Page 12 of 19 First Next Previous Last

UNSTABLE ROCK AND ITS TREATMENT SNOWY MOUNTAINS SCHEME

Figure 10

10.—Area of partly decomposed granite 20 ft wide in roof of Eucumbene-Snowy Tunnel. Supported by grouted rock bolts and steel channels and heavy wire mesh spanning between bolts.

Final treatment (continued)

Thereafter it is subject to continuous saturation with water, to the erosive action of flowing water, and in some tunnels, occasionally, to rapidly fluctuating water pressures. The kinds of final treatment are concrete lining, grouted rock bolts, pneumatically applied mortar both plain and reinforced with mesh.

Concrete lining

As mentioned previously, the practice is to concrete line all sections of tunnels in which steel rib supports are installed. The timber blocking which transmits the rock load between rock and steel cannot be relied upon indefinitely to remain firm and strong and not to crush. Failure of blocking could lead to large scale collapse of the rock. Also, in most sections of tunnels where steel ribs have been used, there are extensive seams of weak erodible material which require protection against water.

Grouted rock bolts

Where rock bolts are used for permanent support in unlined tunnels they are grouted to protect them against rusting which could lead to loss of tension and failure (Leech and Pender, 1961). Cement grout is injected to fill the space in the hole between the bolt and the rock. The problem of how to remove the air displaced by the grout in upward sloping holes was solved initially by attaching to the bolt a separate small diameter air-vent tube about the same length of the bolt. A more efficient method has been recently developed by the Authority in which hollow-core bolts are used, the displaced air passing out down through the centre of the bolts. Grouting pressures are kept to the minimum necessary to fill the hole, to avoid the risk of causing jointed rock to fail by hydraulic jacking action.

Pneumatically applied martar

This consists of mortar composed of a graded mixture of natural sand or crushed-rock sand up to 3/16 in. size, cement and water applied to rock, surfaces through a nozzle by pneumatic pressure (Fig. 11). Current specifications provide for mortar to be applied in layers such that the finished coating will cover steel mesh reinforcement to a depth of at least one in. or if reinforcement is not used will have a thickness appropriate to the local conditions, but not less than one in. Surfaces to be treated are cleared of loose or shattered rock and washed with a stream of water and high pressure air.

Pneumatically applied mortar was used initially in the Murrumbidgee-Eucumbene and Tooma-Tumut Tunnels and is now used extensively for the final treatment of a variety of potentially unstable conditions in unlined tunnels.

Details for this article:

Unstable rock and its treatment in underground works in the Snowy Mountains Scheme

X

Author: Moye, D. G (1965)

Article Title: Unstable rock and its treatment in underground works in the Snowy Mountains Scheme.

From: Proc Eighth Commonwealth Mining and Metallurgical Congress, Aust and N.Z. Vol.6 p. 429-441

Other Available Articles

Engineering geology for the Snowy Mountains Scheme

Moye, D.G. (1955)

Engineering geology for the Snowy Mountains Scheme.

J.I.E.Aust., Vol. 27 No.10 pp287–298

Rock Mechanics in the Investigation and Construction of T.1 Underground Power Station, Snowy Mountains, Australia

Moye, D.G. (1958)

Rock Mechanics in the Investigation and Construction of T.1 Underground Power Station, Snowy Mountains, Australia

In Engineering Geology Case Histories No.3 123–54 Geological Society of America 69 (12) p.1617

Existence of high horizontal rock stresses in rock masses.

Moye, D.G. (1962)

Existence of high horizontal rock stresses in rock masses.

Proc. Third Australia-New Zealand Conference on Soil Mechanics and Foundation Engineering. pp 19–22

Seismic Activity in the Snowy Mountains Region and its Relationship to Geological Structures

J. R. Cleary, H. A. Doyle, D. G. Moye (1964)

SEISMIC ACTIVITY IN THE SNOWY MOUNTAINS REGION AND ITS RELATIONSHIP TO GEOLOGICAL STRUCTURES

Journal of the Geological Society of Australia

Unstable rock and its treatment in the Snowy Mountains Scheme.

Moye, D.G. (1965)

Unstable rock and its treatment in the Snowy Mountains Scheme.

Proc. 8th Commonwealth Mining and Metallurgical Congress, Australia & New Zealand. Vol. 6, p. 423–441.

Diamond drilling for foundation exploration

Moye, D.G. (1967)

Diamond drilling for foundation exploration.

Paper 2150 presented at I.E.Aust. Site Investigation Symposium, September 1966. In Civil Engineering Transactions, with Discussion, April 1967.

Geology in Practice

Moye, D.G. (1970)

Geology in Practice. Presidential Address Section 3, Geology, ANZAAS Meeting.

Australian Journal of Science, 32 (12) June, p454–461.

* This paper was presented when Dan had been Director of Exploration of BHP for 3 years.

Field and Laboratory Tests in Rock Mechanics

Alexander, L. G (1960)

Field and Laboratory Tests in Rock Mechanics

Proceedings, 3rd Australian-New Zealand Conference on Soil Mechanics and Foundation Engineering, Sydney Australia, 1960, pp. 161–168.

Discussion at Technical Session No. 9—Rock Mechanics

Alexander, L. G. Moye, D. G. (1960)

Discussion at Technical Session No. 9—Rock Mechanics

Proceedings, 3rd Australian-New Zealand Conference on Soil Mechanics and Foundation Engineering, Sydney Australia, 1960, pp. 254–250