JP4219210B2 - Advanced ground improvement pile and its construction method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a tip ground improved pile and a construction method thereof, and particularly enables an increase in pile tip supporting force.
[0002]
[Prior art]
When a prefabricated pile such as a PHC pile is embedded in the ground by an embedding method such as a pre-boring method, the prefabricated pile after embedding is simply mounted on the support layer as it is. small. For this reason, "rooting" is performed to increase the supporting force.
[0003]
In this case, a method of integrating the tip of the pile and the support layer by injecting cement milk into the support layer at the tip of the pile is performed.
[0004]
As for the root consolidation part (overexcavation part) of the pile tip, the main purpose of root consolidation is to smoothly transmit the load from the pile to the support layer. Since the construction is shallow (short) about twice the maximum diameter of the pile, conventionally, the peripheral frictional force of the rooting portion has not been particularly considered as a support force of the pile.
[0005]
[Patent Document 1]
JP 2000-64275 A
[Patent Document 2]
JP2002-201638
[Patent Document 3]
JP-A-1-250523
[0006]
[Problems to be solved by the invention]
Conventionally, when designing a pile, the pile support force is composed of a pile tip support force and a peripheral surface friction force. Therefore, in order to obtain the support force, the pile is deeply embedded in a strong support layer.
[0007]
Further, for example, as illustrated in FIG. 3A, in the case where the support layer 20 is uneven, in the place of the high support layer 20a, the pile length of the ready-made pile 21 must be shortened, There was a problem that the peripheral frictional force of the pile would be reduced accordingly.
[0008]
On the other hand, in the place of the low support layer 20b, for example, as shown in FIG. 3B, it is necessary to lengthen the pile length of the ready-made pile 21 to the support layer 20, and there is a problem that the cost increases accordingly. It was.
[0009]
For example, as shown in FIGS. 4 (a) and 4 (b), a soil cement synthetic pile in which up to the middle is constructed with the ready-made pile 21 and the remaining support layer 20 is constructed with the soil cement pillar 22 is also known. (See Patent Documents 1 and 2).
[0010]
However, in any example, part or the entire length of the soil cement column 22 is formed in the relatively soft formation 23 above the support layer 20, so that the restraining force from the surroundings is small. There was a possibility that the soil cement pillar 22 would be broken by a force due to excessive deformation.
[0011]
The invention of the present application was made to solve the above problems, and in particular, the tip ground improved pile capable of increasing the support force of the pile tip ground, and capable of freely setting the pile tip support force, and its The object is to provide a construction method.
[0012]
[Means for Solving the Problems]
The tip ground improvement pile according to claim 1 is a tip ground improvement pile constructed on a non-land surface composed of a high support layer and a low support layer, and can be regarded as a pile body in an overexcavated portion formed in the support layer. It is composed of a soil cement column or mortar column formed with a certain degree of strength, and a ready-made pile formed in the formation above the soil cement column or mortar column, and the ready-made pile extends to the lower support layer The prefabricated pile on the high support layer side and the prefabricated pile on the low support layer side are formed in the same length, and the tip of the prefabricated pile on the high support layer side and the ready pile on the low support layer side are formed. The tip is installed in a soil cement column or mortar column formed in the overexcavated portion of the support layer, and the pile on the high support layer side is changed by changing the length and / or diameter of the soil cement column or mortar column Supportive power It is characterized in that you have to equalize the supporting force of the lower support layer side piles.
[0014]
The construction method of the tip ground improvement pile according to claim 2 is a construction method of the tip ground improvement pile which is constructed on the non-land ground composed of a high support layer and a low support layer, and an overexcavation portion is formed in the support layer. Then, a soil cement column or a mortar column is constructed in the surplus digging portion , and a prefabricated pile is constructed in the formation above the soil cement column or the mortar column, and the tip of the prefabricated pile is a soil cement column or By installing the mortar column and changing the length and / or diameter of the soil cement column or mortar column, the bearing capacity of the pile on the high support layer side and the support capacity of the pile on the low support layer side are set equal. It is characterized by doing.
[0015]
The present invention regards the peripheral frictional force of the soil cement column or mortar column formed in the support layer deeper than the tip of the pile as the support force of the pile, and adds this as the support force of the pile to add more than the actual pile length. In addition, the bearing capacity of the pile can be greatly increased.
In this case, by setting the diameter of the soil cement column or mortar column to be equal to or greater than the excavated diameter and the length (depth) to be at least three times the maximum diameter from the tip of the ready-made pile, the peripheral surface of the soil cement column or mortar column The frictional force can be regarded as the support force of the ready-made pile and added to the tip support force of the ready-made pile. Further, the supporting force can be arbitrarily set by adjusting the diameter and length (depth) of the soil cement column or the mortar column as necessary.
