WO2007015614A1

WO2007015614A1 - Preceding tension type lock bolt and construction method using the same

Info

Publication number: WO2007015614A1
Application number: PCT/KR2006/003008
Authority: WO
Inventors: Jong Duck Shin
Original assignee: Jong Duck Shin
Priority date: 2005-08-03
Filing date: 2006-07-31
Publication date: 2007-02-08

Abstract

A preceding tension type rock bolt comprises a pipe; two or more expansion members detachably coupled to one end of the pipe to be uniformly spaced apart from one another, having a substantially sectorial section shape, and defining a tensioning member opening and a frusto- conical opening; a tensioning member installed through the pipe and the expansion members such that both ends thereof project out of the pipe and the expansion members; and a wedge secured to one end of the tensioning member and inserted into the frusto-conical opening of the expansion members to expand the expansion members radially outward.

Description

PRECEDING TENSION TYPE LOCK BOLT AND CONSTRUCTION METHOD USING THE SAME

Technical Field

[1] The present invention relates, in general, to a preceding tension type rock bolt and a construction method using the same which reinforces the support force of discontinuous rock formations in tunnel excavation work or rock-based construction and, more particularly, to a preceding tension type rock bolt and a construction method using the same, wherein expansion members are expanded by a wedge secured to an end of a tensioning member to be securely fixed against the inner surface of a drilled hole, a pipe is removed, tension force is applied to the tensioning member, and the tensioned state of the tensioning member is maintained to thereby apply a preceding load, so that, since the discontinuous surfaces of rock formations can be restrained, the safety of a rock slope is increased, and because it is possible to immediately carry out subsequent excavation work without waiting for grouting material to cure, a construction period can be shortened. Background Art

[2] As is generally known in the art, a rock bolt is employed in a ground reinforcement technique for reinforcing the stiffness of an underground structure, a tunnel, etc. In the ground reinforcement technique, a hole is drilled in a rock formation inside a tunnel to have a predetermined diameter and depth, and the rock bolt is inserted into the drilled hole to be fixed therein.

[3] Concretely speaking, in order to install the rock bolt in civil engineering and construction work, in particular, tunneling work, a hole is drilled in the ground, including a rock formation in a mountain. Then, a predetermined explosive, for example, dynamite, is placed in the drilled hole and detonated to blast the rock formation to thereby enlarge the initial opening of the tunnel. After a base tunnel is formed to have predetermined height and width, in order to prevent the base tunnel from caving in, a plurality of rock bolts (foundation bolts) are driven into the wall of the base tunnel, a lattice- shaped wire mesh is installed, and concrete is finally cast, to carry out reinforcement work.

[4] In the reinforcement work, holes in which rock bolts are to be inserted are first drilled in the rock formation using a rock drill or a rock splitter. Thereafter, cement mortar is cast and then the rock bolts are inserted into the drilled holes, or the rock bolts are inserted and then cement mortar is cast in the drilled holes. By curing the cement mortar, the rock bolts are firmly fixed in the rock formation. Since the rock bolts are installed at regular intervals, they can be maintained in a firmly fixed state while withstanding the concrete load distributed over the wire mesh.

[5] However, in the conventional rock bolts, cement mortar is cast in the drilled holes, bearing plates are mounted only after waiting until the cement mortar is cured, and the rock bolts are fixed through the bearing plates. Then, only when the cement mortar has completely hardened, which takes 2 or 3 weeks, a pull test is conducted to ascertain whether the rock bolts can withstand a load of no less than a predetermined level, and various construction parts are installed in place. Therefore, problems are caused in that the construction period is lengthened and a large number of rock bolts must be installed in order to improve support force.

[6] In consideration of this fact, devices or methods for reinforcing rock bolts have been continuously developed and disclosed in the art. For example, Korean Patent No. 108419 discloses an anchoring bolt structure for tunnel lining.

[7] In this patent document, the anchoring bolt structure for tunnel lining includes a bolt shank which has a first tapered wedge member on the distal end thereof and a threaded portion on the proximal end thereof to be threadedly coupled with a nut, and an expansion bushing which can be expanded by the first tapered wedge member. The expansion bushing has a tubular configuration which defines tapered wedge receiving spaces on both end portions thereof. Each of the outer surfaces of both end portions of the expansion bushing is formed with a saw tooth-shaped spiral projection. Each of both end portions of the expansion bushing is cut in the lengthwise direction thereof to form a plurality of expansion pieces. With the bolt shank inserted through the expansion bushing, a second tapered hollow wedge member is fitted around the bolt shank inside the proximal end of the expansion bushing to be positioned opposite the first tapered wedge member. Then, a pressing pipe for moving the second tapered hollow wedge member forwards is inserted around the bolt shank. Disclosure of Invention Technical Problem

[8] However, the conventional anchoring bolt structure disclosed in Korean Patent No.

108419 and constructed as mentioned above suffers from defects in that, since the first tapered wedge member is integrally formed with the bolt shank, it is difficult to manufacture the bolt shank. Also, even when the first tapered wedge member is formed separately from the bolt shank, because the first tapered wedge member must be integrated with the bolt shank through threaded locking, welding, etc., the manufacturing procedure is made complicated.

