JP2012158891A - Construction method of pit-in type tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a construction method of a pit-in type tank, capable of eliminating the need of a site for keeping surplus soil for banking and shortening a construction period.SOLUTION: The construction method of a pit-in type tank includes: a tank storage part construction step of constructing a pit (tank storage part) 2 in ground G; and a tank body construction step of constructing a tank body 3 inside the pit 2 constructed in the tank storage part construction step. The tank storage part construction step includes: an underground continuous wall construction step of constructing a cylindrical underground continuous wall 6 in the ground G; a sidewall upper part construction step of constructing a sidewall upper part 5a in the form of being supported by the underground continuous wall 6 on the inner side of the underground continuous wall 6 and being projected upwards more than an upper end 6a of the underground continuous wall 6; an inside excavation step of excavating the inside of the underground continuous wall 6 after the sidewall upper part construction step and banking a part of the surplus soil generated by excavation around the periphery of the sidewall upper part 5a; a bottom slab construction step of constructing a bottom slab 4; and a sidewall lower part construction step of constructing a sidewall lower part 5b and integrating the sidewall lower part 5b and the sidewall upper part 5a.

Description

  The present invention relates to a method for constructing a pit-in tank used for storing a low-temperature liquid such as liquefied natural gas.

Storage tanks for low-temperature liquids such as liquefied natural gas (LNG) used in Japan can be roughly divided into ground tanks and underground tanks (see, for example, Non-Patent Document 1).
The ground tank is, for example, a metal double shell tank or a PC outer tank tank, an inner tank made of low temperature steel for storing LNG, an outer tank made of ordinary steel or prestressed concrete, an inner tank and an outer tank. And a cold insulating material disposed between the two.
On the other hand, the underground tank consists of a reinforced concrete bottom plate and a side wall constructed along the periphery of the bottom plate, a cold insulating material arranged on the inner surface of the bottom plate and the side wall, and a stainless steel thin plate installed inside the cold insulating material. (Membrane) and a roof made of metal or reinforced concrete.

In addition, a pit with a bottom plate and side walls made of reinforced concrete in the basement is built, and a pit-in type tank in which a tank body such as a metal double shell tank or PC outer tank type tank usually used on the ground is installed. Has also been used.
Here, the pit-in tank is included in the underground tank, but will be described below as a pit-in tank in order to distinguish it from the above-described underground tank.

Such a pit-in type tank can be configured such that the tank body is supported by the bottom plate via a column attached to the bottom plate, and an air layer is formed between the tank body and the bottom plate.
In the pit-in type tank having such a configuration, since the air layer functions as a heat insulating layer, it is not necessary to control the freezing of the ground as compared with the underground tank, and equipment such as a heater can be dispensed with.

Also, in the pit-in tank, the tank body is installed at a predetermined distance from the side wall, so that a heat insulation layer can be formed by the air layer on the side, and the tank body can be inspected from the outside using this distance. Can do.
Furthermore, in the pit-in type tank, the work of removing or renewing the pit-in type tank performed after the service period is completed can be easily performed as compared with the underground tank.

By the way, such a pit-in tank is constructed by the following construction procedure.
First, a cylindrical underground continuous wall is constructed in the ground, and the bottom plate of the pit is constructed by excavating the inside of the underground continuous wall. Subsequently, the side walls of the pit are constructed around the bottom plate, and the tank body is installed in the pit after the pit is completed.

However, such construction procedures are uneconomical because residual soil is generated when excavating the inside of the underground continuous wall.
Then, when constructing a pit, it is conceivable to use the residual soil generated by excavation as in the underground tank construction method disclosed in Patent Document 1. In this underground tank construction method, the upper side of the side wall is constructed so as to be located above the ground surface before the underground tank is constructed, and the residual soil generated by excavation is formed on the outer periphery of the upper side of the side wall. We perform embankment using part.

