JPH093938A - Method for constructing underground construction inside frozen soil - Google Patents

Abstract

PURPOSE: To secure a frozen state that provides high strength and rigidity on the interior wall surface of a recess so that an underground construction can be constructed by digging the recess while installing a melt preventing member inside frozen soil, and constructing the underground construction inside the recess. CONSTITUTION: Drilling and removing processes and a process for installing the freezing pipe of a melt preventing member 10 and a heat insulating material are performed alternately to remove an existing underground tank completely and to perform boring to a predetermined depth. In this case, the melt preventing member 10 is installed to eliminate the influence of outside air and to maintain the freezing temperature so as to form a recess inside frozen soil 5 while preventing embrittlement due to the melting of the interior wall surface 5a. The interior wall surface 5a is given a frozen state that provides high strength and rigidity, so as to eliminate the need for constructing an earth retaining wall 8. Further, a new underground tank 17 is easily constructed by effective use of the frozen soil 5, which serves as a cut-off wall for enhanced cut-off performance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for constructing an underground structure, and more particularly to a technique for constructing an underground structure in frozen soil.

[0002]

2. Description of the Related Art As an underground structure, for example, there is an underground tank buried in the ground for storing LPG or LNG in a liquefied state at a low temperature. This underground tank is, for example, after a cylindrical concrete underground continuous wall is constructed in the ground, and the underground continuous wall is used as a mountain retaining wall to prevent the ground from collapsing and excavate the inside thereof to form a recessed portion. , Is to be built in this recess.

[0003]

The above underground tank may be required to be repaired due to measures against deterioration due to long-term use or measures to increase storage capacity. However, the underground tank may freeze the surrounding ground due to the low temperature of the liquefied gas that it stores, and when constructing a continuous underground wall as a mountain retaining wall on this frozen soil due to repair work. Has a problem that it is necessary to take measures against low temperature such as prevention of freezing of stable liquid during excavation and securing of concrete curing conditions. Further, such a problem is not limited to an underground tank, and is common to, for example, an underground structure constructed on frozen soil in a cold region. On the other hand, frozen soil has properties such that it has higher strength and rigidity than ordinary ground and does not collapse, so there is demand for the development of an effective construction method for underground structures that actively utilizes this property. It was

The present invention has been made in view of the above-mentioned circumstances, and provides a method for constructing an underground structure in a frozen soil by which the underground structure can be easily constructed by effectively utilizing the frozen soil. With the goal.

[0005]

In order to achieve the above object, a method for constructing an underground structure in frozen soil according to the present invention is to excavate a recess in frozen soil while preventing weakening due to melting of an inner wall surface. It is characterized in that an underground structure is constructed in the recess.

[0006]

According to the present invention, since a concave portion is excavated in frozen soil while preventing weakening due to melting of the inner wall surface, the inner wall surface of the concave portion collapses while maintaining a frozen state having high strength and rigidity. Is eliminated, thus eliminating the need for a mountain retaining wall. Then, an underground structure is built in the recess thus formed.

[0007]

EXAMPLE A method of constructing an underground structure in frozen soil according to an example of the present invention will be described below with reference to the drawings. In this example, an underground tank is taken as an example of the underground structure, and as a construction method thereof, a case where a new underground tank is constructed in frozen soil caused by the existing underground tank after the existing underground tank is removed Will be explained.

FIG. 1 shows an existing underground tank 1 buried in the ground 2. The existing underground tank 1 stores LPG or LNG in a liquefied state at a low temperature. It has a schematic structure having a side wall 3 mainly made of reinforced concrete and having a cylindrical shape and having an axis extending vertically, and a bottom plate 4 mainly made of reinforced concrete which closes the lower portion of the side wall 3. Here, reference numeral 5 in the figure indicates frozen soil generated around the cold storage of the existing underground tank 1.
In the present embodiment, the ground surface 6 side around the existing underground tank 1 is non-frozen soil, and all other surroundings except this part are frozen soil 5.

