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|Title:||Verification of empirical method for determining riverbank stability, 1967 data|
|Authors:||United States. Mississippi River Commission.|
Calhoun, Charles C., 1946-
Flanagan, C. P.
|Publisher:||U.S. Army Engineer Waterways Experiment Station.|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Potamology investigations report ; no. 12-20.|
Summary: This report is the fifteenth of a series in which new data obtained from borings made for revetment construction are analyzed to determine the applicability of an empirical method for predicting riverbank stability with regard to flow (liquefaction) failure. Boring data obtained in 1967 are analyzed, and stability predictions are made for 12 new areas. Failures during 1967 at sites previously analyzed also are discussed. Based on analyses made in 1958 of previous performance data, the classification criteria for zone A and zone B sands were modified in 1959. The failures at sites previously studied, new site predictions, and current year performance are analyzed using the modified criteria. During 1967, 19 bank failures along the Lower Mississippi River at 12 revetment sites occurred within 500 ft of boring locations for which stability predictions with regard to flow failures had been made. Four flow failures occurred near three boring locations predicted to be unstable with regard to flow failure. Two flow failures occurred near two boring locations predicted to be stable with regard to flow failure. Two shear failures occurred near one boring location predicted to be unstable with regard to flow failure; 11 shear failures occurred near 8 boring locations predicted to be stable with regard to flow failure. Two flow failures, three shear failures, and two failures considered neither shear nor flow failures were reported in areas where no borings were located within 500 ft. Two shear failures occurred near two boring locations for which no prediction was possible because the depth of the zone A sand had not been determined. Since 1954 (when riverbank stability predictions were initiated) and through 1966, 1271 boring locations at 102 revetment sites on the Mississippi River in the Memphis and Vicksburg Districts have been studied using performance data furnished by the Districts. Flow failures reported through 1967 have occurred within 500 ft of 14 boring locations in the Memphis District and 42 boring locations in the Vicksburg District; of these, 43 had been predicted to be unstable according to the modified criteria, 6 occurred at boring locations for which no prediction could be made because the depth of zone A sand had not been determined, and 7 occurred at boring locations predicted to be stable. The modified criteria have proved reliable, with only seven exceptions, in predicting flow failure. However, many locations predicted to be unstable have not experienced flow failure, and it is possible that either the density of zone A sand may be such that flow failure will not occur or the severity of river attack has not been sufficient to initiate flow failure.
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