Pile design method, and pile construction method

Abstract

To provide a pile design method capable of improving the construction accuracy of a new prefabricated pile when constructing the new prefabricated pile nearby a backfilled area where an existing pile has been removed, which is formed by backfilling a drilled area after removing an existing pile.SOLUTION: A pile design method is configured to, when an overlap ratio between an existing pile removal backfilling part 14 formed by backfilling a drilled section 12 after removing an existing pile 10 and a new pile shaft drilled part 30 formed in the ground G when a new prefabricated pile 20 is newly installed in a planned position is outside the allowable value, change at least one of the planned position of the new prefabricated pile 20 and the pile diameter P so that the overlap rate is within the acceptable range.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a pile design method and a pile construction method.

Background Art

[0002] There is a ground improvement method of backfilling while improving the ground in the bored hole after removing an existing pile (see, for example, Patent Documents 1 and 2).

[0003] Also, there is a construction method of constructing a cast-in-place concrete pile in the backfilled portion where the bored hole after removing the existing pile is backfilled (see, for example, Patent Documents 3 and 4).

[0004] Furthermore, there are documents on constructing a new pile in the backfilled portion where the bored hole after removing the existing pile is backfilled (see Non-Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Documents

[0006]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] By the way, it is conceivable to install a precast pile (hereinafter referred to as "newly installed precast pile") in a backfill area (hereinafter referred to as "existing pile removal and backfill section") that fills a drilling hole for removing an existing pile.

[0008] In the construction of a newly installed precast pile, first, a drilling hole (hereinafter referred to as "newly installed pile shaft drilling hole") is formed in the ground, and the newly installed precast pile is dropped into the formed newly installed pile shaft drilling hole in a state where a root fixing liquid, a pile circumference fixing liquid, etc. are injected.

[0009] Here, if an existing pile removal and backfill section exists in the construction area of the newly installed pile shaft drilling hole, the newly installed pile shaft drilling hole may bend due to the strength difference between the existing pile removal and backfill section and the original ground, etc., and the construction accuracy of the newly installed precast pile may decrease.

[0010] In consideration of the above facts, the present invention aims to improve the construction accuracy of a newly installed precast pile when constructing the newly installed precast pile near an existing pile removal and backfill section formed by filling a drilling hole after removing an existing pile.

Means for Solving the Problems

[0011] When the lap rate between the existing pile removal and backfill section formed by filling a drilling hole after removing an existing pile and the newly installed pile shaft drilling hole formed in the ground when installing a newly installed precast pile at the planned position is outside the allowable value, according to the pile design method described in claim 1, at least one of the planned position and the pile diameter of the newly installed precast pile is changed so that the lap rate becomes the allowable value.

[0012] According to the pile design method according to claim 1, when the lap rate between the existing pile removal and backfill section formed by filling a drilling hole after removing an existing pile and the newly installed pile shaft drilling hole formed in the ground when installing a newly installed precast pile at the planned position is outside the allowable value, the eccentricity of the newly installed pile shaft drilling hole may increase. As a result, the construction accuracy of the newly installed precast pile may decrease.

[0013] In contrast, in the present invention, when the lap rate between the existing pile removal and backfilling portion and the bored hole portion of the new pile shaft is outside the allowable value, at least one of the planned position and the pile diameter of the new precast pile is changed so that the lap rate becomes the allowable value. Thereby, the amount of eccentricity of the bored hole portion of the new pile shaft is reduced. Therefore, the construction accuracy of the new precast pile can be improved.

[0014] The pile design method according to claim 2 is the pile design method according to claim 1, wherein when the pile diameter of the new precast pile is changed, the new precast pile is redesigned.

[0015] According to the pile design method according to claim 2, when the pile diameter of the new precast pile is changed, the vertical bearing capacity and the horizontal bearing resistance of the new precast pile also vary. Therefore, in the present invention, when the pile diameter of the new precast pile is changed, the new precast pile is redesigned. Thereby, in the present invention, a new precast pile having a predetermined vertical bearing capacity and horizontal bearing resistance can be constructed.

