Statistical Study of the Geology, Topography, and Pore Fluid Salinity Controls on the Large Slope Failures Observed in North Dakota

A geospatial database of over 24,000 slope failures across the state of North Dakota was developed. The database revealed that nearly 1,500 slopes failures were larger than 100,000 m(2) in area posing significant safety concerns and engineering issues. To better understand the influence of various conditioning factors, a statistical study was undertaken in this paper. The slope failures were found to be concentrated in western North Dakota primarily occurring in the Sentinel Butte Formation. Statistical analyses suggest that this is likely due to the steeper topography and the abundance of Sentinel Butte Formation in this region in comparison to eastern North Dakota. The number of slope failures were log-normally distributed with the slope inclination. The mean slope inclination on which slope failures occurred was found to be 9.5 degrees with a standard deviation of 5.7 degrees. Interestingly, despite the presence of high salt concentrations in the soils underlying the majority of the state, the slope failures were found to be concentrated in areas with low salt concentrations. This may be attributed to the lower shear strengths of the soils with lower pore fluid salinity than that of soils with greater concentrations of salinity in the pore fluid.