A hypoplastic model was investigated to describe the monotonic and cyclic behavior of gravelly soil. A new model was established through introducing the fundamental concepts of hypoplasticity theory and the critical state parameters. The formulae were derived; and their parameter determination method was also illustrated. The monotonic and cyclic stress-strain relationship response of a few gravels in practical projects were predicted and compared with the test results. The new model has few parameters

three-dimensional format and succinct formulae without loading criterion. The model is able to capture main monotonic and cyclic behaviors of gravelly soil

including the nonlinear relationship between the strength and confining pressure

the volumetric strain behavior dependent on confining pressure

contraction due to unloading and volumetric strain accumulation due to loading.