CHAPTER XXI. 

 FOUNDATIONS. 



Introduction. The design of the foundations for mill buildings 

 is ordinarily a simple matter for the reason that the buildings are usu- 

 ally located on solid ground and the loads on the columns are small. 

 Where the soil is treacherous or when an attempt is made to fix the 

 columns at the base the problem may, however, become quite com- 

 plicated. 



Bearing Power of Soils. The bearing power of a soil depends 

 upon the character of the soil, its freedom from water, and its lateral 

 support. The downward pressure of the surrounding soil prevents lat- 

 eral displacement of the material under the foundation and adds ma- 

 terially to the bearing power of treacherous soils. 



The safe bearing power of soils given in Table XXIII may be 

 used as an aid to the judgment in determining on a safe load for a 

 foundation. However no important foundations should be built with- 

 out making careful soundings and bearing tests. 



A soil incapable of supporting the required loads may have its 

 supporting power increased (i) by increasing the depth of the foun- 

 dation; (2) by draining the site; (3) by compacting the soil; (4) by 

 adding a layer of sand or gravel; (5) by using timber grillage to in- 

 crease the bearing area ; (6) by driving piles through the soft stratum, 

 or far enough into it to support the loads. 



A method used in France for compacting foundations is to drive 

 holes with a heavy metal plunger and then fill these holes with closely 

 rammed sand or gravel. 



Several kinds of patented concrete piles are now in use to a limited 

 extent in this country for building foundations. 



