General method for estimating the active and passive earth pressures on retaining walls assuming different strength criteria

Equation (13), taking into account equations (11) and (14), adopts the form:

In other words, n is a functional of the failure line Y =Y(X).

In this integral the function Y(X) must be sought, which will make it extremal, in other words the maximum or minimum of the functional must be found depending on whether active or passive thrust is sought. This can be done by applying Euler’s variational method.