JP2009036010A - Method of building subsidence prevention pile and subsidence prevention pile - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of building a subsidence prevention pile capable of reducing the subsidence of a cast in-place pile even if an axial force larger than that in a conventional construction method acts on the in-place pile. <P>SOLUTION: After a gravel layer is formed by laying gravel at the bottom of an excavated hole, a reinforcement basket assembled of column main reinforcements and tie hoops and a filling tube are inserted into the excavated hole. The end of the filling tube is projected by a predetermined length from the reinforcement basket so that the filling tube can be inserted into the gravel layer. Next, a tremie tube for placing concrete is installed in the reinforcement basket, the concrete is placed, and the concrete is cured until predetermined strength is imparted to the concrete. Next, a grout material is poured from a grout pump to the bottom of the excavated hole through a valve to be filled in a space of the gravel layer. After the filling of the grout material is determined to be completed, a valve on the ground is closed by pressure applied to the grout material to solidify the grout material while holding internal pressure. Consequently, a supporting ground body is formed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a settlement prevention pile construction method and settlement settlement pile, and grout material is press-fitted into the tip of the cast-in-place pile to improve and compact the ground near the pile tip, and an upward force is applied to the pile. The present invention relates to a subsidence prevention pile construction method for preventing subsidence and a subsidence prevention pile constructed by the same method.

  The cast-in-place concrete pile method (hereinafter referred to as the cast-in-place pile method) is widely used as a foundation method for high-rise buildings and the like that require a large bearing capacity because construction of large-diameter piles is easy. In particular, in the field of construction, a cast-in-place expanded pile having a large supporting force by expanding the diameter of the tip of the pile is often used.

  In general, the cast-in-place pile method has a drawback in that the cast-in-place pile is accompanied by considerable settlement before the tip support force is exerted because the surrounding ground is disturbed and stress is released during excavation. For example, the amount of settlement of cast-in-place piles that occurs until the ultimate bearing capacity of the ground reaches about 10% of the pile diameter. In addition, even in a normally managed construction, settlement of the order of several centimeters often occurs. Therefore, with the construction of the superstructure, uneven settlement due to differences in pile position and axial force occurred, which sometimes caused problems.

  The bearing capacity expected of piles tends to increase with the increase in the height and span of building structures. Therefore, even when a large axial force is applied to the cast-in-place pile, a cast-in-place pile construction method that can reduce the amount of settlement is expected compared to the conventional construction method.

  FIG. 13: is the conceptual diagram which showed the front-end | tip part of the constructed conventional cast-in-place pile. As a factor of the settlement of this type of cast-in-place concrete pile 90, for example, the following can be cited. First, it is caused by the slime in which the excavated soil at the bottom of the excavation hole and the hole-protecting mud are mixed. When concrete is cast in a state where the slime is deposited, a sufficient supporting force cannot be obtained, which causes the cast-in-place pile 90 to sink. Second, it is caused by the weak layer portion 81 of the ground formed at the bottom of the excavation hole. The upper surface of the bottom of the excavation hole is disturbed by excavation, and a layer weaker than the ground strength is formed. Third, it is caused by the loosened area 86 generated in the natural ground 80 in the vicinity of the tip of the cast-in-place pile 90 due to the stress release by the earth and sand excavation. When the sediment in the excavation hole is excavated, there is no medium for transmitting the weight and stress of the sediment. As a result, the restraint pressure of the natural ground 80 is reduced, and the surrounding natural ground 80 is expanded. In this state, since the rigidity of the natural ground supporting the cast-in-place pile 90 is lowered, the cast-in-place pile 90 is subsidized with an increase in load due to the construction of the upper structure, and there is a problem such as uneven settlement. Is generated. In addition, the slime and the weak layer portion 81 often cause the sinking synergistically.

As a method for treating slime accumulated at the bottom of the excavation hole, Patent Document 1 discloses that the slime removal means is controlled based on the measurement result of the physical properties of the stable liquid containing the recovered slime. An invention is disclosed in which slime removal in a hole can be efficiently and reliably performed by performing control with horizontal movement. Moreover, in patent document 2, when constructing a cast-in-place pile with a tapered portion, slime is narrowed at the tip of the pile by injecting cement milk or the like without lifting the excavation bit or excavation bucket immediately after excavation. And there is little loosening of the bottom-expanded ground, so that it is possible to secure the supporting capacity of the pile according to the original ground strength.
JP 2005-213866 A JP 2004-263561 A

  However, in the invention disclosed in Patent Document 1, it is possible to prevent settlement of cast-in-place piles due to slime, but it is not possible to prevent settlement due to other factors described above. Moreover, in the invention disclosed in Patent Document 2, slime can be processed, and the settlement of cast-in-place piles can be reduced by improving the ground of the bottom of excavation. However, in consideration of the tendency that the bearing capacity of piles is increasing with the increase in the number of buildings, a construction method that more effectively suppresses settlement of cast-in-place piles is desired.

