JPH09177360A - Underground storage tank and constructing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize the control of the transmission of shearing force from the sidewall of a tank to an underground continuous wall in response to the state of the operation of the tank by a simple structure. SOLUTION: In this underground storage tank T, an underground continuous wall 1 is executed around a sidewall 15 constituting a part of a tank building frame. A shearing-force transmission section 20 consisting of a peripheral groove 22 formed to the inner circumferential surface of the top section of the underground continuous wall 1 and a projecting shearing key 21 formed to the outer circumferential surface of the top section of the sidewall 15 so as to be fitted while interposing a cushioning material in a specified thickness at the place of a lower end in the peripheral groove 22 is installed between the top section of the sidewall 15 and the top section of the underground continuous wall 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an underground tank and a method for constructing the same, and more particularly to liquefied natural gas (hereinafter referred to as LNG).
It is written. ), Etc., relates to an underground tank in which a shearing force transmitting portion at the top of a tank side wall resists a pumping pressure received by a tank body and a construction method thereof.

[0002]

2. Description of the Related Art An underground tank for storing LNG is generally constructed by a reinforced concrete structure for the bottom slab and the side wall. Therefore, in the LNG underground tank, the bottom slab, the side wall and the joint between the bottom slab and the side wall leg are frozen by LNG cold heat, and the low water level operation is performed until the water stop of the tank skeleton can be confirmed. In this low water level operation, as shown in FIG. 7, continuous drainage treatment operation is performed by the drainage means P provided in the crushed stone layer 52 provided under the bottom slab 51 of the underground tank 50, so Pumping pressure is bottom plate 51
It is also possible to prevent the joint portion 53 from acting.
The drainage means P is usually composed of a known drainage pump or the like having a predetermined drainage capacity.

Low water level operation is carried out for a certain period,
After the freezing of the side wall 54 of the tank, the bottom slab 51 and the joint portion 53 was confirmed, the drainage treatment operation from the crushed stone layer 52 was stopped, and the high water level operation in which the groundwater level below the bottom slab 51 was restored to the natural water level was performed. To do. Therefore, a predetermined pumping pressure acts on the bottom slab 51 and the joint portion 53 during the high water level operation (see FIG. 8).

By the way, since the specific gravity of the LNG 55 stored in the underground tank 50 is only about 0.5, it is expected that buoyancy will be generated in the tank body during high water level operation depending on the tank scale. For this reason, in the conventional design, in order to stably hold the tank body, the outer surface of the tank side wall and the underground continuous wall 60 constructed on the outer periphery thereof are joined to each other to join the underground continuous wall 6 to each other.
It often takes a reaction force to zero. For this reason, in the conventional tank structure, a joining type in which a shearing force can be transmitted between the side wall 54 and the underground continuous wall 60 is adopted. Typical examples of this joining type include the dowel type and the continuous wall concave shear key type.

In the gibber form, as shown in FIG. 9 (a), a gibber streak 61 is formed in a hole drilled in the surface of the underground continuous wall 60.
(Shearing force-bearing muscles) are loaded so that the shearing force can be transmitted between the side wall concrete 53 and the underground continuous wall 60 that are to be post-cast. In the continuous wall concave type shear key type, as shown in FIG. 9 (b), the side wall concrete 53 is spliced into a plurality of recesses 62, 62 formed in advance on the underground continuous wall 60 side, and shearing is performed between them. I am trying to transmit power.

By the way, since the pumping pressure does not act from the lower side during the low water level operation, the liquid load at the time of fullness and the tank own weight act on the side wall via the bottom plate 51 and the anchor 56 as the load state of the tank. Therefore, the tank body is in a supporting state in which it is suspended by the underground wall 60. Generally, in designing a tank structure, the number of gibber muscles 61 and the size of a shear key are often determined during this low water level operation.

[0007]

However, any of the joining means has the following problems. (Gibel type) (1) From the original purpose, the number of gibber muscles required only during high water level operation is often determined by the shear force during low water level operation. In addition, the construction man-hours of the dowel reinforcement are large and the construction cost is high. (2) The embedding position of the gibber bar interferes with the position of the reinforcing bar of the continuous underground wall, and the efficiency of drilling work for placing the gibber bar is not improved. (Continuous wall concave shear key type) (1) Poor concrete filling occurs around the recess formed in the underground wall, and the water stopping property of the joint decreases. (2) Side-wall concrete shear key's reinforcing bar reinforcement becomes complicated, which limits the construction method of side wall.

Therefore, an object of the present invention is to solve the problems of the above-mentioned conventional techniques, and to provide a simple shear transmission mechanism so that a load can be reasonably loaded in each operating state of the tank and the underground tank. It is to provide a construction method.

