JPH08239842A - Structure and method for liquefaction prevention - Google Patents

Abstract

PURPOSE: To prevent liquefaction phenomenon generated in a ground when an earthquake occurs. CONSTITUTION: A permeable layer extending in vertical direction is formed in a structure buried in a ground such as a sheet pile, pile, etc. For example, a permeable layer 3 is formed in a recessed part 2a of a main body part 2 comprising conventional concrete sheet parts. The permeable layer 3 is formed by placing permeable concrete into the recessed part 2a of the main body part 2. Also the permeable layer 3 is formed so that it is extended vertically along the, side surface of the main body part 2. By this, when the concrete sheet pile 1 is driven into the ground, underground water (water in clearance) flows into the permeable layer 3 when the pressure of the underground water (water in clearance) in the ground rises. Because the underground water (water in clearance) flowed into the permeable layer 3 is drained from the top of the concrete sheet pile 1, a rise of the underground water (water in clearance) pressure can be prevented. Then, liquefaction can be prevented by preventing a rise of underground water (water in clearance) pressure in earthquake.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquefaction-preventing structure and a liquefaction-preventing method which are effectively used in the ground where liquefaction is likely to occur.

[0002]

2. Description of the Related Art In recent years, a liquefaction phenomenon that occurs in a landfill site during an earthquake has become a problem. The liquefaction phenomenon is
In the sand ground where the groundwater level is high and loose, the sand particles were normally arranged so that the force was transmitted between the sand particles, but when the earthquake shakes, the arrangement collapses and In such a condition that no force is transmitted, that is, the sand particles are groundwater (such as pore water in the gap between sand particles).
The load suspended by the sand particles before the earthquake was applied to the sand particles and the groundwater, the groundwater pressure (pore water pressure) suddenly increased, and the groundwater containing the sand particles was grounded. It blows out to.

When the above-mentioned liquefaction phenomenon occurs, water containing sand or soil particles is blown out as described above.
In addition, the sand particles are suspended in the groundwater, causing a flow in the ground and displacing the ground. In addition, groundwater will be spouted, which will cause ground subsidence.

Further, due to these, the pipes and the like buried in the ground are damaged. In addition, if the ground is in the above-mentioned state, the supporting force of the ground is reduced, and the building may collapse.

Conventionally, as a method for preventing the above problems, for example, as a method for preventing collapse of a building,
There has been a technique in which the piles that support the foundation of a building are driven deeper than the liquefiable layer of the ground so that the liquefied layer does not affect the building even if it is liquefied. As a method of preventing the liquefied ground from flowing and being displaced, for example, by constructing a structure such as a retaining wall in the ground, the ground can be prevented from flowing.

[0006]

By the way, the method of burying the pile in the above-mentioned conventional example deeper than the layer that is easily liquefied can prevent the collapse of the building, but does not prevent the liquefaction of the ground itself. Absent. Therefore, underground pipes such as water pipes, gas pipes, sewer pipes, electric wires, and telephone lines buried underground are
It will be affected by the liquefaction, and even if the building remains, water and energy cannot be supplied to the building.

Further, even when a structure such as a retaining wall is provided in the ground so as to divide the layer that is easily liquefied, it is not possible to prevent the liquefied ground from rocking during an earthquake, It is not possible to prevent the above-mentioned underground piping from being damaged. In addition, when the back ground is liquefied in a common retaining wall or retaining wall, which is a general retaining wall, horizontal earth pressure increases, and these structures themselves are damaged.

The present invention has been made in view of the above-mentioned problems, and it is installed in the ground to structurally suppress damage to the structure and flow of the ground at the time of liquefaction, and at the time of liquefaction. It is an object of the present invention to provide a liquefaction prevention structure and a liquefaction prevention method that can prevent an increase in pore water pressure and suppress liquefaction itself.

[0009]

The structure for preventing liquefaction according to claim 1 of the present invention extends vertically in a structure installed such that at least one side surface of a pile, a sheet pile or the like is buried. The water permeable layer is formed, and the water permeable layer is in contact with the earth and sand in which the structure is buried.

