The research on K0 behavior under different stress states is important in grasping the mechanical parameter of the soils.However

there are few apparatuses and methods applicable for measuring K0 of coarse grained soil

therefore

as for the K0 behavior of coarse grained soil in different stress states

the relevant researches are almost blank. For coarse grained

in order to study the transformation law of at-rest earth pressure coefficient（K0） during loading and unloading

a new large-size K0 test apparatus was developed and used to conduct a serial of K0 tests for sandy gravel and rockfill in different stress states. The results of K0 test show the particle morphology、stress state and grading all have certain effect on the value of K0 of coarse grained soil

and the effect of stress state is the most obvious. During loading or unloading

K0 of coarse grained soil will decrease with the increasing of vertical stress.Furthermore

based on the results

a description of the K0 considering effective vertical stress during loading is established and verified. Lastly

based on this description and the relation between K0 and over consolidation ration（OCR） developed by former researcher

an empirical equation is obtained

which can well describe the relationship between K0 and stress state under an arbitrary consolidation condition.