5. In treacherous earth do not locate a railway close to a road, except at a station, as if the line be placed above the road, a slip upon the railway may result in a slip upon the road; and should the line be below a road, the extra weight or vibration may cause the road to follow the railway and act, as it were, in unison with it.
6. In treacherous soil, where practicable, have stations nearly upon the surface of the natural ground.
7. Remember that upon one side of even the narrowest gorge or valley the earth may be much more solid than upon the other.
8. In exposed situations in a hilly country ascertain upon which side snow remains the longer, note which receives the greater amount of sunshine, and is the wetter and more covered with trees and vegetation. In a hill or mountain, the side to leeward of the prevailing winds almost invariably receives the greater rainfall.
9. In mountainous or hilly districts it may be advantageous to place a railway or road at a high level upon the sunny side of a hill or valley, as obviously it dries quicker; snow does not accumulate with the same facility, unless it happens to be exposed to the direction of the prevailing storms; the sunny side may be practically clear of snow, the shady almost impassable; but there is one drawback to the sunny side, namely—the more frequent occurrence of snow-slips, which may or may not be serious in extent. On the whole, experience seems to show that the wooded side of a valley is the best to select—sometimes one side is bare and the other wooded—unless there are special reasons to the contrary. In the winter season in certain districts abroad, for instance, in parts of Afghanistan and the adjacent mountain passes, the days are sometimes as hot as the summer of European countries, but at night the thermometer may fall below freezing-point, hence the value of tree-protection. It is obvious that in such climates the soil is peculiarly liable to disintegrating forces, and likely to slip, unless of a solid character, and that upon one side earthworks may be stable, and upon the other treacherous.
10. In many countries it may be advisable to adopt a valley in preference to a hill-side line, especially if the district is free from floods, or if the waters flowing down the side of the hills are considerable and suddenly appear, and there is a river and ample means available of controlling the hill-side torrents and conducting them to the river. If not, and the line must be on the mountain side, it may be advisable, in exposed places where water rapidly accumulates and becomes a torrent, to adopt the system of short tunnels round the hill spurs, in preference to deep cuttings, drainage, and slope protection works, and to place the railway or road at the highest level, so as to be free from the influence of floods.
11. Bear in mind that in high mountainous districts the drift deposit is generally torrential alluvium.
12. Avoid as much as possible high embanked approaches to a river bridge, especially when a deep river, which frequently changes its course, is in a flat country.
13. Consider if the simple erection of an embankment may in time cause its destruction, by the arrest or attempted diversion of the usual flow of the land waters.
14. In treacherous soils, on the side of a cliff facing the sea, determine whether it is preferable to erect timber trestles at its base instead of a solid embankment, or to place the line in a tunnel. The trestles can either be erected upon sills, resting on the ground and on short piles well secured from movement, or on piles driven some distance into the ground. The system may also be adopted if the ground be of a yielding character.