Effects of Freeze-thaw and Dry-wet Cycles on the Collapsibility of the Ili Loess With Variable Initial Moisture Contents

Abstract

Suffering from seasonal climate changes, the loess in the Ili region of Xinjiang is frequently subject to cycles of freezing-thawing(F-T) and wetting-drying(W-D), and the engineering properties of the loess are highly variable. In the present research, the collapsibility characteristics of the loess slope located in Xinyuan country is investigated, for which the uni-axial compression tests were carried out with the consideration of various F-T and W-D cycles. In parallel, both the SEM and NMR tests were carried out. Test results obtained from the research indicated that both F-T cycles and W-D cycles exacerbate the deterioration of the loess and the most serious situation will be reached after after 6–10 cycles. Under these two physical cycles, the micro-structure of the loess generally develops from relatively aggregated state to the dispersed one. Correspondingly, the porosity of the loess increases initially, followed by an obvious descending with wet-dry cycles. Whereas, the characteristics of the loess subjected to the F-T cycles is opposite.The in-behind reason is that the irreversible alteration of the loess micro-structure attributed to the frost heave force generated by F-T cycles and the water absorption-swelling effect are accounted for. The main contribution of this study is to give more explanations for the causes and action mechanisms of loess wet subsidence in seasonal permafrost zones, and provide a scientific basis for loess wet subsidence disaster prevention and control.