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|Title:||Verification of empirical method for determining riverbank stability, 1964 data|
|Authors:||United States. Mississippi River Commission.|
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. 12-17.|
Summary: This report is the twelfth 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 1964 are analyzed, and stability predictions are made for seven new areas. Failures during 1964 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 1964, seven bank failures along the Lower Mississippi River at seven revetment sites occurred within 500 ft of boring locations for which stability predictions had been made. Three flow failures occurred near three boring locations predicted to be unstable with regard to flow failure. One shear failure occurred near one boring location predicted to be unstable with regard to flow failure; two shear failures occurred near two boring locations predicted to be stable with regard to flow failure. One shear failure occurred near one boring location for which no prediction had been made because of insufficient data on the depth of zone A sand. Since 1954 when riverbank stability predictions were initiated, data from 1072 boring locations at 98 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 27 boring locations in the Vicksburg District. Of these 37 locations where flow failures have occurred, 30 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. It was postulated that there might be a relation between duration and rate of decrease of high river stages with the number of flow failures that occurred at particular sites. Therefore, a study was made of the variations in high river stages and frequency of flow failures at Marshall Browns Point, La. and Miss., and Reid Bedford, La., for the years 1955 through 1960. Although the specific dates on which the flow failures occurred are not known, it was considered worthwhile to investigate whether the type of river stage variation for a particular high-water period could be related in a general way to the number of flow failures that occurred in that year. However, the study produced no conclusive results.
|Rights:||Approved for public release; distribution is unlimited.|
|Appears in Collections:||Potamology Investigations Report|
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