First, as shown in FIG. 1, when removing the existing underground tank 1 having the above-mentioned structure, a plurality of, for example, a plurality of pieces are provided on the radially outer side of the existing underground tank 1 so as to surround the outside of the range where the frozen soil 5 exists. A heater fence 7 configured by arranging vertically extending heater pipes at a predetermined pitch is provided so as to have a substantially circular shape in a plan view and extend to a predetermined amount below the bottom slab 4 of the existing underground tank 1. And this heater fence 7
, Circulate a liquid medium such as cold water maintained at about 0 ° C,
As a result, the frozen soil 5 is prevented from growing outside the heater fence 7 while maintaining the frozen and healthy state. If a heater fence is already provided for the purpose of preventing the growth of the frozen soil 5 in the existing underground tank 1, this existing heater fence will be used.

Next, since the ground 2 near the ground surface 6 is not frozen soil, this portion is filled with a stabilizing liquid as usual (because there is no influence of temperature), and an annular groove is formed while preventing the wall surface from collapsing. Further, concrete is poured while substituting with the stabilizing solution to construct the upper mountain retaining wall 8 as shown in FIG. Here, when the upper mountain retaining wall 8 is constructed, a sheet pile 9 extending into the frozen soil 5 is provided on the outer wall surface side. If the height is such that the wall does not collapse, the mountain retaining wall 8 can be constructed without using the stabilizing solution.

Then, the ground 2 around the existing underground tank 1
Is excavated to a predetermined depth while removing the existing underground tank 1. Here, in the initial stage of excavation, the inner wall surface 8a of the upper mountain retaining wall 8
The inner side is excavated, and the excavation is further advanced substantially along the inner wall surface 8a. When the excavation area reaches the inside of the frozen soil 5 during this excavation, a predetermined depth is excavated (the existing underground tank 1 is also gradually removed in accordance with the excavation depth), and as shown in FIG. The melting prevention member 10 is installed on the entire inner wall surface 5a of the frozen soil 5. In this embodiment, the melting prevention member 10 includes a heat transfer freezing pipe 11 which is held on the inner wall surface 5a by spraying concrete 12 or the like, and the spraying concrete 12 and the inner wall surface 5 of the freezing pipe 11.
It is composed of a heat insulating material 13 such as a heat insulating concrete panel attached to the entire surface by an anchor 14 on the opposite side to a. Here, in the freezing tube 11, a liquid medium whose temperature is controlled to such an extent that it is possible to prevent weakening due to melting of the inner wall surface 5a of the frozen soil 5 is circulated. A control device (not shown) for controlling the circulation of the liquid medium and the temperature control is constructed, for example, on the ground surface 6 before the start of excavation.

The excavation and removal process and the installation process of the freezing pipe 11 and the heat insulating material 13 of the thaw prevention member 10 are alternately performed to completely remove the existing underground tank 1 as shown in FIG. Along with excavation to a predetermined depth,
A recess 15 that is one size larger and deeper than the existing underground tank 1.
Will be formed in the frozen soil 5 (for convenience, the inside of the mountain retaining wall 8 constructed in the non-frosted soil is referred to as an opening 16 different from the recess 15). And it was excavated in this way,
After the flooring is completed, the bottom plate 18 and the side wall 19 of the new underground tank 17 similar to the existing underground tank 1 are constructed in the opening 16 and the recess 15 by the usual method. The storage capacity of this new underground tank 17 is increased by increasing the depth.

It should be noted that the depth of excavation for one time is such that even if the freeze pipe 11 and the heat insulating material 13 of the thaw preventing member 10 are installed after the excavation, the frozen soil 5 is weakened by melting and the inner wall surface 5a collapses. So that there are no freezing tubes 11 and heat insulating materials 1
3 is set appropriately according to the installation work time and the like. In addition, the freezing pipe 11 is prepared in advance for a length corresponding to, for example, substantially the entire range of excavation of the recess 15 and circulates the liquid medium, and corresponds to the exposed inner wall surface 5a as the excavation progresses. The method of installing only the part that has been set up, or the length corresponding to the exposed inner wall surface 5a is prepared and installed, and the freeze pipe 11 is sequentially connected and expanded as the excavation and removal process progresses. There are ways to do it. In the case of the latter method, since it is necessary to connect the additional portion to the freezing pipe 11 up to the previous drilling, at the time of this connection,
The circulation by the control device is stopped while preventing liquid leakage from the connecting point.

