報告書番号

U02008

タイトル（和文）

せん断弾性係数による砂礫の非排水繰返し強度評価

タイトル（英文）

Evaluation of undrained cyclic strength of gravelly soil by shear modulus

概要 （図表や脚注は「報告書全文」に掲載しております）

貫入試験においては，大きな礫の存在が貫入抵抗値を過大に評価する場合がある．従って，この場合には礫地盤の非排水繰返し強度は過大評価される．そこで，本研究では貫入抵抗値に代わる新たな指標としてせん断弾性係数に着目し，せん断弾性係数から砂礫地盤の非排水繰返し強度を推定する方法について検討した．その結果，比較的大きいひずみにおける砂礫のせん断弾性係数は，非排水繰返し強度と密接に関係し，その関係は，有効拘束圧，粒度分布によらず，また供試体が不撹乱試料か否かに依らないことがわかった．また，ひずみの増大に伴ってせん断弾性係数が低下する割合を不撹乱試料と詰直し試料で比較し，その結果を不撹乱試料の初期せん断弾性係数で整理した．更に，これらの結果に基づき，初期せん断弾性係数と撹乱試料に対する繰返し変形試験結果から原位置の非排水繰返し強度を推定する方法を提案した．

概要 （英文）

Relationships between undrained cyclic strengths and shear moduli were investigated on intact samples of gravelly soils obtained by in-situ freeze sampling and on their reconstituted samples. The possibility of evaluating undrained cyclic strength of natural gravelly deposits using shear moduli was investigated. Through this study, the following conclusions are drawn. 1) It was found that cyclic shear moduli at relatively large strain amplitude were closely related with undrained cyclic strengths, irrespective of the effective confining pressure, grain size distributions and whether or not the samples are intact, whereas there seems no unique relationship between initial shear moduli and undrained cyclic strengths.2) It was found that shear modulus ratio of a intact sample can be approximated by that of the reconsitited sample depending on the initial shear modulus of the intact sample. Based on this fact and the relationship mentioned in 1), a procedure to evaluate undrained cyclic strength of gravelly soil by initial shear modulus of the ground and shear modulus of the disturbed sample was proposed.3) It was revealed that reduction in shear modulus with increase in shear strain is closely related to void ratio. Based on this fact and the relationship mentioned in 1), a simplified procedure to evaluate undrained cyclic strength of gravelly soil by initial shear modulus and void ratio of the ground was proposed.

報告者

キーワード