WO2010005137A1

WO2010005137A1 - Geogrid structure preventing bulging failure of stone column and method constructing the stone column by the geogrid structure

Info

Publication number: WO2010005137A1
Application number: PCT/KR2008/004769
Authority: WO
Inventors: Chung Sik Yoo; Dae Young Lee; Sun Tae Jung; Boo Rak Lee; Si Sam Park
Original assignee: Gs Engineering & Construction Corp.; Il Yang Ind Co., Ltd.; Dong-A Geological Engineering Co., Ltd.; Korea Institute Of Construction Technology; Sungkyunkwan University Foundation For Corporate Collaboration
Priority date: 2008-07-07
Filing date: 2008-08-16
Publication date: 2010-01-14
Also published as: KR20100005383A; KR101008478B1

Abstract

The present invention is provided to construct a geogrid-attached structure to prevent bulging failure in a process of forming a uniform stone column to provide an economical reinforcement construction because the geogrid-attached structure for preventing bulging failure is simple and a reinforcement work and drawing-out work is easy and efficient and to surely prevent bulging failure and shear failure of the stone column by reinforcing only the shallow layer of 2.5D-5D under an upper end of the stone column with a circular geogrid having a high rigidity, easily inducing the geogrid into a ground and placing the geogrid in a predetermined position. The present invention relates to a geogrid-attached structure for preventing bulging failure of a stone column wherein a circular geogrid is contacted to an outer circumference of a round hollow pipe, a fixing portion of a hook shape is formed in a lower end of the circular geogrid towards an inner circumference of the round hollow pipe, the diameter of the round hollow pipe is larger than that of the auger casing, and the length of the round hollow pipe is 2.5D-5D when the diameter of the stone column is D.

Description

GEOGRID STRUCTURE PREVENTING BULGING FAILURE

OF STONE COLUMN AND METHOD CONSTRUCTING THE

STONE COLUMN BY THE GEOGRID STRUCTURE

Technical Field

[1] The present invention relates to a geogrid- attached structure for preventing bulging failure of a stone column and a method for constructing a stone column using the same.

[2] A stone column construction method is widely used as a method for forming a compaction pile by using smashed stones with a relatively high rigidity and small compressibility to reinforce a soft ground, increase an ultimate bearing capacity, and accelerate consolidation of a base ground and thereby improving a soft ground.

[3] However, it is impossible to apply this method in a ground in which a lateral confining pressure is not exerted enough because there is no resistance to bulging failure. This is because the bulging failure of a stone column causes bulging failure and shear failure.

[4] The present invention is provided to prevent a bulging failure phenomenon by reinforcing a stone column using a geogrid and easily attach a reinforcement material due to its simple structure.

[5]

Background Art

[6] A stone column construction method is used to induce consolidation by forming a modified structure of a circular shape such as a pile in a soft and fine soil ground using gravels, smashed stones or slags, increase a bearing capacity of a native ground, and reduce a settlement amount thereof. Additionally, the stone column construction method is used to prevent liquefaction which can occur in a soft or loose sedimentary layer when an earthquake happens.

[7] Such a stone column construction method has many advantages such as dissipation of a pore water pressure due to a foundation or earthquake load by a vertical drain material, improvement of a bearing capacity of a soft ground, reduction of a settlement amount of a foundation, and increase of consolidation effect.

[8] The size of a gravel that is used for the stone column ranges from 6 mm to 40 mm.

The diameter of the stone column is 500-800 mm. The diameter of the stone column is generally 750-800 mm. The distance between the center of the stone columns is 1.5~3.0m.

[9] The stone columns are used for stabilizing a ground of a wide area having a undrained shear strength of l.O~1.5t/m². However, the ground cannot provide enough lateral bearing capacities to the stone column in a ground having a undrained shear strength lower than l.O~1.5t/m². There is a problem that lack of the lateral bearing capacity causes bulging failure by a vertical load.

[10] A schematic view for a lateral bulging failure phenomenon of a stone column is shown in FIG. 1.

