Dynamic Characteristics Of Remolded Soil And Its Influence On Ground Motion

The ground will be shaken or changed by earthquake, and geological hazards are often caused by it. People’s life will be influenced seriously by its potential destructive power. In the early 20 t h century, the site conditions have significantly effect o n ground motion was found by domestic and foreign scholars. With the accumulation of seismic damage data and the deepening of theoretical study, the degree of seismic damage is closely related to the dynamic characteristics of soils is confirmed.The dynamic shear modulus and damping ratio of soils are basic soil parameters, they are sensitive parameters for the seismic response of soil layer and the site safety evaluation. At present, the study techniques of dynamic shear modulus and damping ratio of undisturbed soils are already mature, but the study on dynamic parameters of remolded soils is relatively less. This paper is combined with the site safety evaluation of actual projects, the dynamic parameters of clay、silty clay、silt and silty sand are measured by resonant column test. The dynamic characteristics and the seismic response of remolded soils and undisturbed soils are studied comparatively according to the results of test, the main conclusions are as follows:1) The remolded soils and undisturbed soils of clay、silty clay、silt and silty sand are measured by resonant column test. The differences between maximum dynamic shear modulus、the curves of dynamic shear modulus ratio and shear strain、the curves of damping ratio and shear strain of remolded soils and undisturbed soils are proposed. The discrete degree of relative differences of maximum dynamic shear modulus of silty clay are bigger than clay、silty and silty sand. Generally speaking, the differences are little among the four kinds of soils. The discrete degree of relative differences of dynamic shear modulus of clay are bigger than silty clay、silty and silty sand.2) The factors that affect the differences and similarities of dynamic parameters of remolded soils and undisturbed soils are analyzed. All of these factors, it’s harder to control the differences of the mineral composition、the structural and the size of sample. But the influences of the gradation、the experimental operation and the preparation of sample can be improved to reduce the differences of dynamic characteristics parameters of remolded soil and undisturbed soil in the future.3) The influence of consolidation time on the dynamic characteristics of remolded clay、silty clay、silt and silty sand are studied. The consolidation time have regular effect on the maximum dynamic shear modulus and the curves of dynamic shear modulus ratio and shear strain of remolded soils. The regularities show that the maximum dynamic shear modulus and dynamic shear modulus ratio are increase with consolidation time.4) Based on the seismic response calculation of three profile soil layers, the effects of dynamic shear modulus on the ground peak acceleration、the response spectrum of surface acceleration and the characteristic cycle of surface response spectrum are analyzed comparatively. The different nonlinear parts of dynamic shear modulus ratio will produce different results. The calculations of the average ground peak acceleration from undisturbed soils are greater than the results from remolded soils, and the calculations of the average characteristic period from undisturbed soils are less than the results from remolded soils. The relative differences of the ground motion parameters between remolded soils and undisturbed soils are changed with soil thickness and earthquake amplitude.