ONE-DIMENSIONAL SEEPAGE FORCE AND BUOYANCY

For the sake of simplicity, two methods of deriving seepage force and buoyancy associated with one-dimensional fluid flow in saturated soil were developed to give a uselful supplement to conventional macro-scale method of isolated pore fluid. To study the seepage force and buoyancy, three fundamental governing equations, namely, equilibrium differential equation in elasticity, Terzaghi's effective stress equation and simplified Bernoulli's equation in fluid mechanics, are utilized for the derivation of seepage force and buoyancy. Based on the fundamental governing equations, it is readily to derive the differential equations of equilibrium corresponding to the isolated soil skeleton and the isolated pore fluid, and hence, the connotation and nature of seepage force and buoyancy can be disclosed. The seepage force per unit volume of saturated soil arises from the gradient of fluid pressure in terms of total head. The buoyancy originates in the vertical component of gradient of fluid pressure in terms of position head. Both the seepage force and the buoyancy can be embodied in equilibirium differential equation with respect to skeleton or pore fluid of satured soil. In geotechnical practice, the three governing equations can be directly applied to the calculation of effective stress. Only in some simplified cases, the distribution of effective stress can be obtained using the seepage force and buoyancy. Additionally, some hot topics are also discussed in this study, and emphasis shall be put on the discussion on the rationality and the potential application risk of the new definition of seepage force, i.e., j= nγ _w i. The strictness of one classic formulation of seepage force in history was thoroughly validated when considering the derivative of seepage velocity with respect to time. It is noteworthy that in the study of seepage force and buoyance from the perspective of soil mechanics, the Terzaghi's effective stress equation shall be reasonably implemented with practical significance.