UNSTABLE ROCK AND ITS TREATMENT SNOWY MOUNTAINS SCHEME
ACKNOWLEDGEMENTS
The author is indebted to the Snowy Mountains Hydro-Electric Authority for permission to present this paper. However, the views expressed therein are those of the author and not necessarily those of the Authority. The material presentcd in the paper is derived from experimental investigations and actual practice extending over a considerable period, involving the co-operative work of many geologists and engineers of the Authority and of the Contractors.
The author is indebted particularly to Mr. D. H. Probert and Mr. D. W. Jordan, engineering geologists, who supplied material for drawings showing methods of treatment used in Snowy-Eucumbene Tunnel.
REFERENCES
Andrews, K. E., McIntyre, A. R., and Mattner, R. H., 1964. Some aspects of high speed hard rock tunnelling in the Snowy Mounmins. Instn. Eng. Aust., Civil Engg. Trans. CE6 (2): 51-70.
Dann, H. E., Hartwig, W. P., and Hunter, J. R., 1963. Unlined tunnels of the Snowy Mountains Hydro-Electric Authority. A paper presented at Symposium on Unlined Power Tunnels. Amer. Soc. Civil Eng., Power Divn., Oct., 1963, San Francisco.
Lang, T. A., 1958. Rock bolting speeds Snowy Mountains Project. Civil Engg. 28: 40-42.
Lang, T. A., 1959. Underground experience in the Snowy Mountains Australia. Proc. Second Protective Construction Symposium, Rand Corporation. Rand Report R-341: 767-853.
Leech, T. D. J., and Pender, E, B., 1961. Experience in grouting rock bolts. Proc. Fifth Int. Conf. Soil Mechanics and Foundation Engg., Paris 2: 445-452.
Pender, E. B., Hosking, A. D., and Mattner, R. H., 1963. Grouted rock bolts for permanent support of major underground works. . Instn. Eng. Aust. 35 (7-8): 1-22.
Proctor, R. V., and White, T. L., 1946. Rock Tunnelling with Steel Supports (Commercial Shearing and Stamping Co., Youngstown).
DISCUSSION
Prof. J. J. Reed (Colorado School of Mines, Golden, U.S.A.): I should like to ask if thought has been given to placing bolts with an initial installation more nearly equal to the minimum yield load? Also, has hydraulic tensioning of bolts been developed in Australia, as it has in South Africa, so as to eliminate the combined torque-tension stresses in a normal torqued bolt?
D. G. Moye: With the present method of installation, the bolts, during installation, are taken close to yield in combined torque-tension, the useful loads in the bolts being less than half the load at which they would yield in pure tension. It would be a considerable advantage to be able to double the installed load in the bolts but this would require a different method of installation. The hydraulic jacking method of tensioning in use in mines in Africa (Hunter, 1964)1 is such a method. It has not been used in the Snowy Mountains for routine installation of bolts although a similar jack is used for checking the tension in samples of bolts after they have been installed by the torqueing method.
G. B. Connor (The Zinc Corporation Ltd., Broken Hill, Australia):
1. How do you overcome the difficulty encountered by having rock faces which are not normal to the bolt hole?
2. How do you check that the bolts have the correct tension?
1Hunter, J. K., 1964. Rock bolting practice at Rhokana Corporation Limited, J. South African Inst. Min Met, 64, 293-301.
