An analysis of field and laboratory data for unstable river banks in the Metropolitan Winnipeg area

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Janzen, Paul
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Over the years, there has been an increasing demand to develop river bank areas In the Metropolitan Winnipeg area. With increased population, greater use has been made of the banks for apartments, bridges, pipe line crossings and parks. Areas previously deemed unsuitable for construction are now receiving consideration for development. A lack of adequate data, particularly with regard to pore pressures, is the cause of considerable uncertainty in analyzing the stability of the river banks. Uncertainty has also existed in knowing the actual configurations of existing failure surfaces, shear strength parameters, and when slope movements occur. GENERAL DESCRIPTION OF THE STUDY The locations of the two sites studied, namely the Tache Avenue and St. Vital sites, are given in Figure l. Data on pore pressures and slope movements had been previously obtained on the river bank at the St. Vital site for a limIted time only. lt was decided to continue monitoring this site with additional instrumentation to provIde more detail. To give a more general basis for analysis, a second site (Tache Avenue) was selected and instrumented. For both sites, pore pressure and slope indicator readings were obtained for a full cycle of winter, spring, summer and fall conditions. A simple means of analysis of failed banks was developed to permit an appropriate correlation of piezometer readings, river levels, slope movements and shear strength parameters*. It was realized that with only two banks investigated, the results of the study should not necessarily be considered typical for all river banks in the Winnipeg area. A limited number of laboratory tests were performed to determine residual shear strength parameters. The complete range for these parameters might not have been established. Although it is an important factor, the variation in river bank profile at the toe of each bank due to scour and silting during flood stage was not included in the present study...