JP2004353217A - Suction foundation construction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a foundation construction method unnecessitating measures such as widening of area by improving earth retaining force even when water depth is shallow and making it possible to realize an economic design. <P>SOLUTION: In the suction foundation construction method, a caisson body provided with a skirt is loaded with a suction load in the condition that the tip end of the skirt is penetrated in the water bottom ground to immerse it down to a specified depth, After that, the upper structure and the lower structure are constructed in sequence at the upper part of the caisson body. When the skirt part is penetrated into the water bottom ground by the suction load, a load large corresponding to the load of the lower structure is actuated (step 3). When the construction of the lower structure is finished, a cut off part is formed right below the bottom slab of the caisson body. Water is injected in the space formed on the inner face of the skirt and a preload 2 is added on the right under water bottom ground of the bottom slab part (step 7). In this case, water is charged as a load equivalent to the upper structure. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a crisp foundation method.
[0002]
[Prior art]
As one type of a construction method for constructing a substructure in water, a crisp foundation construction method as disclosed in Patent Document 1 is known. In this type of foundation method, a cylindrical side wall portion, a bottom plate portion provided at a lower end of the side wall portion, an upper plate portion provided at an upper end of the side wall portion, and extending downward from a lower end of the side wall portion. A caisson body having a skirt is used.
[0003]
When constructing the substructure, a suction load is applied with the tip of the skirt part penetrating into the bottom of the water to sink the caisson body to a predetermined depth. Construction work and superstructure work will be constructed sequentially.
[0004]
However, such a conventional suction foundation method has a technical problem described below.
[0005]
[Patent Document 1]
JP 2000-24066 A
[Problems to be solved by the invention]
That is, in the above-mentioned suction foundation method, at the time of completion of the substructure and the superstructure, in order to minimize the amount of settlement, it is necessary to apply a load acting on the ground at the time of completion as a preload beforehand. Assuming that the load is 3000 tf, the superstructure is 5000 tf, and the substructure is 3000 tf, the necessary suction load is 8000 tf (superstructure 5000 tf + substructure 3000 tf) if the load during use is loaded by suction when the caisson skeleton is penetrated. ).
[0007]
In order to apply a suction load of such a size, for example, if the area of the caisson body is 400 m ² , a water depth of 20 m or more is required, and it is difficult to perform construction at a shallow place, and the ground bearing capacity In order to satisfy the above, the area of the caisson body must be increased.
[0008]
In addition, in the suction foundation method described above, the suction load applied when the caisson body penetrates is preloaded, but since this preload only acts on the skirt, the effect of the supporting force of the bottom slab is expected. It was not possible to do so and the design was uneconomical.
[0009]
The present invention has been made in view of such conventional problems, and an object of the present invention is to improve the ground support force so that measures such as an increase in area can be taken even when the water depth is shallow. An object of the present invention is to provide a suction foundation method which is unnecessary and enables an economical design.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a cylindrical side wall portion, a bottom plate portion provided at a lower end of the side wall portion, an upper plate portion provided at an upper end of the side wall portion, A caisson skeleton having a skirt portion extending downward from the lower end, with the tip of the skirt portion penetrating into the underwater ground, applying a suction load to sink the caisson skeleton to a predetermined depth. Then, in a suction foundation method of sequentially constructing a lower part and an upper part above the caisson frame, the suction load is to be applied to the skirt part in accordance with the load of the lower part, After constructing the substructure on the upper side of the caisson skeleton, after forming a water blocking portion in the underwater ground below the bottom plate portion, introducing a water injection load between the water blocking portion and the bottom plate portion, The bottom plate It was to apply a preload to the sea bed ground below.
[0011]
According to the suction foundation construction method configured in this manner, the suction load corresponds to the load of the substructure, so that the preload is applied to the skirt portion, so that when penetrating the caisson skeleton, the substructure and the superstructure are included. Compared to the case where a preload equivalent to a load is applied, construction can be performed at a shallower water depth, and measures such as enlarging the area of the caisson frame are not required to satisfy the ground support force.
[0012]
Also, in the present invention, after constructing a substructure on the upper side of the caisson body, after forming a water stop portion in the underwater ground below the bottom plate, introducing a water injection load between the water stop portion and the bottom plate, Since the preload is applied to the underwater floor under the bottom slab, the supporting capacity of the bottom slab can be expected.
[0013]
The preload applied to the underwater ground below the bottom slab can be set to a size corresponding to the load of the superstructure.
