JP2006132100A - Head-enlarged pile - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a head-enlarged pile for being sunk in a hole excavated in advance, which can suppress a decrease in bearing capacity of a foot-protection bulb part at a lower end. <P>SOLUTION: In this head-enlarged pile 20 as a prefabricated pile 20 for being sunk in the excavated hole 10 formed in advance, a head part constitutes a large-diameter part 21 with a diameter larger than that of its downside. An inflow part 24, where a fluid can flow inward from the outside of a pile 20, is provided in a jointing part between the large-diameter part 21 and the small-diameter part 22 on the downside of the large-diameter part 21. For example, an outside-diameter surface of an upper part of the small-diameter part 22 and an inside-diameter surface of a lower part of the large-diameter part 21 are connected together by means of a plurality of radially arranged ribs, and sections among the plurality of ribs serve as the inflow parts 24. Both a jointing angle θ2 of a lower end of the rib with respect to the outside-diameter surface of the upper part of the small-diameter part 22 and a jointing angle θ1 of an upper end of the rib with respect to the inside-diameter surface of the lower part of the large-diameter part 21, in a side view, are set as acute angles, so that concentrated stress can be reduced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a hollow ready-made pile that is set in an excavation hole formed in advance by a preboring method or the like, and relates to a head-expanded pile in which a pile head is expanded.

As a method for constructing a pile in which a drilling hole is formed by a pre-boring method and a head-up pile made of a ready-made pile is sunk, there is one described in Patent Document 1, for example.
In this construction method, pre-boring is performed by a drilling rod provided with an enlarged bit at the tip, and a mudified drilling hole is provided, and further, an enlarged drilling hole is formed at the lower end of the drilling hole by the above-mentioned enlarged bit. Then, the earth and sand in the support layer are mixed and stirred while injecting the root-setting liquid into the enlarged excavation hole to form an enlarged root-setting bulb. After that, ready-made piles are built into the excavation hole and set.

Here, the head-expanded pile as the ready-made pile includes a large-diameter portion having a large-diameter head and a small-diameter portion below the head, and includes a hollow portion extending in the axial direction, and the hollow portion is an upper end of the pile. Open only at the bottom and bottom.
JP 62-253817 A

When the above-mentioned expanded pile 20 is sunk in the excavated hole 10 that is mud as shown in FIG. 5A, the fluid mud 31 flows from the opening at the lower end of the pile to the hollow portion in the pile 20 according to the settling of the pile 20. Enters. As shown in FIG. 5 (b), in the state where only the small-diameter portion 22 of the pile 20 is inserted into the mud 31, depending on the settling speed of the pile 20, the mud 31 in the hollow portion of the pile 20 The height of the upper surface and the upper surface of the mud 31 outside the pile 20 are substantially the same. However, the sedimentation of the pile 20 proceeds, the large diameter portion 21 of the pile 20 is also inserted into the excavation hole 10, and the mud 31 that enters the pile 20 when the tip of the pile 20 reaches the enlarged excavation hole 10 b. Is only the inflow from the tip of the pile 20, the head difference between the upper surface of the mud 31 in the hollow portion of the pile 20 and the upper surface of the mud 31 outside the pile 20 is as shown in FIG. Occurs. In this state, when the pile 20 sinks to the final position, the tip of the pile 20 is inserted into the root-solidifying liquid 30, so that the head-solidifying liquid 30 reduces the head difference in a direction to eliminate the head difference. While only flowing into the pile 20, the mud 31 above the enlarged excavation hole 10b flows into the root bulb as shown in FIG. 5 (d), so that the mud 31 is mixed in the root bulb. There is a possibility that the amount increases or the root hardening liquid 30 becomes in a non-uniform state, which may contribute to a decrease in the supporting force in the root hardening bulb.
The present invention has been made by paying attention to the above points, and in a head-expanded pile for sinking in a previously excavated hole, it is possible to suppress a decrease in supporting force at a root-fixed bulb at the lower end. The issue is to provide expanded piles.

