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

ROCK MATERIAL USED IN CANAL CONSTRUCTION. 47 Mechanical analyses of samples of alluvial materials collected at the site of the Corozal Dam and from the sand bars in the bay beyond La Boca are given below. They were made at the request of the consulting engineers, Messrs. Noble, Stearns, and Freeman, in order to determine the permeability of these materials and then- availability for use in constructing the dams. Mechanical analyses of sand and mud from La Boca, Canal Zone. [Made at the laboratory of the United States Bureau of Soils.] Constituent. No. of sample. 2 3 4 5 6 7 Pct cent. Per cent. Per cent. Per cent. Per cent. Per cent. 0.8 1.8 0.8 7.5 5.8 2.1 Fine gravel, 2 to 1 mm 7.1 1.1 7.8 3.1 2.8 18.9 14.9 .8 39 9 .7 3.3 21.2 m sand 0.5 to 0.25 mm 13.3 .6 26 8 .9 2.5 19.7 Fine sand 0 25 to 0.1 mm 42.2 2. 7 11 0 6. 2 23.6 15.7 Very fine sand, 0.1 to 0.05 mm .8 2.6 .4 3.4 7.1 2.2 Siït^O.05 to 0.005 mm 1.4 43.1 4. 7 31.4 25.9 9.6 Clay, 0.005 to 0 mm 3.0 49.2 9.3 54.4 34.6 12.6 No. 2. Coarse sand, 18 inches below surface, sand bar, La Boca. No. 3. Alluvial clay from dredge, one-fourtli mile south of dock, La Boca. No. 4. Sand from river bank, near north end of Sosa-Corozal Dam site. No. 5. Mud from surface of mud flat opposite ship’s ways, La Boca near oil station. No. 6. Mud from dredge, one-half mile south of dock, La Boca. No. 7. Dry sample, hole No. 14, La Boca Dam, elevation—18.5, 20 feet below surface. FOUNDATION OF NEW ADMINISTRATION BUILDING, BALBOA. The now administration building at Balboa, a very heavy structure, was built on a little hill some 50 feet or so above the flat ground in front of it. One corner of the building is rather close to a steep slope, so it was thought that the weight of the structure might cause this slope to slide, and thus wreck the building. It was said that this corner of the building rested on bowlders and clay which might not support the added weight. The writer was detailed to investigate this matter. He found that the supposed bowlders and clay constituted only the weathered surface part of a jointed rhyolite mass. Weathering had progressed from the surface downward along the joint planes, thus leaving semirounded unweathered core masses, which looked somewhat like bowlders, between the weathered zones of the joints. With depth the weathering grew less and the rock became much more solid, so that the building was in no danger whatever. The following report, covering the matter, was then made by the author to the chairman and chief engineer of the Isthmian Canal Commission : The rock under the surface soil on which the new administration building at Bal- boa stands is the same rhyolite rock that forms Ancon Hill, and it has about the same degree of jointing. The fragments of this rock, between the joints, are strong and tough. Any slides that might occur in it would be due to steepness of slope and would consist in a mere sloughing off of loose material. There would be no deformation or flowagelike movement such as that which gave rise to some of the large slides in the cut near Culebra.