[0014]
The preload applied to the underwater ground under the bottom slab is a size corresponding to the sum of the weight of the caisson frame, the load of the substructure, and the resistance obtained by adding the peripheral surface resistance of the caisson frame. Can be set to
[0015]
Further, in the present invention, after applying a preload to the undersea ground under the bottom slab, before constructing the superstructure above the substructure, grout material is injected under the bottom slab in place of the water injection load. be able to.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. 1 to 4 show an embodiment of a suction foundation method according to the present invention.
[0017]
In the suction foundation method shown in these figures, a foundation is constructed in water using a caisson frame 18 having a side wall portion 10, a bottom plate portion 12, an upper plate portion 14, and a skirt portion 16.
[0018]
The side wall portion 10 is formed in a cylindrical shape having a closed cross-sectional shape such as a circle, a polygon, and an ellipse. The bottom plate portion 12 is formed at the lower end side of the side wall portion 10 and is formed integrally with the side wall portion 10 so as to close the side wall portion 12. In the case of the present embodiment, the center swells downward. It has a shape.
[0019]
The upper plate portion 14 is on the upper end side of the side wall portion 10, has a flat shape that closes the upper end side of the side wall portion 10, and is formed integrally with the side wall portion 10. Note that the upper plate portion 14 does not necessarily need to have a shape that closes the upper end of the side wall portion 12.
[0020]
The skirt portion 16 is an annular body having the same shape as the side wall portion 10 and extending downward from the lower end of the side wall portion 10 and having an open lower end, and a blade edge portion is provided at the open end. The skirt portion 16 does not necessarily need to be formed in the same shape as the side wall portion 10.
[0021]
The caisson frame 18 having such a shape is manufactured, for example, in a production yard near a construction site of a reinforced concrete foundation. FIG. 4 shows a procedure for constructing the substructure 20 and the superstructure 22 on the caisson body 18 manufactured as a base, and the basic procedure of the present embodiment will be described below according to the procedure. The construction method of the construction method will be described.
[0022]
The caisson skeleton 18 manufactured in the production yard is towed to the construction site, then positioned at a predetermined position, and immersed in water (step 1). When the skirt portion 16 provided at the tip of the caisson frame 18 reaches the underwater ground 24, first, as shown in FIG. 1, the caisson frame 18 is penetrated by its own weight (step 2).
[0023]
When the self-penetration has been completed, a step of reducing the pressure in the skirt portion 16 and applying a suction load to the caisson body 18 to cause the skirt portion 16 to penetrate into the underwater ground 24 by the suction load is performed. (Step 3).
[0024]
The suction penetration at this time is to apply a preload (1) to the skirt portion 16 and correspond to the load of the substructure 20. In this case, the load of the caisson skeleton 18 (self-weight) of 3000Tf, the superstructure 22 5000Tf, lower Engineering 20 is assumed to be 3000Tf, the load of the lower Engineering 20, so 3000Tf, if basic area 400 meters ^2, the 8m It is only necessary to have a water depth, and construction can be performed at a shallower water depth than the conventional method that requires a water depth of 20 m or more in the same basic area.
[0025]
When the skirt portion 16 sinks to a predetermined depth of the underwater ground 24 by applying a suction load (step 4), the application of the suction load is stopped, and then, as shown in FIG. A substructure 20 is constructed on the part 14 (step 5).
[0026]
When the substructure 20 is constructed in this manner, a preload corresponding to the load is applied to the skirt portion 16 in advance, so that the caisson body 18 does not sink due to the construction of the substructure 20.
[0027]
When the construction of the substructure 20 is completed, the water stop portion 26 is formed immediately below the bottom plate portion 12 of the caisson frame 18. The water stopping portion 26 is formed by injecting a viscous agent such as bentonite into the underwater ground 24 surrounded by the skirt portion 16 to form the water stopping portion 26 below the bottom plate portion 12 (step 6).
[0028]
When the water stopping portion 26 is formed, a space defined by the water stopping portion 26, the skirt portion 16, and the bottom plate portion 12 is formed on the inner surface of the skirt portion 16, so that water is injected into this space. Then, a preload (2) based on the water injection load is added to the underwater bottom ground 24 immediately below the bottom plate portion 12 (step 7).
[0029]
The preload (2) that can be added in this case is that the caisson body 18 has a load (self-weight) of 3000 tf, the substructure 20 has 3000 tf, and the peripheral surface resistance is 2000 tf. Can be loaded.
