JP7284104B2 - Method for constructing cast-in-place concrete piles and concrete structures - Google Patents

Description

The present invention relates to cast-in-place concrete piles and methods of constructing concrete structures.

Concrete structures have different acting stresses depending on the location, and the required design bearing capacity differs from location to location. For example, cast-in-place concrete piles generally experience greater stress during an earthquake as they go up. Therefore, when designing a cast-in-place concrete pile, it is common to design the entire pile according to the concrete strength and cross-sectional dimensions that ensure the necessary bending and shear strength at the pile head.
However, the design yield strength required for the pile head where the bending stress and shear stress are maximum may greatly exceed the design yield strength required for other portions. Therefore, if the concrete strength of the entire pile is designed based on the pile head, the cost may increase.
Therefore, Patent Document 1 discloses a cast-in-place concrete pile that can secure the required strength for each part by increasing the amount of cement in the concrete as it goes from the bottom of the pile body to the middle part of the pile body and the head of the pile body. It is In Patent Document 1, concrete with a different mix is poured from about 2m below the planned height (for example, the boundary between the bottom of the pile body and the middle part of the pile body) for changing the mix of concrete of the cast-in-place concrete pile. ing.
In the cast-in-place concrete pile, since the tip of the tremie pipe is inserted into the existing concrete, the existing concrete is spread out by the concrete that is placed later. The behavior of the expanded concrete changes depending on the cross-sectional dimensions of the concrete structure, the arrangement of reinforcing materials such as reinforcing bars, the insertion depth of the tremie pipe used for concrete placement into the already placed concrete, and the like. Therefore, if the timing for switching the mixing ratio of the placed concrete is set at a constant depth from the changing point of the concrete mixing ratio, the changing point of the concrete may not be formed as designed.

JP 2006-16787 A

An object of the present invention is to solve the above problems. The object of the present invention is to propose a cast-in-place concrete pile having a set structure and a method of constructing a concrete structure.

The cast-in-place concrete pile of the present invention for solving the above-mentioned problems is formed by placing an upper concrete made of a different type of concrete from the lower concrete on the lower concrete, and comprising a hoop bar. A plurality of annular members arranged at predetermined intervals in the vertical direction are provided inside the . It is arranged between the height position of the lower end and 1000 mm or less below .
When the upper concrete is supplied below the pre-casting height, the area of the upper concrete expands outward, pushing the lower concrete upward while pushing it outward. However, the cast-in-place concrete pile of the present invention, Since it is difficult for the upper concrete to spread outside the annular member disposed inside the hoop reinforcement, the height of the lower concrete pushed up along the outer surface (hole wall of the borehole) can be limited. By reducing the height of the lower concrete that is pushed upwards from the pre-placement height, the height of the area where the lower concrete is switched to the upper concrete is reduced, and as a result, the quantity of the upper concrete can be reduced. , can construct reasonable cast-in-place concrete piles.

In addition, it is preferable that the annular member arranged on the uppermost stage is arranged 1500 mm or less above the height position of the concrete placing surface where the supply of the lower concrete is stopped. In this way, the lower concrete pushed up above the pre-placement height can be guided along the annular member.

A method of constructing a concrete structure according to the present invention is a method of constructing a concrete structure in which an upper concrete made of a different type of concrete from that of the lower concrete is placed on the lower concrete, and an excavation is performed to form an excavation hole in the ground. a rebar arrangement step of arranging a reinforcing bar cage in which a guide member is arranged inside the main reinforcement in the excavation hole; and a first placing step of supplying the lower concrete to a preset pre-placement height; a second placing step of starting supply of the upper concrete from an upper concrete supply start height lower than the preceding placing height and supplying the upper concrete to a preset switching completion height; and and a third placing step of supplying the upper concrete above the height. The guide members are arranged within a range from a height position of 1000 mm or less below the upper concrete supply starting height position to a height position of 1500 mm or less above the preceding placing height position. Further, in the second placing step, the upper concrete is supplied to the inside of the guide member below the pre-placement height, and a part of the lower concrete is placed outside the guide member by the pre-placement. Pushed upwards above height.
When the upper concrete is supplied below the pre-placement height, the area of the upper concrete expands outward, pushing the lower concrete outward while pushing it upward. According to the present invention, the upper concrete is guided. Since it becomes difficult to spread outside the member, it is possible to limit the height of the lower concrete pushed up along the outer surface (bore wall of the borehole). By reducing the height of the lower concrete that is pushed upwards from the pre-placement height, the height of the area where the lower concrete is switched to the upper concrete is reduced, and as a result, the quantity of the upper concrete can be reduced. , it is possible to construct rational concrete structures.

