JP2881224B2 - Structure liquefaction countermeasure system and its construction method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a countermeasure method for preventing or mitigating damage to a structure due to a ground liquefaction phenomenon induced by an earthquake, and more particularly to an effective method for liquefaction countermeasures of an existing structure. The present invention relates to a liquefaction countermeasure system and its construction method.

[0002]

2. Description of the Related Art When a relatively large-scale earthquake occurs and the ground, such as a sand layer, which has been loosely saturated with groundwater, is violently shaken by seismic motion, engagement of the sand particles is disengaged and the liquid in which the sand particles are suspended. When the pore water pressure rises (excess pore water pressure), sand and water erupt to the surface of the ground and the ground surface sinks. In general, various damages occur to various structures in a process in which these liquefaction phenomena occur. Various methods have been proposed as a countermeasure against liquefaction of structures.However, these principles can be broadly divided into measures to design structures to be safe even if the ground liquefies, and measures to liquefy the ground. And measures to prevent the occurrence of A typical example of the former method of designing a structure to be safe even if it is liquefied is a pile foundation method in consideration of the degree of liquefaction. On the other hand, for the latter, some countermeasures have been proposed based on the principle of liquefaction. In other words, liquefaction of the ground
First, sandy soil, second, loose accumulation, and third, water saturation, occur when the three conditions are met. To prevent this, one or more of the above conditions for liquefaction may be removed.

[0003] Meanwhile, as the perception of the conventional earthquake disaster is being changed in all directions, civil engineering construction is not limited to ensuring the earthquake resistance of newly constructed structures, but also to improving the safety of existing structures. An appropriate and reliable countermeasure that can be taken is an important issue to be reconsidered. Compared with newly-built structures, there are more restrictions on the countermeasures to be applied to existing structures, so construction methods are limited.Because it is necessary to pay attention not to affect structures and ground during construction, effective countermeasures are more It becomes difficult.

[0004] As a typical liquefaction countermeasure method applied to existing structures, a gravel drain method based on the principle of dissipating pore water pressure is known. FIG. 12 is a cross-sectional view showing a structure in which liquefaction countermeasures are taken by the gravel drain method. The gravel drain is a water-permeable drainage passage made of gravel, crushed stone, etc. In this method, a plurality of pile-shaped gravel drains serving as a drainage passage are embedded in the ground around the structure. This is to form a closed state. As a result, even if the pore water pressure of the liquefied layer increases instantaneously due to the earthquake, the energy of the excess pore water pressure is absorbed by the drain, and the pore water is drained to the ground surface through the gap of the drain. You. That is, there is an effect of suppressing the liquefaction of the ground by dissipating the excess pore water pressure. The construction of the gravel drain method generally involves forming a plurality of vertically elongated holes in the ground around the structure from the ground surface to an impermeable layer (non-liquefied layer).
Subsequent to the step of excavating to a nearby depth, a drain material made of a material having water permeability such as crushed stone is inserted into the excavation hole to form a drain. In addition,
The layout and shape of the drain may be arbitrarily designed in consideration of the degree of liquefaction predicted based on the properties of the ground, etc., and as shown in FIG. Alternatively, a structure in which a drain material is disposed may be used.

[0005]

