| Sandy-gravel material has the engineering properties of good compaction ability, strong hydraulic permeability, high fill density, high shear strength, small settlement deformation, high bearing capacity. Therefore, it has been widely used in earth-rock dams. Sandy-gravel material was considered as materials which have high anti-liquefaction strength because it's high hydraulic permeability and have coarse grain. However, this kind of knowledge was validated not enough by more and more earthquake engineering records. Liquefaction may occur in sandy-gravel material under earthquake, which is attached great important to the liquefaction problem of saturated sandy-gravel. The big grain in the sandy-gravel often rejected when the cyclic test was carried out due to the restriction of the equipments. The diameter of the sample always was small. If the properties of the real sandy-gravel could be presented by this kind of test and the results between different diameters could be comparable. So, it is necessary to study the size effect of sandy-gravel material under dynamic loading. The main works in the paper according the study problems are listed as follow:1) . The cyclic tests were carried out under diameters d = 3．91cm, d =6．18cm and d = 10．0cm respectively. The dynamic strength of different diameter samples was studied subjected to cyclic loading, the dynamic strength increased in different degree by the sample diameters. The dynamic strength of small sample couldn't reflect real strength of the sandy-gravel. Strength of the different diameter sample which influence by inverse-shear strength was studied, the result show the different exist in dynamic strength by the inverse-shear strength in varies degree. The dynamic shear stress ratio decrease when the diameter equals = 3．91cm, but the result of diameter d = 6．18cm sample increase.2) . The development of pore water pressure between different diameter samples under dynamic loading was studied. The sample diameter d= 3．91cm and d= 6．18cm with isotropic consolidation could be well fitted by the B type pore water pressure curve which put forward by Zhangjianmin. The development of pore water pressure of sample diameter d = 10．0cm could be fitted by hyperbolic. The rule of the pore water pressure of sample diameter d = 3．91cm with different anisotropic consolidation ratio could be fitted by hyperbolic and the rule of sample diameter d = 6．18cm could be fitted by a kind of arcsine function. The pore water pressure model of Guganchen was studied between different diameters, the results show that d = 6．18cm sample need more dynamic shear strengthen than d = 3．91cm sample when reach the same pore water pressure ratio under same virbration times.3) . The deformation properties between different sample diameters were studied. The characteristic during the deform process between different sample diameters was analyzed; the change rules of permanent strain potential were discussed, the results show that permanent strain potential of different sample diameters could be represented by a group of curves which defined by 8 parameters, parameter tables and the meaning of the parameters under two different pressure were provided. And permanence strain between different diameters was compared and analysed.The dynamic property of different diameter samples was compared by laboratory test. The results show that the dynamic strength of small diameter is lower than the real material, it is conservative to use to engineering design. The different of pore water pressure and deformation rules also exist; the results of the dynamic tests between different diameter samples could provide suggestion for the engineering practice.
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