# Numerical Analysis of the Installation Process of Screw Piles Based on the FEM-SPH Coupling Method
## 3 Numerical Simulations
### Numerical Model  
In order to verify the numerical model, the field tests of screw piles were carried out. The field tests were carried out at the South China Agricultural University in Guangzhou. The soil of Guangzhou is latosol. The description and relevant characteristics of the soil are shown in Table 1. As is shown in Figure 4, field tests of four types of screw piles were carried out to measure the installation torque; the structural parameters of the test screw piles are shown in Table 2. The test pile is referred to as \"TP\"; for example, \"TP2\" indicates field test 2, namely, the screw pile with the pile diameter 90 mm and spiral pitch 100 mm. All screw piles were instrumented with strain gauges to measure the torque. During the field test, ensure that all screw piles are installed to a depth of 700 mm to reduce errors during measurement. In this paper, the field test data of the installation torque were compared with the simulation results. As shown in Figure 5, the key steps of the numerical simulation are listed. As for the establishment of the numerical model, considering the small deformation of the screw pile, we adopted the finite element method (FEM) to establish the model of screw piles. The models were developed to match the full size of the test piles, and the smaller size (0.007 m) was used for meshing to improve the computational accuracy of the numerical model. According to the complexity of the structure in the model, the grid type of the screw pile was determined as tetrahedron; the FE screw pile model is shown in Figure 6a. The screw piles are made of Q235 steel (the keyword \"MAT_RIGID), the material parameters and as shown in Table 3. In addition, a rotational speed was applied to the screw pile (the keyword \"BOUNDARY_PRESCRIBED_MOTION_RIGID), ensuring that it could only move along the vertical direction (Z-axial) so as to simulate the actual installation of the screw pile. To avoid the confusion between the field test and numerical simulation, numerical simulations are referred to as \"NT\"; for example, \"NT2\" indicates numerical simulation2, namely, the test screw pile TP2. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \(\rho\) (kg/m\({}^{3}\)) & \(c\) (kPa) & **Poisson’s Ratio \(\mu\)** & \(E\) (kPa) & \(G\) (MPa) & \(K\) (MPa) \\ \hline
1850 & 20 & 0.3 & 20 & 7.7 & 16.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Soil parameters. Figure 3: The idea of numerical simulations. Compared to the screw pile, the soil had a large deformation and the SPH method was adopted to develop the soil model in LS-DYNA. In addition, the conventional finite element method (Arbitrary Lagrangian-Eulerian Formulation) was also adopted to establish the soil model to compare the applicability with the FEM-SPH method. According to the research of [PERSON] [29], in the numerical simulation of the SPH method, with the reduction in the SPH particles' spacing, the particle splash phenomenon was improved. Therefore, as is shown in Figure 6b, the smaller particle spacing (0.01 mm) was used to establish the soil model. In the numerical simulation, the soil parameters of the test site are applied to the SPH soil model (the keyword *MAT_SOIL_AND_FORM). As shown in Figure 5, for the contact between the screw pile and the soil, the FEM-SPH method adopts point-surface contact (the keyword CONTACT_AUTOMATIC_NODE_TO_SURFACE), and the FEM method (ALE) uses the CONSTRAINED_LAGANGE_IN_SOILD keyword to define the contact. In addition, the soil is simulated as isotropic, and the influence of pore pressure on the soil model is not considered in numerical simulation.