When the above-mentioned conventional gravel drain method is applied to an existing structure, the ground is excavated from the ground surface around the structure, and the ground is directly below the foundation of the structure. It is difficult to take countermeasures. Therefore, drilling is performed in the vertical direction and a drain is provided in the ground around the structure. The effect of the countermeasures is maximized mainly on the ground around the structure, but the structure considered to be the most important is The effect of the countermeasure was small on the ground directly below the area, and the effect was insufficient as a liquefaction countermeasure. That is, the pore water pressure of the ground immediately below the foundation, which instantaneously increases during an earthquake,
It was not possible to uniformly and instantaneously propagate to the drain, and it was difficult to obtain the effect of dissipating excess pore water pressure in the ground near the center of the structure, which was at a distance from the drain. The above tendency is particularly remarkable for structures with a large occupied area.Even if the above method is applied to large-scale structures, its effectiveness as a liquefaction countermeasure method that dissipates excess pore water pressure in the ground beneath it Is less.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquefaction countermeasure system which is superior in workability as compared with other conventional methods applied to existing structures, enables uniform and reliable liquefaction countermeasures, and has a low construction cost. It is to provide the construction method.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention firstly provides a drainage drainage pipe having water permeability through which water can be introduced from outside the pipe through the pipe body and into the pipe. The drainage pipe having an arbitrary shape filled with a drain material such as the above, and the drainage pipe having water permeability is arranged in an arbitrary arrangement in the ground immediately below the foundation of the structure. A drainage ditch is provided near a foundation of the structure, and at least one open end of the water-permeable drainage pipe communicates with the drainage ditch. . According to the configuration in which the drainage pipe having the water permeability is arranged on the ground immediately below the foundation of the structure, even in the ground near the center of the structure where the distance to the drain is far, sufficient water permeability is provided through the drainage pipe. Sexuality can be obtained. Therefore, it is possible to immediately propagate the pore water pressure immediately below the structure that increases instantaneously with the earthquake to the drainage ditch through the drain pipe, and uniformly and reliably dissipate the excess pore water pressure of the ground immediately below the foundation, Liquefaction of the ground can be suppressed. Secondly, the present invention is the structure liquefaction countermeasure system according to the first system, wherein the drainage ditch has a shape surrounding the entire periphery of the ground immediately below the foundation of the structure. According to the above features, the excess pore water pressure associated with the earthquake can be uniformly and promptly propagated omnidirectionally and quickly through a drain pipe to a drain provided continuously over the entire circumference of the ground beneath the foundation, enabling drainage. Therefore, even if the occupied area of the structure is relatively large,
The effect of reliably dissipating excess pore water pressure in the ground immediately below the foundation can be obtained, and liquefaction of the ground can be suppressed. Thirdly, in the first system, the perimeter of the drainage ditch is surrounded by a sheet pile, and the perimeter of the ground immediately below a foundation of a structure is continuously surrounded by a sheet pile without gaps. This is a liquefaction countermeasure system for a structure. According to the above feature, since the deformation of the ground due to the shearing force of the ground seismic motion immediately below the foundation of the structure can be suppressed by the sheet pile surrounding the ground immediately below the foundation, the liquefaction of the ground is less likely to occur. In addition, the surrounding water can be shut off by surrounding it with sheet piles, so that excess pore water pressure propagates from the surrounding ground to the ground immediately below the foundation of the structure, causing liquefaction of the ground immediately below the foundation. Can be prevented. The present invention is the fourth
Further, in the second system, there is provided a liquefaction countermeasure system for a structure, comprising a sheet pile continuously surrounding an outer peripheral side of the drainage groove. According to the above features, claim 3
Similarly to the liquefaction countermeasure system according to the invention, an effect of suppressing shear deformation of the ground immediately below the foundation and blocking propagation of pore water pressure from the surrounding ground can be obtained. The present invention has a fifth, first
The liquefaction countermeasure system for a structure according to any one of the above-mentioned systems, wherein a drain pipe having a spiral grooved hole in a pipe is used as the water-permeable drain pipe. In the above-mentioned system, by using the drainage pipe having the above-mentioned characteristic that relatively high water permeability is obtained as the drainage pipe constituting the drain, good drainage performance of the ground portion immediately below the foundation of the structure is achieved. Can be realized. Sixth, the present invention provides a step of continuously driving a sheet pile along the shape of a groove to be excavated in the ground near a structure, and excavating a part surrounded by the sheet pile to form a groove. Providing a water-permeable drainage pipe through which water can pass through the pipe body from outside the pipe to be introduced into the pipe, from the side wall surface in the groove, through the sheet pile, and into the ground immediately below the structure. Placing the drain pipe drain on the ground immediately below the foundation of the structure, and filling the groove with a permeable stone material such as crushed stone. A liquefaction countermeasure method for a structure, comprising a step of backfilling and forming a drain of a drain. According to the above construction method, a configuration in which a drainage pipe having water permeability is arranged on the ground immediately below the foundation of the structure can be easily realized, and the drainage pipe can be easily disposed in the ground near the center of the structure at a distance to the drainage ditch. , Sufficient water permeability can be obtained. Therefore, by immediately transmitting the pore water pressure that increases instantaneously due to the earthquake to the drainage ditch, it is possible to uniformly and reliably dissipate the excess pore water pressure in the ground directly below the foundation and to suppress the liquefaction of the ground. Becomes The groove serving as a drain functions as a work space for placing a drainage pipe during construction work, and is filled with a drainage material such as crushed stone before completion of the construction, thereby forming a drainage groove according to the present invention. can do.
In addition, when the drainage pipe serving as the drain is to be driven, the length, the number, and the arrangement can be arbitrarily set in accordance with the characteristics of the ground, so that appropriate measures can be taken corresponding to various characteristics of the ground. Furthermore, in the above method, the drainage pipe is inserted by direct driving without drilling the ground immediately below the structure, so that there is little influence on the ground and the structure immediately below the foundation, which may cause defects. Also less. Seventhly, the present invention is characterized in that, in the fifth method, a step of surrounding the drainage groove with a sheet pile and continuously driving a sheet pile around the ground immediately below the foundation of the structure without any gaps. This is the method of liquefaction countermeasures for structures.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an example of a structure liquefaction countermeasure system according to the present invention will be described with reference to the drawings. As an example of an existing structure, a case is shown in which the liquefaction countermeasure system of the present invention is applied to a pier portion of a highway. FIG.
Is an underground sectional view of a pier portion to which the liquefaction countermeasure system of the present invention is applied, and FIG. 6 is a plan view of the structure viewed from above.

