JP6664697B2 - Foundation structure using existing piles - Google Patents

Description

  The present invention relates to a foundation structure obtained by reusing an existing pile.

  Conventionally, when constructing or redeveloping an aging building, after dismantling the ground part of the existing building, a new building is placed on the ground with the foundation pile (existing pile) of the existing building remaining. A construction method of constructing and supporting a building with existing piles and newly constructed piles has been proposed and put into practical use (for example, see Patent Literature 1, Patent Literature 2, Patent Literature 3, and Patent Literature 4).

  On the other hand, when such existing piles are reused, the existing piles and the pillars of the new building are located at different positions. . For this reason, it is necessary to take measures such as thickening the base slab.

  In addition, when the bearing capacity of the existing pile is small and the load of the new building is large, a load exceeding the allowable bearing capacity may act on the existing pile.

  On the other hand, after digging the ground around the upper end of the existing pile and cutting off the upper end of the existing pile, backfill with a material that is less rigid than the surrounding ground, or use a low-rigidity material such as Styrofoam (trademark) A method has been proposed and put into practical use to alleviate the stress concentration exerted on the new foundation by the existing pile by sandwiching the pile.

JP 2010-133206 A JP 2012-246656 A JP 2012-112218 A JP 2003-82688 A

  However, measures to be taken when the bearing capacity of existing piles is small depend on the cutting length of the pile head of existing piles, materials such as what materials are to be backfilled at what density, and construction conditions such as compaction degree. The load acting on the existing pile changes. For this reason, it is difficult to define a clear specification for keeping the load acting on the foundation slab within a safe range.

  Also, depending on the settlement rigidity ratio of the new pile and the existing pile, the existing pile head may need to be largely removed.For example, the construction may be performed under conditions where deep excavation is difficult to apply, for example, when the existing pile is located near the retaining wall. It may be impossible to do so.

  Furthermore, it is very difficult to control the construction of the ground material with high precision so as to have a prescribed soft rigidity, and it is also difficult to ensure reliability. For this reason, the design is such that the ground reaction force of the existing pile portion that has been subjected to such processing is not expected, and the existing pile having high rigidity and high supporting force is wasted.

  In addition, even when existing piles are reused as piles, design is often performed before the demolition of existing buildings.If the location and properties of the piles surveyed after demolition differ greatly from those set in the design, This requires a rework, which results in a significant loss of time and effort.

  In view of the above circumstances, the present invention provides a foundation structure using an existing pile that can bear a load corresponding to the supporting capacity of an existing pile or a newly installed foundation slab, and enables the existing pile to be suitably reused. The purpose is to provide.

  In order to achieve the above object, the present invention provides the following means.

The foundation structure using the existing pile of the present invention is provided between the existing pile and the new foundation slab, or between the existing pile and the existing foundation slab and the new foundation slab, from the bearing capacity of the new foundation slab and the bearing capacity of the existing pile. The pile head load adjusting member is formed with a predetermined yield load determined and adjusts a load acting on the existing pile, and the pile head load adjusting member is formed by integrating a plurality of members having different yield loads. It is characterized by being constituted .

  In the foundation structure using the existing pile according to the present invention, it is preferable that a head expanding member for increasing an apparent pile head cross-sectional area is provided at a pile head of the existing pile.

Further, in the basic structure using existing pile of the present invention, the pile reinforcing bars protruding from the pile head of the existing pile, and connected to the newly base slab through the pile head load adjusting member configured It is desirable to have been.

  Further, in the foundation structure using the existing pile of the present invention, it is more preferable that the elasticity and thickness of the pile head load adjusting member are set in consideration of the settlement of the new structure.

  In the foundation structure using the existing pile according to the present invention, by using the pile head load adjusting member that suppresses the pile head load of the existing pile to a certain level or less, the load according to the supporting capacity of the existing pile or the foundation slab is borne. Can be. This makes it possible to appropriately reuse the existing piles according to the performance without causing excessive stress on the foundation slab.

  In addition, since the load borne by the existing piles becomes clear, the load borne by the new foundation structure can be clarified.

  Furthermore, by using a lightweight and highly compressible member such as polystyrene foam as the pile head load adjusting member, the thickness of the countermeasure can be reduced and the laying operation can be facilitated.

  Furthermore, by using a member having a small shear rigidity as a pile head load adjusting member, it becomes possible to reduce the load of an existing pile having a small shear or bending strength compared to a newly installed pile.

