94 kaye. PRINCIPLES OF SOIL MECHANICS [Ch. 5 



nize the same problems in the same terms. However, a fact less well 

 recognized by geologists is that soil mechanics can be of great value 

 to other fields of geological investigation. Tools have already been 

 fashioned by engineers which geologists could profitably use in such 

 problems as estimating the former depth of burial of clays, the critical 

 conditions of instability in landslides, and the active pressures neces- 

 sary to produce shearing and failure in soils. But perhaps the greatest 

 value soil mechanics can have for geology is the introduction of 

 mechanical concepts into geological thinking. The mechanical tech- 

 niques are already well-advanced in soil mechanics. The geologist 

 may be able to extend these methods to hard-rock problems and 

 thereby in time derive a more refined understanding of the nature and 

 intensities of earth stresses. 



On the other side of the ledger, there is no doubt that soil mechanics 

 at this stage of its development needs the geologist's sensitive under- 

 standing of the variations of earth materials. Furthermore, there 

 is a growing recognition that additional progress in soil mechanics 

 awaits the solution of a number of problems concerning the funda- 

 mental properties of soils which fall into a common ground between 

 geology and soil science. In view of these common needs it does not 

 seem unrealistic to expect a close harmony between geology and soil 

 mechanics in the near future. It is therefore the purpose of this 

 chapter to arouse the geologist's curiosity in soil mechanics. For a 

 formal introduction and ensuing acquaintanceship with the subject the 

 student is referred to the list, at the end of this chapter, of several 

 excellent textbooks on soil mechanics which have appeared in recent 

 years. 



WHAT IS SOIL MECHANICS? 



The quantitative appraisal of the stress-strain relationships of soils 

 in the engineering works of man is the subject of soil mechanics; or, 

 to quote Professor Terzaghi (1943, p. 1), "Soil mechanics is the ap- 

 plication of the laws of mechanics and hydraulics to engineering prob- 

 lems dealing with sediments and other unconsolidated accumulations 

 of solid particles produced by the mechanical and chemical disin- 

 tegration of rocks, regardless of whether or not they contain an ad- 

 mixture of organic constituents." 



The investigation of the mechanics of soil behavior is the logical 

 extension of the engineer's interest in the strength of materials. The 

 strength and elastic constants of steel and concrete, for example, have 

 long since been determined with satisfactory precision. This knowl- 

 edge has permitted engineers to design highly economical and safe 