JP 2009-127263 A

Atsushi Kubota, LNG tank, “The Journal of the Japan Institute of Energy (Vol. 85, No. 5)”, 2006, p398-404

However, when the pit is constructed by using a part of the remaining soil as in the underground tank construction method disclosed in Patent Document 1, the embankment is performed after the side wall is completed. It is stored for a certain period of time. For this reason, there is a problem that it takes effort to secure a site for storing the remaining soil and to manage the remaining soil.
In particular, when the construction site is small, the remaining soil is stored outside the construction site, so that it is costly to secure a site for storing the remaining soil, and the procedure is also required and troublesome.
Further, there is a problem that it takes time (construction period) and cost to transport the remaining soil between the site for storing the remaining soil and the pit-in tank construction site.

  The present invention has been made in view of the above-mentioned problems, and provides a construction method for a pit-in tank that can eliminate the site for storing the remaining soil for embankment and can shorten the construction period. There is.

  In order to achieve the above object, a method for constructing a pit-in type tank according to the present invention includes a tank storage portion having a bottom plate and a cylindrical side wall constructed along the periphery of the bottom plate, and an inside of the tank storage portion. A construction method of a pit-in-type tank comprising a constructed tank body, a tank housing part construction step for constructing the tank housing part in the ground, and the tank housing part constructed in the tank housing part construction step A tank body construction step for constructing the tank body inside, and the tank storage portion construction step comprises a underground continuous wall construction step for constructing a cylindrical underground continuous wall in the ground, and the underground A side wall upper construction step of constructing an upper portion of the side wall in a form that is supported by the underground continuous wall inside the continuous wall and projects upward from the upper end of the underground continuous wall, and after the side wall upper construction step , The underground Excavating the interior of the wall and embedding a portion of the excavated soil around the upper portion of the side wall; constructing the bottom plate to construct the bottom plate; constructing the lower part of the side wall; And a side wall lower part constructing step of integrating the lower part with the upper part of the side wall.

In the present invention, since the internal excavation process is performed after the side wall upper construction process, a part of the residual soil generated by excavating the inside of the underground continuous wall can be directly filled on the outer periphery of the upper part of the side wall. Accordingly, it is not necessary to store the remaining soil used for the embankment, and it is not necessary to secure a site for storing the remaining soil or to manage the remaining soil, so that it is possible to reduce costs and labor required for storing the remaining soil.
In addition, it is possible to eliminate the process of transporting the remaining soil used for embankment from the construction site of the pit-in type tank to the site for temporarily placing the residual soil and returning it to the construction site of the pit-in type tank again, thus reducing costs. The construction period can be shortened.
Moreover, since the remaining soil can be filled as it is with internal excavation, a construction period can be shortened compared with the conventional construction method which performs filling after a tank storage part is constructed.
By installing the tank body in the tank storage section constructed in this way, a pit-in tank excellent in heat insulation and maintenance can be constructed at low cost and in a short construction period.

Further, in the construction method of the pit-in tank according to the present invention, in the front side wall lower part construction step, the lower part of the side wall is constructed stepwise from the upper side to the lower side in parallel with the internal excavation step, The bottom plate construction step may be performed after the construction step.
Thus, in the side wall lower part construction process, the lower part of the side wall can be constructed at the same time as the internal excavation process by constructing the lower part of the side wall stepwise from the upper side in parallel with the internal excavation process. Furthermore, the construction period can be shortened.

According to the present invention, a part of the remaining soil generated by excavating the inside of the underground continuous wall can be directly embanked on the outer periphery of the upper portion of the side wall, so there is no need to store the remaining soil used for embankment. Since there is no need to secure a site for storage and management of the remaining soil, it is possible to reduce costs and labor for storing the remaining soil.
Moreover, since the remaining soil can be embanked with internal excavation, a construction period can be shortened compared with the conventional construction method which performs embankment after a tank storage part is constructed.
And by installing a tank main body in the tank storage part constructed in this way, it is possible to construct a pit-in type tank excellent in heat insulation and maintainability at a low cost and in a short construction period.

It is a figure which shows an example of the pit in type tank by embodiment of this invention. It is a figure explaining an underground continuous wall construction process. It is a figure explaining a side wall upper part construction process. It is a figure explaining an internal excavation process. It is a figure explaining a bottom plate construction process and a side wall lower part construction process.

