Caisson construction method

Abstract

To provide a caisson construction method capable of improving adhesion between the cutting edge fitting of a caisson installed at a cutting edge portion and a concrete base.SOLUTION: The caisson construction method includes the following steps: setting, to a cutting edge portion S1, a steel caisson cutting edge fitting 10 that includes an annular outer peripheral frame portion 10a and an annular inner peripheral frame portion 10b that is connected therewith at the bottom, and opens at the top, and in which a groove V, which is concave when viewed from the internal space, is formed extending in the circumferential direction, and tapers outwards towards the bottom end; lowering caisson bodies S2, S3, and S4 constructed on top of the cutting edge portion S1, which has the cutting edge fitting 10 to a predetermined depth and installing the same; and after the sinking, pouring concrete base C into the bottom of the hollow interior to the thickness of covering the groove V formed in the inner peripheral frame portion 10b.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a caisson construction method. [Background technology]

[0002] Concrete or steel caissons are used to construct underwater or underground structures such as bridge piers and breakwaters. Caissons are cylindrical structures with a rectangular or circular horizontal cross section. The caisson method is a construction method for building foundation structures by excavating the ground inside the hollow caisson body, causing it to sink, and then repeatedly constructing the caisson body on top of it.

[0003] Foundation structures using caissons have a larger cross section than other foundation structures, which means they have greater rigidity and less displacement, and they can be expected to have greater horizontal resistance and vertical support.

[0004] The cutting edge formed at the deepest part of the caisson body, which is sunk into the ground by excavating the ground vertically, is protected by a cutting edge metal fitting (caisson cutting edge metal fitting) made of steel plate because loads are concentrated on the cutting edge when the caisson sinks. This cutting edge metal fitting is composed of an annular outer frame and an inner frame. The inner frame is tapered, widening outward toward the bottom end, and the surface of the inner frame that comes into contact with the ground is made smooth to prevent resistance when the caisson sinks.

[0005] Regarding caissons, for example, the technology described in Patent Document 1 (Japanese Patent No. 6423045) is known. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6423045 Summary of the Invention [Problem to be solved by the invention]

[0007] Now, because the inner periphery of the caisson's nose hardware has a smooth surface, it is uncertain how well it will adhere to the concrete poured after installation. In the open caisson construction method (a construction method in which the hollow interior of the caisson body is gradually lowered while being excavated), excavation is carried out under atmospheric pressure, and once the specified depth is reached, the base concrete is poured into the bottom of the hollow interior. In this case, if the base concrete does not become integrated with the caisson's nose hardware, there is a risk that groundwater will flow into the caisson through the gap between the base concrete and the nose hardware.

[0008] For this reason, improving the adhesion between the cutting edge hardware and the base concrete is an issue.

[0009] The present invention was made based on the above-mentioned technical background, and aims to provide a technology that can improve the adhesion between the caisson cutting edge hardware installed at the cutting edge portion and the base concrete. [Means for solving the problem]

[0010] In order to solve the above problem, the caisson construction method of the invention described in claim 1 is characterized in that a steel caisson cutting edge fitting consisting of a ring-shaped outer frame and a ring-shaped inner frame connected to the outer frame at its lower end, open at the top, with a groove that extends circumferentially and is concave when viewed from the internal space, and tapered toward the lower end, is installed at the cutting edge, and the caisson body is constructed above the cutting edge where the caisson cutting edge fitting is installed, while it is lowered into the ground to a predetermined depth, and a base concrete is poured at the bottom of the hollow interior after the sunk to a thickness that will enclose the groove formed in the inner frame.

[0011] The caisson construction method of the invention described in claim 2 is characterized in that, in the invention described in claim 1, soil and sand adhering to the surface of the inner frame portion facing the internal space are removed prior to pouring the base concrete.

[0012] The caisson construction method of the invention described in claim 3 is characterized in that, in the invention described in claim 1 above, soil and sand adhering to the groove formed in the inner frame portion are removed prior to pouring the base concrete. [Effects of the Invention]

[0013] According to the present invention, the poured base concrete is filled into the groove, causing the base concrete to become caught in the groove, thereby improving the adhesion between the caisson cutting edge hardware installed at the cutting edge and the base concrete, and improving the water-tightness of the boundary surface. [Brief explanation of the drawings]

[0014] [Figure 1] An explanatory diagram showing an outline of the construction procedure for a caisson using a caisson cutting edge fitting according to one embodiment of the present invention. [Figure 2] 1 is a cross-sectional view showing a caisson cutting edge fitting according to one embodiment of the present invention. [Figure 3] This is a cross-sectional view showing the poured base concrete and the groove formed in the inner frame of the caisson cutting edge fitting. [Figure 4] A cross-sectional view showing a modified example of a caisson cutting edge fitting according to one embodiment of the present invention. [Figure 5] A cross-sectional view showing another modified example of a caisson cutting edge fitting according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the drawings for explaining the embodiment, the same components are generally designated by the same reference numerals, and repeated description thereof will be omitted.