It is a sectional view showing the foundation structure using the existing pile concerning one embodiment of the present invention. It is sectional drawing which shows the pile head load adjustment member of the foundation structure using the existing pile which concerns on one Embodiment of this invention. It is a figure showing the relation of stress and strain of a pile head load adjustment member. It is sectional drawing which shows the foundation structure using the existing pile which concerns on one Embodiment of this invention, Comprising: It is a figure which shows the structure when there is room in the bearing capacity of the existing pile. It is sectional drawing which shows the foundation structure using the existing pile which concerns on one Embodiment of this invention, Comprising: It is a figure which shows the structure at the time of changing a burden load according to the difference of the relative position of a new pile and an existing pile. It is sectional drawing which shows the foundation structure using the existing pile which concerns on one Embodiment of this invention, and is a figure which shows the structure at the time of reusing an existing foundation slab. It is sectional drawing which shows the foundation structure using the existing pile which concerns on one Embodiment of this invention, and is a figure which shows the structure at the time of making a pile head load adjusting member into a two-layer structure. It is sectional drawing which shows the foundation structure using the existing pile which concerns on one Embodiment of this invention, and is a figure which shows the sharing situation of a horizontal load. It is sectional drawing which shows the foundation structure using the existing pile which concerns on one Embodiment of this invention, and is a figure which shows the structure at the time of making an existing pile resist a tensile load.

  Hereinafter, a foundation structure using an existing pile according to an embodiment of the present invention will be described with reference to FIGS. 1 to 9. This embodiment relates to a foundation structure in which a new building / structure is supported by a new pile (or a new direct foundation) and an existing pile.

Specifically, as shown in FIG. 1 and FIG. 2, the foundation structure A using the existing pile of the present embodiment has a pile head of an arbitrary depth h from the bottom of the new foundation slab 2 with respect to the existing pile 1. A pile head load adjusting member 3 having a clear yield load σ _y such as styrene foam and a small rigidity after yielding is placed on the existing pile 1 from which the part is cut off and the pile head is cut off, and the new foundation slab 2 is placed thereon. It is constructed by installation or construction.

Here, since a load higher than the yield load (σ _y · A) does not act on the existing pile 1, the remaining load acts on the new pile. A is the existing pile cross section.

  The thickness h of the pile head load adjusting member 3 is set so as to fall within a range (for example, 10%) where the compression of the pile head load adjusting member 3 is too large and the load adjusting function is not lost.

For example, the subsidence prediction of new building 4 and [delta] _c, the compressive strain epsilon of pile head load adjusting member 3, yield strain epsilon _y as within the range of _(2-4%) to about 10%, i.e. h = It is set to be δ _c / ε (see FIG. 3).

The yield load σ _y of the pile head load adjusting member 3 is determined from the strength of the new foundation slab 2 and the bearing capacity of the existing pile 1. In a case where there is a different pile bearing capacity in existing pile 1 may be changed yield load of sigma _y for each pile.

In addition, when the bearing capacity that can be expected of the existing pile 1 has a margin for (σ _y · A), as shown in FIG. (Member) 5 may be provided, and the pile head cross-sectional area may be expanded to the apparent pile head cross-sectional area A ′ so that the load of σ _y · A ′ acts on the pile head.

  On the other hand, as described above, even the existing piles 1 having the same specifications have different effects on the new foundation slab 2 depending on the position from the pillar 4a of the new building 4.

On the other hand, as shown in FIG. 5, in the existing pile 1 close to the new pillar 4a (new pile 6) having little effect on the slab 2, the yield load σ _y of the pile head load adjusting member 3 and the expanded head area A ′ By increasing the value, a large load can be borne. In the high impact far existing pile 1, it is possible to reduce the influence of the slab 2 by reducing the pile head yield load sigma _y and拡頭area A of the load adjusting member 3 'reversed.

  Next, when there is an existing foundation slab 7 on the existing pile 1, as shown in FIG. 6, the pile head load adjusting member 3 is spread over the existing foundation slab 7, and the new foundation slab 2 is placed thereon. May be provided, and the existing foundation slab 7 may be reused.

In this case, supports the σ _y · A _S of the load of the new building 4 with the existing foundation slab 7 in existing pile 1, it is sufficient to support the other load in new pile 6. Incidentally, A _S is the area of the pile head load adjusting member 3 laid on the existing foundation slab 7.