  The present invention has been made to solve such a problem, and compared to the conventional construction method, subsidence that can reduce the settlement of the cast-in-place pile even when a large axial force is applied to the cast-in-place pile. It aims at providing the construction method of a prevention pile.

  In order to achieve the above object, a method for constructing a settlement-preventing pile according to the first aspect of the present invention includes a grouting material injection pipe in which a pipe bottom is located at a pile bottom and is erected in a pile hole with a reinforcing bar supported. After cast-in-place concrete is cast into the pile hole, a grout material is press-fitted into the pile bottom through the injection pipe, and the grout material is cured while maintaining a predetermined internal pressure after the pile bottom is injected. And a support ground body is formed on the bottom of the pile.

  In order to achieve the above object, according to the second aspect of the present invention, there is provided a method for constructing an anti-sedimentation pile, in which a grout material injection pipe whose pipe bottom is located at the bottom of the pile is supported in the pile hole by supporting a reinforcing bar. After placing cast-in-place concrete in the pile hole, grout holes are drilled from the pile bottom to the ground via the injection pipe, grout material is press-fitted into the grout holes, and the grout material is After the pile bottom is injected, it is cured while maintaining a predetermined internal pressure, and a support ground body is formed on the pile bottom.

  It is preferable to form a gravel layer at the bottom of the pile before placing the cast-in-place concrete, and press-fit the grout material into a gap between gravel in the gravel layer.

  It is preferable to embed a pressure gauge housed in a casing at the outer edge of the gravel layer and measure the grout material working pressure.

  The grout material working pressure when the grout material is press-fitted is preferably determined based on an upward force acting on the cast-in-place pile.

  Moreover, in order to achieve the said objective, the settlement prevention pile which concerns on this invention was constructed | assembled by the creation method mentioned above, It is characterized by the above-mentioned.

  As described above, according to the present invention, it is possible to reduce the settlement of the cast-in-place pile even when a large axial force is applied to the cast-in-place pile compared with the conventional method.

  Fig.1 (a) and FIG.1 (b) are the partial expansion schematic diagrams which showed the pile bottom part of the cast-in-place bottom pile 10 formed by another construction procedure mentioned later, respectively. In the upper part of the figure, a state in which the reinforcing bar 17 and the injection pipe 20 are inserted in a process described later is shown, and a supporting ground body 35 is formed on the bottom of the cast-in-place expanded pile 10 through the final process. The state is shown. FIG.1 (c) is sectional drawing shown by arrow cc in FIG.1 (a) and FIG.1 (b). As shown in the figure, four injection pipes 20 are disposed and supported at predetermined positions along the main bar 24 on the reinforcing bar 17 assembled from the main bar 24 and the band bar 25, and concrete 19 is cast and hardened. After that, the grout material is press-fitted from the injection pipe 20 to form the support ground body 35 at the bottom of the cast-in-place expanded pile. Hereinafter, the construction procedure of the cast-in-place expanded pile 10 will be described using the drawings.

  FIGS. 2 and 3 are each a construction sequence diagram showing a construction process of the cast-in-place expanded pile 10 by the earth drill method in order to create the cast-in-place expanded pile 10 shown in FIG. 2 (a) to 2 (c) are the same as the conventional construction process for cast-in-place piles, and will be described briefly.

[Surface excavation process] (Fig. 2 (a))
The drill bucket 13 with a blade at the bottom is rotated, and the ground is excavated while the earth and sand are scraped into and discharged from the drill bucket 13. After excavating the ground to the expected depth of installation of the casing 14, the casing 14 is built vertically for the purpose of protecting the hole wall

[Shaft excavation process] (FIG. 2B)
When the installation of the casing 14 is completed, the drill bucket 13 is rotated again, and the excavation hole 26 is excavated to a predetermined support layer depth while injecting the stabilizing liquid 15 made of bentonite solution.

[Bottom excavation, primary slime treatment process] (FIG. 2 (c))
When the excavation of the shaft portion is completed, the widened drill bucket 16 is installed at the bottom of the excavation hole, and the diameter of the excavation hole at the bottom is expanded. When the diameter of the drilling hole is increased to a predetermined diameter, the bottomed drill bucket 16 is pulled up. At this stage, since slime is often deposited at the bottom of the excavation hole, the slime is removed using a bottom rough bucket (not shown) (primary slime treatment).

[Reinforcing bar scissors, injection tube insertion process] (FIG. 2 (d))
Next, the reinforcing bar 17 to which the injection pipe 20 is attached is inserted into the excavation hole 26. The injection tube 20 is formed, for example, by cutting a φ30 to φ50 mm steel pipe into straight cuts. The distal end of the injection tube 20 is preferably protruded from the reinforcement rod 17 by a predetermined length so that the injection tube 20 comes into close contact with the bottom of the excavation hole when the rebar rod 17 is inserted into the excavation hole 26.

