## 4 FLC Feasibility Study
### Load Stability Calculations  
When pouring FLC on soft ground sections, problems such as uneven settlement may occur due to the increase in additional stresses, so it is essential to check the bearing capacity stability of FLC. A typical cross-section of the FLC is shown in Figure 3.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Distance from the Bottom of the** & **Wet Density R\({}_{\text{fw}}\)/(kg\(\cdot\)m\({}^{-3}\))** & **28 d Compressive Strength/MPa** \\ \hline
0–0.8 & R\({}_{\text{fw}}\)\(\leq\) 650 & \(\geq\)1.2 \\ \textgreater{}0.8 & R\({}_{\text{fw}}\)\(\leq\) 650 & \(\geq\)0.8 \\ \hline \hline \end{tabular}
\end{table}
Table 2: FLC key design performance indicators.  
Figure 3: Cross-sectional view of foam lightweight concrete.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Strength** & **Water-** & **Composition of FLC per** & & & & **7 d** & **28 d** \\
**Grade/MPa** & **Cement** & **Square/(kg/m\({}^{3}\))** & **Bubble** & **Density/(kg/m\({}^{3}\))** & **Flow Value** & **Compressive** & **Compressive** \\ \hline
0.8 & 0.65 & 319 & 207 & 68.7 & 560 & 180 & 0.56 & 0.86 \\
0.8 & 0.65 & 309 & 201 & 69.6 & 545 & 175 & 0.47 & 0.75 \\
0.65 & 328 & 213 & 67.8 & 575 & 182 & 0.6 & 0.92  
According to the specification of highway foundation design [25], the combined value of action effect should not exceed the allowable value of foundation bearing capacity, as shown in Formula (1). the FLC replacement filling calculation model is shown in Figure 4.  
\[K_{0}\geq H_{\rm L}\times\gamma_{\rm L}+H_{\rm F}\times\gamma_{\rm F}+P_{\rm 1}, \tag{1}\]  
where \(K_{0}\) indicates the bearing capacity of the plain fill foundation; \(H_{\rm L}\) indicates the thickness of the structural layer of the pavement; \(\gamma_{\rm L}\) indicates the structural layer capacity of the pavement; \(H_{\rm F}\) indicates the thickness of the FLC; \(\gamma_{\rm F}\) is the natural capacity of the FLC; and \(P_{\rm 1}\) is the live load of the pavement.  
For the second phase project of the southern end of the Foqingcong Expressway under the buried existing high pressure gas pipe section to carry out load bearing stability calculations. According to the field survey report, the bearing capacity of the fill depth section is 110 KPa, and the live load of the pavement is converted to a uniform load of 15 \(\rm{KN/m^{3}}\) (based on the empirical value of 70 tonnes of vehicles required for first-class highways and motorways). The load-bearing capacity stability test is shown in Formula (2).  
\[K_{0}=110\;\rm{KPa}\geq 0.83\times 26+5.63\times 5.5+15=67.545\;\rm{KPa}, \tag{2}\]  
The calculation results show that the use of FLC can meet the foundation bearing capacity stability requirements of the Fuqingcong Expressway project.  
According to the project ground investigation report and borehole records, the FLC pre-replacement depth (\(-0.15\;\rm{m}\)) of the second phase of the Foqingcong Expressway project has not reached the depth of the water table (\(-2.1\;\rm{m}\)), so there is no need to carry out anti-floating test. For the small amount of pore water, impermeable geomembranes were laid at the top layer and steps.