JP2803409B2 - Liquefaction countermeasure structure for embankment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an embankment liquefaction countermeasure structure using a liquefaction inhibiting pile or a liquefaction inhibiting sheet pile having a drainage function.

[0002]

2. Description of the Related Art For embankment structures on the ground where liquefaction is likely to occur (hereinafter, simply referred to as liquefaction ground), liquefaction countermeasures that have been studied so far include a wall structure method and a discrete pile arrangement. System, compaction system and drainage system. These features are described below.

(1) Wall Structure Method As shown in FIG. 11, a wall structure made of a steel sheet pile 21 or a steel pipe sheet pile (not shown) is formed on both sides of an embankment 1 as shown in FIG. To connect the heads of the wall structures at a predetermined pitch. In soft ground that does not liquefy, this can prevent deformation of the embankment 1 during earthquakes (general term of subsidence, slip of the slope, lateral flow of the ground under the embankment), and rapid construction is possible.

In application to embankment on liquefied ground,
When the width of the embankment section is narrow, even under the seismic force where the ground around the embankment 1 becomes liquefied, the ground restraining effect due to the strength and rigidity of the structure of this method is exerted, and the excess pore water pressure at the lower part of the embankment 1 is reduced. The rise and the decrease in the strength of the ground can be suppressed, and the deformation of the embankment 1 can be suppressed.

(2) Discrete pile placement method In the pile discrete placement method, as shown in FIG. 12, piles 22 are staggered on both sides of the embankment 1 at a center interval 2D (D: pile diameter). .

In this method, the heads of the piles 22 in the extending direction of the embankment 1 are connected to each other by a reinforced concrete cap or concrete foundation 6, and the piles 22 on both sides of the embankment 1 are connected at a predetermined pitch by using a tie rod 20. doing.

This method also has the same advantages as the sheet pile wall structure method on soft ground that does not liquefy, and furthermore, since the piles 22 are arranged discretely, the flow of groundwater is not interrupted.

(3) Ground Compaction Method The ground compaction method is a method of compacting both sides of the embankment 1 on the liquefied ground 4 (sand compaction pile method and the like) as shown in FIG. Depending on the size of the cross section, there is also a method of using the holding embankment 24 together, as illustrated in FIG. In the figure, reference numeral 13 denotes a ground compaction work such as a sand pile.

This method suppresses the rise of excess pore water pressure in the compacted ground by the compacting effect and suppresses the deformation of the embankment by the ground restraining effect even under the seismic force that liquefies the surrounding ground. Can be. Further, in this method, since the liquefied ground 4 itself is compacted by using the sand material, the flow of the groundwater under the embankment 1 is not interrupted.

(4) Drainage system As shown in FIG. 15, the drainage system is provided on both sides of the embankment 1 with the purpose of suppressing excessive rise in pore water pressure in the liquefied ground 4 during an earthquake. Drainage material such as drain 2
5 is provided in a columnar shape.

In this method, when the embankment width and height are small,
Even if the surrounding ground of the embankment 1 is liquefied, the drainage effect of the drainage material 25 suppresses the rise of the excess pore water pressure of the surrounding ground,
In addition to suppressing sand blasting, it is possible to suppress a decrease in ground strength and deformation of the embankment 1. Also, this method does not interrupt the flow of groundwater.

[0012]

The liquefaction countermeasure structure of the embankment structure on the liquefied ground has the following problems.

(1) Wall structure method As the cross section width of the embankment (particularly the slope) becomes wider, the ground restraining effect due to the strength and rigidity of the wall structures provided on both sides of the embankment is reduced, and the embankment is surrounded by the wall structure. Excess pore water pressure also rises in the ground, the wall surface becomes streamline, sand erosion is seen along the wall surface, and the deformation of the embankment increases.

When the excess pore water pressure rises, the water pressure (1-K ₀ ) Δu (K ₀ : initial earth pressure coefficient, Δu: excess pore water pressure) acting on the wall structure also increases, so that the excess pore water pressure rises. It is necessary to further increase the strength and stiffness of the wall structure as compared with the case where it is not performed, which is uneconomical.

Furthermore, the groundwater environment changes because the wall structure blocks the flow of groundwater.

(2) Discrete pile arrangement method In the event of an earthquake, the ground strength is reduced due to an increase in excess pore water pressure on the ground under the bottom of the embankment method, and sand is released from between the piles to cause deformation of the embankment. This method is not suitable for embankment on liquefied ground.

(3) Soil compaction method When this method is applied to an existing embankment, compaction ground must be formed outside the bottom of the embankment method regardless of the width of the embankment, and compaction on both sides of the embankment. The width between the grounds becomes wider, and the same tendency as the wall structure is observed. For this reason, it is necessary to use it together with the embankment (FIG. 14) or the like, which is uneconomical.