[9] In the anchoring bolt structure, as the nut is tightened, the bolt shank is moved forward, and the pressing pipe is moved rearward, by which the first wedge member and the second wedge member radially expand the expansion pieces formed on both end portions of the expansion bushing. In this regard, as the expansion pieces of the expansion bushing are gradually expanded radially outward, loads applied to the bolt shank and the pressing pipe are suddenly increased so that the nut cannot be tightened any more. Therefore, since it is difficult to properly expand the expansion pieces of the expansion bushing, a problem is caused in that the anchoring bolt structure cannot be firmly fixed in a drilled hole.

[10] In particular, when the first wedge member, formed on the distal end of the bolt shank, and the second wedge member, biased by the pressing pipe, expand the expansion pieces radially outward, since the expansion pieces cut in the lengthwise direction on both end portions of the expansion bushing remain integrated with the expansion bushing, the expansion pieces are expanded only in the pattern of a wedge. In other words, because the outer surfaces of the first and second wedge members are not brought into complete contact with the inner surface of the wedge receiving spaces, fixing force is decreased, whereby limitations necessarily exist in applying tension force to the bolt shank. Technical Solution

[11] Accordingly, the present invention has been made in an effort to solve the problems occurring in the conventional rock bolt employed when carrying out tunnel excavation work or rock-based construction, and an object of the present invention is to provide a preceding tension type rock bolt and a construction method using the same, wherein expansion members are expanded by a wedge secured to an end of a tensioning member to be securely fixed against the inner surface of a drilled hole, a pipe is removed, tension force is applied to the tensioning member, and the tensioned state of the tensioning member is maintained to thereby apply a preceding load, so that, since the discontinuous surfaces of rock formations can be restrained, the safety of a rock slope is increased, and because it is possible to immediately carry out subsequent excavation work without waiting for grouting material to cure, a construction period can be shortened.

[12] Another object of the present invention is to provide a preceding tension type rock bolt and a construction method using the same wherein, as a pipe is removed after expansion members are expanded and is securely fixed against the inner surface of a drilled hole, the pipe, which is a costly construction material, can be reused in the assembly of another rock bolt at the construction site, so that the economic burden imposed by costly construction materials, which is becoming more serious, can be decreased by no less than one-third.

Advantageous Effects [13] The preceding tension type rock bolt and the construction method using the same according to the present invention provide advantages in that expansion members are expanded by a wedge secured to the end of a tensioning member to be securely fixed against the inner surface of a drilled hole, a pipe is removed, tension force is applied to the tensioning member, and the tensioned state of the tensioning member is maintained to thereby apply a preceding load. As a consequence, since the discontinuous surfaces of rock formations can be restrained, the safety of a rock slope is increased. Therefore, because it is possible to immediately carry out subsequent excavation work without waiting for grouting material to cure, a construction period can be shortened.

[14] Also, in the present invention, due to the fact that the pipe is removed after the expansion members are expanded and securely fixed against the inner surface of the drilled hole, the pipe, which is a costly construction material, can be reused in the assembly of another rock bolt at the construction site. Hence, the economic burden due to costly construction materials, which is becoming more serious, can be decreased by no less than one-third. Brief Description of the Drawings

[15] The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description when taken in conjunction with the accompanying drawings, in which:

[16] FIG. 1 is a cross-sectional view schematically illustrating the construction of a preceding tension type rock bolt in accordance with an embodiment of the present invention;

[17] FIG. 2 is an exploded perspective view independently illustrating the embedded fixing section inserted into a drilled hole in the preceding tension type rock bolt in accordance with the present invention;

[18] FIG. 3 is an assembled cross-sectional view of FIG. 2;

[19] FIG. 4 is a side view of FIG. 3, with a wedge cap removed;

[20] FIG. 5 is an exploded perspective view independently illustrating the outside fixing section mounted to the entrance of the drilled hole in the preceding tension type rock bolt in accordance with the present invention;

[21] FIG. 6 is an assembled cross-sectional view of FIG. 5;

[22] FIGs. 7 through 11 are cross-sectional views illustrating a construction method using the preceding tension type rock bolt in accordance with the present invention;

[23] FIGs. 12 and 13 are an exploded perspective view and a cross-sectional view illustrating another embodiment of the embedded fixing section in the preceding tension type rock bolt in accordance with the present invention;

[24] FIGs. 14, 15, 16 and 17 are an exploded perspective view, cross-sectional views and a side view illustrating other embodiments of the wedge of the embedded fixing section in the preceding tension type rock bolt in accordance with the present invention; and

[25] FIG. 18 is a cross-sectional view illustrating another embodiment of the outside fixing section in the preceding tension type rock bolt in accordance with the present invention. Best Mode for Carrying Out the Invention

[26] In order to achieve the above object, according to one aspect of the present invention, there is provided a preceding tension type rock bolt comprising a pipe; two or more expansion members detachably coupled to one end of the pipe to be uniformly spaced apart from one another, having a substantially sectorial sectional shape, and defining a tensioning member opening and a frusto-conical opening; a tensioning member installed through the pipe and the expansion members such that both ends thereof project out of the pipe and the expansion members; and a wedge secured to one end of the tensioning member and inserted into the frusto-conical opening of the expansion members to expand the expansion members radially outward.

