Method for constructing the foundation structure

Abstract

To provide a foundation structure construction method capable of improving quality of a pile hole by forming the pile hole using an optimal excavation tool by setting a soil discharge section and a soil left section.SOLUTION: A foundation structure construction method comprises steps of: setting an area of a pile hole foot protection part 42 in a pile hole 40; setting a soil discharge segment where excavated soil is discharged upward; and setting a left soil section where the excavated soil is left downward and an excavated left soil amount. Then, the soil discharge segment is excavated (a, b, c) while discharging the excavated soil with a first excavation tool 10. In the left soil segment continued downward from the soil discharge segment, the ground is excavated with a second excavation tool 15 while loosening the ground, and in the foot protection part 42, by pumping out cement milk, the excavated soil and the cement milk are agitated and mixed or the excavated soil is replaced with the cement milk to form the pile hole foot protection part 42. The pile hole 40 is formed by injecting the cement milk while pulling up the second excavation tool 15 (d, e). A foundation structure 60 is constructed (h) after inserting a precast pile 30 into the pile hole 40 (f, g).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This invention relates to a method for constructing a foundation structure, which uses an excavation bucket for so-called site-cast piles, for example, to excavate a pile hole with a diameter of 50 cm or more, and embed a precast pile in the pile hole to form the foundation structure.

Background Art

[0002] There are a so-called site-cast pile method in which reinforcing cages and concrete are poured into a pile hole excavated at a foundation pile construction site to construct a foundation pile, and a so-called precast pile method in which a precast pile (made of concrete, steel pipe, etc.) is poured into a pile hole excavated at a foundation pile construction site together with cement milk, and various devices have been made for each. In addition, a method has been proposed in which the site-cast pile method and the precast pile method are combined, and a Kelly bar and a screw rod, which are excavation machines used for site-cast piles, are used to excavate a pile hole, and a stabilizing liquid (cement milk or soil cement) used in the precast pile method is injected to embed a precast pile (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In an earth drill using a Kelly bar, unlike an excavation machine used in the precast pile method, it is difficult to inject a stabilizing liquid or the like through the inside of the Kelly bar. Even if a separate pipe is prepared inside the Kelly bar, the Kelly bar frequently expands and contracts and is lifted to the ground to discharge soil, so it is also complicated to prepare a separate pipe for injecting the stabilizing liquid into the Kelly bar and make the tip reach the bottom of the pile hole. Therefore, it has been difficult to realize this method.

Means for Solving the Problems

[0005] This invention solves the aforementioned problems by using separate excavation equipment for the pile hole shaft portion up to the vicinity of the support layer assumed in the design, and for the pile hole foundation reinforcement portion located at the design support layer. For the excavation of the pile hole shaft portion, an excavation bucket-like device used in cast-in-place pile construction is used to discharge the excavated soil to the surface, and for the excavation of the pile hole foundation reinforcement layer, foundation reinforcement portion, and pile perimeter portion, equipment used in precast pile construction is used.

[0007] In other words, this invention is This is a method for constructing a foundation structure characterized by setting pre-fabricated piles in pile holes equipped with pile hole root reinforcement sections in predetermined sections within the ground, as described below. (1) The area of ​​the pile hole foundation reinforcement section is set at the lower end of the pile hole, a soil discharge section is set above the pile hole for discharging excavated soil, and a residual soil section and the amount of residual excavated soil are set below the pile hole. (2) The pile hole shaft from the ground to the supporting layer or its vicinity is excavated using an excavation bucket used for cast-in-place piles. has Excavation is performed using a drilling machine equipped with the first drilling tool. The excavated soil within the aforementioned soil removal section is removed to the surface, leaving the soil removal section virtually free of soil and sand. . (3) Once the excavation of the pile hole shaft is completed, the first excavating tool is lifted to the ground and removed from the excavating machine. (4) Next, a coupling device to which a fluid supply means from the ground is connected is attached to the tip of the drilling machine, and Used in precast pile construction methods The second drilling tool is attached and inserted into the pile hole. (5) Using the second excavating tool, the pile hole foundation reinforcement portion is excavated below the pile hole shaft portion. (6) Next, once the excavation of the pile hole foundation is completed, cement grout is supplied from the above-ground plant to the connecting device through the fluid supply means, and cement grout is discharged from the second excavator to form the pile hole foundation. (7) Next, while raising the second excavating tool, cement grout is injected above the pile hole foundation to form the pile hole. (8) Next, the pre-fabricated pile is inserted into the pile hole, and once the cement grout has solidified, the foundation structure is constructed.

