Stress Release–Induced Suction in Unsaturated MX80 Bentonite Pellet and Powder Mixtures
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 150, Issue 7
Abstract
In this study, a series of suction-control oedometer tests were conducted on unsaturated and saturated MX80 bentonite pellet/powder mixtures. The mixture samples were imposed with various suctions from 0 to 113 MPa under a low vertical stress (0.1 MPa). Then, the mixture samples were loaded in steps with controlled suction until reaching three different target stresses (0.1, 3.2, and 12.8 MPa) and instantaneously unloaded. The microstructure of unloaded samples was observed with mercury intrusion porosimetry (MIP) and microcomputed tomography (), together with the determination of suction, water content, void ratio, and saturation degree. Results showed that the water-retention behavior of bentonite pellet/powder mixture was rather characterized by pellets instead of powder. Due to the stress release, the measured suction after unloading was larger than the imposed suction . The suction difference between and depended on both suction and load. Under a given , the suction effect was characterized by an increase of when decreased from 113 to 4.2 MPa, but by a noticeable decrease of when further decreased to zero. This was found to be related to the changes of the slopes of soil-water retention curves (SWRCs): the slope was decreasing with suction increases after 4.2 MPa suction, but was increasing with suction increases before 4.2 MPa suction. As far as the stress effect was concerned, a larger was identified at a higher for a given . The narrowing difference between and the reduction of mean stress of pellet with increasing load was because of the decrease of larger pores due to loading. The total mixture void ratio was highly dependent on suction and vertical stress, whereas the total pellet void ratio was only dependent on suction in the stress range considered.
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Data Availability Statement
Some or all data, models, or code that support the findings of this study are available from the corresponding author upon reasonable request.
Acknowledgments
The authors would like to thank the China Scholarship Council (CSC). The support provided by Ecole des Ponts ParisTech (ENPC) and Institut de Radioprotection et de Sûreté Nucléaire (IRSN) are also greatly acknowledged.
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Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 150 • Issue 7 • July 2024
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© 2024 American Society of Civil Engineers.
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Received: May 8, 2023
Accepted: Jan 29, 2024
Published online: May 13, 2024
Published in print: Jul 1, 2024
Discussion open until: Oct 13, 2024
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