Based on the balance equations for mass, linear momentum, energy in porous media theory and some hypotheses in unsaturated soil mechanics, an expression of the total deformation work W is derived, and with the help of the specific expression of the work, the effective stress conjugated with the displacement of the soil skeleton is suggested by the authors, which has the similar form as the expressions proposed by Wheeler (2003) and some other researchers according to their experience and intuition, but the effective stress presented in this paper is derived on the basis of porous media theory and its assumptions, whose premise and hypothesis are clear. It is also pointed out that due to the complexity of the physical mechanism and various influencing factors, it is impossible in unsaturated soil mechanics to determine the deformation of solid skeleton by the effective stress only, like in the saturated soil mechanics. Besides, by using the expression of the deformation work and the free energy A α for each phase, the applicability of the Phase Separation Principle proposed by Passman (1984) in unsaturated soil is discussed, and it is considered that the principle should not strictly apply to unsaturated soil mechanics. total deformation work, effective stress, unsaturated soil, Phase Separation Principle, porous media theory After several decades' research work of unsaturated soil mechanics, great achievements have been achieved, but most of which are based on intuition, experience, or macroscopic recognition, and they are lack of scientific theoretical basis. The porous media theory (namely theory of mixture), which could uniformly describe the complicated interactions among phases under external forces and the responses in various environments, could provide a rational and scientific basis and guidance of the establishment of constitutive relationships for porous media (including partially

Existing sequential parameter estimation methods use the acoustic pressure of a line array as observations. The modal dispersion curves are employed to estimate the sound speed profile (SSP) and geoacoustic parameters based on the ensemble Kalman filter. The warping transform is implemented to the signals received by a single hydrophone to obtain the dispersion curves. The experimental data are collected at a range-independent shallow water site in the South China Sea. The results indicate that the SSPs are well estimated and the geoacoustic parameters are also well determined. Comparisons of the observed and estimated modal dispersion curves show good agreement.