Procedure for evaluating seismic compression in sands based on R-N cumulative damage fatigue nonlinear model
The strain-controlled cyclic direct simple shear tests are conducted using step loading with drafted different loading sequences. Based on the R-N model and classic P-M model, the damage values of the soil materials are evaluated and compared with the test ones in order to verify the validity of R-N model. In view of the characters of R-N model which can reflect the influence of loading amplitude as well as loading sequence, the evaluating procedure for seismic compression in sands is derived according to R-N cumulative damage fatigue nonlinear theory. Using GCTS testing system, 404 groups of strain-controlled dynamic simple shear tests are carried out for the U. S. Filter clean sand. Considering the effects of loading amplitude, overburden pressure and relative density of sand, the parameters of the model are tested, and a regression model for parameters is established. Also 202 groups of strain-controlled dynamic simple shear tests using input real seismic loads with different properties are performed to determine the vertical deformations of sand samples due to seismic loading under different cases. Finally, both history curves and cumulative seismic compression values predicted by the proposed procedure are compared with those from tests for the purpose of verifying the validity.