JP5071852B2 - Structure subsidence suppression structure - Google Patents

Description

  The present invention relates to a structure for suppressing settlement of structures constructed on the ground.

  Conventionally, when constructing a structure on the ground having a viscous soil layer with a low overconsolidation ratio, foundation work for suppressing settlement of the structure has been performed. For example, in the case of a ground where there is a support layer (intermediate support layer) with a ground strength that can secure the support capacity of the pile at a position shallower than the viscous soil layer, a support pile was placed in the intermediate support layer A pile structure is built.

  FIG. 6 shows a pile structure using a conventional support pile 8. When the clay soil layer G3 is in a deep part of the ground G, the intermediate support layer G2 is present in a shallower part. The load of the entire structure 2 acts on the intermediate support layer G2, and the load stress S of the structure 2 is transmitted from the intermediate support layer G2 to the viscous soil layer G3, and the stress acting on the viscous soil layer G3 is consolidated and yielded. The stress Sb is exceeded (range P in FIG. 6), and consolidation settlement occurs. In this case, the support pile 8 is driven so as to reach a support layer (lower support layer G4) such as a bedrock located deeper than the viscous soil layer, and the pile structure is supported by the lower support layer G4. Has become commonplace.

In addition, as a pile structure of other structures, there is one that uses friction piles, and the structure is supported by using a direct foundation (raft) and pile (pile) that form the foundation base of the structure in combination. There is a piled raft foundation that reduces the uneven settlement of structures (see, for example, Patent Document 1). The piled raft foundation has a structure that can support the structure using the friction force between the friction pile and the ground without placing the friction pile in the support layer that can secure the support force. Yes.
Patent Document 1 discloses a pile structure in which the friction pile is elongated at a portion where the distributed load of the structure is increased, and the friction between the ground and the friction pile is increased.
JP 2002-61203 A

However, the conventional structure settlement suppression structure has the following problems.
That is, in the pile structure (refer to FIG. 6) in which the support pile is provided in the support layer (intermediate support layer) existing at a position shallower than the viscous soil layer, as described above, the bearing capacity is deeper than the viscous soil layer and large like a rock. It is necessary to drive the support pile until it reaches the support layer (lower support layer) with a large thickness, especially when the thickness of the cohesive soil layer is large, and the pile length of the support pile becomes long and a large foundation Since this was a construction work, there was a problem of significant cost increase.

  In the case of piled raft foundations, the structure is supported directly by the foundation and friction piles, so ground that can secure the support capacity of the foundation directly is necessary near the flooring of the structure. However, in the case of soft ground, there was a problem that it was impossible to reliably suppress the uneven settlement. In addition, if the tip of the piled raft foundation friction pile is positioned and supported on the intermediate support layer G2 as shown in FIG. 6, an excessive load may be applied to the friction pile and the yield strength of the pile body may be exceeded. there were.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a structure subsidence suppression structure that can reliably suppress the subsidence of the structure and can reduce the cost.

In order to achieve the above object, in the structure settlement suppression structure according to the present invention, in the construction region of the structure, there is an intermediate support layer that can support the load of the structure in a portion shallower than the viscous soil layer. It is a structure that suppresses the settlement of the structure to be installed in the friction piles that are driven to a depth that reaches in the viscous soil layer or deeper than the viscous soil layer, and a depth that reaches the intermediate support layer. together, Ri do from the improved ground support made in reclamation so as to surround the friction piles in plan view, improved ground support in the form of stress acting on the cohesive soil layer does not exceed the consolidation yield stress of the viscous soil layer It is characterized by being created .

In the present invention, the friction pile is placed in a viscous soil layer or in a deeper layer than the viscous soil layer (hereinafter, simply referred to as a viscous soil layer), so that the bearing force against the load of the structure is increased with that of the intermediate support layer. Since it can be dispersed in the soil layer, the stress (load stress of the structure) generated by receiving the load of the structure in the intermediate support layer reached by the improved ground support can be reduced, and the intermediate support layer The effective stress transmitted from the soil to the viscous soil layer can be reduced. Therefore, the effective stress acting on the viscous soil layer (that is, the sum of the initial effective stress and the load stress of the viscous soil layer) does not exceed the consolidation yield stress of the viscous soil layer, preventing the consolidation settlement of the viscous soil layer. Sedimentation of things can be suppressed.
In this pile structure, the improved ground support is provided so as to reach the intermediate support layer, and the friction pile is provided in the viscous soil layer or deeper than the viscous soil layer. It is not necessary to install a friction pile having a long pile length so as to reach a formation (lower support layer) such as a bedrock that has a supporting force that exists below, and cost can be reduced.