In FIGS. 5 and 6, the structure 1 is located on a ground 4 (hereinafter referred to as a liquefied layer 4) where sand and gravel are loosely deposited and easily liquefied during an earthquake. A footing (foundation) 2 of the structure 1 is provided in the ground near the ground surface, and is supported by a plurality of foundation piles 3. The foundation pile 3 is cast to reach the depth of a water-impermeable layer 5 (hereinafter referred to as a non-liquefied layer 5) having a hardened non-liquefied geology such as clay, and is provided in the liquefied layer 4. The non-liquefied layer 5 supports a part of the load applied to the footing portion of the structure 1. A drainage pipe 7 having water permeability constituting a drain for liquefaction countermeasures is provided in the ground immediately below the foundation 2 of the structure 1 in a liquefied layer between the foundation piles 3 while avoiding the foundation pile 3. Four regions are evenly arranged in one direction. The end of the drain pipe 7 on the left side with respect to the drawing is open, and the drain provided on the left side with respect to the drawing of the footing 2 of the structure 1 pier.
And protrudes into a drain 6 forming a drain, and both drain portions communicate with each other. The drain groove 6 has a width of about 3 m,
The length is slightly longer than one side of the footing 2 facing the drainage groove 6 and is formed to a depth near the deepest part of the liquefied layer 4. And is filled with crushed stone 9 as a drain material.

Structure 1 to which the system of the present invention is applied
The energy of the pore water pressure during the earthquake is absorbed by the drain portion composed of the permeable drain pipe 7 and the drain groove 6, and the pore water is drained to the ground surface through the gap of the crushed stone 9 in the drain groove 6. Therefore, excess pore water pressure is dissipated, and liquefaction of the ground immediately below the foundation can be suppressed. By the drainage pipe 7 having water permeability disposed on the ground immediately below the foundation of the structure, sufficient water permeability can be obtained through the drainage pipe 7 even in the ground near the center of the structure 1 distant from the drainage groove 6. Will be able to Therefore, the pore water pressure that increases instantaneously with the earthquake can be immediately transmitted to the drainage ditch 6, and the excess pore water pressure in the ground immediately below the foundation can be uniformly and reliably dissipated.

Next, as an example of an embodiment of the liquefaction countermeasure method of the present invention, a construction procedure when applied to a pier portion of an existing highway will be described with reference to FIGS. FIG.
The underground sectional view of the existing structure 1 to which the liquefaction countermeasure system of the present invention is applied, FIG. 2 is a plan view of the structure, and shows a state before any countermeasure is applied. First, a steel sheet pile 8 is driven continuously and without gaps along the shape of an arbitrary groove 60 to be excavated in the ground near the pier. Next, the steel sheet pile 8
Excavating the portion enclosed by the square to provide a groove 60 serving as a working space; and passing the drainage pipe 7 through the steel sheet pile 8 from the side wall surface in the groove 60 toward the underground just below the structure. Laying the drain of the drain pipe 7 on the ground immediately below the foundation. In this embodiment, in order to facilitate the construction work, the above-mentioned steps are not separately performed one by one, but when the groove 60 is excavated to a depth at which the drain of the drain pipe 7 is to be cast. Then, the drainage pipes 7 are sequentially driven by a drilling machine for setting drainage pipes, and after all the driving in the side-by-side direction have been completed, the excavation work of the groove 60 is performed again, so that the trenches 60 are dug deeper. By repeating the above operation and providing the groove (work space) 60 to a predetermined ground depth,
The installation of the water distribution pipe by the excavator can always be performed on the ground at the bottom of the groove 60, and the above process can be easily performed. 3 and 4 are a cross-sectional view and a plan view showing the working state of the above steps.

