The theory of cylindrical cavity expansion has been widely used in many geotechnical engineering

such as analysis of pressure meter testing and effect of pile driving. Extended spatial mobilization plane (SMP) theory

which can display the effects of intermediate principal stress

in combination of finite strain theory

is used to analyze cylindrical cavity expansion problem in homogeneous soil. An analytical procedure to determine average volumetric strain of plastic zone is developed according to stress path hypothesis. Accordingly

“nondimensional” plastic zone radius and factors of cylindrical cavity expansion are estimated for varied rigidity index

Poisson ratio v and frictional angle . It is concluded that average volumetric strain decreases and “nondimensional” plastic zone radius and factors of cylindrical cavity expansion increase with the increase of 、 、 . Variation of has significant effects on factors of cylindrical cavity expansion in the case of greater . Furthermore

a comparative study of the solutions based on extended SMP and those based on Mohr-Coulomb is made to examine the effects of intermediate principal stress on cylindrical cavity expansion for various soils. The values of factors of cylindrical cavity expansion considering the effects of intermediate principal stress presented in this paper are of great significance for analyzing in-situ tests and estimating ultimate lateral friction of piles.