[0018] Regardless of whether the embankment is new or existing, the transmission of the excess pore water pressure generated in the liquefied ground to the compacted ground reduces the shear strength of the compacted ground near the boundary surface. Since the degree of the decrease is unknown, it is necessary to allow some space in the compaction width. As a result, economic efficiency is impaired and the construction period is lengthened.

(4) Drainage method In this method, the area where the drainage effect in the event of an earthquake is expected is about 1 m from the drainage position, so the area where the decrease in ground strength due to excessive pore water pressure suppression is not as large as about 1 m. In addition, since a crushed stone drain or a resin drain is used for the drainage material itself, the shear strength is lower than when steel drainage material is used. Therefore, compared with the case where a steel drainage material is applied, the construction width is widened, and as a result, economic efficiency is impaired and the construction period is lengthened.

An object of the present invention is to solve the problems in the prior art as described above. In other words, when a large-scale embankment is installed on the liquefied ground, the excess pore water pressure generated around the embankment and the ground under the embankment during the earthquake is dissipated without interrupting the groundwater flowing under the embankment, The purpose is to prevent deformation of the embankment in combination with the effect, and to improve the workability and economic efficiency of the liquefaction countermeasure structure.

[0021]

An outline of the present invention will be described below with reference to the drawings corresponding to the embodiments.

The liquefaction countermeasure structure of the embankment of the present invention comprises a row of liquefaction-inhibiting piles 2 or a wall-shaped liquefaction having both water permeability and drainage on the slope surface or near the bottom of the embankment 1. The installation of the deterrent sheet pile 3 does not interrupt the flow of groundwater in the liquefied ground 4 and the non-liquefied ground 5 under the embankment 1, and increases the excess pore water pressure in the liquefied ground 4 generated during an earthquake. To prevent sand blasting along the liquefaction inhibiting pile 2 and the liquefaction inhibiting sheet pile 3, and to prevent deformation of the embankment by its strength and rigidity.

For this reason, in the present invention, a liquefaction-preventing pile having, as a pile constituting the liquefaction-preventing pile 2, a perforated portion having a large number of small holes 11 formed in a portion of the pile body located in the liquefied ground 4, for example 2a, or a liquefaction prevention pile 2b having a drainage member 13 having a hollow portion in the longitudinal direction and having a number of small holes 11 formed in a portion located in the liquefied ground 4 is used.

In the case of the liquefaction inhibiting sheet pile 3, at least a part of the sheet piles constituting the wall-like structure, for example, a steel pipe sheet pile type liquefaction inhibiting sheet pile 3a in which the entire sheet pile body is perforated, or the aforementioned liquefaction inhibiting sheet pile 3a. A plate-like liquefaction-inhibiting sheet pile 3b having a drainage member 13 similar to the liquefaction-inhibiting pile 2b is used.

In addition, the liquefaction prevention pile 2a or 2
b. As a countermeasure against drainage of underground water flowing into the liquefaction-preventing sheet pile 3a or 3b, a crushed rock mat in the embankment extension direction from the periphery of the liquefaction-suppressing pile or the head of the liquefaction-suppressing sheet pile to a position higher than the groundwater level. 8, or a crushed stone mat 8 and a blind culvert 9 may be provided.

[0026]

[Function] This structure is designed to provide a liquefaction-preventing pile or liquefaction-preventing sheet pile with high strength and rigidity to the most liquefiable part of the embankment up to the non-liquefied ground under the liquefied ground. It is possible to suppress the rise of the excess pore water pressure around the liquefaction inhibiting pile or liquefaction inhibiting sheet pile, prevent the ground strength from decreasing, and suppress the deformation of the embankment by the soil restraining effect as the pile or the sheet pile.

Further, the drainage function of the liquefaction suppression pile or the liquefaction suppression sheet pile prevents the formation of streamlines on the same surface, thereby preventing sand blasting.

In this structure, the liquefaction-prevention piles or the liquefaction-prevention sheet piles arranged in the form of walls are made permeable so that the groundwater environment can be reduced without interrupting the flow of groundwater. maintain.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the illustrated embodiment will be described.

FIG. 1 shows an embodiment in which a liquefaction inhibiting pile 3a having a drainage function and water permeability is used for liquefaction countermeasures for embankment.

That is, a liquefaction-preventing sheet pile 3a (see FIG. 4) in which a number of openings and filters are provided in a predetermined section of a steel pipe sheet-pile is used instead of a normal pile sheet pile in a wall structure system. The liquefaction-preventing sheet piles 3a in the embankment extension direction are connected to each other by a shading concrete or concrete foundation 6 at the head of the 3a, and the liquefaction suppression sheet piles 3a in the direction perpendicular to the embankment extension direction are connected by tie rods 7. In addition, a crushed stone mat 8 is provided by backfilling at a drain position above the liquefaction inhibiting sheet pile 3a.

