## 5 Discussion  
The above test results highlight that the influence of the water content on loess' tensile behavior significantly differs between specimens that were prepared according to the wetting and drying paths and that it is associated with the distribution of pore water and the evolution of the soil structure as well as the soil-water interaction mechanism. Generally, the tensile strength of loess derives from the cohesion of its soil particles [43], which is related to four kinds of physical and physiochemical origins: (1) clay bonding arising from the short-range clay-water interaction [28; 29; 31]; (2) capillary attraction due to the existence of a water bridge or capillary meniscus between soil particles [13; 44]; (3) soluble and less soluble bonding agents [45] and (4) carbonate cementations (an origin which is only considered for intact loess) [46]. By considering these four mechanisms and combining the results of the tensile test, microstructural observation and NMR analysis, a conceptual model for interpreting the tensile strength variation of loess with its water content is proposed and illustrated in Figure 15.  
Figure 14: Capillary and adsorbed water contents within DM and WM specimens for the arrow in DM represents the drying direction and the arrow in WM represents the wetting direction. A remolded loess specimen that has been compacted with a low water content usually possesses an aggregated structure as it is prepared by reconstructing the crushed soil powder of intact loess [47]; part of the intact structure is preserved and presented in the form of the large aggregate particles which are assemblies of clay, silt and sand that are created through clay and carbonate cementation, as is shown in Figure 15a. Water mainly exists inside of the aggregates, with little water bridging or connecting the aggregates. In this case, the mechanical behavior of a loess specimen with a low water content is more like that of granular soil and it exhibits very low tension resistance. As more water is added to the loess, the water gradually surrounds the surfaces of the aggregates, with liquid bridges forming between the aggregates. The liquid bridges at the contact points act as bonding agents that effectively improve the cohesion of the aggregates (see Figure 15b). Furthermore, the hydration of the clay commences, which provides additional cementation between the skeleton particles (e.g., silt-silt or silt-aggregate). All of these factors contribute to the increase in the loess' tensile strength [44]. When the water content reaches a certain value (i.e., 10%), the liquid bridge is fully developed and the clay cementation is enhanced to its maximum; at this point the peak tensile strength is attained. This explains the reason for the observed increase in the tensile strength of the WM specimens with the increase in the water content to 10%. When the loess is compacted with a relatively high water content, the dissolution of soluble salt and clay hydration leads to the formation of a dispersed structure, which is characterized by the individual silt and sand particles or small-sized aggregates being surrounded by fully dispersive clay platelets. The connection that is provided by a liquid bridge or clay cementation is lost. Furthermore, the soil suction and capillary attraction forces decrease with the increase in the saturation degree [32]. Therefore, the tensile strength reduces and shows a decreasing trend with the increase in the water content, as is illustrated by the Figure 11b at \(w>10\%\). Unlike the specimens that were prepared with the wetting method, the DM specimens were prepared by air-drying the previously compacted specimens of high water content  
Figure 15: A conceptual model for interpreting the evolution of tensile behavior of loess for (a) WM-\(w=6\%\) specimen (b) WM-\(w=10\) specimen (c) WM-\(w=26\) specimen (d) DM-\(w=6\) specimen (e) DM-\(w=18\) specimen (f) DM-\(w=26\) specimen. to different target water contents.