Caisson construction method and caisson bottom structure

Abstract

To provide a construction method of a caisson capable of reducing installation cost and shortening an installation period with fewer construction steps upon construction of a sediment arch center.SOLUTION: A construction method of a concrete caisson 1 comprises: an excavation step of excavating an excavation groove 2 in an annular shape in the ground GL to construct a sediment arch center 20 surrounded by the excavation groove 2; and a concrete installation step of installing concrete around the sediment arch center 20 to construct a bottom slab 12 of the caisson 1 and a cutting-edge part 11.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to a method for constructing a caisson and a caisson bottom structure.

Background Art

[0002] In the pneumatic caisson method, a frustum-shaped earth and sand center is constructed on the ground, and the earth and sand center is used as an inner formwork to construct the bottom of a concrete caisson. Then, the earth and sand forming the earth and sand center are discharged from the holes provided in the bottom plate of the caisson, and a cylindrical cutting edge portion and a working chamber surrounded by the cutting edge portion are formed below the bottom plate of the caisson. In the conventional pneumatic caisson method, after leveling the ground, good-quality earth and sand are piled up on the ground to construct an earth and sand center (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the above-described conventional caisson construction method, when constructing an earth and sand center, it is necessary to level the ground and carry in good-quality earth and sand. And it has been demanded to reduce the construction cost of the caisson construction method and shorten the construction period. An object of the present invention is to solve the above-described problems, provide a caisson construction method and a caisson bottom structure that can reduce the number of man-hours when constructing an earth and sand center, reduce the construction cost, and shorten the construction period.

Means for Solving the Problems

[0005] To solve the aforementioned problems, the first invention is a method for constructing a concrete caisson having a cylindrical cutting edge formed at its lower end, comprising: an excavation step of excavating an annular trench in the ground and constructing a soil center surrounded by the trench; and a concrete pouring step of pouring concrete around the soil center to construct the base plate and the cutting edge of the caisson. To solve the aforementioned problems, the second invention is a caisson bottom structure comprising a soil center surrounded by an annularly excavated trench in the ground, and formed along the outer surface of the soil center Concrete The cutting edge and formed on the soil centering Concrete It has a base plate and In this invention, a circular trench is excavated in the ground, and the ground surrounded by the trench is used as a soil centering. As a result, in this invention, when constructing the soil centering, it is not necessary to transport high-quality soil to the construction site and fill it in a truncated shape. Therefore, in this invention, the number of man-hours required to construct the soil centering is reduced, the construction cost of the caisson bottom structure can be reduced, and the construction period can be shortened.

[0006] In the method for constructing the caisson described above, it is preferable to construct the soil center on the surface layer of the ground that has been improved. In the caisson bottom structure described above, it is preferable that the soil centering be constructed on the surface layer of the ground that has been improved. Furthermore, if the ground is improved by constructing compaction piles underground, the upper end of the compaction piles shall be placed within the soil centering. Thus, when the soil centering is improved, the bearing capacity of the soil centering against loads from above increases, which prevents the caisson from tilting or sinking when it is constructed. Furthermore, if a crushed stone layer is formed on the upper surface of the soil centering, the load of the caisson can be distributed to multiple compaction piles via the crushed stone layer, thereby increasing the stability of the caisson. [Effects of the Invention]

[0007] In the caisson construction method and caisson bottom structure of the present invention, the ground surrounded by the excavation trench is used as a soil centering, thus reducing the number of man-hours required to construct the soil centering, thereby lowering the construction cost of the caisson and shortening the construction period. [Brief explanation of the drawing]

[0008] [Figure 1] This is a cross-sectional view showing the bottom of a caisson according to an embodiment of the present invention. [Figure 2] This is a cross-sectional view showing the ground improvement step in a caisson construction method according to an embodiment of the present invention. [Figure 3] This is a cross-sectional view showing the excavation process in a method for constructing a caisson according to an embodiment of the present invention. [Figure 4] A cross-sectional view showing the soil centering and shaping process in a caisson construction method according to an embodiment of the present invention. [Figure 5] This is a cross-sectional view showing the concrete pouring process in a caisson construction method according to an embodiment of the present invention. [Modes for carrying out the invention]