After the step of placing the water distribution pipe 7 is completed, the groove 60 is filled with crushed stone 9 as a water-permeable drain material and backfilled to form a drain for the drain groove 6. Countermeasures are completed. 5 and 6 are a cross-sectional view and a plan view showing a state after the completion of construction.

It is also possible to complete the countermeasure work by repeating backfilling of crushed stones and placing of drainage pipes after excavation of the drainage ditch 60 is completed in advance.

In the above method, the drainage groove 6 serving as a drain functions as a work space (groove 60) for setting a drainage pipe during construction work, and is filled with a drainage material such as crushed stone before completion. By doing so, the drainage groove 6 is easily provided, and the water from the drainage pipe 7 can be discharged to the ground through the gap between the nine crushed stones. In addition, when the drainage pipe 7 serving as a drain is placed, the length, the number, and the arrangement can be arbitrarily set in accordance with the characteristics of the ground, so that appropriate measures corresponding to various characteristics of the ground are possible. . Furthermore, since the drainage pipe is arranged by direct casting, that is, the ground immediately below the foundation of the structure 1 is not drilled, the influence on the ground immediately below the foundation and the structure 1 is small,
There is little risk of causing defects.

In the present embodiment, the drainage pipe 7 having a culvert drainage, "Drain Nail", developed by the Company, is used as the water-permeable drainage pipe 7 through which water can pass through the pipe from outside the pipe and be introduced into the pipe. It is used to form a drain.
This "drain nail" is characterized in that it has a structure in which a helical slot is cut in the pipe, and the aperture ratio is as high as about 20% as compared with a general perforated pipe. The drainage is extremely high because the inside of the pipe is hollow. In addition, since it can be directly installed on a wall surface by an impact-type grinding machine, there is little influence on the ground and the structure immediately below the foundation, and there is little possibility of causing a defect such as loosening of the ground. Long ones can be added and welded. Further, since the above-mentioned impact type grinding machine (the machine length is l = 1.54 m) is used, no heavy equipment is required, the working space is small, and the width of the groove serving as the working space is about 3.0 m. . Therefore, if the method is used in the countermeasure method according to the present invention, it is possible to easily drive the ground at an appropriate position and depth on the ground. In addition, a drain can be formed as long as it satisfies required characteristics even if it is other than the above-mentioned water distribution pipe such as a normal perforated pipe.

As another embodiment of the present invention, an example in which the direction of placing the drainage pipe 7 having water permeability is changed depending on the depth of the ground is shown in plan views and underground sectional views of FIGS. Here, the structure 1 is a huge liquid storage tank. As shown in the drawing, it is possible to drive in an arbitrary direction that is horizontal to the side wall surface of the work space, and effective construction can be performed without being restricted by the shape of the groove 60 that becomes the drainage groove 6. Although not shown, the right half of FIGS. 7 and 8 is provided with the same drain groove 6 and drain pipe 7 symmetrically with the left half.

As another embodiment of the present invention, FIG. 9 is a plan view showing a case where the drainage groove 6 has a shape surrounding the entire periphery of the ground immediately below the foundation of the structure 1. As shown in the figure, drainage pipes 7 are provided on the four sides of the building having the rectangular structure 1 toward the center of the structure 1, and the excess pore water pressure accompanying the earthquake is
The water can be uniformly and promptly propagated in all directions via a drain pipe 7 to a drain groove 6 provided continuously over the entire lateral side of the ground immediately below the foundation, and can be drained.

FIGS. 10 and 11 show another embodiment of the present invention, in which a liquefaction countermeasure system is applied to a structure 1 which is a pier of an expressway. The structure 1 is continuously surrounded by steel sheet piles 8 without any gaps around the entire ground area immediately below the foundation of the structure 1. That is, footing 2
An outer peripheral sheet pile (sheet pile) which is one size larger than that is provided. By steel sheet pile 8 surrounding the ground right under the foundation,
Shear deformation is suppressed, and a restraining effect of preventing flow of the ground under the foundation is obtained, and inflow of excess pore water due to liquefaction of the surrounding ground is prevented. Thereby, the effect of suppressing the liquefaction of the ground and improving the horizontal strength of the foundation pile 3 that supports the load applied to the footing 2 can also be obtained.

