Investigation on unsaturated critical state and Hvorslev surface of compacted bentonite under high suction conditions

In high-level radioactive waste repositories, compacted bentonite used as buffer/backfill materials should have enough strength and stiffness to enhance the stability of the repository and to protect the waste canisters from the surrounding rock. Therefore, it is essential to understand the strength and deformation behavior of compacted bentonite. In this paper, isotropic loading tests and triaxial shear tests were carried out on unsaturated compacted GMZ bentonite. With the results of compaction and isotropic consolidation tests, the compressibility and yield behavior under isotropic condition were investigated. Based on the results of triaxial shear tests, the stress-strain relationships and dilatancy were analyzed. The overconsolidation ratios for all the specimens were determined. For normal consolidated and lightly overconsolidated soils, existence of a critical state on the compacted GMZ bentonite was confirmed. The evolution of the critical state stress ratio with change of confining pressure was analyzed. For highly overconsolidated soils, the peak strength lies above the CSL. In this regard, the Hvorslev Surface was introduced and related parameters were determined for describing the peak strength of unsaturated highly overconsolidated GMZ bentonite. •Compaction, isotropic loading and constant water content shear tests were conducted on GMZ bentonite.•The compressibility and yield behavior under isotropic loading were investigated.•The stress-strain relationships and dilatancy were analyzed.•The evolution of the critical state stress ratio with changing of confining pressure was analyzed.•Hvorslev Surface was introduced for describing the peak strength of unsaturated overconsolidated GMZ bentonite.