Elucidation of solar-induced thermal weathering process of rock using acoustic emission method

2020 Fiscal Year Final Research Report

• Project/Area Number: 18K01124
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 04010:Geography-related
• Research Institution: Nihon University
• Principal Investigator: WARAGAI Tetsuya 日本大学, 文理学部, 教授 (30201271)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: 熱風化 / 日射風化 / アコースティックエミッション / マイクロクラック / 熱破砕 / 熱サイクル / 岩石物性 / 温度勾配

Outline of Final Research Achievements

We experimentally investigated the fracture of rock specimens based on changes in pore-size distribution, P-wave velocity, and the occurrence of acoustic emission (AE). Three rock types which are often used as stone materials were used in the experiment. We repeatedly subjected the rock specimens to changes from 4℃ to 84℃ using a temperature-controlled chamber at a rate from ±4℃/min to ±0.5℃/min. Consequently, the P-wave velocity decreased by approximately 5%, 28%, and 2% for the granite, marble, and sandstone, respectively. Furthermore, the pore-size distribution changed by approximately 5-6% and 16% for the granite and marble, respectively. The variation in pore size of the sandstone was negligible. The occurrence of AE was detected in all rock types, but its amplitude for the granite was the largest, followed by the marble and sandstone, respectively. Therefore, a low-temperature thermal cycle causes thermo-mechanical fracture inside rocks.

Free Research Field

地形学

Academic Significance and Societal Importance of the Research Achievements

日射や熱による岩石の破砕機構は，地形学における重要課題のひとつであるが，十分な解明は進んでいない。本研究が岩石内部における弾性波の発生を実験的に捉えたことは，加熱―冷却の繰り返しに伴う微小な亀裂の形成やその伸展が熱による岩石破砕のきっかけになることを示唆する。実験に用いた３種類の岩石は，文化財の建築石材として多用されている。このため本研究の成果は，石造文化財の劣化や保全の対策を検討するうえで有効な基礎資料となるであろう。