[0030]
In this case, since the load of the superstructure 22 is 5000 tf, at least a load corresponding to the load may be the water injection load. In addition, if the water stopping portion 26 is provided, when the water injection load described later is removed, the water bottom ground 24 is raised, and the effect of the preload (2) due to the water injection load is prevented from being lost.
[0031]
When a predetermined water injection load is applied and a preload (2) is applied to the underwater ground 24 immediately below the bottom slab portion 12, next, as shown in FIG. Material 28 is injected (step 8).
[0032]
The grout material 28 is, for example, mortar, and the grout material 28 is injected into a space defined by the water stop portion 26, the skirt portion 16, and the bottom plate portion 12, and solidified.
[0033]
When the grout material 28 is injected and solidified, a superstructure 22 is constructed above the substructure 20 (step 9), and the construction is completed. When the superstructure 22 is constructed, a preload (1) of 3,000 tf of the skirt portion 16 acts, and a preload (2) of at least 5,000 tf (maximum 8000 tf) acts on the base plate 24 of the bottom plate portion 12. Therefore, the safety against subsidence when constructing the superstructure 22 is extremely high.
[0034]
Now, according to the suction foundation method constructed as described above, the suction load (1) is to be applied to the skirt portion 16 in accordance with the load of the substructure 20, so that when the caisson body 18 penetrates, As compared with the case where a preload equivalent to the load including the lower part 20 and the upper part 22 is applied, the work can be performed even at a shallower water depth, and the area of the caisson frame 18 is increased in order to satisfy the ground support force. Measures are no longer necessary.
[0035]
Further, in the present embodiment, after constructing the substructure 20 on the upper side of the caisson body 18, forming the water stop portion 26 in the underwater ground 24 below the bottom plate portion 12, the water stop portion 26 and the bottom plate portion 12 And a preload (2) corresponding to the load of the superstructure 22 is applied to the water bottom ground 24 under the bottom slab 12, so that the supporting force of the base slab 12 can be expected. . For this reason, the permissible supporting force at all times becomes large, and it becomes safer against settlement.
[0036]
The preload (2) in this case is a value equivalent to the load of the superstructure 22, or the sum of the weight of the caisson frame 18, the load of the lower frame 20, and the peripheral resistance of the caisson frame 18. The force can be set to a size corresponding to the sum of these forces. By applying the preload (2) having such a size, the safety against settlement is further enhanced.
[0037]
【The invention's effect】
As described above in detail, according to the suction foundation method according to the present invention, by improving the ground support force, even when the water depth is shallow, it becomes unnecessary to take measures such as enlarging the area, and economically. Design is also possible.
[Brief description of the drawings]
FIG. 1 is an explanatory view of an initial step of a suction foundation method according to the present invention.
FIG. 2 is an explanatory view of a step performed subsequent to FIG. 1;
FIG. 3 is an explanatory view of a step performed subsequently to FIG. 2;
FIG. 4 is a flowchart showing a construction procedure of a suction foundation method according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Side wall part 12 Bottom plate part 14 Upper plate part 16 Skirt part 18 Caisson frame 20 Substructure 22 Superstructure 24 Water bottom ground 26 Waterproof part 28 Grout material

Claims (4)

A cylindrical side wall portion, a bottom plate portion provided at a lower end of the side wall portion, an upper plate portion provided at an upper end of the side wall portion, and a skirt portion extending downward from a lower end of the side wall portion. With the caisson body provided, with the tip of the skirt portion penetrating into the bottom of the water, a suction load is applied to sunk the caisson body to a predetermined depth. In the suction basic construction method that sequentially builds and superstructure,
The suction load is to apply a preload to the skirt portion in accordance with the load of the substructure,
After constructing the substructure on the upper side of the caisson skeleton, after forming a water blocking portion in the underwater ground below the bottom plate portion, introducing a water injection load between the water blocking portion and the bottom plate portion, A suction foundation method, wherein a preload is added to the underwater ground below the bottom slab. The suction foundation method according to claim 1, wherein the preload applied to the underwater ground below the bottom slab is set to a size corresponding to the load of the superstructure. The preload applied to the underwater ground under the bottom slab is a size corresponding to the sum of the weight of the caisson frame, the load of the substructure, and the resistance obtained by adding the peripheral surface resistance of the caisson frame. 2. The suction foundation method according to claim 1, wherein A grout material is injected under the bottom slab in place of the water injection load before applying the preload to the underfloor ground under the bottom slab and before constructing the superstructure above the substructure. Item 4. The suction foundation method according to any one of Items 1 to 3.

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