JP2002188157A - Aseismatic reinforcing method for foundation of existing structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To augment the bearing power in the vertical direction and the horizontal direction of the foundation of an existing structure and increase the reliability of aseismatic reinforcement. SOLUTION: A composite column 10 is formed in the ground 3 around existing piles 4 supporting the footing 2 of an existing pier 1, and the composite column 10 and the existing footing 2 are integrally connected by an extension footing 11. The composite column 10 comprises a large-diameter improvement body 12 generated by a high-pressure injecting/stirring method, existing piles 14 inserted into the vertical holes 13 provided in the improvement body 12, and a fixing layer 15 of hardening agent grout fixing the existing piles 14 to the improvement body 12. Each existing pile 14 is formed into a large-diameter section 16 on the upper side only, and its shape has nodes 18 over the whole length so that the improvement body 12 and the existing piles 14 integrally exert large bearing force in the horizontal direction and the vertical direction. After the composite column 10 is formed, the extension footing 11 is placed to enclose the pile head sections 14a of the existing piles 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a seismic retrofitting method for seismic retrofitting a foundation of an existing structure such as a pier or a building.

[0002]

2. Description of the Related Art Conventionally, as a typical method of reinforcing a foundation of an existing structure, an additional pile (cast-in-place pile) is cast around an existing pile foundation, and this additional pile is integrated with an existing footing. There has been a steel pile pile foundation method in which steel pipe sheet piles are cast in place of pile piles and integrated with existing footings.

[0003]

However, according to the above-mentioned additional pile method, in order to obtain a desired vertical supporting force, the pile must be driven to a support layer existing deep underground. On the other hand, in order to increase the horizontal supporting force, a large-diameter pile must be cast, and if a large vertical and horizontal supporting force is required, the construction will be large In addition, there was a problem that the construction period and the construction cost were inevitable. Also, even if the vertical supporting force is increased, it depends exclusively on the tip support.Even if the supporting force in the pushing direction is sufficient, the supporting force in the pulling-out direction cannot be expected. In the case where the structure caused a large roll, the supporting force in the pull-out direction was insufficient, and the structure was insufficient for earthquake-resistant reinforcement.
In addition, according to the steel pipe sheet pile foundation extension method, the use of large-diameter steel pipes provides sufficient horizontal support,
In general, since a press-fitting method is used, a vertical supporting force, particularly a pulling-out supporting force, cannot be expected, and the seismic reinforcement is insufficient in the same manner as the additional pile method described above.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a vertical (both pushing and pulling) and horizontal supporting force without large-scale construction. Therefore, it is an object of the present invention to provide a method for reinforcing an existing structure foundation which is sufficiently effective in terms of seismic reinforcement.

[0005]

In order to achieve the above object, the present invention is to form an improved body in a ground by a high-pressure jet stirring method, and then construct a composite pile by building a ready-made pile in the improved body. Performing the construction around the foundation under the footing of the existing structure, arranging the composite piles at intervals around the foundation, and then expanding the footing to wrap the pile head of the ready-made pile It is characterized by doing.

[0006] In the high-pressure injection stirring method, grout (ground improvement material) is applied to the injection rod at the tip thereof in a direction perpendicular to the injection rod while rotating and axially moving the injection rod into the ground, or by high-pressure water or compression. This is a construction method in which the ground improvement material and the surrounding earth and sand are mixed by stirring and mixing the ground improvement material and the surrounding earth and sand to form an improved body. The present invention is to construct a composite pile by building a ready-made pile on the improved body created by this high-pressure injection stirring method. According to the present invention, each of the ready-made piles is supported by the large-diameter improved body in the vertical direction. (Both pushing and pulling directions) and a large supporting force in the horizontal direction.

In the present invention, the composite pile may be formed as a vertical pile, but a part or all of the vertical pile may be replaced with a slant pile. It is known that a slanted pile exerts a large supporting force in the horizontal direction. By using a part or all of the composite pile as a slanted pile, it works advantageously in terms of seismic reinforcement. However, if the inclination angle of the inclined pile is too small, the above-described effect is small, and if it is too large, problems such as interference between the construction machine and the existing structure and problems of infringement on adjacent structures occur, and the workability is deteriorated. It is preferable to set the angle to about 10 to 20 ° because the angle decreases.