[27] According to another aspect of the present invention, the expansion members are not completely separated from one another and are partially coupled with one another by a coupling element; and a ring groove is defined in the expansion members adjacent to one end of the frusto-conical opening, and a snap ring is fitted into the ring groove such that the wedge is prevented from being released. In this case, since the tensioning member and the wedge secured to one end of the tensioning member are prevented from being released from the pipe, transportation and construction is made possible. Therefore, the rock bolt according to the present invention can be put on the market without assembling an outer fixing section to the tensioning member, and the outer fixing section can be assembled later to the tensioning member at a construction site.

[28] According to another aspect of the present invention, the tensioning member opening and the frusto-conical opening of the expansion members are concentric with an axis of the expansion members which are in an assembled state; and, when three expansion members are uniformly spaced apart from one another, three tensioning member openings and frusto-conical openings are defined inside the expansion members so as to be aligned with boundary regions between two adjoining expansion members.

[29] According to another aspect of the present invention, the wedge comprises a hollow frusto-conical wedge which is inserted into the frusto-conical opening of the expansion members, grips an outer surface of the tensioning member and is uniformly split into at least two wedge pieces, and a wedge cap which is threadedly coupled to a large diameter end of the frasto-conical wedge to prevent the frasto-conical wedge from being released.

[30] According to another aspect of the present invention, the wedge includes a hollow frusto-conical liner which is inserted into the frusto-conical opening of the expansion members, defines a frusto-conical opening therein and has a frusto-conical outer surface; a hollow frusto-conical wedge which is uniformly split into at least two wedge pieces and is inserted into the frusto-conical opening of the hollow frusto-conical liner to grip the outer surface of the tensioning member; and a liner cap which is threadedly coupled to a large diameter end of the hollow frusto-conical liner to prevent the frusto- conical wedge from being released.

[31] According to another aspect of the present invention, the wedge includes a hollow frusto-conical wedge housing which is formed to have a configuration corresponding to that of the frusto-conical opening of the expansion members, is defined with frusto- conical openings at three uniformly spaced-apart positions and a tensioning member opening for collecting three tensioning member branches extending through the frusto- conical openings into one tensioning member; hollow frusto-conical wedges respectively inserted into the frusto-conical openings of the hollow frusto-conical wedge housing to grip the outer surface of the tensioning member branches which extend through the hollow frusto-conical wedges; and a wedge housing cap threadedly coupled to a large diameter end of the wedge housing to prevent the frusto-conical wedges from being released.

[32] According to another aspect of the present invention, at boundary regions where the three frusto-conical openings communicate with the tensioning member opening in which the three tensioning member branches are combined with one another, the inner surface of the frusto-conical wedge housing is rounded, so that the tensioning member is not bent in a lengthwise direction thereof.

[33] According to another aspect of the present invention, each of the wedge cap, the liner cap, and the wedge housing cap defines a tensioning member accommodating part so that the liner cap can be threadedly coupled to the frusto-conical wedge in the state in which the tensioning member projects rearward beyond the frusto-conical wedge.

[34] According to another aspect of the present invention, the respective expansion members are fastened to a flange which is formed on one end of the pipe, by means of at least one bolt.

[35] According to another aspect of the present invention, an outside fixing section is installed on the other end of the tensioning member to maintain the tensioning member in a tensioned state.

[36] According to another aspect of the present invention, the outside fixing section comprises a bearing plate installed at an entrance of a drilled hole corresponding to the other end of the tensioning member and defined with a tensioning member opening through which the tensioning member passes, and a tension maintaining member provided to the other end of the tensioning member which projects out of the bearing plate to maintain the state in which tension force is applied to the tensioning member. Alternatively, a packer is installed on the outside fixing section to closely plug the entrance of the drilled hole. At this time, two hose openings must be defined in each of the packer and the bearing plate so that a grouting material can be poured into the drilled hole and foreign substances can be removed.

[37] The tension maintaining member comprises a fixed body which is defined with a tensioning member opening and a frusto-conical opening, at least two outer wedge pieces which are inserted into the frusto-conical opening of the fixed body to secure the tensioning member, and a body cap which is threadedly locked to the fixed body to cover the other end of the tensioning member.

[38] In order to achieve the above object, according to another aspect of the present invention, there is provided a construction method using a preceding tension type rock bolt, comprising the drilling step of drilling a hole in a rock formation; the rock bolt insertion step of inserting an embedded fixing section of the rock bolt into the drilled hole; the tensioning step of pulling and tensioning a tensioning member while supporting a pipe using the embedded fixing section of the rock bolt; and the outside fixing step of installing a bearing plate and a tension maintaining member on the other end of the tensioning member so that the bearing plate and the tension maintaining member can be supported at the entrance of the drilled hole, pulling the tensioning member and maintaining the tensioned state of the tensioning member, wherein the tensioning step includes the inside fixing step, in which, as the tensioning member is tensioned, a wedge secured to one end of the tensioning member biases expansion members radially outward, by which bolts are cut to separate the expansion members and the pipe from each other, and then, the expansion members are expanded radially outward to be fixed against the inner surface of the drilled hole; and wherein the method further comprises the pipe removing step, in which tension force applied to the tensioning member to fix the expansion members against the inner surface of the drilled hole in the inside fixing step is released, and the pipe is removed from the drilled hole.

