Assessment of factors leading to the failure of slopes in North Dakota

A total of 66,894 landslides were observed in North Dakota. The characteristics of these landslide locations were compared with the properties of areas without landslides to assess the factors that may be contributing to the landslides. Specifically, 68,395 control point locations randomly distributed across the state were selected for these comparisons. All the landslides for this study were found in areas with slopes less than 64°, with the majority of the failures occurring on slopes with inclinations between 9° and 14°. The largest fraction of the landslides occurred in the Sentinel Butte Formation (34,063 or 51% of the total), followed by Bullion Creek (8695 or 13% of the total) and river sediment of the Oahe Formation (6421 or 9.6% of the total). In the t tests, all of the surficial geologic formations had statistically significant differences between the landslides and control points. The t test for the slope inclination indicated statistically significant differences with a p-value less than 0.001 and a huge effect size between the landslide and control points. The sodium adsorption ratio and total dissolved solids were also found to be statistically significant from the t test results. Pearson’s correlation matrix showed a negative correlation between the amount of rainfall and various measures of the salt concentrations at the landslide locations, pointing to the reductions in shear strength and slope stability that might result as pore fluid salinity is leached.