Experimental study and modeling of instability and time effects of granular materials.

摘要

This study presents the results of experimental and numerical investigations of two factors that affect the conditions for stability and instability of granular materials. These are (1) imposed volume changes and (2) time-dependent behavior. These factors are studied in triaxial compression tests and are modeled by an existing single hardening constitutive model.; The effects of imposed volume changes on the instability of granular materials are studied in experiments on a fine sand in which water is forced into or out of a sand specimen during shearing. The effects on stress-strain behavior and stability are recorded and discussed. Specimens forced to dilate more than desired in a standard drained test exhibited a tendency toward unstable behavior. Specimens forced to contract more than desired exhibited a tendency toward stable behavior. The conditions of imposed volume changes are then simulated with a single hardening constitutive model and compared with the experimental results. It is shown that the model can predict the corresponding loading paths and sand behavior as well as the resulting stable and unstable conditions.; The experiments conducted for investigation of time effects were performed on a crushed coral sand. The testing series involved shearing at different strain rates as well as jumps between strain rates, creep and relaxation tests, and stress drop tests followed by constant stress creep or constant strain relaxation tests. The experimental results are presented and discussed as a basis for development of a time-dependent version of the single hardening model. It was found that correspondence between creep and relaxation does not necessarily exist.