[Insertion of tremy tube, secondary slime treatment process] (Fig. 3 (a))
Next, a tremy pipe 18 for placing concrete is installed inside the reinforcing bar 17. The tremy pipe 18 is formed by connecting several steel pipes, and a hopper 27 is attached to the upper part as a concrete placing opening. If slime has settled at the bottom of the borehole at this point, the slime is sucked up and removed by a special slime processing machine (not shown) such as a suction pump, air lift, or sand pump (secondary slime treatment). .

[Concrete placing process] (FIG. 3B)
Subsequently, the concrete 19 is poured from the hopper 27 and the concrete 19 is placed in the excavation hole. The arrows in the figure indicate the flow of the concrete 19. When placing concrete, the tip of the tremy tube 18 is always in the concrete 19 that is being cast, and the concrete 19 is continuously driven to a predetermined position while gradually lifting the tremy tube 18. To do. Thereby, it is possible to prevent the stabilizing liquid 15 and the concrete 19 from being mixed. Further, it is necessary to ensure that the injection pipe 20 is in close contact with the bottom of the excavation hole so that the concrete 19 does not enter the inside of the injection pipe 20. For example, the injection pipe 20 may be pushed downward when placing the concrete 19 so that the tip of the injection pipe 20 and the bottom of the excavation hole are brought into close contact with each other.

[Preparation process for concrete curing and grout press-fitting equipment] (Fig. 3 (c))
When the placement of the concrete 19 is completed, the concrete 19 is cured until a predetermined concrete strength is developed. Predetermined concrete strength refers to the strength that does not cause problems such as excessive cracking in the concrete portion 19 of the pile body due to the pressure at the time of injecting the grout material described later, and a curing period of about 1 to 2 weeks. Provide. A valve 23 is attached to the upper portion of the injection tube 20 in order to maintain the pressure inside the injection tube 20 as will be described later. A grout pump 21 and a grout mixer 22 are disposed on the ground, and the grout pump 21 and the injection pipe 20 are connected via a valve 23.

[Grouting material injection process] (FIG. 3D)
The grout material 30 is kneaded by a grout mixer 22 disposed on the ground, and injected from the grout pump 21 to the bottom of the excavation hole through the valve 23 and the injection pipe 20. The arrows in the figure indicate the flow of the grout material 30. The grout material 30 has good fluidity in order to spread over the entire bottom of the excavation hole, and, as will be described later, since it is necessary to maintain the pressure in the injection pipe 20 after the grout material 30 is press-fitted, the viscosity is sufficiently high, The one with less penetration into the ground is selected. Moreover, it is desirable that the grout material 30 has a strength equal to or higher than that of the concrete portion 19 constituting the main body of the cast-in-place expanded pile 10 so as not to become a weak point after the cast-in-place expanded pile 10 is formed. Examples of the grout material 30 satisfying these conditions include high-strength cement paste, mortar to which fly ash is added as an admixture, or mortar to which a thickener is added.

  FIG. 4 is a construction sequence diagram showing the vicinity of the bottom of the excavation hole, focusing on the state in which the grout material 30 constituting the characteristic part of the present embodiment is injected into the natural ground 80 through the injection pipe 20. FIG. 4A shows a situation immediately after the start of the injection of the grout material 30. An arrow in the injection tube 20 indicates the flow of the grout material 30. The grout material 30 is press-fitted into the bottom of the excavation hole from the grout pump 21 (FIG. 3C) disposed on the ground via the injection pipe 20. The injected grout material 30 spreads to the bottom of the excavation hole while pressing the natural ground 80 (a part penetrates the natural ground 80). At this time, the weak layer portion 81 (FIG. 13) formed at the bottom of the excavation hole is pushed out of the excavation hole bottom and eliminated, or the grout material 30 is improved and the support ground body 35 is formed.

  FIG. 4B shows a situation in which the grout material 30 has been injected and the supporting ground body 35 is expanding. The supporting ground body 35 is formed over the entire bottom of the excavation hole by the injection of the grout material 30. Since pressure is applied to the grout material 30 by the grout pump 21 (FIG. 3C), the pressing force 36D of the ground 80 at the bottom of the excavation hole is opposite to the upper and lower surfaces of the supporting ground body 35. The lifting force 36U of the cast-in-place pile 10 acts in the vertical direction.

  FIG. 4C shows the entire support ground body 35 formed after the injection of the grout material 30 is completed. A ground region 85 in which the ground is compacted by the pressure of the grout material 30 is formed below the support ground body 35 that spreads at the bottom of the excavation hole. When the grout material 30 is injected, the internal pressure is generated as described above. However, in order to maintain the force for pushing up the cast-in-place pile 10, it is necessary to maintain this internal pressure even after the grout material 30 has been injected. It becomes. The injection pressure of the grout material 30 is measured by a pressure measuring device (not shown). When the grout material 30 is injected at a predetermined pressure and the set internal pressure of the grout material 30 does not fluctuate for a certain time and is in a constant state, it is determined that the injection of the grout material 30 has been completed. And the working pressure to the support ground body 35 is hold | maintained by closing the valve | bulb 23 (FIG.3 (c)) of a ground part in the state which applied the pressure to the support ground body 35 before the grout material 30 solidifies.

