JP5687887B2 - Construction method of new foundation using existing piles and foundation constructed by the same method - Google Patents

Description

  The present invention relates to a construction method for a foundation of a building and a foundation constructed by the method, and in particular, using an existing pile, an existing pile cap located on the top of the pile, and an existing foundation bottom plate. It relates to a building constructed in the same way as a new pile and foundation.

  JP 2000-45295 A (Patent Document 1) focuses on the fact that existing piles and new piles have different subsidence characteristics in the pile foundation of a new building constructed by mixing existing piles and new piles. The invention regarding the construction method of the existing pile mixed-type pile foundation structure improved so that the stress degree of the existing pile to be utilized can be suppressed below an allowable value and the foundation structure is disclosed. According to the existing pile mixed-type pile foundation structure described in Patent Literature 1, a through hole with a bottomed hole or a lid is provided in the foundation plate, and the existing pile is inserted to form a gap between the upper end of the existing pile. It is characterized by that.

  Specifically, a plurality of hollow holes are uniformly arranged on the upper end surface of the head of the existing pile. A steel bottom plate is laid on the bottom surface of the hollow hole to support the elasto-plastic material being laid on the existing pile head. The said structure is considered so that the vertical load more than a predetermined value may not be added with respect to the existing pile from a foundation plate by providing an elastic body in the pile head upper part. However, in the structure described in Patent Document 1, no special consideration is given to controlling the bending moment applied to the existing pile head.

  Japanese Patent Laid-Open No. 2000-45296 (Patent Document 2) discloses an axial stress between a foundation plate and an existing pile in a pile foundation structure configured by mixing existing piles to be reused in a foundation plate and a new pile. The existing pile mixed type pile foundation structure characterized by interposing the shock absorbing material which does not transmit is disclosed. The existing pile-mixed pile foundation structure is provided so that the existing pile to be reused can be kept below the allowable value by sharing only the horizontal force with the existing pile. In the existing pile mixed pile foundation structure, a cushioning material is interposed between the foundation plate and the existing pile. Specifically, a bottomed hole is provided in the foundation slab and an existing pile is inserted to form a gap between the top of the existing pile and the bottom of the bottomed hole, or a through hole is provided in the foundation slab to replace the existing pile. It is characterized in that a gap is formed between the upper end of the existing pile and the upper surface of the foundation plate.

  The invention described in Patent Document 2 is intended to load only the horizontal load and the bending moment applied to the pile head without causing the existing pile to bear the load in the vertical direction.

  Japanese Patent Laid-Open No. 2000-154549 (Patent Document 3) leaves existing foundations such as existing foundation slabs and existing piles, and provides through holes for newly installed piles at important points of the existing foundation slabs. The new foundation slab is then installed on the pile head of the new pile, and the existing foundation slab and the existing foundation slab are interposed between the existing foundation slab and the existing foundation slab. The present invention discloses an existing foundation reuse construction method characterized by preventing a horizontal force from being applied to the pile.

  According to this method, since the existing pile remains bonded to the existing foundation slab, the rotation of the pile head is restricted, and consideration is given to reducing the horizontal force and bending moment generated on the pile head due to deformation of the ground. It has not been.

Conventionally, regardless of existing piles or newly built piles, it has been common practice to fix the main reinforcement of the piles to the pile cap and to bond them together to make a rigid connection that reliably transmits the load. For this reason, in order to fix the main bar of the existing pile in the pile cap to be newly installed, measures have been taken to disassemble the existing pile cap and expose the main bar.
On the other hand, in this invention, since the semi-rigid joining which does not connect a pile, a pile cap, or a foundation slab with a main reinforcement is applied, it is not necessary to start the main reinforcement of a pile head. In addition, by devising the evaluation method, it became possible to evaluate the semi-rigid connection behavior on the square pile cap surface, so the joint position of the existing pile and the newly installed foundation slab was not the pile head but the existing pile cap. It is also possible to make it at the top.
JP 2000-45295 A JP 2000-45296 A JP 2000-154549 A

  The present invention aims to solve the above-mentioned problems of the prior art, and in the construction method of the foundation using both the existing pile and the new pile, according to the stress generated after the new building construction, By controlling the bending moment or horizontal load acting on the pile head by adjusting the method of joining the pile cap located on the upper part and the newly installed foundation, the stress acting on the existing pile is made less than the allowable value, and the existing pile and The objective is to provide a foundation construction method that allows the maximum use of existing foundations.

  The present invention further provides a construction method of a foundation structure that relaxes restraining rotation of an existing pile head by an existing foundation, or a construction method of a foundation structure that restricts transmission of bending moment between an existing pile head and a newly installed foundation plate. The task is to do.

In order to solve the above-mentioned problems, the present invention is a construction method in which a new pile and a foundation are newly established by using an existing pile, an existing pile cap located at the top of the pile, and an existing bottom plate. In addition to providing an opening in the existing bottom plate and providing a new pile , a groove is provided between the existing pile cap or a part of the existing pile cap and the existing bottom plate to reduce the fixing degree of the pile head of the existing pile. In addition, the present invention provides a construction method for a new foundation in which the existing pile cap or a part of the existing pile cap and the new foundation are adjusted from rigid joint to pin joint, or completely separated.

