Wave-shaped grouting bulb of micropile and method for forming same

Abstract

The present invention provides a wave-shaped grouting bulb (100) for securing an underground bearing capacity of a steel bar (10), the bulb comprising a plurality of protrusions (120), which have a predetermined maximum diameter (D1) and are formed along the longitudinal direction of a cylindrical pillar part (110) extending downward, wherein the neighboring protrusions (120) are formed to be spaced from each other by a predetermined formation distance (s). The present invention has an advantageous effect of improving a skin friction force and resistance to compression and pullout in the grouting bulb integrated with the steel bar and thus enhancing structural stability in the micropile body.

Claims

1. A method for forming a wave-shaped grouting bulb for securing an underground bearing capacity of a steel bar, wherein a micropile is constructed using jet-grouting, the method comprising: a first step of forming a drilled hole by using a jet-grouting device which comprises a drilling machine that drills a ground to form the drilled hole, a grout material spray hole that sprays a grout material, and a grout material feeding pipe that supplies the grout material to the grout material spray hole, and forming the grouting bulb by spraying, at high pressure, the grout material from the grout material spray hole into the drilled hole; the wave-shaped grouting bulb comprising: a plurality of protrusions, which have a uniform maximum diameter and are formed along the longitudinal direction of a cylindrical pillar part extending downward, wherein the neighboring protrusions are formed to be spaced from each other by a predetermined formation distance, the wave-shaped grouting bulb, wherein a longitudinal cross-section of the wave-shaped grouting bulb forms a waveform, the wave-shaped grouting bulb, wherein the steel bar is inserted into the pillar part, the wave-shaped grouting bulb, wherein a length of the protrusions is twice the maximum diameter, the wave-shaped grouting bulb, wherein the formation distance is the maximum diameter or twice the maximum diameter.

2. The method of forming the wave-shaped grouting bulb of claim 1, further comprising: a second step of withdrawing the jet-grouting device out of the drilled hole, and forming the pillar part inside the drilled hole by spraying the grout material from the grout material spray hole into the drilled hole; and a third step of inserting the steel bar into the pillar part.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a view illustrating a cross-section of a micropile in which a general and conventional waveform cross-section is applied.

(2) FIG. 2 is a view illustrating a cross-section of a micropile according to one embodiment of the present invention.

(3) FIG. 3 is a perspective view of a grouting bulb into which a steel bar according to one embodiment of the present invention is inserted.

(4) FIG. 4 is a view illustrating a method for forming a wave-shaped grouting bulb according to one embodiment of the present invention.

(5) FIG. 5 is a view illustrating shapes of various grouting bulbs which are tested for securing a maximum ultimate bearing capacity when a length of a protrusion is a maximum diameter of a grouting bulb.

(6) FIG. 6 is a view illustrating ultimate bearing capacities of various grouting bulbs which are tested for securing a maximum ultimate bearing capacity when a length of a protrusion is a maximum diameter of a grouting bulb.

(7) FIG. 7 is a view illustrating shapes of various grouting bulbs which are tested for securing a maximum ultimate bearing capacity when a length of a protrusion is twice a maximum diameter of a grouting bulb.

(8) FIG. 8 is a view illustrating ultimate bearing capacities of various grouting bulbs which are tested for securing a maximum ultimate bearing capacity when a length of a protrusion is twice a maximum diameter of a grouting bulb.

MODE FOR CARRYING OUT THE INVENTION

(9) Embodiments of a micropile with a wave-shaped grouting bulb and a method for forming same in accordance with the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention with reference to the accompanying drawings, identical or corresponding elements will be assigned with same reference numerals, and no redundant description thereof will be provided.

(10) Terms such as first and second can be used in merely distinguishing one element from other identical or corresponding elements, but the above elements should not be restricted to the above terms such as first and second.

(11) When one element is described to be coupled to another element, it does not refer to a physical, direct contact between these elements only, but it shall also include the possibility of yet another element being interposed between these elements and each of these elements being in contact with said yet another element.

(12) FIG. 1 is a view illustrating a construction state of a micropile in which a grouting bulb with a conventional waveform cross-section is applied.

(13) The waveform cross-section of the conventional grouting bulb has a shape in which a plurality of protrusions 120 forming the waveform is continuously connected.

(14) Also, since shapes and sizes of the protrusions 120 are irregular, there has been a phenomenon that concentrated stress occurs at specific portions of the protrusions 120, which has made it difficult to secure stable bearing capacity of the micropile.

(15) Accordingly, the present invention intends to provide a shape of a wave-shaped grouting bulb allowing a steel bar 10 to have a maximum ultimate bearing capacity by suggesting a length (L) and a formation distance (s) of the protrusions 120.

