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|Title:||Verification of empirical method for determining riverbank stability : report 12-23, 1972 and 1973 data|
|Authors:||Soils and Pavements Laboratory (U.S.)|
United States. Mississippi River Commission.
Gann, Albert R.
|Publisher:||Geotechnical Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
Abstract: This report is the eighteenth 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 1972 and 1973 are analyzed, and stability predictions are made for 31 new areas. Failures that occurred during 1972 and 1973 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 1972, 24 bank failures (11 flow type and 13 shear type) occurred along the Lower Mississippi River at 8 revetment sites within 500 ft of boring locations for which stability predictions with regard to flow failure had been made. All 11 flow failures occurred near 10 boring locations predicted to be unstable with regard to flow failure. Three shear failures occurred near 3 boring locations predicted to be stable, 6 shear failures occurred near 5 boring locations predicted to be unstable, and 4 shear failures occurred near 3 boring locations for which no prediction was possible because the thickness of zone A sand had not been determined. In addition, 4 failures occurred that could not be classified as to type failure; 3 of these were judged to be the direct result of severe scour. Four flow failures (at 3 revetment sites) and 4 shear failures (at 3 revetment sites) were reported in areas where no borings were located within 500 ft. In 1973, 27 bank failures (16 flow type and 11 shear type) occurred at 15 revetment sites within 500 ft of boring locations for which stability predictions with regard to flow failure had been made. There were 13 flow failures near 11 boring locations predicted to be unstable, 3 flow failures near 3 boring locations predicted to be stable, 7 shear failures near 6 boring locations predicted to be stable, 3 shear failures near 3 boring locations predicted to be unstable, and 1 shear failure near a boring location for which no prediction was possible because boring depth was not sufficient and zone A sand had not been penetrated. In addition, 23 failures occurred that could not be classified as to type of failure; 16 of these were judged to be the direct result of severe local scour. Also, 9 flow failures near 7 boring locations and 13 shear failures near 11 boring locations were reported in areas where no borings were located within 500 ft. From 1954 (when riverbank stability predictions were initiated) through 1973, 2047 boring locations at 212 revetment sites on the Mississippi River have been studied. The majority of the borings were in the Vicksburg and Memphis District areas. Data on sites in the New Orleans District were included only in the first report of this series (Report 12-3). However, boring data beginning in 1968 from the New Orleans District are included herein. Flow failures reported through 1973 have occurred within 500 ft of 21 boring locations in the Memphis District and 154 boring locations in the Vicksburg District; of these, 141 occurred near locations that had been predicted to be unstable according to the modified criteria, 24 occurred at boring locations predicted to be stable, and 10 occurred at boring locations for which no prediction had been made because the thickness of zone A sand had not been determined. The modified criteria have proven reliable in predicting stability with regard to flow failure. Of the total of 175 flow failures recorded since 1954 within 500 ft of analyzed borings, 24 failures (18 violations of criteria or 10 percent) were near boring locations predicted to be stable. However, many locations predicted to be unstable have not experienced flow failure, and it is possible that either the density of the 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:||Miscellaneous Paper|
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