In the above method, the new foundation has a new pile and a new foundation version. The soundness of existing piles means the stress-bearing capacity at the time of constructing a new foundation. Appearance survey, length (exact size) survey, concrete Young's modulus and strength test, It is judged by tests such as a neutralization depth test, a tensile test of reinforcing bars, and an integrity test to confirm that there are no cracks or cracks across the pile depth. For example, when a reinforcing bar or a concrete does not reach a predetermined strength, or when it is confirmed that there is a crack or a crack in a certain portion in the depth direction of the pile body, it is determined that the existing pile is not healthy. For existing piles judged unhealthy, it is judged that it is not appropriate to expect vertical force, bending moment and horizontal load in design.
Between rigid joint and pin joint is a rigid joint that anchors the vertical reinforcing bar of the existing pile and the vertical reinforcing bar of the existing pile cap to the new foundation, a semi-rigid joint that does not anchor these reinforcing bars to the new foundation, For example, pin support.

  The groove may penetrate the existing bottom plate in the thickness direction, or may be a groove that has been cut to a certain depth in the thickness direction. What is necessary is just to reduce the fixing degree of the pile head of an existing pile as needed. Further, the groove may completely surround the periphery of the existing pile cap or may not have a completely closed shape.

  The degree of fixation can be reduced by making the contact area between the existing pile cap or a part of the existing pile cap and the new foundation smaller than the horizontal cross-sectional area of the pile head of the existing pile. By making the contact area with the new foundation smaller than the horizontal cross-sectional area of the pile head of the existing pile, the support state of the pile head becomes a so-called semi-rigid joint. At that time, the pile head of the existing pile can be evaluated as a joint having a predetermined rigidity corresponding to a pin joint or a bending moment on the bottom surface of the new foundation in terms of structural calculation.

  The relationship between the bending moment and the vertical force and the deformation angle at the contact surface between the pile head and the new foundation can be obtained by the following method. In other words, the material stiffness is set considering the cross-sectional area and nonlinearity of the contact surface, the deformation amount of the contact surface with the deformation conditions adapted to the bending moment and vertical force generated on the contact surface is calculated, and the deformation angle of the contact surface Ask for. The bending moment and vertical force generated on the contact surface are increased as needed, and the increase in the deformation angle of the contact surface due to the increase is calculated in the same way. By repeating this, the relationship between the bending moment and vertical force of the contact surface and the deformation angle can be obtained. This method is described in Kazumasa Imai, Takeyoshi Korenaga, Katsumi Higuchi “Analysis Method of Rotational Deformation at the End of RC Member Considering Indentation”, Architectural Institute of Japan, 562, pp99-106, December detailed.

  Further, according to the present invention, the existing pile cap is used so that the load (vertical force, bending moment, horizontal load) is not transmitted between the existing pile determined to be unhealthy and the new foundation as a result of the test described above. Alternatively, a gap or an elastic body may be provided between a part of the existing pile cap and the new foundation so as to be completely separated. The present invention further relates to a foundation constructed by the construction method.

FIG. 1 is a conceptual diagram of existing piles, existing foundations and existing buildings. FIG. 2 is a conceptual diagram showing a state where an existing building is demolished. FIG. 3 is a conceptual diagram showing a state in which a new pile and a new foundation are added to the existing pile and the existing foundation based on the present invention. FIG. 4 is a conceptual diagram showing a state in which a framework is erected on a foundation newly established based on the present invention.

  Specific embodiments of the present invention will be described below on the basis of examples. However, the examples are only described to help the understanding of the invention, and therefore the present invention is not limited to the examples described below. Needless to say, it is not limited.

  FIG. 1 is a conceptual diagram showing an existing building 500 supported by a foundation 100 supported by an existing pile 200. The existing pile 200 has a pile cap 220 on the pile head, and the pile cap 220 supports the building 500 integrally with the foundation 100. A side surface of the underground portion of the building 500 is in contact with the underground wall 120.

  FIG. 2 is a conceptual diagram illustrating a state in which the existing building 500 is removed. The existing pile 200, the pile cap 220, the foundation 100 and the underground wall 120 are left as they are, and only the building 500 is dismantled and removed.

FIG. 3 is a conceptual diagram showing a state in which most of the existing piles 200, 202, and 204 and the foundation 100 are left and the new pile 400 and the new foundation 300 are built. The method of joining the existing pile caps 220, 222, and 224 located on the upper portions of the existing piles 200, 202, and 204 to the existing foundation 100 and the new foundation 300 that are the foundation bottom slabs that follow the existing pile caps In consideration of soundness, the stress generated in existing piles and existing pile caps after building a new building will be set below the allowable value. For soundness judgment, confirmation of blueprints and construction records, external appearance investigation with existing piles and existing pile caps exposed, dimensional investigation, concrete Young's modulus and strength test, neutralization depth test, rebar tensile test An integrity test is performed to confirm that there are no cracks or cracks across the depth of the pile. As a result of the material test, when the concrete strength of the existing pile and the strength of the reinforcing bar are low, the strength of the existing pile will be evaluated low. In addition, when long years have passed since the construction of existing piles, or when design information is not sufficient, the material strength for calculating pile strength is reduced and evaluated according to the degree. The method for reducing the material strength of existing piles is shown in Equation (1).

