JP5286611B2 - Improved pile foundation and its construction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pile foundation improving body which achieves a reduction in the cost of a conventional pile foundation improving body and the shortening of a construction period, and which increases the degree of freedom of installation of the improving body. <P>SOLUTION: A bearing pile, which has a leading end borne by a bearing layer below soft subsurface ground 5, is arranged; and the pile foundation improving body 3 is formed along a through-core of the bearing pile in the subsurface ground. The improving body 3 is individually provided for each bearing pile, and formed in such a manner as not to continue into the adjacent improving body 3, in the state of horizontally overhanging in a cross shape at a required depth from a head of the bearing pile 2. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a construction method for improving a soft ground surrounding a pile in a pile foundation, and further relates to an improved body with improved workability and less cost and a construction method thereof.

  Conventionally, in a ground having a supporting ground below a soft surface layer ground, as shown in FIG. 8, a supporting pile 21 having a tip supported by the supporting layer is disposed as an increase in horizontal rigidity of the pile foundation. In addition, there is known a structure in which a surface layer ground along the core of a support pile 21 disposed on the ground is provided with a high-rigidity shallow layer improvement body 22 in which a cement-based solidified material is mixed (Patent Document 1). reference).

  The shallow layer improvement body efficiently performs the improvement method using the improvement bodies arranged in a lattice shape. The support pile 21 is driven so that the tip of the pile is supported by the support layer below the surface ground. A lattice-shaped shallow layer improvement body 22 is formed along the core of the support pile 21 by a shallow layer processing method.

JP 2007-262882 A

  However, in the conventional pile foundation shallow body improvement body and its construction method, if the span between adjacent piles 21 is long, the cost for constructing the improvement body 22 continuously increases and the construction period is also long. Become. In addition, in the case of deep-layered improvements, in the SMW method (Soil Mixing Wall) with a multi-axis (3-axis or 5-axis) auger, when the adjacent drilling is semi-wrapped, the continuous part is constructed over 2 days. It is necessary to do this, and the construction period is prolonged. Furthermore, the degree of freedom of arrangement of the improved body according to the installation situation when improving the horizontal resistance force of the soft ground is low. The improvement body of the pile foundation and its construction method according to the present invention are proposed in order to solve such a problem and prevent the improvement effect of the horizontal resistance of the pile from being lowered as compared with the related art.

  The gist for achieving the object by solving the above problems of the improved pile foundation according to the present invention is that a support pile having a tip supported by a support layer below a soft surface layer ground is disposed, and the surface layer In the improved body formed along the core of the support pile in the ground, the improved body is provided individually for each support pile and protrudes in a cross shape horizontally from the head of the support pile to the required depth. It is formed discontinuously with the adjacent improvement body.

In the case of deep improvement with the improved body, the improved body is formed by excavating the surface layer ground with a single-axis or multi-axis excavator and arranging continuous walls in a cross shape;
The length of the cross-shaped improved body: (2B) should be 30% ≦ (2B / L) × 100 ≦ 55% in the case of shallow layer improvement with respect to the span between support piles: (L) Alternatively, in the case of deep layer improvement, it is included that 16% ≦ (2B / L) × 100 ≦ 80%.

  The gist of achieving the object by solving the above problems in the construction method of the improved body according to the present invention is that a pile foundation having the cross-shaped improved body is arranged on the soft ground in the head of the support pile. In the construction method of the improved body that reduces the horizontal displacement of the ground due to the horizontal rigidity of the head, the support pile is supported by the support layer and arranged in a lattice shape, and then the diagonal line of the support pile and the overhang portion of the improved body The improvement body was formed so that the shaft core was substantially parallel to each other, and the adjacent improvement bodies were arranged so as to be discontinuous with each other.

According to the improved pile foundation of the present invention and the construction method using the improved body, since the improved body is not continued to the adjacent one, the horizontal displacement of the surface ground is reduced for the continuous improved body. However, the reduction rate of the horizontal displacement of the surface ground is large for the reduction of the improved length. Therefore, the improvement effect per improvement length is large, thereby reducing the material cost for forming the improved body and shortening the construction period, thereby reducing the cost.
When the improved body is formed on a continuous wall with a single-axis or multi-axis auger, it is not wrapped in a grid shape with the adjacent continuous wall, so that efficient construction is possible.
Since a cross-shaped improved body is formed for each support pile, for example, as shown in FIG. 7-B (a), construction is possible without sticking to the core a direction of the support pile, and improvement of soft ground Depending on the situation, the degree of freedom of arrangement of the improved body increases. For example, by arranging the improved bodies 3 and 4 along the diagonal b direction of the support piles 2 and 2 so that the axial cores of the overhang portions 3a and 4a of the improved body are substantially parallel, the diagonal b direction It will resist the shearing force.

