# Numerical Analysis of the Installation Process of Screw Piles Based on the FEM-SPH Coupling Method
## 1 Introduction  
Due to the advantages in the aspects of ease and fast installation with minimal vibration and high bearing capacity [1], screw piles have been widely used in various situations [2]. In China, as a new foundation type, screw piles have been applied in the field of the foundation of solar power plants or heightening dams, slopes, landslides and so on. These piles, also known as micro screw piles, are usually hollow metal piles with continuous spiral blades, the pile lengths of which are generally between 1 and 2 m. They are mainly composed of the smooth cylindrical segment on the top, the cylindrical segment with blades in the middle and the conical tapered segment with blades at the bottom. These micro screw piles are usually screwed into the soil, which inevitably causes them to interact with the soil, bringing various problems to the installation, such as large settlement and excessive damage to the soil. The application of screw piles depends primarily on their load-bearing capacity, which in turn is influenced by the pile-soil interaction during the installation process. However, most of the research on this kind of pile focuses on the load-bearing process. Therefore, it is of great practical implication to study the installation process of screw piles. At present, a lot of research has already studied pile-soil interaction during the installation process of screw piles, including theoretical analysis, field tests and model tests. Many scholars, by analyzing the forces on the screw pile during the installation process [3, 4, 5, 6], or based on the installation tests of screw piles and the Cone Penetration Test(CPT) [8; 9; 10], have proposed the theoretical calculation method of the installation torque and the resistance of screw piles. The installation of screw piles can cause damage to the soil, and some researchers have investigated this behavior of the soil. [PERSON] et al. [11] conducted model tests using centrifugal devices and found that the soil disturbance generated during the installation process was influenced by soil density. [PERSON] and [PERSON] [12] introduced a generalized nonlinear mechanical formulation to solve nonlinear behavior between piles and soils and analyzed the effect of soil damping on pile-soil interaction. When [PERSON], [PERSON] et al. [13] studied the influence of rotational speed on the plugging and installation behavior of the screw pile, he found that increasing the rotational speed can significantly reduce the penetration resistance of open and closed piles during the installation process. However, pile-soil interaction is a microscopic mechanical behavior, which means the analysis of this process cannot be well completed by field experiments and theoretical analysis alone. Numerical simulation seems to provide the feasibility for this research. [PERSON] et al. [1] studied the effect of pile structure parameters on pile-soil interaction and load transfer under compressive loads by using a discrete element model. The finite element numerical analysis of single screw piles and pile groups in cohesion and cohesionless soils was conducted by [PERSON] and [PERSON], [PERSON] to analyze the effect of soil parameters and pile structure parameters on pile-soil action and bearing capacity [14]. [PERSON] and [PERSON] [15] used the finite element method to simulate the installation of large screw piles in sandy and cohesion soils, and the factors affecting the pile-soil dynamic response were analyzed. [PERSON] and [PERSON] [16] analyzed the interaction between the screw pile and the surrounding soil by the finite element approach and derived an equation to describe the pile-soil interaction. [PERSON] et al. [17] analyzed the effect of the drilling speed ratio (the ratio of rotational speed to descent speed) on the penetration characteristics of screw piles by the DEM model, revealing the micro-mechanical relationships between soil particles and macroscopic penetration properties of screw piles.