JP3643571B2 - Pile foundation reinforcement structure - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a pile foundation reinforcing structure for reducing stress generated by a horizontal load such as an earthquake in a plurality of piles.
[0002]
[Prior art]
In order to construct a structure on soft ground, there are some in which a plurality of piles reaching the support layer are placed in the ground, and a foundation structure is configured by the plurality of piles. However, if the ground is composed of alluvial sand layers or sand layers mixed with fine-grained soil, the earthquake may cause liquefaction of the ground, resulting in extremely large stresses and deformations in each pile, exceeding the structural strength. It may lead to damage. Therefore, in such a soft ground, in a new structure, the footing plane will be larger than usual and the number of piles will be larger than usual, and in existing structures, the footing will be widened, increased, etc. Although it is considered to reinforce the foundation, there is a problem that large-scale construction is required and the construction cost is high.
[0003]
[Problems to be solved by the invention]
The present invention has been made to solve the above-described conventional problems, and the problem is that it can be constructed with a smaller construction than the conventional pile foundation reinforcing structure, and the construction cost can be reduced. It is to provide a pile foundation reinforcement structure that can be used.
[0004]
[Means for Solving the Problems]
According to the present invention, the piles arranged on the outer periphery are connected to the piles for reducing the stress generated during the earthquake in the plurality of piles placed in the ground to support the structure. A pile foundation reinforcing structure is provided, which is provided in a depth direction underground portion of a pile separated from the structure so as not to include a pile arranged in the center.
In such a support pile reinforcing structure, the reinforcing body is formed so as to include a pile disposed on the outer periphery among a plurality of piles and not to include a pile disposed in the center, and the pile disposed in the center. Is not directly joined to the reinforcement. However, earth and sand are interposed between the reinforcing body and each pile in the central area, and the binding force of the reinforcing body is transmitted to each pile in the central area through the earth and sand. In this way, the plurality of piles are all restrained by the reinforcing body, and the foundation structure composed of the plurality of piles and the reinforcing body is the same as the two-layered ramen structure. That is, from the top of the pile to the reinforcing body part in the plurality of piles corresponds to the first layer of the ramen structure, and from the reinforcing body part to the structure corresponds to the second layer of the ramen structure, thereby increasing the rigidity of the plurality of piles. For example, even if a liquefaction phenomenon occurs in the ground due to an earthquake or the like, the maximum bending strain generated at the joint between the pile and the structure is greatly suppressed. Moreover, in the said support pile reinforcement structure, weight reduction is achieved because there is no reinforcement body in the center area | region of a some pile, and a vertical load is reduced in a some pile. Moreover, since the movement of the groundwater between the upper and lower sides of the reinforcing body is not cut off, an effect that buoyancy generated during liquefaction is reduced can be obtained.
[0005]
Further, according to the present invention, the reinforcing body for reducing the stress generated at the time of the earthquake in the plurality of piles placed in the ground to support the structure, surrounds the plurality of piles from the outer periphery and contacts the piles. Therefore, a support pile reinforcing structure characterized by being provided around the underground portion of the pile separated from the structure is provided.
In such a support pile reinforcing structure, a reinforcing body is provided so as to surround the plurality of piles on the outer periphery in the intermediate portion of the pile, and the plurality of piles and the reinforcing body are not directly connected at all, Sediment or the like is interposed between the reinforcing bodies, and the restraining force from the reinforcing bodies is indirectly transmitted to the plurality of piles via the earth and sand, etc., and a foundation structure composed of the plurality of piles and the reinforcing bodies is formed. It will be similar to a two-layered ramen structure. That is, even if a liquefaction phenomenon occurs in the ground around the reinforcing body due to an earthquake or the like, the restraining force from the reinforcing body acts on multiple piles via earth and sand, etc., so the rigidity of the multiple piles is maintained, Bending strain can be suppressed. This bending strain suppression effect is particularly effective at the joint between the pile and the structure and the contact portion between the pile and the support layer.
[0006]
In this invention, the reinforcement body should just be arrange | positioned so that the maximum bending moment which arises in the junction part of a some pile and a structure can be restrained collectively can be restrained. In addition, the reinforcing body may be arranged at any height as long as it is an intermediate portion from the lower end of the pile to the upper end, but preferably the stress generated in the pile is the smallest with respect to the horizontal load during an earthquake. It is provided at such a height.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the accompanying drawings.
