35. As shown in FIG. 6 , by aligning the air flue pipe 10 and the concrete pouring pipe 21 with the positions of these piping grooves 59, the weight component 35 can be installed in the annular space 33 while avoiding interference with these pipes. Note that the positions of the air flue pipe 10 and the concrete pouring pipe 21 may be determined in advance based on the planned placement of the weight component 35 in order to align the positions of the air flue pipe 10 and the concrete pouring pipe 21 with the piping grooves 59.

[0036] Next, the connecting structure for connecting the weight components 35 together in the longitudinal direction will be described. Fig. 7(a) is an enlarged plan view showing the vicinity of the connecting portion between adjacent weight components 35, 35, Fig. 7(b) is a cross-sectional view taken along line VIIb-VIIb of Fig. 7(b), and Fig. 7(c) is an exploded view of a connecting device 37. As shown in Fig. 7(c), the connecting device 37 includes a connecting bolt 61 and a nut 63 threaded onto the tip of the connecting bolt 61. The connecting bolt 61 has a spherical bolt head 61a and a linear bolt shank 61b. The connecting device 37 also includes a rubber packing 65 through which the bolt shank 61b is inserted, a rubber washer 67, and a washer 69. The rubber packing 65 and the rubber washer 67 are made of an elastic material (rubber) and are elastically deformable in the thickness direction (the axial direction of the bolt shank 61b).

[0037] As shown in Figures 3, 4, and 7, the connector attachment portion 49 of the weight part 35 has a bolt groove 71 for receiving the bolt shank 61b of the connecting bolt 61, and a bolt head hole 73 for receiving the bolt head 61a. The width of the bolt groove 71 is smaller than the diameter of the bolt head 61a. The bolt groove 71 is a U-shaped cross-sectional groove that opens to the top surface 39 and has a depth direction extending in the vertical direction, and extends in the longitudinal direction of the weight part 35. One end of the bolt groove 71 opens to the convex end surface 45, and the other end of the bolt groove 71 opens to the inner wall surface of the bolt head hole 73. In other words, the bolt groove 71 connects the convex end surface 45 and the bolt head hole 73. The bolt head hole 73 is a cylindrical, bottomed hole that opens to the top surface 39 and has an axial direction extending in the vertical direction.

[0038] The connector attachment portion 51 of the weight component 35 includes a bolt groove 75 that accommodates the bolt shank 61b of the connecting bolt 61 and a nut hole 77 that accommodates the nut 63 attached to the tip of the bolt shank 61b. The width of the bolt groove 75 is smaller than the diameters of the nut 63, rubber washer 67, and washer 69. The bolt groove 75 opens to the top surface 39, has a U-shaped cross section with its depth extending vertically, and extends in the longitudinal direction of the weight component 35. One end of the bolt groove 75 opens to the recessed end surface 47, and the other end opens to the inner wall surface of the nut hole 77. In other words, the bolt groove 75 connects the recessed end surface 47 and the nut hole 77. The nut hole 77 is a generally rectangular parallelepiped hole formed at the corner between the top surface 39 and the outer peripheral surface 34, and is open to both the top surface 39 and the outer peripheral surface 34.

[0039] 7(a) and 7(b), at the connection portion between the weight components 35, 35, the weight components 35, 35 are arranged with their convex end faces 45 and concave end faces 47 facing each other, and the convex end faces 45 fit into the concave end faces 47. Then, the connector 37 is inserted into the connector mounting portions 49, 51 from above so as to straddle the two weight components 35, 35. At this time, the bolt head 61a is inserted into the bolt head hole 73, and the bolt shank 61b is inserted across the two bolt grooves 71, 75. The nut 63, washer 69, and rubber washer 67 previously attached to the bolt shank 61b are inserted into the nut hole 77, and the rubber packing 65 is inserted between the opposing convex end faces 45 and concave end faces 47. After the connector 37 is inserted in this manner, the nut is tightened with a predetermined tightening torque, which compresses the rubber packing 65 and rubber washer 67 by a predetermined amount in the thickness direction, connecting the two weight components 35, 35 together.

[0040] As shown in Figure 7(a), the groove width of bolt grooves 71, 75 is larger than the thickness of bolt shank 61b. The groove width of bolt grooves 71, 75 is, for example, 1.5 to 2.5 times the diameter of bolt shank 61b. Furthermore, since bolt head 61a is spherical and housed in cylindrical bolt head hole 73, in a plan view, bolt head 61a rotates horizontally within bolt head hole 73, allowing bolt shank 61b to change direction within bolt grooves 71, 75. With this configuration, the play of bolt shank 61b within bolt grooves 71, 75 allows for misalignment of the positions and orientations of bolt shank 61b, bolt grooves 71, and bolt grooves 75 relative to each other.

