報告書番号

U98053

タイトル（和文）

事例調査に基づく砂礫地盤の液状化発生条件の検討

タイトル（英文）

Evaluation of liquefaction potential of gravelly soil layer based on field performance data

概要 （図表や脚注は「報告書全文」に掲載しております）

原子力発電所の新立地技術の一つである第四紀地盤立地では，洪積砂礫地盤が炉心建屋の支持地盤として有望な候補のひとつである．従って，地震時に液状化しないことが必要条件の一つである．一方，最近では考古学的な発掘調査の際に砂礫が液状化した事例がいくつか発見されている．また，1995年兵庫県南部地震においても砂礫地盤が液状化した事例がある．これらの事例は，ほとんどが沖積砂礫地盤や埋戻し砂礫地盤であるが，洪積砂礫地盤が液状化した可能性が指摘されている事例もある．そこでまず，洪積砂礫地盤で液状化が発生した可能性が指摘されている地点において詳細な地盤調査実施した．その結果，自然堆積した砂礫層が液状化した証拠は得られなかった．次に過去に大きな地震動を受けた砂礫地盤の液状化強度を当所の提案式に基づいて評価し，液状化判定を行った．その判定結果と液状化発生の有無は良く対応していた．

概要 （英文）

The Quaternary ground siting is one of a new siting type of nuclear power plants in Japan. Diluvial gravelly ground is considered to be one of the sufficient bearing strata for nuclear power plants. Therefore, it is necessary for diluvial gravelly ground not to liquefy during earthquakes. However, traces of liquefaction which occurred in gravelly soil layers are discovered by archaeological excavation conducted recently. Furthermore, some gravelly ground liquefied during 1995 Hyogoken-Nambu Earthquake. All most all the gravelly soil layer which liquefied are alluvial deposits or reclaimed deposits, whereas only one diluvial gravelly soil layer might have liquefied during a strong earthquake. Firstly, detailed site investigation was conducted at the site where a diluvial gravelly soil layer might have liquefied during a strong earthquake. As a result, no evidence showing that the gravelly soil layer at the site had liquefied was found. Secondly, liquefaction assessment was conducted for the gravelly ground which experienced large earthquakes using the equation proposed by CRIEPI by which liquefaction strength could be evaluated. As a result, the results of the assessment were consistent with field performance data of the ground during earthquakes.

報告者

キーワード