Chapter 7 



SEDIMENTATION AND HIGHWAY ENGINEERING 



Arthur B. Cleaves 



Professor of Engineering Geology 



Washington University 



St. Louis, Missouri 



A knowledge of sediments, whether they be unconsolidated strata or 

 bedrock, can be vital to successful highway construction. The science 

 of soil mechanics in which the physical characteristics of soils are 

 studied, measured, and evaluated has already achieved signal success 

 in helping the engineer toward better construction. The geologists, 

 as a whole, have not as yet made the fundamental contributions of 

 which they are capable. 



Soil and sedimentary rock origin, age, mineralogic composition, de- 

 gree of weathering, and attitude in the earth's crust are all functions of 

 the physical characteristics observed by the soils engineer. The sedi- 

 mentary processes and natural or artificial agents which have brought 

 the sediments into the position where the engineer finds them afford 

 logical explanations for the non-isotropic characteristics of those soils 

 and rock strata. The density, layering, intertonguing, porosity, per- 

 meability, and similar features of soils and sedimentary rock are 

 directly related to the processes responsible for their origin and place- 

 ment. 



The physiographic history of an area is fundamental to an under- 

 standing of the general physical characteristics of the recent overbur- 

 den and often of the configuration of the bedrock profile. 



A knowledge of structural geology prepares the geologist for in- 

 terpretations of the effects of joints, faults, inclined strata with their 

 infinite variations, weathered zones, and similar features with respect 

 to the structures placed above, or excavations made in, them. 



A petrographic study involving X-ray and differential thermal an- 

 alysis will determine whether the clay in a cut is the dangerous mont- 

 morillonite, or the petrographic study alone will determine whether 

 the stream gravel or bedrock selected for aggregate has deleterious re- 

 action in the presence of high-alkali cement. 



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