# Digital Twin-Driven Stability Optimization Framework for Large Underground Caverns
## 2 Digital Twin Framework for Real-Time Monitoring and Optimization of Underground Caverns
### Digital Twin Methodology  
A seven-step DT-driven methodology based on the above-mentioned six modules is developed for deformation monitoring and optimizing rock support design to ensure the stability of underground caverns during the construction and post-construction phases. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Category** & **Name** & **Description** \\ \hline \multirow{4}{*}{**Extended Types**} & IfcRealTimeSensor & A specialized sensor type for capturing real-time deformation and stress. \\  & IfcSmartRockBolt & A rock bolt equipped with integrated strain and stress sensors. \\  & IfcAutomatedSurveySystem & A system capable of continuous real-time geotechnical surveying. \\ \hline \hline \end{tabular}
\end{table} 
Table 2: _Cont._  
Figure 3: UML diagram of proposed IFC schema extension for digital twin for underground convergence monitoring. Figure 4 shows the proposed seven-step process in the virtual environment and physical world driven by continuous real-time data generated for monitoring deformation and the iterative optimization of rock support measures needed. _Step 1:_ A comprehensive feasibility study is carried out to collect rock samples, and extensive laboratory testing is performed to determine geological conditions. The cylindrical rock samples are collected by using drilling and coring techniques. These samples are securely preserved in durable core boxes with partitioned compartments, and unique identification sample numbers are assigned to provide the location and depth from where these samples were collected. The core samples provide structural geological information about the rock formation and important geological parameters such as rock quality designation (RQD), hardness, and orientation of joints/beddings. Laboratory testing is performed to determine the properties of natural intact rock, which are specific gravity, comprehensive strength, tensile strength, elastic modulus, slake durability test, Poisson's ratio, triaxial test, and direct shear test. This step is crucial and provides the information to decide the location and orientation of the underground cavern based on geological information. _Step 2:_ The location and geometric design of the underground cavern is one of the most critical aspects of its long-term stability and deformation behavior. The underground cavern  
Figure 4: Digital twin-driven stability optimization framework for large underground caverns. cavern should be located in the best available rock masses and be orientated as favorably as possible with respect to geological structure and the assumed orientation of principal stresses. The optimum position of the underground cavern, detailed geometric design, and rock support design strongly depend on actual ground conditions. In this stage, only general information on actual ground conditions is available from Step 1, and it is difficult and impractical to have detailed information at this stage of this project due to the nature of the underground construction environment. In all deep underground structures, detailed actual information is available during actual construction. It leads to a risk in finalizing the design's critical aspects, especially related to deformation problems posing a threat to long-term stability. In this developed DT, based on the information available, BIM-based design and geological models are developed, providing not only geometric information but also non-geometric information, providing a better understanding of geological information and underground cavern design. _Step 3:_ For the optimization of underground cavern design, virtual numerical analysis is performed to carry out design optimization and iterative calculations to simulate the real construction deformation. This step is a core part of optimizing the design strategy, because it not only guides the designers to understand the deformation behavior but also verifies the deformation during the actual construction and post-construction stages.