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

Co to ENGINEERING PROBLEMS OF PANAMA CANAL. STRUCTURAL GEOLOGY IN RELATION TO ENGI- NEERING. Under the subject of structural geology the folding, faulting, shearing, jointing, and some of the other changes that the rocks have undergone since they were formed is briefly discussed. All of these changes have some bearing on the engineering problems of the canal, but it is necessary to discuss many of them in connection with other topics treated under different headings, so only the main features and relations are here summarized. FOLDING. The bedded rocks were, of course, deposited in a relatively hori- zontal position. Since their deposition they have been folded and warped to various degrees. From Gatim to the Caribbean the rocks of the Gatun formation dip gently northward and pass under the ocean at a slight inclina- tion. The upper part of this formation is relatively fine grained and the lower part averages coarser. From such, an arrangement of material, ono would expect artesian conditions at Colon, especially now that Gatun Lake is almost 82 foot higher than that city. How- ever, the rocks may bo too fine grained and dense to permit flow of water through oven their coarser lower beds. It is said that a well, some 600 feet or more deep, sunk by the Panama Government in Colon, furnishes considerable water, but develops no pressure at the surface. A noticeable downfold or syncline in the bedded rocks crosses Culebra Cut in the vicinity of Gold and Contractors Hills. The axis of this trough trends almost northeast and southwest. Its greatest engineering significance is that it causes the stronger limy sandstones of the upper part of the Culebra formation to be bowed downward far below the bottom of the canal, so that they do not strengthen the slopes in the deepest part of Culebra Cut. The slopes where tho worst slides have developed are composed only of the rocks of the Cucuracha formation, already described. The stronger limy beds lie below this formation, and outcrop as strengthening factors in the slopes of Culebra Cut on both sides of this downwarpod trough or syncline, which is nearly 2 miles across. There are many other minor flexures and small folds which have tilted tho beds at angles up to 45° or moro, but in general the bedded rocks arc relatively Hat and horizontal. FAULTING AND SHEARING. From the various oscillations of the land above and below sea level, as already noted, one would expect that the rocks constituting the isthmian land mass would have become broken and dislocated.