[H-DS08] Landslides and related phenomena

[HDS08-P13] Exploring Shear Strength Weakening Mechanisms: Insights from Microscopic Structures of Experimental Shear Surface

*Shengshan WU¹, Gonghui Wang² (1.Kyoto University, 2.Disaster Prevention Research Institute, Kyoto University, Kyoto, Japan)

Keywords:Rock avalanches, High mobility, Nanomaterials, Ring shear test, Microscopic Structures

The hypermobility of rock avalanches remains a prominent subject of research in geological disasters. Distinguished by their large volume, unexpected slide velocity, and long runout, rock avalanches result in greater damage. Recently, nanoparticles (with particle diameters ranging from 1 to 100 nanometers) were found in rock avalanches and natural faults. Much research supported that the nanoparticles may play a crucial role in reducingshear resistance along the shear surface, thereby attracting considerable attention. However, the mechanism of shear strength weakening resulting from nanoparticles is unclear. To address this question, a series of ring shear tests were conducted on Silicon dioxide nanoparticles (SN) to check their mechanical effect under different normal stress and shear velocities. The findings reveal that the shear resistance of SN exhibits high and stable at lower normal stress levels but diminishes significantly with increasing normal stress. Interestingly, the shear strength of SN does not present a significant change with the shear velocity, even through the shear velocity reaches approximately 2.1 m/s. Furthermore, microscopic analysis of the experimental shear surface indicates the formation of some powder rolls during shearing, particularly under high normal stress (619 and 1000 kPa in this study). It is inffered that these powder rolls may play a key role in reducing nanometer shear strength by facilitating a transition in particle movement mode from sliding to rolling.