WO2006080617A1

WO2006080617A1 - Soil nailing structure of using prestress and method of reinforcing the foundation with it

Info

Publication number: WO2006080617A1
Application number: PCT/KR2005/003106
Authority: WO
Inventors: Juseok Park; Hongkyu Lee; Jihyun Park; Sisam Park
Original assignee: Juseok Park; Hongkyu Lee; Jihyun Park; Sisam Park
Priority date: 2004-09-18
Filing date: 2005-09-17
Publication date: 2006-08-03

Abstract

A primary object of the present invention is to modify passiveness of a conventional soiling nailing method by using activeness of an earth anchor method. Another object of the present invention is to combine advantages of the conventional soil nailing method and earth anchor method to develop a new technology. In other words, a technology according to the present invention is a new technology having the following features. Firstly, a fixed length of the conventional earth anchor method is not required in a method according to the present invention because the length of a grouting body may act as a reinforcement element only with a length corresponding to a free length of the conventional earth anchor method. Secondly, although the free length of a coated wire is formed in the conventional earth anchor method, grout is injected to a pipe in the method according to the present invention, a reinforced grouting body is formed and resists a shear stress and thereby the pipe does not receive any tensile force due to a prestress.

Description

SOIL NAILING STRUCTURE OF USING PRESTRESS AND METHOD OF REINFORCING THE FOUNDATION WITH IT

Technical Field

[1] The present invention relates to a soil nailing assembly using a prestress and a method for reinforcing a ground therewith. More particularly, the present invention modifies weak points of a conventional soil nailing method by using strong points of a conventional earth anchor method. Background Art

[2] Firstly, a conventional soil nailing method is described.

[3] A soil nailing method is defined as a technology stabilizing a soil mass by using a nail as a reinforcement element.

[4] A soil mass is retained by several nails. A feature of the conventional soil nailing method is that nails act in a body. An applied load is shared by the nails because the nails act in a body. Another feature of the conventional soil nailing method is that if an active soil pressure area above a virtual rupture line does not act, no nail acts. In this regard, a nail is called 'a passive bar'

[5] A nail is installed to a passive soil pressure area through a virtual rupture line as shown in FIG. 1. Generally a nail is grouted and has an almost uniform diameter. The acceptable force per each nail is designed to be about 11 ton/ m². A soil nailing method has an advantage that construction work in a narrow space is possible using a small equipment and construction cost are low. However the conventional soil nailing method is passive because the nail is not prestressed, and has a nail having a remarkably low shear resistance to a ground displacement. The conventional soil nailing method has a disadvantage that a front plate may be easily damaged because a stress is concentrated on the front plate on a ground when a ground displacement occurs.

[6] Secondly, a conventional earth anchor method is described.

[7] An earth anchor method is a technology compulsorily retaining an active earth pressure area above a virtual rupture line. Compulsory retainment is performed by a tensile force applied to a steel wire. The tensile force compulsorily retains the active earth pressure area. The tensile force is sustained by two retaining points. One of the two retaining points is a soil pressure plate on a ground, another is a fixed length area under the ground.

[8] The soil pressure plate is supported by the ground.

[9] The fixed length area acts as a lower anchor of the wire and is retained by a skin friction force.

[10] The earth anchor assembly basically comprises steel wires, two retaining points of a soil pressure plate on a ground and a fixed length area under the ground. A feature of the earth anchor method is that there is no grouting body in a free length area because a tensile force of the wire is applied to the free length area.

[11] The soil pressure plate is a steel plate compulsorily pressing a surface of the ground and has a predetermined size. The fixed length area is resisting a tensile force by a skin friction force, and should have a predetermined length I (shown in FIG. 1).

[12] The earth anchor method is an active reinforcement technology in which a tensile force is applied from the beginning, which is different from the passive soil nailing method.

[13] In conclusion, disadvantages of the conventional soil nailing method are caused by its passiveness and advantages of the earth anchor method are caused by its activeness. Disclosure of Invention Technical Problem

[14] A primary object of the present invention is to modify a passive property of a conventional soil nailing method by using an active property of a conventional earth anchor method.

[15] Another object of the present invention is to combine strong points of the conventional soil nailing method and earth anchor method to develop a new technology.

[16]

[17] Firstly, a conventional soil nailing method has problems that a front plate on a ground may be easily damaged and a nail acts passively. The problems may be solved by advantages of the earth anchor method, which has activeness of wires to which a tensile force is applied.

