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

ROCK MATERIAL USED IN CANAL CONSTRUCTION. 39 made. The procedure should be about as follows: (1) An accurate topographic map of the region to be examined should be made; (2) the geology of the region should be carefully plotted on the topographic map and on sections, not only from surface indications, but from borings as well, the number of the borings depending on the requirements, the surface conditions, etc.; (3) the bore holes and any test pits that may be sunk should be plotted on the geologic map and all data as to elevation of the ground water in the different holes, flow of water from holes, depth at which water is encountered, character of material passed through, character of jointing and fissuring, slope and thickness of all the beds, hardness of material, etc., should be carefully recorded; (4) the fineness or coarseness of grain of the material and the proportion of each for all the geologic units should be carefully determined by experiment; (5) the per- meability and absorptivoness of the different kinds of material should be carefully tested. For very heavy structures it may be necessary to take care that none of the foundation piers or sills are set on a faulted or crushed zone in the rocks or on any locally soft area that would settle faster than would the other parts of the foundation. It is also necessary to be sure that the nature of the foundation rock is such that it will not be subject to slow swellings, deformations, or sliding move- ments toward contiguous excavations or valleys or toward caves or underground openings. It might bo well to mention here another rather remote con- tingency. In planning permanent structures of great cost, such, as great churches or other delicately adjusted buildings or monu- ments, effort should be made to avoid building them across any major fault plane showing evidence of considerable differential movement in recent geologic time. A differential movement of only a few inches along a fault plane might almost wreck a building, even though the motion were slow enough not to produce an earth- quake. FOUNDATIONS OF THE GATUN DAM AND LOCKS. POSITION OF GATUN LAKE. The northern rim of the Gatun Lake Basin is formed by the Quobrancha Hills, which are a few hundred feet above sea level and trend northeast-southwest in a well-defined ridge. The sea- ward or northern slope of these hills is relatively gentle. Their southern or Gatun Lake Basin slope is much steeper and is a rela- tively straight line, except where modified by stream erosion. 3 hey seem to be monoclinal and give strong physiographic evidence that their southern escarpment is the locus of a large fault. Un- fortunately, because of lack of outcrops, no definite stratigraphic