[0009] Embodiments of the present invention will be described in detail with reference to the drawings as appropriate. Figure 1 is a cross-sectional view showing the bottom of a caisson according to an embodiment of the present invention. Figure 5 is a cross-sectional view showing the concrete pouring process in the caisson construction method according to an embodiment of the present invention. In this embodiment, as shown in Figure 1, the method for constructing the caisson 1 in the pneumatic caisson method and the bottom structure 10 of the caisson 1 will be described. In this embodiment, the caisson 1 is a reinforced concrete foundation member installed within the ground G. As shown in Figure 5, the bottom structure 10 of the caisson 1 in this embodiment comprises a truncated pyramidal soil centerer 20, a cylindrical cutting edge portion 11 formed along the outer circumferential surface of the soil centerer 20, and a bottom plate 12 formed on the soil centerer 20.

[0010] The soil centering tool 20 is used when constructing the bottom structure 10 of the caisson 1, and is removed after the initial construction, which includes the cutting edge 11, bottom plate 12, and surrounding wall 13. When the soil centering 20 is removed from the bottom structure 10 of the caisson 1, a working chamber 15 is formed at the bottom of the caisson 1 by a space surrounded by the cutting edge 11 and the bottom plate 12, as shown in Figure 1. In the pneumatic caisson method, compressed air is sent into a working chamber 15 formed at the bottom of the caisson 1 to prevent groundwater from flowing into the working chamber 15, while excavating the ground within the working chamber 15 and sinking the caisson 1.

[0011] Next, the method for constructing the aforementioned caisson 1 will be explained. [Soil improvement process] Figure 2 is a cross-sectional view showing the ground improvement process in a caisson construction method according to an embodiment of the present invention. As shown in Figure 2, prior to the ground improvement process, steel sheet piles P are first installed within the ground G so as to surround the construction area S of caisson 1 (see Figure 1). Furthermore, in the ground improvement process, within the ground G surrounded by the steel sheet piles P, multiple compaction piles K are constructed at regular intervals using a static compaction method (sand compaction method) to compact sand and crushed stone, thereby improving the ground G of the construction area S. At this time, each compaction pile K is formed down to the ground level (GL), improving the surface layer of the ground G as well. Furthermore, the compaction piles K constructed on the outer perimeter of the construction area S are formed to a deeper position than the compaction piles K in the center of the construction area S. As a result, the outer perimeter of the construction area S has greater bearing capacity against loads from above than the center.

[0012] [Excavation Process] Figure 3 is a cross-sectional view showing the excavation process in a caisson construction method according to an embodiment of the present invention. As shown in FIG. 3, in the excavation process, an excavation groove 2 is annularly excavated in the ground GL on the outer peripheral part of the construction area S. In the present embodiment, the outer peripheral surface of the excavation groove 2 is formed perpendicular to the ground GL. Further, the inner peripheral surface of the excavation groove 2 is inclined with respect to the ground GL so as to enter the inside of the annular excavation groove 2 from the lower end part toward the upper end part. When the excavation groove 2 is formed in the ground G, an earth and sand center 20 having a frustum of a square pyramid shape surrounded by the excavation groove 2 is constructed. Thus, the earth and sand center 20 of the present embodiment is formed by digging into the ground GL without piling up earth on the ground GL. The earth and sand center 20 is formed in the surface layer part of the ground G whose ground has been improved, and the upper end parts of a plurality of compacted piles K are arranged inside the earth and sand center 20. That is, the entire earth and sand center 20 has been ground-improved.

[0013] [Earth and Sand Center Shaping Process] FIG. 4 is a cross-sectional view showing the earth and sand center shaping process in the caisson construction method according to the embodiment of the present invention. As shown in FIG. 4, in the earth and sand center shaping process, the outer peripheral surface of the earth and sand center 20 is covered with earth and sand to adjust the inclination angle of the inclined surface of the earth and sand center 20. Further, a crushed stone layer 21 is formed on the upper surface of the earth and sand center 20.

[0014] [Concrete Placing Process] As shown in FIG. 5, in the concrete placing process, a steel formwork 22 is arranged along the surface of the earth and sand center 20 and the inner surface of the excavation groove 2, and further, reinforcing bars (not shown) are arranged in the formwork 22. Then, concrete is placed in the formwork 22 to form the blade edge part 11 and the bottom plate 12. Thereby, the bottom structure 10 of the caisson 1 is constructed. Subsequently, the earth and sand forming the earth and sand center 20 is discharged to the outside of the caisson 1 from the hole part 14 formed in the bottom plate 12. Thereby, as shown in FIG. 1, a work chamber 15 surrounded by the blade edge part 11 and the bottom plate 12 is formed inside the bottom structure 10.

