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|Title:||Verification of empirical method for determining riverbank stability, 1963 data|
|Authors:||United States. Mississippi River Commission.|
Strohm, William E.
Caldwell, W. K.
|Publisher:||U.S. Army Engineer Waterways Experiment Station.|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||Potamology investigations report ; no. 12-14.|
Summary: This report is the eleventh 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 fiscal year 1963 are analyzed, and stability predictions are made for 23 new areas. Failures during 1963 at sites previously analyzed also are discussed. Based on analyses made in 1958 of previous performance data, the classification criteria for zone A sands and zone B sands were modified. The failures at sites previously studied, new site predictions, and current year performance are analyzed using the modified criteria. During 1963, 15 bank failures along the Lower Mississippi River at 13 revetment sites occurred within 500 ft of boring locations for which stability predictions had been made. Five flow failures occurred near four boring locations predicted to be unstable with regard to flow failure (two of the failures occurred near the same boring location). Three shear failures occurred near four boring locations predicted to be unstable with regard to flow failure (one of the failures occurred between two of the boring locations); seven shear failures occurred near six boring locations predicted to be stable with regard to flow failure (two of the failures occurred near the same boring location). Since 1954, when riverbank stability predictions were initiated, data from 874 boring locations at 90 revetment sites on the Mississippi River in the Memphis and Vicksburg Districts have been studied. Flow failures have occurred within 500 ft of 10 boring locations in the Memphis District and within 500 ft of 26 boring locations in the Vicksburg District. Of these 36 locations where flow failures have occurred, 29 had been predicted to be unstable according to the modified criteria. Six flow failures have occurred at boring locations for which no prediction could be made because of insufficient data on the depth of zone A sand. Flow failures have occurred at only one boring location predicted to be stable. The modified criteria have proved reliable, with one exception, 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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