2019 Fiscal Year Final Research Report

Estimation method for validation of liquefaction strength considering aging effects and its verification tests

Research Project

PDF

Project/Area Number	17H03302
Research Category	Grant-in-Aid for Scientific Research (B)
Allocation Type	Single-year Grants
Section	一般
Research Field	Geotechnical engineering
Research Institution	Nagaoka University of Technology
Principal Investigator	Toyota Hirofumi 長岡技術科学大学, 工学研究科, 准教授 (90272864)
Co-Investigator(Kenkyū-buntansha)	杉本光隆長岡技術科学大学, 工学研究科, 教授 (50196755) 原忠高知大学, 教育研究部自然科学系理工学部門, 教授 (80407874)
Project Period (FY)	2017-04-01 – 2020-03-31
Keywords	液状化 / 年代効果 / せん断波速度 / 三軸試験 / 砂質土 / 原位置試験
Outline of Final Research Achievements	It has been well known that liquefaction potential of the ground is increased with an increase of construction or sedimentation ages. However, the mechanism of this aging effect on liquefaction has not been elucidated. To clarify the mechanism of aging effect in sand, liquefaction resistance, secant shear modulus including G0 and penetration resistance of long-term consolidated sand were respectively measured using undrained cyclic triaxial test, local small strain (LSS) test, bender element (BE) test and static penetration test. Liquefaction resistances obtained from the triaxial test and the static penetration test were respectively increased by about 15% and 7% in one year consolidated specimen. However, G0 was scarcely changed with the consolidation time. The difference is that elastic strain region, where linear elastic behavior was exhibited, tend to extend to larger strain for long-term consolidated specimen.
Free Research Field	地盤工学
Academic Significance and Societal Importance of the Research Achievements	液状化抵抗が圧密時間とともに増加するメカニズムについて，力学特性の変化に着目して研究を行った．その結果，初期せん断剛性率や貫入抵抗（せん断強さと関係）についての変化は小さく，主に線形弾性を示すひずみ領域が拡大することによって，液状化抵抗が増加することを明らかにした．つまり，実際の地盤の年代効果を考慮した液状化抵抗の変化を評価するためには，地盤のせん断弾性波や貫入抵抗値を測定するだけでは不十分で，弾性ひずみ領域の拡大を推定する必要がある．しかしながら，これは難しいため，初期せん断剛性率ではなく，ダイラトメータ等により，もう少しひずみの大きいところの割線せん断剛性率を測定する方法が推奨される．