JP4815248B2 - Pile foundation structure and its construction method - Google Patents

Description

  The present invention relates to a pile foundation structure and a construction method thereof.

When a pile foundation is used as a support method for a building in a ground with a supporting ground below a soft surface ground, the vertical bearing force of the building is secured, but horizontal rigidity is insufficient. Displacement will increase. In such a case, improving the surface ground and increasing the horizontal stiffness of the pile head is an effective method for suppressing horizontal displacement during an earthquake. As a general method, as shown in FIG. 6, the support pile 11 is surrounded by an improved body 10 by a deep mixing process using a cement-based solidified material. As another pile foundation structure, for example, the invention of JP-A-2005-320692 is known.
JP 2005-320692 A

  However, the method of surrounding support piles with an improved body by the above-mentioned deep-mixing method using cement-based solidified material is to construct the improved body one by one from the ground surface to a depth of 4-5 m, so the construction cost and the construction period are greatly increased. There was a problem that it took.

  This invention is made | formed in view of these problems, The objective is to provide the pile foundation structure which can suppress a horizontal displacement efficiently, and its construction method, without requiring a construction cost and a construction period. is there.

A pile foundation structure for solving the above-mentioned problem is that a support pile having a tip supported by a support layer below a soft surface layer ground is disposed on the ground composed of the surface layer ground and the support layer, and the surface layer ground The improvement body along the core of the support pile arranged in the base is formed by a shallow layer mixing treatment method using a cement-based solidifying material, and the improvement body is formed in a lattice shape and the depth of the improvement body Is within 2 times the pile diameter of the support pile, and the width of the improved body is within 2 to 4 times the pile diameter of the support pile.
The pile foundation structure is constructed by placing a support pile on the surface ground so that the support layer supports the tip of the pile on a soft surface ground and a support layer below the soft ground. Then, in forming an improved body improved ground by a shallow mixed processing method along the core of the support pile, the improved body is formed in a lattice shape, and the depth of the improved body is the depth of the support pile. It is within 2 times the pile diameter and the width of the improved body is within 2-4 times the pile diameter of the support pile.

  The construction cost and construction period can be greatly reduced by improving only the surface layer ground by the shallow mixing method with respect to the deep mixing method in which the improved bodies are constructed one by one. Moreover, the horizontal displacement of the support pile can be sufficiently suppressed even when the surface ground is improved (for example, the displacement before the improvement can be reduced to 40% or less). Even if the improved body is in a lattice shape, the horizontal displacement reduction effect is almost the same as in the case of the entire surface improvement, but the construction period can be greatly reduced and the construction cost can be reduced by about 35% or more. In addition, the environmental load can be reduced by reducing the amount of improved material used and shortening the work time of heavy machinery.

  Hereinafter, the pile foundation structure of this invention and the construction method of a pile foundation structure are demonstrated. First, the pile foundation structure will be explained, and then the construction method of the pile foundation structure will be explained. This pile foundation structure is a ground improvement area necessary to suppress the horizontal displacement of the pile head, and the surface layer ground is made into a grid of improvements by the shallow mixed treatment method along the core where the piles are arranged. It is formed, and the horizontal rigidity of the pile head is ensured by a lattice-like improved body formed only on the surface layer.

  1 to 3 show an embodiment of a pile foundation structure. This pile foundation structure 1 is constructed on a ground 4 having a support layer 3 below a soft surface layer 2, and a support pile 5 whose tip is supported by the support layer 3 is disposed on the ground 4. A grid-like improvement body 7 is formed along the core 6 of the disposed support pile 5. This improved body 7 is obtained by improving the surface layer ground 2 by a shallow layer processing method. The depth H is within 2 times the pile diameter, the lateral width W is within 2 to 4 times the pile diameter, and the rigidity is the original ground 2a. 10 to 20 times the rigidity. Thus, even if it is the lattice-shaped improvement body 7 formed in the surface layer, the required horizontal rigidity in a pile head can be ensured.

  Fig. 4 also shows the horizontal displacement reduction effect of the horizontal displacement at the pile head of the deep layer improvement and the shallow layer improvement (pile head horizontal displacement amount δ 'of the improved ground / pile head horizontal displacement amount δ of the original ground). The difference is shown by changing the improvement depth H, and shows the case where the rigidity of the lattice-like improvement body 7 is improved to 10 times and 20 times that of the original ground 2a. From this result, even when the improved depth H is about 0.5 times the pile diameter D, the horizontal displacement reduction effect is large with respect to the original ground 2a, and the displacement can be suppressed to 40% or less of the original ground 2a. Further, the higher the rigidity of the improved body 7, the greater the effect. However, regardless of the rigidity of the improved body 7, when the improved depth H exceeds twice, the reduction effect hardly changes. Therefore, when the improved depth H is within twice the pile diameter and the surface layer is improved, horizontal displacement can be suppressed more economically, so the depth H of the improved body 7 is within twice the pile diameter. The effect can be confirmed.

