A Regional Study of Landsliding Near Ottawa

Abstract

The stability of natural slopes near Ottawa has been examined from a regional approach. With the aid of aerial photographs, the density and distribution of past landslides have been ascertained, and the development of more recent slides has been traced. This information, combined with details of the present day topography, groundwater conditions, and soil characteristics, leads to a conclusion that factors influencing slope stability vary markedly throughout the region, and certain areas are much more prone to sliding than others.The strength of soils in the region is discussed, including the development of a logical shear strength relationship which incorporates the effects both of cementation strength and fissuring. The influence of sample size on the extrapolation of laboratory triaxial test results to the field situation is introduced. Details of the method of landslide analysis used are given.Considerable evidence is presented to support the presence of separate marine and freshwater clay layers in the Ottawa area, and to suggest that flow slides are confined to the upper freshwater deposit. These two clay soils are most graphically distinguished by differences in fissure spacing and pore water chemistry.