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

抗震设计在维护土工结构中起着重要的作用。在本研究中，我们对小岛湾围垦堤坝和淡路岛修复土坝的堤坝进行了现场微动测量和弹性波测量，以获得第一卓越频率，即，地球结构的特征值。通过对实测时间序列进行FFT变换，得到了地震动的H/V谱，并与弹性波测量得到的S波速度估计值进行了比较。此外，我们还测量了岐阜县樽井镇地下灌溉管道穿过的地面。结果表明：（1）小岛湾围堤的脉动频率比实测值低10%左右， ...更多信息 这意味着存在比PS测量更深的弱沉积。(2)At位于浅谷上的井之尻水库，采用水泥土法对底座进行修复，根据H/V谱获得的卓越频率与根据采用1/4波长理论的折射法获得的S波速度估计的卓越频率大致相同。(3)At Origatani水库位于深谷上，其脉动测量结果比采用楔形理论的折射法测量结果的卓越频率低15%左右，说明水库下方存在软弱沉积物。(4)At结果表明，由H/V谱得到的结构-地基系统的卓越频率代表了结构-地基系统的特征值，说明在刚性基础上进行包括地表土层的地震反应分析是必要的。少

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