[0016]
In particular, cement milk that forms soil cement columns or mortar columns, in principle, cement milk that can form soil cement columns or mortar columns as strong as piles is used, but soil cement columns or mortar columns are used. As long as it is possible to form the column with a strength that can be regarded as a pile body, it may be the same as the cement milk used for the soil cement of the pre-made pile peripheral surface portion.
[0017]
In addition, since the soil cement column or mortar column is formed in a good support layer, sufficient strength can be obtained due to the restraining effect of the surrounding support layer, and the tip of the pile is not bent. There is no need to reinforce the cement or mortar columns with reinforcing bars.
In general, as the support layer referred to here, a formation having an average N value of about 30 to 40 can be assumed. Moreover, a concrete pile, a steel pipe pile, etc. can be used as a ready-made pile.
[0018]
In addition, the support layer here refers to a formation relatively determined from the relationship with the upper load, and assumes a formation capable of stably supporting at least the upper structure. Therefore, if the formation can stably support the superstructure even if the N value is small, the formation is the support layer referred to here.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
1 (a) and 1 (b) show an example of a tip ground improved pile and its construction method according to the present invention. A tip ground improved pile (hereinafter referred to as “pile”) 1 is a good support layer 2 deeper than the tip of the pile. It is formed continuously and integrally from a soil cement column or mortar column (hereinafter referred to as “soil cement column”) 3 formed inside and a node pile 5 embedded as a ready-made pile in the formation 4 above it. Yes.
[0023]
The soil cement column 3 is a case where the support layer 2 is a good support layer such as a sand layer or a gravel layer, the diameter is equal to or greater than the outer diameter (excavation diameter) of the pile 1 and the depth is 3 from the tip of the joint pile 5 to its maximum diameter. Each is formed more than double.
[0024]
The soil cement pillar 3 is formed by overexcavating the support layer 2 deeper than the pile tip and injecting cement milk into the overexcavated portion.
[0025]
In this case, cement milk that can be formed to have a strength sufficient to allow the soil cement pillar 3 to be regarded as a pile body is used as a principle. However, the soil cement pillar 3 must be formed to have a strength that can be regarded as a pile body. If possible, it may be the same as the cement milk used for the soil cement 5a on the peripheral surface portion of the joint pile 5.
[0026]
The joint pile 5 is embedded in the soil cement 5a while injecting cement milk to form the soil cement 5a, and the tip 5b of the joint pile 5 is about the diameter of the joint pile 5 or more at the upper end of the soil cement column 3. By being rooted, the soil cement pillar 3 and the joint pile 5 are continuously and integrated.
[0027]
In addition, FIG.1 (b) shows the example by which the soil cement pillar 3 is diameter-expanded, and when the surplus digging cannot fully be carried out especially, a required peripheral surface friction force is ensured by diameter-expanding. be able to.
[0028]
In such a configuration, when examining the support force of the pile of the present invention next, when the tip support force of a normal pile of this type is Rp ₁ , the tip support force of the pile of the present invention is Rp ₂ ,
Rp ₂ = Rp ₁ + ΔR _f .
Here, ΔR _f is an increased frictional force (a peripheral frictional force of the soil cement column).
[0029]
In addition, when considering the frictional force of the soil cement column (overexcavated part) 3 (in the case of long-term support),
On the good ground with an average N value of 50, the pile 5 with a maximum diameter D = 600 is buried as an existing pile with an excavation diameter of φ700, and the diameter of the soil cement column (excavated part) 3 is the excavation diameter φ700, its depth Is assumed to be 3000 mm, which is five times the diameter of the joint pile 5.
[0030]
Since the strength of the soil cement column (overexcavated portion) 3 can be regarded as a pile body, the frictional force can be evaluated by the excavation diameter.
[0031]
Suppose that the peripheral frictional force is calculated from the authorization formula corresponding to the sand layer of the joint pile 5 of f _s = (30 + 5N _s ) / 3 [kN / m ² ]. However, N _s is an average N value of the surrounding ground of the soil cement column (overexcavated portion) 3.
[0032]
f _s = (30 + 5 × 50) / 3
= 93.3 [kN / m ² ]
From the above, the frictional force Rf of the soil cement column (excess dug portion) 3 having an excavation diameter of φ700 mm and a depth L of 3000 mm is:
Rf = f _s × φ × (LD)
= 93.3 × 0.7π × (3.0−0.6)
= 492 [kN]
It becomes. That is, the supporting force is increased by 492 [kN] from the pile having the same diameter and the same length.
