Slope safety factor (FoS): decoding definitions through analogical discussion

The factor of safety or safety factor (FoS) is a dimensionless quantity and a fundamental concept in slope stability analysis, as it measures the factor by which a slope can resist failure. Despite its widespread use, the definition and interpretation of the slope safety factor can vary across different contexts (i.e., overall FoS, local FoS, static FoS, dynamic FoS, short-term FoS, long-term FoS, seepage FoS, reinforcing FoS) and often leading to confusion and misapplication. This paper explores different literature-based FoS definitions on various analytical approaches (i.e., moment-based, shear strength-based, shear stress-based, work rate-based, transfer coefficient method-based, deformation energy-based, and strength reduction-based). The objective is to enhance the understanding and reliability of these methodologies. Additionally, a comprehensive effectiveness analysis is presented, supported by practical examples to illustrate the application and performance of each approach. The paper aims to clarify the principles of slope stability, limitations, and significance by comparing the safety factors with analogical examples. The paper also emphasizes the practices used to increase slopes' safety factor. The ultimate goal of this study is to make slope safety factors more understandable so that engineers may use the idea more skillfully while evaluating and controlling slope stability concerns.