In order to solve the above-mentioned problems, the invention described in claim 1 of the present invention is the ready-made pile used in a method for constructing a pile in which a hollow ready-made pile is sunk in an excavation hole formed by excavation previously. In the head-expanded pile in which the head constitutes a large-diameter portion having a larger diameter than the lower side,
An inflow part into which a fluid can flow in from the outside of the pile to the inside is provided for at least one of the joint part between the large diameter part and the small diameter part below the large diameter part and the side surface of the large diameter part. It is characterized by providing.

Next, the invention described in claim 2 is different from claim 1 in that the joining structure of the small diameter portion and the large diameter portion is between the outer diameter surface of the upper portion of the small diameter portion and the inner diameter surface of the lower portion of the large diameter portion. Are connected by a plurality of radially arranged ribs, and the ribs constitute the inflow portion, and
In the side view, the joining angle of the lower end of the rib with respect to the outer diameter surface of the upper portion of the small diameter portion and the joining angle of the upper end of the rib with respect to the inner diameter surface of the lower portion of the large diameter portion are both acute angles to reduce the concentrated stress. It is what.

  According to the present invention, the mud head difference between the inside and outside of the large-diameter portion when sinking the expanded pile is eliminated by the mud flowing into the pile through the inflow portion provided in the upper portion of the pile. It is possible to suppress a decrease in supporting force at the part.

Next, embodiments of the present invention will be described with reference to the drawings.
First, the structure of the expanded pile according to the present embodiment will be described.
FIG. 1 is a side view showing a head-expanded pile 20 according to the present embodiment, and FIG. 2 is a diagram showing a structure of a joint portion between a large-diameter portion 21 and a small-diameter portion 22 of the head-expanded pile 20.
As shown in FIG. 1, the head-expanded pile 20 includes a large-diameter portion 21 having a large head and a small-diameter portion 22 below the head. In the expanded pile 20 of this embodiment, the large-diameter portion 21 is made of a large-diameter steel pipe (hereinafter also referred to as a large-diameter steel pipe 21), and the small-diameter portion 22 is smaller than the large-diameter steel pipe 21 (hereinafter, small-diameter steel pipe 22). The small diameter steel pipe 22 and the large diameter steel pipe 21 are joined by a plurality of rib panels 23 as shown in FIG.

  The joint structure between the small diameter steel pipe 22 and the large diameter steel pipe 21 will be described in detail. As shown in FIG. 2, the inner diameter side end faces of the plurality of rib panels 23 are welded to the outer diameter face of the upper end portion of the small diameter steel pipe 22. The plurality of rib panels 23 are arranged radially around the small diameter steel pipe 22, and the outer diameter side end face of each rib panel 23 is welded to the lower end inner diameter face of the large diameter steel pipe 21.

As shown in FIG. 2A, each rib panel 23 has a rectangular shape in a side view. Sides (side end surfaces) extending in the left and right vertical directions are parallel and extend along the axis of the pile 20, and The two sides (upper end surface and lower end surface) that are opposed to each other are inclined upward as they go outward in the radial direction. As a result, the joint angle θ2 of the lower end portion of the rib panel 23 with respect to the outer diameter surface of the small diameter portion 22 and the joint angle θ1 of the upper end portion of the rib panel 23 with respect to the inner diameter surface of the large diameter portion 21 in the side view are both acute angles. . Note that the joint angles θ1 and θ2 need not be the same angle.
In FIG. 2, the side end surfaces of the rib panels 23 are welded to the outer diameter surface of the small diameter steel pipe 22 and the inner diameter surface of the large diameter steel pipe 21 along a line parallel to the axis of the pile 20. On the other hand, it may be welded along a slightly oblique line.

  The space between the rib panels 23 constitutes the inflow portion 24. The cross-sectional area of the inflow portion 24 only needs to be large enough for the fluid mud 31 to flow into the pile 20 without hindrance. That is, it is only necessary that the size of the mud 31 is such that the inflow of the mud 31 is ensured such that no head difference occurs in the mud 31 inside and outside the pile 20 according to the settling speed when the pile 20 sinks into the excavation hole 10. If the settling speed of the pile 20 is slow, the cross-sectional area of the inflow portion 24 may be small, and if the settling speed is high, the cross-sectional area of the inflow portion 24 is set such that an amount corresponding to the inflow portion 24 flows.

