Chapter 9 



FOUNDATIONS FOR HIGHWAY BRIDGES AND SEPARA- 

 TION STRUCTURES ON UNCONSOLIDATED SEDIMENT 



C. H. Harned 



Geologist, Bridge Department 



California State Division of Highways 



Sacramento, California 



Bridges, in common with all other civil engineering works, must be 

 dependent for support upon earth materials. Since bedrock support is 

 the exception rather than the rule, it is appropriate that space be al- 

 located in this volume to a brief discussion of foundation study tools 

 and techniques applicable to the solution of problems involved in the 

 frequent practice of transmitting structure loads to unconsolidated sedi- 

 ment. 



The engineer is often confronted with serious problems posed by the 

 design and construction requirements of safe economical support for 

 bridges. This is particularly true when a dependence for support must 

 be placed upon recently deposited sediment which has not been sub- 

 jected to loads greater than those which exist at present. 



The purpose of this chapter is to present a description of some of 

 the tools, methods, and personnel requirements of a modern founda- 

 tion investigation. It is hoped that by so doing additional interest may 

 be encouraged among workers engaged in this and related fields of ap- 

 plied sedimentation, to the end that reflections may be observed in 

 both the curricula of personnel training and ultimate practical achieve- 

 ment in this important field of application. 



Normally the bridge engineer is allowed little choice regarding the 

 location of his structure because such determinations are usually de- 

 pendent upon the requirements imposed by highway grades and align- 

 ments. This situation presents the problem of economic conformity to 

 any type or variety of material types that occur at a specific site 

 regardless of either the physical characteristics of the material or the 

 magnitude of the problems involved. It follows that, if economically 

 sound, practical substructure designs are to be consistently realized, 

 they must be based upon accurate observations and interpretations of 



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