  Moreover, in the structure subsidence suppression structure according to the present invention, it is preferable that the improved ground support is partitioned in a lattice shape in plan view.

  In the present invention, by placing the friction pile in the section of the improved ground support formed in a lattice shape, the friction pile is surrounded by the improved ground support, and therefore surrounded by the improved ground support. The horizontal movement of the friction pile and the ground within the specified range is restricted, and the rigidity against the horizontal resistance can be increased. And by setting it as a grid | lattice-like improved ground support body, for example, since it becomes a large cross section compared with a column-shaped improved ground support body, a larger building load can be borne.

  Moreover, in the settlement suppression structure for a structure according to the present invention, the improved ground support is preferably composed of a plurality of wall-like bodies arranged in parallel at a predetermined interval.

  In the present invention, the friction pile is in a state in which a part of the periphery is blocked by the improved ground support by adopting a structure in which the friction pile is arranged between the wall-like bodies arranged in parallel. The friction pile within the range sandwiched between the wall-like bodies of the improved ground support and the horizontal movement in the direction sandwiched by the wall-like bodies in the ground are restricted, and the rigidity against the horizontal resistance is increased. Can do. And by making the improved ground support into a plurality of wall-like bodies, for example, since it has a larger cross section than a cylindrical improved ground support, it is possible to bear a larger building load.

  In the structure settlement suppression structure according to the present invention, it is preferable that the improved ground support is composed of a plurality of prismatic bodies having a substantially rectangular shape in a plan view arranged with a predetermined interval.

  In the present invention, by arranging the improved ground support that forms a plurality of prisms around the friction pile, the friction pile is in a state in which a part of the periphery is blocked by the improved ground support. The movement in the horizontal direction in the direction sandwiched by the prismatic bodies in the friction pile and the ground within the range sandwiched by the prisms of the body is restricted, and the rigidity against the horizontal resistance can be increased. And, by forming the improved ground support that forms a prismatic body so as to overlap a plurality of cylindrical improved ground support, for example, because it has a large cross section compared to the cylindrical improved ground support, Larger building loads can be borne.

  Moreover, in the structure settlement suppression structure according to the present invention, it is preferable that the improved ground support is improved over substantially the entire construction range of the structure in plan view.

  In the present invention, by placing the friction pile within the improved range of the improved ground support, the friction pile is covered with the improved ground support, so the friction located within the range of the improved ground support The movement of the pile in the horizontal direction is restricted, and the rigidity against the horizontal resistance can be increased. And in the improved ground support improved over substantially the whole construction range of a structure, since it becomes a large cross section compared with a column-shaped improved ground support, for example, a bigger building load can be borne.

According to the structure settlement suppression structure of the present invention, a part of the load of the structure is supported by the friction pile placed in the viscous soil layer or in the deeper layer than the viscous soil layer. It is possible to reduce the burden of the improved ground support built in the intermediate support layer by the amount of support force, and to reduce the load (load stress) of the structure transmitted from the intermediate support layer to the viscous soil layer Therefore, consolidation settlement of the viscous soil layer can be prevented and settlement of the structure can be reliably suppressed.
And since it becomes possible to make the improved ground support function as a support pile, an inexpensive ground improvement method is adopted instead of the conventional method of placing expensive precast concrete piles, cast-in-place concrete piles, steel pipe piles, etc. Therefore, the construction cost can be reduced.

Hereinafter, a structure settlement suppression structure according to the present invention will be described with reference to FIGS. 1 and 2.
FIG. 1 is a diagram showing a configuration of a pile structure and a stress distribution in the ground according to the first embodiment of the present invention, and FIG. 2 is a cross-sectional view taken along line AA shown in FIG.

