# Study on the Influence of File Installation Disturbance on the Settlement of Composite Foundation
## 2 Materials
### In-Situ CPTU  
Compression modulus is an essential parameter for settlement calculation and prediction. In order to eliminate disturbances beyond pile installation, in-situ testing is a suitable method for obtaining compression modulus.  
The commonly used in-situ methods for testing and estimating soil mechanical properties include standard penetration test (SPT), pressuremeter test, flat dilatometer test (DMT), vane shear test (VBT), and piezocone penetration test (CPTU).  
The SPT, DMT, and VBT methods are not suitable for the compression modulus determination. The SPT assesses foundation bearing capacity, the DMT measures lateral pressure and consolidation coefficients, and the VBT determines soil sensitivity. Although the pressuremeter test can directly obtain deformation parameters such as the pressuremeter modulus, the method for deducing the compression modulus is still not mature. While the CPTU cannot directly obtain deformation parameters, numerous studies have shown the correlation between cone resistance and compression modulus [19; 20]. Due to its low disturbance and ease of implementation, CPTU is often combined with laboratory tests for compression modulus determination.  
Therefore, this paper used CPTU to estimate the compression modulus change of soil between piles before and after pile installation. See Table 3 for the equipment parameters used in CPTU.  
\begin{table}
\begin{tabular}{c c c c} \hline  & \multicolumn{2}{c}{**Parameters**} & \multicolumn{2}{c}{**Value**} \\ \hline \multirow{6}{*}{CMP} & \multirow{3}{*}{Machine} & Drilling speed & 0.5–0.8 m/min \\  & & Rotation speed & 40–50 r/min \\  & & Drill diameter & 500 mm \\ \cline{2-4}  & & Pile length & 8 m \\  & & Pile spacing & 1.2 m \\  & & Installation process & four stirring and four spraying \\  & & Curing agent & PO42.5 Portland cement \\  & & Water cement ratio & 0.6 \\  & & Cement dosage per meter & 65 kg \\ \hline \multirow{6}{*}{PHC pile} & \multirow{3}{*}{Machine} & Pile hammer & Tubular diesel pile hammer \\  & & Hammer Weight & 4.0 \(\times\) 10\({}^{3}\) kg \\  & & Hammer drop distance & 1.0\(\sim\)1.5 m \\ \cline{2-4}  & & Pile length & 20 m \\  & & Pile spacing & 1.8 m \\  & & Outside diameter & 400 mm \\  & & Wall thickness & 70 mm \\  & & Water cement ratio & 0.31 \\  & & & Cement = 436 kg/m\({}^{3}\) \\  & & & Fly ash = 35 kg/m\({}^{3}\) \\  & & Aggregate content & slag powder = 75 kg/m\({}^{3}\) \\  & & & fine aggregate = 705 kg/m\({}^{3}\) \\  & & & coarse aggregate = 1032 kg/m\({}^{3}\) \\ \hline \end{tabular}
\end{table}
Table 2: Technical parameters of CMP and PHC pile.  
\begin{table}
\begin{tabular}{c c c c c} \hline \(\mathbf{D_{m}}\) & \(\mathbf{F_{pp}}\) & \(\mathbf{F_{ru}}\) & \(\mathbf{V_{p}}\) & \(\mathbf{A_{cpp}}\) \\ \hline
20–30 m & 30 kN & I: 15 kN II: 25 kN & 2 cm/s & 10 cm\({}^{2}\) \\ \hline \end{tabular} where \(D_{m}\) = measurement depth, \(F_{fp}\) = rated penetration force, \(F_{ru}\) = rated uplift force, \(V_{p}\) = penetration rate, \(A_{cpp}\) = cross-section area of cone penetration probe.  
\end{table}
Table 3: Technical parameters of CPTU equipment.  
In the section before K2 + 350, CMP was used, and after that, PHC pile was adopted. Four tests were conducted at K2 + 335 and K2 + 365, and the specific location was in the middle of the roadbed cross-section. The first test (A1 & B1) was conducted to determine the parameters of undisturbed soil layer. Then, after the pile installation, a second test (A2 & B2) was carried out. As shown in Figure 2, the distance between first and second test points are less than 5 m. It is aimed at minimizing the impact of actual geological differences. The experimental results will be discussed in the conclusion section.