Some Engineering Problems Of The Panama Canal In Their Relation To Geology And Topography

SLIDES. 63 fault zones and to prevent excessive water from seeping into them where practicable. There might be cases ill which, it would pay to reinforce these weak zones with steel and concrete to prevent initial motion, but no such case came to notice in the work on the Canal Zone. SLIDES DUE TO EROSION. The soft and easily weathered rocks of Culebra Cut are much trenched and washed by heavy rains where they slope steeply and are unprotected by vegetation. The rapid weathering of those rocks is due to the peculiar effects of leaching and oxidation, as explained on page 52. Each, heavy rain removes the disintegrated soil from the slopes of the excavation., fresh surfaces being exposed for further weathering action. It is estimated that the sediment washed into Culebra Cut in this way during the first few years would cover the bottom of the cut to a depth of 2 inches or more each year. This would amount to something over 65,000 cubic yards, which, at 25 cents per cubic yard for dredging, would add over $16,250 per year to maintenance charges. REMEDIES. Fortunately, the luxurious growth of vegetation that characterizes the region provides a remedy for erosion, for the slopes will suffer rela- tively little when carpeted with grass and shrubs. It was therefore proposed to promote the growth of vegetation on the permanent slopes of the canal where necessary. Such vegetation will have no effect on the large slides, but will minimize the wash from heavy tropical rains. In order to alleviate the weathering and washing effects in certain steep parts of the cut, a thin veneer of cement was spread on the slope from a spraying cement gun. This plan was not a success, however, because within a few months the thin veneer of cement began to crack and peel off, owing the the following causes: (1) Oxygenated surface waters seeped through the cement and through the rock and oxidized the rock along its contact with the cement, thus causing the adhesive zone, or contact, to become loose and crumbly; (2) leaching by ground water loosened the rock and tended to destroy the adhesion of the cement veneer; (3) irregular swelling of the rock due to oxidation, adjustment of pressures, etc., cracked the cement veneer and further weakened it; (4) blasting vibrations tended also to crack and scale off the veneer. SLIDES DUE TO WASH OF STEAMERS. Another erosion problem arising in connection with soft rocks results from the wash of steamers passing through the canal. Any protective covering used to obviate this will have to be designed with some understanding of the geologic conditions of the rocks that it is to protect. For instance, the rocks will swell somewhat