[11] The stone column is expanded and destroyed due to an ultimate capacity q_u when a foundation is constructed on the stone column as shown in the schematic view showing a bearing capacity of the stone column in FIG. 1. The bulging failure phenomenon occurs from an upper end of the stone column to the shallow layer of 2.5D-3D. Here, D is the diameter of the stone column.

[12] The bulging failure of the stone column occurs mainly at a shallow layer of 2.5D-3D because a confining pressure of the shallow layer is smaller than that of a deep layer. Therefore reinforcement of the shallow layer of 2.5D-3D is enough for the construction of the stone column because the bulging failure of the stone column occurs mainly at the shallow layer of 2.5D-3D.

[13] Because of the above reason, in Korean Patent No. 10-0603140 of the applicant of the present invention, reinforcement of the shallow layer of 2.5D-3D from the upper end of the stone column was performed by using a geogrid to prevent a bulging failure phenomenon of the stone column.

[14] Reinforcement of the shallow layer of 2D-5D that is larger than the shallow layer of

2.5D-3D is performed in consideration of a construction tolerance and unevenness of the ground.

[15] A conventional construction method for forming a stone column is described as follows.

[16] Step 1; A ground is bored by an auger device 10, and a casing 12 is remained in the ground. The diameter Dl of the casing 12 is generally 800 mm.

[17] Step 2; Smashed stones are filled to a certain height in the casing 12, and tamping is performed by a tamping hammer 14 while the casing 12 is drawn out slowly. Smashed stones discharged from a bottom of the casing 12 are tamped to form a uniform first step stone column H₁ [Refer to (b) of FIG. 2]. Here, the diameter D2 of stone column 32 is 900 mm. The diameter D2 of stone column 32 is larger than the diameter Dl of the casing 12 of 800 mm.

[18] Step 3; Step 1 and step 2 are repeated to form a second step stone column H₂, third step stone column H₃, ^{• • • •} to nth step stone column H_n, Namely, a stone column H is formed that reaches the ground surface [Refer to (b) and (c) of FIG. 2].

[19] However, it is described in Korean Patent No. 10-0603140 only that reinforcement of a shallow layer of 2D-5D from an upper end of a stone column 30 is performed by a geogrid 24 of a circular shape to prevent a bulging failure phenomenon of the stone column. No description was made for construction measures such as construction of the stone column 30 and attachment of the circular geogrid 24.

[20] Additionally, it is not easy for any one to be able to attach the circular geogrid 24 at the shallow layer of 2D-5D from the upper end of the stone column 30.

[21] It will be described in more detail.

[22] It is most efficient for prevention of the bulging failure phenomenon to attach the circular geogrid 24 in the circumference of the stone column 30 while forming the stone column 30. It is not easy to wrap the outer circumference of the stone column 30 with the circular geogrid 24 after formation of the stone column 30 because the stone column 30 formed step by step in the ground is not smooth in its outer circumference and is not uniform in its diameter.

[23] A conventional construction method for forming a stone column 30 is described as follows.

[24] Strong impact should be added to smashed stones because a stone column (diameter

D2 = 900 mm) larger than the diameter Dl of 800 mm of a casing 12 is formed by an auger device 10. The smashed stones have large surface frictions due to their shapes. Strong tamping by a high vibration or tamping hammer 14 is necessary.

[25] A) A case of wrapping an entire stone column 30 with a geogrid

[26] It is not easy to wrap an entire stone column 30 with a geogrid.

[27] For example, a circular geogrid 24 should be inserted into an auger casing 12 to wrap an entire stone column 30 with the geogrid. At this time, the height of the inserted circular geogrid 24 is at least equal to that of the casing 12. An inlet of the circular geogrid 24 should be fixed to an upper end of the casing 12. The circular geogrid 24 should be located at a predetermined position because smashed stones should be input through a smashed stone insert hole 18 to the inlet of the circular geogrid 24 and the input smashed stones should be tamped.

[28] When a first step stone column H₁ is formed in this state, the casing 12 rises upwards by a height of H₁. The circular geogrid 24 fixed to the upper end of the casing 12 also rises upwards and is displaced from the predetermined position. Therefore reinforcement of an outer circumference of the stone column 30 can not be performed by using the circular geogrid 24.