[0009]

In order to achieve the above object, the present invention relates to a method for constructing an underground tank in which a continuous underground wall is constructed around a side wall forming a part of a tank body, wherein the side wall top portion is provided. And a top of the underground continuous wall, a shearing force transmitting portion for transmitting only the upward shearing force acting on the side wall to the underground continuous wall is provided.

The shearing force transmitting portion is fitted with a circumferential groove formed on the inner circumferential surface of the top of the underground continuous wall so that the shearing force transmitting portion is fitted with a predetermined clearance at the lower end position of the circumferential groove. It is preferable that the protrusion-shaped shear key is formed on the outer peripheral surface of the.

Alternatively, the shear force transmitting portion has a shear key formed on the inner peripheral surface of the top of the underground continuous wall so as to project toward the side wall, and a wall thickness above a portion where the shear key projects. It is preferable that the side wall has a wall thickness reduced by an amount of the shear key protruding.

In this case, it is preferable that a cushioning material made of resin is interposed at the lower end position in the circumferential groove to secure the clearance.

Further, as a method for constructing the underground tank, a coping concrete which constitutes a part of the shearing force transmitting portion is constructed so as to be connected to the top of the previously constructed underground continuous wall, and the underground continuous wall is constructed. Excavate the inner ground surrounded by the wall to a predetermined depth, divide the bottom slab concrete and the predetermined number of placing steps into the side wall concrete in order, and at a position facing the shear force transmitting part of the underground continuous wall, It is characterized in that a site for transmitting a shearing force from a side wall to the underground continuous wall is constructed at the same time when the side wall concrete is cast.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of an underground tank and a construction method thereof according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a partial cross-sectional view showing an embodiment of an underground tank provided with a shearing force transmitting portion having a shearing key between the top of the underground wall and the top of the tank. As shown in FIG. 1, the underground tank T of the present invention has an overall structure substantially similar to that of a known LNG underground storage tank. That is, the underground continuous wall 1 constructed as a water stop wall, the crushed stone layer 11 provided on the ground surrounded by the underground continuous wall 1 and excavated to a predetermined depth, and the predetermined crushed stone layer 11 A slab 12 of a reinforced concrete structure of a strength slab format set to a slab thickness, and a side wall 15 of a reinforced concrete structure erected via a joint portion 14 to a recess 13 formed in the periphery of the bottom slab 12, It is composed of a steel dome roof R supported on the entire circumference of the top of the side wall 15.
Of these, a drainage pipe network (not shown) is laid in the crushed stone layer 11. This drainage pipe network is connected to a drainage pump (not shown) and can drain groundwater within a range surrounded by the underground continuous wall 1. As a result, the tank is L
The low water level operation described above can be performed with NG stored.

A joint portion 14 is formed between the bottom plate 12 and the leg portion of the side wall 15. The cross-sectional shape of the joint portion 14 is shown in FIG.
As shown in FIG. 5, it is L-shaped, and a steel plate 16 as a liner plate is laid on the flat surface portion. The side wall 15 is erected on the steel plate 16. Therefore, the vertical load transmitted in the side wall 15 is directly transmitted to the bottom plate 12 via the steel plate 16. The concrete volume of the side wall 15 contracts due to the cold heat effect of LNG (liquid temperature -162 ° C) stored in the tank. Therefore, the side wall 15 and the underground continuous wall 1
There is a certain amount of separation between and. Since it is necessary to cut off the adhesion between the side wall 15 and the underground continuous wall 1 concrete, it may be possible to interpose a synthetic resin sheet 17 therebetween.

Further, a shearing force transmitting portion 20 is formed between the top of the side wall 15 and the top of the underground continuous wall 1. The shearing force transmitting portion 20 includes a shearing key 21 formed on the entire outer peripheral surface of the side wall 15, and a circular groove 22 formed on the inner peripheral surface of the underground continuous wall 1 fitted with the shearing key 21.
Consists of As shown in the enlarged view of FIG. 2, the shear key 21 is formed by projecting a part of the side wall 15 into a rectangular protrusion shape. The outer peripheral surface of the shear key 21 is covered with a reinforcing steel plate 23. Further, the shear reinforcing bar 24 welded to the back surface side of the reinforcing steel plate 23 is connected to the fixing bar 26 via the mechanical joint 25.
Is linked to The amount of the reinforcing bar of the shear reinforcing bar 24 is set to such an extent that the shear key 21 can sufficiently resist the upward acting force of the pumping pressure acting on the tank bottom plate 12.

