The Malheur River siphon, a feature of the Owhyee Project of the Bureau of Reclamation, U. S. Department of the Interior, comprises 21,976 feet of 80-inch welded steel pipe and 1,020 feet of 78-inch, precast, reinforced concrete pipe. The siphon was completed in 1935, but within three years the supports of the steel pipe showed severe distress in the section lying north of the Malheur River and representing approximately 10 per cent of the total length of the siphon. Field and laboratory studies show that the displacements are due to expansion of bentonitic shales and claystones of the Idaho formation, which underlies the siphon in this section and into which water penetrated after the siphon was put into operation. The nature of the distress at the supports, the investigations into causes of the foundation displacements, and preventive measures designed to avoid future displacements are discussed.

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