[39] Thanks to the features of the present invention, the preceding tension type rock bolt and the construction method using the same provide advantages in that expansion members are expanded by a wedge secured to the end of a tensioning member to be securely fixed against the inner surface of a drilled hole, a pipe is removed, tension force is applied to the tensioning member, and the tensioned state of the tensioning member is maintained to thereby apply a preceding load. Consequently, since the discontinuous surfaces of rock formations can be restrained, the safety of a rock slope is increased. Therefore, because it is possible to immediately carry out subsequent excavation work without waiting for grouting material to cure, a construction period can be shortened. As a result, a construction cost can be decreased, and the efficiency of construction work can be improved. Mode for the Invention

[40] Reference will now be made in greater detail to preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numerals will be used throughout the drawings and the description to refer to the same or like parts.

[41] FIG. 1 is a cross-sectional view schematically illustrating the construction of a preceding tension type rock bolt in accordance with an embodiment of the present invention, FIGs. 2 through 4 are views illustrating the embedded fixing section inserted into a drilled hole in the preceding tension type rock bolt in accordance with the present invention, FIG. 5 is an exploded perspective view independently illustrating the outside fixing section mounted to the entrance of the drilled hole in the preceding tension type rock bolt in accordance with the present invention, and FIG. 6 is an assembled cross-sectional view of FIG. 5.

[42] Referring to the drawings, the preceding tension type rock bolt according to the present invention comprises an elongate pipe 10 which is formed with a flange 12 at the distal end thereof, expansion members 20 which are fastened to the flange 12 of the pipe 10 by means of bolts 14, a wedge 40 which is provided inside the expansion members 20 to expand the expansion members 20, a tensioning member 30 which has a distal end secured to the wedge 40 and extends through the pipe 10, and an outside fixing section 50 which is provided to the proximal end of the pipe 10 adjacent to the proximal end of the tensioning member 30.

[43] The expansion members 20 concentrically define a tensioning member opening 21 and a frusto-conical opening 22. The expansion members 20 are regularly spaced apart from one another around the tensioning member opening 21. In this embodiment, three expansion members 20, each having a sectorial sectional shape, are provided. The expansion members 20 are fastened to the flange 12 by means of the bolts 14 to define a circular configuration.

[44] While the three expansion members 20 are illustrated as each having the sectorial sectional shape and being uniformly spaced apart from one another, it can be envisaged that two expansion members each having a semi-circular sectional shape are uniformly spaced apart from each other when the diameter of the circular configuration is small, or that four or more expansion members each having a sectorial sectional shape are uniformly spaced apart from one another when the diameter of the circular configuration is large.

[45] The tensioning member 30 extends through the pipe 10 and the expansion members

20 which are fastened to the distal end of the pipe 10, in a manner such that both ends of the tensioning member 30 project out of the pipe 10 and the expansion members 20. The tensioning member 30 is formed in a manner such that one steel wire is centrally positioned and six steel wires are twisted around the central wire. The tensioning member 30 can be replaced with a steel rod.

[46] The wedge 40 is secured to the distal end of the tensioning member 30 and is inserted into the frusto-conical opening 22 of the expansion members 20. When the wedge 40 is pulled along with the tensioning member 30, the wedge 40 is gradually inserted into the frusto-conical opening 22 of the expansion members 20 in the tensioning direction of the tensioning member 30, and expands the expansion members 20 radially outward.

[47] The wedge 40 comprises a hollow frusto-conical wedge 42 which is inserted into the frusto-conical opening 22 of the expansion members 20, grips the outer surface of the tensioning member 30 and is uniformly split into at least three wedge pieces, and a wedge cap 43 which is threadedly coupled to the large diameter end of the frusto- conical wedge 42 to prevent the frusto-conical wedge 42 from being released. Since the inner surface of the frusto-conical wedge 42 performs the main function of gripping the outer surface of the tensioning member 30, the inner surface of the frusto- conical wedge 42 is formed with a plurality of saw teeth such that the outer surface of the tensioning member 30 can be reliably gripped by the frusto-conical wedge 42.

[48] Because the wedge 40 may have any configuration so long as it can expand the expansion members 20 radially outward, the wedge 40 can be directly secured to the distal end of the tensioning wire 30 or can be indirectly secured to the distal end of the tensioning wire 30 through threaded locking.

[49] The bolts 14 can be formed to be easily cut by the force (pushing force) of the wedge 40 pushing the expansion members 20 radially outward to allow the expansion members 20 to be easily expanded. To this end, each bolt 14 can be formed, at a boundary region between the expansion members 20 and the flange 12, to have a neck portion which has a diameter less than the nominal diameter of the bolt 14.

[50] The outside fixing section 50 comprises a bearing plate 51 and a tension maintaining member 55. The bearing plate 51 is defined with a tensioning member opening 52 through which the tensioning member 30 passes. The tension maintaining member 55 is provided to the proximal end of the tensioning member 30 which projects out of the bearing plate 51 to maintain the state in which tension force is applied to the tensioning member 30. The tension maintaining member 55 comprises a fixed body 56 which is defined with a tensioning member opening 56a and a frusto- conical opening 56b, three outer wedge pieces 57 which are inserted into the frusto- conical opening 56b of the fixed body 56 to secure the proximal end of the tensioning member 30, which extends through the tensioning member opening 56a, and a body cap 58 which is threadedly locked to the fixed body 56 to cover the distal end of the tensioning member 30 and prevent the outer wedge pieces 57 from being released.

