Construction method of cast-in-place concrete pile

Abstract

To provide a construction method of a cast-in-place concrete pile allowing good quality concrete to be constructed by making the concrete flow outside of a steel cage through gaps between steel bars of the steel cage so as to reach a cover part.SOLUTION: A construction method of a cast-in-place concrete pile excavating a pile hole in the ground, placing a steel cage in the excavated pile hole and installing concrete in a pile hole in which the steel cage is placed using a tremie pipe provided with an excitation device, promotes fluidity of the concrete by applying vibration on concrete in a pile head part such that the concrete flow outside of the steel cage though gaps between steel bars of the steel cage through excitation of the tremie pipe by operating the excitation device, when installing concrete in an area of dense reinforcement in the pile head part.SELECTED DRAWING: Figure 10

Description

Technical Field

[0001] The present invention relates to a construction method of cast-in-place concrete piles using Tremie pipes.

Background Art

[0002] In recent years, with the increase in the size and performance improvement of excavation machines, it has become possible to construct large-diameter and deep piles. Along with the revision of design and construction guidelines and design requirements, higher performance has been demanded. In particular, due to the review of seismic design, the steel bars at the pile head are especially densely reinforced. In the casting of cast-in-place concrete piles using Tremie pipes inserted into the center of the pile, it has become difficult for concrete to flow outside the steel bars (the covered part).

[0003] In the construction of cast-in-place concrete piles by the all-casing method, the casing tube is pressed in while rotating over the entire length of the excavation hole, and the earth and sand inside the casing tube are excavated and the soil is removed repeatedly with a hammer grab. After reaching the predetermined depth of the ground, hole bottom treatment is performed. After installing the steel cage, concrete is poured into the pile hole using a Tremie pipe. As the concrete is poured, the casing tube and the Tremie pipe are pulled out and recovered. In the cast-in-place concrete pile method, when pouring concrete, the Tremie pipe is inserted to the bottom of the pile hole and the hole bottom is filled with concrete. As the concrete rises, the concrete flows through the spaces between the steel bars of the steel cage due to the overburden pressure caused by the self-weight of the concrete, and the covered part is filled with concrete up to the outside of the steel cage. In addition, in the cast-in-place concrete pile method, the top end part of the concrete deteriorates due to contact with the water and sediment in the directly above hole. Therefore, a surplus of concrete is raised about 1.0 m higher than the top end when the cast-in-place concrete pile is completed. By doing this surplus, where the overburden pressure due to the self-weight of the concrete is small at the pile head, the overburden pressure is increased by the self-weight of the surplus concrete, so that the concrete flows outside the steel cage.

[0004] However, in recent years, due to the review of seismic design, the amount of steel bars at the pile head has increased, resulting in over-dense reinforcement. As a result, with only the overburden pressure caused by the self-weight of the surplus concrete, it becomes difficult for the concrete to flow to the outside of the steel bars (the covered part), and insufficient filling of the concrete in the covered part occurs.

[0005] Typically, to prevent the insufficient flow of fresh concrete between steel bars caused by over-dense reinforcement at the pile head, vibration is generally applied to the concrete in the hole. As a method of applying vibration, a method of inserting a rod-shaped vibration device from above into the concrete at the pile head to vibrate is known (see, for example, Patent Document 1). However, this method may deteriorate the quality of the concrete at the pile head by entraining low-quality concrete accumulated at the upper part of the pile hole into the vibration area.

[0006] There is also a method of providing a ring-shaped protrusion on the tremie pipe and stirring the concrete by moving the tremie pipe up and down (see, for example, Patent Document 2). However, this method applies a large load when moving the tremie pipe up and down, and there is a risk of damage and deformation of the tremie pipe. If the tremie pipe is damaged or deformed, there is a possibility of damage to the inner wall of the pile hole and the casing tube due to contact with the ring-shaped protrusion.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] As described above, in the method of inserting a rod-shaped vibration device from above into the concrete of the pile head and vibrating it, there is a risk of deteriorating the quality of the concrete at the pile head by entraining low-quality concrete accumulated at the upper part of the pile hole into the vibration area. In the method of providing a ring-shaped protrusion on the tremie pipe and stirring the concrete by moving the tremie pipe up and down, there is a risk that the tremie pipe may be deformed or damaged due to a large load being applied when the tremie pipe is moved up and down. Furthermore, when the tremie pipe is damaged or deformed, there is a possibility that the inner wall of the pile hole and the casing tube may also be damaged due to contact with the ring-shaped protrusion.