[0041] Therefore, the positional relationship between the weight components 35 connected by the connecting bolts 61 can be adjusted by the play of the connecting bolts 61. Specifically, as illustrated in FIGS. 8( a) and 8(b), the relative orientation of the connected weight components 35, 35 in a plan view can be adjusted, and the size of the gap between the opposing convex end surface 45 and concave end surface 47 can also be adjusted. This makes it possible to adjust the number of weight components 35 included in the temporary weight 30, the size of the gap between the weight components 35, and the orientation of each weight component 35, and as a result, the diameter of the temporary weight 30 can be changed. Note that, to fill the gap between the convex end surface 45 and the concave end surface 47, a rubber packing 65 of an appropriate thickness may be selectively employed, or an appropriate number of rubber packings 65 may be stacked.

[0042] In this way, the diameter of the temporary weight 30 can be changed using a single type of weight component 35, making it possible to accommodate caissons 1 of different diameters and highly versatile. The weight component 35 of this embodiment can accommodate all so-called "slim caissons," for example, those with diameters of 6 to 8 meters. For example, a temporary weight 30 applicable to a caisson with a diameter of 6 meters can be constructed by arranging 14 weight components 35 circumferentially, or a temporary weight 30 applicable to a caisson with a diameter of 8 meters can be constructed by arranging 19 weight components 35 circumferentially. Furthermore, differences in the arrangement of the weight components 35 can be absorbed by the play of the bolt shafts 61b within the bolt grooves 71, 75, so that the weight components 35 can be appropriately connected to each other using the connectors 37 regardless of the diameter of the temporary weight 30.

[0043] The pneumatic caisson construction method of this embodiment is carried out using the temporary weights 30 as described above. The pneumatic caisson construction method of this embodiment includes a weight installation process in which the temporary weights 30 are installed on the side walls 5, a subsidence process in which the ground G is excavated in the excavation work chamber 9 (FIG. 1) after the weight installation process to subside the caisson 1, a weight removal process in which the temporary weights 30 on the side walls 5 are removed after the subsidence process, and a side wall addition process in which a new lot of side walls 5 is constructed on top of the side walls 5 after the weight removal process. By repeating these processes, the caisson 1 is submerged to the planned depth. Each process will be described below.

[0044] [Weight installation process] 2, in the weight installation process, a plurality of weight components 35 are installed around the entire circumference of the annular space 33 on the upper end surface 5a of the side wall 5. After that, all of the weight components 35 are endlessly connected in the circumferential direction by connectors 37, and a closed annular temporary weight 30 is completed on the upper end surface 5a.

[0045] Here, the operation of connecting weight components 35 together using connector 37 will be described with reference to Figure 7. First, of the weight components 35 lined up circumferentially on top end face 5a, one weight component 35 to be connected (referred to as "weight component 35A") is slightly lifted by a lifting device so that it is slightly suspended above top end face 5a. Then, weight component 35A is slightly moved so that it moves slightly away from the adjacent weight component 35 (referred to as "weight component 35B") to which it is to be connected. This widens the gap between convex end face 45 of weight component 35A and concave end face 47 of weight component 35B to a size that allows rubber packing 65 to be inserted.

[0046] Next, the connecting bolt 61, to which the rubber packing 65 and rubber washer 67 are attached, is installed so as to straddle the two weight components 35A and 35B. That is, the bolt head 61a is inserted from above into the bolt head hole 73, and the bolt shank 61b is inserted from above into the bolt grooves 71 and 75. The rubber packing 65 is then inserted between the convex end face 45 and the concave end face 47, and the rubber washer 67 is inserted into the nut hole 77. Next, a washer 69 and a nut 63 are attached to the tip of the bolt shank 61b within the nut hole 77, and the nut 63 is tightened. As the nut 63 is tightened, the weight component 35A, which is slightly lifted from the upper end face 5a, gradually moves closer to the weight component 35B, and the rubber packing 65 is gradually crushed between the convex end face 45 and the concave end face 47. When the weight part 35A is displaced to a predetermined position, the tightening of the nut 63 is stopped, and then the weight part 35A is hung down from the lifting device and comes into contact with the upper end surface 5a.