[29] Additionally, even when the circular geogrid 24 is inserted into the casing 12, it will be impossible for the circular geogrid 24 in a folded state to overcome a friction force of the inner circumference of the casing 12 and be inserted to a lower end of the casing 12 because the diameter of the circular geogrid 24 is larger than an inner diameter of the casing 12 and its rigidity is high.

[30] It is not easy to insert the circular geogrid 24 having a diameter larger than the inner diameter of the casing 12 into the casing 12. This is because the circular geogrid 24 having a rigidity and flexibility is closely attached to an inner circumference of the casing 12 having a smaller diameter and a circumferential friction force with the casing 12 is large. Especially, a circular geogrid 24 formed with a polyester resin has a high rigidity.

[31] Additionally, because strong tamping is added to the inside of the casing 12, the circular geogrid 24 may be broken in a state that the circular geogrid 24 is folded in the casing 12. When the circular geogrid 24 is broken, the circular geogrid 24 loses its retaining ability and can not work as a geogrid.

[32] As far as the circular geogrid 24 is fixed to the upper end of the casing 12, it is impossible to wrap the entire stone column 30 with the geogrid. This is the reason why the geogrid rises upwards along the casing 12 because the casing 12 rises upwards while the stone column 30 is formed.

[33] The circular geogrid 24 can not be attached to the outer circumference of the stone column 30 by a common means. A special means is needed for that.

[34] B) A case of wrapping the shallow layer of 2D-5D from the upper end of stone column 30 with the circular geogrid 24

[35] The casing 12 is placed on the stone column 30 until formation of the stone column

30 is completed because the stone column 30 is formed while drawing out the casing 12 in a state that an auger casing 12 is input from a ground 40.

[36] When the stone column 30 reaches the shallow layer of 2D-5D under the ground 40, the upper end of the casing 12 has already risen above the ground 40. If the stone column 30 is formed to the shallow layer of 2D-5D in a state that the circular geogrid 24 is attached to the upper end of the casing 12, the circular geogrid 24 should have the same height as the height H of the casing 12. Therefore it is not economical and efficient.

[37] A method of attaching a geogrid to an outer circumference of the casing 12 or stone column 30 after digging the ground 40 to the shallow layer of 2D-5D without fixing of the geogrid to the upper end of the casing 12 can be considered.

[38] Namely, two methods may be considered such as a method of digging soil around the outer circumference of the casing 12, wrapping the outer circumference of the casing 12 with the geogrid, sewing and fixing the geogrid, and a method of digging soil around the stone column 30 after formation of the stone column 30 is completed and the casing 12 is removed, wrapping the stone column 30 with the geogrid, sewing and fixing the geogrid.

[39] Because soil around the casing 12 is dug to the shallow layer of 2D-5D and sewing operation is followed in the above two methods, soil should be dug to be wider than the diameter of the casing 12 or the diameter of the stone column 30. Digging soil is not economical and efficient. Additionally, the stone column 30 should act against a horizontal soil pressure of the ground 40 when digging the shallow layer of 2D-5D because the horizontal soil pressure of the ground 40 presses the side of the stone column 30.

[40] The stone column 30 and geogrid are not closely contacted because the outer circumference of the stone column 30 is not smooth.

[41] A technology for wrapping the shallow layer 2D-5D from an upper end of stone column 30 with a geogrid to prevent bulging failure of the stone column 30 is known in a conventional technology. However, a means for wrapping the stone column 30 with the geogrid is not described at all, and attaching the circular geogrid 24 while forming the stone column 30 as described in the above is a difficult technology.

[42]

Disclosure of Invention Technical Problem

[43] An object of the present invention is to construct a geogrid- attached structure for preventing bulging failure in a process of forming a uniform stone column.

[44] Another object of the present invention is to provide an economical reinforcement construction because the geogrid- attached structure for preventing bulging failure is simple, and a reinforcement work and drawing-out work is easy and efficient.

[45] Another object of the present invention is to surely prevent bulging failure and shear failure of the stone column by reinforcing only the shallow layer of 2.5D-5D of the upper end of the stone column with a circular geogrid having a high rigidity, easily inducing the geogrid into a ground and placing the geogrid in a predetermined position.