[0009] In view of the above circumstances, an object of the present invention is to provide a construction method for a cast-in-place concrete pile that can obtain good-quality concrete up to the covering part by flowing the concrete through between the reinforcing bars of the reinforcing cage to the outside of the reinforcing cage without causing damage to the tremie pipe, the inner wall surface of the pile, and the casing tube.

Means for Solving the Problems

[0010] To achieve the above object, the method of the present invention is A construction method for a cast-in-place concrete pile in which a pile hole is excavated in the ground, a reinforcing cage is placed in the excavated pile hole, and concrete is placed using a tremie pipe equipped with a vibration device in the pile hole where the reinforcing cage is placed, When placing the concrete in the over-reinforced area of the pile head, the vibration device is operated to vibrate the tremie pipe, so that vibration is applied to the concrete at the pile head to promote the fluidity of the concrete so that the concrete flows through between the reinforcing bars of the reinforcing cage to the outside of the reinforcing cage. It is a method.

[0011] According to the present invention, when placing concrete in the over-reinforced area of the pile head, by operating the vibration device to vibrate the tremie pipe, vibration is applied to the concrete in the pile head so that the concrete flows through the space between the reinforcing bars of the reinforcing cage to the outside of the reinforcing cage, thereby promoting the fluidity of the concrete. This can prevent the occurrence of insufficient filling of the concrete in the covering part, which is caused by the low overlying pressure due to the self-weight of the concrete in the pile head.

Brief Description of the Drawings

[0012]

Figure 1

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Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments of the construction method of the cast-in-place concrete pile according to the present invention will be described with reference to the drawings. FIGS. 1 to 12 are diagrams showing the construction method of the cast-in-place concrete pile of this embodiment.

[0014] In this embodiment, as the construction method of the cast-in-place concrete pile, the case where the all-casing method is used is assumed, and the description will focus particularly on the construction method of the pile head. However, the present invention is not necessarily limited to the all-casing method, and it can also be adopted in a method of constructing a cast-in-place concrete pile by driving concrete into the pile hole using a tremie pipe.

[0015] The all-casing method is a method of pressing a casing tube into the ground while rotating or swinging it over the entire length and excavating inside the casing tube. The casing tube is a steel pipe used to prevent the collapse of the inner wall of the excavation hole and ensure the excavation diameter as designed. There are connection parts for adding the casing tube at the upper and lower ends of the casing tube. The standard effective length of one is 6m, and there are shorter adjustment casing tubes of 4, 3, 2, and 1m so that the length of the casing tube can be adjusted according to the excavation length.

[0016] The all-casing method has advantages such as being able to suppress ground collapse by pressing the casing tube into the ground while rotating or swinging it, and being able to suppress the occurrence of boiling and piping by equalizing the water level in the excavation hole with the groundwater level.

[0017] In the all-casing method, an excavator 1, a hammer grab 3, a casing tube 5, an auxiliary crane 7, a tremie pipe 9, etc. are used.

[0018] The excavator 1 is a device that performs the swinging or rotary pressing / pulling operation of the casing tube 5. The earth and sand generated by excavation inside the casing tube 5 is discharged to the outside using the hammer grab 3 that moves in and out of the casing tube 5.

[0019] The auxiliary crane 7 is used for the assembly and disassembly of the excavator 1, the excavation work by the hammer grab 3, the handling of the casing tube 5 and the tremie pipe 9, the erection of the steel cage 11, the concrete placement, and the movement operation of the excavator 1, etc. Since relatively long materials such as the steel cage 11, the casing tube 5, and the tremie pipe 9 are frequently moved, a crawler crane is generally used for the auxiliary crane 7.

[0020] Furthermore, although not shown in the figure, at the construction site of the cast-in-place concrete pile, a water storage tank for storing water supplied into the hole and a slush tank for storing the hole water discharged by the concrete placement are also prepared.

[0021] Next, the specific construction procedures of the construction method of the cast-in-place concrete pile of this embodiment will be described. First, at the site, the excavation position of the pile is determined by surveying. After leveling the surrounding ground including the determined excavation position of the pile, as shown in Fig. 1, the excavator 1 is horizontally installed on the leveled ground using the auxiliary crane 7.