Hereinafter, a construction method of a pit-in tank according to an embodiment of the present invention will be described with reference to FIGS.
(Pit-in tank)
As shown in FIG. 1, the pit-in tank 1 according to the present embodiment is used as, for example, an LNG storage tank, and is constructed in a pit (tank storage unit) 2 constructed underground and in the pit 2. And a tank main body 3 in which LNG is accommodated.

The pit 2 includes a bottom plate 4 having a substantially circular shape in plan view and a substantially cylindrical side wall 5 disposed below the ground G surface.
The ground G on the outer periphery on the lower end side of the side wall 5 is provided with an underground underground wall 6 having an annular shape in plan view in a shape along the outer peripheral surface of the side wall 5.

The bottom slab 4 is made of reinforced concrete, and is constructed on the crushed stone layer 11 provided on the ground G excavated.
The side wall 5 is made of reinforced concrete, and the lower end portion 5 c is rigidly joined to the outer edge portion 4 a of the bottom plate 4. That is, the bottom plate 4 and the side wall 5 are formed in a bottomed cylindrical shape.
If the ground surface before the pit-in tank 1 is constructed is the pre-construction ground surface Ga, the side wall 5 has an upper portion 5a positioned above the pre-construction ground surface Ga and a lower portion 5b below the pre-construction ground surface Ga. positioned. The outer periphery of the upper part 5a of the side wall 5 is provided with embankment Gc above the ground surface Ga before construction. Therefore, the pit 2 is arranged underground.
Here, the upper part 5a of the side wall 5 will be described as a side wall upper part 5a, and the lower part 5b of the side wall 5 will be described as a side wall lower part 5b.

The underground continuous wall 6 has a function to prevent the ground G from collapsing and a water stop function as a soil retaining. The underground continuous wall 6 is constructed deeper than the bottom plate 4 of the pit-in tank 1. At this time, it is preferable that the lower end portion of the underground continuous wall 6 reaches a non-illustrated poorly permeable layer (depressed clay soil layer).
Such underground continuous wall 6 is constructed of concrete or the like, for example.

The tank body 3 is a metal double shell tank or a PC outer tank tank that is usually installed on the ground, an inner tank made of low-temperature steel for storing LNG, an outer tank made of ordinary steel or prestressed concrete, And a cold insulating material disposed between the tank and the outer tank.
When the tank body 3 is constructed in the pit 2, the tank body 3 is supported on the bottom plate 4 via the support columns 12 installed on the bottom plate 4. The tank body 3 is installed with a predetermined distance from the side wall 5.
Thereby, air layers 13 and 14 are formed between the tank body 3 and the bottom plate 4 and between the tank body 3 and the side wall 5. The air layers 13 and 14 function as a heat insulating layer.

(Pit-in tank construction method)
Next, the construction method of the above-described pit-in tank 1 will be described with reference to the drawings.
The construction method of the pit-in type tank according to the present embodiment includes a pit construction process (tank storage part construction process) for constructing the pit 2 and a tank body construction process for constructing the tank body 3 inside the pit 2. And in the pit construction process, the side wall upper part 5a is constructed prior to excavation of the ground G inside the underground continuous wall 6 where the pit 2 is constructed.

(Pit construction process)
(Underground continuous wall installation process)
First, the underground continuous wall 6 is constructed.
As shown in FIG. 2, the underground continuous wall 6 is constructed by providing an underground continuous wall excavator along the periphery of the place where the pit-in tank 1 is to be installed, and arranging a reinforcing bar in the groove. It is constructed by a well-known technique for placing concrete. At this time, it is preferable to construct the underground continuous wall 6 so that the lower end portion of the underground continuous wall 6 reaches a hardly water-permeable layer (not shown).