  As shown in FIG. 1, the structure settlement suppression structure (hereinafter referred to as “pile structure 1”) according to the first embodiment includes a viscous soil layer G3 having a low overconsolidation ratio and the viscous soil. The structure 2 is constructed on the ground G where the support layer (intermediate support layer G2) is present above the layer G3, for example, with an N value of 30 to 50 or more and sufficient support for the structure 2 but not so thick. This is a structure that is applied in order to suppress the settlement of the structure 2.

  Specifically, the ground G is a ground layer in which a soft layer G1, an intermediate support layer G2, a cohesive soil layer G3, and a lower support layer G4 are stacked in this order from the surface side toward the depth direction. The soft layer G1 is a ground layer that cannot secure the supporting force of the direct foundation of the structure 2 such as a landfill, and the intermediate supporting layer G2 has a sufficient supporting force for the structure 2 as described above. The stratum is not so thick and the overconsolidation ratio of the viscous soil layer G3 is smaller than the load of the structure 2. The lower support layer G4 is a formation having sufficient support force and layer thickness for the structure 2.

As shown in FIG. 1, the pile structure 1 has an improved ground support 3 formed to a depth reaching into the intermediate support layer G2 and is longer than the depth of the improved ground support 3 and is viscous. It consists of a plurality of friction piles 4, 4,... Driven to a predetermined depth in the soil layer G3.
That is, this pile structure 1 is the load of the structure 2 by the peripheral frictional resistance and the tip support force of the improved ground support 3 and the plurality of friction piles 4, 4,. It has a structure that supports.

  The improved ground support 3 is formed by, for example, a ground improvement by a cement-based solidifying material such as soil mortar, a ground improvement by chemical injection solidification, or a ground improvement by a compacted sand pile, and the like. The load of the structure 2 is supported by the circumferential frictional resistance received and the tip support force of the intermediate support layer G2. Such an improved ground support 3 is constructed by a ground improvement method such as an injection method, a mechanical agitation method, a jet agitation method, etc., and a continuous wall body is formed so as to provide an overlap between columnar bodies having a circular cross section. Is formed.

As shown in FIG. 2, specifically, the improved ground support 3 is partitioned in a lattice shape in a plan view in the construction region of the structure 2, and one friction pile 4 is disposed in each partition. , And formed to a depth reaching the intermediate support layer G2. That is, each friction pile 4 is in a state surrounded by the improved ground support 3. Therefore, the horizontal movement of the friction pile 4 and the ground within the range surrounded by the improved ground support 3 is restricted, and the structure has increased rigidity against horizontal resistance.
The wall thickness of the improved ground support 3 is preferably designed in consideration of conditions such as the layer thickness of the soft layer G1, the ground strength, and the geology.

The friction piles 4, 4,... Are provided to support the load of the structure 2 by the peripheral frictional resistance received from the soft layer G1, the intermediate support layer G2, and the viscous soil layer G3 and the tip support force of the viscous soil layer G3. And plays a role of suppressing the consolidation settlement of the structure 2.
The friction piles 4, 4,... Are not uniform in length in the first embodiment, and the friction piles 4 </ b> A, 4 </ b> B (of the depth dimension) that form a plurality of pile lengths (two in the present embodiment). The shallower one is the first friction pile 4A and the deeper one is the second friction pile 4B), which are alternately arranged in the vertical and horizontal directions.

And the length dimension and placement number of these friction piles 4, 4, ... are set by conditions, such as the improvement range (improvement shape) of the improved ground support body 3. FIG. That is, although the improved ground support 3 will be described in detail later, stress acting on the viscous soil layer G3 (effective stress in the viscous soil layer G3 and the structure 2 transmitted to the viscous soil layer G3 by the improved ground support 3). The shape is such that the sum of the load stress and the load stress does not exceed the allowable value, that is, the consolidation yield stress Sb of the viscous soil layer G3.
And in this pile structure 1, since it is the structure which provides the improved ground support body 3 and the friction pile 4 in the intermediate | middle support layer G2 and the viscous soil layer G3, the lower support located under the viscous soil layer G3 like the past It is not necessary to install a friction pile having a long pile length to reach the layer G4, and the structure can reduce the cost.

