JP7630362B2 - Caisson method - Google Patents

Description

The present invention relates to a caisson construction method that reduces the amount of excavation work done by excavation machines such as clamshells, shortening the process and reducing costs.

For example, the caisson method has been used for constructing underground structures such as bridge foundations, building foundations, water cutoff walls, underground tanks, and tunnel shafts. The caisson method is broadly divided into the open caisson method, and the improved press-in open caisson method and the pneumatic caisson method. The open caisson method is a method in which the inside of a cylindrical structure with open top and bottom sides is excavated and removed from the ground by an excavation machine such as a clamshell, while the structure constructed on the ground is gradually submerged (for example, see Patent Document 1 below). The press-in open caisson is a method in which a gripper rod is connected to a ground anchor driven into the ground, a cylindrical structure with a cutting edge at the bottom is constructed, a loading girder is placed on the top of the structure via a bearing material, and the loading is applied while the inside ground of the structure is excavated by an excavation machine such as a clamshell. This is a construction method in which a gripper rod is tensioned by a hydraulic jack attached to the girder, and the structure is pressed (sunk) into the ground while the ground anchor is used to provide a reaction force (see, for example, Patent Document 2 below). The pneumatic caisson method is a construction method in which an airtight work chamber is provided under the structure, and compressed air is pumped into the bottom in an amount that matches the pore water pressure of the ground to prevent groundwater from seeping in, and the structure constructed above ground is gradually sunk while the soil is excavated and removed by hand or excavation machinery in a dry state (see, for example, Patent Document 3 below).

Japanese Patent Application Publication No. 11-50464 JP 2006-207152 A Patent No. 6653510 construction method

In particular, in the case of the open caisson method and the press-in open caisson method, taking into consideration that the top of the structure is open and the excavation depth is deep, excavation is usually carried out using a clamshell bucket suspended by a wire rope from a crane.

However, due to its structure, the clamshell bucket has a lower digging capacity than a backhoe, and the excavation work takes up a lot of time and effort in the entire work process. This makes it difficult to shorten the construction period and increases excavation costs.

The main objective of the present invention is to provide a caisson construction method that reduces the amount of excavation work using excavation machines such as clamshells, shortens the process, and reduces costs.

In order to solve the above problems, the present invention relates to a caisson construction method in which a structure is constructed above ground, and then gradually sunk into the ground while repeatedly excavating the inside of the structure to construct an underground structure of a predetermined depth.
Prior to starting to sink the pipe into the ground, a number of cylindrical boreholes of a predetermined depth are formed in the area to be excavated inside the structure using a drilling bucket or hammer grab of the earth drill method , and the borehole walls are stabilized by filling the boreholes with a highly water-absorbent polymer stabilizing liquid.
Next, a caisson method is provided, which is characterized by constructing an underground structure of a predetermined depth by repeating the steps of constructing a structure on the ground, sinking it into the ground, and excavating the inside of the structure according to normal construction procedures.

In the invention described in claim 1, before starting to sink into the ground, a plurality of cylindrical excavation holes of a predetermined depth are formed in the area to be excavated inside the structure using a drilling bucket or hammer grab of the earth drill method, and the hole walls are stabilized by filling the holes with a highly water-absorbent polymer stabilizing liquid. The cylindrical excavation holes are formed using an excavation device such as a drilling bucket or hammer grab of the earth drill method . The excavation efficiency of these excavation devices can be more efficient than excavation using a clamshell bucket inside a caisson, and by forming a plurality of the excavation holes in advance, it is possible to reduce the amount of soil excavated by the clamshell, which makes it possible to shorten the process and reduce costs.

In addition, bentonite stabilizing liquid is generally used to protect the borehole walls, but this bentonite stabilizing liquid is a type of clay that contains iron ores such as montmorillonite, quartz, and opal, and when it is disposed of, the entire amount must be treated as industrial waste, resulting in high disposal costs. However, in the case of the highly water-absorbent polymer stabilizing liquid used in the present invention, by adding divalent metal ions such as calcium chloride to increase the electrical conductivity of the solvent, the water adsorbed in the polymer material is separated, making it possible to reduce the amount of waste liquid to be disposed of, and therefore disposal costs.

As a second aspect of the present invention, there is provided a caisson construction method as described in claim 1 , in which the excavation holes are formed in a plurality of places inside the structure in a regular lattice arrangement or a staggered check arrangement when viewed in a plane.

The invention described in claim 2 specifies the formation pattern of the boreholes. Specifically, it is preferable to form a plurality of boreholes in a regular lattice arrangement or a staggered lattice arrangement in a plan view. In this case, from the viewpoint of protecting the borehole walls, it is preferable that the area of the boreholes relative to the area of the caisson excavated inside the structure in a plan view is about 15 to 30%.

