Evaluation of Time-Dependent Behavior of Soils

The time-dependent behavior of soils has been investigated extensively through one-dimensional and triaxial test conditions. Most of the observations in literature have focused on the determination of the time-dependent behavior of clayey soils, whereas the reported experimental studies of granular materials are few. This paper presents an up-to-date review of the various observed time- and rate-dependent phenomena that are known to exist for both clay and sand. The description is carried out separately for creep, stress relaxation, rate dependency, and structuration in laboratory experiments. All of the above-mentioned phenomena are present in both sand and clay. The time-dependent phenomena are more pronounced in clay than sand. However, sand exhibits relatively large deformations at high confining pressures because of grain crushing. Furthermore, the review revealed an essential characteristic situation for soils. That is whether the time-dependent behavior can be characterized as isotach or nonisotach. It seems that the isotach behavior is adequate for describing the time effects in clays in most situations. But for sand, the isotach description is inadequate. Further, the phenomenon of structuration plays a role in both clay and sand.The time-dependent behavior of soils has been investigated extensively through one-dimensional and triaxial test conditions. Most of the observations in literature have focused on the determination of the time-dependent behavior of clayey soils, whereas the reported experimental studies of granular materials are few. This paper presents an up-to-date review of the various observed time- and rate-dependent phenomena that are known to exist for both clay and sand. The description is carried out separately for creep, stress relaxation, rate dependency, and structuration in laboratory experiments. All of the above-mentioned phenomena are present in both sand and clay. The time-dependent phenomena are more pronounced in clay than sand. However, sand exhibits relatively large deformations at high confining pressures because of grain crushing. Furthermore, the review revealed an essential characteristic situation for soils. That is whether the time-dependent behavior can be characterized as isotach or nonisotach. It seems that the isotach behavior is adequate for describing the time effects in clays in most situations. But for sand, the isotach description is inadequate. Further, the phenomenon of structuration plays a role in both clay and sand