Cuttings.
9. In passing through the consecutive cuttings of a great railway, the traveller usually considers that those through rock must have been desperate undertakings, infinitely more expensive than those through clay. The cost of both, however, is nearly equal; for, not only does the perpendicular rock-cutting require infinitely less excavation than the wide yawning earth one of the same depth, but when once executed the former is not liable to the expensive slips which subsequently occasionally afflict the latter.
In determining whether the line should proceed by tunnelling or by cutting, the engineer’s rule usually is to prefer the latter for any depth less than sixty feet; after which it is generally cheaper to tunnel. If, however, earth be wanted for a neighbouring embankment, it becomes of course a matter of calculation whether it may not be cheaper to make a cutting instead of what abstractedly ought otherwise to have been a tunnel.
In the construction of the Tring cutting alone of the present London and North-Western Railway, there were excavated 1,297,763 cubic yards of chalk, of which about fifteen cubic feet weighed a ton.