地震時の地下RC構造物の有効応力解析

Abstract

地下構造物の地震時挙動を，多重せん断機構に基づく砂の力学モデルに基づいて有効応力解析した。解析対象は，矩形断面の鉄筋コンクリート製（RC）が飽和および乾燥地盤の基盤に埋設されたもので，30g場での遠心実験に基づく。地震動加振の結果，RC構造物の側壁に作用する土圧は加振とともに増加し，RC構造物の側壁は降伏に至った。有効応力解析の結果は，RC構造物の地震時挙動をよく説明するものとなった。

Effective stress analyses are performed on seismic response of underground structures subjected to strong earthquake motions. The model of sand used for the analysis is based on the multiple shear mechanism. The seismic response data analyzed are based on the 30g centrifuge tests of an underground reinforced concrete (RC) box culvert, 9 m high and 12 m wide, buried at the bottom of saturated and dry model ground 16 m deep in prototype scale. Subject to a strong earthquake motion with a peak acceleration of 0.8 to 0.9g in prototype scale, earth pressures acting on the sidewalls of the RC structure increased after shaking in both saturated and dry model grounds. These earth pressures together with the effect of the lateral displacement due to shaking result in yielding of the side RC walls. The portion of the RC walls that are put into yielding is larger in saturated model ground than in dry model ground. The effective stress analyses are capable of capturing the essential features of the response of underground structures.