Next, an example of a method for constructing the head-expanded pile 20 having the above-described configuration by a pre-boring method will be described. FIG. 3 shows the construction procedure.
First, the excavation rod 3 to be used will be described. The excavation rod 3 used in this construction example is composed of a lower first excavation rod member 1 and a second excavation rod member 2 connected to the upper side thereof (see FIG. 3C and the like).

The first excavation rod member 1 is provided with an excavation bit 4 as an excavation blade protruding downward from the distal end with respect to the distal end, and a known enlarged bit 5 is provided at the distal end. Furthermore, a plurality of stirring blades 6 called agitators are provided on the side surface of the first excavation rod member 1 along the axial direction. The excavation rod 3 member in which the protruding amount of the stirring blade 6 is slightly larger than the small diameter portion 22 of the head pile 20 is used.
In addition, the tip of the first drilling rod member 1 is provided with an ejection hole 12 through which liquid can be ejected, as in the prior art, and the drilling fluid and solidifying agent can be injected into the drilling hole 10 from the ejection hole. It has become. As the solidifying agent, cement milk is most often used, so the case where cement milk is used will be described.

  Moreover, the 2nd excavation rod member 2 is provided with the some stirring blades 7 and 8 along the axial direction with respect to the side surface. Of the stirring blades 7 and 8 of the second excavation rod member 2, when the tip of the first excavation rod member 1 is excavated to a target depth, the embedded position (the large diameter portion 21) of the large diameter portion 21 of the head pile 20. The upper agitating blade 8 that should be located at a position where expansion excavation is required) is set to have a larger protruding amount than the lower agitating blade 7, and the large-diameter portion 21 of the expanded pile 20 described above. The diameter is set to be slightly larger than the diameter. The amount of protrusion of the lower stirring blade 7 is the same as the amount of protrusion of the stirring blade 6 of the first excavation rod member 1. That is, the diameter of the second excavation rod member 2 has the same diameter as that of the first excavation rod member 1 on the lower side, but the larger diameter than that of the first excavation rod member 1 on the upper side.

And the stirring blade part in which the said protrusion amount was set large in the said 2nd excavation rod member 2 comprises an upper stirring rod part.
Here, in the following description, when the stirring blades are distinguished, the stirring blades having a relatively small protruding amount are the small-diameter stirring blades 6 and 7, and the stirring blade having a relatively large protruding amount is the large-diameter stirring blade 8. Call it.
Among the large-diameter agitating blades 8 set to have a large protruding amount, the large-diameter agitating blade 8 located at the lowermost portion projects 1 downward from the outer peripheral portion projecting from the lower-diameter agitating blade below. Two or more excavation bits (not shown) are provided as excavation blades.

  Furthermore, an upper ejection hole (not shown) through which liquid can be ejected is also provided at the height position where the excavation bit is provided in the second excavation rod member 2. The upper ejection hole may be provided in the shaft portion or may be opened on the outer peripheral side of the large-diameter stirring blade 8. In addition, the passage composed of a pipe or the like for supplying liquid to the upper ejection hole may share the passage for supplying liquid to the ejection hole 12 of the first excavation rod member 1 or may be provided with a separate passage. Also good. In addition, the said channel | path is provided so that the inside of the axial part of the excavation rod 3 may be extended up and down.

Next, a construction example of this embodiment will be described with reference to FIG.
First, as shown to Fig.3 (a), the upper part of the 1st excavation rod member 1 is connected with the rotation drive part 9 of an excavator, and excavation work is started. That is, as shown in FIG. 3B, the rotation driving unit 9 is driven to rotate the excavation rod 3 and excavation is performed with the excavation bit 4 at the tip. At this time, excavation is performed while cement milk is injected into the excavation hole 10 from the ejection hole 12 at the tip of the excavation rod 3.

