JP5041838B2 - Pile foundation structure construction method - Google Patents

Description

  The present invention relates to a method for constructing a pile foundation structure.

As a method of coping with liquefaction of the surface layer near the pile head in soft ground, (1) the support piles 22 in the liquefied layer 21 are surrounded by a wall-like deep layer improvement body 20 or the like, and the cause of liquefaction (2) Method of preventing the occurrence of liquefaction by placing a number of compacted sand piles, (3) Allowing the occurrence of liquefaction, There is a method of dealing with steel pipe wound piles (SC piles) with high toughness and proof stress. As another method for constructing a pile foundation structure, for example, the invention of Japanese Patent Application Laid-Open No. 2007-46343 is known.
JP 2007-46343 A

  However, although the above methods (1) and (2) can prevent the occurrence of liquefaction, the ground rigidity of the surface layer near the pile head cannot be improved dramatically. In addition, since the method (3) allows the occurrence of liquefaction, the horizontal displacement of the pile head cannot be reduced. For the same reason, it cannot be a measure to reduce the horizontal displacement of piles for soft ground such as alluvial silt layers. Therefore, these methods are measures that are expected only to prevent the occurrence of liquefaction, or because they are measures that increase the yield strength and toughness of piles with respect to large bending stresses that occur in piles whose surface layer is soft ground. The horizontal displacement of the pile head at the time could not be reduced.

  The present invention has been made in view of these problems, and its purpose is to significantly reduce the horizontal displacement of the pile head during an earthquake and to reduce the bending stress of the pile body. It is to provide a construction method for the foundation structure.

The method for constructing the pile foundation structure to solve the above problems is the same as or equal to the pile diameter in order to ensure the horizontal rigidity while leaving the pile diameter interval at the intersection of the lattice in the surface layer part of the soft ground. Form the depth improvement body in a lattice shape with the following width ,
After forming excavation holes for forming support piles at the intersections of the grids while cutting a part of the deep layer improvement body, the support piles are formed integrally with the deep layer improvement bodies in the excavation holes.

In addition, in the case of soft ground without a liquefied layer, the depth of the deep layer improvement body is set to a depth within 3 to 5 times the pile diameter of the support pile in order to reduce the bending moment, or there is a liquefied layer. In the case of soft ground, this includes making it deep enough to prevent liquefaction.

  The pile head with the greatest bending moment is supported by the grid-like deep improvement body, that is, the support pile is placed at the intersection of the lattice of the lattice-like deep improvement body. Horizontal displacement and bending stress can be greatly reduced. For example, the bending stress of a pile body at the time of an earthquake can also be reduced, such as changing a steel pipe winding pile to a ready-made pile. Further, by forming the lattice-like deep layer improvement body on the soft liquefied layer, the occurrence of liquefaction can be prevented and the safety factor against liquefaction can be improved.

  Hereinafter, the construction method of the pile foundation structure of this invention is demonstrated. First, the pile foundation structure will be explained, and then the construction method of the pile foundation structure will be explained. In order to suppress the horizontal displacement of the pile head, this pile foundation structure secures the horizontal rigidity of the pile head by forming a depth improvement body of a suitable depth in the surface layer of the soft ground. Here, the appropriate depth is 3 to 5 times the diameter of the pile when there is no liquefied layer in soft ground, and the depth of the liquefied layer when there is a liquefied layer.

  FIG. 1 shows a pile foundation structure 1 according to the first embodiment. This pile foundation structure 1 is constructed on a soft ground 2 having no liquefied layer, and a lattice-like deep layer improvement body 4 formed on the surface layer portion 3 of the soft ground 2 and a lattice of the deep layer improvement body 4 It is comprised from the support pile 5 laid in the intersection of these.