  The upward force acting on the pile bottom described above is transmitted to the circumferential ground as the circumferential frictional force of the pile, and most of the force acts on the side surface of the bottom portion of the cast-in-place expanded pile 10. For this reason, the cast-in-place expanded pile 10 does not sink until a downward load that balances with the upward force is applied.

As described above, the following effects can be obtained by the configuration of the settlement prevention pile according to the embodiment of the present invention.
(1) The slime remaining at the bottom of the excavation hole and the weak layer at the bottom of the excavation hole can be improved and solidified by injecting a grout material.
(2) By press-fitting the grout material, the loosened area spread at the bottom of the excavation hole can be compacted.
(3) An upward force can be applied to the cast-in-place expanded pile by the injection pressure of the grout material. The pile will not sink until a downward load that balances this upward force is applied.
As is apparent from these effects, in the present invention, the sinking of the cast-in-place pile can be reduced even when a large axial force is applied to the cast-in-place pile compared with the conventional method.

  In the above-mentioned embodiment, in order to prevent the intrusion of concrete into the injection pipe, the method of placing the concrete with the injection pipe in close contact with the bottom of the excavation hole has been described. However, when the following methods are used in combination, it is possible to prevent the concrete from entering more reliably. Each figure of FIG. 5 is the schematic which showed the example of the concrete penetration | invasion prevention measure of an injection pipe. For example, FIG. 5A shows an example in which a flange 31 is attached to the distal end portion of the injection tube 20 and a check valve 32 is attached so as to engage with the flange 31. As another method, as shown in FIG. 5B, the tip of the injection tube 20 may be sealed with a low-strength solidified material 33 and removed after placing the concrete. Further, as shown in FIG. 5C, when the sheath tube 34 is movably attached to the distal end of the injection tube 20 or an elastic member (such as an expansion joint) is attached, the distal end portion of the injection tube 20 and the excavation hole Adhesion with the bottom can be made more reliable.

  The present invention can also be implemented by the following method. Other embodiments will be described below.

  The construction procedure of the pile in the present embodiment is the same as that shown in FIGS. 2A to 3A described in the first embodiment. Each drawing in FIG. 6 is a construction sequence diagram showing a construction procedure after placing concrete in the excavation hole. As shown in FIG. 6 (a), when a predetermined strength is developed in the concrete portion 19 and the injection pipe 20 is fixed in the concrete portion 19, the ground located below the bottom of the excavation hole from the injection pipe 20. Boring on the mountain 80. At this time, since the injection pipe 20 can be used as a guide pipe, the bore hole 29 can be easily and accurately constructed. By this boring operation, the concrete 19 that has entered the injection pipe 20 can be removed. Moreover, the grout material 30 can be pressed in deeply in the natural ground 80 located below the bottom of the excavation hole. When the boring hole 29 is formed, as shown in FIG. 6 (b), the grout material 30 described in the first embodiment is transferred from the grout pump 21 (FIG. 3 (c)) disposed on the ground. Through the bore hole 29. The grout material 30 injected into the boring hole 29 spreads to the boring hole 29 and the bottom of the excavation hole while pressing the natural ground 80 (a part penetrates the natural ground 80). The grout material 30 will eventually fill the entire bottom of the borehole. The injection pressure of the grout material 30 is measured by a pressure measuring device (not shown). When the grout material 30 is injected at a predetermined pressure and the internal pressure in the range as the unsolidified support ground body 35 does not change and becomes constant, it is determined that the injection of the grout material 30 is completed. Then, by closing the ground valve 23 (FIG. 3C) in a state in which the supporting ground body 35 is pressurized, it is possible to maintain the acting force on the supporting ground body 35. FIG. 6C shows a situation in which the injection of the grout material 30 has been completed and the support ground body 35 has been formed over a predetermined range. Similar to the first embodiment, an internal pressure generated in the grout material 30 (support ground body 35) causes a push-up force 36U of the cast-in-place pile 10 and a push-down force 36D at the bottom of the excavation hole to act. A compacted ground region 85 is formed below the bottom of the excavation hole. As described above, the present embodiment can obtain the same effects as those of the first embodiment.

  Further, gravel may be laid on the bottom of the excavation hole before the concrete is placed in the excavation hole, and a gap due to the gravel layer may be formed on the entire bottom of the excavation hole. Hereinafter, before placing concrete, a method for constructing a settlement prevention pile by laying gravel at the bottom of the excavation hole will be described.