Next, the effect | action of the pile structure 1 comprised in this way is demonstrated with reference to drawings.
The stress distribution diagram shown on the right side of FIG. 1 shows the stress acting on the ground according to the first embodiment. In this stress distribution diagram, the line Sa in the figure indicates the effective stress of the ground not affected by the structure 2 (hereinafter referred to as “original ground”), and the dotted line Sb indicates the consolidation of the viscous soil layer G3. Yield stress is shown. And the area | region (shaded part in a figure) shown with the code | symbol S shows the stress (load stress) which the load of the structure 2 gives to the ground G via the pile structure 1 (the improved ground support body 3, the friction pile 4). Yes.

The effective stress Sa of the original ground is a compressive force or shear force transmitted through the skeletal structure of the soil particles, and controls the deformation and fracture of the soil. In this ground G, the stress increases as the depth increases. It has become.
The consolidation yield stress Sb of the cohesive soil layer G3 increases in stress value from the upper part to the lower part of the cohesive soil layer G3, and in the first embodiment, near the upper end of the cohesive soil layer G3 (intermediate support layer G2). In the vicinity of the boundary), the consolidation yield stress Sb is the minimum value.

  As shown in the stress distribution diagram, the load stress S of the structure 2 in the pile structure 1 is affected by the first load stress S1 affected by the grid-like improved ground support 3 and the first friction pile 4A. The second load stress S2 that is received and the third load stress S3 that is affected by the second friction pile 4B can be dispersed.

  That is, in the present pile structure 1, the load stress S of the structure 2 acting on the viscous soil layer G3 is obtained by making the friction pile 4 arranged to reach the viscous soil layer G3 into two types of pile lengths. Can be dispersed in the depth direction without being concentrated in one place. That is, since the maximum value of each of the first to third load stresses S1, S2, and S3 can be suppressed, the stress generated by receiving the load of the structure 2 in the intermediate support layer G2 reached by the improved ground support 3 (Load stress S of the structure 2) can be reduced, and the effective stress transmitted from the intermediate support layer G2 to the viscous soil layer G3 can be reduced. Therefore, the effective stress acting on the viscous soil layer G3 (that is, the sum of the initial effective stress of the viscous soil layer G3 and the load stress S) does not exceed the consolidation yield stress Sb of the viscous soil layer G3. The settlement of the structure 2 can be suppressed by preventing the consolidation settlement.

  And in this pile structure 1, the friction pile 4 will be in the state where the circumference | surroundings were enclosed by the improved ground support body 3 by arrange | positioning the friction pile 4 in the division of the improved ground support body 3 formed in a grid | lattice form. Therefore, the horizontal movement of the friction pile 4 and the ground within the range surrounded by the improved ground support 3 is restricted, and the rigidity against the horizontal resistance can be increased. And by setting it as the lattice-shaped improved ground support body 3, since it becomes a large cross section compared with a column-shaped improved ground support body, a larger building load can be borne.

  Further, in the present pile structure 1, the improved ground support 3 is provided so as to reach the intermediate support layer G2, and the friction piles 4, 4,... Are provided in the viscous soil layer G3 or a deeper layer than the viscous soil layer G3. Therefore, it is not necessary to install a friction pile with a long pile length so as to reach the formation layer (lower support layer G4) such as the bedrock that exists below the cohesive soil layer G3 and has a supporting force as in the past. Reduction can be achieved.

  Furthermore, in this pile structure 1, since the soft ground is seismically strengthened by the improved ground support 3, not only supporting the building load but also reducing the response of the soft ground during an earthquake and anti-liquefaction effects are expected. be able to.

In the structure settlement suppression structure according to the first embodiment described above, by supporting a part of the load of the structure 2 with the friction piles 4, 4,... The load on the improved ground support 3 formed in the intermediate support layer G2 can be reduced by the support force of the friction piles 4, 4,... And transmitted from the intermediate support layer G2 to the viscous soil layer G3. Since the load (load stress) of the structure 2 can be reduced, the settlement of the viscous soil layer G3 can be prevented and the settlement of the structure 2 can be reliably suppressed.
And since it becomes possible to make the improved ground support body 3 function as a support pile, an inexpensive ground improvement construction method is used instead of the conventional construction method for placing an expensive ready-made concrete pile, cast-in-place concrete pile, steel pipe pile, or the like. Since it can be adopted, construction costs can be reduced.