  This deep layer improvement body 4 is formed by a mixed material 8 produced by mixing cement milk with excavated soil (formed along the core 6 of the support pile 5), and is within 3 to 5 times the pile diameter. It has a depth, a width equal to or less than the pile diameter, and a rigidity 10 times or more that of the surface layer ground 2. The support pile 5 driven at the intersection of the lattice of the deep layer improvement body 4 is a ready-made pile, and is joined to the deep layer improvement body 4 via a pile peripheral fixing material 9. In addition, the depth of the deep improvement body 4 is set within 3 to 5 times the pile diameter, as shown in Fig. 2, the largest bending moment is applied to the pile head having a depth within 3 to 5 times the pile diameter. This is to effectively reduce this bending moment. Moreover, the reason why the width of the deep layer improvement body 4 is made equal to or less than the pile diameter is that the required horizontal rigidity in the pile head can be sufficiently secured by the depth within 3 to 5 times the pile diameter. It is. In addition, since the deep improvement body 4 and the support pile 5 are constructed | assembled separately, the pile periphery fixing material 9 has reached the support ground 7. FIG.

  FIG. 3 shows a pile foundation structure 10 according to the second embodiment. This pile foundation structure 10 is formed in the soft ground 2 with the liquefied layer 11, and the depth improvement body 4 is not at a depth within 3 to 5 times the pile diameter, but at the depth of the liquefied layer 11. Except having been formed until now, it is the same structure as the pile foundation structure 1 of 1st Embodiment. In this way, when the lattice-like deep layer improvement body 4 is formed to the depth of the liquefied layer 11, the occurrence of liquefaction can be effectively prevented. The depth of the liquefied layer is the bottom of the liquefied layer, half or two thirds of the depth of the liquefied layer, the layer thickness of the liquefied layer, the improvement range of the liquefied layer, or economic matters. In consideration of these, etc., it shall be determined corresponding to these.

  FIG. 4 shows a pile foundation structure 12 according to the third embodiment. In this pile foundation structure 12, the support pile 5 is not a ready-made pile as described above but a cast-in-place concrete pile, and other than this, the pile foundation structure 1 has the same configuration as the pile foundation structure 1 of the first embodiment. In the case of this cast-in-place concrete pile, the concrete 14 is directly cast in the excavation hole 13, so that it can be joined to the deep improvement body 4 at the point where the concrete 14 is cast, and the pile peripheral fixing material 9 as described above Do not need.

  The configuration in which the support pile 5 is a cast-in-place concrete pile can be applied to the pile foundation structure 10 of the second embodiment, that is, the pile foundation structure 10 formed on the soft ground 2 having the liquefied layer 11. .

  Next, the construction method of the pile foundation structure of 1st Embodiment is demonstrated using the pile foundation structure 1 of 1st Embodiment. This method is intended for the soft ground 2 having no liquefied layer. First, as shown in FIG. 5, the depth improvement unit 15 is placed along the core 6 of the support pile 5 on the surface layer portion 3 of the soft ground 2. Form.

  This deep improvement unit 15 is a triple excavator, and a cross-shaped excavation hole (four crosses forming a cross) 16 centering on the placement site 18 of the support pile 5, which is the intersection of the lattice, has a pile diameter. While excavating to a depth of 3 to 5 times or less, cement milk is added to and mixed with the excavated soil in the excavation hole 16 to produce the mixed material 8. And when this mixed material 8 hardens | cures, the depth improvement which consists of the cross-shaped deep-layer improvement body unit 15, ie, the improvement body 19 arrange | positioned in the cross centering on the intersection (placement place 18 of a support pile) which has not been excavated. A body unit 15 is formed. At this point, each deep improvement unit 15 exists independently (without each unit being joined).

  Next, as shown in FIG. 6, the drill holes 16 are formed with the triple excavator between the deep layer improvement unit units 15 in the same manner as described above, and part of the improvement units 19 in the deep layer improvement unit units 15 on both sides. Excavate while cutting the tip. Then, cement milk is put into and mixed with the excavated soil in the excavation hole 16 to produce the mixed material 8. Then, when the mixed material 8 is cured and a new improved body 17 is formed, the independent deep layer improved body units 15 are joined together to form the lattice-shaped deep layer improved body 4. At this point, the grid intersection 18 which is the place where the support pile is placed has not been excavated.