[0047] By repeating this connecting operation for all weight components 35, the annular temporary weight 30 is assembled and completed on the upper end surface 5a. The temporary weights 30 may be constructed in one layer on the upper end surface 5a, or, for example, as shown in FIG. 9, multiple temporary weights 30 may be stacked vertically on the upper end surface 5a. That is, the above-described assembly work for the temporary weights 30 may be repeated the number of layers to construct multiple layers of temporary weights 30 stacked vertically. In this case, each weight component 35 of the upper layer temporary weight 30 is positioned so that it exactly overlaps each weight component 35 of the lower layer temporary weight 30 in a plan view. The weight components 35 are then installed so that the tenons 53 of the lower layer weight components 35 fit into the mortises 57 of the upper layer weight components 35. Therefore, when the weight component 35 is hung down in the assembly work of the second and subsequent tiers of temporary weights 30, the taper of the mortise 57 is guided by the taper of the lower tenon 53, and the weight component 35 is placed on the weight component 35 of the lower tier of temporary weights 30, making it easier to position the weight component 35.

[0048] [Subsidence process] In the subsidence process, as shown in FIG. 1 , an excavator 11 excavates and removes ground G below the bottom slab 3 in the excavation workroom 9. The excavated soil is discharged to the outside via a shaft 13. When the ground G below the bottom slab 3 is removed by excavation, the weight of the caisson 1, temporary weight 30, and rigging causes the caisson 1 to sink while the cutting edge 7 penetrates the ground. The posture of the caisson 1 during sinking is controlled by a predetermined control means so as to maintain a vertical position. In this subsidence process, because the temporary weight 30 is installed on the side wall 5, the weight of the temporary weight 30 increases the sinking force of the caisson 1. Therefore, the possibility of the caisson 1 not having enough sinking force is reduced, and the caisson 1 sinks smoothly.

[0049] [Weight removal process] After the caisson 1 sinks a predetermined depth into the ground G during the subsidence process, the weight removal process is performed. In the weight removal process, the connector 37 of the temporary weight 30 on the upper end surface 5a is removed to separate one weight component 35, and the weight component 35 is lifted and removed from the upper end surface 5a by a lifting device. By repeating this process, all weight components 35 on the upper end surface 5a are removed, i.e., the temporary weight 30 is removed from the upper end surface 5a. The removed and recovered weight components 35 and connector 37 may be reused, for example, in the next weight installation process and subsidence process, or at another pneumatic caisson construction site. Note that, because the subsidence force acting on the caisson 1 is reduced during the weight removal process, the working pressure in the excavation chamber 9 may be lowered to reduce the uplift force before removing the temporary weight 30.

[0050] [Side wall addition process] After the temporary weights 30 are removed from the upper end surface 5a in the weight removal process, the side wall addition process is carried out. In the side wall addition process, an outer formwork 15 and an inner formwork 17 (Fig. 1) are installed on the top of the side wall 5 and concrete is poured, thereby adding a new lot of side wall 5 and increasing the height of the caisson 1. At this time, the reinforcing bars 19a, 19b protruding upward from the upper end surface 5a of the side wall 5 are joined to the new lot of reinforcing bars 19a, 19b using a predetermined joint structure.

[0051] The effects of the pneumatic caisson construction method of this embodiment as described above will be explained below.

[0052] According to the pneumatic caisson construction method of this embodiment, temporary weights 30 are installed on the side walls 5 during the subsidence process, which increases the sinking force of the caisson 1. In particular, for small-diameter caissons 1, the weight relative to the peripheral friction force is small, and the amount of water ballast W that can be held between the side walls 5 and the shaft 13 is also relatively small. Therefore, there are cases where the water ballast W alone is not enough to increase the sinking force of the caisson 1. For such small-diameter caissons 1, the construction method of this embodiment, which uses temporary weights 30, is particularly effective.

[0053] 2(a), the temporary weight 30 is installed on the annular upper end surface 5a of the side wall 5 so as not to protrude horizontally from the upper end surface 5a. With this configuration, the temporary weight 30 is installed in the annular space on the upper end surface 5a, which would have been hardly used in the past, and does not protrude horizontally from the upper end surface 5a, so the presence of the temporary weight 30 is less likely to interfere with other work in the pneumatic caisson construction method. Among the spaces on the upper end surface 5a, the temporary weight 30 is installed in the annular space 33 between the outer periphery reinforcing bars 19a and the inner periphery reinforcing bars 19b, in particular, so the temporary weight 30 is even less likely to interfere with other work.

[0054] The temporary weight 30 is formed by arranging multiple weight components 35 circumferentially around the entire upper end surface 5a and connecting them endlessly with connectors 37. Because the temporary weight 30 is separable, the weight components 35 can be moved one by one using a lifting device during the weight installation and removal processes. This reduces the capacity required of the lifting device. Furthermore, because the weight components 35 are endlessly connected to each other with connectors 37 and the temporary weight 30 forms a closed annular shape, there is little chance that the weight components 35 will tip inward or outward from the side wall 5. Therefore, there is little chance that the weight components 35 will tip over due to vibrations during the sinking of the caisson 1, and there is little chance that the weight components 35 will damage the piping (air supply pipe 10, concrete pouring pipe 21) or the reinforcing bars 19a, 19b.