(16) A wave-shaped grouting bulb according to one embodiment of the present invention is characterized in that there are formed a plurality of protrusion 120, which have a uniform maximum diameter (D1) and are formed along the longitudinal direction of a cylindrical pillar part 110 extending downward, wherein the neighboring protrusions 120 are formed to be spaced from each other by a predetermined formation distance (s) (FIG. 2).

(17) Accordingly, the longitudinal cross-section of a grouting bulb 100 according to the present invention forms a waveform.

(18) A steel bar 10 generally includes: a steel bar 11 inserted into the ground; and a head part 12 connected to an upper portion of the steel bar 11 which are exposed above the ground, and preventing the steel bar 11 from being introduced inside the ground (FIG. 1).

(19) The steel bar 11 of the steel bar 10 is inserted and fixed into a pillar part 110.

(20) The steel bar 11 is inserted into the pillar part 110 before a grout material for forming the pillar part 110 is cured, and then as the pillar part 110 is being cured, the grouting bulb 100 and the steel bar 10 may be integrally formed.

(21) When compared to the protrusions 120 of the conventional wave-shaped grouting bulb in which the neighboring protrusions 120 are continuously formed, the protrusions 120 of the wave-shaped grouting bulb according to the present invention, in which the neighboring protrusions 120 are formed spaced from each other by a predetermined formation distance (s), may secure much higher ultimate bearing capacity.

(22) This effect can be confirmed with reference to FIGS. 5 and 6.

(23) FIG. 5 is a view illustrating shapes of various grouting bulbs which are tested for securing a maximum ultimate bearing capacity when a length of a protrusion is a maximum diameter of a grouting bulb.

(24) FIG. 6 is a view illustrating data with regard to ultimate bearing capacities of the micropiles corresponding to the grouting bulbs shown in FIG. 5.

(25) Referring to the data of FIG. 6, when compared to a conventional grouting bulb WM1 in which a formation distance (s) is formed to be zero and an ultimate bearing capacity is 723 (kN), it may be confirmed that grouting bulbs WM2 and WM3 according to one embodiment of the present invention, in which protrusions 110 are formed spaced from each other by a formation distance (s), exert a higher ultimate bearing capacity although including a smaller numbers of protrusions 110 than the conventional grouting bulb.

(26) When a distance (L) of a protrusion 120 is a maximum diameter (D1), a formation distance (s) which is twice the maximum diameter (D1) may secure a maximum ultimate bearing capacity (FIG. 6).

(27) Also, when a distance (L) of a protrusion 120 is twice a maximum diameter (D1), a formation distance (s) which is twice the maximum diameter (D1) may secure a maximum ultimate bearing capacity (FIG. 8).

(28) When a distance (L) of a protrusion 120 is a maximum diameter (D1) or less, it is difficult to form grouting bulbs in a construction site because the spacing between the grouting bulbs becomes too small.

(29) When the distance (L) of the protrusion 120 is twice the maximum diameter (L), there is a limitation such as excessive construction and a rise in construction costs due to increased grout volume.

(30) Therefore, considering site constructability and economic feasibility, experiments have been performed with respect to the lengths (L) of the protrusion 120, which range from the maximum diameter (D1) to twice the maximum diameter (D1).

(31) Referring to the data in FIG. 6 and FIG. 8, it may be confirmed that WM3 has a higher ultimate bearing capacity than WM1.

(32) That is, since the ultimate bearing capacity may be secured without forming continuous protrusions 100, construction difficulties may be solved and construction expenses may be reduced by saving grout materials. Most of all, the high bearing capacity may be secured to achieve the structural stability in a micropile-based structure.

(33) Hereinafter, a method for forming the wave-shaped grouting bulb according to one embodiment of the present invention will be described.

(34) In the method for forming the wave-shaped grouting bulb, a first step (A100) is performed of forming a drilled hole 2 by using jet-grouting device 200 which includes a drilling machine 230 that drills a ground 1 to form the drilled hole 2, a grout material spray hole 220 that sprays a grout material, and a grout material feeding pipe 210 that supplies the grout material to the grout material spray hole 220, and forming the grouting bulb by spraying, at high pressure, the grout material from the grout material spray hole 220 into the drilled hole 2.

(35) After the first step (A100), a second step (A200) is performed of withdrawing the jet-grouting device 200 out of the drilled hole 2, and forming the pillar part 110 inside the drilled hole by spraying the grout material 3 from the grout material spray hole into the drilled hole 2.

(36) Furthermore, after the second step (A200), a third step (A300) is performed of inserting the steel bar 10 into the pillar part 110.

(37) The grout material 3 according to one embodiment of the present invention includes a first grout material 3a for forming the protrusion 120 and a second grout material 3b for forming the pillar part 110.

(38) The above is merely described with respect to preferred embodiments that may be implemented according to the present invention, and thus as is well known, the scope of the present invention should not be construed as being limited by the above embodiment, the technical ideas of the present invention described above and technical concepts on the basis of these technical ideas are considered to be included in the scope of the present invention.