Engineering designs must be legally defensible. Calculations generated using unlicensed or modified software are invalid in legal disputes, insurance claims, and regulatory reviews. If a slope failure occurs, the use of non-compliant software can result in severe legal and financial penalties for both the individual engineer and the firm.
Here's a general write-up:
A widely used method that satisfies vertical force equilibrium but ignores interslice shear forces. It is highly efficient for circular failure surfaces.
Advanced 2D Limit Equilibrium Slope Stability Analysis: A Deep Dive into Rocscience Slide2 (2021)