The strength of coarse-grained soils changes over time and space. Large-scale tests on Tacheng sand-gravel showed that yield strength and maximum shrinkage happen when there is no volume strain increase. Failure strength and maximum dilatancy occur at the lowest ratio of volume strain to axial strain. Failure strength is usually higher than yield strength, and the difference between them grows with stress softening. Yield strength has less cohesive force but a greater internal friction angle compared to failure strength.