The Studies of Rock Damage Softening Statistical Constitutive Model under True Triaxial Stress State

From the feature of rock micro-unit failure obeys Poisson random distribution, the damage softening statistical constitutive of was established under true triaxial confinement based on D-P criterion, so the impact of the intermediate principal stress on rock deformation and failure was considered in theory, and the actual engineering rock complex stress path evolution was reflected more realistically. Furthermore, according to the geometrical conditions of stress-strain relationship, the theoretical relationship between constitutive model parameters and the stress-strain curve characteristic parameters during the process of rock softening and deforming, which enhance the adaptability of the model. Finally, the rationality of the model verified by the measured data.

Modified state-surface approach to the study of unsaturated soil behavior. Part I: Basic concept

The traditional state-surface approach to the study of unsaturated soil behavior is becoming much less popular these days, as it uses unique constitutive surfaces to represent unsaturated soil behavior. This approach is essentially a nonlinear elastic formation and cannot be used to explain complex stress-path dependency for unsaturated soils. In this paper, a modified state-surface approach (MSSA) is proposed to represent unsaturated soil behavior under isotropic stress conditions in which a conventional void-ratio state surface is considered to be made up of an elastic surface and a plastic hardening surface. The plastic hardening surface remains stationary at all times, whereas the elastic surface remains unchanged when the soil experiences elastic deformation and moves downward when there is plastic hardening occurrence. Using the MSSA, the loading–collapse (LC) and the suction increase (SI) yield curves in the Barcelona basic model (BBM) are derived. The prediction of three typical cases of soils under isotropic conditions and experimental results using the proposed approach confirmed its feasibility, simplicity, and potential for the study of unsaturated soil behavior.