The test results of three different coarse-grained soils are obtained with conventional triaxial cyclic loading test. Based on these results

some useful conclusions are drawn from the discussion and analysis of the phenomenon of volume-contraction in unloading of coarse-grained soils: The phenomenon of the volume-contraction in unloading of coarse-grained soil is more obvious with the increasing of stress level and with the decreasing of confining pressure. According to the test data

a relationship formula among volume contraction in unloading and stress level and confining pressure is obtained. Rebound modulus presents the curve of hump shape with the increasing of stress level and the maximum is obtained when stress level is 0.7. The ratio of average rebound modulus and initial elastic modulus with monotonic loading present decrease of a power function

this ratio of soil material whose mother rock is high hardness is larger and the ratio of soil material whose mother rock is soft is smaller. The general relationship between kur and nur which is obtained from rebound in unloading and k and n which is obtained from monotonic loading is that kur is approximately from 2.46 times to 4.60 times of k and nur is approximately from 0.540 times to 0.885 times of n respectively.