On the other hand, the circumferential groove 22 of the underground continuous wall 1 is formed in a part of the coping concrete 2 which is post-cast on the upper end of the underground continuous wall 1 which has been previously constructed. As will be described later, the coping concrete 2 is cast using the reinforcing steel plates 23 and 27 located on the inner peripheral surface side as an embedded formwork. For this reason, the shear reinforcing bar 3 having the same degree as the shear key 21 is previously installed on the concrete side of the reinforcing steel plate 27, and the labor of the bar arrangement of the coping concrete 2 is reduced. In addition, FIG. 2 shows a state after the completion in which the outer peripheral portion of the tank is backfilled.

Further, a cushioning material 4 is provided at the lower end position in the circumferential groove 22. In this embodiment, the cushioning member 4 has a width equal to the depth of the circumferential groove 22 and a thickness of about 50 mm.
Foamed plastic is used. This cushioning material 4
Acts as a spacer when constructing the shear key 21 at the same time as the sidewall concrete is cast in the n-th stage casting block of the sidewall 15. As a result, a clearance having a predetermined thickness is formed below the shear key 21. In this way, by providing a clearance of a predetermined thickness below the shear key 21 of the side wall 15 with respect to the circumferential groove 22 on the underground continuous wall 1 side, the side wall 15 slightly sinks downward during low water level operation. However, the shearing force is not transmitted to the underground continuous wall 1. As the material of the cushioning material 4, a predetermined thickness of clearance is obtained under the shear key 21 when the concrete of the side wall 15 is cast, and the downward shearing force from the side wall 15 is underground when the tank is in service and at a low water level operation. Various materials can be used as long as they are not transmitted to the continuous wall 1.

In the above description, it has been stated that the circumferential groove 22 is provided over the entire circumference of the inner peripheral surface of the underground continuous wall, but if the necessary shearing force transmission effect is obtained, the underground continuous wall will be formed. It goes without saying that a recess may be partially formed on the surface and a protruding shearing key may be provided at a portion of the outer peripheral surface of the side wall facing the recess.

Next, referring to FIGS.
A method of constructing the orbiting groove 22 of the coping concrete 2 and the shear key 21 of the side wall 15 constituting the above will be described. First, the top crown surface 1a of the underground continuous wall 1 is subjected to a splicing treatment, and the reinforcing steel plates 23 and 27 to be the formwork of the inner peripheral surface of the coping concrete 2 are built. This reinforcing steel plate 23,
Reference numeral 27 denotes two steel plates having a substantially L-shaped cross section, which are vertically stacked and temporarily fixed. The lower steel plate 23 has a shear key 21.
The ends of the side shear reinforcement bars 24 are welded. on the other hand,
An end portion of the shear reinforcing bar 3 on the coping concrete 2 side is welded to the upper steel plate 27. Further, the main bar 28 extending from the underground wall 1 is bent into a predetermined shape, and the reinforcing bar assembled in the predetermined shape is incorporated to arrange the coping concrete 2 portion. Then, the outer mold 30 is assembled at the outer peripheral position of the side wall. (See FIGS. 3 (a)-(b)).

Next, the coping concrete 2 is poured (see FIG. 3 (c)). The compressive strength of the concrete used is equal to that of the sidewall concrete, or it is preferable to use high-strength concrete. After that, the inner peripheral portion of the underground continuous wall 1 is excavated to a predetermined depth, and after the crushed stone layer and the bottom slab are constructed, a predetermined joint portion construction (not shown) is performed, and the side wall 15 is divided into predetermined casting blocks to form leg portions. It is placed by the normal winding method.
At this time, in the present embodiment, the form segment 31 is used as an inner form for placing concrete on the side wall 15. It goes without saying that a conventional steel form may be used instead of the form segment 31.

FIG. 4 (e) shows a state in which the side wall concrete has been cast to just below the shear key (n-1th stage casting block). As shown in the figure, shear key 2
An anchor line 26 is connected to the first shear reinforcement line 24 via a mechanical joint 25. Circular groove 2 in parallel with the above work
The cushioning material 4 is attached to the lower end position in 2. In the present embodiment, as the cushioning material 4, a foam material processed into a predetermined shape, such as expanded polystyrene, is installed so as to be spread. FIG. 4 (f) shows a state in which the concrete of the final stage casting block is cast. In the n-th stage casting block, the shear key 21 was simultaneously constructed integrally with the sidewall concrete casting. The outer peripheral portion of the tank is backfilled to a predetermined level.