  FIG. 5 shows an example in which the improvement rigidity ratio (the rigidity Ek of the ground improvement body / the rigidity Eo of the original ground) is 20 times with respect to the horizontal displacement reduction effect at the pile head with respect to the lateral width W of the lattice-like improvement body 7. Show. From this figure, even in the case of the lattice-shaped improvement body 7, there is a sufficient displacement reduction effect with respect to the original ground 2a, and even if the width W of the improvement body 7 is twice the pile diameter, there is an effect of 70% or more. However, even if the width W of the improved body 7 is wider than this, the reduction effect does not change much. For example, when the width W of the improved body 7 is 4 times the pile diameter, and when the entire surface is improved (pile arrangement interval is assumed to be within 10 times the pile diameter, the case where W = 10D is the entire surface improvement. (Representing), the reduction rate with respect to the original ground 2a changes only by about 5%. Therefore, the effect that the width W of the improved body 7 is within 2 to 4 times the pile diameter can be confirmed.

  FIG. 5 also shows the reduction effect (economic effect) of the construction range of the improvement body 7 with respect to the construction range of the entire ground improvement as the reduction rate of the construction period and construction cost with respect to the width W of the grid-like improvement body 7. From this figure, when the width W of the improved body 7 is not more than three times the pile diameter, the economic effect is great, and the improvement range can be suppressed to half or less of the construction range in the case of the entire ground improvement. However, the increase in the improvement range with respect to the increase in the lateral width W of the improved body 7 is large in the initial stage, and when the improved lateral width W is 5 times the pile diameter (W = 5D), the reduction amount of the construction range with respect to the entire ground improvement is It will be about 25%. And if it exceeds 5 times thereafter, the economic effect will gradually become smaller. Therefore, the effect that the grid-like improvement body 7 was more economical than the entire ground improvement could be confirmed.

  Next, the construction method of the pile foundation structure 1 will be described. This method is performed for the ground 4 having the support layer 3 below the soft surface ground 2. First, the support pile 5 is formed by supporting the tip of the support layer 3 below the surface ground 2. To cast.

  Next, when a lattice-like improvement body 7 is formed along the core 6 of the support pile 5, a pile foundation structure 1 as shown in FIG. 1 is constructed. The improved body 7 is formed to have a rigidity 10 to 20 times that of the original ground 2a by mixing a cement-based solidified material with the surface ground 2 and using a shallow mixing process. Further, the depth of the improved body 2 is set to be within twice the pile diameter and the lateral width W is set to be within 2 to 4 times the pile diameter.

It is a top view of a pile foundation structure. It is a perspective view of a pile foundation structure. It is sectional drawing of a pile foundation structure. It is the figure which showed the relationship between the improvement depth and the horizontal displacement reduction effect. It is the figure which showed the horizontal displacement reduction effect of the pile head with respect to the improvement width | variety of a grid | lattice-like improvement body. It is the conventional pile foundation structure, (1) is a top view, (2) is a perspective view.

Explanation of symbols

1 Pile foundation structure 2 Surface ground 2a Raw ground
3 Support layer 4 Ground 5, 11 Support pile 6 Street core 7, 10 Improved body W Width

Claims (2)

A support pile, the tip of which is supported by a support layer below the soft surface layer ground, is disposed on the ground composed of the surface layer ground and the support layer, and along the core of the support pile disposed on the surface layer ground The improved body is formed by a shallow mixing method using a cement-based solidification material, and the improved body is formed in a lattice shape, and the depth of the improved body is within twice the pile diameter of the support pile. The width of the improved body is within 2 to 4 times the pile diameter of the support pile,
Pile foundation structure characterized by In a ground with a soft surface ground and a support layer below it, the support pile is placed on the surface ground so that the support layer supports the tip of the pile , and then the core of the support pile is placed. Along with forming the improved body improved ground by the shallow mixed treatment method, the improved body is formed in a lattice shape, and the depth of the improved body is within twice the pile diameter of the support pile, And the width of the improved body was formed within 2 to 4 times the pile diameter of the support pile ,
A method of constructing a pile foundation structure characterized by

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