JP7019360B2 - Freezing method - Google Patents

Description

The present invention relates to a freezing method.

Conventionally, as a protective work for stabilizing the ground and forming a waterproof layer, a freezing method in which a bearing wall or a waterproof wall is formed by a frozen soil wall has been used (see, for example, Patent Document 1).

On the other hand, when the bearing wall is constructed by the freezing method, the required frozen soil thickness is determined by performing structural calculation. Further, the load is usually set to the earth pressure separation type, the vertical earth pressure of the working earth pressure is the total earth pressure, and the horizontal earth pressure is the static earth pressure in consideration of some freezing expansion pressure (see, for example, Non-Patent Document 1). ).

Japanese Unexamined Patent Publication No. 2005-264717

Japanese Geotechnical Society: Geotechnical Society, Practical Series 31 "Survey, Design and Construction of Ground Improvement-From Detached Houses to Artificial Islands-", pp. 160-170, 2013

Here, when the freezing method is used for ground protection in underground widening work or the like, frozen soil is created outside the excavation range to perform freezing protection. At this time, if cohesive soil is present in the ground to be frozen, water is absorbed from the surrounding ground due to freezing, which may cause an excessive freezing expansion pressure and adversely affect the surrounding structure. It was necessary to take separate measures such as reinforcement of the.

For this reason, it has been strongly desired to develop a method that can accurately grasp the freezing expansion pressure and make it possible to eliminate or reduce measures such as reinforcement of surrounding structures.

In view of the above circumstances, it is an object of the present invention to provide a freezing method capable of accurately grasping the freezing expansion pressure and making it possible to eliminate or reduce measures such as reinforcement of surrounding structures.

In order to achieve the above object, the present invention provides the following means.

The freezing method of the present invention is a freezing method for freezing the ground in the frozen soil area where the sandy soil layer and the cohesive soil layer exist, so that the cohesive soil layer is not frozen and the cohesive soil layer is the sandy soil. It is characterized by freezing at least a part of the sandy soil layer when it is on the side to be protected from the layer .

In the freezing method of the present invention, it is possible to reduce the reinforcement of the structure and the required frozen soil thickness, and it is possible to realize a rational freezing method.

It is a figure which shows an example of the construction method of the tunnel constructed by using the freezing method. It is a figure which shows an example of the construction method of the tunnel constructed by using the freezing method. It is a figure which shows an example of the tunnel constructed by using the freezing method. It is a figure which shows an example of the tunnel of the branching / merging part constructed by using the freezing method. It is a figure which shows an example of the construction method of the tunnel constructed by using the freezing method. It is the figure which compared the difference between the conventional method, the frozen soil range of this invention, and the required frozen soil thickness.

Hereinafter, the freezing method according to the embodiment of the present invention will be described with reference to FIGS. 1 to 6.

Here, in the present embodiment, for example, when starting / arriving at the time of constructing a large cross-section tunnel such as a branch / confluence part of a road tunnel or a cross-section part of a railway tunnel, or at the time of opening a segment (when widening the shield tunnel underground). ) Etc. will be explained assuming that the freezing method is used.
However, the method for calculating the freezing expansion pressure of the freezing method of the present invention can be applied to all cases where the freezing method is used in the field of civil engineering and construction.

First, as shown in FIGS. 1 to 4, when constructing a large-section tunnel such as a branch / confluence of a road tunnel, for example, the main line shield 1 and the ramp shield 2 (two shafts) are laterally oriented. In addition to constructing in advance at intervals, the underground shaft 3 is constructed by forming a frozen soil wall 6 by the freezing method to stabilize the ground through the lamp shield 2, and two tunnels starting from this underground shaft 3. Build a starting base 4 with a tunnel shield. A plurality of outer shell shields 5 are constructed from the starting base 4 with a tunnel boring machine having a small diameter so as to surround the main line shield 1 and the lamp shield 2.

Further, as shown in FIGS. 2 and 5, the frozen soil wall 8 is formed by using the freezing method, and the adjacent outer shell shields 5 are cut open and communicated (freezing pipe 9, cut open portion 10), the main line shield 1, and the lamp. A main lining 7 surrounding the shield 2 is constructed. Then, the ground surrounded by the main lining 6 is excavated from the main shield 1 and communicated with each other to construct a large cross-section tunnel that serves as a branch / confluence.

Here, in the conventional freezing method, if cohesive soil is present in the ground to be frozen, water is absorbed from the surrounding ground due to freezing, which causes an excessive freezing expansion pressure, which adversely affects the surrounding structures. It was necessary to take additional measures such as reinforcement so that it would not occur.

On the other hand, in the freezing method of the present embodiment, when a cohesive soil layer and a sandy soil layer exist in the ground of the area to be frozen, the cohesive soil layer is prevented from being frozen (frozen soil range S1 / conventional). Frozen soil range S2). That is, the frozen soil was created while avoiding the cohesive soil layer. This makes it possible to avoid the occurrence of excessive freeze expansion pressure.

An example in which the freezing method is applied to an underground shaft for underground widening work will be described.

The freezing expansion pressure generated in the lower part of the underground shaft is 770 kN / m ² by the conventional method, but it is 280 kN / m ² when the freezing method of the present embodiment is applied, which is reduced to about 1/3. It was confirmed that it could be done.

As a result, it was confirmed that the required frozen soil thickness was 7.5 m by the conventional method, but it can be reduced to 4.3 m by applying the freezing method of the present embodiment.

Therefore, by reducing the acting load, it is possible to simplify the steel shell structure of the surrounding structure and reduce the reinforcement measures of the surrounding structure.

Therefore, according to the freezing method of the present embodiment, it is possible to reduce the reinforcement of the structure and the required frozen soil thickness, and it is possible to realize a rational freezing method.

Although the embodiment of the freezing method according to the present invention has been described above, the present invention is not limited to the above embodiment and can be appropriately modified without departing from the spirit of the present invention.

1 Main line shield 2 Lamp shield 3 Underground shaft 4 Starting base 5 Outer shell shield 6 Frozen soil wall 7 Main lining 8 Frozen soil wall 9 Frozen pipe 10 Opening part

Claims (1)

In the freezing method that freezes the ground in the frozen soil area where the sandy soil layer and the cohesive soil layer exist.
While preventing the cohesive soil layer from freezing ,
A freezing method comprising freezing at least a part of the sandy soil layer when the cohesive soil layer is on the side to be protected from the sandy soil layer .

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