[46]

Technical Solution

[47] A geogrid- attached structure 20 for preventing bulging failure of a stone column according to the present invention is described in detail with reference to drawings as follows.

[48] A circular geogrid 24 is contacted to a round hollow pipe 22, a fixing portion 26 having a hook shape is formed in a lower end of the circular geogrid 24 towards an inner circumference of the round hollow pipe 22, the diameter of the round hollow pipe 22 is larger than that of the auger casing 12, the length of the round hollow pipe 22 is 2.5D-5D when the diameter of the stone column 30 is D, and a drawing ring 28 is formed at the upper end of the round hollow pipe 22.

[49] A. A round hollow pipe 22

[50] The diameter of the round hollow pipe 22 is larger than the outer diameter of an auger casing 12 by about 10-30 mm. If the diameter of the round hollow pipe 22 is larger than the outer diameter of the casing 12 by less than 10mm, insertion of the casing 12 is difficult. If the diameter of the round hollow pipe 22 is larger than the outer diameter of the casing 12 by more than 30mm, a friction surface of the round hollow pipe 22 with a ground 40 becomes high and its insertion into the ground 40 is not easy. Specially, the round hollow pipe 22 is inserted into the ground 40 by strong impact if the surface friction is high, and the circular geogrid 24 may be easily damaged because the circular geogrid 24 is contacted to the outer circumference of the round hollow pipe 22.

[51] The length of the round hollow pipe 22 is preferably 2.5D-5.5D. Because the length reinforced with the circular geogrid 24 is 2.5D-5D, the length of the round hollow pipe 22 should be a little larger than the the circular geogrid 24 for easily drawing out the round hollow pipe 22 after the stone column 30 is reinforced. It is preferable that the height of the round hollow pipe 22 is a little higher than the reinforcement length of 2.5D-5D of the circular geogrid 24 because drawing rings 28 should be above the ground surface for a wire 16 to be easily put into the drawing rings 28 . Here, D is the diameter of the stone column.

[52] The drawing rings are formed at the upper end of the round hollow pipe 22. It is preferable to form 3 drawing rings because it is safe to draw out the round hollow pipe 22 by holding 3 drawing rings by the wire. The drawing rings held by the wire are drawn out by the auger device.

[53] B. A circular geogrid 24

[54] The circular geogrid 24 is attached to wrap the outer circumference of the round hollow pipe 22.

[55] The lower end of the circular geogrid 24 is fixed to the inner circumference of the round hollow pipe 22 at the lower end of the round hollow pipe 22 by a fixing portion 26 having a hook shape. The circular geogrid 24 is contacted to the outer circumference of the round hollow pipe 22 because the circular geogrid 24 is made of a material having a rigidity and elasticity. The contacted circular geogrid 24 is not easily separated from the outer circumference of the round hollow pipe 22 due to its rigidity and elasticity.

[56] C. Insertion/ drawing-out of a geogrid-attached structure 20

[57] into/from the ground 40 to prevent bulging failure

[58] As the circular geogrid 24 is wrapped on the outer circumference of the round hollow pipe 22, and a fixing portion 26 of a hook shape of the lower end of the circular geogrid 24 wraps the inner lower circumference of the round hollow pipe 22, the circular geogrid 24 is not distorted or separated from the inner and outer circumferences of the round hollow pipe 22 and its shape is not maintained to be inserted into the ground 40.

[59] This is possible because the round hollow pipe 22 guides the circular geogrid 24 to be inserted into the ground 40 and the round hollow pipe 22 has a high rigidity.

[60] The geogrid-attached structure 20 for preventing bulging failure is inserted into the ground 40 together with the round hollow pipe 22. Because prevention of the bulging failure of the stone column 30 is performed by the circular geogrid 24, the round hollow pipe 22 is not related to the prevention of the bulging failure of the stone column 30. The round hollow pipe 22 only guides the circular geogrid 24 to be inserted into the ground 40 in a state that it is not distorted.

[61] The round hollow pipe 22 is drawn out after the circular geogrid 24 is inserted into the ground 40.

[62] The round hollow pipe 22 is easily drawn out from the ground 40 after the wire 16 is put into the drawing rings 28 of the round hollow pipe 22 and is moved upwards by the auger device 10.