[0009] The term "excavation bucket" as used above refers to a general term for excavators used in so-called cast-in-place pile construction methods. In this invention, any construction method such as the all-casing method, reverse drilling method, or earth drilling method can be adopted, and an excavator appropriate to each method can be used.

[0010] Furthermore, the term "cement milk" in the above-mentioned context refers to cement milk of various concentrations, soil cement (a mixture of cement milk and muddy water in the pile hole), and so on.

[0011] The fluid supply means mentioned above can be any means, such as pipes or hoses, that can supply water or cement grout from the ground to the connecting device.

[0012] Furthermore, the amount (percentage) of soil and sand mixed into the foundation reinforcement section is measured as follows, and can be pre-set based on this. Typically, the process for constructing a foundation reinforcement involves first excavating the supporting ground while discharging drilling water from the tip of the drilling head, turning the foundation reinforcement section into mud, and then switching the drilling water to foundation reinforcement liquid (cement grout) and injecting a predetermined amount (for example, the volume of the foundation reinforcement). The construction is carried out under the assumption that the foundation reinforcement section will be replaced from mud to cement grout by the injection of this foundation reinforcement liquid. However, since the specific gravity and viscosity of the original mud in the foundation reinforcement cannot be confirmed (it is unknown and cannot be controlled during construction), a clean replacement phenomenon like that performed in a glass of air does not occur. Furthermore, in the conventional pre-boring method, where pre-cut piles are placed in pre-excavated pile holes, the pile hole shaft is generally not discharged to the surface but rather broken down and turned into mud by excavation water. As a result, a large amount of soil remains in the pile hole shaft, which can either settle naturally or be pushed in during pile insertion and mixed into the foundation reinforcement. In a case where cores were taken from the foundation reinforcement area after construction, and their solidification strength was examined, followed by component analysis to investigate the cement content, the mixing ratio of cement grout and slurry was found to be: 9:1~5:5 The situation was such that the quality of the foundation reinforcement, specifically the cement grout replacement rate (or soil and sand mixing rate), varied greatly depending on the ground conditions and construction methods. A higher replacement rate results in a larger amount of cement grout in the foundation reinforcement components, fewer impurities, and a higher quality foundation reinforcement. However, this cannot be verified, and therefore cannot be controlled with current technology.

[0013] Figure 4 shows the results of a laboratory experiment conducted at an actual site. After excavating the supporting layer that would form the foundation reinforcement section, mud was collected from that depth, and the mixing ratio of the mud with the foundation reinforcement liquid (cement grout with a water-cement ratio of approximately 60%) was varied. In this experiment, the compressive strength after solidification decreased as the mud mixing rate increased. Plotting the solidification strength results of samples taken from the actual foundation reinforcement section in Figure 4 suggests that the mud mixing rate at this site was approximately 12%.

