JP2008223348A - Earthquake resisting reinforcement structure of pile foundation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an earthquake resisting reinforcement structure of a pile foundation, coping as liquefaction and settling suppression measures for peripheral ground while coping by structural improvement using an anchor as measures for damage to a pile in the actual liquefaction to a great earthquake in a pile foundation. <P>SOLUTION: This earthquake resisting reinforcement structure of a pile foundation includes an anchor fixed to a footing 4 on the pile 3 of the pile foundation 2 constructed in the ground and support ground 5 in the ground, respectively, and stretched between them. An anchor 11 with a drain function is used as the anchor. That is, the anchor 11 with a drain function is diagonally stretched so that a fixing part 12 on the support ground 5 side is located outside a fixing part 13 on the footing 4 side. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a seismic reinforcement structure using a pile foundation anchor.

For example, the damage and destruction mechanisms of structural foundations associated with liquefaction during the Hyogoken-Nanbu Earthquake are complex phenomena, and the R & D period for these phenomena is short. This is not necessarily a rational design and construction, such as solidification improvement around the pile foundation and placing continuous underground walls and additional piles on the outer periphery of the foundation. It was.
In recent cases, earthquake-proof reinforcement by micro piles and slant piles, and ground improvement by injecting chemicals have been proposed mainly for bridge foundations such as roads and railways, and construction is being carried out.
Ground improvement, including liquefaction countermeasures, is implemented as a method of seismic reinforcement, including methods based on principles such as compaction, solidification, and drainage around the pile, and structural improvements such as increased piles with increased pile diameter and pile rigidity. Can be mentioned.
In recent years, the occurrence of a huge earthquake is predicted with a high probability from the earthquake cycle. For example, in the Hyogoken-Nanbu Earthquake, the magnitude of the ground motion was unprecedented and caused tremendous damage to many foundation structures. After the Hyogoken-Nanbu Earthquake, each research institution has been engaged in powerful research, but the damage mechanism has not been fully elucidated, and an economical and rational seismic reinforcement method has not been established. is there.
Therefore, it is considered that the following conventional construction method alone does not have sufficient seismic reinforcement effect.
1) “Ground improvement”: Chemical solution injection method (for example, osmotic solidification method)
2) “Structural improvement”: anchor (for example, refer to Patent Documents 1 and 2), additional pile, continuous wall placement, micropile, slant pile placement, etc. Describes a vertical ground anchor penetrating a footing constructed on a pile foundation. Patent Document 2 describes a structure in which anchor bars are horizontally stretched between a pile foundation and a surrounding soil cement wall.
3) “Pile head seismic isolation method”: bearings, laminated rubber, etc.
Japanese Patent Laid-Open No. 10-82057 JP 2006-316490 A

The main issues of conventional methods are described below.
1) “Ground improvement”: Chemical solution injection method (for example, seepage solidification method)
-The range of liquefaction countermeasures based on the current specifications and standards is large, and the material costs of injection materials (silica materials, etc.) for liquefaction countermeasures are high.
2) “Structural improvement”: anchors, additional piles, continuous wall placement, micropile, slant pile placement, etc., supported by anchors; for example, in Patent Document 1, when the surrounding ground is completely liquefied Due to the muddy condition, elastic deformation occurs due to the inertial force from the superstructure, and the anchor alone will not only affect the magnitude of the seismic motion but also the duration of the seismic motion will increase the impact on the pile foundation structure. It is done. As a countermeasure, it is necessary to increase the diameter of the anchor bars or increase the number of installations innumerably, which increases the cost.
・ Upgrading the entire area surrounded by continuous underground walls will increase the cost.
3) “Pile-head seismic isolation method”: Bearings, laminated rubber, etc. ・ Although some examples of application to important structures, etc. are seen, it is difficult to construct and inadequate construction space for in-service structures. Although the input ground motion to the footing can be expected to be reduced, countermeasures against damage to piles in deep underground are not necessarily expected.The seismic reinforcement method described above has been proposed, and some construction work has actually been carried out. In short, there is a problem that the construction range is large and the cost is still high.

  The object of the present invention is to provide a seismic strengthening structure that can cope with liquefaction and subsidence suppression of the surrounding ground while dealing with structural improvements by anchors as countermeasures against pile damage during actual liquefaction in response to a huge earthquake in a pile foundation Is to provide.

