JP2015203233A - Soil improvement structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a shear fracture of a soil improvement body during earthquakes while enabling tensile force to be transferred to the soil improvement body.SOLUTION: A soil improvement body 10 includes: a soil improvement body 20 that is formed under a structure 12; a bearing body 30 that is provided on an undersurface 20L of the soil improvement body 20; and a tension member 24 that passes through the soil improvement body 20 and that connects the structure 12 and the bearing body 30 together.

Description

  The present invention relates to a ground improvement structure.

  There is known a ground improvement structure including a ground improvement body formed under a structure and a tensile material (tensile force transmission member) embedded in the ground improvement body and connecting the ground improvement body and the structure. (For example, refer to Patent Document 1).

  In the technique disclosed in Patent Document 1, the foundation and the ground improvement body are connected by a tensile material, and the tensile force (pulling force) resulting from the overturning moment of the structure during an earthquake is transmitted to the ground improvement body. , Have improved seismic performance.

JP 2009-7865 A

  However, in the technique disclosed in Patent Document 1, since the tensile stress acts on the ground improvement body via the tensile material at the time of an earthquake, the shear strength of the ground improvement body may be reduced. In this state, if the ground improvement body receives a shearing force (horizontal shearing force) from the ground, the ground improvement body may easily shear and break.

  An object of the present invention is to suppress the shear failure of the ground improvement body at the time of an earthquake, considering the above-mentioned fact, enabling transmission of tensile force to the ground improvement body.

  The ground improvement structure according to claim 1, a ground improvement body formed under the structure, a support body provided on a lower surface of the ground improvement body, the ground improvement body, and the structure A tension member that connects the support body.

  According to the ground improvement structure of the first aspect, the supporting body provided on the lower surface of the ground improvement body and the structure are connected by the tensile material penetrating the ground improvement body. Therefore, when a tensile force (withdrawal force) resulting from the overturning moment or the like of the structure is applied to the tensile material during an earthquake, the lower surface of the ground improvement body is pushed up by the bearing member, and the ground improvement body is compressed. Thereby, the tensile force resulting from the overturning moment etc. of a structure is transmitted to a ground improvement body. Therefore, the fall of the structure is suppressed.

  Here, the tensile force due to the overturning moment etc. of the structure is transmitted to the ground improvement body as upward compression stress from the bottom through the bearing body, and by the reaction force of the ground improvement body's own weight and peripheral friction force Balance. Thereby, since compressive stress acts on the ground improvement body, the fall of shear strength is suppressed. Therefore, the shear failure of the ground improvement body at the time of an earthquake can be suppressed.

  As described above, according to the present invention, it is possible to suppress the shear fracture of the ground improvement body at the time of an earthquake while enabling transmission of a tensile force to the ground improvement body.

  The ground improvement structure according to claim 2 is the ground improvement structure according to claim 1, wherein the tensile material is inserted into a through hole formed in the ground improvement body, and the ground improvement structure is inserted into the through hole. A filler that joins the body and the tensile material is filled partway.

  According to the ground improvement structure according to claim 2, since the ground improvement body and the tensile material are coupled to each other by the filler filled in the through hole of the ground improvement body halfway, the tensile force transmitted to the bearing body is reduced. Reduced. Thereby, when the lower surface of the ground improvement body is pushed up by the bearing body, the supporting force destruction on the lower surface side in the ground improvement body is suppressed. Therefore, the tensile force can be reliably transmitted by the ground improvement body.

  As described above, according to the ground improvement structure according to the present invention, it is possible to transmit the tensile force to the ground improvement body and to suppress the shear failure of the ground improvement body during an earthquake.

It is sectional drawing which shows the structure to which the ground improvement structure which concerns on one Embodiment of this invention was applied. It is sectional drawing which shows typically the ground improvement body shown by FIG. It is sectional drawing which shows the structure to which the modification of the ground improvement structure which concerns on one Embodiment of this invention was applied.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 shows a structure 12 to which the ground improvement structure 10 according to the present embodiment is applied. The structure 12 includes a foundation 14 and a pillar 16 that stands on the foundation 14. The foundation 14 is formed by, for example, slab or footing.

  The ground improvement structure 10 includes a ground improvement body 20, a bearing body 30, and a tension member 24. The ground improvement body 20 is formed in a columnar shape under the foundation 14 constituting the structure 12. The ground improvement body 20 is formed, for example, by mixing and stirring the excavated soil and a solidified material such as cement slurry while excavating the ground G under the foundation 14 with an excavating auger or the like.