Advantageous Effects

[63] The geogrid-attached structure according to the present invention is simple, easy to handle and economical because the round hollow pipe and circular geogrid are used, the round hollow pipe may be easily removed, and the geogrid is used to reinforce the swallow layer of 2.5D-5.5D from the upper end of the stone column to prevent bulging failure.

[64] Bulging failure and shear failure of the stone column is surely prevented because the geogrid is guided into the ground by the round hollow pipe and is contacted to the outer circumference of the stone column without distortion.

[65] Work according to the present invention is efficient and useful by forming the stone column and reinforcing the upper end by the auger device because the geogrid-attached structure is installed on the ground, the center of the auger casing is bored, stepwise stone columns are formed by the casing, and reinforcement of the upper end of the stone column is performed.

[66]

Brief Description of Drawings

[67] FIG. 1 is a schematic view showing a lateral bulging failure phenomenon of a stone column.

[68] FIG. 2 is a sectional view showing a construction procedure of a conventional stone column.

[69] FIG. 3 is a perspective view showing a geogrid-attached structure for preventing bulging failure according to the present invention.

[70] FIG. 4 is an exploded sectional view showing a geogrid-attached structure for preventing bulging failure according to the present invention.

[71] Fig. 5 is a perspective view showing a construction procedure of a stone column using a geogrid- attached structure for preventing bulging failure according to the present invention.

[72] •;*:• Brief description of drawing numerals

[73] 10; auger device

[74] 12; casing

[75] 14; tamping hammer

[76] 16; wire

[77] 18; smashed stone insert hole

[78] 20; geogrid-attached structure for preventing bulging failure

[79] 22; round hollow pipe

[80] 24; geogrid

[81] 26 ; fixing portion

[82] 28; drawing ring

[83] 30; stone column

[84] 32; stepwise stone column Hi, H₂, ^{• • •} H_n

[85] 40; ground

Best Mode for Carrying out the Invention

[86] The present invention provides a geogrid-attached structure for preventing bulging failure of a stone column characterized in that a circular geogrid 24 is contacted to an outer circumference of the round hollow pipe 22, a fixing portion 26 of a hook shape is formed towards an inner circumference of the round hollow pipe 22 at the lower end of the circular geogrid 24, the diameter of the round hollow pipe 22 is larger than that of an auger casing 12, the length of the round hollow pipe 22 is 2.5D-5.5D when the diameter of the stone column 30 is D. Mode for the Invention

[87] Smashed stones are filled in a casing 12 in a state that the casing 12 is left in a ground 40, and the casing 12 is drawn out while tamping and pounding by an auger device 10. A stone column 30 larger than the diameter of the casing 12 is formed while the casing 12 is drawn out together with tamping and pounding. Basically a construction method according to the present invention is similar to a conventional construction method of a stone column. However, the construction method according to the present invention is different in that a geogrid- attached structure 20 that is wrapped with a circular geogrid 24 is added to a shallow layer of 2.5D-5D from the upper end of the stone column 30 to prevent bulging failure of the stone column 30.

[88] A construction method of the stone column 30 is different from a conventional construction method because the geogrid-attached structure 20 is added for preventing bulging failure. [89] Firstly a construction method of a conventional stone column is described and secondly a construction method of a stone column according to the present invention is described.

[90] The construction method of a conventional stone column is described as follows.

[91] A construction procedure of a conventional stone column is described in FIG. 2.

[92] The construction procedure of a conventional stone column includes:

[93] D inputting a casing 12 into a ground 40 by an auger device 10;

[94] D filling smashed stones into the casing 12 to a predetermined height [Refer to (a) in

FIG. 2]; [95] D drawing out the casing 12 while tamping and pounding by a strong impact and forming a smashed stone column H₁ that is larger than the diameter of the casing 12

[Refer to (b) and (c) in FIG. 2]; and [96] D repeating D and D, and sequentially forming smashed stone columns H₂, H₃ H_n having the same height as the height of the stone column Hi [Refer to (d) in FIG. 2]. [97] As the smashed stone columns 30 Hi, H₂, H₃ H_n are sequentially formed, the casing 12 moves upwards from the ground 40. [98] A construction method of a stone column according to the present invention is described as follows.

