As shown in Fig. 13a, a relatively

As shown in Fig. 13a, a relatively homogeneous structure with curly schistose and flat particles interconnected in edge-to-face and edge-to-edge patterns is observed. After cyclic treatments, the samples exhibit an aggregated, but deflocculated structure (Figs. 13b, 13c). The aggregates, which are dispersed by cracks and voids induced by the effects of the W–D and F–T cycles, are of different sizes and shapes and interconnected in a point-to-face pattern. Larger numbers of cracks and voids are generated during the W–D–F–T cycles (Fig. 13c) and attributed to the further opening of pre-existing microfractures during the drying process and to new cracks and voids that form under the sufficient pressure generated by the freezing of water. The pore-size distribution (PSD) curves in Fig. 14 display a decrease in the pore volume at approximately 0.5 μm and an increase in the pore volume at approximately 15 μm after the cyclic treatments; these pores correspond to two main pore size regions, namely, intraaggregate and interaggregate pores. Therefore, the aggregates are compacted by the W–D, F–T, and W–D–F–T cycles.Cracks and voids induced by W–D and F–T cycles can cause a decrease in the cohesion. In general, the cohesion is mainly controlled by the distance between aggregates and the degree of cementation. Cracks and voids will damage the cementation among aggregates and consequently lead to a decrease in the cohesion. However, the increasing size of aggregates due to the substantial grain aggregation caused by the W–D and F–T cycles is a potential contributor to the increasing internal friction angle (Alhussaini 1983; Sitharam and Nimbkar 2000). Moreover, the matric suction during the drying process and the pressure caused by the volume change in the water during the freezing process will compact the particles and make them more rigid, thereby increasing the internal friction.