報告書番号

U01037

タイトル（和文）

地震時液状化に伴う地盤流動による単杭の外力評価

タイトル（英文）

Evaluation on External Loads for Single Piles Subjected to Ground Flow Due to Soil Liquefaction during Earthquakes

概要 （図表や脚注は「報告書全文」に掲載しております）

単杭に作用する流動外力を評価することを目的として，振動台実験，簡易事例分析ならびに詳細事例分析などに基づいて検討した．振動台実験ならびに簡易事例分析結果より，非液状化層からの最大外力は，1)３次元的な地盤の崩壊領域を考慮した極限地盤反力で推定できること，2)フーチングが非液状化層に占める空間が大きい場合には２次元的な受働土圧にほぼ等しいこと，3)逆にフーチングが薄い場合等は３次元的な極限地盤反力に達すること，などを見出した．また，液状化層が比較的厚い場合の被災事例を詳細に分析した結果，地盤変位と土圧どちらの外力も，液状化層からの外力算定法として適用可能なことを明らかにした．さらに，地盤変位を外力とする場合の地盤ばねの低減率，土圧を外力とする場合の土圧係数，などについての目安値を提案した．

概要 （英文）

The present study deals with application of current procedures that specify design loads arising from liquefaction-induced lateral flow for single piles. For this purpose, the author conducted a shake table test, simplified and detailed case history studies. The shake table test results provides us an aspect in which external force from non-liquefiable layer resting on ground water table may be well represented with three dimensional ultimate soil reaction theory. The simplified case history study also enables us to realize the fact that estimated loads developed in non-liquefiable layers reach three dimensional ultimate soil reaction when footing slab thickness is relatively small in non-liquefiable layer, otherwise estimated loads are nearly equal to conventional two dimensional passive earth pressure. The detailed case history study, discussed on the damage case under relatively thick liquefiable layer, shows some unique findings for dealing external force in liquefiable layer. Both of displacement-based load as well as earth pressure-based load, essentially developed with viscous flow nature of liquefied soil, give a good estimation on the pile head residual displacement. This implies that these two manners regarding external loads in liquefiable are quite reasonable for engineering purpose. In addition, recommendations to specify soil spring degradation and earth pressure coefficient for displacement-based and earth pressure-based load methods, respectively, are presented.

報告者

キーワード