According to the cast-in-place concrete pile and the concrete structure construction method of the present invention, when concrete of different types is continuously placed in the height direction, the change point of the strength of the placed concrete is rationally set. becomes possible. As a result, the quantity of upper concrete can be reduced, and an economical concrete structure can be constructed.

It is a sectional view showing a part of cast-in-place concrete pile concerning an embodiment of the present invention. Fig. 2 is a cross-sectional view showing each step of a cast-in-place concrete construction method, wherein (a) is an excavation step, (b) is a reinforcing bar arrangement step, (c) is a first placing step, and (d) is a second placing step. Step (e) is the third placing step. It is a perspective view which shows typically the upper concrete supplied below pre-placement height. FIG. 4 is a perspective view schematically showing an annular region; FIG. 10 shows the results of an analysis performed on the construction method of cast-in-place concrete piles, showing the distribution of concrete at the end of placing for each truck mixer of a comparative example. FIG. FIG. 5 shows the results of analysis performed on the construction method of cast-in-place concrete piles, showing the distribution of concrete at the end of placing for each truck mixer of the example. It is the analysis result which was implemented about the construction method of the cast-in-place concrete pile, and (a) is the concrete distribution of a comparative example, (b) is the concrete distribution of an Example.

In this embodiment, in the cast-in-place concrete pile 1, as shown in FIG. A case of continuous casting will be described. FIG. 1 is a cross-sectional view showing part of a cast-in-place concrete pile 1 of this embodiment. In the construction method of the cast-in-place concrete pile 1 (concrete structure) of this embodiment, the upper concrete 3 having a higher design standard strength than the lower concrete 2 is placed on the lower concrete 2 . By doing so, it is possible to increase the concrete strength of the upper portion of the pile where stress increases during an earthquake.
The cast-in-place concrete pile 1 is provided with a reinforcement cage 4 formed by combining a main reinforcement 41 and a hoop reinforcement 42.例文帳に追加The reinforcing bar cage 4 includes guiding bars (guiding members) 6 arranged inside the hoop bars 42 . The guide bars 6 of the present embodiment include a plurality of second hoop bars (annular members) 61 arranged at predetermined intervals in the vertical direction, and second hoop bars (annular members) 61 arranged at intervals in the circumferential direction. and vertical bars 62 that support the hoop bars 61 .

Hereinafter, a construction method of the cast-in-place concrete pile 1 of this embodiment will be described with reference to FIG. FIG. 2 is a sectional view showing each step of the construction method of the cast-in-place concrete pile 1. As shown in FIG. The construction method of the cast-in-place concrete pile 1 includes an excavation step of forming an excavation hole 11 in the ground G, a reinforcing bar arrangement step of arranging reinforcing bars of the cast-in-place concrete pile 1 in the excavation hole 11, and a pre-set pre-casting step. A first placing step of supplying the lower concrete 2 into the excavated hole 11 up to the installation height _HL , and a second placing step of supplying the upper concrete 3 into the excavated hole 11 up to a preset switching completion height H. and a third placing step of supplying the upper concrete 3 above the switching completion height H.

In the excavation step, as shown in FIG. 2(a), an excavation hole 11 is formed by excavating the ground G. As shown in FIG. The excavated hole 11 is formed in a size that can secure the designed diameter and length of the cast-in-place concrete pile 1 . In this embodiment, the excavation hole 11 is formed by an earth drilling method in which the drilling bucket 7 is rotated for excavation. In addition, the excavation construction method of the excavation hole 11 is not limited.