  Since the construction procedure of the pile in a present Example is the same as that of FIG. 2 (a)-(c) demonstrated in Example 1, the subsequent construction procedure is demonstrated. FIGS. 7 and 8 are construction sequence diagrams showing the construction procedure of piles in the present embodiment after construction of excavation holes.

[Stall installation process] (FIG. 7A)
First, the support column 28 is inserted into the excavation hole 26 as indicated by an arrow in the figure, and one end of the support column 28 is made to reach the vicinity of the center of the excavation hole bottom. Next, hitting or the like is applied to the other end of the column 28, and one end of the column 28 is inserted into the bottom of the excavation hole. Thereby, the support column 28 is fixed to the bottom of the excavation hole, and the support column 28 can be self-supported in the excavation hole 26. The support column 28 is formed by connecting a plurality of steel materials, for example. A male screw or a female screw is formed at the end of each steel material, and the degree of unevenness of the joint of the support column 28 can be reduced by abutting and screwing these. Thereby, the inner hole metal fitting 52 (FIG. 7B) to be described later can be smoothly moved along the support column 28.

[Pressure gauge casing installation arm installation process] (FIG. 7B)
Next, a pressure gauge casing installation arm 50 (hereinafter simply referred to as a casing installation arm) is inserted into the excavation hole 26 along the support column 28 as indicated by an arrow in the figure.
The casing installation arm 50 is formed by, for example, pin-connecting a steel arm having a predetermined length, and includes a pin coupling portion 54 serving as a joint portion at a predetermined position from the tip (lower end in the figure). . A wire 53 extending to the ground is attached to the distal end portion 50a of the casing installation arm, and the distal end portion 50a can be rotated around the pin coupling portion 54 by pulling or loosening the wire 53. A plurality of center hole fittings 52 having openings through which the support columns 28 can pass are attached to the casing installation arm 50 along the length direction. The casing mounting arm 50 can be inserted into the excavation hole 26 along the support 28 by passing the center hole metal 52 through the support 28. Further, a grip 51 is provided at the tip of the casing installation arm 50. The gripper 51 descends the excavation hole 26 together with the casing installation arm 50 while gripping the casing 40.

[Case mounting step] (FIG. 7C)
After lowering the casing installation arm 50 until the tip reaches the bottom of the excavation hole, the wire 53 is pulled on the ground, and the tip portion 50a of the casing installation arm is rotated around the pin coupling portion 54. Thereby, the casing 40 grasped by the grasping portion 51 moves to the corner of the bottom of the excavation hole. Subsequently, the gripping portion 51 is released from the gripping state of the casing 40 and the casing 40 is placed at the corner of the bottom of the excavation hole. When the placement of the casing 40 is completed, the casing installation arm 50 is lifted from the excavation hole 26, and the placement process of the casing 40 is completed.

Here, an enlarged view of a portion surrounded by a dotted line in FIG. 7C is shown in FIGS. 9A and 9B. As shown in FIG. 9A, the casing installation arm 50 includes two pieces that engage with the wire 53 with the pin coupling portion 54 interposed therebetween. One is located below the pin coupling portion 54 in the figure, and is a wire fixing piece 55 to which the wire 53 is fastened, and the other is located above the pin coupling portion in the figure, and the through hole of the wire 53 is opened. This is a wire threading piece 56. One end of the wire 53 is fastened to the wire fixing piece 55. Further, the wire 53 is extended to the ground through a through hole formed in the wire passing piece 56. With such a configuration, when the wire 53 is pulled on the ground, the tip end portion 50a of the casing installation arm rotates around the pin coupling portion 54 as shown in FIG. 9B.
The gripping part 51 has a short gripping claw that holds the casing 40, and this gripping claw can be remotely operated using hydraulic pressure or an electric signal transmitted from the ground. As described above, the casing 40 is moved to a predetermined position of the outer edge of the gravel layer at the bottom of the excavation hole, the gripping portion 51 is remotely operated to release the gripping state of the casing 40, and the casing 40 is moved to the outer edge of the bottom of the excavation hole. Place. Thereby, it can be determined from the measurement result of the pressure gauge 42 in the casing 40, which will be described later, whether the grout material is reliably injected up to the outer edge of the excavation hole.