[51] The unexplained reference numeral 80 designates a drilled hole which is drilled in a rock formation to reinforce the discontinuous surfaces of the rock formation, 82 a tensioning member tensioning mechanism for applying tension force to the tensioning member 30, and 84 an outer wedge piece insertion mechanism for inserting the outer wedge pieces 57 of the outside fixing section 50 into the frusto-conical opening 56b of the fixed body 56.

[52] Hereinafter, a construction method using the preceding tension type rock bolt in accordance with the present invention, constructed as mentioned above, will be described with reference to FIGs. 7 through 11.

[53] First, the drilled hole 80 is defined in a discontinuous rock formation in carrying out tunnel excavation work or rock-based construction so that the preceding tension type rock bolt according to the present invention can be inserted into the drilled hole 80. Then, the embedded fixing section of the rock bolt is inserted into the drilled hole 80 to be positioned as shown in FIG. 7.

[54] After the embedded fixing section of the preceding tension type rock bolt is inserted into the drilled hole 80 in this way, the tension maintaining member 55 is removed from the outside fixing section 50, and the tensioning member tensioning mechanism 82 is installed on the proximal end of the tensioning member 30. At this time, the tensioning member tensioning member 82 must be supported by the proximal end of the pipe 10 or by the bearing plate 51.

[55] In this state, as the tensioning member tensioning mechanism 82 is operated, the wedge of the tensioning member tensioning mechanism 82 grips and pulls the tensioning member 30, so that only the tensioning member 30 and the wedge 40 secured to the distal end of the tensioning member 30 are pulled. As the tension load from the tensioning member 82 is increased, only the tensioning member 30 is continuously pulled. As the tensioning member 30 is pulled, by the radial force which is generated by the fact that the wedge 40 secured to the distal end of the tensioning member 30 is introduced into the frusto-conical opening 22 of the expansion members 20 and biases the expansion members 20 radially outward, the bolts 14 which fasten the expansion members 20 to the flange 12 of the pipe 10 are cut, and the expansion members 20 are expanded radially outward and then fixed against the inner surface of the drilled hole 80 (see FIG. 8). At this time, as the bolts 14 which fasten the expansion members 20 to the flange 12 of the pipe 10 are cut, the pipe 10 is separated from the expansion members 20.

[56] In this state, the tension force applied to the tensioning member 30 is released, and the pipe 10, the bearing plate 51 and the tensioning member tensioning mechanism 82 are removed from the tension member 30, as shown in FIG. 9. The pipe 10 removed in this way can be immediately reused in the assembly of another rock bolt at the construction site. Hence, the economic burden imposed by costly construction materials, which is becoming more serious, can be decreased by no less than one-third.

[57] Then, as shown in FIG. 10, the outside fixing section 50, the outer wedge piece insertion mechanism 84 and the tensioning member tensioning mechanism 82 are sequentially installed on the tensioning member 30 with the pipe 10 removed. Thereupon, the tensioning member tensioning mechanism 82 is operated to pull the tensioning member 30 so that predetermined tension force is applied to the tensioning member 30. While pulling the tensioning member 30 in this way, attention must be paid not to press the outer wedge pieces 57 of the outside fixing section 50. In this state, by temporarily operating the outer wedge piece insertion mechanism 84, as the outer wedge pieces 57 are inserted into the frusto-conical opening 56b of the fixed body 56, the outer wedge pieces 57 grip the tensioning member 30, whereby the tensioning member 30 can be maintained in a state in which tension force is applied thereto.

[58] At this time, the more the tensioning member 30 is pulled, the more the expansion members 20 are expanded radially outward by the wedge 40 secured to the distal end of the tensioning member 30, whereby the expansion members 20 an be more firmly fixed to the inner surface of the drilled hole 80 and preceding tension can be applied to the tensioning member 30. Since strength reinforcement is implemented through pressing discontinuous surfaces of the rock formations in this way, the load applied to the rock formation can be supported, and subsequent excavation work can be repeatedly carried out before the curing time of grouting material has elapsed.

[59] Next, after interrupting the operation of the tensioning member tensioning mechanism 82 which applies tension force to the tensioning member 30, the tensioning member tensioning mechanism 82 and the outer wedge piece insertion mechanism 84 are removed, the portion of the tensioning member 30 which projects out of the fixed body 56 is cut away, and the body cap 58 is threadedly coupled to the fixed body 56 to prevent the outer wedge pieces 57 from being released.

[60] The procedure for applying preceding tension to the preceding tension type rock bolt according to the present invention will be more concretely described below. As the tensioning member 30 is pulled in the tensioning direction thereof, that is, toward the entrance of the drilled hole 80, the hollow frasto-conical wedge 42, which constitutes the wedge 40 secured to the distal end of the tensioning member 30, is driven into the frusto-conical opening 22 of the expansion members 20. By this fact, the expansion members 20 are expanded radially outward, that is, against the inner surface of the drilled hole 80.

[61] If the expansion members 20 are expanded, the outer surfaces of the expansion members 20 are brought into contact with the inner surface of the drilled hole 80. Then, as the expansion members 20 are further expanded, in the course of tensioning the tensioning member 30, the expansion members 20 are driven into and firmly fixed to the inner surface of the drilled hole 80.

