Construction method of caisson and bottom structure of caisson

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 technology]

[0002] In the pneumatic caisson method, a cone-shaped soil center is constructed on the ground, and the soil center is used as the inner formwork to construct the bottom of a concrete caisson. After that, the soil that forms the soil center is discharged from a hole in the bottom plate of the caisson, and a cylindrical cutting edge and a working chamber surrounded by the cutting edge are formed on the underside of the bottom plate of the caisson. In the conventional pneumatic caisson construction method, after the ground is leveled, high-quality soil and sand are piled up on the ground to construct a soil center (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 119823 / 1983 Summary of the Invention [Problem to be solved by the invention]

[0004] In the conventional caisson construction method described above, it is necessary to level the ground and bring in high-quality soil and sand when constructing a soil center. There is a demand for reducing the construction cost and shortening the construction period of the caisson construction method. The present invention aims to solve the above-mentioned problems, and to provide a method for constructing a caisson and a caisson bottom structure that can reduce the labor required to construct a soil center, reduce construction costs, and shorten the construction period. [Means for solving the problem]

[0005] In order to solve the above-mentioned 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 process for excavating a circular trench in the ground and constructing a soil center surrounded by the excavation trench, and a concrete pouring process for pouring concrete around the soil center to construct the bottom slab and the cutting edge of the caisson. In order to solve the above problem, the second invention is a caisson bottom structure comprising a soil center surrounded by a circular excavation trench excavated in the ground, a cutting edge portion formed along the outer peripheral surface of the soil center, and a bottom slab formed on the soil center. In the present invention, a circular trench is excavated in the ground, and the ground surrounded by the trench is used as a soil center. As a result, when constructing a soil center, it is no longer necessary to transport high-quality soil to the construction site and pile it up in a frustum shape. Therefore, in the present invention, the number of steps required to construct the soil center is reduced, and the construction cost of the caisson bottom structure can be reduced and the construction period can be shortened.

[0006] In the above-mentioned method for constructing a caisson, it is preferable to construct the soil center in the surface layer of ground that has been improved. In the above-mentioned caisson bottom structure, the soil center is preferably constructed in the surface layer of ground that has been improved. In addition, when the ground is improved by constructing compaction piles underground, the upper ends of the compaction piles are placed within the soil center. In this way, when the soil center is improved in the ground, the soil center's bearing capacity against loads from above is increased, which makes it possible to prevent 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 center, the load of the caisson can be distributed to multiple compaction piles via the crushed stone layer, thereby increasing the stability of the caisson. Effect 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 the soil center, which reduces the labor required to construct the soil center, thereby reducing the construction costs of the caisson and shortening the construction period. [Brief description of the drawings]

[0008] [Figure 1] FIG. 2 is a cross-sectional view showing a caisson bottom according to an embodiment of the present invention. [Diagram 2] A cross-sectional view showing a ground improvement process in a caisson construction method according to an embodiment of the present invention. [Diagram 3] A cross-sectional view showing an excavation process in a caisson construction method according to an embodiment of the present invention. [Figure 4] FIG. 2 is a cross-sectional view showing the soil center shaping process in the caisson construction method according to an embodiment of the present invention. [Diagram 5] A cross-sectional view showing the concrete pouring process in a caisson construction method according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail with reference to the accompanying drawings. Fig. 1 is a cross-sectional view showing the bottom of a caisson according to an embodiment of the present invention. Fig. 5 is a cross-sectional view showing a concrete pouring step in a method for constructing a caisson according to an embodiment of the present invention. In this embodiment, as shown in FIG. 1, a method for constructing a caisson 1 in a pneumatic caisson construction method and a bottom structure 10 of the caisson 1 will be described. The caisson 1 of this embodiment is a foundation member made of reinforced concrete and installed in the ground G. As shown in Figure 5, the bottom structure 10 of the caisson 1 in this embodiment comprises a pyramidal truncated soil center 20, a cylindrical cutting edge portion 11 formed along the outer peripheral surface of the soil center 20, and a bottom slab 12 formed on the soil center 20.

