WO2006041051A1

WO2006041051A1 - Micro pile and method of constructing the same

Info

Publication number: WO2006041051A1
Application number: PCT/JP2005/018681
Authority: WO
Inventors: Masahiro Takeguchi; Mitsutaka Hada; Masao Sagara; Terukatsu Sasaya; Katsunori Hirano; Etsuro Saito; Toshihisa Hatano; Kenichirou Sakamoto; Yasumi Wakabayashi; Yuuji Mishima; Setsuo Iwata
Original assignee: Incorporated Administrative Agency Public Works Research Institute; Fujita Corporation; Hitachi Zosen Corporation
Priority date: 2004-10-08
Filing date: 2005-10-11
Publication date: 2006-04-20
Also published as: JPWO2006041051A1; JP4617315B2; WO2006041051A8

Abstract

A micro pile increased in supporting force and horizontal resistance force and a method of constructing the micro pile. The micro pile (10) for connecting a structure (16) to a support layer (14) in the ground comprises a pile body (18) formed of a grout pressurizingly filled in an excavated hole formed in the ground and hardened. The bottom end portion of the pile body (18) is extended in the support layer (14). Steel tube type reinforcement materials (20) and steel bar type reinforcement materials (30) are buried in the grout of the pile body (18) so as to be disposed roughly concentrical to each other and extended in the longitudinal direction of the pile body (18), and the steel bar type reinforcement materials (30) are positioned at the roughly center of the pile body (18). The steel tube type reinforcement materials (20) extend from the upper end of the pile body (18) into the lower end portion of the pile body (18), and the outer peripheral surfaces thereof are covered by the grout of the pile body (18). The steel bar type reinforcement materials (30) extend from the upper end of the pile body (18) to the lower end (18) of the pile body, and the lower end portions thereof extend from the lower ends of the steel tube type reinforcement materials (20) and are covered by the grout of the pile body (18).

Description

Specification

Micropile and its construction method

Technical field

[0001] The present invention relates to a micropile and a construction method thereof.

Background art

[0002] Micropile is a general term for cast-in-place piles and embedded piles with a diameter of 300mm or less. Construction pile foundations, seismic reinforcement of existing structures (increase pile method), ground reinforcement, slope Widely used in many applications, including stability. There are various types of micropile, for example, those described in Patent Documents 1 to 6 below.

Patent Document 1: Japanese Patent Laid-Open No. 10-140583

Patent Document 2: Japanese Patent Laid-Open No. 2000-027149

Patent Document 3: Japanese Patent Laid-Open No. 2000-290906

Patent Document 4: Japanese Patent Laid-Open No. 2001-146743

Patent Document 5: Japanese Unexamined Patent Publication No. 2001-323459

Patent Document 6: Japanese Patent Laid-Open No. 2002-275907

Disclosure of the invention

Problems to be solved by the invention

[0003] Among various types of micropile, the micropile built in the field does not have the hassle of handling long off-the-shelf piles, so it is very suitable for seismic reinforcement of existing structures with limited heads. It has advantages such as being. However, for such a micropile, there is a strong demand to further improve the resistance against indentation force, pull-out force, and bending stress acting on the micropile. This is strongly demanded when using micropile, because many micropile are often used as one pile group, especially if the resistance of micronail is increased. If the bearing capacity and horizontal resistance are increased, the required number of micropiles can be reduced, thereby shortening the construction period and reducing the construction cost. [0004] The present invention has been devised in view of the above circumstances, and an object of the present invention is to provide a micropile and a method for constructing the same that have improved resistance to resistance and, in particular, improved support and horizontal resistance. It is to provide.

Means for solving the problem

[0005] In order to achieve the above object, the micropile according to the present invention is a micropile for connecting a structure and a support layer in the ground, and is hardened by pressure injection into an excavation hole formed in the ground. A pile body made of grout, wherein at least a lower end portion of the pile body extends in the support layer, and the pile body is embedded in the grout of the pile body so as to extend in a longitudinal direction of the pile body. The extending steel pipe type reinforcing material and the centrally arranged steel bar type reinforcing material, and the steel pipe type reinforcing material and the steel bar type reinforcing material, which are provided at the upper end of the pile body, are joined. A pile head connection structure for connecting a pile head of a micropile to the structure, and the steel pipe type reinforcing material extends from the upper end of the pile body into the lower end portion of the pile body, The outer peripheral surface is covered with the grout of the pile body, and the steel bar The mold reinforcement extends from the upper end of the pile body to the lower end of the pile body, and the lower end portion of the mold reinforcement extends the lower end force of the steel pipe reinforcement and is covered with the grout of the pile body, The space between the inner peripheral surface of the steel pipe reinforcement and the outer peripheral surface of the steel bar reinforcement is filled with the grout of the pile body! It is characterized by scolding.