[18] Secondly, the earth anchor method has problems that a free length area cannot have a skin friction force and a predetermined fixed length area is required. The problems may be solved by advantages of the conventional soil nailing method, which has a grouted nail assembly with a uniform diameter. In the new method according to the present invention, a grouted nail assembly having a skin friction force acts like a fixed length area of the earth anchor method without a fixed length area because the grouted nail assembly having the skin friction is formed corresponding to a free length of the earth anchor method.

[19] Thirdly, a new method according to the present invention is suitable to be applied a ground at which reinforcement is not sufficient when the conventional soil nailing method is used and reinforcement is uneconomically high when the conventional earth anchor method is used. Generally the length of a nail according to the soil nailing method is 6-12 m and the length of an anchor according to the earth anchor method is 10-14 m. The new method according to the present invention adopts a length range between the two methods.

[20]

[21] I) A new method according to the present invention is suitable for reinforcing a ground at which reinforcement is not sufficient when the conventional soil nailing method is used and a fixed legnth is not proper when the earth anchor method is used.

[22] 2) A new method according to the present invention is suitable for reinforcing a ground at which the conventional soil nailing method is not useful because too many nails per unit area are required, and reinforcement length is too long and it is not economical when the earth anchor method is used.

[23] For a reinforcement area resisting the same degree of force, the new technology uses less nails than the conventional soil nailing method and more nails than the earth anchor method in terms of the number of nails per square meter. The acceptable force of the earth anchor method is designed to be above 30 ton/m² per an earth anchor. The acceptable force of the soil nailing method is designed to be 11 ton/m² per a nail and the acceptable force of the new method is above 20 ton/m² per a nail.

[24] If a free length of the earth anchor method is as same as a nail length of the new technology and they can resist the same force, the new technology is more efficient and economical than the earth anchor method because the earth anchor method having a fixed length area should be longer by the length of the fixed length area than the new method.

[25]

[26] Referring to FIG.2, a mechanism of a new technology according to the present invention is described as follows.

[27] The new technology uses basic concepts of the conventional soil nailing method and earth anchor method and their disadvantages are modified by their advantages.

[28] In FIG. 2, a configuration of the earth anchor method is indicated by a solid line, and a configuration of the conventional soil nailing method is indicated by a dotted line.

[29] The configuration of an earth anchor method and reinforcement by a prestress are described as follows.

[30] A earth anchor assembly comprises wires A, a retaining member B, a front soil pressure plate E, a fixing member C fixing the wires A and a supporting member D supporting the fixing member C. The wires A are installed from a surface of a ground to a passive earth pressure area through a virtual rupture line. A prestress is applied to the wires A. The prestressed wires A are fixed by the retaining member B and fixing member C. The retaining member B is connected to a lower end of the pipe P. The fixing member C is supported by the supporting member D and the supporting member

D is installed on the front soil pressure plate E. The front soil pressure plate E is supported by the surface of the ground. [31] The prestress applied in the wires A compulsorily retains an active earth pressure area. The active earth pressure area is reinforced by a retaining force of the prestress. [32] Stresses related herein are fjand f₃.

[33] fj is a soil pressure stress of the front soil pressure plate E caused by the prestress of the wires A and f₃ is a skin friction force resisting the prestress of the wires A. [34] [35] The configuration of the conventional soil nailing method and resistance of wires to the prestress are described.

[36] The configuration of a new soil nailing method has a pipe P.

[37] The pipe P is used as an injection tube of grout, and it becomes a grouting body G after hardening of the grout and acts as a reinforcement element resisting a bending stress and shear stress applied to the grouting body G. Therefore the pipe P is a supporter supporting a retaining member B and acts like a fixed length area of the earth anchor method resisting the prestress. [38] In addition, the pipe P passes through a front soil pressure plate E and is fixed by a fixing nut F.

[39] Stresses related herein are f₂and f₃.