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

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

[0012] [Drilling process] FIG. 3 is a cross-sectional view showing an excavation step in a method for constructing a caisson according to an embodiment of the present invention. As shown in Fig. 3, in the excavation process, an excavation trench 2 is excavated in a ring shape in the ground surface GL on the outer periphery of the construction area S. In this embodiment, the outer periphery of the excavation trench 2 is formed perpendicular to the ground surface GL. In addition, the inner periphery of the excavation trench 2 is inclined with respect to the ground surface GL so as to enter the inner side of the ring-shaped excavation trench 2 from the lower end toward the upper end. When the excavation trench 2 is formed in the ground G, a pyramidal truncated soil center 20 is constructed surrounded by the excavation trench 2. In this manner, the soil center 20 of the present embodiment is formed by digging into the ground GL without filling the ground GL with soil. The soil center 20 is formed in the surface layer of the improved ground G, and the upper ends of a plurality of compaction piles K are arranged inside the soil center 20. In other words, the entire soil center 20 is improved in the ground.

[0013] [Sand center shaping process] FIG. 4 is a cross-sectional view showing the soil center shaping process in the caisson construction method according to an embodiment of the present invention. 4, in the soil centering shaping process, soil is applied to the outer peripheral surface of the soil centering 20 to adjust the inclination angle of the inclined surface of the soil centering 20. In addition, a crushed stone layer 21 is formed on the upper surface of the soil centering 20.

[0014] [Concrete pouring process] 5, in the concrete pouring process, a steel formwork 22 is placed along the surface of the soil center 20 and the inner surface of the excavation trench 2, and reinforcing bars (not shown) are placed inside the formwork 22. Concrete is then poured into the formwork 22 to form the cutting edge 11 and the bottom slab 12. This completes the construction of the bottom structure 10 of the caisson 1. Next, the soil forming the soil center 20 is discharged to the outside of the caisson 1 through the hole 14 formed in the bottom slab 12. As a result, a working chamber 15 surrounded by the cutting edge 11 and the bottom slab 12 is formed inside the bottom structure 10, as shown in FIG.

[0015] [Caisson sinking process] In the caisson sinking 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 excavating the ground G in 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 13 is formed on the upper surface of the base slab 12. In this manner, the caisson 1 is extended upward and is lowered into the ground.

[0016] In the above-described construction method of the caisson 1 and the bottom structure 10 of the caisson 1, as shown in Figure 5, the ground surface GL is excavated to construct the soil center 20 (see Figure 3), which reduces the labor required to construct the soil center 20, thereby reducing the construction cost of the bottom structure 10 of the caisson 1 and shortening the construction period. In addition, the soil center 20 of this embodiment is formed from the surface layer of the improved ground G, and has a large bearing capacity against loads from above, so that when the caisson 1 is constructed, it is possible to prevent the caisson 1 from tilting or sinking. In addition, in this embodiment, a crushed stone layer 21 is formed on the upper surface of the soil center 20, 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 a load from above is greater in the outer periphery of the construction area S than in the center. 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 prevent the caisson 1 from tilting when it is lowered, while keeping down the construction cost and construction period of the ground improvement work. Also, it is possible to prevent the outer periphery of the soil center 20 from collapsing due to arc sliding.

[0017] Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and can be appropriately modified without departing from the spirit of the present invention. In this embodiment, as shown in Figure 5, the soil center 20 is formed in a quadrangular pyramid shape, and the cutting edge portion 11 of the caisson 1 is formed in a quadrangular cylindrical shape, but the shapes of the soil center 20 and the cutting edge portion 11 are not limited. In this embodiment, as shown in FIG. 2, the ground G is improved by constructing compaction piles K, but the method of improving the ground is not limited thereto. In this embodiment, as shown in FIG. 4, the crushed stone layer 21 is provided on the upper surface of the soil center 20, but the crushed stone layer 21 does not necessarily have to be provided on the upper surface of the soil center 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 Work Room 20 Earth and Sand 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, comprising: an excavation step of excavating a circular trench in the ground and constructing a soil center surrounded by the excavation trench; A method for constructing a caisson, comprising a concrete pouring step of pouring concrete around the soil center to construct the bottom plate and the cutting edge portion of the caisson.

2. 2. A method for constructing a caisson as described in claim 1, characterized in that the soil center is constructed in the surface layer of ground that has been improved.

3. The ground has been improved by constructing compaction piles in the ground, 3. The method of claim 2, wherein the upper end of the compaction pile is disposed within the soil center.

4. A method for constructing a caisson according to claim 3, comprising the steps of: A method for constructing a caisson, comprising forming a layer of crushed stone on the upper surface of the soil center.

5. A soil center surrounded by a circular excavation trench on the ground, A cutting edge portion formed along an outer peripheral surface of the soil center; A caisson bottom structure comprising: a bottom slab formed on the soil center.

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

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