[0006] The micropile construction method according to the present invention is based on the micropile construction method for connecting a structure and a support layer in the ground, and excavating the ground while adding a plurality of casing segments. A step of forming a drilling hole having a casing constituted by the casing segments so that at least a lower end portion thereof extends through the support layer; and a plurality of steel pipe segments are formed in the drilling hole. A step of inserting a steel pipe type reinforcing material configured by connecting ends and a steel bar type reinforcing material configured by connecting ends of a plurality of steel bar segments, wherein the steel pipe The steel plate type reinforcing material and the steel bar type reinforcing material extend in the longitudinal direction of the drilling hole substantially concentrically with each other, the steel bar type reinforcing material is arranged in the center, and the steel pipe type reinforcing material is located above the drilling hole. Extending from the end into the lower end portion of the excavation hole, and the steel bar reinforcement extends from the upper end of the excavation hole to the lower end of the excavation hole. Steel pipe type reinforcement A reinforcement insertion step for extending the lower end force of the material, a step for filling the digging hole with grout, and lifting the casing to remove at least some of the plurality of casing segments. A step of exposing the inner wall surface of the excavation hole covered by the casing, and a grout having a grout Z ground joint on the outer peripheral surface thereof by pressurizing and hardening the grout into the excavation hole. Steps to be formed and a pile head connection structure for connecting the pile heads of the micropile to the structure joined to the steel pipe type reinforcing material and the steel bar type reinforcing material at the upper end of the pile body It is characterized by including a step.

The invention's effect

[0007] The micropile according to the present invention transmits a load in the longitudinal direction of the micropile via a steel pipe type reinforcing material and a steel bar type reinforcing material extending substantially concentrically with each other. The outer periphery is covered with grout that has been pressurized and hardened, and the grout Z ground joint is formed over a long area of the outer peripheral surface of the micropile. In particular, it has excellent support and horizontal resistance. As a result, the required number of micropiles can be reduced compared to the conventional micropile, thereby shortening the construction period and reducing the construction cost.

Brief Description of Drawings

[0008] FIG. 1A is a longitudinal cross-sectional view of a micropile according to an embodiment of the present invention, FIG. 1B is a cross-sectional view of the micronail taken along line BB in FIG. 1A, and FIG. 1A is a cross-sectional view of the microphone pile along the line CC of FIG. 1A, and FIG. 1D is a cross-sectional view of the micropile along the line DD of FIG. 1A.

FIG. 2 is an explanatory diagram of a construction procedure in the micropile construction method according to the embodiment of the present invention.

[FIG. 3] FIG. 3A is a chart showing the layer structure of the ground in which the micropile for testing was constructed in the micropile bow I punching test according to the present invention, and FIG. 3B is the hardness of each layer of the ground. FIG. 3C is a longitudinal sectional view of the test micropile.

[Fig. 4] Loaded on a micropile in a pull-out test of a micronile according to the present invention. It is the graph which showed the load cycle of drawing force.

FIG. 5 is a graph showing the relationship between the amount of vertical displacement at the top of the micropile and the loaded bow I extraction force in three test micropiles loaded according to the load cycle of FIG.

FIG. 6 is a graph of axial force acting on one test micropile at each pulling force calculated based on the results of the bow I pull-out test of the micropile according to the present invention.