[99] A geogrid- attached structure 20 for preventing bulging failure is added to the conventional stone column in the present invention. [100] A construction procedure for the geogrid- attached structure 20 for preventing bulging failure is shown in FIG.4. [101] A construction procedure of a stone column using a geogrid- attached structure for preventing bulging failure includes: [102] D inserting a geogrid- attached structure 20 having a circular geogrid 24 contacted to an outer circumference of a round hollow pipe 22 into a ground 40 by striking at a position where a smashed stone column 30 is to be constructed; [103] D perforating the ground 40 at the center of the round hollow pipe 22 in the geogrid- attached structure 20 by a casing 12 of an auger device 10; [104] D leaving only the casing 12 in the ground 40;

[105] D filling the smashed stones to a predetermined height in the casing 12; [106] D forming a smashed stone column Hi having a diameter larger than that of the casing 12 by drawing out the casing 12 while tamping and pounding by a strong impact; [107] (f) repeating D and D, and sequentially forming smashed stone columns H₂, H₃ H_n having the same height as that of the stone column Hi; and

[108] (S) fixing a wire 16 connected to the auger device 10 to a drawing ring 28 of the round hollow pipe 22 in the geogrid- attached structure 20 after forming the smashed stone column H_n, and drawing out the round hollow pipe 22. [109] The construction procedure of a stone column using a geogrid- attached structure for preventing bulging failure further includes: perforating the ground 40 at the center of the round hollow pipe 22 by the casing 12 of the auger device 10 by forming the diameter of the round hollow pipe 22 larger than that of the casing 12 of the auger device 10 by 10-30 mm in D. [110] The circular geogrid 24 is formed of a polyester resin and has a lattice structure of a net shape.

Claims

[1] A geogrid- attached structure for preventing bulging failure of a stone column, wherein a circular geogrid 24 is contacted to an outer circumference of a round hollow pipe 22, a fixing portion 26 of a hook shape is formed in a lower end of the circular geogrid 24 towards an inner circumference of the round hollow pipe 22, the diameter of the round hollow pipe 22 is larger than that of the auger casing 12, and the length of the round hollow pipe 22 is 2.5D-5D when the diameter of the stone column 30 is D.

[2] The geogrid- attached structure for preventing bulging failure of a stone column of claim 1, wherein a drawing ring 28 is formed at an upper end of the round hollow pipe 22.

[3] The geogrid- attached structure for preventing bulging failure of a stone column of claim 1 or 2,wherein the diameter of the round hollow pipe 22 is larger than that of the auger casing 12 by 10-30 mm.

[4] A construction method of a stone column using a geogrid-attached structure for preventing bulging failure comprises:

D inserting a geogrid-attached structure 20 having a circular geogrid 24 contacted to an outer circumference of a round hollow pipe 22 and having a fixing portion 26 of a hook shape formed on an inner circumference of the round hollow pipe 22 into a ground 40 at a position where a smashed stone column 30 is to be constructed by striking;

D perforating the ground 40 by the casing 12 of the auger device 10 at the center of the round hollow pipe 22 in the geogrid-attached structure 20; D leaving only the casing 12 in the ground 40;

D filling the smashed stones to a predetermined height in the casing 12; D forming a smashed stone column Hi having a diameter larger than that of the casing 12 by drawing out the casing 12 while tamping and pounding by a strong impact;

(f) repeating D and D, and sequentially forming smashed stone columns H₂, H₃ H_n having the same height as that of the stone column H₁; and

(g) fixing a wire 16 connected to the auger device 10 to a drawing ring 28 of the round hollow pipe 22 in the geogrid-attached structure 20 after forming the smashed stone column H_n, and drawing out the round hollow pipe 22.

[5] The construction method of a stone column using a geogrid-attached structure for preventing bulging failure of claim 4, further comprises: perforating the ground 40 at the center of the round hollow pipe 22 by the casing 12 of the auger device 10 by forming the diameter of the round hollow pipe 22 larger than that of the casing 12 of the auger device 10 by 10-30 mm in D.