# A Study on the Vertical Bearing Characteristics of Screw Piles in Permafrost Regions
## 1 Introduction  
China's permafrost area accounts for approximately 22% of the country's total land area, with most of it located on the Tibetan Plateau [1, 2]. With the ongoing development of Western China, the engineering projects being constructed and operated in permafrost areas include the Qinghai-Tibet Railway, Qinghai-Tibet Highway, and Qinghai-Tibet Power Transmission Line [2]. Pile foundations are one of the most commonly used forms when designing foundations for these engineering projects [3, 4, 5]. Under the general trend of global warming, an abnormal climate, and the degradation of frozen soil, engineering construction in permafrost regions faces increasing demands related to the foundation-bearing capacity. The drilled screw pile is a new type of pile used in permafrost regions. It interacts with the seasonally active soil layer through a steel sleeve, effectively reducing frost heave damage. Additionally, the outer thread and the frozen soil's mechanical bite provide a good vertical bearing capacity in permafrost.  
Screw piles are widely used in areas with soft soil, and numerous scholars have investigated their bearing capacity and pulling resistance characteristics. [PERSON] et al. [6] provided a preliminary discussion on the bearing capacity design of the screw pile and provided guidance for construction. [PERSON], [PERSON] et al. [7] investigated the end-bearing capacity of screw and straight-pipe piles under similar pile-tip areas and ground conditions. Through laboratory testing and numerical analyses, [PERSON] et al. [8] studied the vertical bearing capacity mechanism of bored, cast-in-place screw piles and proposed that the soil's shear strength index and the screw pitch and the screw width of screw piles are the key factors affecting the vertical bearing capacity of screw piles. [PERSON] et al. [9] measured the relationship between the shear stress and the relative shear displacement of the common pile-soil contact surface with different screw pitches by using a large-scale contact surface shear test and found that there is an optimal screw pitch that causes the maximum arch failure surface of the screw pile and the soil. [PERSON] et al. [10] conducted laboratory tests on screw piles with variable sections and found that the material utilization rate of screw piles with variable sections was approximately 1.3 times that of screw piles with constant sections under the same formation conditions. These studies provide a valuable reference for the engineering practice with regard to screw piles in areas with soft soil. However, the soil in permafrost regions undergoes a water-ice phase transition after freezing [11; 12; 13], and the temperature, water content, and ice content of the frozen soil affect the bearing performance of piles [14; 15; 16]. Currently, there are few studies on drilled screw piles in permafrost areas. Therefore, researching screw piles in permafrost areas is of great value, as their potential application is of significant importance [17; 18; 19].  
In this study, the accuracy of the numerical method is verified by laboratory model tests. Subsequently, the vertical load transfer characteristics and bearing mechanisms of the drilled screw piles in the permafrost regions of the typically humid area of the Qinghai-Tibet Plateau are investigated using numerical methods, and the bearing capacity calculation method is proposed.