It is to be noted that even when the drain groove 6 is formed to surround the entire circumference of the ground immediately below the foundation of the structure 1,
A similar effect can be achieved by surrounding the entire periphery of the ground immediately below the foundation of the structure 1 with the steel sheet pile 8.

[0020]

As described above, the structure liquefaction countermeasure system according to the present invention is provided with a water distribution pipe in an arbitrary arrangement on the ground immediately below the foundation of the structure. And appropriate, uniform and reliable liquefaction countermeasures are possible. In addition, the liquefaction countermeasure method according to the present invention makes it possible to arrange a water distribution pipe in the ground immediately below the foundation of the structure, and has little effect on the ground immediately below the foundation of the structure, and the earthquake of the existing structure Suitable as a countermeasure method. Further, the workability is superior to that of the conventional countermeasure, and the construction cost can be reduced.

[Brief description of the drawings]

FIG. 1 is an underground sectional view of a pier portion showing a start of a construction method according to the present invention.

FIG. 2 is a plan view of the same structure as FIG.

3 is an underground sectional view of the pier portion of FIG. 1 showing one step of the liquefaction countermeasure method of the present invention.

FIG. 4 is a plan view of FIG. 3;

FIG. 5 is an underground sectional view of a pier to which the liquefaction countermeasure system of the present invention is applied.

FIG. 6 is a plan view of FIG. 5;

FIG. 7 is a plan view of another example to which the liquefaction countermeasure system of the present invention is applied.

8 is an underground sectional view of FIG. 7;

FIG. 9 is a plan view of another example to which the liquefaction countermeasure system of the present invention is applied.

FIG. 10 is a plan view of another example to which the liquefaction countermeasure system of the present invention is applied.

11 is an underground sectional view of FIG.

FIG. 12 is a cross-sectional view showing a structure provided with liquefaction countermeasures by a gravel drain method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Structure 2 Footing of structure (foundation) 3 Foundation pile 4 Liquefied layer 5 Non-liquefied layer 6 Drainage groove 7 Drainage pipe 8 Steel sheet pile 9 Crushed stone 60 Groove (work space)

Claims (7)

(57) [Claims] A drain of a water-permeable drainage pipe capable of introducing water from outside the pipe through the pipe body into the pipe, and a drainage groove of an arbitrary shape filled with a drain material such as crushed stone. Wherein the drainage pipe having water permeability is disposed in an arbitrary arrangement in the ground immediately below the foundation of the structure, and the drainage groove is provided near the foundation of the structure, and the drainage pipe is provided with the drainage pipe. A liquefaction countermeasure system for a structure, wherein at least one open end of the drainage pipe has a communication with the drainage groove. 2. The liquefaction countermeasure system for a structure according to claim 1, wherein the drainage groove has a shape surrounding the entire circumference of the ground immediately below the foundation of the structure. 3. The structure according to claim 1, wherein the perimeter of the drainage groove is surrounded by a sheet pile, and the perimeter of the ground immediately below the foundation of the structure is continuously surrounded by the sheet pile without any gap. Liquefaction prevention system for structures. 4. The liquefaction countermeasure system for a structure according to claim 2, further comprising a sheet pile continuously surrounding an outer peripheral side of the drain groove. 5. The liquid of a structure according to claim 1, wherein the drainage pipe having water permeability is an underdrain drain pipe having a spiral groove formed in a pipe body. Mitigation measures system. 6. A step of continuously driving a sheet pile along the shape of an arbitrary groove to be excavated in the ground near a structure, and a step of excavating a portion surrounded by the sheet pile to form a groove. And a drainage pipe having water permeability that allows water to pass through the pipe from outside the pipe and be introduced into the pipe, substantially penetrating the sheet pile from the side wall surface in the groove toward the ground directly below the structure. Cast it horizontally,
Arranging a drain pipe drain on the ground immediately below the foundation of the structure; filling the groove with a water-permeable drain material such as crushed stone to backfill the drain; A liquefaction countermeasure method for a structure, comprising a step of constituting. 7. The structure according to claim 6, further comprising a step of surrounding the drain groove with a sheet pile and continuously driving the sheet pile around the ground immediately below the foundation of the structure without any gap. Liquefaction countermeasure construction method.