In this study, the stability of the Gougerd landslide of Khoy was investigated with respect to changes in the soil internal friction angle. Statistical analysis of the results of changes in the FS of different methods in analyzing the stability of the Gougerd landslide in 282 analyses showed that: 1) In static conditions, under the influence of groundwater conditions, the results of the stability analysis of various methods showed up to 35.2% changes in the FS, and the largest differences in the FS values were obtained in the conventional Fellenius, Spencer, and Morgenstern-Price methods. 2) In static conditions, the FS of various methods showed changes of up to 35% with respect to the effect of the internal friction angle, and the largest difference in the FS values compared to other methods was obtained in the conventional Fellenius method and the Spencer method. 3) In pseudo-static conditions and in the dry state, up to 5% changes in the FS were obtained in different analysis methods, and under the influence of groundwater conditions, the changes in the FS were up to 39.9%. The largest changes in the FS of the dry state were obtained in the simplified Janbu method, Spencer and Morgenstern-Price methods, and under the influence of groundwater, the largest changes in the FS were obtained in the conventional Fellenius method and Spencer method. In examining the results of this research, the effect of different conditions of groundwater level, soil internal friction angle, and earthquake force on the analytical mechanism of the relationships existing in various methods is recognized as the main cause of the difference in the results of different stability analysis methods.