In the liquefaction-preventing structure according to claim 2 of the present invention, the water-permeable layer is made of water-permeable concrete, which is a means for solving the above-mentioned problems.

Further, in the method for preventing liquefaction according to claim 3 of the present invention, when a structure such as a pile or a sheet pile is driven, the structure is preliminarily extended vertically to the structure and a side surface of the structure. The formation of the water permeable layer exposed on the side was followed by driving the structure to solve the above-mentioned problems.

[0012]

According to the structure described in claim 1, it is possible to suppress the flow of the liquefied ground in the portion where the structure is buried and to drain the pore water upward by the water permeable layer. Therefore, it is possible to suppress liquefaction due to increase in pore water pressure during an earthquake. Further, when the soil pressure applied to the structure increases due to liquefaction, the pore water is drained upward, whereby the soil pressure can be reduced.

Further, even under normal conditions, the permeable layer allows the groundwater to be drained so that the rise of the groundwater level can be prevented. Therefore, it is possible to prevent the ground from becoming easily liquefied due to the rise of the groundwater level. Also, in order to drain the pore water to the above structure,
When a groove or space that comes into contact with earth and sand is provided along the vertical direction, there is a high possibility that earth and sand will enter the groove and space, and it is not always possible to ensure water permeability for a long time, By forming a water permeable layer that is in contact with earth and sand, rather than a groove or space that is in contact with earth and sand, it is possible to ensure water permeability in the long term.

Further, according to the structure of claim 2,
Although permeable concrete is slightly inferior to ordinary concrete in terms of strength, it is inexpensive as a substance having water permeability and has relatively high strength, so a structure for preventing liquefaction can be manufactured at low cost. At the same time, the structure for preventing liquefaction having a water permeable layer can be driven in as a normal pile or sheet pile.

Further, according to the configuration of claim 3 above,
In a structure such as a pile or sheet pile, a water-permeable layer that extends vertically and is exposed on the side surface of the structure is formed, and the structure is formed by placing this in a ground that may be liquefied. In the water permeable layer, it becomes possible to drain the pore water in the ground and suppress the liquefaction itself of the ground. Also,
Even during normal times, it is possible to prevent the groundwater level from rising as described above, and prevent liquefaction from occurring.

Further, if the above-mentioned structure is used as a pile for supporting the foundation and driven into the bottom of the stratum having a high possibility of liquefaction, the liquefaction is suppressed as described above and the liquefaction is completely suppressed. If not done, the superstructure on the foundation can be protected.

If the structure is used as a sheet pile and the sheet pile is driven into the ground to form a revetment, a retaining wall, or an underground wall, the pore water is drained as described above. With this, liquefaction can be suppressed, and when liquefaction cannot be completely suppressed, drainage of pore water as described above will cause earth pressure on the revetment, retaining wall and underground wall during liquefaction. It is possible to suppress the rise, and suppress the flow of the ground structurally liquefied wall-shaped structure consisting of the sheet pile,
The displacement of the ground can be minimized.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A liquefaction preventing structure and a liquefaction preventing method according to an embodiment of the present invention will be described below with reference to the drawings. In this example, the present invention is applied to a concrete sheet pile, and FIG. 1 shows a concrete sheet pile 1 as a liquefaction preventing structure of this example. As shown in FIG. 1, a concrete sheet pile 1 which is a liquefaction preventing structure of this embodiment includes a concrete sheet pile main body 2 and a main body portion 2.
The water permeable layer 3 is formed on one side surface of the.

The body 2 is basically made of conventional concrete sheet pile. That is, the main body 2 is a plate-shaped structure made of precast concrete, and a concave portion 2a is formed on one side surface of the main body 2 and a projecting ridge 2b extending vertically is formed on one end surface of the main body portion 2. A 2c groove is formed to extend to. Then, as shown in FIG. 2, the main body portion 2 has a wall-shaped structure in which a plurality of concrete sheet piles 1 are continuously driven in a row so that the ridges 2b and the grooves 2c are fitted to each other. It has become a body.

