JP2995436B2 - Liquefaction floating prevention method by rigid water blocking wall - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention is applicable to low-rise buildings and buried structures having various types of foundations such as pile foundations, direct foundations, floating foundations, caisson foundations, etc., and includes a rigid water-stop wall provided in the ground. The present invention relates to a method for preventing the ground from being lifted due to liquefaction during an earthquake.

[0002]

2. Description of the Related Art As a countermeasure against rising of a structure due to liquefaction of the surrounding ground during an earthquake, as shown in FIG.
As a general countermeasure, a method of providing the water blocking wall 2 in the ground on both side surfaces of the above. The conventional concept of a water stop wall is to block the propagation of excess pore water pressure from the surroundings.If a very rigid wall surrounds the ground under the structure, shear deformation between sand particles does not occur, and liquefaction occurs. The idea is that it will not happen.

[0003] Based on the idea that the fluid rises due to the excess pore water pressure, FS is calculated by the following design calculation formula.
If ≦ 1.0, it was said that it would rise.

[0004]

(Equation 1)

In the above equation, the excess pore water pressure applied to the structure is obtained by a program capable of simulating the liquefaction phenomenon of the ground during an earthquake using a finite element method or the like.

[0006]

However, in the above-mentioned conventional design method, it is necessary to obtain the excess pore water pressure applied to the structure using a program capable of simulating the liquefaction phenomenon of the ground during an earthquake using a finite element method or the like. The difficulty with using this program is that it is difficult to determine the constants used in the calculation, and it is difficult for a general designer to use. In addition, a method of preventing liquefaction immediately below the structure by the rigidity of the prevention wall also needs to rely on this program, making it difficult for general designers to work on. Further, it has been reported in experiments and studies to date that this method is less effective as the width of the structure increases.

The present invention solves the above-mentioned problem, and it is possible to easily obtain an expected lifting amount of a structure during an earthquake, and to design a rigid water blocking wall based on this. It is an object of the present invention to provide a method for preventing the formation of a lift.

[0008]

For this purpose, the method for preventing liquefaction from rising by the rigid water blocking wall according to the present invention determines the pore water pressure difference between the inside and outside of the water blocking wall 2 and deforms the water blocking wall 2 by the pore water pressure difference. Calculate the area, divide the deformed area of the water blocking wall on both sides by the bottom width of the structure 1 to obtain the expected floating amount of the structure 1, and the expected floating amount of the structure is equal to or more than the allowable floating amount Then, the underground beam 3 is provided between the water blocking walls. The numbers added to the above configuration are for comparison with the drawings for easy understanding, and do not limit the configuration of the present invention at all.

[0009]

In the present invention, the rigidity of the water stop wall is intended only for the purpose of countermeasures against floating, and does not require an extremely high rigidity required to prevent liquefaction of the internal ground. In addition to blocking the propagation of excess pore water pressure due to liquefaction of the ground from the outside of the side ground, the rigidity of the ground prevents horizontal inward deformation and prevents the internal ground from being pushed up by this deformation.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. The inventor conducted various experiments and found that the effect of the water blocking wall was considered as follows in accordance with actual behavior. That is, when the unit volume weight of the entire structure is lower than the unit volume weight of the ground of the same volume, the total stress under the structure is lower than the total stress at the same depth outside the water blocking wall, and The pore water pressure during liquefaction will not exceed this total stress.
Therefore, as shown in FIG. 5, the pore water pressure P _I in the water stop wall at the time of liquefaction is lower than the external excess water pressure P _O , and the water pressure difference pushes the water stop wall inward from the outside. FIG. 6
Deform as shown in FIG.

[0011] Due to the deformation, the sand inside is pushed from the side and is sheared under substantially the same volume, so that the buried structure is raised.

As a conclusion obtained from the above, it is necessary to design a countermeasure against floating using a rigid water blocking wall in consideration of the following.