[0016] The pile design method according to claim 3 is the pile design method according to claim 1 or claim 2, wherein the allowable value of the lap rate is set based on at least one of the allowable eccentricity of the new precast pile and the allowable eccentricity of the boring rod for forming the bored hole portion of the new pile shaft.

[0017] According to the pile design method according to claim 3, the allowable value of the lap rate between the existing pile removal and backfilling portion and the bored hole portion of the new pile shaft is set based on at least one of the allowable eccentricity of the new precast pile and the allowable eccentricity of the boring rod for forming the bored hole portion of the new pile shaft. Thereby, since the amount of eccentricity of the new precast pile and the boring rod is reduced, the construction accuracy of the new precast pile can be improved.

[0018] The pile construction method according to claim 4 is to construct the new precast pile designed by the pile design method according to any one of claims 1 to 3 into the ground.

[0019] According to the pile construction method according to claim 4, the construction accuracy of the new precast pile can be improved.

Effects of the Invention

[0020] As described above, according to the present invention, when constructing a newly installed precast pile in the vicinity of an existing pile removal and backfilling portion formed by filling the drilled hole after removing the existing pile, the construction accuracy of the newly installed precast pile can be improved.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0022] Hereinafter, a pile design method according to an embodiment will be described with reference to the drawings.

[0023] (Pile design method) As shown in FIG. 1, the pile design method according to this embodiment is used when there is an existing pile removal and backfilling portion 14 formed by backfilling a drilling portion 12 for removing an existing pile 10 in a construction area of a drilling portion 30 of a new pile shaft of a newly installed precast pile 20.

[0024] (Existing pile removal and backfilling portion) As shown in FIGS. 1 and 2, the existing pile removal and backfilling portion 14 is an area where the drilling portion 12 for removing the existing pile 10 is backfilled.

[0025] Note that the existing pile 10 may be a steel pipe pile or a concrete pile. Also, the existing pile 10 may be a precast pile or a cast-in-place pile.

[0026] As a method for removing the existing pile 10, that is, a construction method for the existing pile removal and backfilling portion 14, for example, as in the construction method disclosed in Patent Document 2 (hereinafter referred to as the "improved wheel throwing method"), first, a casing is driven around the existing pile 10 to form a drilling portion 12, and the existing pile 10 inside the casing is pulled out by a heavy machine. Next, an auger is inserted into the casing, and the tip of the auger is expanded below the lower end of the casing. Then, while pulling out the auger and the casing, the ground is stirred by the auger and cement milk is injected into the ground. Thereby, the existing pile removal and backfilling portion 14 of the existing pile 10 is backfilled with a predetermined strength.

[0027] Also, as another construction method for the existing pile removal and backfilling portion 14, for example, as in the construction method disclosed in Patent Document 4 (hereinafter referred to as the "wheel throwing screw stirring method"), a casing is driven around the existing pile 10 to form a drilling portion 12, and after the casing is pulled out, the existing pile 10 is pulled out. Next, while inserting an auger having a diameter equal to or larger than that of the drilling portion 12, the ground is stirred by the auger and cement milk or the like is injected into the ground. Thereby, the existing pile removal and backfilling portion 14 of the existing pile 10 is backfilled with a predetermined strength.

[0028] Here, the existing pile removal and backfilling portion 14 desirably has a predetermined strength. This predetermined strength is set, for example, to be equivalent to the strength of the original ground. Further, the strength of the existing pile removal and backfilling portion 14 is evaluated by, for example, the N-value or the uniaxial compressive strength.

[0029] In addition, examples of the construction method capable of controlling the existing pile removal and backfilling portion 14 to a predetermined strength include the improved wheel throwing method, the wheel throwing screw agitation method, the PG method, the CD method (full rotation all casing method), etc. described above.

