JP2012036661A - Method for constructing underground tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for constructing an underground tank capable of eliminating the need for a site to store surplus soil for an embankment and shortening a construction period.SOLUTION: A method for constructing an underground tank comprises: an underground continuous wall construction process to construct a cylindrical underground continuous wall 5 in the ground G; a side wall upper section construction process to construct a side wall upper section 31 in a manner that protrudes upward inside the underground continuous wall 5; an inside excavation process to excavate inside the underground continuous wall 5 after the side wall upper section construction process and to heap surplus soil generated by excavation around the side wall upper section 31; a bottom slab construction process to construct a bottom slab 2; a side wall lower section construction process to construct a side wall lower section 32 and integrate the side wall lower section 32 and the side wall upper section 31; and a roof installation process to install a roof 4 on an upper edge section 3a of a side wall 3.

Description

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

  2. Description of the Related Art Conventionally, as a storage tank for a low-temperature liquid such as liquefied natural gas (LNG), an underground tank having a bottom plate, a side wall constructed along the periphery of the bottom plate, and a roof covering the top of the side wall has been used. Since such an underground tank is constructed on the excavated ground, the construction produces residual soil having the same capacity as the underground tank.

  In recent years, an underground tank has been proposed in which the upper part of the side wall is located above the ground surface before the underground tank is constructed, and embedding is performed on the outer periphery of the upper part of the side wall, thereby embedding in the ground. (See, for example, Patent Documents 1 and 2). When constructing such an underground tank, the amount of disposal of the remaining soil can be reduced by using a part of the remaining soil generated by excavation for the embankment on the outer periphery of the upper side wall.

JP 2010-53891 A JP 2009-127263 A

In the construction method of the underground tank which fills the residual soil generated by such excavation on the outer periphery of the upper part of the side wall, the embankment is performed after the upper part of the side wall is constructed. In other words, in general, embankment is performed after the underground tank body is completed.
For this reason, during the period from when the ground is excavated to the completion of the underground tank body (approximately one to one and a half years), it is necessary to store the remaining soil used for embankment, and secure a site for storing the remaining soil In addition, it takes effort to manage the remaining soil.
In particular, when the construction site is small, a site for temporarily placing the remaining soil outside the construction site is required, so that it takes a cost to secure this site and requires a procedure for it. Furthermore, there is a problem that it takes time (construction period) and cost to transport the remaining soil between the site for temporarily placing the remaining soil and the underground tank construction site.

  The present invention has been made in view of the above-described problems, and provides a construction method for an underground tank that can eliminate the site for storing the remaining soil for embankment and can shorten the construction period. With the goal.

  In order to achieve the above object, an underground tank construction method according to the present invention includes a bottom plate, a cylindrical side wall constructed around the bottom plate, and a roof covering an upper portion of the side wall, A method for constructing an underground tank in which a bottom plate and a lower part of the side wall are buried in the ground, and a periphery of the upper part of the side wall is embanked, and a continuous underground wall for constructing a cylindrical underground continuous wall in the ground A construction step, a sidewall upper construction step for constructing an upper portion of the side wall in a form protruding upward inside the underground continuous wall, and excavating and excavating the interior of the underground continuous wall after the sidewall upper construction step An internal excavation step of embedding a part of the remaining soil generated in the periphery of the upper portion of the side wall, a bottom plate building step of building the bottom plate, a lower portion of the side wall, and a lower portion of the side wall integrated with the upper portion of the side wall On the side wall lower part construction process and the upper end of the side wall Characterized in that it comprises a roof installation step of installing the roots, the.

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.
Moreover, since the remaining soil can be embanked as it is with the internal excavation, the construction period can be shortened as compared with a conventional underground tank construction method in which embankment is performed after the underground tank is constructed.

In the underground tank construction method according to the present invention, the bottom slab construction process is performed after the internal excavation process, and the side wall lower construction process is performed after the bottom slab construction process. In the roof installation process, the roof is formed on the bottom plate in parallel with the side wall lower part construction process, and the roof is raised after the side wall lower part construction process. You may let it be installed in the upper end part of the said side wall.
In this way, in the roof installation process, the roof is formed on the bottom plate in parallel with the side wall lower part construction process, and after the side wall lower part construction process, the roof is raised and installed at the upper end of the side wall. Since construction and roof formation can be performed simultaneously, the construction period can be shortened.

Further, in the underground tank construction method according to the present invention, in the side wall lower part construction step, the lower part of the side wall is constructed in stages from the top to the bottom in parallel with the internal excavation step, and the side wall lower part construction step The bottom plate construction step may be performed after the 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. 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 together with the internal excavation, the construction period can be shortened compared with the conventional underground tank construction method in which the embankment is performed after the underground tank is constructed.