  As shown in FIGS. 9C and 9D, a pressure gauge 42 is accommodated in the casing 40. The casing 40 is formed of, for example, a body plate portion 43a formed by cutting a steel pipe, and a lid 43b formed with a grout passage hole 43a that prevents gravel from entering and allows passage of the grout material. As the pressure gauge 42, for example, a known earth pressure gauge that measures the pressure acting on the pressure receiving plate by converting it into oil pressure is used, and measures the working pressure of the grout material that has entered the casing 40. The pressure gauge 42 is connected to a pressure measurement cable 41 for transferring measurement data. The pressure measurement cable 41 extends through the trunk plate portion 43 a to the ground, and the data measured by the pressure gauge 42 is transmitted to the ground via the pressure measurement cable 41. Thereby, the worker on the ground can appropriately confirm whether or not the operation of injecting the grout material 30 is smoothly performed based on the pressure data measured by the pressure gauge 42. Moreover, by accommodating the pressure gauge 42 in the container 43, the pressure gauge 42 is protected from gravel and a bottomed drill bucket, which will be described later, and the working pressure generated in the grout material is directly measured (the gravel 70 is directly applied to the pressure gauge 42). Error measurement by touching can be eliminated). A pressure water conduit can also be used as another means for measuring the grout working pressure. For example, by installing a pressure water conduit filled with internal water at the above-mentioned measurement position of the grout working pressure, and measuring the water pressure (or water head) in the pressure water conduit at the time of grout injection, the grout working pressure is indirectly measured. Can also be measured. In this measurement method, an indirect measurement value can be obtained, but the measurement apparatus can be simplified, so that the cost of the apparatus can be reduced.

[Gravel input process, column removal] (Fig. 7 (d))
Subsequently, the gravel input pipe 60 is inserted into the excavation hole 26 and the tip of the gravel input pipe 60 is made to reach the vicinity of the bottom of the excavation hole. In addition, when inserting the gravel input pipe 60, the gravel input pipe 60 is passed by passing the inner hole metal fitting 62 attached to the gravel input pipe 60 through the support column 28 in the same manner as when inserting the casing installation arm 50. Can be inserted into the borehole 26 along the support column 28. Next, gravel 70 (may be crushed stone) is introduced from the upper part of the gravel input pipe 60, and the gravel 70 is laid at the bottom of the excavation hole. As the gravel 70, it is preferable to select a gravel having a size of about 40 to 60 mm so that a grout material described later can easily penetrate. When the gravel 70 is thrown in, as with the casing installation arm 50, the gravel throwing pipe is operated while pulling or loosening the wire 63 fixed to the tip 60a of the gravel throwing pipe, and flexibly operating the tip 60a. The gravel 70 is laid uniformly on the bottom of the excavation hole by rotating the 60 around the support 28. The thickness of the gravel layer spread on the bottom of the excavation hole is about 200 to 300 mm in consideration of the thickness of the gravel used for infiltration of the grout material from the thickness (about 50 mm) at which concrete described later penetrates the gravel layer. Is preferred. When the construction of the gravel 70 at the bottom of the excavation hole is completed, the gravel input pipe 60 and the support column 28 are removed from the excavation hole 26.
The gravel input pipe 60 is set to have a diameter that is not blocked by the gravel 70, and is formed of, for example, a steel pipe having a diameter of about 200 mm to 300 mm. Further, the gravel charging pipe 60 has a flexible pipe 64 interposed at a predetermined position from the tip (lower end in the figure). The flexible pipe 64 is connected to the tip end portion 60a of the gravel input pipe so as to be bent. Then, by attaching a wire fixing piece to the distal end portion 60a and attaching a wire passing piece 66 above the flexible tube 64 and connecting the wire 63 to these pieces, the wire 63 is pulled or loosened on the ground, The distal end portion 60a can be operated to be freely bent.

[Gravel floor leveling process] (Figure 8 (a))
Next, the bottomed drill bucket 16 used during excavation is installed at the bottom of the excavation hole. Subsequently, the gravel 70 laid at the bottom of the excavation hole is leveled by pressing the gravel 70 laid at the bottom of the bottomed drill bucket 16 while rotating. When operating the bottom expanding drill bucket 16, the bottom expanding drill bucket 16 is prevented from coming into contact with the casing 40 and the pressure measuring cable 41 by expanding the diameter expansion wings of the bottom expanding drill bucket 16 to be smaller than that during drilling. .

[Installation process of reinforcing bar rod and injection pipe] (Fig. 8 (b))
Next, the reinforcing bar 17 to which the injection pipe 20 is attached is inserted into the excavation hole 26. The injection tube 20 is attached to the reinforcing bar rod 17 so as to protrude a predetermined length from its lower end. When the injection pipe 20 reaches the gravel 70 on which the injection pipe 20 is laid, the reinforcing bar 17 is swung, or the upper end of the injection pipe 20 is hit or the like, so that the tip of the injection pipe 20 penetrates into the gravel 70. As the reinforcing bar rod 17, a reinforcing bar rod similar to that shown in the first embodiment can be used. The injection tube 20 is formed of, for example, a steel pipe having a diameter of 30 mm to 50 mm, and the tip of the injection pipe 20 is processed into a conical shape so that it can be easily inserted into the gravel 70. FIG. 10 shows an enlarged view of a portion surrounded by a dotted line in FIG. As shown in the figure, four grout material discharge holes 20a are formed at the tip of the injection tube 20 at equal angles. The grout material discharge hole 20a is formed with a size of about φ10 to 20 mm. Each grout material discharge hole 20 a is formed so as to be shifted in the axial direction of the injection tube 20.

