# Study of Gravelly Soil Core Material Using a Large-Scale Triaxial Wetting Test
## 1 Introduction  
Large dams have a close relationship with social development (i.e., water, food, and energy consumption), and the vital role of large dams in sustaining societies has been recognized [1]. The impermeability and geotechnical characteristics of dam core materials are very important in the design of earth dams [2]. Wetting deformation, which is generated via particle sliding, breakage, and rearrangement, plays a vital role in dam deformation, which determines its safety [3]. Wetting deformation refers to the deformation that occurs when a material transitions from a dry state to a saturation state. Reservoir water storage, water level fluctuations, and rainwater infiltration can all cause wetting deformation. Wetting may accelerate the softening of materials, which adversely affects the strength, deformation, and even stability of the dam body [4; 5; 6; 7]. For example, the Infernillo Dam in Mexico is 148 m high. The dam crest settled about 26 cm during its first impoundment [8]. In October 2014, during the first impoundment of the Guanyinyan composite dam in China, wetting deformation caused four longitudinal cracks on the dam crest, with the largest being about 127 m [9]. Wetting deformation is a key technical problem in the design and function of high earth-rockfill and earth-core rockfill dams [10]. The wetting test can be performed using either the single-line method or double-line method [11; 12]. The two methods both produce similar wetting laws, but they differ significantly in terms of the deformation amount. Since the single-line method is closer to that used in engineering projects, it has been widely adopted [13; 14]. The stiffness of the material refers to its ability to resist external deformation. Wetting significantlyreduces particle strength and stiffness, and particle strength decreases with increasing particle size. The weakening of the material itself will reduce its stiffness; thus, the material will deform [15; 16; 17]. [PERSON] et al. [18] (1985) proposed that, under a constant load, wetting deformation is equal to the deformation difference between a dry and saturated sample under the same conditions, while [PERSON] et al. [19] (2020) suggested that it is unsuitable to directly subtract the deformation of 'dry soil' from that of 'wet soil' in the same stress state in a double-line test. The subtraction should instead be calculated by using the tangent modulus under the same stress state. [PERSON] et al. [20] (2019) investigated the influence of the stress path on the wetting deformation of coarse-grained materials. In contrast to wetting deformation under traditional triaxial test settings, the wetting deformation of coarse-grained soil under an equal stress ratio path is influenced not only by the stress state but also by the loading path. [PERSON] et al. [21] (2023) conducted laboratory tests to determine the wetting deformation law of core wall material, which was discovered to be more complex than that of rockfill material. [PERSON] et al. [22] (2019) studied the wetting mechanism and considered that wetting deformation can be divided into two stages: instantaneous wetting and creep wetting deformation. [PERSON] et al. [23] (2021) added a water distribution controller to study the unsaturated wetting of rockfill materials. The study found that the wetting deformation characteristics in unsaturated conditions are similar to those in saturated conditions. For the purpose of application, it is important to establish a wetting model to describe the mechanical behavior of the material under study. [PERSON] et al. [24] (1989) proposed a classical wetting deformation model based on the law of wetting tests. According to [PERSON]'s wetting model, the relationship between shear deformation and the stress level follows a hyperbolic curve, which is widely accepted. However, the conclusion that the volume deformation is constant during wetting is not universally accepted.