JP2002038545A - Cylindrical underground water tank and method for constructing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an underground water tank which is constructed by using a cylindrical shaft excavated by a cylindrical casing, ensures the watertightness and strength thereof by improving the quality of field-welding of a bottom slab, uses a steel of high corrosion resistance at a portion corresponding to a water tank of the cylindrical casing, and employs bottom-slab concrete in suitably adjusted quantity, for preventing floating of the water tank. SOLUTION: The cylindrical casing having a horizontal bracket on the lower internal periphery is employed, and the shaft is completed by the cylindrical casing, followed by welding the bottom slab to the bracket, to thereby improve the quality of field-welding. Further, by dividing the cylindrical casing into a portion forming the water tank and the lower excavating casing portion, the former is formed of a material of high corrosion resistance, and only the latter is formed of a general material, which leads to reduction of material costs. Further, the quantity of bottom slab concrete can be suitably adjusted depending on the individually different water tank.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a cylindrical water tank installed underground using a shaft excavated with a circular casing, and a method of constructing the same.

[0002]

2. Description of the Related Art Water tanks buried underground can be used more effectively on the ground than those installed on the ground, there is no need to worry about freezing and heating, and there is no damage due to collision of objects. And the like. To this end, groundwater tanks have been constructed in various ways.

[0003] A method of manufacturing a small underground water tank on the ground and burying it in a pit excavated is used. As a typical example, there is a method in which reinforced concrete is built in an excavated pit, and a method in which a casing of a steel shaft excavated by a shaft excavator is closed at the top and bottom of the casing.

[0004] The method of excavating underground is to use shallow ones by excavation, and deep ones by retaining soil with sheet piles or liner plates. Therefore, the excavation must be performed after stopping the water during the ground improvement work. However, ground improvement work may cause troubles, and it is a work that both the orderer and the construction worker want to avoid as much as possible. In addition, these constructions have to rely not only on mechanical power but also on manual excavation, and there is a fear that there is a shortage of workers engaged in this kind of work. Also, when people work in the shaft, there is always the risk of falling and falling, spring water, lack of oxygen, collapse, crash, etc.
These tasks are also considered to be avoided as much as possible. In this regard, the method of press-fitting the casing with a shaft excavator is welcomed as a construction method without these disadvantages. An example is the method disclosed in Japanese Patent No. 1762193.
This method requires a small work area, the casing for excavation becomes a watertight retaining wall as it is, it is safe because people do not enter the shaft, and no ground improvement is required for underwater excavation It has been widely adopted as a short construction period, inexpensive and safe construction method.

If the lower and upper ends of the casing are closed, the casing becomes a vertical cylinder, although there is a restriction that the casing becomes a vertical cylinder. However, there is a difficult problem when welding the bottom plate to the circular casing after excavation of the shaft. Since the shaft is not necessarily a perfect circle after completion, there can be a considerable gap between the bottom plate and the shaft wall, and welding of the bottom plate is often not satisfactory in terms of watertightness and strength because welding of the bottom plate and the casing wall is impossible from the back side .

[0006] Another disadvantage of this shaft is that it is difficult to prevent corrosion of the outer surface of the shaft. The thickness of the wall is increased in anticipation of the amount of corrosion in advance, or painting is performed before work, but if the wall thickness is increased, the price increases and the workability deteriorates, and the amount of corrosion can not be specified depending on the conditions of the installation location There is also a problem called.
In addition, the coating is peeled off by the rotational friction at the time of press-fitting, and the effect cannot be expected. As a countermeasure, it is best to use a steel material with high corrosion resistance in the tank, but this steel material is generally expensive

[0007] There is a possibility that this water tank will float when it is empty due to the groundwater level and soil quality, but in order to prevent this, the bottom slab concrete is poured into a space below the bottom slab and adjusted. This amount is different for each individual site. Therefore, if the circular casing is integrated, each water tank requires its own design.

[0008]

The underground water tank constructed using a circular shaft excavated with a circular casing has a structure in which a strong bottom plate having excellent watertightness is provided, and corrosion-resistant steel can be used in the water tank part, and the surface is lifted. It provides a construction method that also allows for the control of the amount of bottom slab concrete for prevention.

[0009]

Means for Solving the Problems To compensate for the drawbacks of a bottom plate weld of a groundwater tank constructed using a shaft excavated with a circular casing, which has been conventionally performed, a circular bracket having a horizontally mounted bracket in advance on an inner peripheral surface thereof. Drill a shaft using the casing. After the shaft is completed, the bottom plate is placed on the bracket and welded, so that good welding can be easily performed. The bracket attached to the circular casing also has the effect of increasing the rigidity of the casing.

The portion below the bottom plate of the circular casing is divided into a water tank component and a digging portion, and corrosion resistant material is used for the water tank component and a general steel material is used for the digging portion, thereby saving costs and expenses.

[0011] The bottom slab of the shaft is filled with bottom slab concrete to serve as a weight for preventing water stoppage during work and the floating of the water tank by groundwater. Dividing the circular casing in order to individually adjust the amount of concrete according to the groundwater level and the soil quality of the ground makes it possible to design the water tank constituent part and the excavated part separately, which is convenient.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In an underground water tank using a shaft with a circular casing, when welding a bottom plate, high strength and high watertightness are provided, and corrosion resistance is high. Realized in a way.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a construction process of a shaft using a circular casing. FIG. 1A shows a shaft excavation during a shaft excavation.
This shows a state in which a rotary or reciprocating circular motion is given to the circular casing 2 to press it into the ground, and the inside is excavated and discharged by the grab bucket 3 to build a shaft. FIG. 1B shows a state in which the shaft is deepened, the idle casing 4 is added to the circular casing 2, and the circular casing 2 is press-fitted to a predetermined depth. FIG. 1 (c) shows a state in which underwater concrete 5 is cast on the bottom, water is replaced, the idle casing 4 is removed, and the shaft is completed.