[62] Due to the fact that the expansion members 20 are fixed against the inner surface of the drilled hole 80 and the tensioning member 30 is tensioned to apply a preceding load as described above, it is possible to support the load applied to the discontinuous surfaces of the rock formations before pouring the grouting material. Therefore, even when grouting is not performed or is performed for drilled holes 80, other excavation work can be carried out before the grouting material has cured, whereby it is possible to improve work efficiency and significantly shorten a construction period.

[63] FIGs. 12 and 13 are an exploded perspective view and a cross-sectional view illustrating another embodiment of the embedded fixing section in the preceding tension type rock bolt in accordance with the present invention. In this embodiment, the expansion members 20 are coupled with one another at the proximal ends thereof by a coupling element 25. A ring groove 23 is defined on the inner surface of and adjacent to the distal end of the frusto-conical opening 22, and a snap ring 24 is fitted into the ring groove 23 so that the wedge 40 inserted into the frusto-conical opening 22 is prevented from being released.

[64] The coupling element 25 must be easily broken when external force is applied thereto by the wedge 40, and therefore, it is preferred that the coupling element 25 have a thickness of 1-3 mm. If the coupling element 25 has a thickness less than 1 mm, the coupling element 25 can be deformed or broken even by the application of a small force, which is not desirable. Also, if the coupling element 25 has a thickness greater than 3 mm, excessive initial external force is required to expand the expansion members 20 radially outward, which is not desirable.

[65] In the configuration of this embodiment, since the expansion members 20 are initially integrated with one another by the coupling element 25, when locking the expansion members 20 to the flange 12 of the pipe 10 by means of the bolts 14, assembly work can be easily conducted. Also, due to the fact that the wedge 40 secured to the distal end of the tensioning member 30 is fixedly maintained against fluctuation in the frusto-conical opening 22 of the expansion members 20, the tensioning member 30 and the wedge 40 secured to the distal end of the tensioning member 30 are prevented from being released, whereby the rock bolt according to the present invention can be sold without assembling the outer fixing section 50 to the tensioning member 30, and the outer fixing section 50 can be assembled to the tensioning member 30 at a construction site.

[66] FIGs. 14 and 15 are an exploded perspective view and a cross-sectional view illustrating another embodiment of the embedded fixing section in the preceding tension type rock bolt in accordance with the present invention. The wedge 40 includes a hollow frusto-conical liner 41 which defines a frusto-conical opening therein and has a frusto-conical outer surface. A hollow frusto-conical wedge 42 is uniformly split into at least three wedge pieces and is inserted into the frusto-conical opening of the hollow frusto-conical liner 41 to grip the outer surface of the tensioning member 30. A liner cap 43a is threadedly coupled to the large diameter end of the hollow frusto-conical liner 41 to prevent the frusto-conical wedge 42 from being released. The liner cap 43a can define a tensioning member accommodating part 431 so that the tensioning member 30 can be covered by the liner cap 43a in a state in which it extends rearward beyond the frusto-conical wedge 42.

[67] In the configuration of this embodiment, due to the fact that the frusto-conical wedge 42 is inserted in the frusto-conical opening of the liner 41 to be prevented from being released by the liner cap 43a, the release of the frusto-conical wedge 42, which can occur before the expansion members 20 are assembled into the frusto-conical opening 22 or the rock bolt of the present invention is inserted into the drilled hole 80 defined in the rock formation and the tensioning member 30 is tensioned, can be reliably prevented.

[68] Also, in the case where the liner cap 43a defines the tensioning member accommodating part 431, as the frusto-conical wedge 42 is inserted into the frusto- conical opening of the liner 41, the tensioning member 30 can be gripped with increased power. Therefore, as the wires constituting the tensioning member 30 are untwisted behind the frusto-conical wedge 42, advantageous effects can be attained in that the diameter of the tensioning member 30 is increased behind the frusto-conical wedge 42. If the diameter of the tensioning member 30 is increased in this way, because the tensioning member 30 is trapped by the frusto-conical wedge 42, the tensioning member 30 can be more reliably gripped.

[69] FIGs. 16 and 17 are a cross-sectional view and a side view illustrating another embodiment for the embedded fixing section in the preceding tension type rock bolt in accordance with the present invention. The wedge 40 includes a hollow frusto-conical wedge housing 44 which is formed to have a configuration corresponding to the frusto- conical opening 22 of the expansion members 20 and is defined with frusto-conical openings at three uniformly spaced-apart positions and a tensioning member opening for collecting the three tensioning member branches extending through the frusto- conical openings into one tensioning member 30. Hollow frusto-conical wedges 42 are inserted into respective frusto-conical openings of the hollow frusto-conical wedge housing 44 to grip the outer surface of the tensioning member branches which extend through the hollow frusto-conical wedges 42. A wedge housing cap 43b is threadedly coupled to the large diameter end of the wedge housing 44 to prevent the frusto-conical wedges 42 from being released.

[70] At the boundary regions where the three frusto-conical openings communicate with the tensioning member opening, in which the three tensioning member branches are combined with one another, the inner surface of the frusto-conical wedge housing 44 must be properly rounded so that the tensioning member 30 is not bent in the lengthwise direction thereof. If the tensioning member 30 is bent, when tensioning the tensioning member 30, a load is locally concentrated, as a result of which the tensioning member 30 can snap.