As the present invention according to claim 3 , there is provided a caisson construction method according to either claim 1 or 2, which is directed to an open caisson construction method or a press-in type open caisson construction method.

The invention described in claim 3 above specifies the preferred caisson construction method to which the present invention is applicable. In other words, although it is possible to apply the present invention to the pneumatic caisson construction method among the caisson construction methods, the construction to which the present invention is preferably applied is the open caisson construction method or the press-in open caisson construction method, which employs excavation using a clamshell method with relatively low excavation efficiency.

As the present invention according to claim 4 , there is provided a caisson construction method according to either claim 1 or 2, in which the caisson construction method is directed to a press-in type open caisson construction method, and the borehole is formed in parallel with the construction of the ground anchor and within the period of the ground anchor construction.

In the invention described in claim 4 above, since it is undesirable for the formation of the borehole to result in an extension of the construction period, when the caisson method is a press-in type open caisson method, it is desirable that the formation of the borehole be carried out in parallel with the construction of the ground anchor and within that period.

As a fifth aspect of the present invention, there is provided a caisson construction method as described in any one of the first to fourth aspects, in which the soil and sand generated by excavation inside the structure is separated from the superabsorbent polymer stabilizing liquid and then disposed of.

According to the fifth aspect of the present invention, in order to reduce the amount of excavated soil and sand, the highly water-absorbent polymer is separated and then disposed of.

As explained above in detail, the present invention makes it possible to provide a caisson construction method that reduces the amount of excavation work using excavation machines such as clamshells, shortens the process, and reduces costs.

FIG. 1 is an explanatory diagram of a caisson construction method according to the present invention. FIG. This is a construction procedure diagram (part 1) of the caisson construction method according to the present invention. This is a construction procedure diagram (part 2) of the caisson construction method according to the present invention. This is a construction procedure diagram (part 3) of the caisson construction method according to the present invention. This is a construction procedure diagram (part 4) of the caisson construction method according to the present invention.

The following describes in detail the embodiments of the present invention with reference to the drawings.

The caisson method involves constructing a structure on the ground, which is then gradually sunk into the ground while repeatedly excavating the interior of the structure to construct an underground structure 1 of a specified depth. Of the several caisson methods, this embodiment will explain the method of the present invention based on the example of the press-in open caisson method.

In the press-in open caisson method, first, a hole is drilled in the ground for the ground anchor, a tendon (tensile material) 13 is inserted into the hole, and a grout material is injected into the bottom of the hole to create an anchoring section 12. When sinking the caisson body _2n , a center hole jack 6 is set on the tendon 13 to introduce a tensile force, and the body _2n is pressed into the ground by the reaction force. The body 2 is constructed on the ground, rod by rod, and when the body _2n is completed, it is sunk into the ground. By repeating the excavation, an underground structure 1 such as a bridge foundation, a building foundation, a water cut-off wall, an underground tank, or a tunnel shaft is constructed.

In the present invention, in the press-in open caisson method, as shown in Figs. 1 and 2, in the stage before starting to sink the skeleton 2 into the ground, a plurality of cylindrical excavation holes 3, 3 ... of a predetermined depth are formed in the planned excavation area inside the skeleton 2, and the hole walls are stabilized by filling the excavation holes 3, 3 ... with a superabsorbent polymer stabilizing liquid 4,
Next, following normal construction procedures, construction of the structure on the ground, sinking into the ground, and excavation of the inside of the structure are repeated to construct the underground structure 1 to a predetermined depth. The structure 2 is divided into six divided structures ₂₁ to ₂₆ in the vertical direction, and the divided structures ₂₁ , ₂₂ , ₂₃ , ..., ₂₆ are constructed on the ground in this order and sunk into the ground.

The following will explain this in more detail with reference to the drawings.
<Ground anchor construction and drilling hole formation construction>
Prior to the sinking of the structure, as shown in Figure 3, ground anchor work and, in parallel with this, a drilling bucket using an earth drill method are used to form a number of cylindrical drilling holes 3, 3... of a predetermined depth within the planned excavation area inside the structure 2.

In the ground anchor work, as shown in the figure, a hole 3 of a specified diameter is formed to a specified depth using a drilling machine 10. Next, as shown in the drilling position on the left side of the figure, a tendon 13 (tensile material) is inserted and grout material is injected into the tip to form an anchoring part 12, which serves as a fixed part that allows tensile force to be introduced into the tendon 13. As shown in Figure 2, two ground anchors 5 are installed for each loading girder 8 located at the four corners, for a total of eight ground anchors 5.

The tendon 13 is made of tensile materials such as PC steel rods, PC steel strands, multiple PC steel strands, and continuous fiber reinforcement, and is placed underground. A gripper rod 14 is connected to the tendon 13 above ground. The gripper rod 14 is inserted into a center hole jack 6 installed on the top surface of the loading girder 6, and a tensile force is introduced by the center hole jack 6.

