(1. Sino-French Joint Research Center of Rock and Soil Mechanics and Concrete Materials，Hubei University of Technology，Wuhan，Hubei 430071，China；2. State Key Laboratory of Geomechanics and Geotechnical Engineering，Institute of Rock and Soil Mechanics，Chinese Academy of Sciences，Wuhan，Hubei 430071，China；3. Laboratory of Mechanics of Lille，University of Lille，Villeneuve d?Ascq 59650，France)
Abstract：Clay rocks have the advantages of low permeability and crack self-sealing ability and are thus chosen as a potential geological barrier for underground disposal of radioactive waste in France and other countries. The high security and long-term requirements of underground radioactive waste disposal require that it is necessary to investigate the time-dependent behaviors of clay rocks. This paper presents the results of a series of one-step creep tests for the purpose of identifying with a relative high precision the creep rate thresholds of the Callovo-Oxfordian argillite with different moistures under the triaxial creep conditions. Three moisture levels are investigated in this paper for complete creep tests. The results show that the creep rate threshold values are related to the moisture and confining pressure. Generally，if the axial creep rate is smaller than 2.5 µε/h，the tertiary creep does not occur. Otherwise，if the axial creep rate is greater than 58 µε/h，the tertiary creep is likely to happen. Although the values between the two thresholds are still questionable，the thresholds are helpful to know in advance whether the tertiary creep would happen.
2017, Vol. 36 
