The mechanical behavior of unsaturated cohesive soils under different common stress conditions, that is, static compression, dynamic shear, and repetitive compression, is considered as a function of induced initial matrix suction by desorption from the initially saturated state. The hysteresis of moisture retention is considered outside the scope of this work. The test results suggest that the moisture regime can be expressed most suitably in terms of matrix suction. The data suggest that a rather definite change in stress-strain response takes place at a critical value of the matrix suction with modulus values, in general, dropping beyond the critical suction. The direct measurement of the total soil suction in the laboratory in connection with the triaxial compression test is sought by use of thermocouple psychrometers. The total suction of the soil decreases as the applied stresses increase; the quantitative relationship is complicated by a number of factors. The matrix suction appears to be the fundamental suction component controlling the mechanical behavior during a desorption schedule. This implies certain limitations for the use of psychrometers alone in indexing the mechanical behavior of soils, especially if they have a significant osmotic suction component.

The objective of this paper is to describe a new technique for measurement of the poro-elasticity of marine sediments in the laboratory. This technique enables one to determine the composite poro-elasticity factor α′ in one test setup as a function of controlling environmental factors such as stress state and load frequency. α′ includes shear modulus, Poisson's ratio, and hydraulic conductivity of the soil and compressibility and unit weight of the fluid along with frequency of wave loading and a characteristic dimension. The determination of α′ is based on the measurement of pore pressure at different depths in a confined cylindrical specimen. The theoretical basis of the test procedure, the method of analysis of the test results, and the appropriate test boundary conditions for different soils are presented. The results of tests performed on a nonplastic silt soil indicate that the proposed technique provides an efficient means of determining poro-elasticity of marine soils.