Study on the effect of pore structure changes induced by freeze-thaw-wetting-drying cycles on water retention characteristics of compacted loess

Deterioration of earthworks (including compacted soil collapse and loss of suction) as a result of climate change has had a significant negative impact on engineering. To explore the water retention characteristics and microstructural evolution of loess after freeze-thaw-wetting-drying (FTWD) cycles. In this paper, the soil water characteristic curve (SWCC) of unsaturated loess in the full suction range is obtained by using the filter paper method (FPM) and vapor equilibrium technique (VET). Scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) were used to test the two-dimensional images and pore size distribution (PSD) curves of the specimens. The results of the study showed that the SWCC of compacted loess before and after FTWD cycles showed an unimodal pattern. Compacted loess has inter-aggregate pores and intra-aggregate pores, and the PSD curves show a bimodal pattern. The FTWD cyclic action reduces the water retention capacity of loess in the low to medium suction range (0kPa-288kPa). Inter-aggregate pore porosity decreases with an increasing number of FTWD cycles. Finally, to easily predict the SWCC of loess under the condition of pore variation, a prediction model was established in the double-porosity media framework, considering the changes of interaggregate pores and intra-aggregate pores. The rationality and applicability of the present model were verified by experimental data. The present model can reasonably predict the water retention properties of compacted clays with unimodal or bimodal type SWCC under microscopic pore changes, which is suitable for the engineering application of compacted clays.