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Laboratory geophysical observation of grain compression and crushing in synthetic fault gouges

Amin Gheibi, & Ahmadreza Hedayat

Published August 11, 2017, SCEC Contribution #7513, 2017 SCEC Annual Meeting Poster #190 (PDF)

Poster Image: 
Active geophysical monitoring techniques are among the most powerful techniques to identify changes in soil fabric, grain to grain contact network, compressional strength, and void ratio in granular materials. We present experimental results in order to describe the relationship between ultrasonic wave properties and particle scale processes occurring during compression of sandy fault gouges including particles rearrangements, particles elastic deformation, and grain crushing. The test setup in this study incorporated a loading machine to apply constant loading rate to a quartz sand layer of 6 mm thickness sandwiched between two forcing blocks, and a novel ultrasonic wave measurement system to continuously monitor the soil layer during compression up to 48 MPa normal stress. An increasing trend is observed for P-wave velocity, transmitted amplitude and dominant frequency with normal stress. Obtained values for transmitted amplitude and dominant frequency of waves are greater for specimens with smaller particles while the normalized values show an opposite trend. Transmitted amplitude changes are linked to the changes in the true contact area between the particles with a transitional point in the slope of normalized amplitude, coinciding with the yield stress of the gouge layer. Dominant frequency variations and amount of grain crushing with different levels of normal stress are measured and a linear correlation is found between the variations in the normalized dominant frequency and the amount of particle crushing. This research contributes to better understanding of fault gouge deformation and crushing when subjected to high levels of normal stress.

Key Words
geophysical imaging of grain compression, grain crushing, synthetic gouge

Citation
Gheibi, A., & Hedayat, A. (2017, 08). Laboratory geophysical observation of grain compression and crushing in synthetic fault gouges. Poster Presentation at 2017 SCEC Annual Meeting.


Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)