As described above, according to this embodiment,
Since the melting prevention member 10 is installed to eliminate the influence of outside air and to maintain the freezing temperature to prevent the inner wall surface 5a from being weakened by melting, the concave portion 15 is excavated and formed in the frozen soil 5. The inner wall surface 5a of 5 is kept in a frozen state with high strength and rigidity and does not collapse. Therefore, the mountain retaining wall to be provided on all the inner wall surfaces of the recess 15 is unnecessary. Therefore, there is no need to take low-temperature measures when constructing a mountain retaining wall, as well as the cost of constructing a mountain retaining wall can be reduced and the construction period can be shortened. 17 can be easily constructed. Further, in the new underground tank 17 constructed in this manner, the frozen soil 5 is present around the surroundings, and the frozen soil portion serves as a water blocking wall, so that the water blocking performance is improved.

In the above embodiment, the freezing tube 11 is used.
The heat insulating material 13 is installed on the inner wall surface 5a of the frozen soil 5 as an example, but the heat insulating material 13 is used when the temperature is low.
Only one may be provided. Further, in the above embodiment, since the ground surface 6 side is not frozen soil, the mountain retaining wall 8 is partially provided on the ground of this non-frosted soil, but when the ground surface 6 is frozen soil, No Yamadome wall is required. further,
In the above embodiment, an underground tank is taken as an example of the underground structure, and as a construction method thereof, after removing the existing underground tank, a case of constructing a new underground tank in the frozen soil generated by the existing underground tank As explained, if it is not limited to this, if it is an underground structure in frozen soil,
For example, it is also applicable to the case of constructing various other underground structures in frozen soil in cold regions, and further, even in the case of ultra-soft ground where the inner wall surface of the excavation collapses even if a stabilizing solution is used. It can also be applied to the freezing method in which the ground is frozen and forced to excavate in order to prevent collapse.

[0016]

As described in detail above, according to the present invention,
Since the recess is formed by excavation in the frozen soil while preventing the weakening due to melting of the inner wall surface, the inner wall surface of the recess portion is maintained in a frozen state having high strength and rigidity and does not fall down. Is unnecessary. Therefore, there is no need to take measures against low temperatures when constructing a mountain retaining wall, and it is possible to reduce the cost of constructing a mountain retaining wall and shorten the construction period. It will be easy to build.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing a state before execution of a method for constructing an underground structure in frozen soil according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along the vertical direction showing a state of constructing a mountain retaining wall on a non-frozen soil portion in a method for constructing an underground structure in frozen soil according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view taken along the vertical direction showing the installation state of a freezing pipe and a heat insulating material, which are members for preventing melting on the inner wall surface of frozen soil, in a method for constructing an underground structure in frozen soil according to an embodiment of the present invention.

FIG. 4 is a vertical cross-sectional view showing a state in which a recess is formed in frozen soil and a new underground tank is constructed in a method for constructing an underground structure in frozen soil according to an embodiment of the present invention.

[Explanation of symbols]

 5 Frozen soil 5a Inner wall surface 15 Recessed portion 17 New underground tank (underground structure)

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Mitsuo Nemoto 1-5-20 Kaigan, Minato-ku, Tokyo Within Tokyo Gas Co., Ltd. (72) Inventor Miya ▲ Shinichi Shinichi 1-5-5 Kaigan, Minato-ku, Tokyo No. 20 Tokyo Gas Co., Ltd. (72) Inventor Takashi Nakajima 1-3-2 Shibaura, Minato-ku, Tokyo Shimizu Construction Co., Ltd. (72) Inventor Honorable interest 1-3 2-3 Shibaura, Minato-ku, Tokyo Shimizu Construction Co., Ltd. (72) Inventor Sakate Honest Shibaura 1-3-2 Shibaura, Minato-ku, Tokyo Shimizu Construction Co., Ltd. (72) Inventor Yoshihiko Shimizu 1-3-2 Shibaura, Minato-ku, Tokyo Shimizu Construction Co., Ltd. (72) Inventor Takuro Odawara 1-3-2 Shibaura, Minato-ku, Tokyo Shimizu Construction Co., Ltd.

Claims (1)

[Claims] 1. A method for constructing an underground structure in frozen soil, which comprises excavating and forming a recess in frozen ground while preventing weakening due to melting of an inner wall surface, and constructing an underground structure in the recess.