[0030] (Newly installed precast pile) The newly installed precast pile 20 is made of a steel pile (steel pipe pile) or a concrete pile and is manufactured in a factory or the like. Further, the newly installed precast pile 20 is constructed by a pre-boring method or the like. FIG. 3 shows, as an example, the newly installed precast pile 20 constructed by the pre-boring and enlarged root consolidation method.

[0031] In the pre-boring and enlarged root consolidation method, first, a newly installed pile shaft boring portion 30 is formed in the ground G by a boring rod 40 (see FIG. 5), and a newly installed pile root consolidation boring portion 32 is formed at the lower end portion of the newly installed pile shaft boring portion 30. Next, a root consolidation liquid W2 is injected into the newly installed pile root consolidation boring portion 32, and while pulling out the boring rod 40, a pile circumference fixing liquid W1 is injected into the newly installed pile shaft boring portion 30. Next, the newly installed precast pile 20 is dropped into the newly installed pile shaft boring portion 30 and the newly installed pile root consolidation boring portion 32. Thereby, the newly installed precast pile 20 is constructed.

[0032] The newly installed pile root consolidation boring portion 32 may be provided as necessary and can be appropriately changed.

[0033] Here, when constructing the newly installed precast pile 20, for example, the eccentricity of the newly installed precast pile 20 (newly installed pile shaft boring portion 30) is controlled. As shown in FIG. 4, the eccentricity R of the newly installed precast pile 20 is represented by the displacement amount (deviation amount) of the plane position (x, y) of the center (center) C1 of the newly installed precast pile 20 with respect to the design center C0 of the newly installed precast pile 20, and is obtained by the following formula (1).

Equation

[0034] The planar position (x, y) of the center C1 of the newly installed precast pile 20 is measured, for example, as shown in FIG. 5, by causing the bored rod 40 to form the newly installed pile shaft boring portion 30 and the newly installed pile root consolidation boring portion 32, and when the lower end of the bored rod 40 reaches the planned depth (lower end of boring), on the ground surface of the ground G, the planar position (planar coordinates) of the center of the bored rod 40 is measured by an optical wave transit 42 or the like.

[0035] Note that the measurement timing and measurement method of the planar position (x, y) of the center C1 of the newly installed precast pile 20 can be changed as appropriate.

[0036] Here, the eccentricity R of the newly installed precast pile 20 varies depending on the lap rate between the existing pile removal and backfilling portion 14 and the newly installed pile shaft boring portion 30 formed in the ground G when the newly installed precast pile 20 is installed at the planned position. Therefore, in the pile design method according to the present embodiment, first, the lap rate between the existing pile removal and backfilling portion 14 and the newly installed pile shaft boring portion 30 is calculated.

[0037] The lap rate L between the existing pile removal and backfilling portion 14 and the newly installed pile shaft boring portion 30 is obtained by the following formula (2). Lap rate L [%] = (overlap amount d of the existing pile removal and backfilling portion and the newly installed pile shaft boring portion / newly installed pile shaft boring diameter D2 of the newly installed pile shaft boring portion) × 100 ··· (2)

[0038] As shown in FIG. 1, the overlap amount d of the existing pile removal and backfilling portion 14 and the newly installed pile shaft boring portion 30 is the maximum length in the radial direction of the newly installed pile shaft boring portion 30 at the portion where the existing pile removal and backfilling portion 14 and the newly installed pile shaft boring portion 30 overlap in plan view.

[0039] Further, as shown in FIG. 6, when the existing pile removal and backfilling portion 14 and the new pile shaft portion boring portion 30 do not overlap in plan view, the overlapping amount d between the existing pile removal and backfilling portion 14 and the new pile shaft portion boring portion 30 is set to the shortest distance (distance between outer ends) between the existing pile removal and backfilling portion 14 and the new pile shaft portion boring portion 30. Also, when the existing pile removal and backfilling portion 14 and the new pile shaft portion boring portion 30 do not overlap in plan view, the wrap rate L is set to negative (minus).