[0055] In other words, even if the connector 37 were omitted from the temporary weight 30, it would still function as a means for increasing the sinking force of the caisson 1. However, by endlessly connecting the weight components 35 with the connector 37, the temporary weight 30 can be stably installed on the upper end surface 5a. The purpose of endlessly connecting the weight components 35 is to prevent the weight components 35 from tipping over, as described above. Therefore, the nuts 63 of the connector 37 do not need to be tightly tightened when connecting the weight components; for example, a worker may tighten the nuts 63 by hand. Furthermore, because the temporary weight 30 forms a ring shape around the entire circumference of the upper end surface 5a, it can apply a uniform sinking force to the caisson 1 in the circumferential direction. Therefore, it can be said that the temporary weight 30 has almost no effect on the posture control of the caisson 1 during sinking.

[0056] Furthermore, as mentioned above, the diameter of the temporary weight 30 can be changed using one type of weight part 35, making it possible to accommodate caissons 1 of different diameters and highly versatile.

[0057] The present invention can be implemented in various forms, including the above-described embodiment, with various modifications and improvements based on the knowledge of those skilled in the art. Furthermore, it is also possible to configure modified examples by utilizing the technical matters described in the above-described embodiment. The configurations of the respective embodiments may be used in appropriate combination.

[0058] For example, the temporary weights 30 are not limited to those that exist over the entire circumference of the upper end surface 5a of the side wall 5, but may exist over a portion of the circumferential direction of the upper end surface 5a. Furthermore, a plurality of such temporary weights 30 that exist over a portion of the circumferential direction on the upper end surface 5a may be arranged in the circumferential direction. In this case, it is preferable that the temporary weights 30 are arranged evenly in the circumferential direction.

[0059] Furthermore, although the weight component 35 of the embodiment can be used for so-called "slim caissons" in general, for example, those with a diameter of 6 to 8 m, the present invention is not limited to this. For example, by enlarging or reducing the weight component 35 and the connector 37 in a similar shape, it is possible to construct a temporary weight 30 that can be used for caissons with a larger or smaller diameter range. [Explanation of symbols]

[0060] 1...caisson, 3...bottom slab, 5...side wall, 5a...upper end surface, 9...excavation work chamber, 19a...periphery reinforcing bar, 19b...inner periphery reinforcing bar, 30...temporary weight, 35, 35A, 35B...weight parts, 37...connector, 61...connecting bolt, 71...bolt groove, 75...bolt groove, G...ground.

Claims

1. A pneumatic caisson construction method in which a caisson having a bottom plate and a cutting edge surrounding a working chamber for excavating the ground, and a cylindrical side wall that is successively added onto the bottom plate, is lowered into the ground, A subsidence step is provided in which the ground is excavated in the working chamber and the caisson is submerged. In the subsidence step, a temporary weight is installed on the upper end surface of the side wall.

2. 2. The pneumatic caisson construction method according to claim 1, wherein the weight has a plurality of weight parts arranged circumferentially around the entire circumference on the upper end surface and connected endlessly via predetermined connecting devices.

3. The pneumatic caisson construction method according to claim 2, wherein the weight is installed on the upper end surface so as not to protrude horizontally from the upper end surface.

4. 4. The pneumatic caisson construction method according to claim 3, wherein the weight is installed in the space between the outer reinforcing bars protruding upward from the upper end surface and the inner reinforcing bars.

5. a weight installation step of installing the weight on the upper end surface before the lowering step; The sinking step; a weight removing step of removing the weight from the upper end surface after the lowering step; a sidewall adding step of constructing the sidewall of a new lot by adding it onto the upper end surface after the weight removing step; The pneumatic caisson construction method according to claim 1, comprising:

6. A pneumatic caisson weight component for constructing a temporary weight to be installed on a caisson in a pneumatic caisson construction method in which a caisson having a bottom plate and cutting edge surrounding a working chamber for excavating the ground, and cylindrical side walls that are successively added on top of the bottom plate, is lowered into the ground, When the nozzle is placed on the upper end surface of the side wall with its longitudinal direction directed in the circumferential direction of the side wall, the nozzle has a shape in a plan view that does not protrude horizontally from the upper end surface, A weight component for a pneumatic caisson, provided at both ends in the longitudinal direction and having bolt grooves through which bolts for connecting to other weight components installed adjacently in the circumferential direction on the upper end surface are inserted.

7. A weight for a pneumatic caisson comprising a plurality of weight parts for a pneumatic caisson according to claim 6 connected via bolts, A weight for a pneumatic caisson, in which the positional relationship between the weight parts for the pneumatic caisson connected by the bolts can be adjusted by the play of the bolts within the bolt grooves.

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