JPH0663631U - Concrete cast-in-place - Google Patents

Abstract

(57) [Summary] [Purpose] To provide a concrete cast-in-place pile that sufficiently supports a building and has sufficient earthquake resistance to withstand the vibration of the upper building, and that can minimize the size increase of the pile diameter and the like. [Structure] The pile leg portion side of the pile hole 4 dug in the ground is formed of a normal strength concrete layer 3 and the pile head side of which the bending stress is large is formed of a high strength concrete layer 2 capable of withstanding the bending stress.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a cast-in-place pile that is cast at a construction site as a foundation of a building, and particularly to a concrete cast-in-place pile that has a large bending resistance and is excellent in earthquake resistance.

[0002]

[Prior art]

Conventionally, as a concrete cast-in-place pile 1a to be cast at a construction site, the one shown in FIG. 11 has been generally used. This concrete cast-in-place pile 1a is composed of a concrete layer 3a of ordinary strength such as FC210 to FC240, and a pile reinforcing bar 7b is embedded therein. To make this concrete cast-in-place pile 1a, as shown in Fig. 9, excavate a pile hole 4a of an appropriate depth in the ground, and as shown in Fig. 10, insert pile reinforcing bars 7b into the anti-hole 4a while inserting it. After that, it is formed by pouring concrete with a tremie pipe. Further, as shown in FIG. 12, a concrete cast-in-place pile 1b in which a diameter-expanded portion 5a is provided at the bottom of the pile hole 4a is also conventionally used. By forming the expanded diameter portion 5a, the concrete cast-in-place pile 1b has a diameter smaller than that shown in FIG. 11 by the amount of the expanded diameter portion 5a. That is, D _T = D _o and D _o > D ₂ . However, even in this case, normal strength concrete is cast and formed over the entire pile hole 4a.

[0003]

[Purpose of the invention: Problems to be solved by the invention]

 Concrete cast-in-place piles 1a, 1b, etc. need to have sufficient strength to support buildings and have sufficient earthquake resistance against vibration of the upper building and ground due to earthquakes. In order to satisfy the above-mentioned conditions of strength and earthquake resistance in the conventional concrete cast-in-place piles 1a and 1b, the structure of the pile reinforcing bar 7b is examined along with the state of stress at the time of seismic load, and the pile diameter is made to be a diameter that matches it. However, there is a problem that the amount of concrete used increases. Further, the concrete used for the conventional concrete cast-in-place piles 1a and 1b has a normal strength such as FC210 to FC240, and if the whole is made of high strength concrete such as FC320, the cost is high. The problem arises.

The present invention solves the above problems and eliminates the size increase of pile diameters, etc., reduces the amount of excavation in the ground, and provides sufficient support to withstand the weight of buildings and ground vibrations. The purpose is to provide a concrete cast-in-place pile that has strength, bending strength, and earthquake resistance.

[0005]

[Constitution of the present invention: means for solving problems]

 In order to achieve the above object, the present invention is a concrete cast-in-place pile formed by placing concrete with reinforcing bars as reinforcing material in a pile hole dug at a construction site, and at least the pile hole This is to construct a concrete cast-in-place pile in which the pile head side of the upper end is made of high-strength concrete. More specifically, the high-strength concrete is approximately 5 times the pile diameter from the upper end of the pile hole. It features concrete cast-in-place piles that are formed only in length.

[0006]

[Action]

 The bending stress generated in the pile due to the vibration of the upper building is small in the pile leg part (hole side) and the middle part of the pile, and large in the pile head. The present invention uses high-strength concrete for the pile head, which has large bending stress, and uses general concrete. As a result, it is possible to withstand the above-mentioned bending stress, eliminate the increase in size such as the pile diameter, and thereby reduce the amount of excavation in the ground. Further, in order to realize the pile structure of the present invention, after excavating the pile hole and inserting a reinforced basket, first, ordinary concrete is placed halfway, and the inner wall of the pile hole of the injected bentonite liquid etc. The method of completing cast-in-place piles by removing expansive clay to prevent collapse and preventing underwater concrete treatment, and by pouring high-strength concrete into the area corresponding to the pile head is adopted.

[0007]

【Example】

 An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is an axial sectional view showing the overall structure of the concrete cast-in-place pile of this embodiment, and FIGS. 2 to 7 are the construction methods performed at the construction site to form the concrete cast-in-place pile of this embodiment. FIG. 8 is an explanatory axial cross-sectional view showing an example, and FIG. 8 is a stress diagram showing an outline of bending stress generated in a concrete cast-in-place pile due to vibration of the upper building or the like.

