# Time-Dependence of the Mechanical Behavior of Loess after Dry-Wet Cycles
## 1 Introduction  
Loess is a weakly cemented loose sediment with a special material composition, which is widely distributed in the Loess Plateau of China (Figure 1) [1, 2]. Creep phenomenon is common in loess-covered areas, and the creep characteristics of loess pose an important impact on the landslide formation and the construction of engineering structures [3, 4, 5]. The creep properties of loess vary due to the change of the environment. For example, unsaturated loess soils are usually subjected to wetting because of the natural rainfall or artificial irrigation, and loess soils would then be subjected to a drying process, i.e., water evaporation, as rainfall or irrigation stops. Such a process could be called a dry-wet cycle [6, 7] and leads to the following consequences: the loss of soluble salts in the loess [8, 9, 10], the deterioration of the mechanical properties of the loess [11, 12], and the change of shear strength, deformation, and permeability of the loess [13, 14, 15]. Therefore, the creep deformation of the loess was aggravated, which will contribute to the formation of disasters such as landslides. The influence of dry-wet cycles on the time-dependent behavior of rocks has been considered in some research [16, 17, 18, 19], while in the last few years increasing attention has been paid to experimental research into the behavior of loess soils. It is acknowledged that the reduction in the shear strength of the loess due to the dry-wet cycles is obvious [3, 20, 21]. [PERSON] et al. [22] reported that the hydraulic conductivity of the soil gradually increases as the number of dry-wet cycles increases. Until now, extensive attempts have been made on the physical and mechanical properties of loess after dry-wet cycles by using the uniaxial tensile shear test [23], direct shear test [24, 25], the uniaxial compressive test [26],conventional triaxial test [7; 27], the soil-water characteristic curve (SWCC) of loess [28], etc. For example, [PERSON] et al. [23] carried out an experimental study on the tensile strength of the intact loess samples under dry-wet cycles and concluded that the repeated dry-wet cycle destroys the original structure of the intact loess and causes its tensile strength to disappear. Furthermore, [PERSON] et al. [24] investigated the shear characteristics of loess samples under dry-wet cycles through direct shear tests and pointed out that the shear strength of loess gradually decreased as the number of dry-wet cycles increase. By conducting experiments, [PERSON] et al. [26] reported that the unconfined compressive strength, elastic modulus, and cohesive force of the loess specimen decreased with an increase in the number of dry-wet cycles, while the vertical compressive strain and failure deformation increased. [PERSON] et al. [27] conducted triaxial tests considering three influence factors such as dry density, dry-wet cycle amplitude, and the lower bound water content of dry-wet cycles and established a compacted loess deterioration model (CLDM). [PERSON] et al. [29] explored the effect of the dry-wet cycle on the collapsible deformation characteristics of compacted loess, and the results revealed that the compressive strain at all levels of deviatoric stress of specimens with different initial density gradually increases with the increase of the number of dry-wet cycles. The higher the initial compaction degree, the more significant effect of the dry-wet cycle on the mechanical behavior of compacted loess. The studies above have been focused on the variation in conventional mechanical properties such as shear strength, uniaxial tensile strength, uniaxial compressive strength, and triaxial shear strength of the loess after the dry-wet cycles. However, very little  
Figure 1: The study area. attention has been paid to the damaging effect of the dry-wet cycles on the creep properties of loess.