# Analysis of Lateral Displacement of Pile Foundation Caused by Large-Diameter Shield Tunneling
## 4 The Influence of Shield Construction on the Displacement of the Front Pile Foundation Discussion  
It is assumed that there is a single pile in front of the tunnel, and both the soil and the pile are linear, elastic, and isotropic. The pile diameter is 0.9 m, the pile length is 45 m, the elastic modulus is 25 GPa, the soil elastic modulus is 8 MPa, and the Poisson's ratio is 0.5. MATLAB programming language is used to calculate the lateral displacement of the pile under the combined action of the additional thrust of the shield and the friction of the shield shell in the shield construction, and the lateral displacement of the pile foundation under different additional thrusts, excavation surface distances, and tunnel diameters is analyzed. The additional thrusts are 20 kPa, 50 kPa, 100 kPa, and 150 kPa, respectively. The distances between the excavation faces are 1, 1.5, 2.0, 2.5, and 3.0\(D\), respectively (\(D\) is the shield diameter). The tunnel diameters are 11.5 m, 12.5 m, 13.5 m, 14.5 m, and 15.5 m.  
In Figure 7, the impact of the distance between the pile foundation and the excavation face on the lateral displacement of the pile foundation is demonstrated under varying additional thrusts of the shield. The shield's outer diameter is 14.5 m, and due to its significant depth, the excavation surface's proximity has only a small effect on the pile top's lateral displacement, but greatly influences the lower part of the pile body, resulting in the inclination of the pile foundation. Therefore, when constructing the shield near the pile foundation, the evaluation standard of the safety of the pile foundation should consider not only its displacement, but also its inclination. Figure 6: Comparison of calculated and theoretical values of lateral displacement of pile foundations. (a) x = 10 m; (b) x = 20 m. \begin{table}
\begin{tabular}{c c} \hline \hline
**Design Conditions** & **Values** \\ \hline Shield length \(L\)/m & 12 \\ Shield radius \(R\)/m & 7.25 \\ Additive thrust \(p\)/kPa & 20 \\ Friction resistance ratio \(\beta\) & 0.9 \\ Interface friction angle \(\delta^{\prime}/^{\circ}\) & 8.0 \\ Coefficient of earth pressure at rest \(K_{0}\) & 0.5 \\ Foundation parameters of Kerr model \(m\) & 4 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Parameters of theoretical calculation. As the additional thrust of the shield increases, the lateral displacement of the pile foundation gradually increases as well. The decrease in the excavation face distance leads to an exponential increase in the lateral displacement of the pile foundation. When the additional shield thrust is maintained within a reasonable range of \(\pm\)50 kPa, the maximum impact on the lateral displacement of the pile foundation can be controlled within 20 mm. However, at 150 kPa, the disturbance caused by the additional thrust of the shield is significant. When the distance from the pile foundation is equal to the outer diameter, the maximum lateral displacement of the pile foundation is almost 45 mm or 1% of the pile length, which jeopardizes the pile foundation's upper structure's safety. Thus, during the construction of the shield near the pile foundation, especially when the excavation surface's proximity is minimal, minimizing the shield's thrust is critical to reduce its impact on the pile foundation displacement. Figure 8 displays how the diameter of a shield affects the lateral displacement of a pile foundation when the excavation face is 29 m away, or two times larger than the shield diameter. The deformation pattern of the foundation is caused by the varying shield diameter, excavation face distance, and additional shield thrust, which all have similar effects. While increasing the shield diameter leads to greater soil displacement, it has a smaller impact compared to those of the shield thrust and excavation face distance. Therefore, controlling the shield thrust is crucial in managing stratum deformation during construction, and the tunnel-to-pile-foundation distance should be determined appropriately during the design process.