The drilling holes 3, 3... should be formed in parallel with the ground anchor construction, preferably within that period. The drilling hole construction is desirably performed using a drilling bucket 16 used in the earth drilling method, as shown in FIG. 3. In the illustrated example, a rope method is used with a drilling bucket 16 suspended by a crane 15. The depth of the drilling hole 3 may be aligned with the bottom position of the caisson (underground structure 1) constructed underground, or it may be slightly shorter or longer than this. If it is desired to obtain the effect of forming the drilling hole 3 over the entire length of the caisson 1, it is desirably formed to match the bottom position of the caisson 1.

The inside of the boreholes 3, 3... is filled with a superabsorbent polymer stabilizing liquid 4 to protect the hole walls. Compared to conventional bentonite-based stabilizing liquids, the superabsorbent polymer stabilizing liquid 4 improves the stability of the excavated ground, improves the quality of cast-in-place concrete structures, reduces the amount of industrial waste generated by the stabilizing liquid excavation method, and streamlines construction.

The superabsorbent polymer stabilizing liquid 4 is a swelling superabsorbent polymer stabilizing liquid for ground excavation that contains water, superabsorbent polymer particles that have absorbed and swollen, and at least one of a weighting material, a stabilizer, and an auxiliary, and preferably does not contain bentonite and has a specific gravity of 1.20 or less. It is also preferable that the superabsorbent polymer particles are sodium polyacrylate, the weighting material is at least one selected from inorganic sand and sulfate minerals with a maximum particle size of 2.0 mm or less, the stabilizer is polyacrylamide, and the auxiliary is at least one selected from sawdust, pulp, rock wool, and fiber lost circulation prevention materials that improve hole wall stability.

This superabsorbent polymer stabilizing liquid was developed by the applicant in collaboration with others, and is specifically the superabsorbent polymer stabilizing liquid described in Patent No. 6113433.

By using the superabsorbent polymer stabilizing solution 4 to protect the walls of the borehole 3, it is possible to significantly reduce the amount of excavated soil and sand. Specifically, the superabsorbent polymer stabilizing solution 4 can be separated into soil and water components by adding divalent metal ions such as calcium chloride to increase the electrical conductivity of the nutrient solution, thereby taking advantage of the phenomenon in which the water adsorbed in the polymer material separates, making it possible to reduce the amount of industrial waste disposal.

The boreholes 3 may be formed in a regular lattice arrangement in plan view as shown in FIG. 2, or may be formed in a staggered arrangement. In this case, from the viewpoint of protecting the walls of the boreholes 3, it is preferable that the total area of the boreholes 3, 3... with respect to the caisson excavation area inside the structure 2 in plan view is about 15 to 30%, preferably about 17 to 25%.

<Structure work and submerged structure work>
Next, the construction of the structure and the construction of the structure will begin. The structure 2 is divided into six divided structures ₂₁ to ₂₆ in the vertical direction, and the divided structures ₂₁ , _{22, 23, ..., 26 will be constructed on the ground in the order of 21, 22} , ₂₃ , ..., ₂₆ , successively on the upper side of the already constructed structure.

First, as shown in Fig. 4, the most advanced first structure ₂₁ with a cutting edge at its tip is constructed on the ground. Then, a load girder 8 is arranged so as to span between the press-in force transmission members 7, 7 protruding from the upper part of the structure, and a gripper rod 14 connected to a tendon 13 of the ground anchor 5 is inserted into the load girder 8 and connected to the center hole jack 6 placed on the upper surface of the load girder 8.

Next, the center hole jack 6 is hydraulically driven to introduce a tensile force into the ground anchor 5 to press the first body ₂₁ into the ground. Once the pressing is completed, the earth and sand inside the first body ₂₁ is excavated by the clamshell bucket 9 as shown in FIG. 5. The clamshell bucket 9 is an excavator generally used in the open caisson construction method or the press-in open caisson construction method, and is of a type that drops an open clamshell bucket and closes it by pulling it up to grab the earth and sand. The operation method of the clamshell bucket 9 includes a crane lifting method (rope method), a telescopic arm method, a hydraulic clam method, etc. The excavation capacity is approximately 0.6 ^m3 to 1.0 ^m3 in the case of the rope method, and approximately 0.25 ^m3 to 0.6 ^m3 in the case of the telescopic arm method.

When the excavation by the clamshell bucket 9 is completed, the second structure ₂₂ is constructed on the upper side of the first structure ₂₁ as shown in Fig. 5. The second structure ₂₂ can be constructed by the slip method using a slip form device 17 as shown in the figure. The slip form method is a construction method in which a concrete form (FORM) is pushed up with a jack and slid up (SLIP) while concrete is continuously poured to construct the structure. When constructing the second structure ₂₂ , the press-in force transmission member 7 is embedded inside the structure while being continuous with the press-in force transmission member 7 of the first structure ₂₁ .