[FIG. 7] FIGS. 7A to 7C are diagrams showing application examples of the micro-lens according to the present invention. Explanation of symbols

[0009] 10 micronore

12 Soft layer

14 Support layer

16 Structure

18 individual bodies

20 Steel pipe type reinforcement

22 Oka tube segment

30 Steel bar reinforcement

32 Tsubasa segment

50 casing

52 Casing Seg.

54 Reinforcing sleeve

60 drilling holes

70 Micronore

80 Micronore

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a micropile and its construction method according to an embodiment of the present invention will be described with reference to the drawings. The micropile 10 according to the embodiment of the present invention shown in FIGS. 1A to 1D includes a structure 16 and a support layer in the ground, which are built on the ground with a soft layer 12 and a support layer 14 below the soft layer It is a pile for connecting with 14. The micropile 10 has a pile body 18. This pile body 18 is pressurized and injected into a drilling hole formed in the ground. The bottom end portion extends through the support layer 14. In the grout of the pile body 18, a steel pipe type reinforcing member 20 and a steel bar type reinforcing member 30 are embedded. The reinforcing members 20 and 30 are arranged substantially concentrically with each other and extend in the longitudinal direction of the pile body 18. The steel bar type reinforcing member 30 is arranged at the center, that is, extends substantially in the center of the micropile 10. The steel pipe type reinforcing member 20 is configured by connecting ends of a plurality of steel pipe segments 22 via steel pipe joints 24, and the steel bar type reinforcing member 30 is made of a deformed bar (rib bar). The ends of the plurality of steel bar segments 32 are connected via a steel bar force bra 34. The steel bar segment 32 is attached with a centralizer 36 composed of four hoop-shaped steel wires in a radial combination. When the micropile 10 is constructed, the centralizer 36 is used as a steel pipe type reinforcement 20 The steel bar type reinforcing material 30 is held concentrically with the steel pipe type reinforcing material 20 by inertially abutting the inner peripheral surface of the steel pipe type. A pile head connection structure for connecting the pile head of the micropile 10 to the structure 16 is provided at the upper end of the pile body 18, and this pile head connection structure is made of a steel base plate 40. The upper end of the steel pipe type reinforcing member 20 is welded and joined to the base plate 40, and the upper end of the steel bar type reinforcing member 30 is screwed and joined with a nut. The steel pipe type reinforcing member 20 extends from the upper end of the pile body 18 to the lower end portion of the pile body 18 (as described above, this lower end portion extends through the support layer 14). The outer peripheral surface is covered with a grout of the pile body 18. The steel bar type reinforcing material 30 extends from the upper end of the pile body 18 to the lower end of the pile body 18, and the lower end portion of the steel pipe type reinforcing material 20 also extends and is covered with the grout of the pile body 18. I'll be. The space between the inner peripheral surface of the steel pipe type reinforcing member 20 and the outer peripheral surface of the steel bar type reinforcing member 30 is filled with grout of the pile body 18. Furthermore, the outer peripheral surface of the upper end portion of the pile body 18 is covered with a reinforcing sleeve 54 and is reinforced by the reinforcing sleeve 54. The reinforcing sleeve 54 is left out of the plurality of casing segments 52 that formed the casing 50 (see FIGS. 2A to 2G) used when forming a drilling hole in the ground to construct the micropile 10. The upper end portion is embedded in the structure 16 and the lower end portion is embedded in the ground. Although not shown in the drawings, each steel pipe segment 22 has four reinforcing bar pieces each having a diameter of about 10 mm and a length of about 100 mm on the outer periphery of the central portion in the longitudinal direction. Radially arranged to extend in the longitudinal direction of the segment 22 and welded to the steel pipe segment 22, the steel reinforcement 20 is concentric with the casing 52 by means of these four rebar pieces. A centizer for holding in position is constructed.

[0012] Next, with reference to FIG. 2A to FIG. 2G, a method for constructing a micronoir according to an embodiment of the present invention for constructing the micropile 10 described above will be described. In FIG. 2A to FIG. 2G, some components such as the steel pipe joint 24 and the steel bar coupler 34 are omitted for easy understanding. In this construction method, first, as shown in FIGS. 2A and 2B, a ground is excavated while adding a plurality of casing segments 52, and a drilling hole having a casing 50 constituted by the casing segments 52 is provided. 60 is formed so that the lower end portion of the borehole 60 extends through the support layer 14. In the illustrated example, a steel pipe having an outer diameter of 9-5 / 8 inch is used as the casing segment 52. To add the casing segments 52 to each other, their ends are connected to a steel pipe joint (not shown). It joins so that removal is possible. More specifically, this excavation is performed using a boring machine (not shown). The ground is dug by the drill bit 64 attached to the lower end of the drilling rod 62 of the boring machine, and the casing segment 52 is added each time the depth of the drill hole increases by a predetermined depth. As another method for forming the excavation hole 60, a cutting blade is attached to the lower end of the first casing segment 52 and the casing 50 is rotated by a boring machine, or the ground is dug. For example, a method in which excavation by a simple casing 50 and excavation by a drill rod 62 inserted in the casing 50 are used together may be used.