FIG. 5 is a partial sectional view of an underground tank T having a shearing force transmitting portion 20 as another embodiment of the present invention. 5, the configuration is the same as that shown in FIG. 1 except for the shearing force transmitting portion 20 of the present embodiment located at the top of the tank. Therefore, the configuration of the shearing force transmitting portion 20 will be described in detail with reference to FIG. In FIG. 6, a shear key 21 is formed on the top of the coping concrete 2 of the underground continuous wall 1 so as to project inward from the wall thickness portion equal to the underground continuous wall 1 by a predetermined amount. This shear key 21 is one in which a predetermined shear reinforcing bar 3 is arranged when the coping concrete 2 is constructed. Reinforcing steel plates 23 and 27 having the same shape as that of FIG. 1 are arranged between the side wall concrete to be post-cast. On the other hand, in the side wall 15, there are arranged reinforcing reinforcements 26 connected via a shear reinforcement reinforcement 24 welded to the lower reinforcement steel plate 23 and a mechanical joint 25. Shear force transmitting portion 20 of the present embodiment
Since this is configured as described above, the force that pushes up the side wall 15 at the time of pumping pressure is transmitted from the side wall 15 to the underground continuous wall 1 by the shearing force transmitting portion 20. This prevents the tank skeleton T from rising. Further, even if the suspension force acts on the tank body T during the low water level operation,
Since the edge between the side wall 15 and the underground continuous wall 1 is cut, the shearing force is not transmitted from the side wall 15 to the underground continuous wall 1, and the tank skeleton T sinks uniformly. The arrangement of the shear reinforcing bars of the shear force transmitting portion 20 illustrated in the above description is an example,
It is preferable to perform bar arrangement corresponding to the shearing force generated on the side wall 15 by the load assumed by each tank scale.

[0024]

As is apparent from the above description, according to the present invention, it is possible to control the transmission of the shearing force generated on the side wall according to the difference in the usage state of the tank with a simple structure.

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing an embodiment of an underground tank according to the present invention.

FIG. 2 is a partially enlarged cross-sectional view showing details of a shearing force transmitting portion of the underground tank shown in FIG.

FIG. 3 is a construction sequence explanatory view (part 1) showing an example of the construction procedure of the shearing force transmission section of the underground tank shown in FIG. 1.

FIG. 4 is a construction sequence explanatory view (part 2) showing an example of the construction procedure of the shearing force transmission part of the underground tank shown in FIG. 1.

FIG. 5 is a partial cross-sectional view showing another embodiment of the underground tank according to the present invention.

6 is a partially enlarged cross-sectional view showing details of a shearing force transmitting portion of the underground tank shown in FIG.

FIG. 7 is a load diagram showing a load acting on a tank bottom slab during low water level operation of a conventional LNG underground tank.

FIG. 8 is a load diagram showing a load acting on a tank bottom slab during a high water level operation (during pumping pressure action) of a conventional LNG underground tank.

FIG. 9 is a partially enlarged sectional view showing an example of a conventional shear force transmission mechanism between a tank side wall and an underground continuous wall.

[Explanation of symbols] 1 underground continuous wall 2 coping concrete 3,24 shear reinforcement 4 cushioning material 12 bottom slab 15 side wall 20 shear force transmission part 21 shear key 22 orbiting groove 23,27 reinforcement steel plate T underground tank

Claims (5)

[Claims] 1. An underground tank in which an underground continuous wall is constructed around a side wall forming a part of a tank body, and an upward shear acting on the side wall is provided between the side wall top and the underground continuous wall top. An underground tank having a shearing force transmitting portion for transmitting only force to the underground continuous wall. 2. The shearing force transmitting part is fitted to a circumferential groove formed on the inner circumferential surface of the apex of the underground continuous wall so as to be fitted with a predetermined clearance at the lower end position in the circumferential groove. The underground tank according to claim 1, comprising a projecting shear key formed on the outer peripheral surface of the top of the side wall. 3. The shear force transmitting portion is formed on the inner peripheral surface of the apex of the underground wall so as to protrude toward the side wall, and the wall thickness above the portion where the shear key protrudes. 2. The underground tank according to claim 1, wherein the side wall has a wall thickness reduced by an amount corresponding to the overhang of the shear key. 4. The underground tank according to claim 2, wherein a resin cushioning material is provided at a lower end position in the circuit groove to secure the clearance. 5. A coping concrete constructing a part of the shearing force transmitting portion is constructed so as to be connected to the top of the previously constructed underground continuous wall, and the inner ground surrounded by the underground continuous wall is constructed. Excavate to a specified depth, divide it into bottom slab concrete and a specified number of placement steps, and apply side wall concrete in order, and shear from the side wall to the underground continuous wall at a position facing the shear force transmission part of the underground continuous wall. A method for constructing an underground tank, characterized in that a site for transmitting force is constructed at the same time as the placing of the side wall concrete.