[0013] The rigidity of the water stop wall is intended only for the purpose of countermeasures against rising, and does not require extremely high rigidity required to prevent liquefaction of the internal ground.

[0014] The water blocking wall blocks propagation of excessive pore water pressure due to liquefaction of the ground from the outside of the side ground,
Its rigidity prevents horizontal inward deformation and prevents the internal ground from being pushed up by this deformation.

FIG. 1 is a flowchart for explaining a method for preventing liquefaction floating from occurring by a rigid water blocking wall according to the present invention based on the above concept.

First, in step S1, as shown in FIG.
The pore water pressure difference between the inside and outside of the water stop wall is obtained, and then, in step S2, as shown in FIG. 6, the deformation area of the water stop wall due to this water gap is calculated. This is based on the structural calculation where the water stop wall is regarded as a beam. Next, in step S3, the expected floating amount of the structure is determined from (deformed area of the water blocking wall on both sides) / (bottom width of the structure). In step S4, the expected floating amount of the structure is allowed. It is determined whether or not the amount is equal to or more than the rising amount. If the amount is less than the allowable amount, the end is determined. If the amount is equal to or larger than the allowable amount, an underground beam is inserted in step S5. Increase the rigidity of

Here, the difference in pore water pressure during liquefaction can be determined from the total stress difference in a stationary state (normal state in design).

Examples of the construction of the waterproof wall according to the present invention based on the above method include the following. As shown in FIG.
When the width of the structure 1 is narrow and the rigid retaining wall 2 having low rigidity is used for the water blocking wall, it is only necessary to improve the bottom of the structure.

When the width of the structure is wide, it is effective even if the rigidity of the water blocking wall is low. The reason is that (deformed area of side wall) / (width of structure) is reduced.

As shown in FIG. 3, when the liquefied ground is thick, an underground beam 3 is provided between the water blocking walls 2.

[0021]

As is apparent from the above description, according to the present invention, the pore water pressure difference between the inside and outside of the water blocking wall is obtained, the deformation area of the water blocking wall due to the pore water pressure difference is calculated, and the water stopping water on both sides is obtained. Dividing the deformed area of the wall by the width of the bottom of the structure to obtain the expected lift amount of the structure, and if the expected lift amount of the structure is equal to or more than the allowable lift amount, the underground space between the water blocking walls is obtained. By the method of providing the beam, the expected lifting amount of the structure at the time of the earthquake can be easily obtained, and the design of the rigid waterproof wall can be performed based on this.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a method for preventing liquefaction floating from rising by a rigid water blocking wall according to the present invention.

FIG. 2 is a cross-sectional view showing a construction example of a water blocking wall according to the present invention.

FIG. 3 is a sectional view showing a construction example of a water stop wall according to the present invention.

FIG. 4 is a diagram for explaining the concept of a conventional water blocking wall.

FIG. 5 is a diagram for explaining a pore water pressure difference inside and outside a water stop wall.

FIG. 6 is a view for explaining deformation of a water stop wall due to a difference in pore water pressure.

[Explanation of symbols]

 1. Structure, 2. Water stop wall, 3. Underground beam

──────────────────────────────────────────────────続 き Continuing on the front page (72) Takashi Yoshimura, 1-3-2 Shibaura, Minato-ku, Tokyo Shimizu Corporation (72) Inventor Tsukasa Kondo 1-2-3, Shibaura, Minato-ku, Tokyo Shimizu (56) References JP-A-3-212515 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) E02D 27/34 E02D 31/12

Claims (1)

(57) [Claims] 1. A pore water pressure difference between the inside and outside of a water blocking wall is obtained, a deformation area of the water blocking wall due to the pore water pressure difference is calculated, and the deformation area of the water blocking wall on both sides is divided by a bottom width of a structure. The expected lift amount of the structure is obtained, and if the expected lift amount of the structure is equal to or more than the allowable lift amount, the underwater beam is provided between the water stop walls. Floating prevention method.