[0014] Furthermore, we will provide a more detailed explanation of the residual soil and the residual soil section based on Figure 5. An excavation of a foundation reinforcement section 42 to a depth H is set at the lower part of the shaft section 41 of the pile hole 40, and the residual soil section is set to (1 / 3) H (Figure 5(a). The soil above the residual soil section is removed. Here, if cement grout equal to 100% of the volume of the foundation reinforcement section is injected into the foundation reinforcement section 42, then (1 / 3) H of residual soil will remain in the pile hole 40 (Figure 5(b)). Therefore, if cement grout and residual soil are mixed evenly, soil cement of approximately (1 + 1 / 3)H can be produced (Figure 5(c)). Thus, the component ratio of soil cement is: Cement grout content: Residual soil content = (100 / 133):(33 / 133) ≒75:25 This results in soil cement with a residual soil content of 25%. Similarly, if the residual soil section is (1 / 2)H, the component ratio of the soil cement will be: Cement grout content : Residual soil content = (100 / 150) : (50 / 150) ≒67:33 As a result, it becomes soil cement with a residual soil mixing ratio of 33%. Similarly, when the residual soil section is H, the constituent ratio of the soil cement is Cement milk content: residual soil content = (100 / 200):(100 / 200) = 50:50 As a result, it becomes "soil cement with a residual soil mixing ratio of 50%". In addition, when the total amount at a depth of H is excavated (no residual soil), it becomes 100% cement milk.

Advantages of the Invention

[0015] In this invention, the shaft part of the pile hole is excavated with an excavation bucket used in the so-called in-situ pile construction method, and the earth and sand in the shaft part of the pile hole are discharged almost to the ground. Therefore, almost no earth and sand remains in the shaft part of the pile hole, and thus the earth and sand in the shaft part of the pile do not mix into the pile hole consolidation part. Also, although the earth and sand of the designed support layer (designed in advance) left unexcavated at the lower end of the pile hole will mix into the pile hole consolidation part, the amount can be adjusted by the length of the shaft part of the pile hole. Generally, in the construction of precast piles, the shaft part of the pile hole is not discharged to the ground, but is dug and collapsed with excavation water to form mud. Therefore, a large amount of earth and sand remains in the shaft part of the pile hole, and these will settle naturally or be pushed in when inserting the precast pile, and often mix into the pile hole consolidation part. This invention is a construction method that combines the advantages of two construction methods in which the shaft part of the pile hole up to near the support layer (section determined in advance by design) and the pile hole consolidation part located in the support layer are constructed separately with an excavation device. Since a precast pile is buried in the pile hole constructed in this way, the quality of the pile hole such as the consolidation part can be improved.

Brief Description of the Drawings

[0016] [Figure 1] (a) to (h) are longitudinal sectional views for explaining the first embodiment of this invention. [Figure 2] (a) to (h) are longitudinal sectional views for explaining the second embodiment of this invention. [Figure 3] (a) is an enlarged plan view of the state where a precast pile is inserted into a vertical jig, and (b) is a front view. [Figure 4]This is a graph showing an example of measuring the soil-sand mixture ratio in the foundation reinforcement area. [Figure 5] (a) to (c) are diagrams illustrating the residual soil sections in the foundation reinforcement area. [Modes for carrying out the invention]

[0017] 1. First Embodiment

[0018] Embodiments of this invention will now be described. In this embodiment, the pile hole 40 consists of a pile hole shaft portion 41 and a pile hole foundation portion 42 below it, with the pile hole foundation portion 42 being formed with a depth H and a diameter D. Furthermore, the pile hole shaft portion 41 is excavated using an excavation machine used in conventional cast-in-place pile construction, and the pile hole foundation portion 42 is excavated using an excavation machine used in precast pile construction.

[0019] In this configuration, the pile hole shaft section 41 is set as a soil discharge section for removing excavated soil, and the pile hole foundation reinforcement section 42 is set as a residual soil section (depth H) where the excavated soil remains.

[0020] (1) Prepare a rod 11 and a drilling bucket 10 to be used in the earth drilling method applied to cast-in-place piles, and install them on heavy machinery (not shown) used in the earth drilling method. Here, the pile hole 40 consists of a pile hole shaft portion 41 extending to the support layer 7 or near the support layer 7 and a pile hole base reinforcement portion 42 extending into the support layer 7 from the lower end of the pile hole shaft portion 41, with the diameter of the pile hole shaft portion being assumed to be about 1.2m. Furthermore, the rod 11 is normally designed to be easily extendable and retractable, allowing the drilling bucket 10 to be easily lifted from the excavation point to the ground surface 1 during soil removal (not shown in the diagram).

