FOUNDATIONS 



333 



SUPPORTING POWER OF ROCKS 



Loose rock in any of 

 its forms may make a 

 satisfactory subfounda- 

 tion, but it requires 

 very careful examina- 

 tion and, if possible, 

 should be avoided. 



The strength of earth 

 subfoundations is 

 largely affected by the 

 quantity of water they 

 contain; and the extent 

 to which they may be 

 exposed to water in the subfoundations is an important element 

 to be considered in determining their sustaining capacity. 

 The following table gives approximate values. The engineer, 

 however, must in each case be guided largely by judgment 

 based on experience and actual facts. 



SAFE LOADS ON EARTH SUBFOUNDATIONS 



Kinds of Material 



Load in Tons 

 per Square Foot 



Sand and gravel are capable of carrying very great loads; 

 but as they are easily eroded by flowing water great care must 

 be taken to protect them from direct contact with currents of 

 water. Clean dry sand can bear a load of from 2 to 4 T. per 

 sq. f x. 



