## 4 Results
### Variation of Microstructure with Water Content  
Figure 12 shows representative SEM images of the DM and WM specimens with dry densities of 1.6 g/cm\({}^{3}\) at varying water contents. Figure 12a-c presents the evolution of the microstructure of the loess along the drying path (i.e., the DM). It can be seen that, at high water content of 26%, the clay particles were fully hydrated and dispersedly attached onto the surface of the skeleton particles of the loess (i.e., silt, sand or their aggregates) in the form of 'floc' (see the red circle). Obviously, the cementation between the skeleton particles that was provided by the dispersed clay was rather weak; besides this, the particles were in contact with each other in a point-point manner with bracket and'mosaic' pores developed between them (shown by the white rectangle). Such a microstructural configuration led to a lower capacity of the sample to resist external tension. With the decrease in the water content to 18%, the clay started the aggregation process and connected the skeleton particles in the form of clay bridges and clay 'buttresses', as is illustrated by the red circle in Figure 12b. Part of inter-particle pores were filled with aggregated clay-silt clusters (see the white rectangle). Under this condition, the degree of clay cementation together with the cohesion between the particles enhanced leading to the improvement of the tensile strength. When the water content was further reduced to 6%, the clay's cementation significantly increased, which firmly bonded the particles, and the prevalence of inter-particle pores decreased. As is indicated in Figure 12c, the overall soil fabric was stable with the boundaries between the individual particles becoming unclear. Such a stable microstructure contributes to the high tensile strength of the DM specimens with low water contents.  
Figure 12: SEM images of Iii loess with different water contents for (**a**) DM-\(w\) = 26% specimen (**b**) DM-\(w\) = 18 specimen (**c**) DM-\(w\) = 6 specimen (**d**) WM-\(w\) = 26 specimen (**e**) WM-\(w\) = 10 specimen (**f**) WM-\(w\) = 6 specimen.  
The microstructures of the WM specimens are shown in Figure 12d-f. It is obvious that the WM and DM specimens with the same water contents have different microstructural characteristics. For example, the structure of the WM specimen with a water content of 6% is dominated by the point-point contact of the silt particles and large aggregates; these large aggregates are the assembly of clay, silt and sand particles. There is little clay cementation presented at the contact area of the silt aggregates (Figure 12f). These observations are distinct from those that are shown in Figure 12c. The reason for this distinction originates from the two different sample preparation methods. The weak connection between the silt and aggregates of the WM specimens at low water contents led to their low tensile resistance. When the loess was wetted to a higher water content of 10%, the hydration of the clay compositions disassembled the large aggregates into small ones, with the hydrated clay connecting adjacent silts and smaller aggregates, as is indicated in Figure 12e. The enhancement of the clay bonding rendered the improvement of the cohesive force of the soil particles and, hence, the increase in the tensile strength. With a further increase in the water content to 26%, the clay particles were fully dispersive (Figure 12d), causing the clay's cementation between the skeleton particles to vanish. The soil pores were filled with free water, resulting in very weak cohesive force and low tensile strength.