[0040] Note that the diameter D1 of the existing pile removal and backfilling portion 14 of the existing pile is, for example, the largest diameter among excavation equipment such as casings and augers used during construction. Also, the diameter D2 of the new pile shaft portion boring portion 30 of the new pile is, for example, the diameter of the new pile shaft portion boring portion 30 on the ground surface of the ground (construction ground) G.

[0041] FIG. 7 shows, as an example, a graph showing the relationship between the wrap rate L [%] of the existing pile removal and backfilling portion 14 and the new pile shaft portion boring portion 30 and the eccentricity R [mm] of the boring rod 40 for constructing the new pile shaft portion boring portion 30. In FIG. 7, as described above, the existing pile removal and backfilling portion 14 is constructed by various construction methods capable of controlling the existing pile removal and backfilling portion 14 to a predetermined strength.

[0042] The allowable value of the wrap rate L of the existing pile removal and backfilling portion 14 and the new pile shaft portion boring portion 30 is set, for example, based on the allowable value of the eccentricity R of the new precast pile 20 (hereinafter referred to as the "allowable eccentricity").

[0043] Specifically, in the graph shown in FIG. 7, when the allowable eccentricity of the new precast pile 20 is 200 [mm], the wrap rate L of the existing pile removal and backfilling portion 14 and the new pile shaft portion boring portion 30 is in the range of 10 [%] or more and 30 [%] or less (10 to 30 [%]), and the allowable eccentricity of the new precast pile 20 will be exceeded. That is, the allowable value of the wrap rate L of the existing pile removal and backfilling portion 14 and the new pile shaft portion boring portion 30 is less than 10 [%] or more than 30 [%]. This is presumably because the boring rod 40 (see FIG. 5) for constructing the new pile shaft portion boring portion 30 is likely to bend due to the strength difference between the existing pile removal and backfilling portion 14 and the surrounding ground G.

[0044] In this case, in the present embodiment, at least one of the planned position of the newly installed precast pile 20 and the pile diameter P is changed so that the lap rate L of the existing pile removal and backfilling portion 14 and the newly installed pile shaft boring portion 30 becomes an allowable value.

[0045] For example, in the embodiment shown in FIG. 8(A), the planned position (two-dot chain line) of the newly installed precast pile 20 is changed to a position (solid line) away from the existing pile removal and backfilling portion 14 so that the lap rate L of the existing pile removal and backfilling portion 14 and the newly installed pile shaft boring portion 30 is less than 10%.

[0046] On the other hand, in the embodiment shown in FIG. 8(B), the planned position (two-dot chain line) of the newly installed precast pile 20 is changed to a position (solid line) close to the existing pile removal and backfilling portion 14 so that the lap rate L of the existing pile removal and backfilling portion 14 and the newly installed pile shaft boring portion 30 exceeds 30%.

[0047] Further, in the embodiment shown in FIG. 9(A), the pile diameter P of the newly installed precast pile 20 is reduced so that the lap rate L of the existing pile removal and backfilling portion 14 and the newly installed pile shaft boring portion 30 is less than 10%, thereby reducing the newly installed pile shaft boring diameter D2 of the newly installed pile shaft boring portion 30.

[0048] On the other hand, in the embodiment shown in FIG. 9(B), the pile diameter P of the newly installed precast pile 20 is increased so that the lap rate L of the existing pile removal and backfilling portion 14 and the newly installed pile shaft boring portion 30 exceeds 30%, thereby increasing the newly installed pile shaft boring diameter D2 of the newly installed pile shaft boring portion 30.

[0049] Here, when the pile diameter P of the newly installed precast pile 20 is changed as in the embodiments shown in FIGS. 9(A) and 9(B), the vertical bearing capacity and the horizontal bearing resistance of the newly installed precast pile 20 also change. Therefore, in the present embodiment, when the pile diameter P of the newly installed precast pile 20 is changed, the newly installed precast pile 20 is redesigned. In particular, when the pile diameter P of the newly installed precast pile 20 is reduced as in the embodiment shown in FIG. 9(A), there is a possibility that the vertical bearing capacity and the horizontal bearing resistance of the newly installed precast pile 20 are insufficient.

