JP4986041B2 - 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 the support layer (first support layer) has a ground strength that can secure the support force of the pile at a position shallower than the viscous soil layer, the support pile is driven into the first support layer. The installed pile structure is constructed.
FIG. 4 shows a conventional pile structure using support piles 8. When there is a viscous soil layer G3 in the deep part of the ground G, the first support layer G2 exists in a shallower part. However, the load of the entire structure 2 acts on the first support layer G2, and this load stress Sb is transmitted from the first support layer G2 to the viscous soil layer G3, and the stress acting on the viscous soil layer G3 is the consolidation yield stress. When Sb is exceeded (range P in FIG. 4), consolidation settlement occurs. In this case, a pile structure in which the support pile 8 is driven so as to reach a support layer (second support layer G4) such as a bedrock located deeper than the viscous soil layer and supported by the second support layer G4; It has become common to do.

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 as shown in FIG. 4 in which the support pile is provided in the support layer (first support layer) existing at a position shallower than the viscous soil layer, as described above, the pile structure is deeper than the viscous soil layer and large as a rock mass. It is necessary to drive the support pile until it reaches the support layer having the support force (second support layer). Especially when the thickness of the cohesive soil layer is large, the pile length of the support pile becomes long and large. There was a problem of significant cost increase due to the large-scale foundation work.
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 by the first support layer G2 as shown in FIG. 4, an excessive load may be applied to the friction pile and the yield strength of the pile body may be exceeded. It was.

  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 subsidence suppression structure according to the present invention, in the construction region of the structure, there is a support layer that can support the load of the structure in a portion shallower than the viscous soil layer. It is a structure to suppress the settlement of the structure to be constructed, and is a support pile that is driven to a depth that reaches the support layer, and a friction pile that is driven to a depth that reaches a depth within the viscous soil layer or a deeper layer than the viscous soil layer. Ri do from the friction piles, the stress acting on the cohesive soil layer of friction piles is characterized that you have provided so as not to exceed the consolidation yield stress of the viscous soil layer.
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 capacity of the load of the structure borne by the friction pile is reduced. Thus, the number of support piles provided in the support layer can be reduced, and the support force against the load of the structure can be distributed to the support layer and the viscous soil layer. In other words, since the stress (load stress) generated by receiving the load of the structure in the support layer where the support pile is placed is reduced, the stress transmitted from the support layer to the cohesive soil layer can be reduced. The stress acting on the cohesive soil layer (that is, the sum of effective stress and load stress in the cohesive soil layer) can be prevented from becoming larger than the consolidation yield stress of the cohesive soil layer, preventing the consolidation settlement of the cohesive soil layer, The settlement of the structure can be suppressed.

Moreover, in the settlement suppression structure of the structure based on this invention, it is preferable that a plurality of friction piles are provided and they become several pile length.
In the present invention, the friction pile placed in the viscous soil layer has a plurality of pile lengths, so that the load stress of the structure acting on the viscous soil layer is dispersed in the depth direction, and the maximum load stress is obtained. Since the value can be reduced, the stress acting on the viscous soil layer does not exceed the consolidation yield stress, and the effect of suppressing the settlement of the structure by preventing the consolidation settlement of the viscous soil layer can be further enhanced. it can.

Moreover, in the settlement suppression structure of the structure which concerns on this invention, the support pile may be formed of the ground improvement body.
In this invention, since the ground improvement body constructed to the depth which reaches in the inside of a support layer acts as a support pile which supports the load of a structure like a support pile, the load (load stress) of a structure is made into a support layer. It can disperse | distribute to a viscous soil layer, and the stress transmitted to a viscous soil layer from a support layer can be reduced.

According to the structure subsidence suppression structure of the present invention, a part of the load of the structure is put in the viscous soil layer or in a deeper layer than the viscous soil layer (hereinafter simply referred to as a viscous soil layer). By supporting with piles, the number of support piles placed in the support layer can be reduced by the support force of these friction piles, and the load of the structure (load stress) transmitted from the support layer to the viscous soil layer ) Can be reduced. Therefore, it is possible to prevent the stress acting on the viscous soil layer (the sum of effective stress and load stress in the viscous soil layer) from becoming larger than the consolidation yield stress of the viscous soil layer, and prevent the consolidation settlement of the viscous soil layer. The settlement of the structure can be reliably suppressed.
As described above, since the support pile and the friction pile are provided in the support layer and the viscous soil layer or in the deeper layer than the viscous soil layer, the bedrock having the support force that exists below the viscous soil layer as in the past. Thus, it is not necessary to install a friction pile (or support pile) having a long pile length so as to reach a geological formation such as, and cost can be reduced.