  The base 14 and the ground improvement body 20 are respectively formed with through holes 18 and 22 penetrating in the vertical direction. A tensile material 24 is inserted into these through holes 18 and 22. The tension member 24 is formed of, for example, a PC steel bar, a PC steel wire, a reinforcing bar, or the like. For example, a sheath tube or the like may be inserted into the through hole 22.

  A pressure bearing body 30 is provided on the lower surface 20 </ b> L of the ground improvement body 20. The bearing body 30 is formed in a columnar shape by, for example, expanding and excavating the bottom of the ground improvement body 20 with an expanded wing inserted into the through hole 22 and filling and solidifying mortar, grout and the like. The diameter of the pressure bearing body 30 is larger than the through hole 22 and smaller than the ground improvement body 20. The diameter (width) of the bearing body 30 may be larger than that of the ground improvement body 20. Further, the shape of the support body 30 is not limited to a cylindrical shape, and may be a prismatic shape, a block shape, or the like.

  The bearing body 30 and the foundation 14 of the structure 12 are connected by a tensile member 24 that penetrates the ground improvement body 20 in the vertical direction. As a result, a tensile force (pulling force) T is transmitted from the structure 12 to the bearing body 30 via the tensile member 24.

  Specifically, a support plate 26 is provided at the lower end of the tension member 24. The pressure bearing plate 26 is formed of, for example, a circular steel plate that is slightly smaller than the through hole 22, and protrudes in the radial direction from the distal end portion of the tension member 24. By burying the bearing plate 26 in the bearing body 30, the lower end portion of the tension member 24 is fixed to the bearing body 30.

  On the other hand, the upper end portion of the tension member 24 is fixed to the upper surface 14U of the foundation 14 by a fixing tool 28. By this tension material 24, the foundation 14 and the support body 30 are connected so that the tensile force T can be transmitted.

  As shown in FIG. 2, the through hole 22 of the ground improvement body 20 is filled with a filler W such as grout or mortar halfway. With this filler W, a fixing portion 40 and a pressure receiving portion 42 are formed on the bearing body 30 side of the ground improvement body 20. In the fixing unit 40 and the pressure receiving unit 42, the tensile material 24 is fixed to the ground improvement body 20 by the filler W. Thereby, a part of the tensile force (pulling force) T of the tensile member 24 is transmitted to the ground improvement body 20 via the fixing portion 40 and the pressure receiving portion 42, and the remaining tensile force is transmitted to the pressure bearing body 30. It has become so. Here, the tensile force T (pull-out force) transmitted to the ground improvement body 20 through the fixing unit 40 and the pressure receiving unit 42 is equal to or less than the own weight of the ground improvement body and the circumferential frictional force in the range of the non-fixing part 50. As a result, no tensile stress is generated in the ground improvement body 20.

  Note that, on the structure 12 side of the ground improvement body 20, the tensile material 24 is not fixed to the ground improvement body 20, so that a tensile force (pulling force) is not directly transmitted from the tensile material 24 to the ground improvement body 20. It has become. Thereby, the shear failure etc. by the side of the structure 12 in the ground improvement body 20 are suppressed. Hereinafter, a portion where the tension member 24 and the ground improvement body 20 are not fixed is referred to as an unfixed portion 50.

  Here, in the pressure receiving portion 42 on the side of the pressure bearing body 30 with respect to the fixing portion 40, the ground improvement body 20 and the pressure bearing body 30 are coupled by the filler W. By this pressure receiving portion 42, the lower surface 20 </ b> L side of the ground improvement body 20 that receives the support pressure P directly from the support body 30 is reinforced.

  Specifically, the support pressure P of the support body 30 is the lower surface of the ground improvement body 20 via a portion (transmission portion) 30A between the support plate 26 and the lower surface 20L of the ground improvement body 20 in the support body 30. 20L is transmitted. At this time, the support pressure P is directly transmitted to the lower surface 20L of the ground improvement body 20 from a peripheral portion of the support plate 26 to a region having a diameter D spreading in a cone shape at a predetermined angle (for example, approximately 45 degrees). . And if the ground improvement body 20 destroys (for example, slip failure) etc. with respect to the area | region of this diameter D, the resistance force of the bearing body 30 with respect to the tensile force T will reduce, and the bearing body 30 as a drawing-out resistance body will decrease. Function may be impaired.

