# 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
During excavation, extensive rock support measures are to be implemented, including fully cement-grouted rock bolts, layers of steel fiber-reinforced and plain shotcrete, steel straps, wire mesh, and bar and strand anchors. To monitor the deformation during construction and post-construction, two kinds of instruments are used to monitor the rock mass deformation in terms of relative and absolute displacement. First, convergence arrays are utilized to measure the relative displacement between two points at designated convergence stations. Convergence measurement is carried out using reflective targets that are installed as close as possible to an advancing face or a deepening invert. All measured convergences are relative, in that the distance between two targets is monitored. It is relatively easier to install and cheaper to monitor convergence targets during the excavation period. For absolute displacement, extensometers and load cells are generally installed for long-term convergence monitoring and are the permanent monitoring system for both excavation and operation. Extensometers measure absolute displacement, providing critical data on the deformation behavior of the rock mass over time. Anchor load cells monitor the force buildup in anchor bars or cable anchors. These load cells play a crucial role in understanding load distribution and the effectiveness of the rock support systems, ensuring that the rock mass remains stable under the applied forces. Together, these instruments form a comprehensive monitoring system that is essential to maintaining safety and stability throughout the construction process. _Step 6:_ The convergence monitoring data are collected on a regular basis, depending on the deformation behavior. The data monitoring of convergence arrays is relatively straightforward and cost-effective, making them a practical choice for monitoring during the excavation phase. Reflective targets are positioned as close as possible to the excavation face to capture real-time deformation data. Measurements are typically recorded manually by using surveying total stations, though automated systems with data loggers can also be used for continuous monitoring. Data acquisition with extensometers and load cells is typically continuous, with sensors transmitting real-time data to a centralized monitoring system, depending on the project requirements. Automated systems with data loggers collect and transmit data in real time, enabling continuous monitoring. The measurements provide information about the absolute displacement of the rock mass, helping engineers identify zones of instability and assess the effectiveness of support systems. Data from convergence arrays, extensometers, and load cells are integrated into a centralized monitoring system, enabling continuous monitoring and rapid response to changes. _Step 7:_ The final step achieves the virtual monitoring and optimization of rock support based on deformation behavior. This BIM-based module provides semantic and non-semantic information of actual deformation, as built rock and geological support information. It provides the analysis of existing deformation monitoring data and observationswith its current condition and its additional capacity to withstand potential long-term loads from creep and reduction in rock mass strength. This geological mapping information in a BIM-based 3D model provides a detailed and interactive representation of rock types, lithology, geological structure, weak and fault zones, and stratigraphy. This step provides actual deformation feedback to optimize the virtual design and construction process.