In this embodiment, due to the drainage effect of the liquefaction-preventing sheet pile 3a, an increase in excess pore water pressure generated in the liquefaction ground 4 during an earthquake is suppressed in the vicinity of the liquefaction prevention sheet pile 3a. A decrease in strength can be prevented. In addition, the liquefaction-preventing sheet pile 3a having strength and rigidity as a sheet pile is laid into the non-liquefied ground 5 under the liquefied ground 4, thereby exhibiting a ground restraining effect and suppressing deformation of the ground. .

In the design of the self-supporting sheet pile, when the embankment 1 can be stabilized only by the liquefaction-preventing sheet pile 3a, the tie rod 7 and the like can be omitted.

In place of the liquefaction-preventing sheet pile 3a, FIG.
A plate-like liquefaction-inhibiting sheet pile 3b as shown in FIG. 6 or a liquefaction-inhibiting pile 2a, 2b as shown in FIGS. 2 and 3 may be used. In the case of the liquefaction prevention piles 2a and 2b, by sanding them at an appropriate pile pitch, the sand between the liquefaction prevention piles forms a kind of wall structure and has the same effect as the liquefaction prevention sheet pile 3a. Is shown.

FIGS. 2 and 3 show examples of the liquefaction inhibiting pile used in the present invention, and FIGS. 4, 5 and 6 show examples of the liquefaction inhibiting sheet pile used in the present invention.

The liquefaction-preventing pile 2a shown in FIG. 2 has a number of openings 11 formed over a predetermined section of the steel pipe, that is, the thickness of the liquefied ground, and a filter 12 for preventing the inflow of earth and sand into the openings 11. And the inside of the steel pipe is used as a drainage space (see JP-A-61-146910).

The liquefaction prevention pile 2b in FIG. 3 is provided with a drainage member 13 at a predetermined section in the longitudinal direction of the outer surface of the steel pipe. The drainage member 13 has a large number of openings 11 and intrusion of soil from the ground through the openings 11. This is provided with a filter 12 for preventing the above.

The liquefaction-preventing sheet pile 3a shown in FIG.
A number of openings 1 are provided in a predetermined section of a steel sheet pile having
A filter 12 for preventing intrusion of earth and sand is provided in the opening 11, and the inside of the steel pipe is used as a drainage space (see Japanese Patent Application Laid-Open No. 1-226920).

The liquefaction-preventing sheet pile 3b shown in FIGS. 5 and 6 is provided with a drainage member 13 at a predetermined section along the longitudinal direction of a sheet-like sheet pile having joints 16 at both ends. Numerous openings 11 and openings 1 in the deterrent sheet pile 3b
Filter 1 to reduce intrusion of soil from the ground from 1
2 (see Japanese Patent Application Laid-Open No. 1-125413, etc.).

The above is an example of the liquefaction-suppressing pile and the liquefaction-suppressing sheet pile, respectively. The liquefaction-suppressing pile and the liquefaction-suppressing sheet pile used in the present invention are based on the function of the pile or the sheet pile and the function at the time of earthquake. Any type can be used as long as it has a drainage function for dissipating excessive pore water pressure generated in the ground.

FIGS. 7 to 10 show examples of the installation of the crushed stone mat 8 for drainage used in the present invention.

The crushed stone mat 8 for drainage is continuously constructed along the embankment extending direction from the periphery of the head of the liquefaction inhibiting pile 2 or the liquefaction inhibiting sheet pile to a position higher than the groundwater level.

The crushed stone mat 8 may be provided with a blind conduit 9 for smooth drainage. FIG. 10 shows a case where the blind conduit 9 is provided on both sides of the liquefaction prevention pile 2. FIG. 9 shows a case in which it is provided on one side. Culvert 9
Any material such as a vinyl chloride pipe, a reinforced concrete pipe, and a porcelain pipe may be used as long as it can ensure water permeability when draining groundwater.

The crushed stone mat 8 is usually connected to a general drainage channel. However, no drainage channel is provided, the groundwater is stored in the crushed stone mat 8, and the stored groundwater is transferred to the ground after an earthquake. There is also a method of draining by infiltration.

[0045]

The liquefaction countermeasure structure of the embankment of the present invention has a drainage property and a water permeability near the embankment slope or the bottom of the embankment where liquefaction is most likely to occur during an earthquake, and has the strength and rigidity of a pile or sheet pile. Deterrent piles or liquefaction deterrent sheet piles are properly installed in the non-liquefied ground below the liquefied ground. As a result, the following effects can be obtained.