[0021] (2) On the ground surface 1, a surface casing (steel pipe) 5 is driven in according to the excavation position, and a drilling bucket is placed inside the surface casing 5 to start excavating the pile hole shaft 41 (Figure 1(a)). With the drilling bucket 10, once the drilling bucket 10 is filled with excavated soil, the drilling bucket 10 is lifted to the ground surface 1 together with the rod 11, the excavated soil inside the drilling bucket 10 is discharged, and the rod and drilling bucket 10 are lowered to continue excavating the pile hole shaft 41. Also, as in the conventional method, in order to prevent the hole wall from collapsing, the inside of the pile hole shaft 41 is filled with a drilling fluid such as bentonite liquid 46 from the hose 13 while excavating.

[0022] (3) When the drilling bucket 10 reaches a predetermined depth (for example, the supporting layer 7) (Figure 1(b)), the drilling by the drilling basket 10 is stopped, the rod 11 and the drilling basket 10 are pulled up to the ground surface 1, and the drilling basket 10 is removed from the rod 11. Furthermore, the phrase "when a predetermined depth is reached" includes the case of reaching the support layer 7, as well as the case of being slightly before the support layer 7, or having excavated a little further into the support layer 7.

[0023] (4) Next, a connecting device (so-called swivel) 12 (Figure 1(c)(d)) is attached to the tip of the rod 11, to which a hose 13a for injecting water or cement grout can be connected instead of the drilling basket 10. A drilling head 15 used in precast pile construction is then attached to the end of the connecting device 12 (Figure 1(c)). The drilling head 15 is constructed by attaching the base ends of swingable drilling arms 17, 17 to a head body 16 that can be connected to the lower end of the rod 11. The drilling head 15 also has a fixed drilling blade attached to the lower end of the head body 16 and a movable drilling blade attached to the tip of the drilling arm 17, and the swing angle of the drilling arms 17, 17 can be increased to enable drilling of large diameters accordingly. Furthermore, cement grout (or water) is supplied from the cement grout plant on the ground surface 1 to the connecting device 12 through hose 13a, and the structure allows cement grout to be discharged into the pile hole from the discharge port 18 at the tip of the head body 16 of the drilling head 15 (Figure 1(c)). The hose 13a is formed to extend downward as the drilling head 15 and the connecting device 12 descend.

[0024] (5) The drilling head 15 passes through the pile hole shaft portion 41 and is brought into contact with the lower end (bottom) of the pile hole shaft portion 41 to drill the pile hole foundation portion 42, which has a larger diameter D than the pile hole shaft portion 41, to the required depth H (Figure 1(d)).

[0025] (6) Next, the drilling rod 19 and drilling head 15 are pulled up to the ground surface 1 while discharging cement grout 48, set to the required concentration, from the discharge port 18 of the head body 16 of the drilling head 15, starting from the bottom of the pile hole foundation section 42 (Figure 1(d)(e)). As a result, the muddy water and bentonite solution 47 that filled the pile hole 40 (pile hole shaft section 41 and pile hole foundation section 42) are replaced by or mixed with cement grout 48. In addition, the injection of cement grout 48 pushes the bentonite solution 47 out to the ground surface 1, making it easy to recover it on the ground. It is also possible to produce soil cement by mixing muddy water with cement grout in the pile hole foundation section 42.

[0026] (7) Next, the precast piles 30 are embedded in the pile hole 40 by the usual method (Figure 1(f),(g),(h)). That is, the lowest precast pile 31 is suspended from a heavy machine for embedding precast piles (for example, a crawler crane), the lowest precast pile 31 is sunk into the pile hole 40, and is held in place by a standard pile holder 21 installed at the opening of the pile hole, and the next intermediate precast pile 32 is connected to the upper end of the lowest precast pile 31 (Figure 1(f)), and after the holding by the holder 21 is released, the connected precast piles 31 and 32 are sunk into the pile hole 30.

