# Creep Characteristics of Soil in the Sliding Zone of Huangtupo Landslide
## 1 Introduction  
Creep is one of the rheological properties of soils, and the evolution and long-term stability of landslides are profoundly influenced by the creep properties of sliding zone soil. Numerous scholars have explored the mechanism of landslide evolution and development based on the direct shear creep characteristics of sliding zone soil [1; 2]. Creep deformation of sliding zone soil is mainly composed of elastic deformation and plastic deformation. Plastic deformation has timeliness, which is the main reason for creep damage to rock-soil masses [3]. At present, the number of geological disasters caused by the rheology of soil globally is progressively growing, such as those caused by landslides and slope instability. Therefore, it is increasingly important to study the creep characteristics of sliding zone soil [4; 5]. The creep damage process of rock-soil masses is reflected in various aspects over time, including displacement deformation and the stress and strain rate [6; 7; 8]. The engineering properties of sliding zone soil in the reservoir area make it more sensitive to changes in moisture content and vertical load [9]. [PERSON] et al. studied the creep characteristics of sliding zone soil in the Huangtupo landslide under different moisture contents and found that the yield strength of the sliding zone soil was negatively correlated with the moisture content and the relationship between the creep characteristics of the sliding zone soil and the prediction model of slope instability was discussed [10]. [PERSON] et al. studied the creepcharacteristics of rock under the condition of reservoir water level change, discussed the microscopic damage mechanism of rock under the action of the saturation-dehydration cycle, and quantitatively expressed the amount of damage to the rock [11]. [PERSON] et al. conducted an in situ triaxial test, believing that the sliding zone soil of the Huangtupo landslide was part of a creep process, and derived a constitutive equation with linear and nonlinear viscoplastic terms to fit the creep process of the sliding zone soil [2]. At present, the direct shear creep test of sliding zone soil is mostly focused on the creep damage stage but not on the attenuation creep stage of sliding zone soil [12; 13]. Through direct shear tests, [PERSON] et al. found that the red-bed sliding zone soil was in the accelerated creep stage and proposed the long-term strength of the sliding zone soil [14]. [PERSON] et al. found that the creep characteristics of the Suoertou landslide were related to the stress state, and the stress state of the landslide indicated that it was under conditions allowing it to enter an accelerated creep state [15]. Previous studies have shown that the stress history directly affects the distribution of particles in the soil, resulting in shear dilatancy (shrinkage) in the shear process [16]. [PERSON] et al. carried out triaxial tests on expansive soil and found that the soil showed shear shrinkage characteristics at the initial stage of stress loading. When soil enters the accelerated creep stage, its volume strain changes from shrinkage to expansion [17]. The rheological constitutive relation of soil is the key to studying its rheological property [18; 19]. The rheological model is a description of the stress-strain-time relationship of soil during loading, which can effectively and intuitively explain the rheological characteristics of the stress-strain-time of soil [20; 21; 22]. [PERSON] et al. proposed an improved Mesri creep model using triaxial tests [23]. Based on the concept of a binary medium, [PERSON] et al. established a binary medium creep model suitable for frozen soil [24]. With the long-term research on the rheological theory of soil by various researchers, many previous rheological constitutive models applicable to geotechnical materials can be broadly classified into the following four types: the element model, the damage rheological model, the yield-surface model, and the empirical model [17; 25].