[40] f₂ is an upper load functioning as the bending stress and shear stress to the grouting body of the present invention. f₃is the skin friction force resisting the bending stress and shear stress applied to the grouting body by the upper load. [41] [42] As described in the above, a new technology of the present invention is neither a conventional soiling nailing method nor a conventional earth anchor method. It is a new method modifying disadvantages of the conventional soil nailing method by using advantages of the conventional earth anchor method. [43] In other words, a technology according to the present invention is a new technology having the following configuration. [44] Firstly, because the length of the grouting body according to the present invention may act as a reinforcement element only with a length corresponding to a free length L of the conventional earth anchor method, a fixed length I is not required. [45] Secondly, the free length L of a coated wire is formed in the conventional earth anchor method. However grout is injected to the pipe in a method according to the present invention, a reinforced grouting body is formed and resists the shear stress and thereby the pipe does not receive any tensile force due to the prestress. Technical Solution

[46] A configuration of the present invention is described in more detail by the accompanying drawings.

[47] The present invention relates to a soil nailing assembly using a prestress having the following features.

[48] A lower fixing member 20 under a ground and an upper fixing member 40 on the ground are retaining points of wires 30 and a prestress is applied to the wires 30, the lower fixing member 20 is connected to a lower end of a pipe 10. The upper fixing member 40 having a supporting member 42 in a body is supported by a front soil pressure plate 41 through the supporting member 42. The pipe 10 passes through the front soil pressure plate 41, a lower part of the pipe is extended to the lower fixing member 20, an upper part of the pipe is fixed by a fixing nut 49 and has a predetermined distance d from the upper fixing member 40.

[49] A head of the wire 30 placed in the upper fixing member 40 has a wedge 45 and a wedge shaped hole which can accommodate the wedge is formed in the upper fixing member 40.

[50] Another head of the wire 30 placed in the lower fixing member 20 has also a wedge 23 and a wedge shaped hole which can accommodate the wedge is formed in the lower fixing member 20.

[51] A wedge fixing member 24 is installed in the lower fixing member 20 and the head of the wire 30 is inserted into the wedge fixing member 24.

[52] Grout injection holes 12 are formed in the pipe 10 and preferably formed near the lower fixing member 20.

[53] The wires 30 are covered with PE-coated pipes 33. The wires 30 in the PE-coated pipes 33 may move freely and thereby the prestress may be applied to the wire 30 even in a grouted state.

[54] A packer 50 is installed outside the pipe 10 near a surface of the ground. The packer

50 comprises a nonwoven 53 surrounding the packer 50, an upper packing 51 and a lower packing 52. Urethane foam is supplied to adhere the nonwoven 53 closely to the wall of a boring hole h. A urethane foam inserting hole 54 and an air discharge pipe 55 are also installed in the packer 50.

[55]

[56] An upper cap 46 and lower cap 26 are formed in the upper fixing member 40 and lower fixing member 20 respectively. They are used for protecting the wires 30 from erosion and external shock.

[57] A method for reinforcing a ground by a soil nailing assembly using the prestress comprises the steps of: [58] drilling a boring hole h on the ground;

[59] inserting a soil nailing assembly into the boring hole h, the soil nailing assembly having a structure at which a lower fixing member 20 installed under a ground and an upper fixing member 40 installed on the ground are retaining points of wires 30, the lower fixing member 20 is connected to a lower end of a pipe 10, the upper fixing member 40 having a supporting member 42 in a body is supported to a front soil pressure plate 41 through the supporting member 42, the pipe 10 passes through the face soil pressure plate 41, the lower part of the pipe is extended to the lower fixing member 20, the upper part of the pipe is fixed by a fixing nut 49 and has a predetermined distance d from the upper fixing member 40;

[60] forming a grouting body by pressure-grouting with a packer 50;

[61] applying the prestress to the wires 30 from the upper fixing member 40; and

[62] fixing the wires 30 to the upper fixing member 40.

Advantageous Effects

[63] In the present invention, a fixed length of a conventional earth anchor method, in which a fixed length area resists a prestress by a skin friction force, is omitted. A grouting body according to the present invention functions simultaneously as both a grouting body of a conventional soil nailing method and a fixed length area of a conventional earth anchor method due to a skin friction force. The grouting body according to the present invention plays two roles and therefore its structure is simple. A conventional passive soil nailing method is transformed to an active soil nailing method and it may get rid of concern about the conventional soil nailing method.

[64] In addition, while an anchor wire is installed in an earth anchor method, 3 nails should be installed in a conventional soil nailing method. However, in the new method according to the invention, 2 nails may be installed and show enough reinforcement force.

[65] In other words, a new soil nailing method according to the present invention has only a length corresponding to a free length of the conventional earth anchor method. However a fixed length fis additionally required in the conventional earth anchor method and it is not economical. Although the length of a nail of the conventional soil nailing method is almost as same as that of the new method according to the present invention, reinforcement of the conventional soil nailing method is not sufficient and it is not economical.