By securing a drainage route for underground water generated during an earthquake, an excessive rise in pore water pressure can be suppressed, and a decrease in ground strength can be prevented.

The ground restraining effect is exerted by sufficiently staking the liquefaction prevention pile or the liquefaction prevention sheet pile having strength and rigidity into the liquefaction ground.

[0048] The drainage function of the liquefaction inhibiting pile or liquefaction inhibiting sheet pile can prevent the formation of streamlines on the same surface and prevent sand blasting.

By means of the above, deformation of the embankment can be suppressed.

[0050] without interrupting the flow of underground water by water permeability of liquefaction suppression piles or liquefaction suppression sheet pile, also of head
Continuous crushing from the head drainage position to the position higher than the groundwater level
Liquefaction control piles or liquefaction control during an earthquake
Drainage of groundwater flowing into the cut-off sheet can be performed to maintain the groundwater environment.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view showing one embodiment of a liquefaction countermeasure structure for embankment of the present invention.

FIG. 2 is a perspective view showing an example of a liquefaction inhibiting pile used in the present invention.

FIG. 3 is a perspective view showing another example of the liquefaction suppressing pile used in the present invention.

FIG. 4 is a perspective view showing an example of a liquefaction-preventing sheet pile used in the present invention.

FIG. 5 is a perspective view showing another example of the liquefaction-preventing sheet pile used in the present invention.

FIG. 6 is a perspective view showing the back side of the liquefaction-preventing sheet pile of FIG. 5;

FIG. 7 is a vertical sectional view showing an example of a crushed stone mat portion provided on the upper part of the liquefaction suppression pile.

FIG. 8 is a vertical sectional view showing another example of the crushed stone mat portion provided on the upper part of the liquefaction prevention pile.

FIG. 9 is a vertical sectional view showing another example of the crushed stone mat portion provided on the upper part of the liquefaction prevention pile.

FIG. 10 is a vertical sectional view showing another example of the crushed stone mat portion provided on the upper part of the liquefaction prevention pile.

FIG. 11 shows an example of a conventional wall structure method.
(a) is a horizontal sectional view, (b) is a vertical sectional view.

FIG. 12 shows an example of a conventional pile discrete arrangement method, in which (a) is a horizontal sectional view and (b) is a vertical sectional view.

FIG. 13 is a vertical sectional view showing an example of a conventional ground compaction method.

FIG. 14 is a vertical sectional view showing another example of the conventional ground compaction method.

FIG. 15 is a vertical sectional view showing an example of a conventional drainage method.

[Explanation of symbols]

1: embankment, 2: liquefaction deterrent pile, 3: liquefaction deterrent sheet pile, 4
... liquefied ground, 5: non-liquefied ground, 6: concrete or concrete foundation, 7: tie rod, 8: crushed mat, 9: blind culvert, 11: opening, 12: filter,
13 ... Drainage member, 14 ... Male joint, 15 ... Female joint, 16
… Fittings

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yukio Saishimura 1-3-1 Otemachi, Chiyoda-ku, Tokyo Sumitomo Metal Industries, Ltd. (56) References JP-A-2-225712 (JP, A) ( 58) Field surveyed (Int.Cl. ⁶ , DB name) E02D 3/08 E02D 17/18

Claims (4)

(57) [Claims] 1. A liquefaction-inhibiting sheet pile provided with a drainage function for suppressing a rise in excess pore water pressure generated around an embankment and in the ground under an embankment during an earthquake is liquefied near the embankment slope or at the bottom of the embankment. It is provided with a length obtained by adding the required length to the layer thickness of the ground, and further, from the upper drainage position of the liquefaction suppression sheet pile,
A liquefaction countermeasure structure for embankment characterized by providing a continuous crushed stone mat up to a position higher than the water level . 2. The liquefaction inhibiting sheet pile has an opening for allowing groundwater to pass in a direction perpendicular to the liquefaction inhibiting sheet pile continuous direction, and a filter for preventing permeation of sand from the opening. The liquefaction countermeasure structure for embankment according to claim 1, further comprising: 3. In the ground around the embankment and under the ground during an earthquake
Drainage function to suppress the rise in excess pore water pressure
The liquefaction-preventing pile provided with
Nearby, discrete with the length of the liquefied ground plus the required length
From the upper drainage position of the liquefaction suppression pile,
A liquefaction countermeasure structure for embankment characterized by providing a continuous crushed stone mat up to a position higher than the sewage level . 4. The liquefaction prevention pile is permeable to groundwater.
Openings to prevent sand from permeating through the openings.
4. A prosthesis according to claim 3, wherein a filter for stopping the operation is provided.
Soil liquefaction prevention structure.