[Concrete placing process] (Fig. 8 (c))
Since the concrete placing process is the same as that of Example 1, it will be briefly described. First, a tremy pipe 18 for placing concrete is installed inside the reinforcing bar 17. Next, the concrete 19 is poured from the hopper 27 and the concrete 19 is placed in the excavation hole. The arrows in the figure indicate the flow of the concrete 19. When placing concrete, the tip of the tremy tube 18 is always in the concrete 19 that is being cast, and the concrete 19 is continuously driven to a predetermined position while gradually lifting the tremy tube 18. To do.

[Concrete curing, grout material injection process] (Fig. 8 (d))
When the placement of the concrete 19 is completed, a curing period (about 1 to 2 weeks) is provided until a predetermined concrete strength is developed. A grouting pump 21 and a grouting mixer 22 are arranged on the ground, a valve 23 is attached to the upper part of the injection pipe 20, and the grouting pump 21 and the injection pipe 20 are connected via the valve 23. The grout material 30 is kneaded by a grout mixer 22 disposed on the ground, and injected from the grout pump 21 to the bottom of the excavation hole through the valve 23 and the injection pipe 20. The arrows in the figure indicate the flow of the grout material 30. In addition, the grout material 30 used in the present embodiment is the same as the grout material described in the first embodiment.

  FIG. 11 is a flow chart showing the vicinity of the bottom of the excavation hole, focusing on the state in which the grout material 30 constituting the characteristic part of the present embodiment is injected into the excavation hole bottom through the injection pipe 20. FIG. 11A shows a situation immediately after the start of the injection of the grout material 30. An arrow in the injection tube 20 indicates the flow of the grout material 30. The grout material 30 is injected into the bottom of the excavation hole from the grout pump 21 (FIG. 8E) disposed on the ground via the injection pipe 20. The injected grout material 30 fills the gaps in the gravel layer laid at the bottom of the excavation hole and partly penetrates into the natural ground 80. Then, as shown in FIG. 11 (b), when the grout material 30 fills the gap in the gravel layer and does not penetrate into the natural ground 80, the internal pressure of the grout material 30 is increased by the injection pressure from the grout pump 21. . The grouting material 30 with the increased internal pressure acts on the push-down force 36D of the natural ground 80 at the bottom of the excavation hole and the push-up force 36U of the cast-in-place pile pile 10 opposite to it. Therefore, a ground region 85 compacted by the grout material 30 is formed below the cast-in-place expanded pile 10. As described above, the internal pressure of the grout material 30 is measured by the casing 40 embedded in the gravel 70, and the measurement result can be transmitted by the pressure measurement cable 41 and confirmed on the ground. Therefore, if it can be confirmed that the internal pressure of the grout material 30 is maintained at a predetermined pressure (about 2 to 3 MPa) without fluctuating for a certain time, the injection of the grout material 30 is stopped and the valve 23 (FIG. 8 (d)). ). Thereby, since the grout material 30 is solidified while the internal pressure of the grout material 30 is increased, the supporting ground body 35 can be formed while the push-up force 36U of the cast-in-place bottom pile 10 is maintained.

  FIG. 12 is a partially enlarged schematic view showing a pile bottom portion of the cast-in-place expanded pile 10 created in the present embodiment. According to the present embodiment, since the gap filled with the grout material can be formed in the gravel layer laid at the bottom of the excavation hole, the supporting ground body 35 is provided over the entire bottom portion of the cast-in-place expanded pile 10 without depending on the soil quality of the natural ground 80. Can be formed. Therefore, the force which pushes up the entire cast-in-place pile 10 can be made to act reliably.

  In the present embodiment, the use of the injection tube 20 whose tip is processed into a conical shape has been described. However, the above-described injection tube 20 is an example, and other examples are shown in FIGS. As described above, an injection tube having a concrete intrusion prevention measure at the tip may be used. Further, as described in the second embodiment, the bottom of the excavation hole may be bored using the injection pipe as a guide pipe.

  In the above description, the four injection pipes 20 are disposed inside the reinforcing bar rod 17. However, the number, diameter, material, and the like of the injection pipe 20 are preferably determined based on conditions such as the diameter of the cast-in-place expanded pile 10, the injection pressure of the grout material 30, the ground to be excavated, and the like. Therefore, the injection tube 20 described above is an example, and is not limited to the above-described embodiment. Since the injection pipe 20 remains inside the cast-in-place pile 10 even after the cast-in-place pile 10 is formed, the injection pipe 20 receives pressure at the time of pouring the grout material 30 and also has a sectional force as a part of the cast-in-place pile 10. Therefore, it is preferable to use a steel pipe having high material strength and high rigidity for the injection pipe 20. In addition, when the amount of the grout material 30 to be estimated is large and the diameter of the cast-in-place pile 10 is large, the number of the injection pipes 20 is increased or the diameter of the injection pipe is increased. These can be set freely. In addition, in order to fill the grout material 30 evenly in the bottom of the excavation hole, when the number of the injection pipes 20 is increased, it is desirable to arrange the grout material 30 at equal intervals inside the reinforcing bar rod 17.