[0008] In the present invention, the method of erection of the ready-made pile in the above-mentioned improved body is optional, but a relatively small diameter (500 mm or less)
When using the ready-made pile of the above, it is preferable to excavate a vertical hole in the improved body in advance, insert the ready-made pile into this vertical hole, and fill the gap around the ready-made pile with grout, whereby the ready-made pile is Is firmly established. In this case, since the horizontal supporting force is borne by the upper portion of the ready-made pile, the upper portion (for example, approximately 1/3 to 1
By using a different-diameter pile whose diameter is larger than that of the lower part (corresponding to the length corresponding to the length of / 2), the weight of the ready-made pile is reduced as a whole, which is advantageous in cost.

According to the present invention, in order to further increase the horizontal supporting force, a relatively large diameter (500 to 1000 mm) prefabricated pile may be built in the improved body. When building the pile, after the improved body is formed by the high-pressure injection stirring method as described above, the ready-made pile may be directly pressed into the improved body while the improved body is not yet cured. In this case, the pre-drilling and grout filling for the improved body described above can be omitted.

In the present invention, it is desirable that the ready-made pile is knotted irrespective of the size of the above-mentioned diameter, whereby the supporting force in the vertical direction (both pushing and pulling directions) is further increased. .

According to the present invention, when a liquefaction-risk layer is present in the ground, prior to the addition of the footing, an improved body is connected to the liquefaction-risk layer by a high-pressure jet stirring method so as to be connected to the composite pile. The liquefaction hazardous layer under the footing of the existing structure is surrounded by a composite pile consisting of an improved body, and the penetration of seismic waves under the existing structure is suppressed. The liquefaction of the ground is prevented beforehand. In the present invention, as a countermeasure against liquefaction, a hollow drain material (drain pipe) may be cast instead of adding the above-mentioned improved body. By slanting the liquefaction hazard layer toward the liquefaction hazard layer, excess pore water generated in the liquefaction hazard layer during an earthquake is discharged to the ground through the hollow drain material, preventing the liquefaction of the ground under the existing structure Is done.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIGS. 1 to 3 show a first embodiment of a seismic retrofitting method according to the present invention. The first embodiment is directed to a foundation of a pier 1 as an existing structure. The pier 1 has a plurality of piles in which a footing 2 integrally provided on the bottom thereof is cast into a ground 3. 4 and mounted and fixed. Each pile 4 is driven into the ground 3 until its tip reaches the support layer 5, and a plurality of the piles 4 collectively constitute one pile foundation 6 and exhibit a predetermined proof strength (supporting force). It has become. A plurality of composite piles (vertical piles) 10 are formed around the pile foundation 6 by the present construction method, while on the ground surface side of the ground 3, the upper end of each composite pile 10 and the footing of the pier 1 (existing footing). 2) is additionally provided with a footing (additional footing) 11 for connecting and integrating the two.

The composite pile 10 includes a large-diameter improved body 12 formed in the ground 3 by a high-pressure jet stirring method described below,
The improved body 12 includes a ready-made pile 14 inserted into a vertical hole 13 formed at an axial center position of the improved body 12 and a fixing layer 15 filled in a space around the ready-made pile 14.
Is formed between a lateral position of the existing footing 2 and a position shallower than the support layer 5. The ready-made pile 14 is provided so that its upper end (pile head) 14a slightly protrudes from the upper end of the improved body 12, and the additional footing 1
1 is installed so as to cover the pile head 14a of the ready-made pile 14. In addition, the pile head 14a of the ready-made pile 14 is wrapped in the extension footing 11 in a state where the composite piles 10 are connected to each other by a connecting member (not shown) such as a reinforcing bar or a frame. The composite pile 10 and the existing footing 2 are firmly integrated via an additional footing 11.

