31. By blasting laminated rock dipping at a considerable angle towards a cutting in the side of a hill; the result sometimes being that a cavity is made depriving the upper beds of support and causing them to overhang, and a mass extending to the top surface of the hill to slip along the unsupported stratum.
The first ten “heads of the chief causes of slips in cuttings” might be classed as NATURAL, _i.e._ produced or effected by nature and, therefore, beyond the power of man to entirely prevent; the remaining heads as ARTIFICIAL, and therefore, in some degree to be prevented, unless obviously the result of the unavoidable exigencies of construction.
HEADS OF THE CHIEF CAUSES OF SLIPS AND SUBSIDENCES IN EMBANKMENTS.
1. The percolation of surface water into the toe and under an embankment upon the original surface of the ground, and also downwards through the formation.
2. Unequal percolation of water through the formation or the slopes.
3. The surface of the ground upon which an embankment is tipped inclining in one direction, or falling on each side from the centre.
4. The effects of rain, frost, snow, and the atmosphere on the deposited earth.
5. By a crumbling of the lower portion of a slope.
6. By a hurricane or extreme wind force, especially when accompanied by rain and the location is that of a narrow, steep valley, blowing away or dissipating the top and the surface of an uncovered embankment.
7. By a slope becoming honey-combed by rodents, and in some few countries by an embankment in a river or the sea being bored and disturbed by crustacea.
8. Insufficient slope for permanent stability at the time of or after deposition.
9. The want of adhesion between the surface of the ground upon which an embankment is tipped and the deposited material.
10. By the accumulation at the foot of an embankment of boulders or lumps having no cohesion, and no adhesion to the surface of the ground upon which they are deposited.
11. The weight being too great upon the ground upon which an embankment rests.
13. An accumulation of water, caused by the unevenness of the surface of an embankment, or by the ground not being prepared so as to prevent a lodgment of water.
14. By obstructing the established discharge of land-water or by attempting to divert the natural flow of underground waters.