FIG. 2 is a view of a circular casing. FIG.
(A) shows a bracket 7 on the inner periphery of a general circular casing 2.
FIG. 2 (b) shows a case where the excavating casing 8 is attached to the lower end of the circular casing 2 separately by welding 9. The bracket 7 has a triangular cross section to increase the strength and to reduce the resistance of earth and sand during press-fitting.

A shaft is excavated with the circular casing 2, a concrete bottom 5 shown in FIG. 1 (c) is cast just below the bracket 7, water is replaced, and the bottom plate 6 is placed on the bracket 7 and welded. The bottom slab concrete 5 also functions as a weight for preventing floating of the water tank. FIG. 3 shows details of the welding 9 at this portion. Since the welding of the bracket 7 and the circular casing 2 is a factory production, a complete operation is performed. Since the on-site welding is a downward fillet welding which is often defective in quality, it can be a good welding.

After the bottom slab 6 has been attached, mortar or cement milk is grouted into the gaps between the underwater concretes 5. Thereby, the watertightness of the bottom portion can be made more sufficient, and a part of the load applied to the bottom plate 6 can be supported by the underwater concrete.

In general, the inner surface of the water tank is coated to prevent corrosion, but the outer surface is unnecessary because of the friction of earth and sand caused by the rotational motion when the circular casing 2 is pressed. For this reason, it is usual to make the corrosion of the outer surface of the circular casing 2 thicker in anticipation. The amount of corrosion of steel in the ground is 0,0 per year.
Since it is said to be 0.1 to 0.1 mm, if the life of the tank is 100 years, the expected amount of corrosion is usually 1 to 1
It is sufficient to consider about 0 mm. However, depending on the soil conditions, it is possible that it will be worn more than expected. If corrosion-resistant steel is used for the water tank portion of the circular casing 2, wear is reduced. In this case, it is cheaper in terms of cost to use ordinary steel material added from below the bottom plate.

FIG. 4 shows an underground fire protection water tank as an example of use of the underground water tank. A manhole 10 is provided at the top of the circular casing 2.
The fireman's manhole 15 is provided at a position where the suction hose of the fire engine can be easily inserted. In addition, a manhole 10 and a ladder 12 descending into the tank may be provided as needed. The connection between the top plate 11 and the circular casing 2 may be by bolting or welding. In addition, an automatic water supply valve 13 for automatically supplying water from a water pipe and an auxiliary water supply pipe 16 when rainwater is used are connected to this tank. In addition, an air vent pipe 17 and an overflow pipe 18 attached to a normal tank are also arranged.

Another example of the use of the underground water tank is to use it as a temporary storage tank for water supply and a water tank for storing rainwater to be used for irrigation of agricultural lands and parks in a city suffering from chronic water interruption. it can. In addition, if it is used for clearing snow in heavy snowfall areas, it can be melted by geothermal heat in a short time and used as miscellaneous water. (Not shown above)

[0020]

According to the present invention, a groundwater tank can be easily constructed by using a shaft excavation method using a circular casing. In addition, the ground can be effectively used for other purposes. (Claim 1)

In-situ welding for ensuring the watertightness and strength of the bottom plate is easy. (Claim 1)

The cost can be reduced by using a corrosion-resistant steel plate for the water tank main body and using a drilling casing with a blade made of a normal steel plate below. (Claim 2)

The design of the water tank alone and the excavated cylindrical portion can be made independently, and the amount of concrete for preventing the floating of the water tank can be freely determined.
(Claim 2)

[Brief description of the drawings]

FIG. 1 shows a construction process of a shaft using a circular casing.
FIG. 1 (a) is a diagram during excavation by a shaft excavator. Figure 1
(B) shows a state in which the excavation is completed by adding the idle casing. FIG. 1 (c) shows a shaft that is completed by casting underwater concrete.

FIG. 2 is a view of a circular casing. FIG. 2 (a) shows the one with the bracket attached inside and the one with the excavation casing with the bracket inside the FIG. 2 (b).

FIG. 3 is a diagram showing details of welding of a bottom plate.

FIG. 4 is a diagram in which a groundwater tank is used as a fire protection tank.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vertical shaft excavator 2 Circular casing 3 Grab bucket 4 Idle casing 5 Underwater concrete 6 Bottom plate 7 Bracket 8 Drilling casing 9 Welding 10 Manhole 11 Top plate 12 Ladder 13 Automatic water supply valve 15 Fireman's hole 16 Auxiliary water supply pipe 17 Air vent pipe 18 Overflow pipe

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) E21D 5/10

Claims (2)

[Claims] 1. A cylindrical underground water tank constructed by attaching a bottom plate and a top plate to a cylindrical shaft formed by press-fitting a circular casing having a bracket provided on a lower inner circumference of a circular casing into the ground, and a method of constructing the same. . 2. The cylindrical groundwater tank according to claim 1, wherein a drilling casing is attached to a lower end of the circular casing.