In the bar arrangement process, as shown in FIG. 2B, a reinforcing bar cage 4 in which main bars 41 and hoop bars 42 are combined is placed in the excavation hole 11 . The reinforcing bar cage 4 is erected so as to secure a predetermined covering thickness from the hole wall of the excavation hole 11.例文帳に追加At this time, a tremie pipe 5 is laid in the center of the reinforcing bar cage 4 . Further, in the reinforcing bar cage 4, a guiding bar 6 is arranged inside the main bar 41.例文帳に追加The guide muscle 6 comprises a second hoop muscle 61 and a longitudinal muscle 62 . The second hoop bar 61 has an inner diameter smaller than the inner diameter of the hoop bar 42 of the reinforcing bar cage 4 . The second hoop reinforcements 61 are arranged at predetermined intervals in the height direction within a predetermined range. The second hoop reinforcements 61 arranged vertically are fixed to a plurality of vertical reinforcements 62 arranged at intervals in the circumferential direction. The vertical reinforcements 62 are supported by horizontal reinforcements (not shown) extending from the main reinforcements 41 or the hoop reinforcements 42 forming the reinforcing bar cage 4 . In addition, when the second hoop reinforcement 61 is supported by the horizontal reinforcement, the vertical reinforcement 62 may be omitted. In addition, the _second hoop bar 61 is omitted, and a plurality of reinforcing bars (vertical bars 62 ) may be arranged at predetermined intervals in the circumferential direction as the guiding reinforcements 6 .
The guide bars 6 are arranged within a range from a height position equal to or lower than the upper concrete supply start height _HT to a height position equal to or higher than the pre-placement height _HL . In this embodiment, the lower end of the range in which the guide bars 6 are arranged is positioned 600 mm below the upper concrete supply start height _HT . In addition, the upper end of the range in which the guide bars 6 are arranged shall be positioned 300 mm above the pre-placement height _HL . The range in which the guide bars 6 are arranged is between the lower end (lowermost second hoop bar 61) and _the upper end ( There is no limitation as long as the uppermost second hoop reinforcement 61) is at a position equal to or higher than the pre-placement height _HL . For example, the height difference between the lower end of the guide bar 6 and the upper concrete supply start height _HT is 1000 mm or less, and the height difference between the upper end of the guide bar 6 and the pre-placement height _HL is 1500 mm or less, more preferably 500 mm or less. may be set so that

In the first placing step, the lower concrete 2 is placed to the pre-placement height _HL . As shown in FIG. 2(c), the lower concrete 2 is supplied from the lower end of the excavated hole 11 using a tremie pipe 5 inserted into the excavated hole 11 formed in the ground. The lower concrete 2 is placed in a state where the tremie pipe 5 is fixed until a predetermined range of the lower part of the tremie pipe 5 is buried in the placed concrete, and then the tremie pipe 5 is raised as the concrete placing surface 2a rises. . The tremie pipe 5 may be raised each time a certain amount of concrete is placed, or may be raised in accordance with the rise of the concrete placing surface 2a. The pre-placement height _HL is set below the switching completion height H. That is, from the estimated value (design value) of the stress acting on the cast-in-place concrete pile 1, the switching completion height H (the range in which the concrete strength is increased) is set, and the concrete is completely switched at this switching completion height H. , set the pre-placement height _HL .

In the second placing step, as shown in FIG. 2(d), the tip of the tremie pipe 5 is positioned at the upper concrete supply start height _HT lower than the preceding placement height _HL , and the upper portion Supply of concrete 3 is started. The upper concrete 3 is supplied while the height position of the tremie pipe 5 is fixed until the concrete placement surface reaches the switching completion height H. When the upper concrete 3 is supplied to the inner side of the guide bar 6 below the pre-placement height _HL , the lower concrete 2 is pushed away by the upper concrete 3 . As shown in FIG. 3, the upper concrete 3 is supplied in a semielliptical or semicircular shape (tip portion 31) immediately below the tremie pipe 5 at the start of supply in the lower concrete 2, and then immediately above the tip portion 31. and, as shown in FIG. On the other hand, since the upper concrete 3 is supplied, the lower concrete 2 having a volume equivalent to that of the upper concrete 3 supplied to the lower side of the pre-placement height _HL is increased to the pre-placement height _HL. Move from the bottom of the to the top of the pre-placement height. The lower concrete 2 moving above the pre-placement height _HL is pushed upward outside the guide bars 6 . The upper end of the lower concrete 2 pushed up by the outer portion of the guide bar 6 (annular region 21 centered on the tremie pipe 5) is positioned below the switching completion height H.

In the third step, the upper concrete 3 is placed up to the pile head. As shown in FIG. 2( e ), the upper concrete 3 is placed while pulling up the tremie tube 5 with the lower end of the tremie tube 5 inserted into the already placed concrete. By supplying the upper concrete 3 through the tremie pipe 5, the upper concrete 3 is supplied above the switching completion height H.

The pre-placement height _HL is set so that the upper end of the lower concrete 2 pushed up by the upper concrete 3 is positioned at the switching completion height H or less.
In this embodiment, the pre-placement height _HL is calculated by Equation (1). Equation 1 is obtained by subtracting the height h of the annular region 21 of the lower concrete 2 pushed upward by the supply of the upper concrete 3 from the switching completion height H set based on the acting stress of the cast-in-place concrete pile 1. This is for calculating the pre-placement height _HL . The height h of the annular region 21 is obtained by assuming that the volume V of the upper concrete 3 supplied below the pre-placement height _HL is the volume of the lower concrete 2 moved to the annular region 21. Calculated from volume. Here, the upper concrete 3 supplied below the pre-placement height _HL is the total volume of the tip portion 31 and the cylindrical portion 32, as shown in FIG. On the other hand, as shown in FIG. 4, the annular region 21 is a cylindrical body having an inner diameter φ _i and an outer diameter φ ₀ . Here, the inner diameter φ _i is the inner diameter of the guide bar 6 and the outer diameter φ ₀ is the outer diameter of the cast-in-place concrete pile 1 . Also, the diameter _φr of the cylindrical portion is the inner diameter of the guide bar 6 .