[0013] When the excavation hole 60 provided with the casing 50 is completed, the inside of the casing 50 is washed with water and the ij hole rod 60 is lifted and removed. Subsequently, as shown in FIG. 2C, a steel pipe type reinforcing member 20 constituted by connecting ends of the plurality of steel pipe segments 22 to the borehole 60 (ie, in the casing 50), and a plurality of A steel bar type reinforcing member 30 constituted by connecting ends of the steel bar segments 32 is inserted. At this time, the ends of the steel pipe segments 22 are connected to each other via a steel pipe joint 24 (see FIG. 1, not shown in FIGS. While joining, the steel pipe type reinforcement 20 is inserted into the casing 50, and the ends of the steel bar segments 32 are connected to a steel bar force bra. (See Fig. 1; not shown in Figs.2A to 2G), the steel bar reinforcement member 20 is added to the steel bar reinforcement member 30 and the steel bar reinforcement member 20 is inserted into the casing 50. Go to insert. At this time, the steel pipe type reinforcing member 20 is held in a concentric position with respect to the casing 50 by the action of the centizer (not shown) of the steel pipe segment 22 described above, and the centizer 36 (see The steel bar type reinforcing member 30 is held in a concentric position with respect to the steel pipe type reinforcing member 20 by the action of reference 1 (not shown in FIGS. 2A to 2G).

[0014] Further, in this process of inserting the reinforcing members 20 and 30 into the casing 50, as shown in FIG. 2C, the steel pipe type reinforcing member 20 and the steel bar type reinforcing member 30 are concentric with each other. It extends in the longitudinal direction, and the steel bar reinforcement 30 is centered with respect to the drilling hole 60 (and therefore with respect to the microphone mouth pile 10), and the steel pipe reinforcement 20 is drilled. From the upper end of the hole 60, it extends through the support layer 14 to the lower end portion of the drilling hole 60. The lower end portion of the steel bar type reinforcing member 30 extends to the lower end of the excavation hole 60 so that the lower end portion of the steel pipe type reinforcing member 20 also extends. In the example shown in the figure, the inner diameter of the casing 50 is 220 mm, and the outer diameter of the steel pipe joint 24, which is the largest outer diameter portion of the steel pipe type reinforcement member 20, is 195 mm. Therefore, the inner peripheral surface of the casing 50 and the steel pipe type reinforcement are used. As shown in FIG. 1B, an annular gap 66 is secured between the outer peripheral surface of the material 20 (in FIG. 1B, the gap between the inner peripheral surface of the casing segment 52 and the steel pipe segment 22 is secured. Shown! / Speak).

Next, as shown in FIG. 2D, grout is injected into the casing 50 and the grout hole 60 is filled with grout. The step of filling grout hole 60 with grout may be performed prior to the step of inserting reinforcing members 20 and 30 into excavation hole 60. In order to inject the grout, the casing 50 is filled with water, a tremey pipe (not shown) is inserted into the casing 50 from above, and the discharge port at the lower end of the tremey pipe is placed near the lower end of the casing 50. After positioning, the discharge loca also discharges the grout and replaces the water in the casing 50 with the dirt. Then, if the specific gravity of the grout that overflows the mouth force at the upper end of the borehole 60 becomes the same as the specific gravity of the grout injected through the tremy tube, it is understood that the replacement is completed. [0016] Next, the casing 50 is lifted to remove at least some of the plurality of casing segments 52, thereby exposing the inner wall surface of the excavation hole 60 that was previously covered by the casing 50 ( Figure 2E). At this time, one or several casing segments 52 are left at the upper end portion of the excavation hole 60 and the reinforcing casing 54 is constituted by the remaining casing segments. The reinforcing sleeve 54 is formed by embedding the upper end portion of the reinforcing sleeve 54 in the structure 16 after the microphone opening pile 10 is completed and embedding the lower end portion in the ground. Is to increase. As another structural example of the reinforcing sleeve 54, after all the casing segments 52 have been pulled out and removed, a separately prepared sleeve member may be fitted to the upper end of the pile body 18 to form a reinforcing sleeve. Good. Further, the length of the reinforcing sleeve 54 may be appropriately determined according to the j8 value that is the characteristic value of the pile.

