For sand foundations the method of determining the permissible pressure beneath the base of the caisson is that evolved by the author in making his before mentioned computations for the New Orleans Bridge

study. It consists of allowing four tons per square foot plus the intensity of pressure on the adjacent soil at the elevation of the base, due to the net weight of the overlying solid material, after having deducted from the net weight of the caisson and its superimposed load for side friction at the rate of 400 pounds per  square  foot  of  lateral  surface  in  contact  with  solid  material.  The 
net weight of  the  water-soaked  timber  in  the  caisson  is  taken  as  zero