  In order to solve the above-described problems, the invention according to claim 1 includes anchors that are anchored and hung on a footing on a pile of a pile foundation to be constructed in the ground and a support ground in the ground, It is characterized by a seismic reinforcement structure for pile foundations that uses an anchor with a drainage function as this anchor.

  The invention according to claim 2 is the pile foundation seismic reinforcement structure according to claim 1, wherein the anchor with the drainage function is disposed outside the fixing portion on the supporting ground side with respect to the fixing portion on the footing side. It is characterized by being slanted so as to be positioned.

  The invention according to claim 3 is provided with anchors that are anchored and stretched on the footings on the piles of the pile foundation to be constructed in the ground and the underground continuous walls that are constructed in the surroundings. An anchor with drainage function is used, and the anchor with drainage function is spanned diagonally so that the anchoring part on the underground continuous wall side is located below the anchoring part on the footing side. Features.

  Invention of Claim 4 is the earthquake-proof reinforcement structure of the pile foundation as described in any one of Claim 1 to 3, Comprising: The said anchor with a drainage function is an anchor material by the drain material which comprises water permeability. The surrounding area is covered.

  According to the present invention, compared with the construction method and the seismic reinforcement method proposed so far, it can cope with the damage countermeasures of piles at the time of actual liquefaction and the liquefaction and subsidence suppression measures of the surrounding ground for a huge earthquake, It is a simple method using an anchor with a drainage function, and is an economical seismic reinforcement structure that can further reduce costs.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.
First, the seismic retrofit structure is applied to the foundation even if the ground ground reaction force of the ground supporting the pile becomes zero due to the liquefaction of the ground immediately below the pile foundation structure and the surrounding ground, regardless of existing or new construction. Tensioning the main body and the supporting ground with anchors suppresses the horizontal displacement of the foundation, causing major damage to the pile due to large deformation of the ground during a strong earthquake, breakage, and failure at the pile head To prevent catastrophic damage.

According to on-site measurements in the Hyogoken-Nanbu Earthquake and analytical and experimental research conducted after the earthquake, cracks and other damage occur at the head of the pile immediately after the earthquake due to the inertia of the superstructure. After that, the excess pore water pressure in the ground begins to rise rapidly, and the ground around the pile foundation becomes completely liquefied.
Immediately after the earthquake, a liquefaction state in which the horizontal resistance of the surrounding ground is close to zero is maintained for a while after a few seconds. At this time, the pile foundation has a bending moment distribution of the cantilever beam and is extremely dangerous for the pile foundation. Therefore, the pile foundation has been damaged or damaged due to the swinging of the superstructure. It is guessed.

Based on the above-mentioned phenomenon, this seismic strengthening structure is applied to the foundation piles in the liquefied ground layer by tensioning the anchors installed in the support layer with the end of the foundation so Suppress horizontal displacement of the foundation and prevent breakage, damage and destruction.
In addition to this, this seismic strengthening structure allows the anchor to have a drainage function, so that the surrounding ground can be liquefied and the ground reaction force in the vicinity of the anchor can be secured. The deformation of the pile foundation during liquefaction is surely prevented by the friction and the frictional force with the surrounding ground.

Here, the installation of the anchor with the drainage function may be performed by adjusting the number of arrangements, the arrangement method, the diameter, and the rigidity according to the importance of the building, the earthquake scale assumed for each region, and the displacement allowed by the pile foundation. The drain material may be any material that has been confirmed to have a drainage function such as a recycled material. In addition, even if an anchor is put in the center part of the drain material, the drainage function of the drain material is not hindered.
An anchor with drainage function is to insert a tensile material (anchor) such as high-strength steel into the center of a drain material having drainage performance and fix it in a support base.
A continuous underground wall having high rigidity around the foundation may be constructed, and the continuous underground wall and the foundation may be connected by an anchor with a drainage function.

Effects of this seismic reinforcement structure 1) On the structure The actual seismic motion generated during an earthquake is three-dimensional, but by installing the anchor diagonally, the effect of suppressing deformation of the pile foundation in two horizontal directions is improved, This is advantageous in that the tensile force acting is reduced and the diameter does not need to be increased significantly.
2) Workability Since the anchor with drainage function is also light and small in construction machines, it can also be installed in crowded urban areas and small construction spaces.
3) Versatility By adjusting the number and rigidity of anchors, it can be applied to existing structures from small to large scale, and may receive lateral flow such as the back of a quay or a bridge foundation near a river. It can also be applied to existing pile foundation structures with

[First Embodiment]
1 and 2 show a first embodiment of a seismic reinforcement structure for a pile foundation to which the present invention is applied. 1 is an existing structure, 2 is a pile foundation, 3 is a pile, 4 is a footing, and 5 is a supporting ground. , 11 is an anchor with a drainage function, 12 is a supporting ground side fixing unit, and 13 is a footing side fixing unit.