It is a schematic perspective view of the improvement body of a pile foundation in the case of shallow ground improvement concerning the present invention. Boundary conditions and perspective view for analysis when a constant horizontal force is applied to a shallow ground model of an improved pile foundation according to the present invention (a), its plan view (b), its elevation view (c) It is. It is the characteristic view (a) which showed the displacement reduction effect and cost reduction effect by the improvement body 3 of a shallow layer, and the characteristic diagram (b) which showed the bending reduction effect and the cost reduction effect of the bending. It is a schematic perspective view of the improvement body of a pile foundation in the case of the deep ground improvement which concerns on the same invention. Boundary condition and analysis perspective view (a), plan view (b), elevation view (c) when a constant horizontal force is applied to the deep ground model of an improved pile foundation according to the present invention is there. It is the characteristic view (a) which showed the displacement reduction effect and cost reduction effect by the deep improvement body 4, and the characteristic diagram (b) which showed the bending reduction effect and the cost reduction effect of the bending. It is a top view which shows arrangement | positioning in case the span L in the improvement bodies 3 and 4 of this invention differs vertically and horizontally and is not square. The top view (a) when the axial bodies of the overhang portions 3a and 4a are arranged in parallel on the diagonal line, and the plane when the improvement bodies 3 and 4 of the present invention are arranged along the core a of the support pile. It is a figure (b). It is a perspective view which shows the improvement body of the pile foundation which concerns on a prior art example.

  As shown in FIG. 1, the pile foundation improvement body according to the present invention and the construction method of the improvement body are high rigidity, in which a cement-based solidified material is mixed with the surface layer ground on the head of each support pile, as shown in FIG. A cross-shaped improved body is provided to reduce the material cost of the improved body and shorten the construction work period, and at the same time, increase the degree of freedom in arranging the improved body.

  The improved body 3 of the pile foundation 1 according to the present invention will be described. As shown in FIG. 1, a support pile 2 having a tip supported by a support layer below a soft surface ground 5 is disposed, and is formed along the core of the support pile 2 in the surface ground 5. In the high-rigidity improvement body 3 in which cement-based solidified material is mixed with the surface ground, the improvement body 3 is provided individually for each of the support piles 2, 2. Now, it is formed in a cross shape to form a buttress shape, and is formed discontinuously with the adjacent improvement body 3.

The cross-shaped improvement body 3 is for the case of shallow layer improvement. As for the size of the improved body 3, five points of buttress length B of 4.05 m, 2.25 m, 1.2 m, 0.6 m and 0 m are prepared for analysis, and the width W is 1.2 m (width). W is at least twice the pile diameter) and depth H is 0.9 m (depth H is twice the pile diameter and within 2 m, 50 cm or more). As shown in Fig. 2, the model of the analytical study is that the support pile 2 has a pile diameter of 0.6m (pile diameter is mainly 0.3m to 1.2m) and a pile length of 10m. As a Young's modulus of 4 × 10 ⁷ kN / m ² and a solid section. The span L between the support piles 2 and 2 is 9 m. Further, the rigidity of the soft surface layer 5 is 5 MN / m ² , and the rigidity of the shallow improvement body 3 is 80 MN / m ² (the rigidity of the improvement body is 10 times or more that of the surface layer ground).

  Under the above conditions, a load of 100 kN is applied as a horizontal force to the pile head. The analysis results by the three-dimensional finite element method (FEM) are shown in FIGS. The horizontal axis represents the percentage (%) of the buttress length B, which is the improved length of the improved body 3, in the span L, and the vertical axis represents the displacement reduction effect and displacement at 5 points of the buttress length B. This shows the cost reduction effect in reduction, the bending reduction effect, and the cost reduction effect in bending reduction.

  For example, as shown in FIG. 3A, when the buttress length B is 4.05 m, (2B / L) is 90%, and the displacement reduction effect at that time is about 80%, which is more than 90%. The cost reduction effect shown in the figure below is also negative, and although it takes time, the effect of reducing the material cost is not exhibited and the efficient effect is not achieved.

  Next, when the buttress length B of the improved body 3 is 2.25 m, (2B / L) is 50%, and the displacement reduction effect at that time is 60% or more, much higher than 50%. The cost reduction effect in the figure below is also 10% or more. Therefore, although the buttress length B is shortened, the horizontal resistance is strong and the cost can be reduced.

  In view of this, in consideration of the effect of bending shown in FIG. 3B, if the range is such that the reduction effect is 50% or more and the cost reduction effect is 10% or more, the buttress length The thickness B is most preferably 30% ≦ (2B / L) × 100 ≦ 55%.

  In addition, as shown in FIG. 4, in the case of deep improvement with the cross-shaped improvement body 4, the continuous layer wall is excavated with the multi-axis excavator (showing the case of 5 axes in the figure). Are arranged in a cross shape to form the improved body 4. If a 3-axis or 5-axis auger is used, one improvement body 4 can be drilled at a time, and it is not necessary to semi-wrap the adjacent improvement body 4, so that the construction period is shortened.

