# Digital Twin-Driven Stability Optimization Framework for Large Underground Caverns
## 3 Practical Implementation and Case Study
### Digital Twin Application for Monitoring and Stability Assessment
#### 3.2.6 Deformation Data Acquisition  
During construction and post-construction data acquisition, deformation monitoring in the underground powerhouse complex was carried out by using a combination of extensometers, load cells, and reflective targets (Figure 11). A total of 52 three-point vibrating wire extensometers were installed to measure rock mass deformations, and vibrating wire load cells (two in the powerhouse cavern, eight in the bus bar tunnels, and two in bonneted gate niches) were used to monitor anchor load development. For the data collection of these extensometers and load cells, a structured and centralized data acquisition system was implemented to enhance monitoring efficiency. All instrument cables from extensometers and load cells were routed to dedicated panel boards located in the powerhouse control room and transformer hall access gallery. Data collection was conducted by using digital vibrating wire readout units (e.g., BGK-405), which allowed for the direct connection to panel sockets without the need to access individual instruments manually. These readout units featured internal data logging capabilities, enabling the automatic recording of measurements with corresponding timestamps and instrument IDs. Once collected, the data were transferred to central computing systems via USB or Bluetooth, where they were further processed and analyzed by using Excel spreadsheets and specialized monitoring software. This centralized and semi-automated approach ensured the accurate, efficient, and secure handling of deformation monitoring data, facilitating long-term structural performance assessment. Figure 11d shows the sudden increase in load cell readings after a period of zero load in the beginning due to the installation configuration, as these load cells were installed without applying pre-tension or pre-load. In cases where load cells are installed without pre-tension, they do not record any load until the surrounding ground movement or convergence becomes sufficient to mobilize the support system. This behavior is commonly observed in underground monitoring setups and aligns with standard field conditions.  
Convergence stations with reflective targets were installed across the cavern to measure lateral displacements by using a total station. Data were collected by using a total station, which measured the distance between opposing reflective targets with high precision. These measurements were carried out manually at regular intervals, typically once per week, depending on the excavation progress and the observed rock behavior. The recorded measurements were then manually entered into Excel spreadsheets for analysis, enabling the engineers to monitor convergence trends and assess the effectiveness of the installed support systems. However, as structural and electro-mechanical installations progressed, the visibility between targets was obstructed, limiting the effectiveness of this method. Post-construction data acquisition addressed the limitations of the initial reflective targets system. The reflective targets were replaced with a high-precision 3D prism monitoring system, comprising 24 prism targets installed in six sections and two fixed reference targets at the powerhouse end wall. These values are read by an automated total station and linked with the existing data-logging systems of load cells and extensometers.