  Therefore, in the present embodiment, the cylindrical region (diameter approximately D) of the ground improvement body 20 to which the support pressure P of the support body 30 is directly transmitted is used as the pressure receiving portion 42, and the fixing portion 40 described above is divided. Designing. In other words, the resistance force of the bearing body 30 against the tensile force T is determined by the breaking strength (sliding breaking strength) of the pressure receiving portion 42, so that the pressure receiving portion 42 and the fixing portion 40 are separated in design. The fixing portion 40 is mainly a portion that directly transmits the tensile force T of the tensile material 24 to the ground improvement body 20, and the pressure receiving portion 42 is a portion that mainly reinforces the lower surface 20 </ b> L side of the ground improvement body 20.

  Next, the operation of this embodiment will be described.

  According to the ground improvement structure 10 according to the present embodiment, the supporting member 30 provided on the lower surface 20L of the ground improvement body 20 and the foundation 14 of the structure 12 are formed by the tensile material 24 penetrating the ground improvement body 20. It is connected.

  Therefore, when a tensile force (pulling force) T caused by the overturning moment M of the structure 12 acts on the tensile member 24 during an earthquake, the bearing body 30 moves upward, and the ground improvement body is moved by the bearing body 30. The lower surface 20L of 20 is pushed up. At this time, the tensile force T of the tensile member 24 is transmitted to the ground improvement body 20 by the support pressure P of the support body 30 that pushes up the lower surface 20L of the ground improvement body 20. The ground improvement body 20 resists against the supporting pressure P while the ground improvement body 20 compresses and deforms using the weight of the ground improvement body 20 and the peripheral frictional force as a reaction force.

  Here, when tensile stress acts on the ground improvement body 20, there exists a possibility that the shear strength of the ground improvement body 20 may fall. In this state, for example, when the ground improvement body 20 receives a shearing force (horizontal shearing force) from the ground G during an earthquake, the ground improvement body 20 may be sheared and broken.

  On the other hand, in this embodiment, the bearing body 30 is provided on the lower surface 20L of the ground improvement body 20. Therefore, the tensile force T of the tensile material 24 is transmitted to the ground improvement body 20 as a compressive stress through the support body 30. Therefore, since the fall of the shear strength of the ground improvement body 20 is suppressed, the shear failure of the ground improvement body 20 at the time of an earthquake can be suppressed.

  Thus, in this embodiment, the shear failure of the ground improvement body 20 at the time of an earthquake can be suppressed, enabling transmission of a tensile force to the ground improvement body 20.

  In addition, although it is also possible to form the support body 30 in the position away from the lower surface 20L of the ground improvement body 20 in this case, in this case, the state of the ground interposed between the ground improvement body 20 and the support body 30 As a result, the support pressure P transmitted from the support body 30 to the ground improvement body 20 varies. Therefore, there is a possibility that sufficient compressive stress cannot be introduced into the ground improvement body 20.

  On the other hand, in this embodiment, since the bearing pressure body 30 is provided on the lower surface 20L of the ground improvement body 20, and the bearing pressure P is directly transmitted from the bearing pressure body 30 to the lower surface 20L of the ground improvement body 20, the ground improvement is performed. A predetermined compressive stress can be introduced into the body 20. Therefore, the shear fracture of the ground improvement body 20 at the time of an earthquake can be suppressed more reliably.

  Moreover, in this embodiment, the filler W is filled in the through hole 22 of the ground improvement body 20 halfway. Thereby, the pressure receiving part 42 which couple | bonds the ground improvement body 20 and the bearing body 30 is formed in the lower surface 20L side in the ground improvement body 20. As shown in FIG. When the lower surface 20L of the ground improvement body 20 is pushed up by the support pressure body 30 by reinforcing the lower surface 20L side of the ground improvement body 20 that directly receives the support pressure P of the support body 30 by the pressure receiving portion 42. In addition, the destruction or the like on the lower surface 20L side of the ground improvement body 20 is suppressed. Therefore, the tensile force T can be reliably transmitted by the ground improvement body 20.

  Further, a fixing portion 40 for fixing the ground improvement body 20 and the tensile material 24 is formed in the ground improvement body 20, and the tensile force T of the tensile material 24 is applied to the ground improvement body 20 through the fixing portion 40. Is transmitted directly to. Therefore, since the support pressure P received by the lower surface 20L of the ground improvement body 20 is reduced as compared with the configuration without the fixing unit 40, the damage or the like on the lower surface 20L side of the ground improvement body 20 is further suppressed. In other words, the ground improvement body 20 can bear a larger tensile force T.