When the first excavation rod member 1 excavates to a predetermined depth, the second excavation rod member 2 is connected to the upper portion of the first excavation rod member 1, and the rotation drive unit 9 is connected to the upper portion of the second excavation rod member 2. Are connected again to continue excavation (see FIG. 3C).
At this time, since the bit is provided on the outer peripheral side of the large-diameter stirring blade 8 located at the lowermost part, the outer peripheral portion of the hole excavated earlier is expanded and excavated by the bit. At this time, cement milk is also injected into the excavation hole 10 from the position of the second excavation rod member 2 so that only the necessary amount of cement milk is supplied even in the upper portion 10a of the expanded excavation hole 10.

Next, as shown in FIG. 3 (d), the excavation rod 3 is moved up and down by a predetermined stroke while rotating the excavation rod 3, and the injected cement milk and earth and sand are agitated and kneaded to obtain a soil cement (mud 31). To.
Subsequently, as shown in FIG. 3 (e), the expansion bit 5 is expanded in diameter to expand the lower end portion of the excavation hole 10 to form a root-fixing bulb portion. 30 is injected.

When the excavation work is completed as described above, as shown in FIG. 3 (f), the excavation rod 3 is pulled out, and when the second excavation rod member 2 is completely pulled out to the ground, the second excavation rod member 2 is removed, Subsequently, the first excavation rod member 1 is pulled out.
Subsequently, as shown in FIGS. 3G and 3H, the head-expanded pile 20 is sequentially built into the excavated hole 10 formed as described above by its own weight settling and rotary settling. In addition, in this embodiment, the case where the head-expansion pile 20 consists of two ready-made piles 20A and 20B is illustrated. That is, the small-diameter portion 22 is divided into a lower ready-made pile 20A and an upper ready-made pile 20B.

  In the state where only the portion of the small diameter portion 22 is built in the excavation hole 10 mud with earth and sand and soil cement, the pile-up pile 20 is set according to the settling of the pile 20 in the conventional manner. The fluid mud 31 enters the hollow portion in the pile 20 from the opening at the lower end of the slab (see FIG. 5B). While the small-diameter portion 22 of the pile 20 is being inserted into the mud 31, the upper surface of the mud 31 inside the hollow portion of the pile 20 and the upper surface of the mud 31 outside the pile 20 are dependent on the settling speed of the pile 20. Are almost the same height.

When the pile 20 is set and the large-diameter portion 21 of the pile 20 is also inserted into the excavation hole 10, the mud 31 is provided at the joint between the small-diameter portion 22 and the large-diameter portion 21 as shown in FIG. By flowing into the pile 20 also from the inflow part 24, the head difference of the mud 31 inside and outside the pile 20 is small or small. Here, since the mud 31 composed of earth and sand and soil cement has a predetermined viscosity, the mud 31 filled in the large-diameter portion 21 is the lower end of the pile 20 located far from the large-diameter portion 21. It is assumed that it is more easily filled by the inflow from the inflow portion 24 closer to the large-diameter portion 21 than the opening.
Therefore, even if the tip of the pile 20 reaches the enlarged excavation hole 10b and is inserted into the root hardening liquid 30 in the enlarged excavation hole 10b, the root hardening liquid 30 flows into the pile 20 from the tip of the pile 20. As a result, the properties of the root hardening liquid 30 in the enlarged excavation hole 10 are maintained in a desired state, and a decrease in the supporting force in the root hardening bulb portion is prevented.

  Further, when sinking the large diameter portion 21 larger than the small diameter portion 22, the mud 31 is caused to flow into the pile 20 from the inflow portion 24 provided at the joint portion between the small diameter portion 22 and the large diameter portion 21 and extending vertically. However, the sedimentation of the pile 20 is performed, so that the resistance at the time of sedimentation of the large-diameter portion 21 protruding from the small-diameter portion 22 is suppressed by the inflow portion 24 and the lateral movement of the pile 20 is suppressed. Also do. Moreover, in this embodiment, since the taper is formed so that the lower end surface of the rib panel 23 is further directed upward as it goes to the outer diameter, the settling of the pile 20 is facilitated while suppressing lateral deflection. Yes.

