TABLE OF CONTENTS As previously mentioned in Chap. 8, in a comparison of the effective friction angle ? ? from drained direct shear tests on saturated cohesionless soil and the friction angle from direct shear tests on the same soil in a dry state, it has been determined that ? ? is only 1 to 2 lower than ? (Terzaghi and Peck 1967, Holtz and Kovacs 1981). This slight difference is usually ignored, and the friction angle ? and effective friction angle ? ? are typically considered to mean the same thing for cohesionless soils such as sands and gravels. Thus in an engineering analysis using cohesionless soil, the shear strength could be expressed as either ? (friction angle) or ? ? (effective friction angle), and they will essentially have the same meaning and value.
For cohesive soils, the friction angle ? and effective friction angle ? ? not only have different values, but also have significantly different meanings. Friction angle ? and cohesion c determined from undrained shear strength tests should only be used in total stress analyses, while effective friction angle ? ? and effective cohesion c ? should only be used in effective stress analyses. These two types of engineering analyses will be further discussed in Sec. 9.7.
The effective friction angle ? ? and effective cohesion c ? of a cohesive soil could be obtained by performing drained...
