報告書番号

N05037

タイトル（和文）

滑動変形量を考慮したフィルダムの地震リスク評価

タイトル（英文）

Seismic Risk Assessment of Fill Dams Considering Earthquake-induced Sliding Deformation

概要 （図表や脚注は「報告書全文」に掲載しております）

本報研究では，フィルダムの地震に対する信頼性評価法として地震時変形を考慮したフラジリティー（損傷確率）評価手法を提案するとともに，提案手法を用いた地震リスク評価を行った。検討結果は以下のようにまとめられる。(1) Newmark法による滑動解析結果に基づくすべり土塊の変位量を指標としたフィルダムのフラジリティー(PGAを与条件とした損傷確率)の評価手法を提案した。解析モデルは実ダムの法面勾配，設計震度，法面勾配，堤体材料の強度定数を用いて設定している。(2)想定した地震ハザードとフラジリティー評価の結果から，フィルダムの，年損傷確率（地震リスク）の試評価を行った。この結果，従来の震度法で設計されたフィルダムの地震リスクは，滑動変形を許容した場合には10-5のオーダーとなり，リスクレベルとしては低いものであるとの結果が得られている。

概要 （英文）

In Japan, after the 1995 Kobe earthquake, revision works for various seismic design codes started and are mostly completed. Many of the revised codes introduce the concept of seismic performance check for "Level 2 earthquake ground motion", where deformation of structures due to earthquake is required to be evaluated. And attention to seismic risk assessment is increasing in which uncertain factors including occurrence probability of earthquake are taken into account and the risk is evaluated quantitatively. In this report methodology on seismic risk evaluation of fills dams are proposed, where sliding displacement of the soil mass along failure surface is considered with Newmark sliding block model. The feature of this study is probabilistic evaluation of the risk, and variabilities of sliding displacement due to randomnesses of earthquake ground motion, uncertainties of response characteristics of the dam and the friction of sliding block are considered. Each of these effects is evaluated based on Monte Carlo Simulations. Earthquake ground motions used are simulated ones from the sets of magnitude and hypocentral distance assuming uniform areal earthquake source model. Fragility is evaluated as the probability of exceeding allowable displacement of the sliding mass related to the allowable settlement of the dam crest. Fragilities are evaluated for various types of fill dams with different design seismic load, material strength and the gradient of the slope. With these fragilities and the seismic hazard evaluated from the areal source model, annual probabilities of failure of the fill dams are calculated. The result shows that considering allowable displacement, the risk level of existing fill dams designed by conventional design code is the order of 10-5 and comparable with or less than other important civil engineering structures.

報告者

キーワード