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

SLIDES. 65 In length the sliding ground was about 1,700 feet and in width over 1,000 feet. Its surface area was about 29 acres and its bedrock area 23| acres. In volume the sliding .mass contained 3,400,000 cubic yards, or an approximate weight of 4,600,000 tons. It slid on a remarkably flat slope plane of about 1 on 9. Because of the large amount of ground water contained in the shear planes along which sliding took place, and because the rate of move- ment seemed to be controlled somewhat by the precipitation, it was decided to try to stop the slide by means of drainage. A continua- tion of the slide would have cost the city over a quarter of a million dollars, so it was decided to drive a main tunnel with several branch tunnels, so that the planes of sliding could be drained. In all, 2,507 feet of tunnel was driven, at a cost of $14,161, or $5.65 per foot. This main tunnel and the branch tunnels wore connected with the shafts that had been sunk and effectively drained the region. The result was that the sliding stopped, and the ground has scarcely moved since that time. SLIDE ON SLOPES OF DES MOINES RIVER, IOWA. Another, example of drainage that effectively stopped a large slide in clay is on© on the slopes of the Des Moines River, Iowa, described by Merrick.“ In this instance some unusually heavy rains caused a largo area of glacial clay, overlying shales, and coal beds to creep down from the slope toward the bed of the Des Moines River. The movement involved the end pier of a steel bridge of the Chicago & North Western Railway. The remedy applied was to construct three main drains with laterals. These were 5 feet wide on the bottom and 4 to 10 feet deep. They were filled with broken rock, on top of which was placed a layer of willow brush, and the whole covered with the material excavated. During the construction of the drains the ground moved toward the railroad about 2 feet, the plane of slipping being about 8 feet below the surface. The report is that the drainage effectively checked the slide. The discussion explaining this slide speaks of several instances whore landslides on European railroads had boon either obviated or greatly benefited by drainage. SLIDE IN BRITISH COLUMBIA. In an irrigation district in British Columbia the Canadian Pacific Railway cut through some hard clay that resembled soft soapstone. The climate was dry, and the clay stood up well in the railway cuts and gave no sign of sliding. Some years later irrigation was intro- a Merrick, A. W., The clay slide at the Boone Viaduct, Boone, Iowa: Jour. West. Soc. Eng., vol. 11, June, 1906, pp. 332-350. 97348°—Bull. 86—15---5