Here, the ready-made pile 14 has a length of 1 /
The upper portion corresponding to 3 to 1/2 length is a large diameter portion 16 having a relatively large diameter (for example, 250 to 500 mm), and the lower portion is relatively small diameter (for example, 150 to 150 mm). 250m
m) is provided as a small diameter section 17 having a small diameter.
The ready-made stake 14 is also provided as a knotted stake provided with knots 18 at a predetermined pitch over its entire length.

In implementing this method, as shown in FIG. 4, an injection rod (single pipe or double pipe) 21 having an injection nozzle 20 at its tip is prepared.
Is rotated and penetrated into the ground 3. When the injection nozzle 20 at the tip reaches the upper limit depth D ₁ of the planned improvement area (here, the side of the existing footing 2), the super-high pressure ( Water (about 30 to 40 MPa) is supplied (compressed air may be used in some cases), and ultra high-pressure water is jetted from the jet nozzle 20 in the horizontal direction. The ground 3 is cut and agitated (precutted) over a wide area by the injection of the ultrahigh-pressure water, and a large-diameter cutting and stirring layer A is formed in the ground 3. It expands downward accordingly (). The surplus slime generated at this time is discharged to the ground through a space around the injection rod 21.

When the formation of the cutting stirring layer A reaches the lower limit depth D ₂ (here, a position shallower than the support layer 5) of the planned improvement area, the ultrahigh-pressure water is grouted (cement milk: water cement ratio). (W / C = approximately 60 to 70), and the injection rod 21 is rotated upward while injecting an ultra-high pressure (approximately 40 MPa) grout from the injection nozzle 1 in the horizontal direction (in some cases, compressed air is used together) ( ). Due to the high-pressure injection of the grout, the earth and sand in the cutting and stirring layer A is stirred and mixed with the grout and transformed into the grout mixed layer B,
The grout mixed layer B expands upward as the injection rod 21 rotates upward. At this time, the surplus slime is guided and discharged to the ground. At this stage, since the injection of water is stopped, the degree of the guided discharge is small, and wasteful consumption of grout is suppressed. When the formation of the grout mixed layer B reaches the upper limit depth D ₁ of the planned improvement area in this way,
The supply of grout to the injection rod 21 is stopped, and the injection rod 21 is pulled out of the ground 3 and cured as it is.
By this curing, the grout mixed layer B is hardened, and the above-described large-diameter improved body 12 () is formed in the planned improvement area.

Next, the improved body 12 constructed as described above is used.
Then, the vertical hole 13 is excavated using, for example, an earth auger 23. The excavation of the vertical hole 13 is performed to the vicinity of the bottom surface of the improved body 12, and after the excavation is completed, the earth auger 23 is pulled out from the improved body 12 (). Supply (). Thereafter, a ready-made pile (different-diameter pile) 14 with the joint 18 and having a closed end is inserted into the vertical hole 13. Then, the grout 24 supplied in advance overflows into the gap between the ready-made pile 14 and the inner wall of the vertical hole 13, and the grout 24 is filled in the gap. The grout 24 cures while being expanded in volume by being cured for a predetermined time to become the fixing layer 15,
The prefabricated pile 14 is firmly fixed by the fixing layer 15 with the improved body 12.
And integrated.

In this way, one of the composite piles 10 is completed, and thereafter, the above construction is repeated to form a plurality of composite piles 10 at predetermined intervals around the pile foundation 6 below the existing footing 2. . When the formation of the series of composite piles 10 is completed, first, the ground surface on which the composite piles 10 are formed is excavated to prepare the ready-made piles 1.
Then, the pile head 14a and the existing footing 2 are exposed, and then the pile heads 14a of the respective ready-made piles 14 are connected to each other using a connecting member. In parallel with this, the existing footing 2
Remove the rebar from the surface of the steel bar. When the rebar is exposed, a new rebar is incorporated around the existing footing 2 in a state where the rebar and the pile head 14a are connected to a connecting member that connects the rebar and the pile head 14a. The additional footing 11 is cast so as to surround the existing footing 2.

