It is evident that the theory as expressed in Fig. 8.6 does not suggest a particular
plane of failure. Thus, the pressure determination of the Coulomb theory is traditionally
left to graphical methods, in particular those first developed by J.-V. Poncelet, and later
by a German engineer, Culmann. These constructions, which allow for the complete
determination of lateral pressure acting on the wall (i.e., magnitude, direction, and
point of application), are not further discussed herein. However, several failure planes
are usually assumed, pressure from each assumption is graphically determined, and an
envelope line of pressure is developed from these pressure points from which the maximum
pressure can be determined. The methods are laborious but straightforward and
may again gain in popularity with the increasing use of computers