The water permeable layer 3 is provided in a state of being filled in a recess 2a formed on one side surface of the main body portion 2, and one side surface of the main body portion 2 is flat due to the water permeable layer 3. It is said that. The water permeable layer 3 is made of water permeable concrete.

The water-permeable concrete does not use fine aggregate such as sand, but mixes coarse aggregate with a limited grain size and cement paste at a fixed ratio and compacts it. It is a quality concrete. Ordinary concrete uses aggregates with different particle sizes, the voids between large aggregates are filled with medium-sized aggregates, the voids between medium-sized aggregates are filled with fine aggregates, and voids are formed inside. Although it does not occur, it increases the water impermeability, but water-permeable concrete intentionally leaves voids by using aggregates of almost the same particle size instead of using fine aggregates as described above. It is made porous.

Further, the water-permeable concrete may contain bubbles due to the foaming agent. That is, the water-permeable concrete is porous concrete, and has water permeability enhanced by the voids communicating with each other in the concrete.
In addition, in concrete, the water permeability and the strength are inversely proportional to each other, and the water permeable concrete has a lower compressive strength than that of ordinary concrete having high water impermeability.

However, it is possible to add the strength to the extent that the concrete sheet pile 1 is not destroyed when it is driven in and to secure the necessary water permeability. And the concrete sheet pile 1 which consists of the said main-body part 2 and the water permeable layer 3 can be manufactured as follows.

The main body 2 is a conventional concrete sheet pile, which can be manufactured by a well-known method and can be easily obtained. Then, in this embodiment, the concave portion 2 of the conventional concrete sheet pile is used.
The concrete sheet pile 1 of this embodiment can be manufactured by placing water-permeable concrete on a.

Therefore, the concrete sheet pile 1 of this embodiment
Diverts a conventional concrete sheet pile to its body 2,
Moreover, since it is formed by pouring water-permeable concrete into the concave portion 2a of the conventional concrete sheet pile, it is not necessary to develop a concrete sheet pile having a new shape, and it is possible to manufacture it without incurring the development cost. It can be manufactured at low cost.

Next, a liquefaction prevention method using the concrete sheet pile 1 as the liquefaction prevention structure as described above will be described. The concrete sheet pile 1 can be used as a general sheet pile, and can be used as a retaining wall.

In this case, the concrete sheet pile 1 is driven into the ground (shown in FIG. 3) e, but it is possible to drive it as a general concrete sheet pile. When driving, the driving method is not particularly limited, but it is possible to drive the structure by hydraulic force by taking a reaction force from the structure already driven, or press-fitting / pulling the structure.
A pulling machine (not shown) is used.

By using the above press-fitting / pulling-out machine, the concrete sheet pile 1 can be provided without giving impact such as impact or vibration.
Since it is possible to drive, it is possible to prevent the water-permeable layer 3 from being damaged by the driving. In addition, in order to increase the water permeability of the water permeable layer 3 made of water permeable concrete,
Even if the strength of the water permeable layer 3 becomes low, the concrete sheet pile 1 of this embodiment can be driven without damaging the water permeable layer 3 by using the press-fitting / pulling machine.

In other words, by using the press-fitting / pulling-out machine, the water-permeable layer 3 made of water-permeable concrete
The water permeability of the water permeable layer 3
Even if the strength of the concrete sheet decreases, the concrete sheet pile 1 can be driven without being damaged. As described above, the water permeable layer 3 made of water permeable concrete can be adjusted to have a proper water permeability and a proper strength, and can be driven by a pile driving machine other than the press-fitting / pulling machine. It is possible to provide sufficient strength and water permeability capable of distributing pore water.

