FREQUENCY CONTENT EFFECTS ON DYNAMIC BEHAVIOR OF REINFORCED SILTY SANDS USING IMPROVED TRANSFER FUNCTION METHODS

摘要

Little is known about the dynamic behavior of reinforced soils under random excitation conditions. Yet this situation exists when geosynthetically reinforced soils are constructed to strengthen soil conditions during earthquakes. In this study, the effect of frequency content of random torsional excitation on the dynamic soil properties of geosynthetically reinforced silty sands are investigated in the laboratory using a torsional resonant column apparatus. An experimental program was undertaken where both random and sinusoidal torsional vibrations were applied. Improved estimators of the transfer function (H2, H3, H4), in addition to the conventional estimator (H1), were used to estimate the dynamic soil properties and to study the effect of frequency content on the shear moduli and damping of silty sands. Cut-off frequencies in the range of 50 Hz to 10000 Hz were considered using a band pass filter. The silt content ranged from 0 to 40 percent. In this project, geotextile layers consisting of nonwoven, staple, needle punched polypropylene with high tensile strength and puncture resistance were used to reinforce the soil. The results indicate that no correction to the shear moduli of silty sands obtained during random loading using the conventional transfer function estimator is needed. On the other hand, the damping values, particularly at high frequency contents, may have to be corrected to obtain values that are more representative of actual field conditions during earthquakes.