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|Title:||Verification of empirical method for determining riverbank stability, 1962 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. 12-13.|
Summary: This report is the tenth 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 failure. Data obtained in fiscal year 1962 are analyzed, and stability predictions are made for 12 new areas. Failures during 1962 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 1962, 42 bank failures (9 flow failures and 33 shear failures) were reported along the Mississippi River near 43 boring locations at 21 sites for which stability predictions had been made. Seven flow failures occurred near 7 boring locations predicted to be susceptible to flow failure (one of the failures occurred between two boring locations and two of the failures occurred near one boring location). The other two flow failures occurred near two boring locations predicted to be stable with regard to flow failure. Thirteen shear failures occurred near 8 boring locations predicted to be unstable with regard to flow failure (in 5 cases, 2 failures occurred near the same boring location). Sixteen shear failures occurred near 16 boring locations predicted to be stable with regard to flow failure, and two shear failure areas, 3800 and 6000 ft wide, respectively, encompassed 8 boring locations, 4 of which were predicted to be stable and 4 to be unstable with regard to flow failure. The two remaining shear failures occurred near two boring locations where no prediction had been made because the full depth of zone A sand had not been determined. Since 1954, when riverbank stability predictions were initiated, data from 807 boring locations at 86 revetment sites on the Mississippi River in the Memphis and Vicksburg Districts have been studied. Flow failures have occurred at 8 boring locations in the Memphis District and at 35 boring locations in the Vicksburg District. Of these 43 locations where flow failures have occurred, 33 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 occurred near 5 locations predicted to be stable, but in four of these cases, the failure occurred more than 750 ft from the boring and the boring data probably were not representative of the soil conditions at the failure locations. The location of the single flow failure at a site predicted to be stable had, through an oversight, previously been predicted to be unstable. The revision of this prediction is discussed in Appendix A. The modified criteria have proved reliable, with the one exception noted above, 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.
|Rights:||Approved for public release; distribution is unlimited.|
|Appears in Collections:||Potamology Investigations Report|
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|Potamology-Investigations-Report-No.-12-13.pdf||10.06 MB||Adobe PDF|