H _L =H−h Expression 1
h=V/S
V=V1+V2
S=π/4×(φ _o ² −φ _i ² )
V1=πφ _r ² /4×Δh
V2=2/3×πφ _r ² /4×Δh ₀
H. : Switching completion height h : height of annular region V : Volume of upper concrete supplied below the pre-placement height V1 : Volume of the cylindrical portion of the upper concrete supplied below the pre-placement height V2 : Volume of the top part of the upper concrete supplied below the pre-placement height S : Cross-sectional area of the annular area φ _o : Outer diameter of the annular area φ _i : Inner diameter of the annular area φ _r : Diameter of the cylindrical portion of the upper concrete supplied below the pre-placement height Δh : Depth of the tremie pipe inserted into the lower concrete in the second step Δh ₀ : Lower outflow depth, which is the distance from the lower end of the upper concrete supplied in the second step to the tip of the tremie pipe

As described above, according to the method for constructing a concrete structure of the present embodiment, the changeover of concrete can be completed near the designed changeover completion height. When placing concrete, it becomes possible to rationally set the change point of the strength of the placed concrete. As a result, the cast-in-place concrete pile 1 having the necessary bearing strength can be economically constructed.
When the upper concrete 3 is supplied below the pre-placement height, the region of the upper concrete 3 expands outward, pushing the lower concrete 2 outward while pushing it upward, but the concrete structure of this embodiment. According to the construction method of the object, since the upper concrete 3 is less likely to spread outside the guide bars 6, the height of the lower concrete 2 pushed up along the outer surface (hole wall of the excavation hole 11) can be limited. By reducing the height of the lower concrete 2 to be pushed upward from the pre-placement height, the height of the region where the lower concrete 2 is switched to the upper concrete 3 is reduced, and as a result, the quantity of the upper concrete 3 is reduced. Therefore, a rational cast-in-place concrete pile 1 can be constructed.
Since the lower concrete 2 is expected to move on the outer peripheral side of the guide bar 6 above the pre-placement height _HL , by assuming that the outer portion of the guide bar 6 is an annular region, the switching completion height H can be calculated more rationally.

Next, the results of the analysis performed for the construction method of the cast-in-place concrete pile 1 of this embodiment will be described.
In this analysis, hoop reinforcements 42 were arranged at intervals of 160 mm so as to cover a concrete pile having a pile length of 8 m and a pile diameter of 2.4 m so that the covering was 100 mm. Further, at a position 300 mm inside the hoop bar 42, as the guide bar 6, second hoop bars 61 were arranged at intervals of 160 mm. The second hoop reinforcement 61 was arranged in a range of 1.4m to 3.6m above the pile bottom. Concrete piles were constructed by continuously placing an upper concrete 3 of high-strength concrete on a lower concrete 2 of ordinary concrete. Table 1 shows the specifications of the upper concrete 3 and the lower concrete 2.
Concrete was supplied by dropping it from the upper end of the tremie pipe 5, and the behavior of the concrete placed for each truck mixer was analyzed. Table 2 shows concrete placement conditions (concrete type, placement amount, rising height, etc. for each truck mixer).
In addition, as a comparative example, the same method was used to analyze a case in which the guiding muscle 6 (second hoop muscle 61) was not arranged.
FIG. 5 is an axisymmetric model of concrete distribution at the end of placing each truck mixer in the comparative example, and FIG. 6 is an axisymmetric model of concrete distribution at the end of placing each truck mixer in the example. Also, FIG. 7(a) is an axisymmetric model of the final concrete distribution of the comparative example, and FIG. 7(b) is an axisymmetric model of the final concrete distribution of the example.

