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

Abstract

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.