報告書番号

N08029

タイトル（和文）

原子力発電所建屋近傍埋戻し地盤の沈下メカニズムの解明（その2）－遠心力模型実験ならびにFEM地震応答解析による検討－

タイトル（英文）

Settlement mechanism of the backfilled ground around nuclear power plant buildings (Part II)-A series of centrifuge tests and a numerical simulation by using FEM about a typical test result-

概要 （図表や脚注は「報告書全文」に掲載しております）

2007年新潟県中越沖地震により，東京電力柏崎刈羽原子力発電所敷地内では，原子力発電所建屋近傍の埋戻し地盤で局所的に大きな沈下が生じた．この沈下について，地震発生直後に実施された現地調査では，原子力発電所建屋と周囲地盤の相対変位に起因する主働すべりが原因と推測されており，これまでに1G場模型振動台実験によってそのメカニズムが確認されている．本報告では，地盤の沈下量を定量的に評価する手法を提案し，その検証を目的として，地盤内の応力状態を実物に近づけた状態で原子力発電所建屋近傍地盤で生じた沈下現象を再現する，遠心力模型実験を実施した．その結果，地盤のダイレイタンシーによって生じている一般部地盤の沈下は，不規則波による中空ねじり試験で得られる体積ひずみと地盤層厚を乗じることで概略の沈下量評価が実施できること，主働すべりにより発生している構造物近傍地盤の沈下は，すべり土塊に作用する重力加速度と地盤のすべり抵抗ならびに地盤が構造物から剥離する時間によって概ね予測可能であることを確認した．

概要 （英文）

During the Niigataken Chuetsu-oki earthquake, rather large settlements of the backfill ground around the rigid and stable buildings were observed. In this study, five cases of centrifuge tests with shaking events were conducted to reproduce the similar type of the settlements in order to examine the mechanism of the settlements. The results from those tests showed that the ground was settled by the negative dilatancy of sandy soils anywhere in the model ground and the additional settlements were suddenly caused when the backfill ground was apart from the rigid wall modeling the rigid and stable buildings, namely a sliding failure in an active state was occurred in the backfill ground near the structure. It was confirmed that these settlements were able to be estimated by a simple method proposed in this report, in which only the differences between the self-weight of the sliding block and the soil strength calculated at the initial stress conditions were considered as the driving forces of the sliding failure, and then the accelerations calculated from the forces being divided by the mass of the sliding block were simply integrated two times with respected to the time when the ground was apart from the structure. Further, a numerical simulation by using FEM about a typical test result was conducted, and these settlements were well simulated.

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