GB2131854A

GB2131854A - Method of statically fracturing rock

Info

Publication number: GB2131854A
Application number: GB08332640A
Authority: GB
Inventors: Kenji Yagi; Masakuni Matsui; Hiroshi Nakashio; Tooru Hayashida; Noboru Iuchi
Original assignee: Kajima Corp
Current assignee: Kajima Corp
Priority date: 1982-12-13
Filing date: 1983-12-07
Publication date: 1984-06-27
Also published as: JPH0251035B2; FI834563A; JPS59118989A; GB2131854B; GB8332640D0; FI834563A0

Abstract

In a method of fracturing rock 1 a plurality of elastic members 3 are inserted into a hole 2 bored in the rock 1. The elastic members 3 are then compressed in the longitudinal direction of the hole 2 so as to expand them radially until the rock 1 is fractured as a result of the radial expansion of the elastic members 3. <IMAGE>

Description

SPECIFICATION A method of statically fracturing rock Background of the invention Field of the invention This invention relates to a method of fracturing rock, and more particularly to a method of fracturing rock by compressing elastic members placed in a hole of the rock in the longitudinal direction of the hole so as to expand the elastic members in the radial direction of the hole until the rock is fractured by such radial expansion of the elastic members.

Description of the prior art To fracture rock, such as bedrock, a large mass of stone, a solid concrete block and the like, dynamic fracturing methods have been used heretofore. For instance, one or more holes are bored in the rock to be fractured, and an explosive is loaded in the holes thus bored, and the rock is fractured by detonating the explosive. To eliminate unavoidable noise of the dynamic methods, which is a cause of environmental problem, a number of static methods of fracturing rock have been proposed and practiced to a certain extent.

As a static rock fracturing method without using any explosive, it has been known to load an expansive chemical in a hole bored in the rock, but the method using chemical has shortcomings in that it takes a comparatively long time before the chemical becomes effective and that the workability of the method is comparatively low. Other conventional static fracturing methods involve the use of a wedge to be driven into a hole in the rock or a small jack to be placed and operated in the hole of the rock. However, such conventional static fracturing methods have shortcomings in that their workability is comparatively low, that the methods tend to cause damages rather frequently in the tools used therein, and that the structure of the tools therefor is complicated.

Summary of the invention Therefore, an object of the present invention is to obviate the above-mentioned shortcomings of the prior art by-providing an improved method for statically fracturing rock.

To fulfil the above-mentioned object, a method according to the present invention comprises steps of inserting a lower pressing member having a rod at the bottom of a hole bored in rock to be fractured so as to let the rod extend upward through the hole, placing a plurality of perforated elastic members, such as hard rubber members, into the hole so as to let the rod extend through the perforations of the elastic members, placing a perforated upper pressing member on the uppermost surface of the elastic members while allowing the rod to extend through the perforation of the upper pressing member, and compressing the elastic members in the longitudinal direction of the hole by pulling the rod relative to the upper pressing member so as to expand the elastic members in the radial direction of the hole, until the rock is fractured by the radial expansion of the elastic members.The rock to be fractured by the method of the invention, is for instance, bedrock, a large mass of stone, a concrete block, and the like. The compression of the elastic members may be effected by disposing a jack between the rod and the upper pressing member.

The inventors noted that, when only one elastic member with a perforation is used in the hole of the rock for fracturing, the elastic member is required to be very long in order to produce the necessary expanding force to fracture hard rock. As the length of the elastic member increases, the uniformity of the expanding force along the surface of the elastic member is reduced, so that the net compression for effecting the rock fracture also increases. Accordingly, with only one elastic member, a large compressive force must be applied to the elastic member in the longitudinal direction of the hole of the rock.The inventors have found that when a number of elastic members are placed in the rock hole, uniformity of the expanding force along the outer peripheral surface of the elastic members in contact with the inner wall of the rock hole is ensured, and the net compressive force necessary for the rock fracture can be reduced. The present invention is based on such finding of the inventors.

Brief description of the drawings For a better understanding of the invention, reference is made to the accompanying drawings, in which: Fig. 1 is a schematic partial sectional view showing the principles of a rock fracturing method according to the present invention; Fig. 2 and Fig. 4 are schematic perspective views of perforated elastic members to be used in the method of the invention; Fig. 3 is a schematic sectional view illustrating a preferred embodiment of the invention; and Flg. 5 is a diagrammatic illustration of the result of a test of the method of the invention.

