Ultimate Strength Matric Stress Relationship

The stress produced by matric suction, or matric stress, is defined through the intergranular stress tensor and determined with an ultimate strength relationship. An experimental program, consisting of triaxial shear and hydrostatic consolidation tests of unsaturated soil, is used to develop ultimate strength lines, normal and recompression lines, and model parameters. Matric stress is included in both shear and volume relationships in a critical state soil model that uses the modified Cam-clay yield function. Shear is modeled using a constant matric stress that is determined at critical state. Slopes of the normal compression and recompression lines are adjusted for matric stress using a state function, which expresses matric stress as a function of void ratio and degree of saturation. Model predicted curves of deviator stress and axial, lateral, and volumetric strain show satisfactory agreement with data obtained from triaxial tests conducted on samples containing a range of void ratios and water contents.