[0027] (8) Subsequently, intermediate prefabricated piles 32 are connected in order, and finally the uppermost prefabricated pile 33 is connected. The connected prefabricated piles 31, 32, and 33 are then sunk into the pile hole 30. With the lower end 31a of the lowest prefabricated pile 31 located within the pile hole foundation reinforcement section 42, the pile head cap 35 connected to the upper end 33b of the uppermost prefabricated pile 33 is held in place by the holder 21 until the cement grout 48 hardens (Figure 1(g)). Once the cement grout 48 has hardened, the pile head cap 35 and the retainer 21 are removed, and the foundation structure 50 is completed (Figure 1(h)).

[0028] 2. Other Examples of the First Embodiment

[0029] (1) In the above, a pile hole base reinforcement portion 42 with a larger diameter than the pile hole shaft portion 41 was formed following the lower end of the pile hole shaft portion 41, but the pile hole base reinforcement portion 42 can also be formed with approximately the same diameter as the pile hole shaft portion 42 (not shown).

[0030] (2) In addition, as described above, the discharge port 18 for the cement milk is located at the lower end of the head body 16, which improves discharge efficiency, but it can also be located at any position on the head body 16 or the drilling arm 17 (not shown). Furthermore, as described above, the drilling head 15 is constructed by pivotably attaching drilling arms 17, 17, each equipped with a movable drilling blade at its tip, to the head body 16. While this structure is preferable in terms of drilling efficiency, the structure of the drilling head is arbitrary, such as a spiral structure (not shown), as long as it can drill a pile hole enlargement section 42 for sinking the precast pile 30 within the supporting layer.

[0031] (3) In addition, the precast piles 30 described above can be other types of precast piles, such as straight piles, as well as so-called knotty piles with annular ribs in the axial direction. However, it is preferable to have annular ribs only at the lower end of at least the lowest precast pile 31, and to have a structure in which the annular ribs can be placed within the pile hole foundation reinforcement section 42 (not shown). Furthermore, although the pre-fabricated pile 30 is assumed to be a concrete pile, piles with a steel pipe covering the outer circumference of a concrete pile, or so-called steel pipe piles, can also be used, provided that they meet the required strength and other performance requirements (not shown).

[0032] (4) In the above, the surface casing 5 is usually removed after the foundation structure 60 is constructed, but the timing of its removal is arbitrary as long as the pile hole shaft portion 41 has been constructed. It can also be left in place and incorporated into the structure (footing) built on the foundation structure. Furthermore, the surface casing 5 can be omitted (not shown in the diagram).

[0033] (5) In the above, the connecting device 12 and the drilling head body 16 were made hollow, and cement grout was supplied from the plant on the ground surface 1 to the connecting device 12, and cement grout 48 was discharged from the discharge port 18 of the drilling head body 16 into the pile hole foundation reinforcement section 42. However, it is also possible to run a pipe or hose (hereinafter referred to as pipe, etc.) connected from the plant along the drilling rod 11, open the pipe, etc. near the drilling head body 16, and discharge cement grout from the pipe, etc. (not shown).

