Chapter 8 

 FOUNDATION PROBLEMS OF SEDIMENTARY ROCKS 



Shailer S. Philbrick 



Division Geologist, Corps of Engineers 

 Department of the Army 

 Pittsburgh, Pennsylvania 



The geologic map of the United States shows the great expanse of 

 sedimentary rocks which underlie the region from the Piedmont to 

 the Rockies. Because igneous and metamorphic rocks appear through 

 the sedimentary blanket only rarely, most of the major dams and 

 many of the larger buildings in this area are founded upon sedimen- 

 tary rocks. The design of these structures is influenced by the type, 

 degree of weathering, and depth through the overburden to the sedi- 

 mentary rocks. The present physical and structural properties of the 

 rocks are influenced by their inherent geologic characteristics. Hence 

 an understanding of the foundation problems associated with a given 

 rock type at one locality will be of assistance in using that same rock 

 type as a foundation elsewhere. This inferred oversimplification ap- 

 plies to the general problem of each rock type on which is super- 

 imposed the special problems coming from local conditions of weather- 

 ing, geomorphology, geologic structure, the activities of man, and the 

 purpose for which the rock is to be used. Although it may appear 

 that heavy hydraulic structures impose severe requirements on founda- 

 tions, it is not uncommon to find more intense local loadings developed 

 by industrial structures and high buildings. Foundation problems 

 may be created by such diverse causes as reversible loadings occa- 

 sioned by filling and emptying of reservoirs, release of load caused by 

 excavation, and reduction in support of the ground surface by mining. 

 Regardless of the cause of the problem, its importance, frequency, 

 . and magnitude will be related immediately to the particular type 

 of engineering structure and directly to the type of rock upon which 

 the structure will be founded. It is, therefore, difficult to dissociate 

 the problem of foundations from the implications of sedimentation. 

 In fact, by the application of sedimentation to foundation problems 



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