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

60 ENGINEERING PROBLEMS OF PANAMA CANAL. The slopes stood at a much steeper angle before being disturbed than after they had been weakened by deformation. NORMAL OR GRAVITY SLIDES. The normal or gravity type of slide was due to several factors. Locally along Culebra Cut porous material lies on top of relatively impervious clay, shale, or igneous rock. Rain and ground water saturated this porous mass, but were impeded in their downward course by the relatively impervious rock. Thus a muddy, slippery zone was formed along the piano of contact between tho pervious upper and impervious lower materials. When this piano sloped toward the excavation, or where there was thrust or head of pressure toward the excavation from higher ground in the rear, a slide of the normal or gravity typo often resulted (Pl. XXI and fig. 3). Whore bedding and joint planes dip toward the excavation and intersect the slopes they greatly assisted gravity to wedge off rock masses. This typo of slide had certain distinguishing features. The rocks were not deformed or weakened below the plane of actual sliding. Tho sliding material moved off a relatively solid base and this base was not pulled down or squeezed out by the frictional drag. Hence these slides were not as destructive as the break-deformation slides wore, for they did not weaken the slopes below the plane of actual sliding. No saving of excavation could ordinarily be accomplished by removing material from the upper parts of such slides. It was better and cheaper to let them run their course and remove them from the bottom of the cut. Drainage was almost the only remedial factor that could be applied to them. The Cucuracha slide (Pls. XXIII and XXIV), active at intervals since tho French company began operations, was the worst slide of this type. Slides of the normal or gravity type have been relatively numerous, but, with the exception of Cucuracha slide, loss important and much smaller than those of the structural-break type. The following list of these slides shows approximately how much material each involved: Extent and location of past slides in Culebra Cut. Location. Date when slide first developed. Quantity of material excavated. Area of slide. East side: May, 1912 Cubic yards. 68,000 583,000 A cres. 1.2 Lus (J a scad as. February, 1908 11.5 Wh ifphniiQø. October, 1908 609,000 0.0 Powder house 613,000 5.8 20.0 I? m nirn. May, 1912 1,213,700 July,1905 5,359,500 50.0 f'liniir'.iphsi villflPP, - . September, 1911 231,000 4.0 Paraiso March, 1907 385,000 5.7 VoHro M11 January, 1913 13, SOO .2 West side: Whil-nhnlKA Vîirtl June, 1912 75,000 67,000 1.0 W IlltUIlUUov jell'* September, 1910 .9 9,218, (XX) 106.3