  Here, when supplementing the fixing unit 40, the tensile force T is directly transmitted from the tensile material 24 to the fixing unit 40 and the ground improvement body 20 in the vicinity thereof. However, as shown on the right side of FIG. 2, the tensile force T is canceled out by the compressive force C generated by the weight of the ground improvement body 20 in the range of the non-fixing portion 50 and the peripheral frictional force F. Therefore, basically, tensile stress does not act on the fixing unit 40 and the surrounding ground improvement body 20. Therefore, since the fall of the shear strength of the fixing | fixed part 40 and the surrounding ground improvement body 20 is suppressed, the shear failure of the ground improvement body 20 at the time of an earthquake is suppressed. Note that an arrow F in FIG. 2 represents a downward frictional force (circumferential frictional force) generated on the outer peripheral surface of the ground improvement body 20 (a boundary surface between the ground improvement body 20 and the ground G).

  Further, the compressive force C introduced into the ground improvement body 20 by the dead weight of the ground improvement body 20 and the peripheral surface frictional force F becomes smaller toward the upper end of the ground improvement body 20. Therefore, for example, if the filling material W is filled in the entire through-hole 22 and a fixing portion is formed also on the upper portion of the ground improvement body 20, it is directly transmitted from the tensile material 24 to the ground improvement body 20 via the fixing portion. There is a possibility that tensile stress is introduced into the upper portion of the ground improvement body 20 by the tensile force T. In this case, the shear strength of the upper part of the ground improvement body 20 is lowered, and the upper part of the ground improvement body 20 is easily sheared and destroyed during an earthquake.

  On the other hand, in the present embodiment, the unfixed portion 50 is formed on the structure 12 side (upper portion of the ground improvement body 20) in the ground improvement body 20 without filling the entire through hole 22 with the filler W. Yes. Therefore, the tensile force T is not directly transmitted from the tensile material 24 to the structure 12 side in the ground improvement body 20, and basically no tensile stress is introduced. Therefore, the shear failure on the structure 12 side in the ground improvement body 20 is suppressed. That is, in this embodiment, by setting the fixing portion 40 and the non-fixed portion 50 so that tensile stress does not act on the ground improvement body 20, shear failure of the ground improvement body 20 during an earthquake is efficiently suppressed. be able to.

  Next, a modification of the above embodiment will be described.

  In the said embodiment, although the example which formed the one ground improvement body 20 under the foundation 14 was shown, it is not restricted to this. For example, as shown in FIG. 3, a plurality of columnar ground improvement bodies 20 may be formed below the foundation 14 at intervals. At this time, for example, the upper ends of the adjacent ground improvement bodies 20 may be connected by the foundation concrete body 60. Thereby, the shear resistance force of a plurality of ground improvement objects 20 can be raised.

  Further, with respect to the cone-shaped fracture indicated by the two-dot chain line in FIG. 3, the other ground improvement body 20 formed under the adjacent pillar 16 is used as a resistance element, so that the cone-shaped fracture can be efficiently performed. Can be suppressed.

  Moreover, in the said embodiment, although the example which formed the ground improvement body 20 in columnar shape (columnar ground improvement body) was shown, it does not restrict to this. The ground improvement body may be formed in a wall shape (wall-like ground improvement body), or may be formed in a lattice shape (lattice-like ground improvement body) in plan view. Moreover, you may embed core materials, such as a reinforcing bar and H steel which resist tensile force, in a ground improvement body.

  Moreover, in the said embodiment, although the example which provided the fixing | fixed part 40 and the pressure receiving part 42 in the ground improvement body 20 was shown, it is not restricted to this. The fixing unit 40 and the pressure receiving unit 42 may be provided as necessary, and at least one of the fixing unit 40 and the pressure receiving unit 42 may be omitted. Further, the unfixed portion 50 can be omitted.

  As mentioned above, although one embodiment of the present invention was described, the present invention is not limited to such an embodiment, and one embodiment and various modifications may be used in combination as appropriate, and the gist of the present invention will be described. Of course, various embodiments can be implemented without departing from the scope.

10 Ground improvement structure 12 Structure 22 Through hole 20 Ground improvement body 20L Lower surface (lower surface of the ground improvement body)
24 Tensile material 30 Bearing body

Claims (2)

A ground improvement body formed under the structure;
A bearing member provided on the lower surface of the ground improvement body;
A tensile material that penetrates the ground improvement body and connects the structure and the bearing body;
Improved ground structure. The tensile material is inserted into a through hole formed in the ground improvement body,
The through hole is filled with a filler for bonding the ground improvement body and the tensile material partway,
The ground improvement structure according to claim 1.

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