CHAPTER 15 

 GEOLOGIC TECHNIQUES IN CIVIL ENGINEERING 



GEORGE L. ROBB 



Geology in its application to civil engineering is primarily concerned 

 with the rocks, soils, and ground water that make up the surface and 

 shallow subsurface of the earth's crust. The civil engineer builds his 

 structures on rock and soil foundations and uses the soil and rock as 

 construction materials. He adapts his structures to existing terrain and 

 topography, surface and underground water, geologic structures, lithology, 

 and stratigraphy at the construction site. All combine to create the prob- 

 lems that he must surmount if his structure is to be efficient, permanent, 

 appropriate, and economical. On this common ground, that is, topogra- 

 phy and geology, the engineer and the geologist must meet. Engineering 

 structures are custom-made, and their efficiency and economy depend 

 largely on how well they have been adapted to the peculiarities of the 

 site and the valuable construction materials. 



Engineering geology is thus born of the engineer's need that some- 

 one interpret these geologic conditions expertly — not abstractly but in 

 terms of their engineering significance — not in abstruse geologic terms 

 but in words that the engineer can understand and apply specifically to 

 given problems. The engineering geologist must interpret the conditions 

 of the crust with such clarity and discernment that the engineer can 

 design and build the kind of structure that is most appropriate to and 

 compatible with the natural conditions of the site. 



A summary of the functions and responsibilities of the engineering 

 geologist and his relationship to the engineer can be summed up in the 

 following paragraphs by Rhoades: ^ 



In essence, it is the function of the engineering geologist to interpret the 

 character of structure sites and prospective natural construction materials, 

 thus supplying information essential to the engineer and fulfilling his function 

 of developing plans and specifications most effectively, reconciling the engi- 

 neering objectives with the natural conditions. The functions are inseparable. 



It is the engineer's responsibility to define what kind of information he 

 needs concerning materials and surface and subsurface conditions. It is the 

 engineering geologist's responsibility to obtain and interpret that information. 

 The burden of geologic interpretation rests with the geologist. The burden of 

 engineering interpretation and application rests with the engineer. The geolo- 

 gist must assimilate the data and present conclusions and recommendations 

 to the engineer in a concise, practical form. Such conclusions are of value 

 to the engineer only to the extent that they have recognized all the pertinent 



^ Rhoades, Roger, Geology in Civil Engineering : Address before Second Pan-American Congress of 

 Mining Engineering and Geology, Rio de Janeiro, Brazil, Oct. 1946. 



