Friction Angle . Friction angle is proportional to relative density 

 for a given sand. The Appendix presents two charts (Figures 27 and 28) 

 for estimating friction angle. The one by Schmertmann (1978) uses 

 relative density as an intermediate parameter to estimate friction angle 

 as a function of soil type and relative density. The other (Mitchell et 

 al., 1978) represents the practice in the Union of Soviet Socialist 

 Republics and presents friction angle as a function of cone pressure and 

 overburden pressure. 



Undrained Shear Strength of Clay . The undrained strength of clay 

 is back-calculated from the cone pressure by applying the bearing capa- 

 city equation. The difficulty lies in choosing an appropriate bearing 

 capacity factor. The Appendix discusses this problem and provides 

 guidance for selecting a bearing capacity factor. 



Other Properties . The remolded strength, sensitivity, and overcon- 

 solidation of clays can also be estimated, but with less reliable 

 results than undrained shear strength discussed in the preceding para- 

 graph. Compression moduli for both clays and sand can be estimated. 

 The determination of these properties is discussed in the Appendix, but 

 the full development of the procedures is beyond the scope of this 

 report. 



Geotechnical Design 



Many different procedures have been developed for making geotech- 

 nical designs from CPT data. Each has its advantages, disadvantages, 

 and a particular application where it is most suitable. Schmertmann 

 (1978) prepared an extensive set of design guidelines for CPT data, and 

 his work is often referenced. The procedures given in the Appendix have 

 been extracted for the most part from Schmertmann' s work. 



Pile Design . Schmertmann recommends the "Dutch" procedure for 

 estimating pile end bearing and the procedure of Nottingham (1975) for 

 estimating side friction. These procedures are explained in the Appen- 

 dix along with recommendations on how factors of safety should be 

 applied to the results. The reader is also referred to Schmertmann 

 (1978a) for methods used to analyze tapered piles, different shaped 

 piles, and the effects of insertion methods. 



Bearing Capacity . Bearing capacity in sand requires estimating 

 bearing capacity factors from the CPT data and applying them to the 

 Terzaghi bearing capacity equation. In clays, the cone pressure is used 

 directly to estimate bearing capacity. The procedures and recommended 

 factors of safety are given in the Appendix. 



Settlement . Settlement calculations for footings on sand, with CPT 

 data as the basis, are quite adequate. For footings over clays, the 

 results are more uncertain. The procedure for making settlement esti- 

 mates are not given in the Appendix because of their complexity and 

 thus, exceed the scope of this report. 



