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

36 ENGINEERING PROBLEMS OF PANAMA CANAL. SOURCES OF MATERIAL. ANCON HILL. Nature supplied the Canal Zone with some excellent sources from which to obtain rock for concrete work. The best of these is Ancon Hill, which furnished the crushed rock for the Miraflores and Pedro Miguel Locks. It consists of a tabular mass of rhyolite nearly half a mile long and some hundreds of feet thick (fig. 1, and Pl. IX). The rock is rather hard, so that it resisted erosion or wearing down by the streams that cut away tho softer rocks around it. Because of this hardness Ancon Hill stands over 600 feet above tho low lands that nearly surround it. The rock in this hill is much jointed and broken and is easily blasted; relatively little further crushing by machinery is necessary to prepare it for use in concrete or road construction. In this instance tho faulting or breaking of earth blocks in past ages has directly aided construction by cheapening tho cost of crushed rock for the concrete work of the Pacific Locks. Tho same period of faulting, however, has boon a hindrance in the excavation of Culebra Cut, for it locally weakened the rocks there and gave them a greatly increased tendency to slide. A detailed description of this rock is given on page 28. PORTO BELLO QUARRY. Tho Porto Bello quarry and crushing plant, located in Porto Bello Harbor, about 20 miles northeast of Colon, furnished the crushed rock for tho Gatun Locks. This quarry is on a large area of andesitic rock which had few shrinkage joints and was too large and solid to be much broken by faulting. Tho joints arc fairly well developed, but far apart, so that tho rock breaks into coarse pieces when blasted. Each blast loosened a great deal of rock, but a large per- centage of it broke along tho joint planes into big blocks weighing several tons each. Many of those had to be broken by adobe blasting or ‘1 bulldozing ” before they could bo loaded and crushed, thus adding much to tho blasting and loading costs. Here nature rendered little assistance in crushing tho rock and rendering it moro cheaply available for lock building, as it had done in the case of the Ancon Hill rock. Had the Porto Bello rock been well jointed, the United States would have profited to tho extent of many thousands or perhaps millions of dollars. This quarry, however, did good service in furnishing large bowlders, which were used to face the west breakwater at Colon Harbor. UNSATISFACTORY HARD-ROCK DEPOSITS. In Juno, 1913, the Isthmian Canal Commission wished to find a hard-rock quarry that should bo as convenient as possible to Colon and to the new line of tho Panama Railroad. Most of tho rock areas