# Study on Share Rate of Support Structure for Super-Large Span Twin Tunnels with Small Interval
## 4 Results and Discussion
### Discussion  
According to the content of Sections 4.1 and 4.2, the share rate of the primary support and the secondary lining are both reckoned to be 40%. The other 20% of the surrounding rock pressure is taken by multiple factors (mainly the advance support and the surrounding rock itself).  
In other words, the aggregated rock pressure borne by primary support and secondary lining is 80% (of the theoretical load). Combined with the content of Section 4.3, the comparison of the calculation and the measurement is shown in Table 4 and Figure 14.  
From Table 4, measured pressure, which the rock pressure that the primary support and secondary lining exactly bear, is less than 80% of the theoretical load according to the measurement. The main reason for this deviation is that before the installation of the pressure cells and the construction of the primary support, part of the rock pressure was relaxed and cannot be measured. Usually, this part of the rock pressure was supported by the surrounding rock mass itself. So, in consideration of safety, the conclusion that total share rate of the primary support and the secondary lining is 80% is valid for design. The correctness of theoretical calculation of surrounding rock pressure is also verified by Table 4 and Figure 14 as the deviation is acceptable.  
In summary, based on the analysis above, the share rates of the primary support and the secondary lining are both 40% in Daling Tunnel (the super-large span twin tunnel), and other 20% of pressure is mainly born by the advance support and the surrounding rock itself. Although the results of theoretical calculation and the measurement do not match perfectly, the overall deviation is small enough, which basically meets the requirements of design and application in engineering.  
Meanwhile, during the whole process, there are several assumptions and limitation, for example:  
1. The influence of the construction's sequence of the first hole and following hole was not considered in this research, and the way of excavation was assumed as full section excavation.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Measured Point**} & **Theoretical Load** & **80\% of the Theoretical Load /kPa** & **Measured Pressure /kPa** & **Deviation** /kPa** \\ \hline A & 286.90 & 229.56 & 180.94 & 21.18 \\ B & 211.63 & 169.30 & 142.68 & 15.73 \\ C & 98.40 & 78.72 & 65.36 & 16.97 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Comparison of the calculation and measurement.  
Figure 14: Total pressure of the primary support and the secondary lining. There is about 20% deviation at each point and it is believed to be born mainly by advance support and the surrounding rock itself.  
2. This paper supposed that the stratum was consistent and the surrounding rock mass was ideal. 3. The surface of earth was presumed to be horizontal, and so on. These assumptions and limitation are supposed to be concerned when the conclusion is applied to the practical projects. In addition, the share rate is affected by the strength and stiffness of the composite lining as well as the method and time of excavation and construction. Thus, the share rate of the twin tunnels with super-large span in various conditions still needs to be researched systematically.