Mechanism of long-term strength change of cement-improved soil due to water flow

2023 Fiscal Year Final Research Report

• Project/Area Number: 22K20456
• Research Category: Grant-in-Aid for Research Activity Start-up
• Allocation Type: Multi-year Fund
• Review Section: 0303:Civil engineering, social systems engineering, safety engineering, disaster prevention engineering, and related fields
• Research Institution: National Institute of Maritime, Port and Aviation Technology
• Principal Investigator: Sato Itsuki 国立研究開発法人海上・港湾・航空技術研究所, 港湾空港技術研究所, 研究官 (20965628)
• Project Period (FY): 2022-08-31 – 2024-03-31
• Keywords: セメント固化処理土 / 地盤改良

Outline of Final Research Achievements

This study aimed to elucidate the long-term degradation mechanisms of cement-solidified soil, focusing on accelerated alteration and seawater exposure experiments using a newly developed pressurized water permeability testing apparatus. Key findings include the development of a new apparatus capable of testing 30 specimens simultaneously under a water pressure of 200 kPa, identification of a decrease in the permeability coefficient of cement-solidified soil due to water permeation, and discovery of a positive correlation between calcium leaching and strength reduction. Further, it was observed that cement-solidified soil degrades faster in seawater than in freshwater. The study also proposes a formula to represent the degradation due to water exposure, modeled as a curved surface defined by distance from the exposure surface, time, and strength.

Free Research Field

地盤工学

Academic Significance and Societal Importance of the Research Achievements

土木工事において，軟弱な地盤の性状を改良することは構造物の安定化を図る為に非常に重要であり，この目的で最も広く用いられている工法の1つが，土にセメント等の固化材を混ぜて土を強化する地盤改良工法である。これらの基礎技術開発はすでに進んでいる一方で，酸性雨，地下水，海水等の作用がセメント固化処理土の長期的な安定性に与える影響は十分に解明されていない。そのため設計，施工及び維持管理における技術的配慮事項が不明瞭なまま，暗黙知に支えられているのが現状である。その長期的な劣化機構が明らかとなれば，様々な土木構造物の長期的な維持管理の品質向上が期待できる．本研究は，その一助となるものである．