[0050] Therefore, when redesigning the newly installed precast pile 20, for example, measures such as increasing the diameter D3 (see Fig. 3) of the bored hole part 32 of the newly installed pile foundation consolidation part, increasing the pile length of the newly installed precast pile 20, changing the pile type of the newly installed precast pile 20, and changing the shape of the newly installed precast pile 20 can be taken to supplement the insufficient vertical support force and horizontal bearing capacity of the newly installed precast pile 20.

[0051] As an example of changing the pile type of the newly installed precast pile 20, for example, when the newly installed precast pile 20 is a PRC pile (prestressed reinforced concrete pile), by increasing the wall thickness of the newly installed precast pile 20 or increasing the bar diameter of the reinforcing bars, the bending moment and shear bearing capacity of the newly installed precast pile 20 can be increased.

[0052] Also, as another example of changing the pile type of the newly installed precast pile 20, for example, when the newly installed precast pile 20 is a PHC pile (pretensioned centrifugal high-strength prestressed concrete pile), it is conceivable to change the newly installed precast pile 20 to a PRC pile with a large amount of axial reinforcing bars.

[0053] Note that examples of the pile type of the newly installed precast pile 20 include RC piles (centrifugal reinforced concrete piles), PHC piles, SC piles (concrete piles with outer steel pipes), PRC piles, etc. Also, examples of the shape of the newly installed precast pile 20 include ST piles (tip-expanded PHC piles) and joint piles (jointed PHC piles).

[0054] Also, when the pile diameter P of the newly installed precast pile 20 is increased, the vertical support force and horizontal bearing capacity of the newly installed precast pile 20 may become excessive, resulting in uneconomical situations. In such cases as well, it is preferable to redesign the newly installed precast pile 20.

[0055] (Function and Effect) Next, the function and effect of this embodiment will be described.

[0056] As described above, when the lap rate L between the existing pile removal and backfill portion 14 formed by backfilling the boring portion 12 after the removal of the existing pile 10 and the newly constructed pile shaft boring portion 30 formed in the ground G when installing the newly precast pile 20 at the planned position is outside the allowable value, the eccentricity of the newly constructed pile shaft boring portion 30 may increase. As a result, the eccentricity R of the newly precast pile 20 may increase, and the construction accuracy of the newly precast pile 20 may decrease.

[0057] In contrast, in this embodiment, when the lap rate L between the existing pile removal and backfill portion 14 and the newly constructed pile shaft boring portion 30 is outside the allowable value, at least one of the planned position and the pile diameter P of the newly precast pile 20 is changed so that the lap rate L becomes the allowable value. Thereby, the eccentricity of the newly constructed pile shaft boring portion 30 is reduced, and the eccentricity R of the newly precast pile 20 is reduced. Therefore, the construction accuracy of the newly precast pile 20 can be improved.

[0058] Further, in this embodiment, the allowable value of the lap rate L between the existing pile removal and backfill portion 14 and the newly constructed pile shaft boring portion 30 is set based on the allowable eccentricity of the newly precast pile 20. Thereby, since the eccentricity R of the newly precast pile 20 and the boring rod 40 is reduced, the construction accuracy of the newly precast pile 20 can be improved.

[0059] Here, as shown in FIGS. 9(A) and 9(B), when the pile diameter P of the newly precast pile 20 is changed, the vertical bearing capacity and the horizontal bearing capacity of the newly precast pile 20 also fluctuate. In particular, as shown in FIG. 9(A), when the pile diameter P of the newly precast pile 20 is reduced, the vertical bearing capacity and the horizontal bearing capacity of the newly precast pile 20 may be insufficient.

[0060] Therefore, in this embodiment, when the pile diameter P of the newly precast pile 20 is changed, the newly precast pile 20 is redesigned. Thereby, in this embodiment, a newly precast pile 20 having a predetermined vertical bearing capacity and horizontal bearing capacity can be constructed.

[0061] (Modification example) Next, a modification example of the above embodiment will be described.