Further, when a vertical load is applied to the pile 20 after construction, the load concentrates on the lower end portion of the small diameter portion 22 and the rib panel 23 and on the upper end portion of the large diameter portion 21 and the rib panel 23. By making the joining angle θ2 between the small diameter portion 22 and the lower end portion of the rib panel 23 and the joining angle θ1 between the large diameter portion 21 and the upper end portion of the rib panel 23 both acute (when viewed from the notch side, an obtuse angle). As a result of relaxing the stress concentration at the load concentration position, the pile 20 is prevented from yielding at the joint portion between the small diameter portion 22 and the large diameter portion 21 and the rib panel 23.
Here, in the above description, the case where the head-expanded pile 20 is made of steel pipe is exemplified, but it may be made of concrete or other ready-made pile 20.

  Moreover, in the said description, joining of the large diameter part 21 and the small diameter part 22 is comprised from the some rib panel 23, and the space between the rib panels 23 is made into the inflow part 24, However, It is not limited to this. The joining of the large diameter portion 21 and the small diameter portion 22 may be a joining structure that is joined by, for example, an annular plate member. At that time, a hole may be provided in the plate member to form an inflow portion.

  Moreover, although the case where the inflow part 24 is provided in the junction part of the large diameter part 21 and the small diameter part 22 is illustrated in the said description, it is large with the inflow part 24 of a junction part instead of providing in the said junction part. It is good also as an inflow part by making a hole in the side surface of the diameter part 21. In addition, when the hole is formed in the large diameter part 21, the adhesive strength of the pile 20 and the soil cement improves because the mud 31 used as the soil cement communicates through the hole.

In the present embodiment, the upper portion of the large-diameter stirring blade 8 provided on the upper side of the excavating rod 3 is enlarged so that the upper portion of the excavation is expanded by one excavation. In addition, by providing a bit on the outer peripheral side of the large-diameter agitating blade 8, the upper portion of the excavation hole 10 is efficiently expanded. Although it is not necessary to provide a bit, it is necessary to increase the strength of the large-diameter agitating blade 8 and to make sure that expanded excavation is possible. Further, the upper part of the excavation hole 10 is enlarged and excavated again by a large-diameter stirring blade 8 having a large protruding amount, but the cement milk injected from the ejection hole 12 at the tip of the excavation rod 3 has an enlarged large diameter on the upper side. It is hard to be supplied to the part 21 minutes. For this reason, if the ratio of the earth and sand is relatively increased as it is, the quality of the mud 31 is deteriorated and the strength at the upper part is deteriorated accordingly. However, in the present embodiment, the second excavation rod member 2 also uses cement milk. As a result, the newly expanded and expanded excavated cement milk can be properly supplied to the upper part of the excavation hole 10. As a result, even if the upper part of the excavation hole 10 is expanded and excavated, a sufficient quality soil cement can be secured.
In addition, formation of the excavation hole 10 is not limited to the construction method of this embodiment. For example, the upper part of the excavation hole 10 may be excavated using the enlarged bit 5 as in the conventional example, or the upper part of the excavation hole 10 may be separately excavated with a different excavation rod.

Further, in the above embodiment, the explanation is made so that the cement milk at the time of excavation is injected into the excavation hole 10, but at the time of excavation, the excavating liquid such as water is injected, and the cement milk is injected at the time of mixing and stirring. May be.
In addition, when the head-expansion pile 20 of the said structure is diverted to a driving pile, the space between rib panels is block | closed with soil, and the said soil does not enter into the pile 20. FIG. That is, when the head-expanded pile 20 having the above configuration is a driven pile, no inflow portion exists. Only when used as a pile to be laid, the rib panel acts as an inflow part.

The examination result about the junction part shown in FIG. 2 is shown.
Under the conditions described below, a joint structure with higher cost performance was evaluated by FEM analysis in comparison with performance and cost due to differences in the joint angles θ1, θ2, lap length L, and the number n of rib panels.
Pile diameter D2 of the small diameter portion 22: φ500 mm or more and φ1200 mm or less Pile diameter D1 of the large diameter portion 21: φ750 mm or more and φ1800 mm or less Pile head magnification (D1 / D2): 1.2 to 1.5 times Pile thickness t1, t2 : 1% ≦ t1 / D1, t2 / D2 ≦ 3.17%
(T1: thickness of the large diameter portion 21, t2: thickness of the small diameter portion 22)

