Identification Method of Dynamic Properties of Ground Based on the Seismic Observation Record

Abstract eng:
We expressed the average shear strain and stress of the target soil layer using observed absolute accelerations at upper and lower boundary surface in the target soil layer, and the Zeghal method was applied. We examined the applicability of the Modified Zeghal's method using analytical results from multiple reflection theory. In the low shear-strain domain, shear stiffness and damping ratios were widely distributed around the actual position. On the other hand, in the high shear-strain domain, the values were converged to target values. Then, We applied the method to observed seismic records. The identified values of shear stiffness showed good agreement with the result of dynamic tri-axial tests. The variation of the identified damping ratio was large, and the difference from the result of dynamic tri-axial tests was also large. But, the calculated resonant curve showed good agreement with the observed curves, when response analysis was performed using the identified damping ratio. Consequently, the identified damping ratio represents the behavior of the entire layered soil system. The larger identified damping ratio compared to the result of dynamic tri-axial tests suggests radiation and/or scattering damping or the existence of a sand-particle friction effect.

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