(Sidewall construction process)
Subsequently, as shown in FIG. 3, the ground continuous wall 6 is excavated along the inner peripheral surface on the upper end 6a side of the underground continuous wall 6, and the side wall upper portion 5a is brought into contact with the inner peripheral surface while the underground continuous wall The side wall upper part 5a is constructed so as to protrude upward from the upper end 6a of the part 6.
The side wall upper part 5a is constructed by arranging reinforcing bars along the shape and placing concrete. The side wall upper part 5a constructed in this way is formed in a cylindrical shape, and is maintained in a state of being supported by the underground continuous wall 6 by contacting the underground continuous wall 6.
In the present embodiment, in order to support the side wall upper part 5a to the underground continuous wall 6 more reliably, a protruding part 5d protruding outward is provided on the outer periphery of the side wall upper part 5a, and this protruding part 5d is connected to the underground continuous wall 6. The side wall upper part 5a is fixed to the underground continuous wall 6 by being hooked on the upper end 6a of the wall, and the side wall upper part 5a is fixed to the underground continuous wall 6 by the connecting reinforcing bars 5e.
In addition, what is necessary is just to provide the overhang | projection part 5d mentioned above and the connection reinforcing bar 5e as needed.

(Internal drilling process)
Subsequently, as shown in FIG. 4, the ground G inside the pit-in tank 1 is excavated.
In this step, the inside of the underground continuous wall 6 is excavated to a depth where the crushed stone layer 11 (see FIG. 1) can be installed. And a part or all of the remaining soil generated by excavation is directly conveyed to the outer periphery of the side wall upper part 5a, and the embankment Gc is performed outside the side wall upper part 5a. In addition, the remaining soil that exceeds the amount of embankment is used elsewhere in the construction site, or taken out and disposed of outside.
At this time, the side wall upper portion 5a receives the earth pressure from the outside by the embankment Gc, but has a strong structure against the load from the outside such as the earth pressure by being formed in a ring shape in plan view. Therefore, it is kept in a stable state.
In addition, the time for embankment is appropriately selected in the internal excavation process. Generally, it is performed at the initial stage of the internal excavation process, but when the remaining soil is not suitable for embankment, it may be performed in the middle or later stage of the internal excavation process.

(Bottom plate construction process)
Subsequently, as shown in FIG. 5, the bottom plate 4 is constructed on the ground G excavated in the internal excavation process.
The bottom plate 4 is constructed by placing the crushed stone layer 11 on the ground G, placing a reinforcing bar on the top thereof, and placing concrete into the bottom plate 4.

(Side wall bottom construction process)
Subsequently, the side wall lower portion 5b is constructed.
The side wall lower portion 5b is constructed by integrating with the bottom plate 4 and placing the reinforcing bars at predetermined heights in succession from the lower side to the upper side, and successively casting concrete.
The side wall lower part 5b is connected to and integrated with the side wall upper part 5a. As a concrete method of integrating the side wall lower portion 5b and the side wall upper portion 5a, for example, when placing the concrete on the side wall lower portion 5b, the concrete top end is slightly lowered from the lower end of the side wall upper portion 5a, There is a method of filling non-shrinkage concrete into a slight gap formed between the lower portion 5b and the side wall upper portion 5a. By this method, the side wall lower portion 5b and the side wall upper portion 5a can be integrated.
Thereby, the side wall lower portion 5b is completed and the side wall 5 is completed, and the pit 2 is constructed, and the pit construction process is completed.

(Tank body construction process)
Subsequently, as shown in FIG. 1, the tank body 3 is constructed inside the pit 2.
First, the support column 12 is installed on the top of the bottom plate 4, and the tank body 3 is installed on the support column 12. Thereby, an air layer 13 is formed between the bottom plate 4 and the tank body 3.
At this time, the tank body 3 is set apart from the side wall 5 so that an air layer 14 is also formed between the tank body 3 and the side wall 5.
The tank body 3 is constructed by a known method.
And after the tank main body 3 is constructed | assembled, the surface of the embankment Gc is prepared flat. In addition, when preparing the surface of the embankment Gc to be flat, the embankment Gc may be further applied to the surface of the ground that has been embanked.
In this way, the pit-in tank 1 is completed.