Like parts are designated by like numerals and symbols throughout different views of the drawings.

Description of the preferred embodiment Referring to Fig. 1 showing the principles of the method of the present invention, in order to fracture rock 1, a hole 2 is bored in the rock 1 so that two or more perforated elastic members 3 are inserted in the hole 2. The perforated elastic member 3 is, for instance, cylindrical or tubular as shown in Fig. 2, and a central hole 3A is formed along the longitudinal axis thereof. To facilitate the compression of the perforated elastic members 3, a lower pressing member 4 is placed at the bottom of the hole 2, and an operating rod 4A which is integral with the lower pressing member 4 extends upward to the outside of the hole 2 through the central holes 3A of the elastic members 3.A perforated upper pressing member 5 extends downward from the top opening of the hole 2 while allowing the operating rod 4A to pass through the perforation thereof, so that the upper pressing member 5 comes in contact with the uppermost surface of the perforated elastic members 3.

A suitable pressing means (not shown) acts upon the operating rod 4A and the upper pressing member 5, so that the lower pressing member 4 is pulled upward as shown by the arrow A, while the upper pressing member 5 is pushed downward as shown by the arrow B. As a result, the elastic members 3 are compressed in the longitudinal direction of the hole 2 and caused to expand in the radial direction thereof. When the radial expansion of the elastic members 3 reaches a certain limit, the rock 1 surrounding the elastic members 3 is fractured. Whereby, the object of the invention, i.e. the static fracturing of the rock 1, can be fulfilled.

The invention will be described in further detail now, by referring to an example illustrated in Fig.

3, Fig. 4 and Fig. 5.

Example In Fig. 3, a hole 2 with a diameter of 100 mm and a depth of 1,500 mm was bored in a granite bedrock 1A forming the rock 1 to be fractured. A plurality of perforated elastic members 3B with an outside diameter of 95 mm, an inside diameter of 36 mm and a length of 90 mm were prepared by using hard urethane tubes having a JIS (Japanese Industrial Standard) hardness of 95. Each of the elastic members 38 thus formed had opposite ends thereof tapered, as shown in Fig. 4. A pull rod 7 having a nut 6 screwed to one end thereof was inserted in the hole 2 so as to place the nut 6 at the bottom of the hole 2, and the perforated elastic members 3B were loaded in the hole 2 in such a manner that the pull rod 7 extended through the central holes 3A of the elastic members 38.

In the illustrated example, washers 8 were disposed between the adjacent elastic members 3B. A hollow ram 9 was slidably fitted on the pull rod 7 so that the pull rod 7 extended through the inside hollow space of the ram 9 and the lower end of the hollow ram 9 was in contact with the uppermost surface of the elastic members 3B. The jack base 10 of a hollow jack 11 was secured to the top end of the ram 9, so that the pull rod 7 penetrated through the hollow jack 11. Another nut 6 was screwed on the top end of the pull rod 7 so as to face the upper end of the hollow jack 11.Thus, the elastic members 38 were placed in the hole 2 in position: namely, the lower nut 6 engaging the lowermost end of the elastic members 38 through the washer 8 was placed at the bottom of the hole 2 while the lower end of the hollow ram 10 engaged the uppermost end of the elastic members 3B, and the distance between the nut 6 at the bottom of the hole 2 and the nut 6 above the hollow jack 11 was fixed by the pull rod 7, as shown in Fig. 3.

Then, the hollow jack 11 was operated so as to enlarge the distance between the top nut 6 and the jack base 10. Whereby, the lower nut 6 was pulled upward through the pull rod 7 while the hollow ram 9 was pushed downward by the jack base 10, so that the elastic members 38 were compressed in the longitudinal direction of the hole 2. As a result, the elastic members 3B expanded radially, or toward the circumference of the hole 2, and when the expansion of the elastic members 3B exceeded a certain limit, cracks 12 were caused in the bedrock 1A, as shown in Fig. 3 and Fig. 5, and the bedrock 1 A was fractured.

The above-mentioned process was repeated while changing the depth of the hole 2, and pressure when the cracks 12 were formed was measured. The result is shown in Table 1.

Table 1 Fracturing tests of granite

Loading depth Elastic Diameter of elastic Cracking members Test ofhole 2 members 38 pressure used No. (mmJ (mum) (t) (Note 1) Ref 1 100 60 71.0 500x1 Ref 2 100 150 78.0 500x1 1 100 150 47.0 90x4 2 100 60 45.0 90x4 Note 1: (length)x(piece) of the elastic member 38 used.