  Next, as shown in FIG. 7, the excavation hole 13 for the support pile is cut at the intersection 18 of the lattice that has not been excavated, and a part of the deep improvement unit 15 (the tip of the four improvement items 19) is being cut. The excavation hole 13 is filled with a pile fixing material 9 such as cement milk. Next, as shown in FIG. 8, the ready-made pile which is the support pile 5 is built in this pile periphery fixing material 9. As shown in FIG. And if this pile periphery fixing material 9 hardens | cures, the support pile 5 will be joined to the deep-layer improvement body 4, and will become integral. Thereby, the pile foundation structure 1 in which the support pile 5 is supported at the intersection of the deep layer improvement body 4 is constructed. In addition, although the depth improvement body unit 15 is the depth within 3 to 5 times the diameter of a pile, the pile periphery fixing material 9 is formed to the depth of the support ground 7. FIG.

  Next, the construction method of the pile foundation structure of 2nd Embodiment is demonstrated using the pile foundation structure 1 of 1st Embodiment similarly to the above. This method targets the soft ground 2 with the liquefied layer 11 and does not form the depth improvement unit 15 to a depth within 3 to 5 times the pile diameter but to the depth of the liquefied layer 11. Other than this, the configuration is the same as the construction method of the first embodiment. By forming the lattice-like deep layer improvement body 4 to the depth of the liquefied layer 11 in this way, the occurrence of liquefaction due to an earthquake can be prevented. The depth of the liquefied layer is the bottom of the liquefied layer, half or two thirds of the depth of the liquefied layer, the layer thickness of the liquefied layer, the improvement range of the liquefied layer, or economic matters. In consideration of these, etc., it shall be determined corresponding to these.

  Next, the construction method of the pile foundation structure of 3rd Embodiment is demonstrated using the pile foundation structure 1 of 1st Embodiment same as the above. This method is intended for soft ground 2 having no liquefied layer. First, as shown in FIG. 9, a deep layer improvement unit 15 is placed on the surface layer 3 of the soft ground 2 along the core 6 of the support pile 5. Form.

  The deep improvement unit 15 is formed in a cross shape so that the excavation holes are abutted by a triple excavator. The excavation hole 16 is excavated to a depth of 3 to 5 times the pile diameter, and cement milk is put into and mixed with the excavated soil in the excavation hole 16 to produce the mixed material 8. When the mixed material 8 is cured, each of the improved bodies 19 is abutted, that is, a cross-shaped deep improved body unit 15 in which the vertical and horizontal improved bodies 19 intersect each other is formed. At this point, each deep improvement unit 15 exists independently (without each unit being joined).

  Next, as shown in FIG. 10, between the cross-shaped deep improvement unit 15, similarly to the above, the excavation hole 16 is formed by a triple excavator, and the improvement body 19 of the deep improvement unit 15 on both sides is provided. The mixed material 8 is manufactured by excavating while cutting a part, and pouring and mixing cement milk into the excavated soil in the excavated hole 16. And when this mixed material 8 hardens | cures, the deep layer improvement body units 15 which existed independently each other will be joined, and the lattice-shaped deep layer improvement body 4 will be formed. At this point, an improved body 19 is also formed at the intersection 18 of the lattice, which is the place where the support pile is placed.

  Next, as shown in FIG. 7, excavation holes 13 for supporting piles are excavated at the intersection 18 of the lattice until the support ground 7 is reached while the improvement body 19 of the deep improvement unit 15 is being cut. The pile circumference fixing material 9 such as cement milk is filled. Next, as shown in FIG. 8, the ready-made pile which is the support pile 5 is built in this pile periphery fixing material 9. As shown in FIG. And if this pile periphery fixing material 9 hardens | cures, the support pile 5 will be joined to the deep-layer improvement body 4, and will become integral. Thereby, the pile foundation structure 1 in which the support pile 5 is formed at the intersection of the deep layer improvement body 4 is constructed, and the support pile 5 is supported by the deep layer improvement body 4.

  Next, the construction method of the pile foundation structure of 4th Embodiment is demonstrated. This is the construction method of the third embodiment applied to the soft ground 2 with the liquefied layer 11, and the depth improvement unit 15 is formed to a depth within 3 to 5 times the pile diameter. However, it is the same structure as the construction method of the pile foundation structure of 3rd Embodiment except having formed to the depth of the liquefied layer 11 (not shown).

  Next, the construction method of the pile foundation structure of 5th Embodiment is demonstrated. In this construction method of the pile foundation structure according to the first embodiment, the support pile 5 is replaced with an in-situ pile from a ready-made pile.

