SOIL STRUCTURE 



177 



Recently Puchner 1 has found a machine for measuring 

 the crushing strength of dry soil cylinders to be of value 

 in determining the absolute, or maximum, cohesion of 

 soils. The results, as he has already demonstrated in 

 his previous work, are comparable, in relative value at 

 least, to those obtained by simpler methods. 



The great difficulty encountered in measuring the 

 natural cohesion of a soil, either wet or dry, is not so 



FIG. 25. The apparatus used by the United States Bureau of Soils 

 for determining the penetration of soils. (C) is mechanically packed 

 soil ; (A), steel point; (P), pail for receiving sand from funnel (F). 

 (W) is a counterpoise. 



much in the accuracy of the determination as in controlling 

 physical conditions. The cohesion of a soil depends 

 very much on the handling it has received in the prepara- 

 tion, in the amount of water that is added, and in the 

 amount and length of time of drying. Natural granu- 

 lation cannot be secured. The Bureau of Soils attempted 

 to obviate these difficulties by mechanical sifting and 

 packing, but the results were abnormal, due to the sift- 

 ing process. As a consequence, most cohesion results 



1 Puchner, H. Vergleichende Untersuchungen liber die 

 Kohiireszenz verschiedener Bodenarten. Internal. Mitt, fur 

 Bodenkunde, Band III, Heft 2-3, Seite 141-239. 1913. 