[0016] FIG. 1 is an explanatory diagram showing an outline of the construction procedure for a caisson that uses the caisson nodule fitting of this embodiment.

[0017] The caisson construction method in this embodiment is called the open caisson construction method, in which the hollow interior of a cylindrical caisson body constructed and installed on the ground is excavated by machine (or by human power) and the caisson body is gradually lowered, and once it reaches a specified depth, the caisson is used as a foundation structure.

[0018] Specifically, after installing sinking anchors (not shown) that act as a counterforce for sinking the caisson body S, the ground G is leveled and a countersink P is installed. Then, a cutting edge metal fitting (caisson cutting edge metal fitting) 10, which consists of an annular outer peripheral frame portion 10a and an inner peripheral frame portion 10b that are connected at their lower ends and open at the top, is installed at the sinking point and concrete is poured to construct the cutting edge portion S1, which is the caisson body S that will be located at the deepest part of the caisson (Figure 1(a)). Details of the cutting edge metal fitting will be described later.

[0019] Once the cutting edge S1 has been constructed, the press-in equipment is installed and the sinking anchor is connected to a press-in device (not shown). After removing the countersink P, a clamshell (excavator) T is used to excavate the ground inside the hollow, while the sinking anchor begins to be pressed in using the reaction force. Once the cutting edge S1 has been sunk to the specified depth, inner and outer formworks are installed above the cutting edge S1, rebar is placed between the inner and outer formworks, and concrete is poured to construct the next batch of caisson bodies S2 (Figure 1(b)).

[0020] The caisson body S is pressed in while excavating, and the next batch of caisson bodies S is constructed on top of that caisson body S, and this is repeated; in the illustrated example, three caisson bodies S2, S3, and S4 are constructed on top of the cutting edge S1, and once they have reached the specified depth and are set down, base concrete C is poured into the bottom of the hollow interior, as shown in Figure 1(c). Then, as shown in Figure 1(d), contact grout R is injected into the gap between the outer surface of the caisson body S and the ground, completing the construction of the caisson, which is the foundation structure.

[0021] Now, the steel cutting edge fitting 10 installed at the cutting edge S1 located at the deepest part of the cylindrical caisson body S sunk into the ground comprises an outer peripheral frame 10a that is annular in plan view, and an inner peripheral frame 10b that is also annular in plan view, as shown in Figure 2. The outer peripheral frame 10a and the inner peripheral frame 10b are connected to each other at their lower ends and are open at the top, with the inner peripheral frame 10b tapering outward toward the lower end.

[0022] In addition, anchor rebars W are appropriately placed within the space formed by the outer frame portion 10a and the inner frame portion 10b to adhere to the poured concrete to increase its strength and to integrate the cutting edge fitting 10 with the concrete.

[0023] The inner circumferential frame portion 10b is formed with a recessed portion when viewed from the interior space surrounded by this inner circumferential frame portion 10b, i.e., a groove portion V. In this embodiment, the groove portion V extends substantially horizontally in the circumferential direction and is formed continuously around the entire circumference of the inner circumferential frame portion 10b.

[0024] To explain the groove V formed in the inner peripheral frame portion 10b in detail, the inner peripheral frame portion 10b comprises an upper inner frame 10b-1 located on the upper side and a lower inner frame 10b-2 provided below the upper inner frame 10b-1 with a gap therebetween, and a groove steel material 10b-3 forming the groove V is attached between the upper inner frame 10b-1 and the lower inner frame 10b-2. In the case shown in Figure 2, the groove steel material 10b-3 is a plate-shaped steel material 10b-3a attached so as to straddle the upper inner frame 10b-1 and the lower inner frame 10b-2.

[0025] In this embodiment, the groove V described above is formed in the tip hardware 10, and the base concrete C described above is poured to a thickness that will enclose the groove V. When poured in this manner, as shown in Figure 3, the base concrete C is filled into the groove V, causing it to become caught in the groove V, improving the adhesion between the tip hardware 10 and the base concrete C. This improves the watertightness of the interface between the tip hardware 10 and the base concrete C, making it more difficult for groundwater to flow into the caisson from between the base concrete C and the tip hardware 10.

