Perspective View of St. Gothard Spiral Tunnels, in the Alps.
That true economy, which finally secures in a completed work the best results from the investment of capital, in first cost and continued maintenance, is an essential element in the consideration of any really great engineering feat.
The difficulties involved in the construction of a tunnel, after the line and dimensions have been determined, depend generally upon the nature of the material found as the work advances. Solid rock presents really the fewest difficulties, but it is seldom that tunnels of considerable length occur without meeting material which requires special provision for successful treatment. In some cases great portions of the rock, where the roof of the tunnel is to be, press downward with enormous weight, being detached from the adjacent mass by the occurrence of natural seams.
Perspective View of St. Gothard Spiral Tunnels, in the Alps.
That true economy, which finally secures in a completed work the best results from the investment of capital, in first cost and continued maintenance, is an essential element in the consideration of any really great engineering feat.
The difficulties involved in the construction of a tunnel, after the line and dimensions have been determined, depend generally upon the nature of the material found as the work advances. Solid rock presents really the fewest difficulties, but it is seldom that tunnels of considerable length occur without meeting material which requires special provision for successful treatment. In some cases great portions of the rock, where the roof of the tunnel is to be, press downward with enormous weight, being detached from the adjacent mass by the occurrence of natural seams.
At other places soft material may be encountered, and the passage then is attended with great difficulty. Temporary supports, generally of timber, and of great strength, have often to be used at every foot of progress to prevent the material from forcing its way into the excavation already made.