Experimental and Analytical Approaches on the Safety of Earth Structures in occasion to Earthquakes

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Earthquake resistant design plays an important role in case of maintaining the earth structures. In this research, we conducted the in-situ micro tremor measurements and the elastic wave ones on the Kojima Bay Reclamation Dike and the embankments of the repaired earth dams at Awaji Island, in order to obtain the first predominant frequencies, i.e., the characteristic values of the earth structures. Converting the observed time series to the spectral regions by FFT techniques in micro tremor measurements, we obtained the peak frequencies of the earth structures from H/V spectra and compared those with the estimated values from S-wave velocities obtained from the elastic wave measurements. Moreover, we measured the ground sites at Tarui town in Gifu Prefecture where the buried irrigation pipelines passed through. The results are summarized as follows :(1)At Kojima Bay Reclamation Dike, it is shown that the peak frequencies obtained from micro tremor measurements are about 10% less than t … More hose estimated from PS downhole measurements; it means there exists the weak deposits deeper than those conducted by PS measurements.(2)At Idenoshiri Reservoir which stands on the shallow valley, repairing with the soil-cement method on the base, the predominant frequency is about the same both obtained from H/V spectra and estimated from S-wave velocities which are obtained from the refraction method employing 1/4 wave length theory.(3)At Origatani Reservoir which stands on the deep valley, the predominant frequency obtained from micro tremor measurements is about 15% less than that from the refraction methods employing the wedge theory; it means there exists the weak deposits below the embankments.(4)At ground sites where the buried irrigation pipelines passed through, it has the same tendency to the predominant value above (1)(3).In conclusion, the predominant frequencies obtained from H/V spectra represent the characteristic values in ground-structure system, and it clarifies that there is a need to execute the earthquake response analyses including the surface soil layer on the rigid base. Less