[0026] If the base concrete C is poured while soil is still attached to the inner circumferential frame portion 10b, the adhesion between the cutting edge hardware 10 and the base concrete C will be poor. Therefore, prior to pouring the base concrete C, it is desirable to use an ultrasonic measuring device or the like to check the presence and location of soil on the surface of the inner circumferential frame portion 10b facing the internal space (i.e., the surface to which the base concrete C will be attached) (adhered soil confirmation step), and then remove the soil using a soil removal device or the like (soil removal step).

[0027] Furthermore, as mentioned above, since the base concrete C becomes caught in the groove portion V, improving the adhesion between the cutting edge hardware 10 and the base concrete C, the process of checking for adhering soil and the process of removing soil may be performed only on the groove portion V, rather than on the wide area of ​​the surface facing the internal space of the inner frame portion 10b.

[0028] The invention made by the inventor has been specifically described above based on the embodiments, but the embodiments disclosed in this specification are illustrative in all respects and are not limited to the disclosed technology. In other words, the technical scope of the present invention should not be interpreted restrictively based on the description of the above embodiments, but should be interpreted solely in accordance with the claims, and includes technologies equivalent to the technologies described in the claims and all modifications that do not deviate from the gist of the claims.

[0029] For example, the groove steel material 10b-3 is not limited to the plate steel material 10b-3a, and various steel materials capable of forming the groove V can be used. For example, as shown in Fig. 4, an angle steel 10b-3b attached between the upper inner frame 10b-1 and the lower inner frame 10b-2, or a channel steel 10b-3c attached between the upper inner frame 10b-1 and the lower inner frame 10b-2, as shown in Fig. 5, can be used. When the angle steel 10b-3b or the channel steel 10b-3c is used, it is attached between the upper inner frame 10b-1 and the lower inner frame 10b-2 with the recess facing the internal space, as shown in the figure.

[0030] Furthermore, the grooves V formed in the inner peripheral frame portion 10b do not have to be substantially horizontal, and do not have to be formed continuously around the entire circumference of the inner peripheral frame portion 10b. However, if they are formed substantially horizontally and continuously around the entire circumference, the adhesion between the cutting edge metal fitting 10 and the base concrete C will be improved, and the watertightness of the boundary surface will be further improved.

[0031] In this embodiment, four tiers of caisson bodies S2, S3, and S4 are constructed above the cutting edge portion S1, which is the deepest caisson body, but the number of tiers of caisson bodies S constructed is not limited to four. [Industrial Applicability]

[0032] The caisson construction method according to the present invention can be applied to the construction of underwater structures such as bridge piers, quays, and breakwaters, as well as various underground structures. [Explanation of symbols]

[0033] 10. Cutting edge fittings (caisson cutting edge fittings) 10a Outer frame 10b Inner peripheral frame 10b-1 Upper inner frame 10b-2 Lower inner frame 10b-3 Steel material for grooves 10b-3a Plate steel (groove steel) 10b-3b Angle steel (steel material for grooves) 10b-3c Channel steel (steel for grooves) C. Base concrete G Ground P dish plate R Contact Grout S caisson body S1 Cutting edge (caisson body) S2, S3, S4 caisson body V groove W anchor rebar

Claims

1. A steel caisson cutting edge metal fitting is installed on the cutting edge, the steel caisson cutting edge metal fitting comprising an annular outer peripheral frame portion, an annular inner peripheral frame portion connected to the outer peripheral frame portion at its lower end, having an open upper portion, a groove portion that is concave when viewed from the internal space, extending in the circumferential direction, and tapering outward toward the lower end, The caisson is constructed on the upper part of the cutting edge portion where the caisson cutting edge metal fitting is installed, and is then lowered into the ground to a predetermined depth. A base concrete is poured onto the bottom surface of the hollow interior after sinking to a thickness that allows the groove formed in the inner peripheral frame portion to be included. This is a caisson construction method characterized by:

2. Prior to pouring the base concrete, remove soil and sand adhering to the surface of the inner peripheral frame portion facing the internal space.

2. The caisson construction method according to claim 1.

3. Prior to pouring the base concrete, remove soil and sand adhering to the groove formed in the inner peripheral frame portion.

2. The caisson construction method according to claim 1.

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