[0017] Next, a pile 18 having a grout Z ground joint is formed on the outer peripheral surface thereof by pressurizing and hardening further grout into the excavation hole 60 (Fig. 2F). The grout Z ground joint portion is formed over a long range excluding only the portion covered with the reinforcing sleeve 54 out of the total length of the outer peripheral surface of the micropile 10. In addition, when the grout is injected under pressure, the surrounding ground is strengthened by the penetration of part of the injected grout into the surrounding ground. The procedure for pressurizing the grout into the borehole 60 was to remove all the remaining casing segments except for the remaining casing segments among the multiple casing segments 52 that consisted of the casing 50. Later, the pressurized injection of grout into the borehole 60 may be performed in one operation, or the pressurized injection of grout into the borehole 60 is repeated each time one casing segment 52 is removed. Let's run it.

Next, a steel base plate 40 is welded and joined to the upper end of the steel pipe type reinforcing member 20, and the upper end of the steel bar type reinforcing member 30 is screwed and joined to the base plate 40 with a nut ( (Figure 2G). As a result, a pile for connecting the pile head of the micropile 10 connected to the steel pipe type reinforcement 20 and the steel bar type reinforcement 30 to the upper end of the pile body 18 to the structure 16 (see Fig. 1). A head-linking structure is provided. Thus, the micropile 10 is completed, and then the earth and sand around the reinforcing sleeve 54 are backfilled to embed the lower end portion of the reinforcing sleeve 54 in the ground, and the upper end portion of the reinforcing sleeve 54. Structure 16 footing Build up.

Since the micropile 10 is configured as described above, the load in the longitudinal direction of the micropile 10 passes through the steel pipe type reinforcing member 20 and the steel bar type reinforcing member 30 that extend substantially concentrically with each other. In addition, since the grout Z ground joint is formed over a long range of the outer peripheral surface of the micronoil 10, it has a large resistance against pulling force and pushing force. In addition, the structure in which the space between the inner peripheral surface of the steel pipe type reinforcing member 20 and the outer peripheral surface of the centrally arranged steel bar type reinforcing member 30 is filled with grout is suitable for bending load and shear load acting on the micropile 10. The micropile 10 can exert a great horizontal resistance by providing a large resistance and additionally installing the reinforcing sleeve 54 for the required length. Therefore, compared with the conventional micropile, the required number of micropile can be reduced, thereby shortening the construction period and reducing the construction cost. In order to clarify these excellent advantages of the micropile according to the present invention, data obtained by testing a micropile of a specific example are shown below.

[0020] Specific examples

The test micropile 70 shown in Fig. 3C was built in the test yard, and a vertical pull-out test on the vertical axis on the pile shaft was performed using the loading test equipment. Prior to the construction of Micropile 70, core boring was performed to sample the ground in the test yard. As shown in the chart of Fig. 3A, the layer structure of the ground found from the sample is a buried layer from the surface to a depth of 2.9 m, and below, a depth of 2.9 m force to 4.0 m is a loam layer and a depth of 4.0 m force. Fine sand layer up to 6.2m, clay layer from 6.2m to 7.7m depth, second fine sand layer from 7.7m to 8.8m depth, silt layer from 8.8m to 10.5m depth, and 10.5m depth ahead The third fine sand layer.

[0021] In order to know the hardness of each layer of the ground, N values were measured on the samples, and the results shown in the graph of Fig. 3B were obtained. In this graph, the vertical axis represents the depth from the ground surface, and the horizontal axis represents the N value. As is apparent from the graph, the soft layer 12 with an N value of 10 or less is constructed from the buried soil layer on the surface to the silt layer reaching a depth of 10.5 m. This fine sand layer constitutes a support layer 14 having an N value of 30 or more.