As shown in the fifth diagram of FIG. 5, in the comparative example, the upper concrete 3 spreads in a bulbous shape at the tip of the tremie pipe 5 and rises in a columnar shape from the periphery of the tremie pipe 5 while maintaining its diameter. After that, when the concrete from the sixth and subsequent truck mixers was put in, the upper concrete 3 spread over the concrete placement surface. As a result, the diameter of the upper concrete 3, which spreads like a bulb, remains about the inner diameter of the reinforcing bar cage 4. On the other hand, outside the upper concrete 3 (reinforcement cage 4), the lower concrete 2 rose while being pressed against the outer surface. That is, since the upper concrete 3 spreads widely inside the reinforcing bar cage 4, the lower concrete 2 pushed up by the upper concrete 3 rises greatly. As a result, as shown in FIG. 7(a), the switching section where the lower concrete 2 and the upper concrete 3 coexist was 2.1 m above the pre-placement height _HL .
As shown in the fifth figure of FIG. 6, also in the example, the upper concrete 3 spreads in a bulbous shape at the tip of the tremie pipe 5 and rises in a columnar shape while maintaining its diameter. After that, when the concrete from the sixth and subsequent truck mixers was put in, the upper concrete 3 spread over the concrete placement surface. As a result, the diameter of the upper concrete 3, which spreads like a bulb, remains about the inner diameter of the guide bar 6. That is, in the embodiment, by arranging the guide bars 6 in the vicinity of the tip of the tremie pipe 5, the range (diameter) over which the upper concrete 3 spreads can be reduced. By reducing the range (diameter) over which the upper concrete 3 spreads, the volume of the outer periphery of the upper concrete 3 increases, so that the height of the lower concrete 2 can be suppressed. As a result, as shown in FIG. 7(b), the switching section (height) widened above the pre-placement height _HL was 1.4, which was smaller than in the comparative example. If the switching section can be made smaller, the amount of high-strength concrete placed can be reduced, and as a result, rational structural design and construction become possible.

Although the embodiments according to the present invention have been described above, the present invention is not limited to the above-described embodiments, and the constituent elements described above can be appropriately modified without departing from the scope of the present invention.
For example, in the above-described embodiment, a case of constructing a cylindrical cast-in-place concrete pile 1 has been described, but the concrete structure is not limited to the cast-in-place concrete pile 1 .
In the above-described embodiment, as the upper concrete 3, concrete having a higher design standard strength than the lower concrete 2 is cast. There is no limitation as long as the type of concrete is different from that of 2.
Further, in the above-described embodiment, the case where concrete is placed while pulling up the tremie tube 5 in the first placing process and the third placing process has been described, but whether or not the tremie tube 5 is pulled up during concrete placing is determined as appropriate. It may be determined, and the tremie tube 5 may be placed in a fixed state. Similarly, in the second placing process, the case where concrete is placed with the height position of the tremie tube 5 fixed has been described, but in the second placing process as well, the concrete is placed while pulling up the tremie tube 5. You may
In the above-described embodiment, the second hoop bar 61 is used as the annular member, but the material forming the annular member is not limited to reinforcing bars.

REFERENCE SIGNS LIST 1 cast-in-place concrete pile 11 drill hole 2 lower concrete 3 upper concrete 4 reinforcing bar cage 41 main bar 42 hoop bar 5 tremie pipe 6 guiding bar (guiding member)
61 Second hoop muscle (annular member)

Claims (3)

A cast-in-place concrete pile formed by joining an upper concrete made of a different type of concrete from the lower concrete on the lower concrete,
A plurality of annular members arranged at predetermined intervals in the vertical direction inside the hoop muscles,
A casting-in-place characterized in that the annular member arranged at the lowest stage is arranged from the height position of the lower end of the tremie pipe when the placing of the upper concrete is started to 1000 mm or less below. Concrete pile. 2. The method according to claim 1, wherein said annular member arranged at the uppermost stage is arranged at a height of 1500 mm or less above a concrete placing surface where supply of said lower concrete is stopped. Cast-in-place concrete piles. A method for constructing a concrete structure in which an upper concrete made of a different type of concrete from the lower concrete is placed on the lower concrete, comprising:
A drilling step of forming a drill hole in the ground;
A reinforcement arrangement step of arranging a reinforcing bar cage in which a guide member is arranged inside the main reinforcement in the excavation hole;
a first placing step of supplying the lower concrete to a preset pre-placement height;
a second placing step of starting to supply the upper concrete from an upper concrete supply start height lower than the preceding placing height, and supplying the upper concrete to a preset switching completion height;
a third placing step of supplying the upper concrete above the switching completion height,
The guide member is disposed within a range from a height position of 1000 mm or less below the upper concrete supply start height position to a height position of 1500 mm or less above the preceding placing height position,
In the second placing step, the upper concrete is supplied to the inside of the guide member below the pre-placement height, and part of the lower concrete is above the pre-placement height outside the guide member. A method for constructing a concrete structure, characterized in that both are pushed upward.

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