# A Theoretical Study on the Resilience Evaluation Method of Operational Road Tunnel Systems
## 3 Basic Concept of Road Tunnel Resilience  
### Resilience  
The concept of resilience first appeared in the field of engineering [15]. Similar to the concept of elasticity, it is used to describe the ability of a single structural member or a certain material to deform and return to the initial state under external force conditions [16]. Since then, the concept of resilience has been introduced into ecology [17], sociology [18], psychology [19], and many other fields. Gradually, it formed a set of independent concept systems, which were used to describe the ability of complex systems to decline and restore to their original functional state or maintain a certain functional level when subjected to external disturbances. After half a century of evolution, the concept of resilience has experienced three stages of development [15]: engineering resilience, ecological resilience, and social-ecological resilience. Its connotation has been gradually enriched and improved, and it has formed four R basic resilience characteristics [20]: robustness, rapidity, redundancy, and resourcefulness. The meaning of the resilience attributes is shown in Table 1.  
The concept of resilience mainly describes the process of the system resisting external disturbances and recovering. Four main elements can be extracted in this process:  
1. External disturbances.
2. System function.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Basic Attributes of Resilience** & **Interpretation** \\ \hline \multirow{4}{*}{Robustness} & Strength or the ability of elements, systems, and other units of analysis to \\  & withstand a given level of stress or demand without suffering degradation or loss \\  & of function. \\ \multirow{2}{*}{Rapidity} & The capacity to meet priorities and achieve goals in a timely manner in order to \\  & contain losses and avoid future disruption. \\ \multirow{2}{*}{Redundancy} & The extent to which elements, systems, or other units of analysis exist that are \\  & substitutable, i.e., capable of satisfying functional requirements in the event of \\  & disruption, degradation, or loss of functionality. \\ \multirow{4}{*}{Resourcefulness} & The capacity to identify problems, establish priorities, and mobilize resources \\  & when conditions exist that threaten to disrupt some element, system, or other unit \\ \multirow{2}{*}{Resourcefulness} & of analysis; resourcefulness can be further conceptualized as consisting of the \\  & ability to apply material (i.e., monetary, physical, technological, and informational) \\ \multirow{2}{*}{and human resources to meet established priorities and achieve goals.} \\ \hline \hline \end{tabular}
\end{table}
Table 1: The table of resilience 4R basic attributes.  
3. Resistant ability.
4. Recovery ability.  
In the conceptual system of resilience, \"system\" and \"external disturbance\" are two main elements in the process. Among them, \"system\" is the main carrier to withstand \"external disturbance\". The appearance of \"external disturbances\" will affect the \"system function\" and reduce the operating level of the system. \"Resistance\" and \"recovery\" are the coping abilities of the system after suffering \"external disturbance\". The relationship between the four elements can be described as shown in Figure 1.