Then, as shown in FIG. 3, when the concrete sheet pile 1 of this embodiment is driven into the ground e, the water permeable layer 3 made of water permeable concrete is exposed from the main body portion 2 of the concrete sheet pile 1 and the ground sheet e is exposed. Since it is in contact with the earth and sand in e, the pore water (groundwater) in the ground e can be permeable to the permeable layer 3.

When the pore water (groundwater) is under pressure, the pore water (groundwater) flows into the permeable layer 3 as shown by the arrow a ... And inside the permeable layer 3 as shown by the arrow b. Will be drained from the upper part of the concrete sheet pile 1. Therefore, by driving the concrete sheet pile 1 into the ground e, it is possible to prevent the groundwater level from rising due to an increase in groundwater pressure, and the ground e becomes easily liquefied due to the higher groundwater level. Can be prevented.

Also, when the pore water pressure rises during an earthquake, as described above, the pore water flows into the water permeable layer 3 of the concrete sheet pile 1 and is drained from the upper portion of the concrete sheet pile 1, resulting in a liquid state. Suppressing liquefaction or reducing the degree of liquefaction.

Further, since the water permeable layer 3 made of water permeable concrete is a layer having a large number of small voids communicating with each other inside, it is in contact with the earth and sand, and the earth and sand such as grooves and spaces extending vertically. It does not easily intrude, but it can be buried for a long time without reducing its permeability, and it is possible to respond to an earthquake that cannot be predicted when it will occur.

The concrete sheet pile 1 of this embodiment is also used.
Has a structural function as an ordinary sheet pile or a pile, and if the concrete sheet pile 1 is driven as a pile below a layer that is easily liquefied when constructing a foundation of a building, it is a conventional example. As shown, the collapse of the building can be prevented, and the liquefaction can be suppressed as described above.

Also, when the concrete sheet pile 1 is used as a wall surface of an underground structure, the liquefaction is suppressed as described above, and when the earth pressure applied to the underground structure is increased due to the liquefaction without being suppressed, By draining the pore water as described above, the earth pressure can be reduced and the underground structure can be prevented from being damaged. Further, since the concrete sheet pile 1 can suppress an increase in the groundwater level, it is possible to prevent a large buoyancy force from being applied to the underground structure due to the increase in the groundwater level.

Also in the case of earth structures such as embankments and levees, the concrete sheet piles 1 ... Are placed in the ground, for example, along the embankments and levees to suppress liquefaction as described above. In addition, when the liquefaction cannot be completely suppressed, the underground wall composed of the concrete sheet piles 1 ... suppresses the flow of the ground e and reduces the earth pressure as described above, so that the embankment or the embankment due to the liquefaction is reduced. Damage can be prevented.

When the concrete sheet pile 1 is used as a revetment wall, quay wall or other retaining wall, liquefaction can be suppressed, earth pressure can be reduced, and ground e can be prevented from flowing as described above. It is possible to prevent damage to the revetment wall, quay wall and other retaining walls due to liquefaction. Further, by suppressing the liquefaction and the flow of the ground e as described above, it is possible to prevent damage to underground pipes such as water pipes, gas pipes, sewer pipes, electric wires, and telephone lines. It is possible to prevent a situation in which water or energy cannot be supplied even if only the building remains without being destroyed.

In the above embodiment, since the development cost can be reduced by using the conventional concrete sheet pile as the main body 2, the water permeable concrete extending vertically only on one side surface of the plate-like concrete sheet pile 1. Although the water permeable layer 3 consisting of is formed, the water permeable layer 3 may be provided on both side surfaces of the concrete sheet pile 1. Further, even if the water permeable layer 3 is formed only on one side surface side of the concrete sheet pile 1 as described above, there is a risk of liquefaction only on one side surface side of the concrete sheet pile 1 that has been cast, It can be preferably used when only one side surface of the concrete sheet pile 1 is in contact with the earth and sand of the ground e.