FIG. 1 is a side view of the support pile reinforcing structure of the present invention.
In FIG. 1, the ground 12 is a soft ground including an alluvial sand layer or a sand layer mixed with fine-grained soil, and a support layer 13 is present at a predetermined depth. The structure 11 is constructed on the ground 12, and a plurality of piles 14 are driven into the ground 12 so as to reach the support layer 13 from the structure 11 or its footings (not shown). It is provided at an intermediate portion of the pile 14 that is spaced apart from the object 11 by a length H1 and separated from the support layer 13 by a length H3. The reinforcing body 20 can be arranged at the center in the height direction so that H1 and H3 have the same length, but the position in the height direction is preferably against a horizontal load such as an earthquake. It is appropriately determined so that the stress generated in the pile is minimized.
[0008]
2A to 2C are cross-sectional views showing different forms, and these correspond to cross-sections along the line AA in FIG. Each reinforcing body 20 is the same when viewed from the side as shown in FIG. 1, but the cross section can be configured in different forms as shown in FIG. 2.
The reinforcing body 20A in FIG. 2A is formed so as to include the piles 14 arranged on the outer periphery among the plurality of piles 14 and not to include the pile 14 arranged in the center. The body 20A may further reduce the central region 22A that does not include the pile 14 to be smaller than this, for example, the outer peripheral region 21B that includes the pile 14 is relatively large like the reinforcing body 20B of FIG. However, the central region 22B can be configured to be relatively small.
Further, the reinforcing body 20C in FIG. 2C is formed so as to surround the plurality of piles 14 from the outer periphery and not to contact any piles 14.
Among these reinforcing bodies 20A, 20B, and 20C, the horizontal plane can be widened by the reinforcing body 20B, so that it is easy to obtain strength. Therefore, the vertical width H2 can be minimized, while the reinforcing body 20C is horizontally oriented. Therefore, it is necessary to ensure the strength by making the width H2 in the vertical direction relatively large.
Reinforcing bodies 20A, 20B, and 20C use, for example, silica colloidal water glass as a curing agent, a main material such as fine particle slag and a curing accelerator such as alkali calcium are mixed, and this mixture is injected into the ground. Then, it can be formed by solidifying the earth and sand. Therefore, the reinforcing bodies 20A, 20B, and 20C can be applied not only to a newly constructed structure but also to an existing structure.
In addition, the construction method for injecting the mixture into the ground can be carried out by applying a conventional technique, and further description is omitted here.
[0009]
Next, the effect | action of the support pile reinforcement structure of this invention is demonstrated.
The reinforcing bodies 20A and 20B in FIGS. 2A and 2B are joined only to the piles 14 arranged in the outer peripheral regions 21A and 21B, and are not directly joined to the piles 14 arranged in the central regions 22A and 22B. However, the restraining force of the reinforcing bodies 20A and 20B is also transmitted to the piles 14 in the central regions 22A and 22B through the earth and sand in the central regions 22A and 22B. Therefore, the lower end of the pile 14 is fixed by the support layer 13, the middle portion is restrained by the reinforcing bodies 20 </ b> A and 20 </ b> B, and the upper end of the pile 14 is fixed to the structure 11. The basic structure composed of 20B exhibits the same rigidity as the two-layer rigid frame structure. That is, since the rigidity of the plurality of piles 14 is remarkably increased as compared with the case where there are no reinforcing bodies 20A and 20B, the piles 14 in the structure 11 and the support layer 13 even when a liquefaction phenomenon occurs in the ground. The maximum bending strain that occurs in the fixed portion of is greatly suppressed.
Further, the reinforcing body 20C of FIG. 2C is not directly connected to any of the plurality of piles 14, but the restraining force by the reinforcing body 20C is via the earth and sand present in the internal region 22C. Since the plurality of piles 14 are transmitted to each pile 14, the rigidity of the plurality of piles 14 is increased in the same manner as described above, and the maximum bending strain generated at the fixed portion of the pile 14 in the structure 11 and the support layer 13 is also suppressed.