As a result, each composite pile 10 is firmly integrated with the existing footing 2 via the additional footing 11, but since the ready-made pile 14 is built in the improved body 12 formed by the high-pressure jet stirring method, each of the ready-made piles 14 is installed. The pile 14 exerts a large supporting force in the vertical direction without being built up to the support layer 5. Further, since each of the ready-made stakes 14 is integrated with the large-diameter improved body 12 and greatly resists in the horizontal direction, it also exerts a large supporting force in the horizontal direction, and serves as a foundation for the pier 1 as an existing structure. The proof strength (bearing capacity) is remarkably increased, and it can sufficiently withstand the shaking during an earthquake.

In particular, in the first embodiment, the improved body 1
When the ready-made pile 14 is built in the vertical hole 13 of the second
Since the volume expansion type is used as the fixing layer 18,
However, since the space around the ready-made pile 14 is sufficiently filled and the ready-made pile 14 has a shape having the nodes 18, the frictional resistance between the pile and the fixing layer 15 is significantly increased, and the ready-made pile 14 is It will exhibit a remarkably large supporting force.
In addition, since the large-diameter portion 16 is formed on the upper part of the ready-made pile 14 which receives the horizontal force due to the earthquake, the entire length thereof is 1/3 to 1/2. The weight can be reduced, which is advantageous in terms of cost.

FIG. 5 shows a second embodiment of the reinforcing method according to the present invention. The feature of the second embodiment is that the composite pile 10 in the first embodiment is inclined at a predetermined inclination angle θ (= 10 to the vertical direction).
20 °). The structure of the composite pile 10 is basically the same as that of the first embodiment except that a straight pile is used as the ready-made pile 14, so that the same reference numerals are given to the same parts here. And Also,
Since the method of forming the composite pile 10 is the same as that of the first embodiment, the method of forming the composite pile 10 is omitted here.

In the second embodiment, the composite pile 1
Since 0 is formed as a slanted pile, it exerts a large supporting force in the horizontal direction, which is extremely useful for seismic reinforcement. In addition, when trying to secure a horizontal supporting force equivalent to that of the vertical pile (composite pile) 10 as in the first embodiment, it is possible to use a smaller-diameter one as the ready-made pile 14, This is advantageous in terms of cost.

Incidentally, there is a case where the liquefaction risk layer 30 exists in the ground 3 under the existing footing 2 as shown in FIG.
Just by arranging the composite piles 10 intermittently around the pile foundation 6 as in the first embodiment, seismic waves enter the ground below the existing footing 2 and prevent liquefaction due to shear deformation of the ground. It is not possible.

The third embodiment of the reinforcing method according to the present invention is suitable when such a liquefaction-resistant layer 30 is present. As shown in FIGS. When forming the improved body 12 around the pile foundation 6 by the injection stirring method, the composite pile 1
The sub-improved body 31 is wrapped with each other by a high-pressure injection stirring method so as to be connected to the improved body 12 used as the base material 0, and the area around the liquefaction risk layer 30 included in the pile foundation 6 is improved. The improved body 31 is surrounded by a continuous wall 32 that is connected. In the third embodiment, after the above-described continuous wall 32 is formed, the vertical holes 13 are excavated for each improved body 12 and the grout 24 is inserted into the vertical holes 13 in the same procedure as in the first embodiment. Supply and vertical hole 1
The composite pile 10 is completed by inserting the ready-made pile 14 into the inside 3 (FIG. 4 to FIG. 4), and the additional footing 11 is driven.

According to the third embodiment, similarly to the first embodiment, the vertical and horizontal supporting forces are sufficient, and the liquefaction risk layer 30 under the existing footing 2 is provided. Of the liquefaction-resistant layer 30 is prevented by the continuous wall 32 that surrounds the seismic wave, which is extremely useful in terms of seismic reinforcement.

Here, when the liquefaction danger layer 30 exists in the ground 3, instead of the sub-improved body 31 (FIGS. 6 and 7) in the third embodiment, it is shown in FIG. As described above, the hollow drain material (drain pipe) 35 may be cast. The fourth embodiment of the reinforcing method according to the present invention includes a method of driving the hollow drain material 35. As a method of driving the hollow drain material, for example, a method described in Japanese Patent No. 2920501 is disclosed. Can be adopted. In this method, a guide tube with a cutter attached to its tip is rotated and moved in the axial direction to cut a hole in the ground, then a hollow drain material is inserted into this guide tube, and then the upper end of the hollow drain material is pressed. While pulling out the guide tube from the ground, there is an advantage that the hollow drain material can be easily cast by using a small machine similar to the high-pressure injection stirring method or the micropile driving method described above. .