It is a figure which shows an example of the underground tank by embodiment of this invention. It is a figure explaining a ground improvement process. 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. It is a figure explaining a side wall lower part construction process. It is a figure explaining a roof installation process.

Hereinafter, the construction method of the underground tank by embodiment of this invention is demonstrated based on FIG. 1 thru | or FIG.
(Underground tank)
As shown in FIG. 1, the underground tank 1 according to the present embodiment is used as, for example, an LNG storage tank, and has a bottom plate 2 having a substantially circular shape in plan view disposed below the ground G surface, and a substantially cylindrical shape. And a dome-shaped roof 4 supported by the upper end 3 a of the side wall 3.

  Further, the ground G on the outer periphery of the side wall 3 on the lower end 3b side is provided with an underground continuous wall 5 having a shape along the outer peripheral surface of the side wall 3 and having an annular shape in plan view. The ground improvement body 6 is constructed on the ground G. In addition, a bottom heater 12 is installed between the underground continuous wall 5 and the ground improvement body 6 to prevent the ground G from freezing as the cold heat of LNG is transmitted to the ground G through the bottom plate 2.

  The bottom slab 2 is made of reinforced concrete, and is constructed on the crushed stone layer 11 provided on the ground G excavated. A bottom heater 12 that adjusts the temperature in the underground tank 1 is installed inside the bottom plate 2.

The side wall 3 is made of reinforced concrete, and the lower end 3 b is rigidly joined to the outer edge 2 a of the bottom plate 2. That is, the bottom plate 2 and the side wall 3 are formed in a bottomed cylindrical shape.
Assuming that the ground surface before the underground tank 1 is constructed is the pre-construction ground surface Ga, the side wall 3 has an upper portion 31 located above the pre-construction ground surface Ga and a lower portion 32 located below the pre-construction ground surface Ga. is doing. The outer periphery of the upper portion 31 of the side wall 3 is provided with embankment Gc above the ground surface Ga before construction. For this reason, the underground tank 1 has a structure arranged underground.
Here, the upper part 31 of the side wall 3 will be described as the side wall upper part 31 and the lower part 32 of the side wall 3 will be described as the side wall lower part 32.

The underground continuous wall 5 has a function of preventing the ground G from collapsing and a water stop function as a soil retaining. The underground continuous wall 5 is constructed deeper than the bottom slab 2 of the underground tank 1, and the lower end portion 5 b reaches the hardly permeable layer (cold clay layer) 13.
The underground continuous wall 5 is constructed of, for example, concrete.
The ground improvement body 6 is formed by, for example, a sand compaction pile method or the like, and is provided as a countermeasure against liquefaction of the ground G around the underground tank 1.

The roof 4 is formed in a circular shape in plan view, and includes a plurality of frame members 15 installed on the upper end portion 3 a of the side wall 3, a cold insulation material 16 disposed below the frame material 15, and an upper side of the frame material 15. And a roofing material 17 arranged on the roof.
A ring plate 19 for fixing the frame material 15 to the side wall 3 is installed at the upper end portion 3 a of the side wall 3. The ring plate 19 is formed of a steel plate in a circular truncated cone shape along the upper end portion 3 a of the side wall 3.
The structure of the roof 4 may be a structure other than the above.
On the inner surfaces of the bottom plate 2 and the side wall 3, a cold insulation layer (inner tub) 18 including a cold insulation material (not shown) and a membrane material made of, for example, a stainless steel sheet attached inside the cold insulation material is formed. Yes.

(Underground tank construction method)
Next, the construction method of the underground tank 1 mentioned above is demonstrated using drawing.
The construction method of the underground tank according to the present embodiment constructs the side wall upper portion 31 prior to excavation of the ground G inside the underground continuous wall 5 in which the underground tank 1 shown in FIG. 1 is constructed.
(Ground improvement process)
First, as shown in FIG. 2, the ground of the ground G on the outer periphery side of the underground tank 1 is improved.
This ground improvement is performed by, for example, a sand compaction pile method. The shape and size of the ground improvement body 6 are determined in consideration of the shape of the underground tank 1 and the strength of the ground G.

(Underground continuous wall installation process)
Subsequently, the underground continuous wall 5 having an annular shape in plan view is constructed inside the ground improvement body 6.
As shown in FIG. 3, the underground continuous wall 5 is constructed by providing an underground continuous wall excavator along the periphery of the place where the underground tank 1 is to be installed and providing a reinforcing groove in the groove to provide concrete. It is constructed by a well-known technique for setting up. At this time, the underground continuous wall 5 is constructed so that the lower end 5b reaches the hardly water-permeable layer 13.