Hereinafter, a structure settlement suppression structure according to the present invention will be described with reference to FIG.
FIG. 1 is a diagram showing a structure of a pile structure and a stress distribution in the ground according to the first embodiment of the present invention.

  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. For example, the structure 2 is constructed on the ground G where the support layer (the first support layer G2) having an N value of 30 to 50 or more and sufficient support force to the structure but not so thick exists above the layer G3. This is a structure that is applied in order to suppress the settlement of the structure 2.

  Specifically, the ground G is laminated in order of the soft layer G1, the first support layer G2 (corresponding to the support layer of the present invention), the cohesive soil layer G3, and the second support layer G4 from the surface side toward the depth direction. It has become a stratum. 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 first supporting layer G2 has a sufficient supporting force for the structure as described above. The stratum is not so thick, and the viscous soil layer G3 is a stratum with a small overconsolidation ratio as described above. The second support layer G4 is a formation having sufficient support force and layer thickness for the structure.

  As shown in FIG. 1, the pile structure 1 has a structure in which a load of the structure 2 is supported by a plurality of friction piles driven in a substantially vertical direction in a region where the structure 2 is constructed. That is, the pile structure 1 has a plurality of support piles 3, 3,. It consists of a plurality of friction piles 4, 4,.

The support piles 3, 3,... Support the load of the structure 2 by the circumferential frictional resistance received from the soft layer G1 and the first support layer G2 and the tip support force of the first support layer G2.
The friction piles 4, 4,... Support the load of the structure 2 by the peripheral frictional resistance received from the soft layer G1, the first support layer G2, and the viscous soil layer G3 and the tip support force of the viscous soil layer G3. Therefore, it is for suppressing the consolidation settlement of the structure 2. The friction pile 4 is arranged so that the stress on the viscous soil layer G3 does not exceed the consolidation yield stress.

  The number of friction piles 4, 4,... Is set according to the number of support piles 3. That is, although the support pile 3 will be described in detail later, the stress acting on the viscous soil layer G3 (the effective stress in the viscous soil layer G3 and the load stress of the structure 2 transmitted to the viscous soil layer G3 by the support pile 3) The sum is set at an allowable value, i.e., the number of placements that does not exceed the consolidation yield stress of the cohesive soil layer G3.

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 (hereinafter also referred to as “original ground”) that is not affected by the structure 2, and the dotted line Sb indicates the viscous soil layer G3. The consolidation yield stress is shown.
And the area | region (shaded part in a figure) of code | symbol S0 has shown the stress (load stress) which the load of the structure 2 gives to the ground G via the pile structure 1 (support pile 3, friction pile 4).

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 increases in stress value from the upper part to the lower part of the viscous soil layer G3. In the first embodiment, the consolidation yield stress Sb has a minimum value near the upper end of the cohesive soil layer G3 (near the boundary with the first support layer G2).

  As shown in the stress distribution diagram, the load stress S0 of the structure 2 in the pile structure 1 is affected by the first load stress S1 affected by the support piles 3, 3,... And the friction piles 4, 4,. The second load stress S <b> 2 is divided. The first load stress S1 is the maximum stress near the tip (lower end) of the support pile 3, and decreases as the depth increases. The second load stress S2 becomes the maximum stress at a certain depth of the friction pile 4, and decreases as the depth increases.

Specifically, the pile structure 1 includes support piles 3, 3,... That are driven into the first support layer G2, and friction piles 4, 4,. The load of the structure 2 is supported by the circumferential frictional resistance and the tip support force.
In the present pile structure 1, by providing the friction pile 4 reaching the viscous soil layer G3 in a part of the friction pile, the number of the support piles 3 that support the structure 2 in the first support layer G2 is reduced. ing.
The range of influence of the first load stress S1 extends from the first support layer G2 to the upper part of the viscous soil layer G3. Therefore, when the first load stress S1 increases, the stress acting on the viscous soil layer G3 becomes the consolidation yield stress Sb. Will cause consolidation settlement. Therefore, the first load stress S1 is managed so that the stress of the cohesive soil layer G3 does not exceed the consolidation yield stress Sb, and the number of support piles 3 is set.

