## 3 Mechanical Parameters of Deep Hole Soil
### Soil Compression Characteristic  
Soil compressibility is not only related to the basic properties such as composition, state and structure, but also related to the stress conditions of soil. In current civil construction, the layered summation method is the most widely used settlement calculation method. Additionally, it is also the settlement calculation method stipulated in the Code for Design of Building Foundation (GB 50007-2011). The total settlement S consists of consolidation settlement S\({}_{\text{c}}\) and secondary consolidation settlement S\({}_{\text{s}}\). In each layer, the consolidation settlement amount is calculated by Formula (1)  
\[S_{\text{c}}=C_{\text{c}}\frac{H}{1+e_{0}}\log\left(\frac{P_{2}}{P_{1}}\right) \tag{1}\]  
In the formula, S\({}_{\text{c}}\)--compressive deformation of layered soil, m; C\({}_{\text{c}}\)--compression index; H--soil layer thickness, m; e\({}_{0}\)--initial void ratio of soil layer; p\({}_{1}\), p\({}_{2}\)--vertical stresses at the top and bottom of soil layers, kPa. In each layer, the secondary consolidation settlement is calculated by Formula (2)  
\[S_{\text{s}}=C_{\text{s}}\frac{H}{1+e_{0}}\log\left(\frac{t_{2}}{t_{1}}\right) \tag{2}\]  
In the formula, S\({}_{\text{s}}\)--secondary consolidation compression deformation of layered soil, m; C\({}_{\text{s}}\)--secondary consolidation index; t\({}_{1}\)--time of demarcation point between primary and secondary consolidation of soil mass, s; t\({}_{2}\)--the time to obtain the amount of secondary consolidation settlement, s.  
Therefore, the total settlement of soil S\({}_{\text{t}}\) is  
\[S_{\text{t}}=\sum_{i=0}^{n}(S_{\text{ci}}+S_{\text{si}}) \tag{3}\]  
The influence of foundation deformation on a high-speed railway is mainly manifested in the compression characteristics and shear strength of soil. Therefore, we carried out high pressure consolidation tests, direct shear tests and triaxial undrained consolidation tests. The mechanical strength parameters of soil are shown in Table 3.  
Figure 4: Diagram of soil’s basic physical and mechanical parameters by burial depth. From Formulas (1) and (2), it can be seen that the main parameters affecting the soil settlement are the vertical stresses \(\mathrm{p}\), the thickness \(\mathrm{H}\), the initial void ratio \(\mathrm{e}_{0}\), the compression index \(\mathrm{C}_{\mathrm{c}}\) and the secondary consolidation index \(\mathrm{C}_{\mathrm{s}}\). When the vertical pressure and soil thickness are known, \(\mathrm{e}_{0}\), \(\mathrm{C}_{\mathrm{c}}\) and \(\mathrm{C}_{\mathrm{s}}\) of each soil layer are the direct influencing parameters of settlement calculation. Therefore, we just need to analyze the relationship between these three parameters. From Figure 5, there is an obvious linear relationship between soil initial void ratio \(\mathrm{e}_{0}\) and its natural water content \(\omega\). The slope of \(\mathrm{e}_{0}\) and the natural water content \(\omega\) is 0.0262. We obtained an empirical Formula (4). \[\mathrm{e}_{0}=0.0262\omega+0.0697\ \mathrm{R}^{2}=0.92 \tag{4}\]  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{3}{*}{**Sample**} & \multirow{3}{*}{ \begin{tabular}{c} **Soil** \\ **Classification** \\ \end{tabular}