[0022] Next, as shown in Fig. 2, the casing tube 5-1 first used for excavation is vertically set on the excavator 1 using the auxiliary crane 7. As shown in Fig. 3, the excavator 1 is operated to start excavation by the swinging or rotary pressing of the first casing tube 5-1. The excavated soil is discharged using the hammer grab 3 inserted into the casing tube 5. When excavating using the casing tube 5, in order to prevent the collapse of the inner wall of the excavation hole, care should be taken to ensure that the bottom of the excavation hole does not, in principle, go below the lower end of the casing tube 5.

[0023] When the excavation for the full length of the first casing tube 5-1 is completed, as shown in Fig. 4, additional casing tubes 5-2, 5-3, 5-4 are successively added, and excavation and soil discharge are repeated until the excavation reaches the designed depth. One or more casing tubes 5-1, 5-2, 5-3, 5-4 added and connected in this way are called the "casing tube connector 50".

[0024] When the excavation to the predetermined depth is completed, based on the properties of the soil discharged by the hammer grab 3, the design drawings, and the soil investigation data, etc., it is confirmed whether the excavation to the support layer is completed, and the embedment depth is confirmed based on the excavation depth, the design drawings, and the soil investigation data, etc. If the designed embedment depth is confirmed, bottom hole treatment is performed to remove the sediment and floating sediment (slime) in the hole water at the bottom of the excavation hole. The bottom hole treatment in the hole water can be performed using a sediment bucket in addition to the hammer grab 3. For example, after the excavation is completed, immediately lower the sediment bucket to the bottom of the hole, wait for sedimentation, and then lift the sediment bucket with the floating sediment (slime) deposited in it.

[0025] After the bottom hole treatment, as shown in Fig. 5, using the auxiliary crane 7, the steel cage 11 is placed into the excavation hole. The steel cage 11 is assembled by forming steel bars into a cylindrical shape (circular cross-section). The steel cage 11 is composed of main bars, stirrups, reinforcement rings, spacers, etc.

[0026] Next, prepare the Tremie connecting pipe 90. The lengths of the Tremie pipes 9 are mainly standard lengths of 6 m and 3 m, and adjustment Tremie pipes 9 of 1 m and 2 m are also prepared to accommodate changes in the excavation depth and the height of concrete placement. The Tremie pipe 9 is a steel cylindrical material for concrete supply used when manufacturing in-situ concrete piles. By connecting the concrete discharge port of the concrete mixer truck 13 to the location where concrete placement in the pile hole is completed in a pipe shape, it aims to prevent the separation of concrete during placement due to aerial separation of concrete or material separation caused by groundwater inflow, and to prevent deterioration of the concrete quality.

[0027] In this example, the assembly of one or more connected Tremie pipes 9 is called the "Tremie connecting pipe 90". At the bottom of the Tremie connecting pipe 90, the Tremie pipe 9-1 with a built-in vibration device is connected. The Tremie pipe 9-1 with the built-in vibration device vibrates the Tremie pipe 9 itself by the vibration generated by the vibration device, and applies vibration to the concrete around the Tremie pipe 9 to promote fluidity.

[0028] Figure 12 is a diagram showing the configuration of the Tremie pipe 9-1 with a built-in vibration device. The Tremie pipes 9-1, 9-2, 9-3, 9-4 have a steel cylindrical pipe body 21. The pipe body 21 is provided with a concrete passing hole 23 penetrating the center in the pipe axis direction. Each Tremie pipe body 9-1, 9-2, 9-3, 9-4 has a connecting portion 29 at one end or both ends that is detachable from the end of another Tremie pipe. The concrete passing holes 23 of the respective Tremie pipes 9-1, 9-2, 9-3, 9-4 communicate with each other in a state of being connected by the connecting portion 29. The Tremie pipe 9-1 is a Tremie pipe connected so as to be closest to the bottom of the pile hole when the Tremie connecting pipe 90 is inserted into the pile hole. A vibration device 25 is provided on the Tremie pipe 9-1. The vibration device 25 has a vibration portion 25-1 that is a portion that generates vibration and transmits the vibration to the surrounding concrete. A motor 25-2 and a vibration portion 25-3 that generates vibration by the power of the motor 25-2 are arranged on the vibration portion 25-1. The motor 25-2 may be, for example, an air motor using compressed air supplied through an air pipe 27 provided in the pipe body 21 of the Tremie pipe 9 from an external compressor 17 as a power source, an electric motor operated by electricity, or the like.

