Chapter 5 



PRINCIPLES OF SOIL MECHANICS AS VIEWED BY A 

 GEOLOGIST * 



Clifford A. Kaye 



Geologist, U. S. Geological Survey 

 Washington, D. C. 



Soil mechanics, or the study of the mechanical properties of un- 

 consolidated earth materials, is one of the youngest and most promis- 

 ing of the border sciences that lie between the quantitative realm of 

 engineering and the qualitative domain of geology. Soil, as used in 

 soil mechanics, is not simply the organic-rich surface layer of the 

 agriculturist and the geologist. The scope of the word has been broad- 

 ened to include all granular earth materials which cannot be called 

 hard rock. Unconsolidated sediment, regolith, and mantle rock, ir- 

 respective of proximity to the surface, are classed as soil. 



Although a few short decades ago soil mechanics was only an 

 academic specialization in the sprawling technology of civil engineer- 

 ing, it has rapidly grown to become one of the indispensable tools of 

 modern engineering. Within this time the more scientific methods of 

 soil mechanics have almost completely replaced the empirical meth- 

 ods that had traditionally been employed for the design of founda- 

 tions, retaining walls, earth slopes, earth dams and dikes, and high- 

 way subgrades. As part of this new engineering activity, site in- 

 vestigations and soil-sampling techniques have been developed to a 

 point of high refinement, and soil-testing laboratories have sprung 

 into being in many parts of the world. 



Soil mechanics already has had some impact on geology. Most 

 engineering geologists today are obliged to deal quantitatively with 

 the mechanical properties of unconsolidated sediments, and, as a re- 

 sult, geologists are developing an active interest in soil mechanics. 

 This is particularly so because the close collaboration between geology 

 and engineering, which characterizes much of today's engineering plan- 

 ning, demands that both groups speak the same language and recog- 



* Published by permission of the Director, U. S. Geological Survey. 



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