# Study on Disturbance Mechanism of Squeezed and Non-Squeezed Soil Piles on Soft Soil Foundation
## 3 Methodologies  
### Hydrostatic Pile  
(1) Mechanism  
Hydrostatic pile driving is realized by concrete precast piles being pushed into the foundation with static pressure. It has numerous advantages including the absence of noise and vibration, rapid construction speed, higher pile quality, and lower economic costs. When the pile tip starts to penetrate the soil, it destroys the original stress condition of the stratum and then makes compression deformation below the pile tip, providing friction resistance to the pile tip. When the soil stress at the pile tip exceeds its shear strength, the soil mass will deform sharply, resulting in plastic failure, lateral compaction, or drag subsidence. During this process, the soil beneath the pile tip will be squeezed downward and laterally. When the pile continues to penetrate the deep soil, the soil around the pile  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Pile Types** & \multicolumn{2}{c}{**Pile**} & \multicolumn{2}{c}{**Model**} \\ \cline{2-7}
**Pile Types** & **Initial Radius** & **Radius** & **Length** & **Zones** & **Grid Points** \\ \hline Hydrostatic pile & 0.0625 m & 0.25 m & 15 m & 35,008 & 38,660 \\ Bag grouting pile & 0.15 m & 0.2 m & 15 m & 35,008 & 38,660 \\ Bored pile & - & 0.5 m & 15 m & 44,400 & 48,497 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Geometric parameters of the numerical model.  
Figure 3: Model grids division: (**a**) hydrostatic pile; (**b**) bag grouting pile; (**c**) bored pile; (**d**) quarter symmetry model.  
continues to be compressed and crushed, while the pile body is resisted by pile friction and pile tip resistance due to the high normal resistance of the soil.  
(2) Assumptions  
The theory of cavity expansion is used to model the pile driving process, based on the pile-forming mechanism of the hydrostatic pile [28; 29; 30]. The simulation involves gradually enlarging circular openings at predetermined pile positions, from top to bottom, to simulate the driving process of the hydrostatic pile. This simulation method is based on the following assumptions:  
1. Hydrostatic pile has a slow penetration rate, which is considered a quasi-static process.
2. The difference in deformation modulus between the pile and soil is significant, ignoring the deformation of the pile.
3. The disturbance caused by the vertical compression of the pile tip into the soil is approximately characterized by the oblique lateral soil squeezing process.
4. The influence of pile-soil friction force on soil disturbance is ignored.  
(3) Simulative steps  
The main steps of the simulation process are as follows:  
1. Establishment of hydrostatic pile reservation grids: this component consists of a cylindrical pile body and a hemispherical pile tip with a radius equal to one-third of the actual pile diameter.
2. Establishment of soil grids around the pile: the vertical and lateral lengths of the model are both twice the length of the pile, and the grids are slightly dense near the pile.
3. Calculation of initial soil state: define all grids as soil, assign material parameters, set gravity load, and complete the calculation of initial stress as well as initial modulus.
4. Penetrating and expanding from top to bottom: first, close the grids at the pile position; then, apply horizontal displacement to the hole wall at the penetration position and let the hole expand from the initial radius to the actual pile diameter of the precast pile; and finally, continue expanding downward from the top, as illustrated in Figure 3.