  In the present pile structure 1, as described above, by placing the friction piles 4, 4,... In the viscous soil layer G3, only the support force of the load of the structure 2 borne by the friction piles 4, 4,. The number of placement of the support piles 3, 3, ... provided in the first support layer G2 can be reduced. Thereby, the supporting force with respect to the load of the structure 2 can be disperse | distributed to the 1st support layer G2 and the viscous soil layer G3. That is, the stress (load stress S0) generated by receiving the load of the structure 2 in the first support layer G2 in which the support piles 3, 3,. Since the effective stress transmitted to G3 can be reduced, 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 S0) is consolidated yielding of the viscous soil layer G3. It can suppress becoming larger than the stress Sb, the consolidation settlement of the viscous soil layer G3 can be prevented, and the settlement of the structure 2 can be suppressed.

  Further, in the present pile structure 1, as described above, the maximum number of support piles 3 are arranged in the first support layer G2 located at a depth shallower than the viscous soil layer G3 within a range that does not cause consolidation settlement to the viscous soil layer G3. Since it can be driven, many support piles 3 with a short pile length can be used, and the cost can be reduced.

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 number of support piles 3, 3,... To be placed in the first support layer G2 can be reduced by the support force of the friction piles 4, 4,..., And the first support layer G2 is changed to the viscous soil layer G3. The load (load stress S0) of the structure 2 to be transmitted can be reduced. Therefore, the effective stress acting on the viscous soil layer G3 (the sum of the initial effective stress Sa and the load stress S0 in the viscous soil layer G3) can be suppressed from becoming larger than the consolidation yield stress Sb of the viscous soil layer G3. Consolidation settlement of the soil layer G3 can be prevented and settlement of the structure 2 can be reliably suppressed.
Thus, since it is the structure which provides the support pile 3 and the friction pile 4 in the 1st support layer G2 and the viscous soil layer G3, it will reach the 2nd support layer G4 located under a viscous soil layer like before. Thus, it is not necessary to install a friction pile (or support pile) having a long pile length, and the cost can be reduced.

Next, the second and third embodiments of the present invention will be described with reference to FIGS. 2 and 3, but the same reference numerals are used for the same or similar members and parts as those of the first embodiment. A description of the configuration different from that of the first embodiment will be given by omitting the description.
FIG. 2 is a diagram showing the structure of the pile structure and the stress distribution in the ground according to the second embodiment of the present invention.
As shown in FIG. 2, the pile structure 1A according to the second embodiment is applied when the overconsolidation ratio of the viscous soil layer G3 is smaller than the load of the structure 2 as compared with the first embodiment. Has been. In this pile structure 1A, the length of the friction pile 4 is not uniform, and the stress acting on the viscous soil layer G3 is within a permissible value (that is, the consolidation yield stress Sb of the viscous soil layer G3). Friction piles 4A and 4B having the same pile length are used. The support pile 3 is driven into the first support layer G2 as in the first embodiment.

Specifically, this pile structure 1A makes the load stress S0 of the structure 2 acting on the viscous soil layer G3 plural in the depth direction by making the friction piles 4A, 4B in the viscous soil layer G3 have a plurality of pile lengths. Can be dispersed. That is, the load stress S0 is distributed to the first to third load stresses S1, S2, and S3, and the maximum values of the load stresses S1, S2, and S3 can be reduced.
Therefore, in the second embodiment, the stress acting on the viscous soil layer G3 does not exceed the consolidation yield stress Sb, and the consolidation settlement of the viscous soil layer G3 is prevented as in the first embodiment. The effect of suppressing the settlement of the structure 2 can be further enhanced.

  In the present pile structure 1A, many friction piles indicated by the longest reference numeral 4A are arranged in the central region T1 in a plan view in which the amount of settlement of the structure 2 increases, and the amount of settlement is smaller than that of the central region T1. The outer peripheral region T2 of the structure 2 has a structure that can efficiently cope with the settlement of the structure 2 by disposing a large number of friction piles indicated by reference numeral 4B shorter than the friction pile 4A of the central region T1. .