  First, in the same manner as described above, the depth improvement unit 15 is formed in the surface layer portion 3 of the soft ground 2 to a depth within 3 to 5 times the pile diameter. Then, in the same manner as described above, a new improvement body 17 is formed between each of the deep layer improvement body units 15 and the independent deep layer improvement body units 15 are joined together to form the lattice-like deep layer improvement body 4. Form. At this point, the grid intersection 18 which is the place where the support pile is placed has not been excavated.

  Next, as shown in FIG. 11, excavation holes 13 for supporting piles are formed at intersections 18 of the unexcavated lattice, and a part of the deep layer improvement body unit 15 (tips of the four improvement bodies 19) is shaved. The excavation hole 13 is pierced with a reinforcing bar and concrete. And when this concrete hardens | cures, the support pile 5 made from an in-situ concrete will unite with the deep improvement body 4. FIG. Thereby, the pile foundation structure 1 in which the support pile 5 is supported at the intersection of the deep layer improvement body 4 is constructed.

  The construction method of the pile foundation structure of the fifth embodiment can be applied to the construction method of the pile foundation structure of the second to fourth embodiments.

  In addition, in the construction method of the pile foundation structure of said 1st-5th embodiment, although the excavation hole 16 was excavated with the triple excavator, this is not restricted to a triple excavator. Can also be used. The lattice-like deep layer improvement body 4 is a construction method in which the cross-shaped deep layer improvement body units 15 are formed and then connected to each other. However, the present invention is not limited to this, and the deep layer improvement body 4 is constructed in any order. You can also.

It is the pile foundation structure of 1st Embodiment, (1) is a perspective view, (2) is sectional drawing. It is the graph which showed the reduction effect of the bending moment in a pile head. It is the pile foundation structure of 2nd Embodiment, (1) is a perspective view, (2) is sectional drawing. It is the pile foundation structure of 3rd Embodiment, (1) is a perspective view, (2) is sectional drawing. It is a construction method of a pile foundation structure of a 1st embodiment, and is a sectional view of a deep improvement unit formed around an intersection of a grid which has not been excavated. It is a construction method of a pile foundation structure of a 1st embodiment, and is a sectional view with which a deep improvement unit was joined. It is the construction method of the foundation structure of 1st Embodiment, and is sectional drawing which formed the excavation hole for support piles in the intersection of a lattice. It is the construction method of the foundation structure of 1st Embodiment, and is sectional drawing which built the ready-made pile in the excavation hole for support piles. It is a construction method of the pile foundation structure of a 2nd embodiment, and is a sectional view of a deep layer improvement body unit formed by crossing improvement bodies. It is the construction method of the pile foundation structure of 3rd Embodiment, and is sectional drawing with which each deep-layer improvement body unit was joined. It is the construction method of the pile foundation structure of 5th Embodiment, and is sectional drawing with which each deep-layer improvement body unit was joined. It is the conventional pile foundation structure, (1) is a top view, (2) is a perspective view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 10, 12 Pile foundation structure 2 Soft ground 3 Surface layer part 4, 20 Deep improvement body 5, 22 Support pile 6 Core core 7 Support ground 8 Mixed material 9 Pile circumference fixing material 11 Liquefaction layer 13, 16 Excavation hole 14 Concrete 15 Deep improvement unit 17, 19 Improvement 18 Crossing point of lattice

Claims (2)

In the state where the pile diameter interval is left at the intersection of the lattice in the surface layer portion of the soft ground , and to ensure horizontal rigidity, the depth improvement body is formed in a lattice shape with a width equal to or less than the pile diameter ,
After forming excavation holes for forming support piles at the intersections of the lattice while cutting a part of the deep layer improvement body, forming support piles in the excavation holes integrally with the deep layer improvement body ,
A method of constructing a pile foundation structure characterized by In the case of soft ground without a liquefied layer, the depth of the deep layer improvement is set to a depth within 3 to 5 times the pile diameter of the support pile to reduce the bending moment, or soft ground with a liquefied layer In the case of, make the depth to prevent liquefaction,
  The method for constructing a pile foundation structure according to claim 1.

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