A Cyclic Resistance Ratio Model of Sand-Fines Mixtures Based on Cyclic Triaxial Test

Sand-fines mixtures are widely distributed in the world. However, the effect of fines on the liquefaction strength of sand-fines mixtures is still in issue. A series of undrained cyclic triaxial test was carried out to study the liquefaction behaviour of sand-fines mixtures. The influences of the plasticity of fines (PI), fines content (FC), global void ratio (e), relative density (Dr) were considered. The results show that the traditional liquefaction criterion of pure sand can be applied to the sand-fines mixtures with plastic fines. The cyclic resistance ratio (CRR) of the mixtures decreases and then stabilizes with increasing FC when the samples are prepared at a constant Dr. However, the CRR decreases and then increases with increasing FC when the samples are prepared at a constant e. The threshold fines content (FCth) also varies. The CRR of the mixtures increases with increasing Dr. A single Dr or e cannot describe the dense state of the mixture effectively. A new index, Dr/e, is proposed in this study to describe the dense state of the mixtures. A semi-empirical model is proposed to evaluate the CRR of the mixtures using the parameters of Dr/e, FC and PI of the fines based on the back analysis method. The applicability of the model is verified by the test data from this study and other scholars. In addition, the parameters of Dr/e, FC and PI of the fines can be obtained from basic geotechnical tests, which is convenient for the application of the model.