An experimental study on the mechanical properties of silty soils under repeated freeze-thaw cycles

- Systematically studied the deformation and strength properties of silty soils under repeated freeze-thaw cycles
- The thaw subsidence ratio determined after 5-6 freeze-thaw cycles is suggested for assessing thaw subsidence properties.
- With the critical compactness level, the height of samples doesn't change after repeated freeze-thaw cycles.
- The dynamic parameters determined after 6-7 freeze-thaw cycles are suggested for assessing strength properties.

In this study, the subgrade fill material from the Nagqu Logistics Center Yard (NLCY) along the Qinghai-Tibet Railway was investigated. And the thaw subsidence properties and dynamic properties were thoroughly analysed in laboratory tests.1)From the determined thaw subsidence properties, the following results were obtained: samples with a higher degree of compactness exhibited heave deformation, whereas those with a lower degree of compactness exhibited compressive deformation after repeated freeze-thaw cycles. However, there is a critical compactness level at which the height of the samples does not change after repeated freeze-thaw cycles. The consolidation effect of the load restrains frost heave deformation; however, the amount of thaw subsidence deformation increases. The thaw subsidence ratio first increases, then decreases and becomes steady after the fifth freeze-thaw cycle as the number of freeze-thaw cycles increases. It is recommended that the thaw subsidence properties of silty soils be assessed after 5-6 freeze-thaw cycles.2)From the determined dynamic properties, the following results were obtained: the dynamic stress vs. strain curves clearly show a nonlinear trend. The dynamic modulus greatly decreases, whereas the damping ratio increases with additional freeze-thaw cycles; and changes level off after the sixth freeze-thaw cycle; the dynamic properties after 6-7 freeze-thaw cycles are suggested for use in designing and calculating indexes. Moreover, the dynamic modulus increases and the damping ratio decreases as the confining pressure and compactness increase.