36. The want of uniformity of the covering of the slopes or top of an embankment causing unequal percolation of water.
37. By a retaining wall at the toe of a slope preventing the discharge of water that has percolated through the formation and the slope.
38. By an abnormal increase of the load upon the foundation of a wall caused by lateral thrust and tilting forward, or fracture of the footings or the concrete bed.
The first seven heads of “the chief causes of slips in embankments” might be classed as NATURAL, i.e., produced by nature, and, therefore, beyond the power of man to entirely prevent; the remainder as ARTIFICIAL, and, therefore, more or less to be prevented.
In the case of earthworks made to contain or exclude water for the purposes of docks, canals, waterworks, reclamation of land, irrigation or drainage, &c., may be added, without reference to their construction:—
1. Leakage along a discharge culvert, sluice, or tunnel in an embankment, or through the earthwork.
2. Erosion of the land slope or backing of a retaining wall by waves, or spray falling thereon and necessarily passing over the top of an embankment.
3. From abrasion and damage, caused by vessels or barges rubbing or colliding against a slope.
4. From erosion caused by wave action produced by the passage of boats or ships propelled by machinery; or by wind waves.
5. Variation in the water level, causing unequal pressure.