  According to the construction method of the pit-in type tank 1 according to the present embodiment, since the internal excavation process is performed after the side wall upper construction process, the residual soil generated by excavating the inside of the underground continuous wall 6 is directly applied to the outer periphery of the side wall upper part 5a. It can be carried and used for the embankment Gc on the outer periphery of the side wall upper part 5a. Thereby, unlike the conventional construction method, it is not necessary to store the remaining soil used for the embankment Gc during the period when the pit 2 is constructed. For this reason, it is not necessary to secure a site for storing the remaining soil and to manage the remaining soil, and it is possible to reduce costs and labor required for storing the remaining soil.

In addition, it is possible to omit the process of transporting the remaining soil used for embankment from the construction site of the pit-in type tank 1 to the site for temporarily placing the residual soil and returning it to the construction site of the pit-in type tank 1 again. Reduction and construction period can be shortened.
Moreover, since excavation and embankment are performed, the construction period can be shortened compared with the conventional construction method of embankment Gc after the pit 2 is constructed.
And by installing the tank main body 3 in the pit 2 constructed in this way, the pit-in type tank 1 excellent in heat insulation and maintenance can be constructed at a low cost and in a short construction period.

As mentioned above, although embodiment of the construction method of the pit in type tank by this invention was described, this invention is not limited to said embodiment, In the range which does not deviate from the meaning, it can change suitably.
For example, in the above-described embodiment, the bottom slab 4 is constructed after excavating the inside of the underground continuous wall 6, and then the side wall lower part 5 b is constructed from below to above, using the forward winding method. Instead of the construction method, in parallel with the excavation of the underground continuous wall 6, the side wall lower part 5 b is constructed from the upper side to the lower side according to the excavation depth, and after the side wall lower part 5 b is constructed, the bottom plate 4 is constructed. Alternatively, a reverse winding method in which the side wall lower portion 5b and the bottom plate 4 are integrated may be used.

In the above-described embodiment, the pit-in tank 1 may be constructed after the ground G outside the underground continuous wall 6 is improved by, for example, a sand compaction pile method. Thus, by improving the ground G outside the underground continuous wall 6, liquefaction of the ground G around the pit-in tank 1 can be prevented.
In the above-described embodiment, the tank body 3 is supported by the bottom plate 4 via the support column 12, and the air layer 13 is formed between the tank body 3 and the bottom plate 4, but the air layer 13 is not provided. The tank body 3 may be grounded to the bottom plate 4. In this case, it is preferable to install a heater for controlling freezing of the ground G on the bottom plate 4.
Moreover, in the embodiment mentioned above, although the side wall 5 and the underground continuous wall 6 are constructed | assembled in substantially cylindrical shape, you may form in cylinder shapes other than cylindrical shape.

1 Pit-in tank 2 Pit (tank storage)
3 Tank body 4 Bottom plate
5 side walls
5a Upper side wall
5b Lower side wall
6 underground continuous wall
6a Upper end G Ground
Gc embankment

Claims (2)

A tank housing portion having a bottom plate and a cylindrical side wall constructed along the periphery of the bottom plate;
A tank body constructed inside the tank storage unit, and a construction method of a pit-in tank comprising:
A tank storage unit construction step of constructing the tank storage unit in the ground;
A tank body construction step for constructing the tank body inside the tank housing section constructed in the tank housing section construction step, and
The tank storage unit construction process includes:
Underground continuous wall construction process of constructing a cylindrical underground continuous wall in the ground,
Side wall upper construction step of constructing the upper part of the side wall in a form that is supported by the underground continuous wall inside the underground continuous wall and protrudes upward from the upper end of the underground continuous wall;
After the side wall upper construction step, an internal excavation step of excavating the inside of the underground continuous wall and embedding a part of the residual soil generated by excavation around the upper portion of the side wall;
A bottom plate construction step of constructing the bottom plate;
A method for constructing a pit-in-type tank, comprising: a side wall lower part building step of building a lower part of the side wall and integrating a lower part of the side wall with an upper part of the side wall. In the side wall lower part construction process, in parallel with the internal excavation process, the lower part of the side wall is constructed stepwise from above to below,
The construction method for a pit-in tank according to claim 1, wherein the bottom plate construction step is performed after the side wall lower portion construction step.

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