As can be seen from Table 1 , the tests of the example provided that the method of the invention using a plurality of the elastic members 3B ensured static fracturing of rock at a comparatively low cracking pressure. More particularly, the fracturing force in the case of using a plurality of the elastic members 38 proved to be less than 60% of that in the case of using only one elastic member 38, so that the use of the plurality of elastic members improved the efficiency and economy of the static rock fracturing method.

The features of the static rock fracturing method according to the present invention can be summarized as follows.

(1) The method ensures static fracturing of rock in a short operating time.

(2) Tools necessary for carrying out the method are simple and can be produced at a low cost.

(3) The workability of the method is high, because its operation is simple and the tools therefor are easy to operate.

(4; Tools for effecting the method are durable, because the chance of their damage during operation is low.

(5) The method can be carried out in an efficient and economical manner.

Claims

1. A method of statically fracturing rock, comprising steps of boring a hole in the rock, placing a lower pressing member with a rod on bottom of said hole so as to let the rod extend upward through the hole, disposing a plurality of perforated elastic members on the lower pressing member in such a manner that the rod extends through perforations of the perforated elastic members, placing a perforated upper pressing member on the uppermost surface of the elastic members so as to let the rod to extend through the perforation of the upper pressing member, and compressing the elastic members in the longitudinal direction of the hole by pulling the rod relative to the upper pressing member so as to expand the elastic members in radial direction of the hole until the rock is fractured.

2. A method of statically fracturing rock as set forth in claim 1, wherein washers are disposed between the adjacent elastic members disposed in said hole in the rock.

3. A method of statically fracturing rock as set forth in claim 1, wherein each of said elastic members is tapered at opposite longitudinal ends thereof.

4. A method of statically fracturing rock as set forth in claim 1, wherein each of said elastic members is made of hard urethane tube with a JIS hardness of 95.

5. A method of statically fracturing rock as set forth in claim 1, wherein said pulling of the rod relative to the upper pressing member is effected by a hollow jack having said rod extended therethrough so that top end of said rod engages one end of the hollow jack while said upper pressing member engages the opposite end of the hollow jack.

6. A method of staticaily fracturing rock, comprising boring a hole in the rock, inserting into the hole a plurality of elastic members disposed in line axially thereof, and compressing said elastic members in the longitudinal direction of the hole and thus expanding the elastic members radially until the rock is fractured.

7. Apparatus for statically fracturing rock, comprising a first pressing member with a pull rod extending therefrom and adapted to be positioned in a hole in rock to be fractured, a plurality of perforated elastic members adapted to be threaded in turn on the pull rod within the hole, a second pressure member adapted to press on the elastic members within the hole with the pull rod extending through the second pressure member, and means to pull said rod with respect to the second pressure member whereby axially to compress the elastic members on the pull rod.

8. Apparatus according to claim 7, further comprising a washer or washers for positioning one between each two adjacent elastic members.

9. Apparatus according to claim 7 or claim 8, wherein each of said elastic members is of annular form.

1 0. Apparatus according to claim 9, wherein each of said elastic members comprises a hollow cylindrical body.

1 Apparatus according to claim 10, wherein each of said elastic members has tapering ends of generally frusto-conical shape.

12. Apparatus according to any one of claims 7 to 1 wherein said elastic members are of hard urethane material with a JIS hardness of 95.

13. Apparatus according to any one of claims 7 to 12, wherein said first pressing member is threaded on to the pull rod.

14. Apparatus according to any one of claims 7 to 1 3, further comprising a hollow jack through which said pull rod passes, the jack being operative in the axially extending sense between said second pressing member and a nut threaded on the end of the pull rod.

1 5. Apparatus for statically fracturing rock, comprising a plurality of elastic members adapted to be disposed in line axially within a hole bored in the rock to be fractured, and means to compress said elastic members longitudinally of the hole whilst within the latter whereby to expand the elastic members radially sufficiently to fracture the rock.

1 6. A method of statically fracturing rock substantially as herein described with reference to the accompanying drawings.

1 7. Apparatus for statically fracturing rock, substantially as herein particularly described with reference to Figs. 1 and 2, or Figs. 3 and 4, of the accompanying drawings.