In the fourth embodiment, the first
Alternatively, after forming the composite pile 10 around the pile foundation 6 in the same procedure as in the second embodiment, the above-described method of placing the hollow drain material is performed using the space between the composite piles 10. As shown in FIG. 8, a plurality of hollow drain members 35 are cast on the liquefaction danger layer 30, and in this case, not only in the vertical direction but also in the inclined direction toward the liquefaction danger layer 30 below the existing structure. Also, a plurality of hollow drain members 35 are cast. Further, in the ground 3 around the footing 2, an annular drain groove 36 is constructed using, for example, crushed stone or the like,
A communication groove 37 that connects the drain groove 36 and the upper end of each hollow drain member 35 is constructed. By placing the hollow drain material 35 in this manner, the liquefaction-resistant layer 30 can be used during an earthquake.
When excessive pore water is generated, the excessive pore water is discharged through the hollow drain material 35 to the drainage groove 36, and liquefaction of the liquefaction-risk layer 30 is prevented beforehand, as in the third embodiment. In addition, it is extremely useful in terms of seismic reinforcement.

In each of the above-described embodiments, when the ready-made pile 14 is installed in the improved body 12,
The grout 24 for fixing is supplied to the inside of the grout 24.
Is made to overflow into the space around the pile according to the insertion of the ready-made pile 14 (FIG. 4). However, the present invention uses a pile with a check valve as a ready-made pile, and an injection machine (packer) from inside the pile. A so-called micropile driving method in which grout is spouted around a pile through a check valve by using a check valve may be employed.

Further, in each of the above embodiments, the vertical hole 13 is mechanically formed in the improved body 12 formed by the high-pressure jet stirring method, and the ready-made pile 14 is erected in the vertical hole 13. According to the present invention, a grout used in the high-pressure jet stirring method may be added with a retarder for delaying the curing so that the ready-made pile is directly pressed into the improved body before the improved body is cured. In this case, it is not necessary to drill the vertical hole 13 for the improved body 12 described above.
It is not necessary to supply the grout 24 for fixing into the inside 3, and efficient construction can be performed. In addition, since it is not necessary to drill the vertical hole 13, it is possible to build a large-diameter ready-made pile of about 500 to 1000 mm, and by building such a large-diameter ready-made pile in the improved body 12, the horizontal direction is improved. Will also increase significantly.

[0031]

As described above, according to the seismic retrofitting method for an existing structure foundation according to the present invention, a composite pile in which a ready-made pile is built in a large-diameter improved body formed by a high-pressure jet stirring method is used. Since it was used to reinforce the existing footing,
The vertical and horizontal bearing capacity is remarkably increased compared to the case of the additional pile method or the steel pipe sheet pile foundation method, which greatly contributes to the improvement of the reliability of the seismic reinforcement. In addition, since the formation of the improved body by the high-pressure injection stirring method can be performed using a simple construction machine, the construction does not become large and the construction period can be shortened and the construction cost can be reduced. Furthermore, if there is a liquefaction hazard layer in the ground, an improved body is added to the liquefaction hazard layer by a high-pressure jet stirring method so as to be connected to the composite pile, or a hollow body is inserted between the composite piles. By arranging the drain material, liquefaction countermeasures can be easily performed, and the utility value of the present invention is large in general.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of a seismic retrofitting method according to the present invention.

FIG. 2 is an enlarged sectional view showing a main part of FIG.

FIG. 3 is a schematic plan view showing a reinforcing state in the first embodiment in a plan view.

FIG. 4 is a cross-sectional view showing a construction procedure for forming a composite pile according to the first embodiment.

FIG. 5 is a sectional view showing a second embodiment of the seismic retrofitting method according to the present invention.