  Moreover, in the above description, the cast-in-place pile was explained as an example. Naturally, the effect of the present invention can also be enjoyed in a cast-in-place pile where the pile diameter does not change.

  Also, in these examples, the earth drill method was described as an example of the construction method of the cast-in-place expanded pile, but the present invention is also applied to the cast-in-place pile method by other machine excavation methods such as the Benoto method and the reverse method. It goes without saying that it can be implemented.

It is the partial structure figure which showed the settlement prevention pile concerning the example of the present invention, (a) is the settlement prevention pile formed by the creation method shown in Example 1, and (b) is the creation method shown in Example 3. (C) is a cross-sectional view shown by arrows cc. The construction sequence diagram which showed the construction procedure (a)-(d) by the construction method of the settlement prevention pile which concerns on Example 1 of this invention. The construction sequence diagram which showed the construction procedure (a)-(d) by the construction method of the settlement prevention pile which concerns on Example 1 of this invention. Explanatory drawing which showed the formation condition (a)-(b) of the support ground body of the subsidence prevention pile which concerns on Example 1 of this invention. Schematic which showed the concrete penetration | invasion prevention measures (a)-(c) of the injection pipe tip of a settlement prevention pile. Explanatory drawing which showed the formation condition (a)-(c) of the support ground body of the settlement prevention pile which concerns on Example 2 of this invention. The construction sequence diagram which showed the construction procedure (a)-(d) by the construction method of the settlement prevention pile which concerns on Example 3 of this invention. The construction sequence diagram which showed the construction procedure (a)-(d) by the construction method of the settlement prevention pile which concerns on Example 3 of this invention. Explanatory drawing (a)-(b) which showed the procedure which mounts a pressure measuring device in a digging hole bottom, and the detail drawing (c)-(d) of the pressure measuring device to mount. It is an example which showed the front-end | tip part of an injection tube, (a) is a side view, (b) is sectional drawing shown by arrow bb. Explanatory drawing which showed the formation condition (a)-(b) of the support ground body of the subsidence prevention pile which concerns on Example 3 of this invention. Explanatory drawing of the settlement prevention pile which concerns on Example 3 of this invention. Schematic which paid its attention to the pile tip of the conventional cast-in-place pile.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Cast-in-place (expansion bottom) pile 13 Drill bucket 14 Casing 15 Stabilization liquid 16 Expanded bottom drill bucket 17 Reinforcement rod 18 Tremy pipe 19 Concrete (part)
20 Injection Pipe 21 Grout Pump 22 Grout Mixer 26 Drilling Hole 28 Strut 30 Grout Material 35 Support Ground Body 40 Casing 50 Pressure Gauge Casing Installation Arm 54 Pin Joint 60 Gravel Injection Pipe 64 Flexible Pipe 70 Gravel 85 Compacted Ground Area

Claims (6)

A grout material injection pipe with the pipe bottom positioned at the bottom of the pile is erected in the pile hole, supported by a reinforcing bar.
After placing cast-in-place concrete in the pile hole, grout material is press-fitted into the pile bottom through the injection pipe,
A method for creating a settlement-preventing pile, wherein the grout material is cured while maintaining a predetermined internal pressure after the pile bottom portion is injected, and a supporting ground body is formed on the pile bottom portion. A grout material injection pipe with the pipe bottom positioned at the bottom of the pile is erected in the pile hole, supported by a reinforcing bar.
After placing cast-in-place concrete in the pile hole, grout holes are drilled from the pile bottom to the ground via the injection pipe, and grout material is press-fitted into the grout holes,
A method for creating a settlement-preventing pile, wherein the grout material is cured while maintaining a predetermined internal pressure after the pile bottom portion is injected, and a supporting ground body is formed on the pile bottom portion.   A gravel layer is formed at the bottom of the pile before placing the cast-in-place concrete, and the grout material is press-fitted into a gap between gravel in the gravel layer to form a supporting ground body. The construction method of the settlement prevention pile of Claim 1 or Claim 2.   4. The method for constructing a settlement-preventing pile according to claim 3, wherein a pressure gauge housed in a casing is embedded in an outer edge portion of the gravel layer, and the working pressure of the grout material is measured.   The said grout material working pressure at the time of press-fitting the said grout material is determined based on the upward force which acts on the said cast-in-place pile, The Claim 1 thru | or 4 characterized by the above-mentioned. How to create a settlement prevention pile.   A settlement-preventing pile, which is constructed by the construction method according to any one of claims 1 to 3.

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