[0034] (6) In the above, the excavation range of the pile hole shaft portion 41 by the drilling basket 10 can also be determined from the amount of soil mixed in the foundation reinforcement portion. For example, if the depth (length) L of the foundation reinforcement portion corresponding to the supporting layer 7 is 2m, 1m is excavated with the drilling basket 10, and the excavated portion is left at the surface. 1 The soil is then removed. In this case, if the remaining 1 meter below is excavated while loosening the ground with the excavation head 15, 1 meter of soil will remain in the pile hole foundation reinforcement section 42, and this soil will be mixed into the injected cement grout. Therefore, in this case, if mixed evenly, soil cement with a soil content of 33% will be produced in the pile hole foundation reinforcement section 42. Furthermore, if the depth (length) H of the pile hole reinforcement section 42 corresponding to the supporting layer 7 is 2m, 1.4m is excavated with the drilling basket 10, and the excavated portion is removed to the surface 1. In this case, when the remaining 0.6m below is excavated while loosening the ground with the drilling head 15, 0.6m of soil will remain in the pile hole reinforcement section 42, and this soil will be mixed into the injected cement grout. Therefore, in this case, soil cement with a soil mixing rate of 25% will be generated in the pile hole reinforcement section 42. The amount of soil mixed determines the solidification strength of the pile hole reinforcement section 42, and consequently the strength of the foundation structure 60, so the depth to which the drilling basket 10 is to be excavated is set according to the predetermined strength of the foundation structure 60.

[0035] 3. Configuration of the second embodiment

[0036] In this embodiment, a method is used to construct a foundation structure 50 by sinking multiple pre-fabricated piles 30 into a single pile hole 40. Here, we have described the process of burying three pre-fabricated piles 30, 30 into a single pile hole 40, multiple In that case, the number can be anything, such as 2 or 4. Generally, precast concrete piles 30 are widely used in small diameter (1 m or less) types, while cast-in-place piles have many excavation devices that can handle depths of 2 m or more. This embodiment utilizes these advantages to form a single large-diameter pile hole 40 and then sinks multiple precast piles 30, which are smaller in diameter than the large-diameter pile hole 40. In this embodiment, a vertical jig 62 is used. The vertical jig 62 is a cylinder approximately 2m long with an outer diameter corresponding to the outer diameter of the pile hole 40 (pile hole shaft portion 41). The cylinder is configured with openings 63, 63 provided axially within it, corresponding to the outer diameter of the pre-fabricated pile 30 to be used. In this embodiment, the vertical jig 62 has three openings 63, 63 evenly formed in the axial direction of the vertical jig 62 (Figures 3 and 2(f)). The diameter of the pre-fabricated pile 30 is assumed to be approximately 90cm.

[0037] (1)~(6) Similar to the first embodiment, the drilling bucket 10 is used to excavate the shaft portion 41 of the pile hole (Figures 1(a)(b), 2(a)(b)), the drilling head 15 is used to excavate the base portion 42 of the pile hole, and cement grout 46 is filled into the pile hole 40 (shaft portion 41, enlarged base portion 42) (Figures 1(c)~(e)), 2(c)~(e)). Also, similar to the first embodiment, the pile holder 21, pile head cap 23, etc. are used.

[0038] (7) Next, the vertical jig 62 is inserted into the upper end of the pile hole 30 (pile hole shaft portion 31) along the inner surface of the surface casing 5 (Figure 2(f)).

[0039] (8) Next, pre-fabricated piles 30 are constructed in the same manner as in the first embodiment, within each opening 63 of the vertical jig 62 fixed to the upper end of the pile hole 30 (pile hole shaft portion 31). That is, three of the lowest pre-fabricated piles 31 are suspended from a heavy machine (excavator) for ordinary pre-fabricated pile installation (Figure 3(g)), and each pre-fabricated pile 31 is sunk into the pile hole 40 through the opening 61 of the vertical jig 62 and held by an ordinary pile holder (not shown) installed in the opening of the pile hole. Three intermediate pre-fabricated piles 32 are connected to the upper end of each of the lowest pre-fabricated piles 31 (Figure 1(f)), the hold is released, and the three connected sets of pre-fabricated piles 31 and 32 are sunk into the pile hole 30. Subsequently, the necessary intermediate pre-fabricated piles 32 and the uppermost pre-fabricated pile 33 are connected in order, and the three connected sets of pre-fabricated piles 31, 32, and 33 are sunk into the pile hole 30. With the lower end 31a of the lowest prefabricated pile 31 positioned within the pile hole foundation reinforcement section 42, the upper end 33b of the prefabricated pile 33 is held on the ground by a connecting holder 65 until the cement grout 48 hardens (Figure 2(h)). The connecting holder 65 consists of a holding jig 23 attached to the upper end of each prefabricated pile 33, whose height is adjusted using a hydraulic jack or the like to hold it at the upper end of the surface casing 5.

