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Abstract Based on a series of plane strain cyclic tests on air-dried Toyoura sand，the viscous properties of sand under loading-unloading conditions are presented. Comparisons are made on the stress-strain relationships of two sets of tests using different strain loading rates. Creep stages are also performed during the tests. Special attentions are paid to the viscous behavior of sand during unloading. The tests reveal that the viscous behaviors of sand are deeply related to the strain loading rate as well as the stress level. The viscous behaviors of sand caused by the viscosity of loading will be weakened with the increased of load and strain. Furthermore it is found during the unloading test，the vertical strain of sand continues to grow for a certain period of time even when the unloading has already begun. The behavior of creep recovery is also observed during unloading. Based on the general framework of the three-component model，the temporary effects of strain rate and acceleration (TESRA) model is put forward and modified for the simulation of viscous behaviors of sand during loading-unloading. The detailed formulation and controlling parameter are presented，enabling the implementation of a reasonable numerical simulation. Applying this model，simulation is conducted on the primary loading-unloading stage of sand in the plane strain tests. The stress-strain relations as well as the time history of strain are obtained. Through comparisons between the results from test measurement and numerical simulation outputs，the TESRA model is proved both effective and precise for simulating the viscous behaviors of sand during loading-unloading.
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2011, Vol. 30 