  Next, when it is desired to reduce the influence of the reduction of the burden load due to the relaxation of the pile head load adjusting member 3, as shown in FIG. 7, two layers of a member 3a having a small yield load (yield under a design load) and a member 3b having a large yield load are used. What is necessary is just to comprise the pile head load adjustment member 3 with a structure (multilayer structure).

  At this time, the member 3b is in the elastic range under the design load. The settlement of the building corresponds to the amount of elastic-plastic deformation of the member 3a and the amount of elastic deformation of the member 3b. Since the member 3b has an elastic range, the relaxation is small. The thickness of the member 3a can be reduced by the amount of elastic deformation of the member 3b as compared with the case where only the member 3a is used, so that the effect of relaxation can be suppressed.

  When it is desired to further suppress relaxation, the thickness h of the pile head load adjusting member 3 is increased so that the settlement amount of the new building (new construction) 4 falls within the elastic deformation amount of the pile head load adjusting member 3. What should I do? In other words, by setting the elasticity (elastic coefficient, elastic range) and the thickness of the pile head load adjusting member 3 in consideration of the settlement of the new building, it is possible to suppress the relaxation without fail.

  Here, even when the horizontal force acts on the new building 4 and the horizontal strength of the existing pile 1 is smaller than that of the new pile 6, the shear rigidity of the pile head load adjusting member 3 is lower than that of the new pile (concrete). ) By being smaller than 6, the burden horizontal force of the existing pile 1 can be reduced correspondingly, and safety can be ensured (see FIG. 8).

  Further, if a member such as a sheet having a small friction coefficient is provided between the pile head load adjusting member 3 and the existing mat slab, the burden horizontal load of the existing pile 1 can be further reduced.

  When the existing pile 1 is desired to resist the tensile load, the pile head reinforcing bar 9 may be connected to the new foundation slab 2 via the pile head load adjusting member 3 as shown in FIG. In this case, the compressive load is transmitted only up to the yield load of the pile head load adjusting member 3, but the pull-out load can be expected up to the pull-out resistance of the existing pile 1.

  Therefore, in the foundation structure A using the existing pile of the present embodiment, by using the pile head load adjusting member 3 for suppressing the pile head load of the existing pile 1 to a certain level or less, the support capacity of the existing pile 1 and the foundation slab 2 is used. Can be borne. Thereby, the existing pile 1 can be appropriately reused according to the performance without causing excessive stress in the foundation slab 2.

  Further, since the load borne by the existing pile 1 becomes clear, the load borne by the newly installed foundation structure can be clarified.

  Furthermore, by using a lightweight and highly compressible member such as styrofoam as the pile head load adjusting member 3, the thickness of the countermeasure can be reduced and the laying operation can be facilitated.

  Further, by using a member having a small shear rigidity as the pile head load adjusting member 3, it becomes possible to reduce the burden load of the existing pile 1 having a small shearing and bending resistance compared to the newly installed pile 6.

  As mentioned above, although one Embodiment of the foundation structure using the existing pile which concerns on this invention was described, this invention is not limited to the said embodiment, It can change suitably within the range which does not deviate from the meaning.

1 Existing Pile 2 New Foundation Slab 3 Pile Head Load Adjusting Member 4 New Building 4a Column 5 Head Expansion Member 6 New Pile 7 Existing Foundation Slab 9 Pile Head Reinforcement A Foundation Structure Using Existing Pile

Claims (4)

Between the existing pile and the new foundation slab, or between the existing pile and the existing foundation slab and the new foundation slab, formed with a predetermined yield load degree determined from the strength of the new foundation slab and the bearing capacity of the existing pile, It is configured by providing a pile head load adjusting member for adjusting the load acting on the existing pile ,
A foundation structure using an existing pile, wherein the pile head load adjusting member is configured integrally with a plurality of members having different yield loads . In the foundation structure using the existing pile according to claim 1,
A foundation structure using an existing pile, wherein a head expansion member for increasing an apparent pile head cross-sectional area is provided at a pile head of the existing pile. In the foundation structure using the existing pile according to claim 1 or claim 2 ,
Wherein the pile reinforcing bars protruding from the pile head of the existing pile, the pile head basis utilizing existing piles, characterized in that it is configured to connect to the new foundation slab via a load adjustment member structure . In a foundation structure using the existing pile according to any one of claims 1 to 3 ,
A foundation structure using an existing pile, wherein elasticity and thickness of the pile head load adjusting member are set in consideration of settlement of a new structure.

Images