Moreover, FIG. 3 is a figure which shows the structure of the pile structure by 3rd embodiment of this invention, and the stress distribution in a ground.
As shown in FIG. 3, the pile structure 1 </ b> B according to the third embodiment replaces the support pile 3 (see FIG. 1) according to the first embodiment with a cylindrical ground improvement body 6 (support pile according to the present invention). This is a structure in which multiple constructions are applied. Specifically, in the construction region of the structure 2, the ground improvement body 6 made of, for example, soil mortar is formed so as to reach the first support layer G2. Note that a plurality of friction piles 4, 4,... Are placed in the viscous soil layer G3 as in the first embodiment.

This pile structure 1B which comprises such a structure acts as a support pile in which the ground improvement body 6 supports the load of the structure 2 similarly to the support pile 3 of 1st embodiment. The load stress S0 of the structure 2 in the stress distribution acting on the ground G is distributed into the first load stress S1 affected by the ground improvement body 6 and the second load stress S2 affected by the friction pile 4. Will be.
Therefore, in the third embodiment, as in the first and second embodiments, there is an effect that the consolidation of the viscous soil layer G3 can be prevented and the settlement of the structure 2 can be suppressed.

The first to third embodiments of the structure settlement suppression structure according to the present invention have been described above, but the present invention is not limited to the first to third 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 number of support piles 3, friction piles 4, outer diameter dimensions, pile length, etc. are the load, size, shape, etc. of the structure 2, ground G conditions (for example, thickness of each layer, viscous soil layer G3 Can be arbitrarily set according to the settlement distribution of the structure 2.
In the first to third embodiments, the ground layer G is laminated in the order of the soft layer G1, the first support layer G2, the viscous soil layer G3, and the second support layer G4 from the ground surface side. The ground G is not limited. In short, the ground G having the first 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 1 can be applied can be obtained.

And in this 2nd embodiment, although the friction piles 4A and 4B cast in the viscous soil layer G3 are made into two different pile lengths, it is not restricted to this, The friction pile of three or more different pile lengths 4 is also acceptable.
Further, the friction pile 4 may be driven to be rooted until it reaches a deeper layer than the viscous soil layer G3 instead of the tip (lower end) of the friction pile 4 as necessary. It doesn't matter. In this case, as in the first to third embodiments, the number of support piles 3 placed in the support layer G2 can be reduced, and the stress acting on the cohesive soil layer G3 can reduce its consolidation yield stress. Since it can be eliminated, consolidation settlement of the viscous soil layer G3 can be prevented and settlement of the structure 2 can be suppressed.

It is a figure which shows the structure of the pile structure by 1st embodiment of this invention, and the stress distribution in the ground. It is a figure which shows the structure of the pile structure by 2nd embodiment, and the stress distribution in the ground. It is a figure which shows the structure of the pile structure by 3rd embodiment, and the stress distribution in the ground. 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 Pile structure (subsidence suppression structure)
2 Structure 3 Support pile 4 Friction pile 6 Ground improvement body (support pile)
G Ground G1 Soft layer G2 First support layer (support layer)
G3 Cohesive soil layer G4 2nd support layer Sa Effective stress of raw ground Sb Consolidation yield stress of viscous soil layer S0 Load stress

Claims (3)

In the construction region of the structure, the structure is a subsidence suppression structure for the structure to be constructed on the ground where the support layer that can support the load of the structure exists in a portion shallower than the viscous soil layer,
A support pile to be driven to a depth reaching the support layer;
A friction pile that is driven to a depth that reaches in the viscous soil layer or in a deeper layer than the viscous soil layer;
Tona is,
Said friction piles, subsidence suppressing structure of the structure, characterized in Rukoto stress acting on the viscous soil layer of the friction pile provided so as not to exceed the consolidation yield stress of the viscous soil layer. The structure according to claim 1, wherein a plurality of the friction piles are provided, and the piles have a plurality of pile lengths. The structure according to claim 1 or 2, wherein the support pile is formed of a ground improvement body.

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