[0029] As shown in FIG. 6, in the placement of concrete into the pile hole using the above-mentioned Tremie connecting pipe 90, the height positions of the lower end of the Tremie pipe 9-1 (the lower end of the Tremie connecting pipe 90) connected to the lowest position of the Tremie connecting pipe 90 and the upper end of the Tremie pipe 9-4 (the upper end of the Tremie connecting pipe 90) connected to the highest position are important. In the method of this embodiment, in order to ensure smooth supply of concrete into the pile hole from the lower end of the Tremie connecting pipe 90, the lower end of the Tremie connecting pipe 90 is set at a position about 200 mm higher than the bottom of the pile hole. In order to avoid leakage of the concrete overflowing from the upper end of the Tremie connecting pipe 90 outside the pile hole, the upper end of the Tremie connecting pipe 90 is set at a position about 0.5 m to 1.0 m lower than the top end of the casing tube 5-4 connected to the highest position of the casing tube connection body 50.

[0030] A hopper 15 for guiding the concrete supplied from the concrete mixer truck 13 to the supply port at the upper end of the Tremie connecting pipe 90 is attached to the upper end of the Tremie connecting pipe 90.

[0031] Slowly lower the Tremie connection pipe 90 into the pile hole. After confirming that the above height is reached, pour the concrete supplied from the concrete mixer truck 13 through the hopper 15 from the upper nozzle of the Tremie connection pipe 90 to perform concrete placement. As shown in Fig. 7, during concrete placement, measure the pouring height h of the concrete with a measuring tape, and based on the relationship between the measured pouring height h, the lengths of the respective casing tubes 5 that make up the inserted casing tube connector 50, the lengths of the respective Tremie tubes 9 that make up the Tremie connection pipe 90, etc., confirm that the concrete has been placed up to a position a predetermined amount higher (for example, about 2 m) than the lower end of the (next) Tremie tube 9 (connected directly above the lowermost Tremie tube 9 at present) or the lower end of the (next) casing tube 5 (connected directly above the lowermost casing tube 5 at present). If it can be confirmed that the concrete has been placed up to a position a predetermined amount higher (for example, about 2 m) than the lower end of the casing tube 5, then as shown in Figs. 8 and 9, temporarily pause the concrete placement, raise the casing tube connector 50 and the Tremie connection pipe 90 to a position where the uppermost casing tube 5 and the uppermost Tremie tube 9 can be separated and recovered, and separate and recover the uppermost casing tube 5 and the uppermost Tremie tube 9.

[0032] In this embodiment, since both the Tremie pipe 9 and the casing tube 5 are connected with the same length from the bottom, such as 6m, 6m, 6m, 4m, the topmost casing tube 5 and the Tremie pipe 9 are simultaneously separated and recovered. However, when different lengths of the Tremie pipe 9 and the casing tube 5 are used for each stage, the Tremie pipe 9 and the casing tube 5 are not necessarily simultaneously separated and recovered. In any case, if the concrete is placed up to a position a predetermined amount higher (for example, about 2m) than the lower end of the next Tremie pipe 9, the Tremie connection pipe 90 is pulled up by the length of the topmost Tremie pipe 9 to separate and recover the topmost Tremie pipe 9. If the concrete is placed up to a position a predetermined amount higher (for example, about 2m) than the lower end of the next casing tube 5, the casing tube connector 50 is pulled up by the length of the topmost casing tube 5 to separate and recover the topmost casing tube 5. The separation and recovery of the subsequent Tremie pipes 9 and casing tubes 5 are performed in the same manner.

[0033] Here, at the pile head, compared with the part near the pile bottom, the overburden pressure due to the self-weight of the concrete is lower, so the concrete does not flow sufficiently outside the reinforcing cage 11 through the spaces between the reinforcing bars of the reinforcing cage 11, and there is a possibility that the concrete will not be filled well up to the covering part. To reduce this phenomenon, in the method of this embodiment, when placing the concrete at the pile head, the vibration device 25 built in the Tremie pipe 9-1 is operated to vibrate the vibrating part 25-1, and vibration is applied to the surrounding concrete to promote the fluidity of the concrete. Thereby, it is possible to prevent the insufficient filling of the concrete in the covering part caused by the low overburden pressure due to the self-weight of the concrete at the pile head. Note that if excessive vibration is applied to the concrete, bleeding of the fresh concrete will increase, leading to a deterioration in the quality of the concrete. Therefore, it is desirable to perform vibration limitedly on the concrete at the pile head.

