報告書番号

N04041

タイトル（和文）

地震観測記録に基づく地震動の減衰特性 -硬岩地盤における減衰定数の同定と地盤安定性評価に及ぼす影響-

タイトル（英文）

Attenuation characteristics of seismic motion based on earthquake observation records-Identification of damping factor at hard rock sites and its influences on ground stability evaluation-

概要 （図表や脚注は「報告書全文」に掲載しております）

地盤安定性評価における減衰定数の慣用値の妥当性を検証するために，既設の硬岩地盤サイトにおける慣用値を調査した．その結果，調査対象の80%で3%が用いられていることが分かった．次に，焼きなまし法によるスペクトル比の逆解析手法により減衰定数の下限値を考慮できる同定手法を提案し，硬岩地盤サイトでの地震観測データに適用した．これにより，硬岩地盤における内部減衰は，深さ100m以浅で3%から6%程度，深さ100m以深で0.3%から１%程度であり，慣用値は深さ100m以浅の岩盤の内部減衰を意味することが明らかとなった．また散乱減衰については，浅部では周波数の-1.0乗に比例し，深部ではおよそ1.0～5.0Hzにピークが存在することを示した．最後に，減衰定数がすべり安全率に及ぼす影響を検討した結果，減衰定数のすべり安全率への影響は小さく，硬岩地盤での慣用値による地盤安定性評価は妥当であることが分かった．

概要 （英文）

In this report, we examined validity of currently available ground stability evaluation method by applying commonly used damping factor which was invariant for frequency. First, we conducted a survey of the actual conditions of damping factors, which were used in ground stability evaluation, on 10 existing nuclear power plants. As a result, we found that damping factor of 0.03(3%) was used in of 80 percent investigated plants. Next, a spectral inversion method using very fast simulated annealing was proposed for identifying damping factor and its lower limit. Here, the lower limit of damping factor means intrinsic damping factor. The developed inversion method was applied to borehole array data recorded at hard rock ground. From the inversion, it was found that intrinsic damping factor of hard rock ground distributed between about 0.03(3%) and 0.06(3%) at a depth of less than 100m, and between about 0.003(0.3%) and 0.01(1%) at a depth of more than 100m. Furthermore, we indicated that scattering damping factor with in a depth of less than 100m was in proportion to the almost -1.0 power of the frequency, and the factor in a depth of more than 100m had a peak in a frequency range from about 1.0 to 5.0Hz. Therefore, it was recognized that commonly used damping of 0.03(3%) expressed intrinsic damping factor of shallower hard rock ground. Finally, we estimated the influences of damping factor on ground stability evaluation by 2D dynamic FEM analyses of hard rock foundation ground considering 8 slipping lines using 6 combinations of damping factor. It was demonstrated that the variation of damping factor was not so decisive on the results of ground stability evaluation. This suggests present ground stability evaluation method by applying commonly used damping factor is reasonable for hard rock sites.

報告者

キーワード