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

48 ENGINEERING PROBLEMS OF PANAMA CANAL. Toward the surface the jointing in this rock becomes more pronounced, so that the m ividual pieces between the joints are separated by partings of earthy material. 1 hey thus have some resemblance to a mass of bowlders mixed with clay. In reality however, this is not a bowlder-clay formation. From the surface downward the rock becomes much less jointed and much more solid. In a cut of any.depth or in the side of a mountain, this rock, under its present conditions of jointing, would maintain itself at a slope of 2 on 1, except, of course the top covering of earth and broken rock, which would stand only at a much flatter Cross sections show that the maximum slope from the basement floor to the foot of the slope at the railroad is about 7 on 11. This then is well within the limit of 8afetv so far as any slides are concerned. Now, what effect will tho weight of the building, 97 tons per column, have on this mass of rock? 1 f the pier foundations have been put down below the earth and loose rock to the relatively solid, though much jointed, rock below, then there will be no danger of the building causing any slide movement here, for the following reasons: 1. his rock will not deform or flow under any pressure that thia building can pos- si ) y exert on it, in spite of the fact that in large masses it has not much tensile strength because of jointing. No amount of weight that need be considered would cause a sinking m one part of this material, with a corresponding bulging in another part 2. At any slope less steep than 2 on 1 this rock (apart from its soil and loose rock covering near the surface) would stand without any danger whatever from slides The steepest slope from the basement floor to the railway level below is only about 7 on 11, therefore, the margin of safety is ample. 3. /i h^e Trity vS able t0 Wedge °ff maSSeS of rock from any 8teeP sloPe, then any weight added to such rock masses will increase their tendency to slide. Where how- ever, the slope is flat enough for any rock mass to be at repose on a solid foundation, then weight (normal to the horizontal) added to it will decrease its tendency to slide. I his is merely a special application of the principles illustrated by the parallelogram of forces. The weight of the building, therefore, will in this case tendency of this slope to slide because the slope is already well within the angle of repose. 6 4. The weight of the building will, of course, increase the tendency of this rock to e onn and bulge up at the base, but, as already explained, it is strong enough to resist any compression»! pressure that could possibly be brought to bear on it bv any building. J In conclusion, the building is quite safe from the danger of sliding. Of course this memorandum does not consider the question of the possibility of uneven settling of any part of the building, except to state that if the foundation piers have been put down to the relatively solid (though jointed) rock beneath the soil and loose-rock covering there will be no noticeable settling. SLIDES. Culebra Cut is a vast ditch (Pls. XII and XIII) that passes through many varieties of rock in tho 9 miles of its length. Some of those aro weak and unstable, and where the slopes of tho cut were steep and 100 to 300 feet high tho weaker rocks locally crushed down to Hatter slopes. Tho flatness depended on the material involved, but whatever tho material, whenever tho slope got flat enough the sliding stopped At no time did the engineering staff constructing tho canal believe that the slides were a menace to the ultimate completion and success!ul operation of tho canal, in spite of the fact that at times