As shown in FIG. 1, the concrete cast-in-place pile 1 of this embodiment has a high strength concrete layer 2 at the pile head side portion (indicated by the dimension a ₁ ), and the pile middle portion and the pile leg side. The part (indicated by the dimension a ₂ ) is formed by piles of a concrete layer 3 of ordinary strength and having a total length a. Note that a ₁ ≈5D ₁ and a = a ₁ + a ₂ . In this embodiment, FC320 or FC370 is used as the concrete for the high-strength concrete layer 2, and FC210 to FC270 are used as the concrete for the normal-strength concrete layer 3. The pile holes 4 are those in which the enlarged diameter portions 5 are formed on the pile legs to increase the supporting force. The reinforcing bar cage 7 is interposed in the pile hole 4 and integrally hardened as a reinforcing material for the high-strength concrete layer 2 and the normal-strength concrete layer 3, and the pile head main bar 7a of an appropriate length is exposed to the ground side. And stand upright. Incidentally, when the compared to the concrete place pile 1b of pile diameter D ₂ shown in FIG. 12 when the O urchin pile diameter shown in FIG. 1 using the concrete material of the present embodiment when the D _1, D 2 ₌ 1800 It is sufficient that D ₁ = 1500 [mm] with respect to [mm], the diameter is reduced to about 17 [%], and the amount of concrete is reduced by about 30 [%].

As shown in FIG. 8, the horizontal axis shows the bending stress generated in the concrete cast-in-place pile 1 due to the vibration of the upper building, and the vertical axis shows the depth (length) direction of the pile 1 as illustrated. Bending stress due to such a stress diagram acts. That is, assuming that the total length of the pile is a, a bending stress of σ _m is generated at the intermediate position in the minor direction, and the bending stress becomes almost zero on the pile leg side. On the other hand, the maximum bending stress σ _max occurs on the ground line (GL) side, and a large bending stress occurs on the pile head side. Note that σ _max ≉5σ _m . As can be seen from this stress diagram, sufficient earthquake resistance can be secured by using the high-strength concrete layer 2 only on the pile head side indicated by the dimension a ₁ . On the contrary, when using the concrete layer 3 of ordinary strength corresponding to σ _max , an extremely large diameter is required, and there is a high risk of insufficient strength due to insufficient setting of the pile diameter.

Next, a construction method of the concrete cast-in-place pile 1 of this embodiment at a construction site will be described with reference to FIGS. As shown in FIG. 2, a casing (guide pipe) 9 is driven from the ground surface 8 (GL) to a required depth (the casing 9 may not be necessary, but this embodiment is a case of a benot pile which requires it. Will be explained). The inside diameter of the casing 9 corresponds to the pile diameter. The concrete cast-in-place pile 1 of this embodiment has a pile diameter of about 1.5 [m], and the casing 9 has a length of 7.5 [m], which is about five times the pile diameter. . Therefore, the commonly used ones are applied. Next, as shown in FIG. 3, the excavation work is performed by the excavation tool 10 (for example, a hammer grab), and the pile hole 4 having the enlarged diameter portion 5 in the pile leg portion with the total length a is excavated. The casing 9 serves as a guide for pile construction during excavation. Next, as shown in FIG. 4, the bentonite liquid 12 is supplied into the pile hole 4 which has been excavated by the bentonite liquid supply pipe 11 and the like. Bentonite is composed mainly of montmorillonite, a clay whose weathering part is vitreous such as tuff and quartz trachyte, and is a swelling clay that swells with water and is used to prevent collapse of the inner wall of the anti-hole 4. It The supplied bentonite liquid 12 adheres to the inner wall of the pile hole 4 to form a bentonite layer. Next, as shown in FIG. 5, the rebar cage 7 is inserted into the pile hole 4.

Next, as shown in FIG. 6, ordinary strength concrete FC240 or the like is charged through the tremie pipe 14 or the like to form the ordinary strength concrete layer 3. Next, the bentonite liquid 12 accumulated in the upper part of the pile hole 4 is sucked by a suction pipe or the like not shown. Finally, the high-strength concrete FC320 or the like is charged through the tremie pipe 14 or the like, and the casing 9 is pulled out to form the high-strength concrete layer 2 at the portion of the length a ₁ corresponding to the head of the pile. By the above, the concrete cast-in-place pile 1 shown in FIG. 1 is completed.

