Is Terzaghi’s effective stress a stress variable under seepage conditions?

LEI Guo-hui(雷国辉)¹, CHIU Abraham Chung Fai(赵仲辉)¹, NG Charles Wang Wai(吴宏伟)^{1, 2}

(1. Key Laboratory of Geomechanics and Embankment Engineering of Ministry of Education
(Geotechnical Research Institute, Hohai University), Nanjing 210098, China;
2. Department of Civil and Environmental Engineering,
The Hong Kong University of Science and Technology, Hong Kong, China)

Abstract:From the continuum mechanics perspective, an attempt was made to clarify the role of Terzaghi’s effective stress in the theoretical analysis of saturated soil subjected to seepage. The necessity of performing a coupled hydromechanical analysis to solve the seepage-deformation interaction problem was illustrated by examining the equations of static equilibrium among the effective stress, seepage force, pore-water pressure and total stress. The conceptual definition of stress variable that satisfies the principles of continuum mechanics is applied in the coupled hydromechanical analysis. It is shown that Terzaghi’s effective stress is in fact not a stress variable under seepage conditions, and the seepage force acting on the soil skeleton cannot be viewed as a body force. This offers a clue to the underlying cause of a paradox between the real Pascal’s hydrostatic state and the hydrostatic state predicted by a class of continuum hydromechanical theories.

Key words:seepage-deformation interaction; coupled hydromechanical analysis; representative elementary volume; stress variable; stress state variable