FIG. 6 is a sectional view showing a third embodiment of the seismic retrofitting method according to the present invention.

FIG. 7 is a schematic diagram showing a reinforcing state in a third embodiment in a plan view.

FIG. 8 is a sectional view showing a fourth embodiment of the seismic retrofitting method according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Bridge pier (existing structure) 2 Existing footing 3 Ground 4 Existing pile 5 Support layer 10 Composite pile 11 Additional footing 12 Improved body 13 Vertical hole 14 Existing pile 15 Fixing layer 16 Large diameter portion of existing pile 17 Small diameter portion of existing pile 18 Existing Node of pile 30 Dangerous layer for liquefaction 31 Sub-improved body 32 Continuous wall 35 Hollow drain material

 ──────────────────────────────────────────────────続 き Continued on the front page (71) Applicant 390036515 Konoikegumi Co., Ltd. 4-55, Konohana-ku, Osaka, Osaka (71) Applicant 000148346 Sentakagumi Co., Ltd. 2-2-1, Nishihoncho, Nishi-ku, Osaka, Osaka (71) Applicant 391058657 Tone Underground Technology Co., Ltd. 2- 16-2 Minami Kamata, Ota-ku, Tokyo (71) Applicant 000230788 Japan Basic Technology Co., Ltd. 6-22 Matsugaeda-cho, Kita-ku, Osaka-shi, Osaka ( 72) Inventor Kenjiro Oka 4-1-1 Koraibashi, Chuo-ku, Osaka-shi, Osaka Toyo Construction Co., Ltd. (72) Inventor Takeshi Oshita 1 Asahi, Oaza, Tsukuba-shi, Ibaraki Pref. Jiro Fukui 1 Asahi, Asahi, Tsukuba, Ibaraki Pref. Public Works Research Institute, Ministry of Construction (72) Tetsuo Matsuda 2-15-6 Otsuka, Bunkyo-ku, Tokyo設技 surgery in the center (72) inventor Takeo Miki, Chuo-ku, Osaka-shi Kōraibashi 4 chome No. 1 Toyo Construction Co., Ltd. in the F-term (reference) 2D041 AA03 BA13 BA18 BA53 CA03 DB03 EA04 EA05 2D046 DA03 DA11 DA17

Claims (10)

[Claims] After constructing an improved body in the ground by a high-pressure injection stirring method, a prefabricated pile is built in the improved body to form a composite pile around a foundation under a footing of an existing structure. The composite piles are arranged at intervals around the foundation, and then the footing is added so as to cover the pile heads of the ready-made piles. 2. The seismic retrofitting method according to claim 1, wherein the composite pile is formed as a vertical pile. 3. The seismic retrofitting method according to claim 2, wherein a part or all of the vertical pile is replaced with a slanted pile. 4. The seismic retrofitting method according to claim 3, wherein the inclination angle of the inclined pile is 10 to 20 °. 5. When a ready-made pile is built in the improved body, a vertical hole is excavated in advance in the improved body, the ready-made pile is inserted into the vertical hole, and a grout is filled in a space around the ready-made pile. The seismic retrofitting method according to any one of claims 1 to 4. 6. The seismic retrofitting method according to claim 5, wherein a pile having a different diameter is used as the ready-made pile, the upper part of which is larger in diameter than the lower part. 7. The method according to claim 1, wherein when the ready-made pile is built in the improved body, the ready-made pile is press-fitted into the improved body while the improved body is not yet cured. Seismic reinforcement method. 8. The seismic retrofitting method according to claim 1, wherein the ready-made pile is knotted. 9. When a liquefaction risk layer exists in the ground,
9. An improvement body according to any one of claims 1 to 8, wherein prior to the extension of the footing, an improved body is extended by a high-pressure jet stirring method so as to be connected to the composite pile with respect to the liquefaction-risk layer.
Seismic retrofitting method described in section. 10. When a liquefaction-risk layer is present in the ground, prior to the extension of the footing, a hollow drain material is poured into the liquefaction-risk layer through a space between the composite piles. The seismic retrofitting method according to any one of claims 1 to 8.