Climatic influence on the formation of weathering substances as possible slope failure materials

2023 Fiscal Year Final Research Report

• Project/Area Number: 21K04605
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 25030:Disaster prevention engineering-related
• Research Institution: Saitama University
• Principal Investigator: Oguchi Chiaki 埼玉大学, 理工学研究科, 准教授 (20312803)
• Co-Investigator(Kenkyū-buntansha): 若月 強 国立研究開発法人防災科学技術研究所, 水・土砂防災研究部門, 主任研究員 (80510784)
• Project Period (FY): 2021-04-01 – 2024-03-31
• Keywords: 崩壊予備物質 / 花こう岩 / 斜面災害 / 風化指標 / GIS

Outline of Final Research Achievements

The rock properties of basement rocks and weathered materials in several granitic zones were studied with the aim of systematising the relationship between the sequence of material changes - basement rock - weathering - collapse - and climatic conditions. Weathering indices were calculated from the physical properties obtained, and the characteristics of the weakened soil layers were shown in terms of the degree of weathering, as well as the relationship with the average annual temperature in each region. The results showed that the same granite weathered more in warmer regions, producing more fine-grained materials such as clay and reducing hydraulic conductivity. In terms of collapse rates and topographical characteristics such as slope gradient, the study showed that the highest collapse rates occurred at slope gradients of 30-35 degrees in Hiroshima (2014 disaster) and 45-50 degrees in Ishigaki-jima Island (2010 disaster).

Free Research Field

岩石風化論、地形材料学

Academic Significance and Societal Importance of the Research Achievements

本研究では、複数の気候下に置かれた花こう岩類を対象として、風化変質の状況とその生産物質である粘土や砂などの土層すなわち崩壊予備物質の物性の双方を比較考察した。このような崩壊予備物質の生成過程にまで言及した崩壊現象の研究例は僅少である。実際問題として、崩壊が発生した現地から土砂を採取して、毎回、綿密な化学分析を行うことは困難を極める。よって、崩壊予備物質の風化程度や透水係数の地域性に関する知見を得ておくことは、今後の温暖化に伴う崩壊予備物質の物性変化の推察に役立ち、その地域で発生し得る崩壊の特徴の変化を予測するための材料の一つになると考える。