In the above embodiment, the water-permeable layer 3 is formed on the plate-shaped concrete sheet pile 1. However, the present invention is substantially vertical (extends vertically) in the ground like a pile or sheet pile. The structure can be applied to any structure as long as it is installed in (1). For example, the structure for preventing liquefaction may be the steel sheet pile 4 shown in FIG. 4, and in the steel sheet pile 4 shown in FIG. 4, a state in which a water permeable layer 5 is formed by casting water permeable concrete on the concave side thereof. Has become. Then, the steel sheet pile 4 having the water permeable layer 5 can be handled in substantially the same manner as the concrete sheet pile 1 of the above-described embodiment, and has the same operational effect.

Further, the liquefaction preventing structure may be the concrete structure 6 shown in FIG. The concrete structure 6 shown in FIG. 5 is made of precast concrete, and constitutes a wall body such as a revetment wall by continuously driving. The concrete structure 6 has a hollow portion 7 that communicates with the upper and lower portions at the center, and a water-permeable layer 8 that extends vertically. And the permeable layer 8
The concrete structure 6 having is capable of being handled in substantially the same manner as the concrete sheet pile 1 of the above-mentioned embodiment, and has the same operational effect.

Although the water permeable layers 3, 5 and 8 are made of water permeable concrete, any member having high water permeability can be used as the water permeable layer. In addition, the water permeable layers 3, 5 and 8 must have a strength that prevents them from being easily crushed by earth pressure and a water permeability that enables distribution of groundwater (pore water). It is required not to decrease remarkably.

However, the water permeable layers 3, 5 and 8 are not necessarily limited to one layer made of a substantially homogeneous member, and may be formed of a plurality of layers. Therefore, a member having low strength but extremely high water permeability may be arranged inside the water permeable layers 3, 5, 8 made of water permeable concrete, or a cavity may be formed inside the water permeable layers 3, 5, 8. You may.

In this case, the strength of the water permeable concrete prevents the members inside the water permeable layer made of water permeable concrete from being crushed, and the water permeable concrete serves as a kind of filter to form cavities inside the water permeable layer. It is possible to prevent the inflow of earth and sand. For example, the concrete structure 6'shown in FIG.
5 has a shape similar to that of the concrete structure 6 shown in FIG. 5, but the water permeable layer 8 ′ made of water permeable concrete does not extend vertically but at predetermined intervals unlike the water permeable layer 8 shown in FIG. It is arranged so that it is scattered vertically.

The water-permeable layer 8'is formed so as to communicate with the hollow portion 7 inside the concrete structure 6 ', and extends vertically from the two water-permeable layers 8'and the hollow portion 7. The water permeable layer of the present invention is configured. That is, the hollow portion 7 is a space extending vertically inside the concrete structure 6 ′ and does not serve as the water permeable layer of the present invention, and the water permeable layer 8 ′ made of water permeable concrete is in contact with earth and sand. , Which does not extend vertically and does not form the water permeable layer of the present invention, but the water permeable layers 8 ′ that are scattered vertically are in a state of being connected by cavities, and the water permeable layer 8 ′ and the cavity 7 are vertically connected. It is possible to form one permeable layer that extends and is exposed so as to contact the earth and sand.

It should be noted that, when the concrete structure 6'is driven into the hollow portion 7, there is a possibility that the earth and sand may invade to a certain extent. There is no possibility that the earth and sand will intrude densely, and since the earth and sand will come into contact with the earth and sand through the water permeable layer 8 ′ after the driving, the earth and sand will not intrude and deposit in the cavity 7.
Therefore, the water permeability can be secured for a long period of time.

Further, like the concrete structure 6 shown in FIG. 5, a concrete structure 6 having high water impermeability and high strength.
As compared with the case where the water permeable layer 8 made of water permeable concrete that is vertically inferior in strength is provided on one side face of FIG.
Since the concrete structure 6'shown in (1) is provided so that the water permeable layers 8'are vertically scattered, it can be a structure having higher strength than the concrete structure 6 of FIG.