When construction of the second body ₂₂ is completed, the loading girder 8 is installed between the press-in force transmission members 7, 7, and the gripper rod 14 is connected to the center hole jack 6 to complete preparation for pressing in. The center hole jack 6 is hydraulically driven to introduce a tensile force into the ground anchor 5, pressing the first body ₂₁ and the second body ₂₂ into the ground. When pressing in is completed, the soil inside the body 2 is excavated with the clamshell bucket 9.

By sequentially repeating the construction of the separate structures ₂₁ to ₂₆ , pressing the structures into place, and excavating the interior of the structures in the above-described manner, all of the separate structures ₂₁ to ₂₆ are pressed into the ground as shown in Figure 6, the soil inside them is excavated, and the base slab concrete 18 is poured to complete the underground structure 1.
[Effect calculation by the method of the present invention]
In applying the method of the present invention, if the drilling holes 3, 3 ... are formed using a drilling bucket 16 used for an earth drill within the period in which the ground anchors 5 are driven, the process can be shortened by the amount of excavated soil of the clamshell 9 reduced, and the construction costs can be reduced accordingly.

(1) Effect of shortening the work process If the total volume of excavated soil is 5,765 ^m3 and the entire volume is excavated using a clamshell excavator, and the excavation settlement time per 10 ^m3 is 2.16 hours (average), the actual number of operating days will be 38.1 days (7 hours/day).

In contrast, if the method of the present invention is applied and 954.3 m3 of the total excavated soil volume of 5,765 ^m3 is excavated by drilling bucket using the earth drill method,
· Clamshell excavation volume: 4,811 m3 ⇒ Actual operation days: 31.8 days · Earth drill excavation volume: 954.3 m3 ⇒ As this is carried out during ground anchor construction, the actual operation days will be 0 days.

Therefore, the method of the present invention can shorten the process by approximately six days.

(2) Reduction in construction costs If the total volume of excavated soil is 5,765 ^m3 and the entire volume is excavated using a clamshell, the cost will be 5,765 m3 x 5,053 (yen/m3) = 29,132,061 yen.

In contrast, if the method of the present invention is applied and 954.3 m3 of the total excavated soil volume of 5,765 ^m3 is excavated by drilling bucket using the earth drill method,
· Clamshell excavation ⇒ 4,811 m3 x 5,053 (yen/m3) = 24,309,983 yen · Earth drill excavation ⇒ 954.3 m3 x 3,846 (yen/m3) = 3,670,237 yen + equipment removal costs (490,500 yen), for a total of 27,980,221 yen.

Therefore, if the method of the present invention is used, construction costs can be reduced by 1,151,840 yen.

[Other examples]
(1) In the above embodiment, the borehole 3 is formed by the drilling bucket 16 of the earth drill method, but it may be formed by a hammer grab.
(2) The caisson construction method according to the present invention is suitably applied to open caisson construction methods and press-in open caisson construction methods, but can also be applied to pneumatic caisson construction methods.

1... Underground structure (caisson), 2... Main body, 3... Borehole, 4... Superabsorbent polymer stabilizer, 5... Ground anchor, 6... Center hole jack, 7... Pressure force transmission member, 8... Loading girder, 9... Clamshell bucket, 10... Drilling machine, 12... Anchorage, 13... Tendon, 14... Gripper rod, 15... Crane, 16... Drilling bucket, 17... Slip form device, 18... Base slab concrete

Claims (5)

In the caisson method, a structure is constructed above ground, then gradually lowered into the ground, and excavation is repeated inside the structure to build an underground structure of a specified depth.
Prior to starting to sink the pipe into the ground, a number of cylindrical boreholes of a predetermined depth are formed in the area to be excavated inside the structure using a drilling bucket or hammer grab of the earth drill method , and the borehole walls are stabilized by filling the boreholes with a highly water-absorbent polymer stabilizing liquid.
Next, in accordance with normal construction procedures, the caisson method is characterized by constructing an underground structure of a specified depth by repeating the steps of constructing a structure on the ground, sinking it into the ground, and excavating the inside of the structure. The caisson construction method according to claim 1 , wherein the boreholes are formed in a plurality of locations inside the structure in a regular lattice arrangement or a staggered lattice arrangement when viewed from above. The caisson construction method according to claim 1 or 2 , which is directed to an open caisson construction method or a press-in type open caisson construction method. 3. The caisson method according to claim 1, wherein the caisson method is a press-in type open caisson method, and the borehole is formed in parallel with the construction of the ground anchor and within the period of the construction of the ground anchor. The caisson method according to any one of claims 1 to 4 , wherein the soil and sand generated by the excavation inside the structure is subjected to a separation process of a highly water-absorbent polymer stabilizing liquid and then disposed of.

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