(Sidewall construction process)
Then, as shown in FIG. 4, the side wall upper part 31 is constructed in the form which protrudes upward from the underground continuous wall 5 on the inner peripheral side of the underground continuous wall 5.
The side wall upper portion 31 is constructed by arranging reinforcing bars along the shape and placing concrete. The side wall upper part 31 constructed in this way is formed in a cylindrical shape and supported by the underground continuous wall 5.
In order to support the side wall upper portion 31 on the underground continuous wall 5, for example, an overhang portion (not shown) fixed to the side wall 3 is provided on the outer periphery of the side wall upper portion 31, and this overhang portion is the upper end portion of the underground continuous wall 5. The side wall upper portion 31 and the underground continuous wall 5 may be fixed by a reinforcing bar (not shown).

(Internal drilling process)
Subsequently, as shown in FIG. 5, the ground G inside the underground tank 1 is excavated.
In this step, the inside of the underground continuous wall 5 is excavated to a depth where the crushed stone layer 11 (see FIG. 1) can be installed. Then, a part of the remaining soil generated by excavation is directly conveyed to the outer periphery of the side wall upper portion 31, and embankment Gc is performed outside the side wall upper portion 31. 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 31 receives the earth pressure from the outside by the embankment Gc, but has a strong structure against an outside load such as 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. 6, the bottom slab 2 is constructed on the ground G excavated in the internal excavation process. The bottom plate 2 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 2. At this time, the bottom heater 12 is installed on the bottom plate 2.

(Side wall bottom construction process)
Then, as shown in FIG. 7, the side wall lower part 32 is constructed.
The side wall lower part 32 is constructed by integrating with the bottom plate 2 and arranging the reinforcing bars at predetermined heights from the lower side to the upper side and successively casting concrete.
In this embodiment, the side wall lower part 32 is constructed on the upper part of the first side wall lower part 32b, the first side wall lower part 32b constructed on the upper part of the haunch part 32a, the upper part of the haunch part 32a. A second side wall lower portion 32c connected to the side wall upper portion 31 is also included.
For this reason, the hunch 32a, the first side wall lower part 32b, and the second side wall lower part 32c are constructed in this order, and the second side wall lower part 32c is connected to the side wall upper part 31 and integrated. As a specific method for integrating the second side wall lower portion 32c and the side wall upper portion 31, for example, when placing the concrete on the second side wall lower portion 32c, the concrete top end is slightly lowered from the lower end of the side wall upper portion 31 and placed. There is a method of filling non-shrinkage concrete into a slight gap formed between the second side wall lower portion 32 c and the side wall upper portion 31. By this method, the second side wall lower portion 32 c and the side wall upper portion 31 are integrated. Can be achieved.
Thereby, the side wall lower part 32 is completed and the side wall 3 is completed.

  In addition, a ring plate 19 (see FIG. 1) is attached to the upper end portion 3a of the side wall 3 in parallel with the side wall lower portion construction step. When the ring plate 19 is attached, a side wall top member (not shown) made of concrete is installed on the upper end portion 3 a of the side wall 3 so as to be integrated with the upper end portion 3 a of the side wall 3. 19 may be supported.

(Roof installation process)
Subsequently, the roof 4 is installed.
First, as shown in FIG. 8, the roof 4 is assembled on the bottom plate 2. In assembling the roof 4, after the frame material 15 is assembled, the cold insulation material 16 and the roof material 17 are attached to the frame material 15. This roof assembling process may be performed in parallel with the side wall lower part construction process or after the side wall lower part construction process is completed.
Next, the roof 4 is lifted by using lifting means (not shown) such as an air lift, jack-up, lifting by a crane or the like, and the frame material 15 is fixed to the ring plate 19. Thereby, the roof 4 is installed in the upper end part 3a of the side wall 3, as shown in FIG.

And after this roof installation process, the inner tank construction which installs a cold insulating material and a membrane in the inner peripheral side of the side wall 3 is performed. Moreover, while installing the side part heater 8, 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 underground tank 1 is completed.

According to the construction method of the underground 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 5 is conveyed to the outer periphery of the side wall upper part 31 as it is. And it can be used for the embankment Gc of the outer periphery of the side wall upper part 31. Thereby, unlike the conventional underground tank construction method, it is not necessary to store the remaining soil used for the embankment Gc during the period when the main body of the underground tank 1 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.
Moreover, since the excavation and the embankment are performed, the construction period can be shortened as compared with the conventional underground tank construction method in which the embankment Gc is performed after the underground tank is constructed.

