Undrained triaxial compression tests on normally consolidated bentonite considering temperature/confining pressure dependency

Abstract

In the geological repository of high-level radioactive wastes (HLRW), one of the most important issues is the stability of artificial barrier basically using bentonite. However, due to the exist gaps between bentonite block and surround rock mass, the bentonite can swell relatively freely, whose constraining condition is quite different from the normal swelling pressure test. As an extreme case, the bentonite may engage completely into the surrounding ground and become a complete normal consolidated state. Therefore, in order to investigate the thermo-mechanical behavior of saturated bentonite at normally consolidated state, a newly proposed static compaction method for preparing specimen of saturated normally consolidated bentonite was proposed first. Then, a series of undrained triaxial compression tests were conducted under different confining pressure and temperature, by which the thermo-mechanical behavior of bentonite, used as an artificial barrier of geological repository of HLRW, is investigated systematically. The tests results reveal that the specimen prepared by the proposed method is confirmed to have sufficient saturation (> 0.92), meanwhile the prepared specimen is at slightly overconsolidated state that roughly equal to a K0-line consolidation. The deformation of the bentonite in undrained triaxial compression tests changes from plastic to brittle as the temperature increases. Simulation based on a sophisticated constitutive model considering water compressibility at high confining pressure was also discussed. The results are useful for assessing the mechanical behavior of bentonite after hundreds years of geological repository of HLRW.