[0062] In the embodiments shown in FIGS. 8(A) and 8(B), the planned position of the newly installed precast pile 20 was changed so that the lap rate L of the existing pile removal and backfilling portion 14 and the bored hole portion 30 of the newly installed pile shaft becomes an allowable value. On the other hand, in the embodiments shown in FIGS. 9(A) and 9(B), the pile diameter P of the newly installed precast pile 20 was changed so that the lap rate L of the existing pile removal and backfilling portion 14 and the bored hole portion 30 of the newly installed pile shaft becomes an allowable value. However, it is also possible to change both the planned position and the pile diameter P of the newly installed precast pile 20 so that the lap rate L of the existing pile removal and backfilling portion 14 and the bored hole portion 30 of the newly installed pile shaft becomes an allowable value.

[0063] Also, the allowable value of the lap rate L of the existing pile removal and backfilling portion 14 and the bored hole portion 30 of the newly installed pile shaft can be changed as appropriate. For example, when the allowable eccentricity of the newly installed precast pile 20 is 100 [mm], the lap rate L of the existing pile removal and backfilling portion 14 and the bored hole portion 30 of the newly installed pile shaft is in the range of 0 to 60 [%], and it will exceed the allowable eccentricity of the newly installed precast pile 20. That is, the allowable value of the lap rate L of the existing pile removal and backfilling portion 14 and the bored hole portion 30 of the newly installed pile shaft is more than 60 [%].

[0064] Note that the allowable value of the lap rate L of the existing pile removal and backfilling portion 14 and the bored hole portion 30 of the newly installed pile shaft may be more than 60 [%], or less than 10 [%], or more than 30 [%.

[0065] Also, in the above embodiment, when the pile diameter P of the newly installed precast pile 20 was changed, the newly installed precast pile 20 was redesigned. However, the newly installed precast pile 20 may be redesigned as necessary, and it is not always necessary to redesign it.

[0066] In addition, in the above-described embodiment, the allowable value of the wrapping rate L of the existing pile removal and backfilling portion 14 and the bored hole portion 30 of the new pile shaft portion is set based on the allowable eccentricity of the new precast pile 20. However, the wrapping rate L of the existing pile removal and backfilling portion 14 and the bored hole portion 30 of the new pile shaft portion is not limited to the allowable eccentricity of the new precast pile 20, and can be set based on, for example, at least one of the allowable eccentricity of the new precast pile 20 and the allowable eccentricity of the boring rod 40. Further, the wrapping rate L of the existing pile removal and backfilling portion 14 and the bored hole portion 30 of the new pile shaft portion may be set based on, for example, other indices indicating the construction accuracy of the new precast pile 20.

[0067] As described above, one embodiment of the present invention has been described. However, the present invention is not limited to such an embodiment, and one embodiment and various modifications may be used in appropriate combination, and it goes without saying that the present invention can be implemented in various modes without departing from the gist of the present invention.

Explanation of Reference Numerals

[0068] 10 Existing pile 12 Boring 14 Existing pile removal and backfilling portion 20 New precast pile 30 Bored hole portion of new pile shaft portion P Pile diameter of new precast pile

Claims

1. When the lap rate between the existing pile removal and backfill part formed by backfilling the drilled hole after removing the existing pile and the newly installed pile shaft drilled hole part formed in the ground when installing a newly installed precast pile at the planned position is outside the allowable value, at least one of the planned position and the pile diameter of the newly installed precast pile is changed so that the lap rate becomes the allowable value. Pile design method.

2. When the pile diameter of the newly installed precast pile is changed, the newly installed precast pile is redesigned. The pile design method according to Claim 1.

3. The allowable value of the lap rate is set based on at least one of the allowable eccentricity of the newly installed precast pile and the allowable eccentricity of the drilling rod that creates the newly installed pile shaft drilled hole part. The pile design method according to Claim 1.

4. The newly installed precast pile designed by the pile design method according to any one of Claims 1 to 3 is constructed in the ground. Pile construction method.

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