As mentioned above, although embodiment of the construction method of the underground 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 embodiment described above, the bottom slab 2 is constructed after excavating the inside of the underground continuous wall 5, and then the side wall lower portion 32 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 5, the lower side wall 32 is constructed from the upper side to the lower side according to the excavation depth, and the bottom plate 2 is constructed after the lower side wall 32 is constructed. Alternatively, a reverse winding method for integrating the side wall lower portion 32 and the bottom plate 2 may be used.

In the above-described embodiment, the side wall lower portion 32 includes three parts, that is, the hunch portion 32a, the first side wall lower portion 32b, and the second side wall lower portion 32c, and the side wall lower portion 32 includes the hunch portion 32a, the first side wall lower portion 32b, and the first side wall lower portion 32c. Although the two side wall lower parts 32c are constructed in three stages, the entire side wall lower part 32 may be constructed at one time, or the side wall lower parts 32 may be constructed in two stages or four or more stages. Moreover, you may build the base 2 and the haunch part 32a simultaneously.
In the above-described embodiment, the ring plate 19 is attached to the upper end portion 3 a of the side wall 3, and the frame material 15 of the roof 4 is fixed to the ring plate 19, but the roof 4 is fixed to the upper end portion 3 a of the side wall 3. A method other than this may be used.

In the above-described embodiment, the roof 4 is formed on the bottom plate 2 and lifted by an air lift or the like and installed on the upper end portion 3a of the side wall 3. However, even if the roof 4 is formed at a place other than the bottom plate 2, Good. Further, as soon as the upper side wall 31 is constructed, the roof 4 may be attached to the upper side wall 31. At this time, if an opening is provided in a part of the roof 4 so that materials and equipment can be taken in and out and the remaining soil can be carried out from the opening, the internal excavation process can be performed in all weather.
In short, the present invention performs the internal excavation process after the side wall upper part construction process, and the construction timing and order of the bottom plate construction process, the side wall lower part construction process, and the roof installation process are not limited as long as they can be realized.

DESCRIPTION OF SYMBOLS 1 Underground tank 2 Bottom plate 3 Side wall 3a Upper end part 3b Lower end part 4 Roof 5 Underground continuous wall 6 Ground improvement body 31 Side wall upper part 32 Side wall lower part G Ground Gc Embankment

In order to achieve the above object, an underground tank construction method according to the present invention includes a bottom plate, a cylindrical side wall constructed around the bottom plate, and a roof covering an upper portion of the side wall, A method for constructing an underground tank in which a bottom plate and a lower part of the side wall are buried in the ground, and a periphery of the upper part of the side wall is embanked, and a continuous underground wall for constructing a cylindrical underground continuous wall in the ground A construction step, excavating the inside of the underground continuous wall along the upper end side of the underground continuous wall, and being supported by the underground continuous wall inside the underground continuous wall and of the underground continuous wall Side wall upper construction process for constructing the upper part of the side wall in a form projecting upward from the upper end, and excavating the interior of the underground continuous wall after the side wall upper construction process and a part of the residual soil generated by the excavation An internal excavation process for embedding around the upper part of the side wall, and a bottom plate for constructing the bottom plate A side wall lowering step for building the lower part of the side wall and integrating the lower part of the side wall with the upper part of the side wall; and a roof setting step for installing a roof on the upper end of the side wall. And

Claims (3)

The bottom plate,
Cylindrical side walls built around the perimeter of the bottom plate,
A roof covering the upper part of the side wall, and a method of constructing an underground tank in which the bottom plate and the lower part of the side wall are buried in the ground, and the periphery of the upper part of the side wall is embanked,
Underground continuous wall construction process to construct 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 protruding upward inside the underground continuous wall;
An internal excavation step of excavating the inside of the underground continuous wall after the side wall upper construction step 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;
Side wall lower construction step of constructing the lower part of the side wall and integrating the lower part of the side wall with the upper part of the side wall;
And a roof installation step of installing a roof at the upper end of the side wall. The bottom slab construction process is performed after the internal excavation process, and the side wall lower part construction process is performed after the bottom slab construction process, and in the side wall lower part construction process, the lower part of the side wall is constructed stepwise from below to above,
In the roof installation step, the roof is formed on the bottom plate in parallel with the side wall lower part construction step, and after the side wall lower part construction step, the roof is raised and installed on the upper end portion of the side wall. The construction method of the underground tank of Claim 1. 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 an underground 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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