JP2841000B2 - Liquefaction countermeasures - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing damage caused by liquefaction of an underground structure in soft ground.

2. Description of the Related Art Principles of liquefaction countermeasures include (a) improvement of soil grain size or consolidation of soil, (b) increase of soil density, (c) decrease of soil saturation, and (d). Increasing the effective stress, (e) dissipating the soil pore pressure, (f) blocking the pore pressure, and (g) suppressing shear deformation can be considered. This raises the problem of floating and horizontal displacement of the structure due to the occurrence and reduction of the wall frictional resistance. Therefore, the following countermeasures have been taken. (A) Improve the ground immediately below and around the structure where there is a risk of liquefaction, and suppress the occurrence of liquefaction. (B) Drainage layers will be provided on the bottom and periphery of the structure to suppress the rise in excess water pressure. (C) Install an anchor to resist buoyancy acting on the structure. (D) Lower the groundwater level inside the cutoff wall. (E) The liquefied layer immediately below the structure is closed with a water stop wall composed of steel sheet piles that reach the water-impermeable layer to suppress shear deformation of the ground during an earthquake and to prevent water from the surrounding liquefied ground. And prevent the inflow of sand.

However, the countermeasures (a) and (b) cannot be applied to the existing structure, and there is a problem that it takes too much work time and cost. In the above-mentioned countermeasure method (c), stress concentration occurs in the anchor installation portion, and the strength and rigidity of the structure itself must be increased. In the above-mentioned countermeasure method, it is necessary to pump water at all times, which causes a problem in maintenance. In addition, the deadline of (e) can prevent inflow of sand and water from the external liquefied layer, but the pore water pressure locally increases inside the deadline, and it becomes difficult to dissipate the pore water pressure after the earthquake. . Experiments and analyzes have shown that a water-blocking wall as in the method (e) cannot suppress shear deformation during an earthquake. The present invention has been proposed in view of the problems of the conventional method, and the object thereof is to minimize the liquefaction damage of an underground structure during an earthquake in an area where liquefaction may occur. The point is to provide a liquefaction countermeasure method that can be reduced.

In order to achieve the above object, in the liquefaction countermeasure method of the present invention, one side is closed with steel sheet pile and crushed stone is placed in the ground where liquefaction may occur. Reinforcing cages are continuously arranged along the longitudinal direction of the underground structure to suppress shear deformation during an earthquake, dissipate excess pore water pressure around the structure generated during an earthquake, generate liquefaction and It is characterized by preventing the floating.

According to the liquefaction countermeasure method of the present invention, one side is closed with steel sheet piles and crushed stones continuously in the ground where liquefaction may occur, along the longitudinal direction of the underground structure. By arranging the reinforcing bar cage into which water has been introduced and piercing it up to the water-impermeable layer, the reinforcing bar cage functions as a water blocking wall and prevents inflow of water and sand from the surrounding liquefied ground. In addition, the continuous wall of the reinforced cage closed on one side with steel sheet piles and containing crushed stone suppresses shear deformation generated during an earthquake as a column standing in the ground in a cross section, and crushed stone filled inside the reinforced cage is a drain material. As a result, the locally increased excess pore water pressure inside the deadline is dissipated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the liquefaction countermeasure method of the present invention will be described with reference to the illustrated embodiment. FIGS. 1 to 5 show the steps of the liquefaction countermeasure method of the present invention, in which a guide wall 1 is installed along the longitudinal direction of an existing underground structure A constructed on the ground that may be liquefied. (See FIG. 1), a slot 3 along the longitudinal direction of the underground structure is excavated by the clamshell bucket 2 (see FIG. 2), and a reinforcing bar having one side closed with a steel sheet pile 4 in the slot 3. The basket 5 is installed (see FIG. 3), the crushed stone 6 is put into the reinforced cage 5 (see FIG. 4), and the underground continuous wall B of the reinforced basket 5 containing the crushed stone 6 and the ground 7 are integrated by backfilling. The construction is completed (see FIG. 5). As described above, the liquefaction countermeasure construction method of the present invention, as described above, the steel cage 5 in which one side is closed with the steel sheet pile 4 and the crushed stone is put in, prevents water and sand from flowing from the surrounding liquefied ground as a water stop wall, In addition, the continuous wall of the reinforced basket 5 containing the crushed stone 6 suppresses the shear strain and the shear stress at the time of the occurrence of an earthquake as a column standing in the ground in the cross section.
Dissipates the locally increased excess pore water pressure inside the deadline as drain material.

According to the liquefaction countermeasure method of the present invention, liquefaction damage of an underground structure in soft ground can be effectively reduced, so that it can be applied to existing structures. In addition, according to the liquefaction countermeasure method of the present invention, the wall rigidity is expected to be higher than that of steel sheet pile, and it is surrounded by a reinforced cage containing crushed stone, so that the water supply is not interrupted, and the conventional underground continuous wall is not used. Liquefaction countermeasures can be made by construction almost the same as the construction method, and workability is improved.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a guide wall installation process in a liquefaction countermeasure method according to the present invention.

FIG. 2 is a vertical sectional view showing an excavation step.

FIG. 3 is a longitudinal sectional view showing a step of installing a reinforcing cage.

FIG. 4 is a vertical cross-sectional view showing a process of introducing crushed stone into a reinforced cage.

FIG. 5 is a vertical cross-sectional view showing a completed construction state.

FIG. 6 is a longitudinal sectional view showing an embodiment of the present invention.

FIG. 7 is a plan view of FIG. 1;

FIG. 8 is an enlarged vertical sectional view of an underground continuous wall.

FIG. 9 is a partially enlarged view of FIG. 8;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Guide wall 2 Clamshell bucket 3 Slot 4 Steel sheet pile 5 Reinforced basket 6 Crushed stone 7 Ground A Underground structure B Underground continuous wall

Claims (1)

(57) [Claims] 1. A reinforced cage, one side of which is closed with steel sheet piles and containing crushed stone, is continuously arranged along the longitudinal direction of an underground structure in the ground where liquefaction is likely to occur. A liquefaction countermeasure method characterized by suppressing shear deformation, dissipating excess pore water pressure around a structure generated during an earthquake, and preventing liquefaction and floating of the structure.