FIG. 3C shows a longitudinal sectional view of the test micropile 70. Build micropile 70 The outer diameter of the casing used for this purpose was 244.5 mm. Therefore, the outer diameter of the micropile 70 has a value obtained by adding the radial expansion generated by pressure injection of the grout to the outer diameter of the casing. Also, the total length of the micropile 70 is set to 15,500 mm according to the layer structure of the ground, the upper part of about 500 mm protrudes on the ground surface, and the middle part of about 10,000 mm passes through the soft layer 12. The lower end portion of the support layer 14 was extended by about 5,000 mm. The steel pipe type reinforcing member 20 was extended from the upper end of the micronoyle 70 to a position of 2,000 mm before the lower end of the micropile 70. The steel bar type reinforcing material 30 was made to extend from the upper end to the lower end of the micropile 70. Furthermore, in order to measure the axial load acting on the steel bar type reinforcing material 30, nine sets of strain gauges S1 to S9 were attached to various heights on the outer surface of the steel bar type reinforcing material 30. The positions of the strain gauges S1 to S9 are as shown in Fig. 3C. The ground surface GL, which is the reference for the pasting position shown in the figure, is the ground surface at the construction position of the micropile 70 and is 0.5 m lower than the ground surface of the original ground.

In the pull-out test, a pull-out force in the vertical direction was loaded on the upper end of the micropile 70 by a load test device, and the pull-out force loaded at that time was changed by the load site shown in the graph of FIG. As shown in the figure, this loading cycle consists of a total of five loading periods, each of the first to fourth loading periods being approximately 1 hour long, and the fifth loading period being approximately 2 hours long. did. During the first loading period, the pulling force was maintained at 180.2 kN for about 30 minutes in the first half and 359.5 kN for about 30 minutes in the second half. During the second loading period, the pulling force was maintained at 538.9 kN for about 30 minutes in the first half and 726.1 kN for about 30 minutes in the second half. During the 3rd loading period, the pulling force was maintained at 902.0kN for about 30 minutes in the first half and 1080.5kN for about 30 minutes in the second half. During the 4th loading period, the pulling force was maintained at 1259.8kN for about 30 minutes in the first half and 1454.8kN for about 30 minutes in the second half. During the 5th loading period, the pulling force is maintained at 1626.4 kN for the first approximately 30 minutes, 1799.7 kN for the next approximately 30 minutes, 1977.3 kN for the third approximately 30 minutes, and the last For about 30 minutes, it was maintained at 2156.7 kN. Therefore, there were a total of 12 periods during which the pulling force was maintained constant, and during each of these periods, the measured values were read with nine sets of strain gauges S1 to S9 affixed to the steel bar reinforcement 30. Also, at each reading, the top of the micropile 70 is the first position. We measured how much it rose from the position.

[0024] The above pull-out test was performed on three test micropiles. The graph of Fig. 5 shows the results. In this graph, the horizontal axis represents the ascent (vertical displacement) of the upper end of the test micropile, and the vertical axis represents the loaded vertical pulling force. As is apparent from the graph, the three test micro-knobs have a yield strength exceeding 1500 kN, and this yield strength is approximately the portion extending through the support layer with an N value of 30 or more. It is recognized as a very large value for a 5,000 mm micropile.

Furthermore, the axial force acting on one test micropile 70 at each pulling force was calculated based on the strain gauge reading. The graph of Fig. 6 shows the results. This graph shows the axial force calculated based on the readings of the strain gauges S1 to S9 affixed to the steel bar type reinforcing material 30, and acts on the micropile 70 as shown in this graph. The axial force is shallower than the depth of 10.5 m and extends through the soft layer 12, and the axial force decreases in the lower part. Therefore, for the micropile 70, Even in the soft layer 12, a sufficiently effective peripheral friction force acts.

Industrial applicability

FIG. 7A to FIG. 7C are diagrams showing application examples of the micropile 80 according to the present invention. The micropile according to the present invention can be used, for example, as a support pile for connecting the footing 82 of the pier and the support layer (Fig. 7A), or as a pile for fixing the footing 84 of the abutment. It can also be used in conjunction with the new footing extension 90 to reinforce the existing pier foundation 86 supported by the support pile 88 (Figure 7C). ).