  In the embodiment, as shown in the figure, the pile foundation 2 of the existing structure 1 includes footings 4 on a large number of piles 3, and the pile 3 reaches the support ground 5 and is constructed. An anchor 11 with a drainage function is used as an anchor that is fixed (see the fixing portions 12 and 13) and is anchored to the footing 4 and the support ground 5 of the pile foundation 2 respectively. As shown in FIG. 1, the anchor 11 with the drainage function has a structure in which the support ground side fixing unit 12 is obliquely spanned with respect to the footing side fixing unit 13. In addition, the anchor 11 with a drainage function is arrange | positioned radially from the four corner parts of the footing 4 of a planar view square shape, as shown in FIG.

  FIG. 3 is an enlarged view of the anchor 11 with a drainage function. The anchor 11 with a drainage function is covered with a drain material 15 such as a resin having a drainage function around the anchor material 14 such as a steel material by the tensile material. ing. Specifically, as shown in FIGS. 3A and 3B, the anchor material 14 is passed through the central portion of the drain material 15 processed into a cylindrical shape having a hollow portion. Yes. The drain material 15 is porous and penetrates the inner and outer peripheries.

As shown in FIG. 1, the anchor 11 with the drainage function is stretched between the support ground side fixing unit 12 and the footing side fixing unit 13 with the anchor member 14 in a tensioned state, as shown in FIG. 12 and the footing side fixing unit 13 are in a state in which the drain material 15 is located.
In addition, the footing 4 is provided with a pore water discharge hole 21 that opens to the upper surface continuously with the anchor 11 with the drainage function. The pore water discharge hole 21 may be diagonal as shown on the left side of the figure or vertical as shown on the right side of the figure. However, since the anchor 11 is installed at an angle, the hole 21 is cut at an angle in the footing 4 at the time of construction, so that the oblique pore water discharge hole 21 can be used as it is.

  FIG. 4 shows another example of the anchor arrangement pattern. In the illustrated example, the anchor 11 with the drainage function is arranged radially from the four corners of the footing 4 having a rectangular shape in plan view, and further, the footing 4 It is also arranged radially from the center of the four sides.

As mentioned above, according to the earthquake-proof reinforcement structure of the pile foundation of embodiment, since the anchor 11 was installed diagonally so that the support ground side fixing | fixed part 12 was located outside with respect to the footing side fixing | fixed part 13, compared with the vertical anchor of patent document 1 Thus, the effect of suppressing the deformation of the pile foundation 2 in two horizontal directions is improved, the tensile force acting on the anchor 11 is reduced, and there is no need to remarkably increase the diameter.
That is, by anchoring the anchor 11 installed on the support ground 5 (support layer) with the footing 4 (base end) against the structure pile foundation 2 in the liquefied ground layer on the support ground 5 at the time of the huge earthquake The horizontal displacement of the pile foundation 2 due to the swinging back of the upper structure 1 can be suppressed, and breakage, damage and destruction can be prevented.

In addition, since the anchor 11 with the drainage function is also light and small in construction machine, it can be implemented even in an overcrowded urban area or a small construction space. That is, it is excellent in workability.
In addition, by adjusting the number and rigidity of the anchors 11, it can be applied to existing structures from small to large scales, and may receive lateral flow such as the back of a quay or a bridge foundation at the riverside. It can also be applied to existing pile foundation structures with That is, it is excellent in versatility.

Since the anchor 11 has a drainage function, when the ground on the support ground 5 is liquefied in the event of a huge earthquake, the pore water whose excess pore water pressure has increased in the liquefied ground from the outer periphery of the drain material 15. It penetrates and flows into the hollow portion, and blows up toward the upper footing fixing portion 12 through the hollow portion. The effective stress in the liquefied ground is maintained by ejecting the pore water from the pore water discharge hole 21 provided in advance in the footing foundation.
Accordingly, it is possible to secure a ground reaction force in the vicinity of the anchor 11 when the surrounding ground is liquefied, and a pile at the time of liquefaction due to deformation of the anchor 11 during the earthquake, shaking of the anchor 11, and frictional force with the surrounding ground. The deformation of the foundation 2 can be reliably prevented.