Further, the concrete sheet pile 1'shown in FIG.
Is the water permeable layer 9 made of water permeable concrete as described above.
A cavity 10 extending vertically is provided in the interior of the.
Since the cavity 10 is covered with the water permeable layer 9 as described above, the possibility that soil or the like will enter is low, and the water permeability can be ensured for a long period of time.
Further, since the cavity 10 extends vertically, it is possible to improve the drainage performance of the interstitial water above.

[0048]

As described above in detail, according to the structure for preventing liquefaction according to claim 1 of the present invention, the flow of the liquefied ground is suppressed in the portion where the structure is buried. In addition, it is possible to drain the pore water upward by the water-permeable layer, and it is possible to suppress liquefaction due to an increase in the pore water pressure during an earthquake. Further, when the soil pressure applied to the structure increases due to liquefaction, the pore water is drained upward, whereby the soil pressure can be reduced.

Further, even under normal conditions, the above-mentioned permeable layer allows the groundwater to be drained, and the rise of the groundwater level can be prevented. Therefore, the ground becomes liquified easily due to the rise of the groundwater level. Can be prevented. Further, in order to drain the pore water to the structure, if a groove or space that comes into contact with earth and sand is provided along the vertical direction, there is a high possibility that earth and sand will enter the groove and space, and Although it is not always possible to ensure water permeability across
By forming a water permeable layer that is in contact with earth and sand, rather than a groove or space that is in contact with earth and sand, it is possible to ensure water permeability in the long term.

According to the liquefaction-preventing structure described in claim 2, the water-permeable concrete portion is inexpensive as a water-permeable material, has a relatively high strength, and is easily molded, so that it has a low viscosity. Liquefaction can be suppressed at a cost. In addition, since the water-permeable concrete has a relatively high strength as a water-permeable substance as described above, even a part of a pile or a sheet pile is unlikely to be destroyed during driving.

According to the liquefaction prevention method of the third aspect, a water-permeable layer that extends vertically and is exposed on the side of the structure is formed on a structure such as a pile or a sheet pile. By placing the soil on the ground that may be liquefied,
The same excellent effects as those of the structure described in claim 1 can be obtained. Further, the structure also has a function as a pile or a sheet pile, while suppressing liquefaction, it is possible to prevent displacement or collapse of the structure due to the flow of the ground during liquefaction as a pile or sheet pile. .

[Brief description of drawings]

FIG. 1 is a plan view showing a concrete sheet pile which is a liquefaction preventing structure according to an embodiment of the present invention.

FIG. 2 is a plan view showing a state where the concrete sheet piles of the above-described embodiment are placed in a row in the ground.

FIG. 3 is a cross-sectional view showing a state where the concrete sheet piles of the above-described embodiment are placed in a row in the ground.

FIG. 4 is a plan view showing a liquefaction prevention structure of the present invention, which is different from the liquefaction prevention structure of the above-described embodiment.

FIG. 5 is a plan view showing a liquefaction prevention structure of the present invention which is different from the liquefaction prevention structure of the above embodiment.

FIG. 6 is a side view showing a liquefaction prevention structure of the present invention which is different from the liquefaction prevention structure of the above embodiment.

FIG. 7 is a plan view showing a liquefaction prevention structure of the present invention which is different from the liquefaction prevention structure of the above-mentioned embodiment.

[Explanation of symbols]

 1 Concrete sheet pile (structure for liquefaction prevention) 3 Water permeable layer

Claims (3)

[Claims] 1. A permeable layer extending vertically is formed on a structure installed with at least one side face such as piles or sheet piles buried, and the permeable layer is in contact with the earth and sand burying the structure. A structure for preventing liquefaction which is characterized in that 2. The structure for preventing liquefaction according to claim 1, wherein the water permeable layer is made of water permeable concrete. 3. When driving a structure such as a pile or a sheet pile,
A method for preventing liquefaction, which comprises extending the structure in advance in the vertical direction and forming a water-permeable layer exposed on the side surface of the structure, and then driving the structure.