[66] Therefore the new nailing method according to the present invention uses both a reinforcement length corresponding to that of the conventional soil nailing method and the number of reinforcement nails per unit area between two conventional methods. Because nail length of the new nailing method is as same as that of the conventional soil nailing method and reinforcement force of the new nailing method is similar to that of the conventional earth anchor method. Brief Description of the Drawings

[67] FIG.1 is a view showing structural characteristics of a soil nailing method and an earth anchor method. [68] FIG.2 is a sectional view of a soil nailing assembly according to the present invention to illustrate a dynamic mechanism. [69] FIG.3 is a sectional view of a soil nailing assembly according to the present invention using a prestress.

[70] FIG.4 is an exploded sectional view of a lower fixing member of FIG. 3.

[71] FIG. 5 is a sectional view of a soil nailing assembly taken along the line A-A of

FIG. 3.

[72] FIG.6 is an exploded sectional view of an upper fixing member of FIG. 3.

[73] FIG.7 is an exploded sectional view of a packer of FIG. 3.

[74] FIG.8 is a sectional view of an installed soil nailing assembly using a prestress with a packer according to the present invention. [75] <Description of the elements in the drawings>

[76] 10: pipe

[77] 12: grout injection hole

[78] 20: lower fixing member

[79] 23: wedge

[80] 24: wedge fixing member

[81] 25: bolt

[82] 26: lower cap

[83] 30: wire

[84] 32: spacer

[85] 33: PE-coated pipe

[86] 34: pipe spacer

[87] 40: upper fixing member

[88] 41: front soil pres sure plate

[89] 42: supporting member

[90] 45: wedge

[91] 46: upper cap

[92] 49:fixing nut

[93] 50: packer

[94] 51 : upper packing

[95] 52: lower packing [96] 53: nonwoven

[97] 54: urethane foam injection pipe

[98] 55: air discharge pipe

Claims

[1] A soil nailing assembly using a prestress comprising a lower fixing member under a ground, an upper fixing member on the ground, a pipe therebetween and wires, wherein the lower fixing member and upper fixing member are retaining points of the wires, the prestress is applied to the wires, the lower fixing member is connected to a lower end of the pipe, the upper fixing member having a supporting member in a body is supported by a front soil pressure plate through the supporting member, the pipe passes through the front soil pressure plate, a lower part of the pipe is extended to the lower fixing member, an upper part of the pipe is fixed by a fixing nut and has a predetermined distance from the upper fixing member.

[2] The soil nailing assembly using a prestress of claim 1, wherein a head of the wire placed in the upper fixing member has a wedge and a wedge shaped hole which can accommodate the wedge is formed in the upper fixing member.

[3] The soil nailing assembly using a prestress of claim 1, wherein a head of the wire placed in the lower fixing member has a wedge and a wedge shaped hole which can accommodate the wedge is formed in the lower fixing member.

[4] The soil nailing assembly using a prestress of claim 1 or 3, wherein a wedge fixing member is installed in the lower fixing member and the head of the wire is inserted into the wedge fixing member.

[5] The soil nailing assembly using a prestress of claim 1 or 3, wherein grout injection holes are formed in the pipe near the lower fixing member.

[6] The soil nailing assembly using a prestress of claim 1, wherein the wires are covered with PE-coated pipes, and the wires in the PE-coated pipes may move freely.

[7] The soil nailing assembly using a prestress of claim 1, wherein a packer is installed outside the pipe near a surface of the ground.

[8] A method for reinforcing a ground by a soil nailing assembly using a prestress comprises the steps of; inserting a soil nailing assembly into a boring hole, the soil nailing assembly having a structure at which a packer is attached to a pipe, a lower fixing member installed under the ground and an upper fixing member on the ground are retaining points of wires, the lower fixing member is connected to a lower end of the pipe, the upper fixing member having a supporting member in a body is supported to a front soil pressure plate through the supporting member, the pipe passes through the front soil pressure plate, a lower part of the pipe is extended to the lower fixing member, an upper part of the pipe is fixed by a fixing nut and has a predetermined distance from the upper fixing member; forming a grouting body by pressure-grouting with the packer; applying the prestress to the wires from the upper fixing member; and fixing the wires to the upper fixing member.