Development of evaluation method of aging and reliquefaction for liquefied ground considering sand particle's orientation

2023 Fiscal Year Final Research Report

• Project/Area Number: 21H01425
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 22030:Geotechnical engineering-related
• Research Institution: Nagaoka University of Technology
• Principal Investigator: Toyota Hirofumi 長岡技術科学大学, 工学研究科, 教授 (90272864)
• Co-Investigator(Kenkyū-buntansha): 風間 基樹 東北大学, 工学研究科, 教授 (20261597) ; 杉本 光隆 長岡技術科学大学, 工学研究科, 教授 (50196755)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 液状化 / 年代効果 / せん断剛性率 / 三軸試験 / 振動台試験 / サンプリング

Outline of Final Research Achievements

Liquefaction resistance was investigated from the viewpoint of particle orientation to clarify the mechanism of reliquefaction strength. In the shaking table test, the liquefaction resistance was smallest at a particle orientation of 90 degrees and largest at 0 degrees. Moreover, the particle orientation tends to change 90 degrees in original 0 degrees deposition after the liquefaction. In addition, the particle orientation was measured using the undisturbed samples extracted from the Shinano riverbed in Chuo-ku, Niigata City. The particle orientation of the liquefied layers tended to be concentrated in 90 degree-direction, which was generally consistent with the results of the shake table tests. Those results indicate that liquefaction history generates the change of particle orientation. Consequently, the ground changes to be vulnerable to liquefaction, indicating week sedimentary structure against liquefaction.

Free Research Field

地盤工学

Academic Significance and Societal Importance of the Research Achievements

一度液状化した緩い砂地盤は，その後，排水を伴って密になる．したがって，液状化した地盤は，液状化しにくくなると考えられる．しかし，実際には，過去に液状化した地盤が再液状化した事例が数多く報告されている．この再液状化のメカニズムを解明するため，粒子配向性に着目した研究を行った．その結果，液状化履歴によって粒子配向性が変化し，飽和砂地盤は液状化に対し，脆弱な堆積構造へ変化することが示された．今後，液状化履歴を有する地盤に対しては，その液状化強度を低く設定するなどの措置が必要であることがわかった．