In the embodiment described above, the pile diameter D ₁ is 1500 [mm], but of course, an appropriate pile diameter corresponding to the size of the building and the ground structure is adopted. Further, the material of the concrete may be high strength concrete, and is not limited to FC320 to FC370. Further, although the present embodiment has described the one having the expanded diameter portion 5, the present invention is not limited to this. Further, the construction method is not limited to the above construction method. Furthermore, in this embodiment, the high-strength concrete layer 2 is set to about 5 times the pile diameter from the upper end, but when the pile length is extremely long (for example, the pile length is about 20 times the pile diameter), It can be set to about 1/4 of the pile length a. Even in the case of the range of 1/4 · a, the part of the pile head where the bending response is particularly high is reinforced, so that sufficient bearing capacity and seismic resistance can be exhibited. Further, in this embodiment, the two-layer structure of the normal strength concrete layer 3 and the high strength concrete layer 2 is used, but the invention is not limited thereto.

[0013]

[Effect of the present invention]

 According to the present invention, the following remarkable effects are obtained. 1) The diameter of the pile is greatly reduced compared to the one in which the concrete cast-in-place pile is made of concrete of ordinary strength, the amount of concrete can be reduced and the overall cost can be reduced. 2) High strength concrete that can withstand the bending stress is used for the pile head where the bending stress is large, and normal strength concrete is placed on the pile leg where the bending stress is small. Shaped piles can be formed. 3) Since the division range between the high-strength concrete layer and the medium-strength concrete layer is set arbitrarily according to the shape and size of the building and the ground structure, it is easy to construct piles that are the most effective combination at the construction site. Can be formed into 4) It is necessary to pour different types of concrete layers at least twice, but the concrete piling method is not particularly troublesome and is performed in much the same way as ordinary concrete construction, and construction costs do not rise.

[Brief description of drawings]

FIG. 1 is an axial sectional view showing the overall structure of a concrete cast-in-place pile according to an embodiment of the present invention.

FIG. 2 is an axial cross-sectional view showing how a guide rail is placed during concrete construction according to the present embodiment.

FIG. 3 is an axial cross-sectional view showing a state of excavating a pile hole according to the present embodiment.

FIG. 4 is an axial cross-sectional view illustrating an operation of introducing a bentonite liquid according to this embodiment.

FIG. 5 is an axial cross-sectional view for explaining the work of inserting the reinforcing bar cage of the present embodiment.

FIG. 6 is an axial cross-sectional view showing the placing of a normal strength concrete layer according to the present embodiment.

FIG. 7 is an axial cross-sectional view showing a cast state of a high-strength concrete layer in this example.

FIG. 8 is a stress diagram showing the relationship between the pile depth and the bending stress acting on the pile caused by the vibration of the upper building.

FIG. 9 is an axial sectional view showing a pile hole for driving a conventional concrete cast-in-place pile.

FIG. 10 is an axial cross-sectional view showing an inserted state of a reinforcing bar cage in a conventional concrete cast-in-place pile.

FIG. 11 is an axial sectional view showing the entire structure of a conventional concrete cast-in-place pile.

FIG. 12 is an axial sectional view of a conventional concrete cast-in-place pile having an expanded diameter portion on a pile leg portion.

[Explanation of symbols]

 1 Concrete cast-in-place pile 2 High-strength concrete layer 3 Normal strength concrete layer 4 Pile hole 5 Expanded part 7 Reinforcing bar cage 7a Pile head main bar 7b Pile reinforcing bar 8 Ground surface (GL) 9 Casing (guide pipe) 10 Excavator 11 Bentonite liquid supply pipe 12 Bentonite liquid 14 Tremy pipe

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Victory Watanabe 1-25-1 Nishishinjuku, Shinjuku-ku, Tokyo Within Taisei Corporation (72) Inventor Shuichi Matsumoto 1-25-1 Nishishinjuku, Shinjuku-ku, Tokyo Within Taisei Construction Co., Ltd.

Claims (2)

[Scope of utility model registration request] 1. A concrete cast-in-place pile formed by placing concrete using reinforcing bars as reinforcing material in a pile hole dug at a construction site, and at least the pile head side of the upper end of the pile hole is raised. Concrete cast-in-place pile characterized by being formed of high-strength concrete. 2. The length of the high-strength concrete formed is about 5 times the pile diameter from the upper end of the pile hole.
Concrete cast-in-place pile.