Study on a rational liquefaction determination method considering the influence of seismic waveforms

• Project/Area Number: 19K15091
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 22030:Geotechnical engineering-related
• Research Institution: Tokyo Denki University
• Principal Investigator: Ishikawa Keisuke 東京電機大学, 理工学部, 准教授 (00615057)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Project Status: Completed (Fiscal Year 2022)
• Budget Amount: ¥4,030,000 (Direct Cost: ¥3,100,000、Indirect Cost: ¥930,000); Fiscal Year 2021: ¥520,000 (Direct Cost: ¥400,000、Indirect Cost: ¥120,000); Fiscal Year 2020: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000); Fiscal Year 2019: ¥2,080,000 (Direct Cost: ¥1,600,000、Indirect Cost: ¥480,000)
• Keywords: 液状化 / 液状化判定 / 室内土質試験 / 繰返しねじりせん断試験 / 地震波形 / 液状化強度 / 地震波 / 不規則性 / 消散エネルギー / 地盤防災 / 地盤の挙動 / 地震動特性 / 損失エネルギー

Outline of Research at the Start

本研究で対象とした力の釣合に基づく液状化判定方法は，1964年の新潟地震やアラスカ地震を契機に国内外において研究され，1978年に液状化判定方法として確立された．その後，兵庫県南部地震後にレベル2地震動についての見直し，東日本大震災後に設計水平震度や液状化強度比の推定方法の一部が見直された．しかし，地震動特性による補正係数の見直しは行われていない．
本研究は，現行液状化判定方法の高度化を目指し，巨大海溝型地震が液状化強度に及ぼす影響に関して実験的に解明し，地震波荷重のランダム性に関する補正係数を定量的に立証する．また，エネルギー的な解釈や累積損傷度理論とも比較し，同指標の妥当性も評価する．

Outline of Final Research Achievements

The 2011 Great East Japan Earthquake and the 2016 Kumamoto Earthquake resulted in liquefaction-induced disasters. Additionally, there are concerns regarding the potential occurrence of devastating earthquakes with high magnitudes in the Nankai Trough and directly beneath the Tokyo metropolitan area. To effectively prepare for such seismic events, accurate and reliable liquefaction prediction is crucial, considering the specific characteristics of seismic waveforms, such as their amplitudes and frequencies. In this study, cyclic torsional shear tests were conducted to examine the characteristics of liquefaction in sandy soil under various seismic waveforms, assessing the influence of these waveforms on the soil's susceptibility to liquefaction.

Academic Significance and Societal Importance of the Research Achievements

地震波形の形状が液状化強度に及ぼす影響を定量的に定めた．そして現行の液状化判定手法との定量的な違いを示し，合理的な液状化判定の方法を提示したことは社会的意義が大きい．また，一連の実験を通じて不規則な地震動下での砂質土の液状化過程を考察したところ，地震波形の繰返し波数が多い場合はより液状化し易い波形特性であることを実験的に解明したことは学術的に新たな知見が得られて意義は大きい．

Research Products

• [Presentation] Effect of irregular waves on liquefaction strength of sandy soil (2022)
  • Author(s): Keisuke Ishikawa
  • Organizer: 3rd European Conference on Earthquake Engineering & Seismology
  • Int'l Joint Research
• [Presentation] Liquefaction characteristics of sand due to various irregular waves by cyclic torsional shear test (2022)
  • Author(s): Keisuke Ishikawa
  • Organizer: 20th International Conference on Soil Mechanics and Geotechnical Engineering
  • Int'l Joint Research
• [Presentation] 砂質土の液状化強度比及ぼす不規則波の影響 (2022)
  • Author(s): 石川敬祐
  • Organizer: 第57回地盤工学研究発表会
• [Presentation] 砂質土の液状化強度比に及ぼす不規則波の影響 (2022)
  • Author(s): 石川敬祐
  • Organizer: 第57回地盤工学研究発表会
• [Presentation] Liquefaction characteristics of sand due to various irregular waves by cyclic torsional shear test (2022)
  • Author(s): 石川敬祐
  • Organizer: 20th International Conference on Soil Mechanics and Geotechnical Engineering
  • Int'l Joint Research
• [Presentation] Effect of irregular waves on liquefaction strength of sandy soil (2022)
  • Author(s): 石川敬祐
  • Organizer: 3rd European Conference on Earthquake Engineering & Seismology
  • Int'l Joint Research
• [Presentation] 密度条件を変化させた種々な不規則波による砂の液状化特性 (2021)
  • Author(s): 及川晃介
  • Organizer: 第18回地盤工学会関東支部発表会
• [Presentation] 東日本大震災の観測地震動による等価繰返し回数の特徴 (2021)
  • Author(s): 石川敬祐
  • Organizer: 第56回地盤工学研究発表会
• [Presentation] 繰返しねじりせん断試験による種々な不規則波による砂の液状化特性 (2020)
  • Author(s): 石川敬祐・安田進
  • Organizer: 第55回地盤工学研究発表会