The trial wedge method of analysis is shown in Fig.1 below. The following steps are to be followed to make the analysis.
Step 1 – a mass of soil behind the wail is considered as a free body. The force P, which must exist between the free body and the wall, is found by writing the equation of equilibrium for the free body as a whole.
Step 2 – a different free body is considered, having a different boundary through the soil. Once again the required force between the wall and the free body is found.
Step 3 – the actual force against the Wall will be the largest value of P found as the result of considering all possible free bodies.