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

SLIDES. 49 they were somewhat troublesome. They Have made necessary the excavation of about 30,000,000 cubic yards more than was included in the first estimates for Culebra Cut, but they have not in the past and will not in the future endanger the ultimate success of the canal. Because of their importance as a factor in canal construction they are discussed in considerable detail. ANALYSIS OF CONDITIONS LEADING TO SLIDES. The following information, with accompanying illustrations, has largely been given by the author in a paper® read before the Twelfth International Congress at Toronto, Canada. Any excavation in tho earth’s crust sets up stresses in the con- tiguous rocks, because of the unbalanced pressures created by the substitution of atmospheric pressure for the greater pressure of the material excavated. These stresses arc divisible into two distinct groups, as follows : (a) Crushing or direct gravity stresses, which have a maximum effect near tho too of the steep slope of the excavation; and (6) tensional or flowage stresses, also duo, though less directly, Figure 6.—Diagrams showing resultants of deformative pressures. to gravity, which exert a horizontal strain toward the excavation and give maximum deformation near the surface (see fig. 6). Now, what might be called tho resultant (c, fig. 6) of these two groups of stresses may for convenience bo called tho straining or slide-producing factor. Two major classes of excavation set up strains in their slopes, or in the continguous rocks, which may result in slides. They are those duo to processes of nature, as stream erosion, solution, and fault escarpments, and those duo to works of man, chiefly open cuts, under- ground openings, and submarine excavations. Tho extent to which any excavation will cause sliding or deformation of the contiguous rock material depends on the following factors: 1. Crushing and tensile strength of largo masses of the material involved. These factors vary according to (a) the strength of the small component masses, (6) the character of the jointing, (c) the character of the bedding, and (<Z) the fault conditions. 2. Physical and chemical character of the rock units. _____________ « MacDonald, D. F., Excavation deformations: Trans. 12th Int. Geol. Cong., 1913, Ottawa, Canada. 97348°—Bull. 86—15---4