[71] In the configuration of this embodiment, due to the fact that one wedge 40 is provided to the center portion of the expansion members 20 and three tensioning member branches extend through the frusto-conical wedge housing 44 and are gripped by the frusto-conical wedges 42, when compared to the expansion members 20 according to the first embodiment, which has one wedge 40, the expansion members 20 according to this embodiment can be enlarged up to 1.3 times and can be applied to the case where the drilled hole has a diameter of 105-140 mm. Also, because it is possible to apply increased tension force through the three tensioning member branches, the gap between the bolts can be increased and the number of drilled holes for installing rock bolts can be decreased, whereby the construction cost can be remarkably reduced.

[72] FIG. 18 is a cross-sectional view illustrating another embodiment for the outside fixing section in the preceding tension type rock bolt in accordance with the present invention. In this embodiment, the entrance of the drilled hole 80 is plugged by a packer 60 which is defined with a tensioning member opening 61 and the hose openings 62, and the bearing plate 51 is provided outside of the packer 60. The packer 60 and the bearing plate 51 are defined with two hose openings 62 and 53 for pouring the grouting material into the drilled hole 80 and removing foreign substances.

[73] In the configuration of this embodiment, since the entrance of the drilled hole 80 is tightly closed by the packer 60, after the expansion members 20 are fixed against the inner surface of the drilled hole 80, tension force is applied to the tensioning member 30 to apply a preceding load, as described above. Then, cement mortar as the grouting material is poured through one of the hose openings 62 and 53 defined in the packer 60 and the bearing plate 50, and air or foreign substances are discharged through the other of the hose openings 62 and 53. In this way, it is possible to implement compaction grouting. At this time, the curing can be effected with the cement mortar introduced between the discontinuous surfaces of the rock formations.

[74] If the cement mortar as the grouting material is cured, since the cement mortar is introduced between the discontinuous surfaces of the rock formations, strength reinforcement of the rock formations can be reliably performed.

[75] Also, in the construction method using the preceding tension type rock bolt according to the present invention, the rock bolt, in which the outside fixing section is temporarily installed on the tensioning member 30 at the proximal end of the pipe 10 with the expansion members 20 mounted at the distal end of the pipe 10, is inserted into the drilled hole 80. Then, as the tensioning member 30 is pulled using the tensioning member tensioning mechanism 82 as described above, the wedge 40 which is secured to the distal end of the tensioning member 30 expands the expansion members 20, whereby the embedded fixing section can be firmly fixed to the inner surface of the drilled hole 80.

[76] As the expansion members 20 are expanded by the wedge 40 in this way, the expansion members 20 cut the bolts 14 which lock the pipe 10 and the expansion members 20 with each other. As the bolts 14 are cut, construction work can be completed with the separated pipe 20 not removed from, but remaining in, the drilled hole 80, or thereafter, cement mortar, as the grouting material can be poured into the drilled hole 80.

[77] In this construction method, inconvenience caused by the fact that the tensioning member tensioning mechanism must be reinstalled after the tensioning member tensioning mechanism has been disassembled and the pipe 10 has been removed, can be eliminated, whereby workability is improved. Also, since it is possible to directly apply a preceding load to the tensioning member 30 and then carry out subsequent excavation work, a construction period can be further shortened. Moreover, because the pipe 10 remaining in the drilled hole 90 functions as a reinforcing member, reliable strength reinforcement can be ensured, whereby it is possible to increase the gap between the rock bolts and improve safety. Industrial Applicability

[78] In the preceding tension type rock bolt according to the present invention, a hole having a predetermined diameter is drilled in a rock formation inside a tunnel, and the rock bolt is inserted into and fixed in the drilled hole. The rock bolt can be advantageously applied to reinforce discontinuous support force of the rock formation when carrying out tunnel excavation work or rock-based construction. [79] Although preferred embodiments of the present invention have been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

[80]

Claims

[1] A preceding tension type rock bolt comprising: a pipe; two or more expansion members detachably coupled to one end of the pipe to be uniformly spaced apart from one another, having a substantially sectorial sectional shape, and defining a tensioning member opening and a frusto-conical opening; a tensioning member installed through the pipe and the expansion members such that both ends thereof project out of the pipe and the expansion members; and a wedge secured to one end of the tensioning member and inserted into the frusto-conical opening of the expansion members to expand the expansion members radially outward.

[2] The preceding tension type rock bolt as set forth in claim 1, wherein a ring groove is defined in the expansion members adjacent to one end of the frusto- conical opening, and a snap ring is fitted into the ring groove such that the wedge is prevented from being released.

[3] The preceding tension type rock bolt as set forth in claim 1, wherein the expansion members are not completely separated from one another, and are partially coupled to one another by a coupling element.

[4] The preceding tension type rock bolt as set forth in claim 1, wherein the tensioning member opening and the frusto-conical opening of the expansion members are concentric with an axis of the expansion members which are in an assembled state.

[5] The preceding tension type rock bolt as set forth in claim 1, wherein, when three expansion members are uniformly spaced apart from one another, three tensioning member openings and frusto-conical openings are defined inside the expansion members to be aligned with boundary regions between two adjoining expansion members.

