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Show PROBLEMS OF IMPERIAL VALLEY AND VICINITY. 17 Prior to placing the cofferdam or any of the rock fill, it is proposed to drive a row of sheet steel piling as deeply as practicable across the upstream toe of the dam, to be later connected and sealed firmly to the toe of the concrete pavement on the water face of the dam. The placing of the rock fill should be completed a year or more before beginning the construction of the concrete pavement. This time would be occupied in sloping up the water face preparatory to placing the pavement. The construction of the pavement would be so planned that the sealing of the pavement to the rock of the abutments would be the last' finishing touch of the dam so as to give the mass the maximum time for settlement before making this junction. The control of the river during construction and immediately after would form a pond of varying magnitude just above the dam filled with the muddy waters of the Colorado and these would deposit their sediment on the river bed and lower toe of the dam in such manner as to form something of a seal and tend to prevent water entering the foundation at any considerable velocity. This plan of construction was discussed with Secretary Lane in obtaining authority for the extensive investigations of the Colorado River in 1914. It had previously, and has since been discussed by the author with many engineers in order to bring out, if possible, any weak points connecte.d with the plan, and some of the details of this plan have been modified as the result of such discussions. They are of course subject to further modification by further thought, and especially by the experience obtained during construction. The plans were worked out in more detail and estimates made, on the basis of such a structure as compared with a dam built of concrete under the direction of the chief engineer of the Reclamation Service by Mr. John L. Savage, designing engineer, United States Reclamation Service, and his assistants. > , These investigations seemed to indicate that no material saving could be made by adopting such a plan as compared with a concrete structure carried to bedrock providing the latter proved feasible at all. A depth of 135 feet to bedrock while presenting serious difficulties in foundation work is believed to be entirely feasible if proper preparations are made and proper plans are followed. It is not believed that in view oi the cost it is desirable or necessary to divert the entire flood flow of the Colorado River, which may at times reach 200,000 cubic feet per second. The plan is to design a thin arch of such radius and dimensions as to be safe with its base upon the foundation rock and its summit about 40 feet above the low-water level of the river. Within this limit the canyon is quite narrow, being at all points less than 350 feet in width, and therefore a structure of short radius and light section would be safe. After the construction of a cofferdam and of diversion tunnels of sufficient capacity to carry the ordinary flow and moderate floods of the river, excavation would be undertaken of only sufficient width' to secure foundation for this thin arch, and this would be completed and the arch poured during the nine joaonths or so in which it would be possible to unwater the • foundation by means of the tunnels and cofferdam. This thin arch could serve as a subsequent cofferdam and aiso foi* the heel of the masonry structure to be built. If this wer«> overr topped by floods they would fill the pit with water only, wnich could |
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Original book: [State of Arizona, complainant v. State of California, Palo Verde Irrigation District, Coachella Valley County Water District, Metropolitan Water District of Southern California, City of Los Angeles, California, City of San Diego, California, and County of San Diego, California, defendants, United States of America, State of Nevada, State of New Mexico, State of Utah, interveners] : |