CHAPTER II. 



EXTERIOR WALLS, FIRE WALLS, 

 AND ENCLOSURES. 



Foundations The stability of any building depends to a great 

 extent upon the nature of the foundations and 

 the bearing power of the soil upon which these foundations 

 rest. Not only must the walls have footings of sufficient size, 

 but all piers which support columns or isolated loads must also 

 be provided with ample bearing surface. Heavy machines or 

 equipment may be supported upon foundations which are sep- 

 arate from the main foundations of the building. This is 

 advisable in all cases where heavy shocks or vibrations are 

 likely to occur. 



The footings and foundation walls of modern mill buildings 

 are of plain or reinforced concrete. A lean mixture of one 

 part Portland cement, three parts clean sand, and five parts 

 of broken stone or screened gravel, should be suitable for 

 footings in ordinary cases, while a 1:2:4: mixture will make 

 strong, watertight foundation walls if the materials are care- 

 fully graded and properly handled. It is essential that the 

 concrete be extremely well mixed. 



Safe bearing values for different kinds of soil to be used 

 in preliminary estimates are as given in Table I. If exact 

 values are needed in doubtful soils, bearing tests should be 

 made. 



Table I. Bearing Power of Soils. 



Kock 10 to 200 tons per sq. ft. 



Gravel, compacted 8 to 10 



Sand, clean and compact 4 to 6 



Clay on thick beds, always dry 4 to 6 



Clay on thick beds, moderately dry 2 to 4 



Sand, clean and dry 2 to 4 



Dry earth 1 to 2 



Quicksand and wet soil y 2 to 1 



The unit bearing on footings should be proportioned in 

 such a manner as to allow equal settlement under all parts 

 of a structure. In general, footings for natural foundations 

 should be made 1 foot 6 inches, or 2 feet thick. If pile founda- 



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