“Necessary range to satisfy performance based on FEM analysis results”
According to the FEM analysis results, the three factors of the joining angles θ1, θ2, the wrap length L, and the number of rib panels satisfying the required performance in all of the plate thickness diameter ratios (t1 / D1, t2 / D2) at each heading magnification. The range of was as follows.
10 degrees ≦ θ1, θ2 ≦ 90 degrees L = 0.0 to 0.8 × D2
Number of rib panels n = 8 to 16

"Cost comparison based on FEM analysis"
Among the combinations of factors (θ1, θ2, L, n) that satisfy the required performance at each plate thickness-diameter ratio at each heading magnification, economical specifications were examined by FEM analysis.
The following factors were considered in the cost estimation.
・ Lap length L: Waste of steel pipe material cost due to overlap of steel pipe ・ Rib panel height L1, L2: Welding cost and rib material cost for joining ・ Number of rib panels n: Rib material cost and welding for joining Expense

The trend of cost comparison is as follows.
In order to alleviate stress concentration at the joint portion of the rib panel, the sharper the joint angles θ1 and θ2, the more advantageous the structure.
(If the same rib panel is installed, the sharper angle requires fewer ribs.)
-If the angle is too acute, the required rib panel height (L1, L2) becomes long, and the welding costs and material costs for mounting become high.
-At the same angle, the longer the lap length L, the more the number of ribs can be reduced. However, the cost is the steel pipe material cost for the overlap of steel pipes, and the welding cost for installation (number n, rib panel height L1, L2 Depending on the thickness ratio of each head expansion magnification.

“Specifications with high cost performance based on trial calculation results”
From the above examination results, it was found that the specifications with the highest cost performance according to each thickness ratio at each head-expansion magnification vary in each case, but are within the following ranges.
10 degrees ≦ θ1, θ2 ≦ 45 degrees Lap length L = 0 to 0.4 × D2
Therefore, it is preferable to design so as to satisfy this condition. For example, based on the complexity of cost and specifications, the wrap length L = 0.3 × D2 and the joining angle θ1 = θ2 = 30 degrees are fixed, and based on this value, the rib panel according to the head expansion magnification and the plate thickness-diameter ratio is fixed. The required number n is determined.

It is a side view which shows the head-expansion pile which concerns on embodiment based on this invention. It is a figure explaining the joining structure of the large diameter part and small diameter part which concern on embodiment based on this invention, (a) is sectional drawing, (b) is a top view. It is a figure explaining construction of a pile concerning an embodiment based on the present invention. It is a figure which shows the relationship between the pile and mud etc. which concern on embodiment based on this invention. It is a figure explaining the conventional subject.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st excavation rod member 2 2nd excavation rod member 3 Excavation rod 4 Excavation bit 5 Expansion bit 6, 7 Small diameter stirring blade 8 Large diameter stirring blade 9 Rotation drive part 10 Excavation hole 10b Expansion excavation hole 12 Lower ejection hole 20 Expanded pile 21 Large diameter portion 22 Small diameter portion 23 Rib panel 24 Inflow portion θ1, θ2 Joining angles θ1, θ2

Claims (2)

A prefabricated pile used in the construction method of a pile in which a hollow ready-made pile is sunk in an excavation hole formed by excavation first, and the head has a large-diameter portion whose diameter is larger than its lower side. In the pile,
An inflow portion into which a fluid can flow from the outside of the pile toward the inside of the pile with respect to at least one of the joint portion between the large diameter portion and the small diameter portion below the large diameter portion and the side surface of the large diameter portion. Expanded pile characterized by providing. The joining structure of the small diameter portion and the large diameter portion is configured by connecting a plurality of radially arranged ribs between the outer diameter surface of the upper portion of the small diameter portion and the inner diameter surface of the lower portion of the large diameter portion, and Between the plurality of ribs constitute the inflow portion,
In the side view, the joining angle of the lower end of the rib with respect to the outer diameter surface of the upper portion of the small diameter portion and the joining angle of the upper end of the rib with respect to the inner diameter surface of the lower portion of the large diameter portion are both acute angles to reduce the concentrated stress. The expanded head pile according to claim 1.

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