Abstract: The pre-strain process can be considered to be the effect of stress history. To investigate the stress relaxation characteristics of Lanzhou loess, a series of laboratory stress relaxation tests under confined conditions are conducted. The relaxation curves of loess under different pre-strains are analyzed. The experimental results indicate that the initial relaxation stress increases with the growth of the magnitude of pre-strain, which ultimately leads to bigger instantaneous relaxation. According to the characteristics of relaxation curves, a new conception of relaxation degree (RD) is proposed. With the pre-strain gets bigger, the time to reach the same relaxation degree becomes shorter; and with the development of relaxation, this kind of difference tends to be more obvious. Based on the analysis of experimental data, the stages of relaxation are analyzed and the whole process can be divided into three stages, including instantaneous relaxation stage, attenuation relaxation stage and stable relaxation stage. The constant strain rate loading is chosen; and its influence on the relaxation process under different strain rates is analyzed. Based on the experimental results, a new rheological relation is obtained and its reliability is verified by the validation test.

Key words: Lanzhou loess, relaxation, pre-strain, rheological relation