From the test results, a load-settlement curve should be plotted as shown in the fig. The allowable pressure of the prototype foundation for an assumed settlement may be found and by making use of the following equations as suggested by Terzaghi and Peck.

For granular soils,

For clay soils,

Where, = permissible settlement of the foundation in mm,

              = settlement of the plate in mm,

              B = size of plate in metres,

             = size of plate in metres.
The permissible settlement for a prototype foundation should be known. Normally a settlement of 2.5cm is recommended. In the equation the values of and are known. The unknowns are and B. The value of for any assumed value of B may be found out from the equation. Using the plate load settlement curve the value of the bearing pressure corresponding to the computed value of is found out. This bearing pressure is the safe bearing pressure for a given permissible settlement .