As shown in FIG. 5, the model of the analytical study is that the improved body 4 has a hole diameter of 600 mm (construction diameter of 550 to 900 mm) and a depth H of 5 m (depth H is 3 m or more and within 10 m). ), The support pile 2 is the same as described above. The span L between the support piles 2 and 2 is 9 m. Moreover, the rigidity of the soft surface layer 5 is 5 MN / m ² , and the rigidity of the deep improvement body 4 is 350 MN / m ² (the rigidity of the improvement body is 100 MN / m ² or more).

  A load of 100 kN is applied to the improved body 4 as a horizontal force on the pile head in the same manner as described above. In the analysis of the deep improvement body, the boundary condition shown in FIG. 4 based on the research result different from the boundary of the normal single pile considering the influence of the improvement body pushing the pile is used. The analysis results are as shown in FIGS. 6 (a) and 6 (b). Considering the displacement, assuming that the reduction effect is 50% or more and the cost reduction effect is 5% or more, the buttress length B is 16% ≦ (2B / L) × 100 ≦ 80%. Is most preferred. In consideration of the same cost reduction and displacement reduction effect, the buttress length B is most preferably 38% ≦ (2B / L) × 100 ≦ 50%.

  A series of analysis results are cases where the span L is 9 m, but the same result is obtained when the span L is 6 m to 10 m. As the span L, the square span L was used in the series of explanations. However, as shown in FIG. 7-A, as a result of making the length correspond to the shape of the structure, Similarly in the case of the vertical L2, 2B1 / L1, 2B2 / L2 gives the same result as above.

  In the improved bodies 3 and 4, considering the effect of reducing displacement and cost reduction, the buttress length B is the most technically preferable range, and the buttress length B in the shallow layer and deep layer is the technology. The range is limited.

  Moreover, since the improvement bodies 3 and 4 of this invention are not continuous with the adjacent improvement body, an installation rotation angle becomes free, for example, as shown to FIG. 7-B (a), the head of a support pile In the construction method of the improved body in which the pile foundation having the improved body composed of the cross-shaped projecting portions 3a and 4a is disposed on the soft ground and the horizontal displacement of the ground is reduced by the horizontal rigidity of the pile head, After the pile 2 is supported by the support layer and arranged in a lattice pattern, the improved body is set so that the diagonal line b of the support pile 2 and the axial centers of the overhang portions 3a and 4a of the improved body are substantially parallel to each other. 3, 4 can be formed and arranged. Thereby, when the direction which wants to strengthen the horizontal resistance force of the soft surface layer ground 5 exists on the diagonal b of the support pile 2 arrange | positioned at a grid | lattice form, arrange | position so that it may resist a main shear surface. In addition to the lattice arrangement shown in FIG. 7B (b), the degree of freedom in design is increased.

  The pile foundation improvement body and the improvement body construction method of the present invention are suitable for ground improvement work that requires efficient construction for cost reduction and shortening of the construction period. In addition, since the degree of freedom of the improved body is large, this method is suitable for soft ground with complex terrain.

1 pile foundation,
2 support piles,
3 Improved shallow layer, 3a Overhang,
4 Deep improvement body, 4a Overhang part,
5 Soft surface ground,
21 Support pile,
22 Shallow improvement body,
B Buttress length,
W width,
H depth,
a Street core,
b Diagonal line.

Claims (4)

In the improved body in which the support pile supported at the tip is supported by the support layer below the soft surface ground, and is formed along the core of the support pile in the surface ground,
The improved body is individually provided for each support pile, and is formed discontinuously with the adjacent improved body by projecting in a cross shape in the horizontal direction from the head of the support pile at a required depth.
Improved pile foundation characterized by In the case of deep improvement with an improved body, the improved body is formed by excavating the surface ground with a single-axis or multi-axis excavator and arranging continuous walls in a cross shape,
The improvement body of the pile foundation of Claim 1 characterized by these. The length of the cross-shaped improved body: (2B), the span between the support piles: (L),
In the case of shallow layer improvement, 30% ≦ (2B / L) × 100 ≦ 55%, or
In the case of deep layer improvement, 16% ≦ (2B / L) × 100 ≦ 80%,
An improved body of a pile foundation according to claim 1 or 2. A pile foundation having the improved body according to any one of claims 1 to 3 formed in a cross-shaped projecting portion at a head portion of a support pile is disposed on a soft ground, and horizontal displacement of the ground is reduced by horizontal rigidity of the pile head. In the improved construction method,
After the support pile is supported by the support layer and arranged in a lattice pattern, the improved body is formed and arranged so that the diagonal line of the support pile and the axis of the overhang portion of the improved body are substantially parallel. Set up,
A construction method for improved bodies.

Images