Introduction

SLOPE/W is based on what is called a Limit Equilibrium (LE) formulation. Fundamentally, the objective in a LE formulation is to find the point or condition where all of the driving or destabilizing force is equal to all of the resisting or stabilizing forces. This condition is determined by satisfying all equations of statics. That is, the summation of forces in the horizontal (𝐹𝑥) and vertical (𝐹𝑦) directions must equal zero and the summation of moments (𝑀0) about any point must equal zero. 

In order to achieve this, it is necessary, through an iterative procedure, to find a number by which the shear strength of the soil must be reduced. This number is called the factor of safety. The equation of statics is the extent of the physics underlying a LE formulation. No stress-strain constitutive relationship, for example, is invoked. This creates some limitations in the LE formulation. To make effective use of a LE stability formulation, it is essential to recognize and comprehend the fundamentals and consequences of the formulation. This SLOPE/W document highlights the essence of the SLOPE/W LE formulation, draws attention to the resulting limitations and provides meaning to the end results.