[0015] [Caisson Sinking Process] In the caisson settlement process, compressed air is sent into the work chamber 15 through the hole 14 of the caisson 1 to prevent groundwater from flowing into the work chamber 15, while the ground G is excavated within the work chamber 15, causing the bottom of the caisson 1 to sink into the ground. After the bottom of the caisson 1 has sunk to a predetermined depth, a peripheral wall portion 13 is formed on the upper surface of the base plate 12. In this way, the caisson 1 is extended upward while sinking into the ground.

[0016] In the construction method of caisson 1 and the bottom structure 10 of caisson 1 described above, as shown in Figure 5, the soil center 20 is constructed by excavating the ground level (GL) (see Figure 3). This reduces the number of man-hours required to construct the soil center 20, thereby lowering the construction cost of the bottom structure 10 of caisson 1 and shortening the construction period. Furthermore, the soil centering 20 in this embodiment is formed from the surface layer of the ground-improved ground G, and has a large bearing capacity against loads from above, so when the caisson 1 is constructed, it can prevent the caisson 1 from tilting or sinking. Furthermore, a crushed stone layer 21 is formed on the upper surface of the soil centering 20 in this embodiment, and the load of the caisson 1 is distributed to multiple compaction piles K via the crushed stone layer 21, thereby increasing the stability of the caisson 1. Furthermore, in this embodiment, the bearing capacity of the ground G against an upward load is greater in the outer periphery of the construction area S than in the central part. In other words, the bearing capacity of the ground G directly below the cutting edge 11 of the caisson 1 is greater. This makes it possible to reduce the construction cost and period of ground improvement while preventing the caisson 1 from tilting when it is settled. It also prevents the outer periphery of the soil centering 20 from collapsing due to circular sliding.

[0017] Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and can be modified as appropriate without departing from its spirit. In this embodiment, as shown in Figure 5, the soil centerer 20 is formed in the shape of a truncated square pyramid, and the cutting edge portion 11 of the caisson 1 is formed in the shape of a square cylinder, but the shapes of the soil centerer 20 and the cutting edge portion 11 are not limited. In this embodiment, as shown in Figure 2, ground improvement is performed by constructing compaction piles K in the ground G, but the method of ground improvement is not limited to this. In this embodiment, as shown in Figure 4, a crushed stone layer 21 is provided on the upper surface of the soil centering 20, but it is not necessary to provide a crushed stone layer 21 on the upper surface of the soil centering 20. [Explanation of Symbols]

[0018] 1 Caisson 2 Excavation trench 10 Bottom structure 11 Blade mouth part 12 bottom plate 13 Peripheral wall section 14 Hole 15. Workshop 20 Soil Center 21 Crushed stone layer 22 formwork G Ground GL ground K Compaction pile P steel sheet pile S Construction area

Claims

1. A method for constructing a concrete caisson having a cylindrical cutting edge formed at its lower end, An excavation process involves excavating a circular trench in the ground and constructing a soil center surrounded by the trench, A method for constructing a caisson, comprising a concrete pouring step of pouring concrete around the soil center to construct the base slab and the cutting edge of the caisson.

2. The method for constructing a caisson according to claim 1, characterized in that the soil center is constructed on the surface layer of ground that has been improved.

3. The aforementioned ground has been improved by constructing compaction piles underground. The method for constructing a caisson according to claim 2, characterized in that the upper end of the compacted pile is positioned within the soil centering.

4. A method for constructing a caisson according to claim 3, A method for constructing a caisson, characterized by forming a crushed stone layer on the upper surface of the aforementioned soil centering.

5. A soil center surrounded by a circular excavation trench in the ground, A concrete cutting edge formed along the outer surface of the aforementioned soil centerer, A caisson bottom structure characterized by comprising a concrete bottom slab formed on the aforementioned soil centering.

6. The caisson bottom structure according to claim 5, characterized in that the aforementioned soil center is constructed on the surface layer of ground that has been improved.

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