Claims

The scope of the claims

[1] In the micropile for connecting the structure and the support layer in the ground,

A pile made of grout that has been hardened by being injected into an excavation hole formed in the ground, and at least a lower end portion of the pile that extends through the support layer;

A steel pipe type reinforcing material and a centrally arranged steel bar type reinforcing material which are embedded in the grout of the pile body and extend in the longitudinal direction of the pile body and are substantially concentric to each other;

A pile head connection structure for connecting the pile head of the micropile to the structure, which is provided at an upper end of the pile body and to which the steel pipe type reinforcing material and the steel bar type reinforcing material are joined;

The steel pipe type reinforcing material extends from the upper end of the pile body into the lower end portion of the pile body, and an outer peripheral surface thereof is covered with a grout of the pile body,

The steel bar type reinforcing material extends from the upper end of the pile body to the lower end of the pile body, and the lower end portion extends from the lower end force of the steel pipe type reinforcing material and is covered with the grout of the pile body. In the space between the inner peripheral surface of the steel pipe type reinforcing material and the outer peripheral surface of the steel bar type reinforcing material, the grout of the pile body is filled,

A micropile characterized by that.

[2] A reinforcing sleeve for covering the outer peripheral surface of the upper end portion of the pile body and reinforcing the upper end portion of the pile body is provided, and the upper end portion of the reinforcing sleeve is embedded in the structure and the lower end portion is provided. The micropile according to claim 1, wherein is embedded in the ground.

[3] The reinforcing sleeve is constituted by at least one remaining casing segment among a plurality of casing segments constituting the casing used to form the excavation hole. 3. The micronail according to claim 2, wherein:

[4] The steel pipe type reinforcing material is configured by connecting ends of a plurality of steel pipe segments, and the steel bar type reinforcing material is configured by connecting ends of a plurality of steel bar segments. The micropile according to claim 1, wherein:

[5] According to the method of constructing a micropile for connecting the structure and the support layer in the ground, the ground is excavated while adding a plurality of casing segments, and the casing sections are excavated. Forming a borehole provided with a casing made of a cement such that at least a lower end portion thereof extends through the support layer;

A steel pipe type reinforcing material configured by connecting ends of a plurality of steel pipe segments and a steel bar type reinforcing material configured by connecting ends of a plurality of steel bar segments are inserted into the excavation hole. In this step, the steel pipe type reinforcing material and the steel bar type reinforcing material extend substantially concentrically in the longitudinal direction of the excavation hole, and the steel bar type reinforcing material is arranged in the center, and the steel pipe The mold reinforcement extends from the upper end of the excavation hole into the lower end portion of the excavation hole, and the steel bar type reinforcement extends from the upper end of the excavation hole to the lower end of the excavation hole. A reinforcing material insertion step, wherein a lower end portion of the steel bar type reinforcing material extends from a lower end of the steel pipe type reinforcing material;

Filling the borehole with grout;

Lifting the casing to remove at least some of the plurality of casing segments to expose an inner wall of the borehole covered by the casing;

By grouting the grout with pressure and hardening it,

Forming a pile body having a Z ground joint;

A step of providing, at the upper end of the pile body, a pile head connection structure for connecting the pile head of the micropile, which is joined to the steel pipe type reinforcement and the steel bar type reinforcement, to the structure;

A method for constructing a micropile, comprising:

[6] A reinforcing sleeve for covering the outer peripheral surface of the upper end portion of the pile body and reinforcing the upper end portion of the pile body is provided on the upper end portion of the pile body, and the upper end portion of the reinforcing sleeve is provided on the structure. 6. The method of constructing a micropile according to claim 5, wherein the method is embedded and the lower end portion is embedded in the ground.

[7] When the casing is lifted to remove at least some of the plurality of casing segments, at least one casing segment of the plurality of casing segments is left in an upper end portion of the drilling hole. 7. The micropipes according to claim 6, wherein the reinforcing sleeve is constituted by the remaining casing segment. How to build

[8] The present invention is characterized in that, after removing all the casing segments to be left out of the plurality of casing segments, the grout is injected into the excavation hole by a single operation. The method for constructing a micropile according to claim 5.

9. The method for constructing a micropile according to claim 5, wherein each time the plurality of casing segments are removed, the pressure injection of grout into the borehole is repeatedly performed.