[0010]
An experiment for verifying the bending strain suppressing effect in the support pile reinforcing structure of the present invention was conducted, and the result is shown in FIG.
(Experiment overview)
In order to grasp the behavior of the pile foundation during liquefaction, this experiment was carried out by installing the model of the support pile reinforcement structure of the present invention on a 1G field shaking table using a sheared soil layer.
In the shaking table, the shear soil layer has a width of 1.5 m, a depth of 0.4 m and a height of 0.6 m, and the ground is composed of two layers using silica sand No. 5, the upper layer relative density Dr = 50%, the lower layer A horizontal ground having a relative density Dr = 90% was targeted. For the ground preparation, a sanding device capable of dispersing sand evenly was used, and a soil layer was formed every 5 cm by an underwater dropping method, and a predetermined relative density was confirmed. Water was used as the interstitial water. The pile model uses four steel pipes with an outer diameter of 19.1 mm, a wall thickness of 1.2 mm, and a length of 600 mm. These four steel pipes are arranged in two rows and two rows at an equal interval of 150 mm (7.8D). Supported the footing. The upper end of the pile was rigidly attached to the footing, and the lower end of the pile was fixed to the bottom plate of the shaking table. All three cases shown in FIG. 3 are saturated sand, case (1) is not reinforced, case (2) is reinforced corresponding to FIG. 2 (c), and case (3) is The reinforcement corresponding to FIGS. 2A and 2B is performed. The input waveform in each case was the same.
[0011]
(Experimental result)
FIG. 3 shows the distribution. The occurrence of bending strain increased with the progress of liquefaction and decreased rapidly after complete liquefaction. When the reinforcement corresponding to FIGS. 2 (a) to 2 (c) was performed, the maximum bending strain was reduced by about 40 to 50% at the upper and lower ends of the pile as compared with the case where the reinforcement was not performed. In addition, the case (3) has a two-layered ramen structure because the outer peripheral pile intermediate parts are integrally connected to each other by the reinforcing body (20A) or the reinforcing body (20B). As a result, it became rigid and the maximum bending strain was slightly smaller than in case (2).
[0012]
【The invention's effect】
The support pile reinforcing structure of the present invention is configured so that the reinforcing body includes the piles arranged on the outer periphery among the plurality of piles and the reinforcing body does not include the piles arranged in the center. Are connected by a reinforcing body to increase the rigidity, and even when a liquefaction phenomenon occurs, the maximum bending strain generated at the joint between the pile and the structure is greatly suppressed. Further, in the present invention, the reinforcing body is provided so as to surround the plurality of piles on the outer periphery in the intermediate portion of the pile, and the binding force from the reinforcing body is indirectly transmitted to the plurality of piles via earth and sand. Similarly, the maximum bending strain generated at the joint between the pile and the structure can be suppressed. Furthermore, in the support pile reinforcement structure of the present invention, the effect of suppressing the maximum bending strain as described above can be obtained simply by providing a reinforcement in the middle part of the pile. It has become possible to reduce construction costs.
[Brief description of the drawings]
FIG. 1 is a side view of a support pile reinforcing structure according to the present invention.
2 is a cross-sectional view taken along the line AA in FIG. 1, and (a) to (c) show different embodiments, respectively.
FIG. 3 is a graph showing the results of an experiment conducted to verify the effect of the present invention.
[Explanation of symbols]
11 Structure 12 Ground 14 Pile 20, 20A, 20B, 20C Reinforcing body

Claims (3)

In order to reduce the stress generated in the event of an earthquake in a plurality of piles placed in the ground to support the structure, a reinforcing body that connects the piles is placed in the center, including the piles arranged on the outer periphery. A pile foundation reinforcement structure characterized by being provided in the depth direction underground part of the pile separated from the structure so as not to include the pile. Reinforcement to reduce the stress generated during earthquakes in multiple piles placed in the ground to support the structure from the structure so as to surround the multiple piles from the outer periphery and not to contact the piles A pile foundation reinforcement structure characterized by being provided around the ground in the depth direction of separated piles.   The pile reinforcement structure according to claim 1 or 2, wherein the reinforcing body is formed by injecting a solidifying agent into the ground to solidify the earth and sand.

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