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

74 ENGINEERING PROBLEMS OF PANAMA CANAL. (b) The very warm, moist atmosphere. The tropical sun produces a temperature sufficiently high to greatly promote oxidation, especially in the presence of slight moisture. (c) Once oxidation of the pyrite has been started the heat thus generated tends to accelerate chemical action, and thus the heating increases in geometric progression. (<Z ) When the heat of pyrite oxidation reaches the comparatively low tempera- ture of oxidation of the hydrocarbons present in the lignitic ehale, they, too, become oxidized and still further add to the temperature. Finally the fixed-carbon content tends to become oxidized, at least in part, and gives maximum intensity to the action. (o) Some heat is also generated by the action of the free sulphuric acid on the calcium carbonate for the formation of gypsum. Other minor chemical actions added their quota to the total heat. As the temperature rises, all chemical activity is vastly stimulated and the heating increases to a maximum. After the most readily oxidizable substances are consumed the heat gradually dies down toward normal temperaturse, which may be reached in a few weeks or months. The intensity and duration of the heat depend largely upon the percentage of finely divided pyrite, volatile matter, and fixed carbon in the rocks. In order to alleviate the danger of premature explosion from loading dynamite in holes which have become hot, Col. Gaillard has inaugurated the practice of testing holes in the vicinity of the heating areas, by dropping into them a email iron pipe longer than the hole. This is withdrawn at the end of 10 minutes and quickly passed through the hand. In this way not only is heating detected but the location of the heated zone with respect to the depth of the hole is also made known; for the heating is at times only local and may be at, or well above the bottom of the hole. Certain geologic considerations have been suggested by a study of this heating phe- nomenon, the chief of which are: (a) Chemieo-thermal springs. Whenever jointing, fissuring, or change of ground- water level gives free access of oxygen-bearing surface waters to beds that contain the necessary finely divided pyrite and carbonaceous matter, heating of such beds is likely to result. Ground water flowing over such heated beds and coming to the surface in the general vicinity of them would constitute thermal, or hot, springs. (&) The very fine pyrite sparingly disseminated through the carbonaceous shales herein described seems to have resulted from the action of sulphur, segregated from decaying animal and vegetable life, on the ferromagnesian silicate fragments that are abundant in these sediments. EARTHQUAKES AS AN ELEMENT OF DANGER TO THE CANAL. The earthquake belts of Central and South America are approxi- mately coextensive with the regions of fairly high mountains. Within the Canal Zone only two peaks roach elevations approximating 1,000 feet. There are no peaks within 20 miles of the canal that are higher than 2,000 feet, and not within 100 miles could one find mountains over 4,000 feet in elevation. The canal is therefore far removed from the great mountain masses—those that, by their settling and adjust- ment, mighü cause stresses that would culminate in rock ruptures sufficiently great to give destructive earth vibrations. Furthermore, the relative weakness of most of the rocks within the Canal Zone region prohibits the accumulation of stresses sufficiently great to cause violent rock rupture with concomitant earth jars of destructive proportions. Theoretically, then, one would expect the Canal Zone to be outside the Central American earthquake belt. Such a con-