[0034] Particularly, in many cases, the area from the top end of the pile down to 2.0 m is over-reinforced. Therefore, it is more effective to apply vibration to the concrete in the over-reinforced area of the pile head. More specifically, as shown in FIG. 10, there is a method of operating the vibration device 25 for a predetermined time with the height of the vibration part 25-1 of the vibration device 25, for example, the lower end height, aligned with the height of the lower end of the over-reinforced area of the pile head to vibrate the tremie pipe. Alternatively, as shown in FIGS. 11-A and 11-B, there is a method of sequentially aligning the intermediate height or substantially intermediate height of the vibration part 25-1 of the vibration device 25 at a plurality of different heights within the over-reinforced area and operating the vibration device 25 for a predetermined time at each height position to vibrate. When vibrating at a plurality of different height positions within the over-reinforced area, in order to suppress the bleeding of fresh concrete, it is desirable to shift the height of each adjacent vibration position by a predetermined distance (for example, 0.5 m).

[0035] The operating time of the vibration device 25 at one height position can be set to a time corresponding to the pile diameter. Specifically, for a pile diameter of 1000 mm to 1500 mm, it is 20 seconds to 60 seconds; for a pile diameter of 1600 mm to 2000 mm, it is 30 seconds to 60 seconds; and for a pile diameter of 2100 mm to 2500 mm, it is 30 seconds to 90 seconds.

[0036] When the over-reinforced area is in a range longer than the range from the top end of the pile down to a height of 2.0 m, vibration may be applied at multiple heights. In this case, it is preferable that the vibration time at the height position closest to the top end of the pile is longer than that at other height positions. This is because the overlying pressure of the concrete becomes smaller at the height position closer to the top end of the pile. For example, in the case of a pile diameter of 1000 mm, the vibration time at the height position closest to the top end of the pile can be set to 30 seconds, and the vibration time at the height position below it can be set to 20 seconds, etc. Alternatively, instead of changing the vibration time, the vibration intensity may be changed according to the height to correspond to the difference in the overlying pressure of the concrete.

[0037] When concrete is poured into a pile hole in which the reinforcing bar cage 11 is installed, muddy water and soil are mixed into the upper layer as the fresh concrete rises from the bottom of the hole, and the quality of the concrete at the top of the pile deteriorates. For this reason, a surplus concrete is created by placing concrete directly above the top of the pile as determined by the design. The amount of the surplus concrete is generally about 0.8m to 1.0m when there is water in the hole. It is preferable that the upper limit of the vibration is set to a position where the vibration unit 25-1 of the vibration device 25 is 0.5m lower than the top of the surplus concrete. In other words, if vibration is applied to a part near the top of the surplus concrete, the water in the hole and sediment that have gathered at the top part will move toward the head of the pile, which may deteriorate the quality of the concrete at the head of the pile. The above-mentioned excess reinforcement is removed to expose the main reinforcement bars after the concrete has cured. [Explanation of symbols]

[0038] 1. Excavator 5 Casing tube 7 Auxiliary crane 9 Ptolemy Tube 9-1 Tremie tube with built-in vibration device 11 Reinforced Concrete Cage 9-1 Tremie tube with built-in vibration device 25 Vibration device 50 Casing tube connector 90 Tremie connecting pipe

Claims

1. A construction method of a cast-in-place concrete pile, comprising: excavating a pile hole in the ground, placing a steel cage in the excavated pile hole, and placing concrete using a tremie pipe equipped with a vibration device in the pile hole where the steel cage is placed, when placing concrete in the over-reinforced area of the pile head, by operating the vibration device to vibrate the tremie pipe, applying vibration to the concrete at the pile head so that the concrete flows through the spaces between the steel bars of the steel cage to the outside of the steel cage, thereby promoting the fluidity of the concrete A construction method of a cast-in-place concrete pile.

2. A construction method of a cast-in-place concrete pile according to Claim 1, positioning the vibration part of the vibration device at the height of the over-reinforced area of the pile head and operating the vibration device for a predetermined time to vibrate the tremie pipe A construction method of a cast-in-place concrete pile.

3. A construction method of a cast-in-place concrete pile according to Claim 2, sequentially positioning the vibration part of the vibration device at a plurality of different heights belonging to the over-reinforced area of the pile head and operating the vibration device at each position for a time set for each height to vibrate the tremie pipe, wherein the operating time of the vibration device at the highest position among the plurality of different heights belonging to the over-reinforced area is longer than the operating times at other heights A construction method of a cast-in-place concrete pile.

4. A construction method of a cast-in-place concrete pile according to any one of Claims 1 to 3, wherein the over-reinforced area of the pile head includes the range from 2.0 m below the pile top end A construction method of a cast-in-place concrete pile.

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