[6] The preceding tension type rock bolt as set forth in claim 1, wherein the wedge comprises a hollow frusto-conical wedge which is inserted into the frusto-conical opening of the expansion members, grips an outer surface of the tensioning member and is uniformly split into at least two wedge pieces, and a wedge cap which is threadedly coupled to a large diameter end of the frusto-conical wedge to prevent the frusto-conical wedge from being released.

[7] The preceding tension type rock bolt as set forth in claim 6, wherein the wedge cap defines a tensioning member accommodating part so that the wedge cap can be threadedly coupled to the frusto-conical wedge in a state in which the tensioning member projects rearward beyond the frasto-conical wedge.

[8] The preceding tension type rock bolt as set forth in claim 1, wherein the wedge includes a hollow frusto-conical liner which is inserted into the frusto-conical opening of the expansion members, defines a frusto-conical opening therein and has a frusto-conical outer surface; a hollow frusto-conical wedge which is uniformly split into at least two wedge pieces and is inserted into the frusto- conical opening of the hollow frusto-conical liner to grip the outer surface of the tensioning member; and a liner cap which is threadedly coupled to a large diameter end of the hollow frusto-conical liner to prevent the frusto-conical wedge from being released.

[9] The preceding tension type rock bolt as set forth in claim 8, wherein the liner cap defines a tensioning member accommodating part so that the liner cap can be threadedly coupled to the frusto-conical wedge in a state in which the tensioning member projects rearward beyond the frusto-conical wedge.

[10] The preceding tension type rock bolt as set forth in claims 1 or 2, wherein the respective expansion members are fastened to a flange, which is formed on one end of the pipe, by means of at least one bolt.

[11] The preceding tension type rock bolt as set forth in claim 10, wherein each bolt is formed, at a boundary region between the expansion members and the flange, with a neck portion which has a diameter less than a nominal diameter of the bolt, so that the expansion members can be reliably expanded radially outward by the wedge.

[12] The preceding tension type rock bolt as set forth in claim 1, wherein the wedge includes a hollow frusto-conical wedge housing which is defined with frusto- conical openings at three uniformly spaced-apart positions and a tensioning member opening for collecting three tensioning member branches extending through the frusto-conical openings into one tensioning member; hollow frusto- conical wedges respectively inserted into the frusto-conical openings of the hollow frusto-conical wedge housing to grip the outer surface of the tensioning member branches which extend through the hollow frusto-conical wedges; and a wedge housing cap threadedly coupled to a large diameter end of the wedge housing to prevent the frusto-conical wedges from being released.

[13] The preceding tension type rock bolt as set forth in claim 12, wherein, at boundary regions where the three frusto-conical openings communicate with the tensioning member opening in which the three tensioning member branches are combined with one another, an inner surface of the frusto-conical wedge housing is rounded so that the tensioning member does not bend in a lengthwise direction thereof.

[14] The preceding tension type rock bolt as set forth in claim 12, wherein the wedge housing cap defines a tensioning member accommodating part so that the wedge housing cap can be threadedly coupled to the frusto-conical wedge in a state in which the tensioning member projects rearward beyond the frusto-conical wedge.

[15] The preceding tension type rock bolt as set forth in claim 1, wherein an outside fixing section is installed on the other end of the tensioning member to maintain the tensioning member in a tensioned state.

[16] The preceding tension type rock bolt as set forth in claim 15, wherein the outside fixing section comprises a bearing plate installed at an entrance of a drilled hole corresponding to the other end of the tensioning member and defined with a tensioning member opening through which the tensioning member passes, and a tension maintaining member provided to the other end of the tensioning member which projects out of the bearing plate to maintain a state in which tension force is applied to the tensioning member.

[17] The preceding tension type rock bolt as set forth in claims 15 or 16, wherein a packer is installed on the outside fixing section to closely plug an entrance of the drilled hole.

[18] A construction method using a preceding tension type rock bolt, comprising: the drilling step of drilling a hole in a rock formation; the rock bolt insertion step of inserting an embedded fixing section of the rock bolt into the drilled hole; the tensioning step of pulling and tensioning a tensioning member while supporting a pipe using the embedded fixing section of the rock bolt; and the outside fixing step of installing a bearing plate and a tension maintaining member on the other end of the tensioning member so that the bearing plate and the tension maintaining member can be supported at an entrance of the drilled hole, pulling the tensioning member and maintaining a tensioned state of the tensioning member, wherein the tensioning step includes the inside fixing step in which, as the tensioning member is tensioned, a wedge secured to one end of the tensioning member biases expansion members radially outward, by which bolts are cut to separate the expansion members and the pipe from each other, and then, the expansion members are expanded radially outward to be fixed against an inner surface of the drilled hole; and wherein the method further comprises the pipe removing step, in which tension force applied to the tensioning member to fix the expansion members against the inner surface of the drilled hole in the inside fixing step is released, and the pipe is removed from the drilled hole.

[19] The method as set forth in claim 18, wherein, in the outside fixing step, after an entrance of the drilled hole is closely plugged by a packer, cement mortar, as a grouting material, is poured through one of hose openings defined in the packer and the bearing plate, and air or foreign substances are discharged through the other of the hose openings, whereby compaction grouting is implemented.