# Digital Twin-Driven Stability Optimization Framework for Large Underground Caverns
## 3 Practical Implementation and Case Study
### Digital Twin Application for Monitoring and Stability Assessment
#### 3.2.5 Actual Construction  
The excavation was carried out primarily by using the drill and blast method, with smooth blasting techniques incorporated to minimize overbreak and maintain an optimal excavation profile. The excavation sequence followed the heading and bending methods, with adjustments made based on real-time geological feedback from the DT-integrated monitoring system. The DT model continuously updated excavation progress, linking blast sequencing, stress redistribution, and deformation trends, ensuring that modifications to the excavation approach were data-driven and proactive. In actual construction based on the proposed digital twin, the as-built geology, excavation sequence, and support measures were implemented along with the installation of convergence equipment replicating the virtual world (Figure 10). Geological mapping was conducted through continuous face mapping after each blast, ensuring the real-time documentation of rock mass quality and geomechanical properties. The DT team utilized Q-system classification, categorizing the exposed rock into Q2 to Q5 classes, which dictated the intensity and type of support measures required. This allowed the engineers to simulate different support configurations before implementation, ensuring stability and safety. Support systems were applied immediately after excavation, with  
Figure 10: (a) Powerhouse Stage 3 excavations in real world; (b) powerhouse cross-section showing location of convergence arrays, load cells, and extensometers; (c) geological mapping of powerhouse during construction. reinforcement strategies dynamically adjusted based on DT-driven predictions of stress and deformation behavior. A total of 42 sets of three-point extensometers were installed throughout the power-house cavern to monitor deformation and convergence. In addition, 17 anchor load cells were installed to measure the load buildup in cable anchors and bolt anchors. Therefore, the combined total of measurement units installed for deformation and load monitoring in the powerhouse section amounted to 59 units. In addition, during the construction phase of the powerhouse cavern, several convergence stations were established by using reflective targets placed at various locations to monitor deformation across the cavern openings. The installation of convergence monitoring instruments during the actual construction was a fundamental aspect of the real-world application of the DT framework, facilitating the continuous deformation monitoring and stability assessment of the underground powerhouse cavern. Reflective targets were employed at designated convergence stations to monitor the relative displacement between two fixed points. This method proved to be highly effective in detecting ground convergence around excavation zones, offering reliable insights into the stability of the surrounding rock mass. A total of eight convergence arrays were installed along the 137 m length of the powerhouse cavern. These arrays were strategically positioned around the cavern's periphery--including the crown, sidewalls, and invert--ensuring the comprehensive capture of displacement data from all critical structural zones. The installation process was executed in a phased manner, synchronized with the excavation progress. Targets were fixed as close as possible to the advancing excavation face or the deepening invert, enabling the early detection of deformation trends and enhancing the responsiveness of support measures. In the post-construction phase, convergence stations were replaced with a 3D prism target system; the original reflective target-based convergence stations became largely ineffective due to the obstruction of lines of sight caused by the installation of electro-mechanical equipment and false walls. A total of 24 prism targets were planned across six sections, with two additional fixed reference targets at the end wall. Measurements were taken by using a total station, enabling precise 3D displacement tracking throughout the underground complex.