Strength reduction rate α = α1 × α2 × α3 × α4 × α5 --------------------- Equation (1)

α1: 0.9 to 1.0, coefficient representing the degree of completeness of design information α2: 0.8 to 1.0, proportional to specimen sampling rate α3: 0.9 to 1.0, aging degradation factor of existing building α4: 0.9 to 1.0, during earthquake of upper frame Reliability of structural verification method α5: 0.9 to 1.0, reliability of ground and pile structural verification method during earthquake

Thus, when the material strength is low or when strength reduction is required by the value of Equation (1), there is a possibility that the existing pile cannot be loaded with a large bending moment or horizontal force. Therefore, a groove 360 is provided around the existing pile cap 222 positioned at the upper part of the existing pile 202 so as to penetrate the existing foundation 100, and the existing pile cap 222 and the existing foundation 100 are separated, and the upper surface of the existing pile cap 222 A buffer body 370 is provided on the outer periphery of the existing pile cap 222 on the surface where the new foundation 300 comes into contact, and the contact area between the existing pile cap 222 and the new foundation 300 is reduced so that the existing pile 202 and the existing pile cap 222 are vertically By not fixing the reinforcing bars in the direction to the new foundation 300, the transmission of the bending moment can be limited. As a material of the buffer body 370, for example, an elastic body such as hard rubber, wood, and styrofoam, and an elastic-plastic body with low strength are used, but this is not a limitation. By adjusting the contact area, the connection between the existing pile cap 222 and the new foundation can be a pin connection or a semi-rigid connection. In some cases, the buffer 370 is not inserted and the contact area is the entire horizontal cross section of the pile cap. It is also possible to select the rigid joint by fixing the vertical reinforcing bars of the existing pile 202 and the existing pile cap 222 to the new foundation 300 without inserting the buffer body 370.

  The new pile 400 is provided with a through-hole 460 in the existing foundation 100 and is constructed at that portion. The gap between the new pile 400 and the existing foundation 100 may be simply backfilled so as not to be mechanically joined. However, by inserting an elastic body or injecting mortar to some extent, the new pile 400 and the existing foundation 100 are somewhat fixed. It is also possible to transmit the power of.

  The pile 204 and the existing pile cap 224 are examples in which the existing pile cap 224 and the new foundation 300 are separated from each other while being joined to the existing foundation 100. If cracks or cracks are found in the deep part of the pile body in the integrity test, the buffer body 380 covers the entire top surface of the pile cap between the upper part of the existing pile cap 224 and the new foundation 300. The vertical force, bending moment and horizontal force can be hardly transmitted. Leaving the existing pile cap 224 and the existing foundation 100 in the upper part of the existing pile 204 in a rigid connection is a matter to be determined independently of the force transmission relationship between the existing pile cap 224 and the new foundation 300, The new foundation 300 may be the semi-rigid joint or the rigid joint.

  The existing pile cap 220 at the upper part of the existing pile 200 remains rigidly connected to the existing foundation 100 and is semi-rigidly connected to the new foundation 300 by the buffer 390.

  FIG. 4 is a conceptual diagram showing a state in which a new building 600 having columns 620 and beams 640 is built on the foundation structure.

  According to the present invention, existing piles and foundations are left in place and used effectively, while considering the structural soundness of existing piles and foundations and the stress generated when building a new building. Can be selected in the range of cut-off, semi-rigid and rigid joints, and the existing base and new foundation can be selected in the range of cut-off, semi-rigid and rigid joints. The existing structure can be used most effectively. At the same time, there is an advantage that the process of removing the existing piles becomes unnecessary, and the work such as backfilling associated therewith becomes unnecessary.

100 Existing foundation 120 Underground wall 200, 202, 204 Existing pile 220, 222, 224 Existing pile cap 300 New foundation 370, 380, 390 Shock absorber 400 New pile 500 Existing building 600 New building

Claims (4)

This is a construction method in which a new pile and foundation are newly constructed using an existing pile, an existing pile cap located on the top of the pile, and an existing bottom plate, and an opening is provided in the existing bottom plate and a new pile is installed. In addition , a groove is provided between the existing pile cap or a part of the existing pile cap and the existing bottom plate to reduce the fixing degree of the pile head of the existing pile. The construction method of a new foundation that adjusts the joint state between the part and the new foundation between rigid joint and pin joint or completely separates it. The construction method of the new foundation according to claim 1, wherein the degree of fixation is reduced by making the contact area between the existing pile cap or a part of the existing pile cap and the new foundation smaller than the horizontal cross-sectional area of the pile head of the existing pile. As the load transmission between the new foundation and the existing pile is not performed, according to claim 1 or 2 provided with voids or elastic member between the new basic part of the existing pile cap or existing pile cap Construction method for new foundation. A foundation constructed by the construction method according to any one of claims 1 to 3 .

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