[0040] (9) Once the cement milk 48 has hardened, the connecting retainer 65 and the surface casing 5 are removed, and the foundation structure 50 is completed (Figure 2(i)). The timing for removing the surface casing 5 is the same as in the first embodiment.

[0041] 4. Other examples of the second embodiment

[0042] (1) In the above, three pre-fabricated piles 31, three pre-fabricated piles 32, and three pre-fabricated piles 33 were suspended together and sunk simultaneously in three sets while being connected. However, it is also possible to construct pre-fabricated piles 30, 30 by passing each one through the opening 63 of the vertical jig 62 and connecting them one set at a time (not shown in the diagram).

[0043] (2) In addition, although the vertical jig 62 is cylindrical in shape as described above, the structure is arbitrary as long as it has openings 63, 63 that allow pre-fabricated piles 30 to be inserted at predetermined intervals (not shown).

[0044] (3) In addition, the other embodiments described above are the same as those of the first embodiment. [Explanation of Symbols]

[0045] 1. Earth's surface (ground level) 5. Surface casing 7 Support layer 10 Drilling Buckets 11 rods 12 Coupling device 13, 13a hose 15 drilling heads 16. Head body of the drilling head 17. Drilling arm of drilling head 18. Discharge port of the drilling head 19 Drilling Rod 21 Pile holder 23 Pile head cap 30 Pre-fabricated piles (connected state) 31. Pre-fabricated piles at the bottom 31a Lower end of precast pile 31b Upper end of precast pile 32 Pre-fabricated piles for the intermediate stage 33. Pre-fabricated piles at the top 33b Upper end of precast pile 40 Pile hole 41 Pile hole shaft 42. Pile hole foundation reinforcement section 46 Bentonite solution (drilling fluid) 48 Cement Milk 60 Basic structure 62 Vertical jig 63. Opening of the vertical jig 65 Connection holder

Claims

[Claim 1] A method for constructing a foundation structure, characterized by setting pre-fabricated piles in pile holes equipped with pile hole root reinforcement sections in predetermined sections within the ground, as described below. (1) The area of ​​the pile hole foundation reinforcement section is set at the lower end of the pile hole, a soil discharge section is set above the pile hole for discharging excavated soil, and a residual soil section and the amount of residual excavated soil are set below the pile hole. (2) The pile hole shaft from the ground to the supporting layer or its vicinity is excavated using an excavation machine equipped with a first excavation tool having an excavation bucket used for cast-in-place piles, and the excavated soil in the soil removal section is removed to the ground, so that the soil removal section is left with almost no soil remaining. (3) Once the excavation of the pile hole shaft is completed, the first excavating tool is lifted to the ground and removed from the excavating machine. (4) Next, a coupling device connected to a fluid supply means from the ground is attached to the tip of the drilling machine, and a second drilling tool used in the pre-fabricated pile construction method is attached, and the second drilling tool is inserted into the pile hole. (5) Using the second excavating tool, the pile hole foundation reinforcement portion is excavated below the pile hole shaft portion. (6) Next, once the excavation of the pile hole foundation is completed, cement grout is supplied from the above-ground plant to the connecting device through the fluid supply means, and cement grout is discharged from the second excavator to form the pile hole foundation. (7) Next, while raising the second excavating tool, cement grout is injected above the pile hole foundation to form the pile hole. (8) Next, the pre-fabricated pile is inserted into the pile hole, and once the cement grout has solidified, the foundation structure is constructed.

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