  As a result of the above, compared to the construction methods and seismic reinforcement methods proposed so far, it can cope with damage countermeasures for piles 3 during actual liquefaction and liquefaction and subsidence suppression measures for the surrounding ground, This is a simple method using the anchor 11 with a drainage function, can further reduce the cost, and can provide an economical seismic reinforcement structure.

  In the first embodiment, the anchor 11 with the drainage function is used as an anchor that is installed obliquely so that the support ground side fixing unit 12 is positioned outside the footing side fixing unit 13. However, paying attention to the drainage function. For example, it is also possible to use for the vertical anchor of patent document 1. FIG.

[Second Embodiment]
5 and 6 show a second embodiment of a seismic reinforcement structure for a pile foundation to which the present invention is applied. Like the first embodiment, 1 is an existing structure, 2 is a pile foundation, and 3 is a pile. 4 is a footing, 5 is a supporting ground, 11 is an anchor with a drainage function, 13 is a footing side fixing part, 15 is a drain material, 21 is a hole for discharging pore water, 6 is an underground continuous wall, 16 is a ground This is a middle continuous wall side fixing section.

  That is, in 2nd Embodiment, the underground continuous wall 6 which reaches to the support ground 5 is constructed around the pile foundation 2 like illustration. Then, anchors 11 having drainage functions are set up on the footings 4 on the piles 3 of the pile foundation 2 constructed in the ground and the upper portions of the underground continuous walls 6 (see the fixing portions 16 and 13). Has been.

  Therefore, as shown in FIG. 5, the anchor 11 with the drainage function has a structure in which the outer underground continuous wall side fixing part 16 is obliquely stretched over the footing side fixing part 13 so as to be positioned below. Yes. As shown in FIG. 6, the anchor 11 with the drainage function is arranged radially from the four corners of the footing 4 having a square shape in plan view, and is also arranged radially from the center of the four sides of the footing 4. .

  As mentioned above, the effect substantially the same as 1st Embodiment mentioned above is acquired also by the earthquake-proof reinforcement structure of the pile foundation of 2nd Embodiment. That is, in the operation and effect of the first embodiment described above, the supporting ground 5 may be replaced with the underground continuous wall 6 and the supporting ground side fixing unit 12 may be replaced with the underground continuous wall side fixing unit 16.

In addition, in the above embodiment, although it was set as the pile foundation of the existing structure, this invention is not limited to this, You may apply to the pile foundation of a new structure.
Further, the shape and number of the drain material are arbitrary, and it is needless to say that other specific detailed structures can be appropriately changed.

BRIEF DESCRIPTION OF THE DRAWINGS It is the longitudinal cross-sectional view which showed the earthquake-proof reinforcement structure of the pile foundation to which this invention is applied, and showed the structure of 1st Embodiment. It is the top view which showed the anchor arrangement | positioning pattern of FIG. FIG. 2 is an enlarged view of an anchor with a drainage function, and is a side view (a) and a sectional view (b). It is the top view which showed the other example of the anchor arrangement pattern. The seismic reinforcement structure of the pile foundation which applied this invention is shown, and it is the longitudinal cross-sectional view which showed the structure of 2nd Embodiment. It is the top view which showed the anchor arrangement | positioning pattern of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Existing structure 2 Pile foundation 3 Pile 4 Footing 5 Support ground 6 Underground continuous wall 11 Drain anchoring anchor 12 Support ground side fixing part 13 Footing side fixing part 14 Anchor material 15 Drain material 16 Underground continuous wall side fixing part 21 Hole for pore water discharge

Claims (4)

With anchors anchored and stretched to the footing on the pile of the pile foundation to be constructed in the ground and the support ground in the ground,
Seismic reinforcement structure for pile foundation, characterized by using an anchor with drainage function as this anchor.   2. The seismic reinforcement structure for a pile foundation according to claim 1, wherein the anchor with drainage function is slanted over the anchoring portion on the footing side so that the anchoring portion on the support ground side is located outside. . It has anchors that are anchored and stretched on the footings on the piles of the pile foundation that is constructed in the ground and the underground continuous walls that are constructed in the surrounding area,
Use this anchor with drainage function as this anchor,
An anti-seismic reinforcement structure for a pile foundation, wherein the anchor with a drainage function is obliquely passed over the anchoring part on the footing side so that the anchoring part on the underground continuous wall side is positioned below.   The seismic reinforcement structure for a pile foundation according to any one of claims 1 to 3, wherein the anchor with the drainage function is covered with a drain material having water permeability.

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