[0033]
Further, the increased frictional force ΔRf per unit length of the excavation diameter of φ700 mm is
ΔRf = 93.3 × 0.7π × 1.0
= 205 [kN / m]
It becomes. If this is utilized, a supporting force can be easily set by adjusting the length (depth) of the soil cement pillar (excavated part) 3 irrespective of the pile length of the joint pile 5.
[0034]
Similarly, if a straight pile with a maximum diameter of φ600 mm is embedded as an existing pile with an excavation diameter of φ700 mm, the bearing force can be set easily if the peripheral frictional force is calculated from the notification formula of f _s = 10/3 N _s. Can be done.
[0035]
Next, a method for dealing with unevenness will be described. It is assumed that there is unevenness in a good support layer.
[0036]
In the conventional construction method, as shown in FIG. 3A, in the place of the high support layer 20a, the pile length of the ready-made pile 21 must be shortened, and the support force (circumferential frictional force) is small. However, in the present invention, as shown in FIG. 2A, in the place of the high support layer 2a, even if the pile length of the joint pile 5 is short, the soil cement column (excavated portion) 3 is provided. By making it long (deep), equivalent support force can be obtained.
[0037]
Similarly, in the conventional construction method, as shown in FIG. 3B, the pile length of the ready-made pile 21 can only be increased in the place of the low support layer 20b. However, in the present invention, FIG. As shown in Fig. 2, in the place of the lower support layer 2b, the pile length of the joint pile 5 is left as it is, and the soil cement column (excavated portion) 3 is lengthened (deeply), so that the same pile length or more Support force is obtained.
[0038]
【The invention's effect】
The present invention is as described above, and in particular, the soil cement column formed in the support layer deeper than the tip of the ready-made pile is formed so that the peripheral friction force can be regarded as the support force of the ready-made pile. Even if the length of the ready-made pile is constant, the bearing capacity of the pile can be increased more than the actual pile length.
[0039]
Moreover, the front-end | tip support force of a pile can be freely set by adjusting the diameter and length (depth of a surplus digging part) of a soil cement pillar.
[0040]
In addition, the soil cement pillar is formed in a good support layer deeper than the pile tip, so that sufficient strength can be secured by the restraining effect of the good support layer, and the force caused by excessive deformation during an earthquake. It has enough strength to withstand.
[0041]
Even when the support layer is uneven, it is possible to obtain the same strength by adjusting the length and diameter of the soil cement column (overexcavated portion).
[0042]
In addition, by adjusting the penetration (swallowing) of the ready-made piles into the soil cement pillar (overexcavated part), it is also possible to easily align the pile heads. Can cope without changing the pile length.
[Brief description of the drawings]
1A and 1B are longitudinal sectional views showing an example of a tip ground improvement pile. FIG.
FIGS. 2A and 2B are longitudinal sectional views showing a construction example of a tip ground improvement pile. FIG.
FIGS. 3A and 3B are longitudinal sectional views showing an example of construction of a conventional ready-made pile.
FIGS. 4A and 4B are longitudinal sectional views showing an example of construction of a conventional ready-made pile.
[Explanation of symbols]
1 pile (tip ground improvement pile)
2 Support layer 3 Soil cement pillar (Soil cement pillar or mortar pillar)
4 The stratum above the support layer 5 Node pile (ready-made pile)
5a soil cement

Claims (2)

It is a tip ground improvement pile constructed on a non-land surface consisting of a high support layer and a low support layer, and is formed with a strength that can be regarded as a pile body in the overexcavated part formed in the support layer It is composed of a soil cement column or mortar column and a pre-made pile formed in the formation above the soil cement column or mortar column, and the pre-made pile is formed longer than the depth to the low support layer, and a high support layer The ready-made pile on the side and the ready-made pile on the lower support layer side are formed to the same length, and the tip of the ready-made pile on the high support layer side and the tip of the ready-made pile on the lower support layer side are formed on the support layer. The bearing capacity of the pile on the high support layer side and the support capacity of the pile on the low support layer side are equalized by changing the length and / or diameter of the soil cement column or mortar pillar installed in the cement column or mortar column It is Tip ground improvement pile characterized by. It is a construction method of the tip ground improvement pile constructed on the uneven ground consisting of a high support layer and a low support layer, and an overexcavation part is formed in the support layer , and a soil cement column or a mortar column is formed in the overexcavation part. The ready-made piles are respectively constructed in the stratum above the soil cement column or the mortar column, the tip of the ready-made pile is installed in the soil cement column or the mortar column of the overexcavated portion, and the soil cement column or the mortar A method for constructing a tip-up ground improved pile characterized in that the support force of a pile on the high support layer side and the support force of a pile on the low support layer side are set equal by changing the length and / or diameter of the column.

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