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UNSTABLE ROCK AND ITS TREATMENT SNOWY MOUNTAINS SCHEME

Fig. 11—Mortar being applied pneumatically over light wire mesh.

Reinforcement of pneumatically applied mortar.

Where mortar is used over wide areas of weak rock it is reinforced with mesh. The type of reinforcement used has varied slightly in different tunnels. The general aim is to use mesh which is flexible enough to be moulded to follow closely the rock contours and with openings large enough to minimize wastage of mortar rebounding from the wires.

In Eucumbene-Snowy and Snowy-Geehi tunnels light mesh in the form of 17 gauge wire netting with 1 ½ in. openings and “heavy” mesh in the form of 8 or 10 gauge chain-wire netting with 2-in. openings have been used. Recent practice is to use heavy mesh almost exclusively. The mesh is fastened either directly to the rock or to the initial layer of mortar with surface anchors so that it fits firmly and snugly to the surface.

Surface anchors penetrate the rock to a depth of less than one ft and include nails, staples and embedded wire ties. Depending on the character of the rock treated, surface anchors are supplemented by rock anchors consisting of 5/3 in. diameter bolts 1 to 3 ft long, embedded in the rock, and by standard grouted rock bolts usually 8 ft long (Fig. 12).

Figure 12

Fig. 12.—Support and final treatment of a large area of weak rock of varying quality.

Application of pneumatically applied mortar over wet rock.

The mortar after setting adheres strongly to wet rock. Problems arise where ground water flows freely out of the rock and down the rock face washing away the mortar before it can set. Under these conditions it is necessary first to control the flow by locating its source and concentrating the flow in short tubes or pipes attached to the rock by quick-setting mortar or set in holes specially drilled to intercept the flows.

Determination of final treatment of unlined tunnels

Blasting and excavation of broken rock causes the rock surfaces in the walls and roof to become coated with a layer of rock dust which obscures many details of the rock including details of joints and seams. Under these conditions it is very difficult to assess reliably the treatment the rock requires. Commencing with the Tooma-Tumut Tunnel it has become the practice to wash thoroughly the rock in unlined tunnels before detailed geological mapping and inspection for determination of final treatment.

Details for this article:

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

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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