  Next, second to fourth embodiments of the present invention will be described with reference to the drawings. The same reference numerals are used for the same or similar members and parts as those of the first embodiment described above. A configuration different from that of the first embodiment will be described.

FIG. 3 is a horizontal sectional view showing a structure of a pile structure according to the second embodiment of the present invention, and corresponds to FIG.
As shown in FIG. 3, the pile structure 1 </ b> A according to the second embodiment is formed by changing the molding shape of the improved ground support 3 (see FIG. 2) of the first embodiment. That is, the improved ground support 3A is composed of a plurality of planar wall-like bodies, and is constructed in a state of being arranged in parallel with each other at a predetermined interval. And it has the structure where the friction pile 4 was arrange | positioned between the wall-shaped bodies arranged in parallel. And the friction piles 4, 4, ... are arrange | positioned along the extending direction of each wall-shaped body.

  In the pile structure 1A according to the second embodiment, since the friction pile 4 is partially closed by the improved ground support 3A, the friction pile 4 is sandwiched between the wall-like bodies of the improved ground support 3A. The movement in the horizontal direction in the direction sandwiched between the friction piles 4 and the wall-like body in the ground is restricted, and the rigidity against the horizontal resistance can be increased. And in this improved ground support body 3A, since it becomes a large cross section compared with a column-shaped improved ground support body, for example, a larger building load can be borne and the same action as the first embodiment described above. , Effective.

FIG. 4 is a horizontal sectional view showing the structure of the pile structure according to the third embodiment of the present invention, and corresponds to FIG.
As shown in FIG. 4, the pile structure 1 </ b> B according to the third embodiment changes the molding shape of the improved ground support bodies 3, 3 </ b> A (see FIGS. 2 and 3) of the first and second embodiments. It was created. That is, the improved ground support 3B is composed of a plurality of rectangular pillars having a substantially rectangular shape in plan view, and is formed in a state of being arranged at a predetermined interval. And it has the structure where the improved ground support body 3B which makes a some prismatic body around the friction pile 4 is arrange | positioned.

  In the pile structure 1B according to the third embodiment, the friction pile 4 is sandwiched between the prisms of the improved ground support 3B because the surrounding part of the friction pile 4 is blocked by the improved ground support 3B. Movement in the horizontal direction in the direction sandwiched between the friction piles 4 and the prisms in the ground within the range is restricted, and the rigidity against the horizontal resistance can be increased. And, by forming the improved ground support 3B that forms a prismatic body so as to overlap a plurality of cylindrical improved ground supports, for example, a larger cross section than a cylindrical improved ground support is obtained. A larger building load can be borne, and the same operations and effects as in the first and second embodiments described above can be achieved.

FIG. 5 is a horizontal sectional view showing the structure of a pile structure according to the fourth embodiment of the present invention, and corresponds to FIG.
As shown in FIG. 5, the pile structure 1 </ b> C according to the fourth embodiment is an improved ground support 3, 3 </ b> A, 3 </ b> B (see FIGS. 2, 3, and 4) according to the first to third embodiments. It was created by changing the molding shape. That is, this improved ground support 3C is improved over substantially the entire construction range of the structure 2 (see FIG. 1) in plan view, and a plurality of friction piles 4, 4,... Are provided within the improved range. The improved ground support 3 </ b> C is constructed so as to cover the periphery of the friction piles 4.

  In the pile structure 1C according to the fourth embodiment, since the friction piles 4, 4,... Are covered with the improved ground support 3C, the friction piles 4 positioned within the range of the improved ground support 3C, 4... Are restricted from moving in the horizontal direction, and the rigidity against the horizontal resistance can be increased. And in this improved ground support body 3C, since it becomes a large cross section compared with a column-shaped improved ground support body, for example, a larger building load can be borne, and with the first to third embodiments described above, The same action and effect are exhibited.

The first to fourth embodiments of the structure settlement suppression structure according to the present invention have been described above. However, the present invention is not limited to the first to fourth embodiments described above, and the gist thereof is described. As long as it does not deviate from the above, it can be appropriately changed.
For example, the concrete thickness dimensions, depth dimensions, etc. of the improved ground supports 3, 3A, 3B, 3C of the first to fourth embodiments, and the number, outer diameter dimension, pile length in the friction pile 4 Are arbitrarily set according to the load, size, shape, etc. of the structure 2, the conditions of the ground G (for example, the thickness of each layer, the consolidated state of the cohesive soil layer G3), and the settlement distribution of the structure 2. can do.

  Moreover, the arrangement | positioning form of the friction pile 4 with respect to the improved ground support body constructed | assembled by a suitable shape is arbitrary, for example, in 1st Embodiment, in the division of the improved ground support body 3 divided in the grid | lattice form, one piece Although the friction pile 4 is arrange | positioned, it is not limited to this, You may make it arrange | position the several friction pile 4 in 1 division.

  In the first to fourth embodiments, the ground G is laminated in the order from the ground surface to the soft layer G1, the intermediate support layer G2, the viscous soil layer G3, and the lower support layer G4. It is not limited to being. In short, the ground G having the intermediate support layer G2 at a position shallower than the viscous soil layer G3 may be used, and the target ground to which the present pile structure (subsidence suppression structure) can be applied.

Further, in the first to fourth embodiments, the friction piles 4A and 4B placed in the viscous soil layer G3 are two different pile lengths. However, the present invention is not limited to this, and three or more different pile lengths are used. The friction pile 4 may be used.
Furthermore, the friction pile 4 is driven by a root (bottom end) thereof as necessary until it reaches a deeper layer than the viscous soil layer G3. It doesn't matter. In this case, as in the first to fourth embodiments, the stress acting on the viscous soil layer G3 can be prevented from exceeding the consolidation yield stress, so that the consolidation settlement of the viscous soil layer G3 is prevented. The sinking of the object 2 can be suppressed.

It is a figure which shows the structure of the pile structure by the 1st Embodiment of this invention, and the stress distribution in the ground. It is the sectional view on the AA line shown in FIG. It is a horizontal sectional view which shows the structure of the pile structure by the 2nd Embodiment of this invention, Comprising: It is a figure corresponding to FIG. It is a horizontal sectional view which shows the structure of the pile structure by the 3rd Embodiment of this invention, Comprising: It is a figure corresponding to FIG. FIG. 5 is a horizontal sectional view showing a structure of a pile structure according to the fourth embodiment of the present invention, and corresponds to FIG. It is a figure which shows the structure of the conventional pile structure, and the stress distribution in the ground.

Explanation of symbols

1, 1A, 1B, 1C Pile structure (subsidence suppression structure)
2 Structures 3, 3A, 3B, 3C Improved ground support 4 Friction pile G Ground G1 Soft layer G2 Intermediate support layer G3 Viscous soil layer G4 Lower support layer Sa Effective stress of the original ground Sb Consolidation yield stress S Structure Load stress of objects

Claims (5)

In the construction area of the structure, the structure is a subsidence suppression structure constructed on the ground where there is an intermediate support layer that can support the load of the structure in a portion shallower than the viscous soil layer,
Friction piles driven to a depth reaching in the viscous soil layer or deeper than the viscous soil layer,
An improved ground support that is disposed up to a depth reaching the intermediate support layer, and is formed so as to surround the friction pile in a plan view;
Tona is,
The improved ground support is constructed so as to prevent the stress acting on the viscous soil layer from exceeding the consolidation yield stress of the viscous soil layer . The structure for suppressing settlement of a structure according to claim 1, wherein the improved ground support is partitioned in a lattice shape in a plan view. 2. The structure subsidence suppression structure according to claim 1, wherein the improved ground support is composed of a plurality of wall-like bodies arranged in parallel at a predetermined interval. 2. The structure settlement suppression structure according to claim 1, wherein the improved ground support body is composed of a plurality of prismatic bodies having a substantially rectangular shape in a plan view arranged with a predetermined interval. The structure subsidence suppression structure according to claim 1, wherein the improved ground support is improved over substantially the entire construction range of the structure in plan view.

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