## 5 Conclusions  
This study presents an innovative methodology for monitoring tunnel cross-section deformation using an MLS system, SILSS, designed to address the limitations of traditional and less advanced MLS systems. Unlike prior methods that often rely on stationary equipment or MLS systems with lower spatial resolution, SILSS enables high-density, accurate, and efficient data acquisition in challenging tunnel environments. This precision and efficiency distinguish SILSS, making it uniquely suited for real-time, non-invasive tunnel monitoring.  
The proposed approach integrates advanced computational techniques, including the ICP algorithm for aligning data from the two measurements and a novel point density denoising technique, to significantly enhance point cloud quality and improve tunnel lining extraction. These advancements enable a maximum observed displacement accuracy of 1 mm, with a correlation coefficient of 0.99, surpassing the precision of conventional methods and offering unprecedented detail.  
To validate the methodology, SILSS data were compared with data collected using the Leica Pegasus Two Ultimate scanner, a widely recognized system for tunnel deformation monitoring. Comparative metrics, including average point cloud displacement and ovality, demonstrated strong agreement between the two systems, confirming SILSS as a reliable and precise alternative to existing MLS-based technologies.  
A standout feature of this methodology is its ability to detect and analyze localized deformations, such as shield ring point cloud displacements, ovality changes, and center-line deviations, with remarkable sensitivity. Traditional methods often focus on broader measurements, limiting their ability to identify critical localized deformations. In contrast, SILSS provides spatially resolved assessments of tunnel health, offering actionable insights into potential problem areas. The fine-grained analysis of shield ring 53 highlights the system's capability to identify subtle but significant deformations, ensuring early detection of structural issues.  
Overall, the SILSS-powered MLS system represents a significant leap forward in tunnel deformation monitoring. This methodology sets a new benchmark in tunnel safety assessments by combining cutting-edge hardware with advanced data processing algorithms. Its innovations in precision, efficiency, and spatial resolution establish SILSS as a superior, non-invasive, and versatile tool for continuous monitoring. Future research could extend its application to tunnels with diverse geometries and explore the integration of complementary data sources, further enhancing its utility and effectiveness.  
Conceptualization, M.C. and L.W.; Formal analysis, M.C.; Methodology, M.C. and L.W.; Validation, M.C. and Z.Y.; Writing--original draft, M.C. and Z.Y.; Funding acquisition, L.W.; Data curation, L.W.; Writing--review and editing, L.W.; Supervision, L.W. All authors have read and agreed to the published version of the manuscript.  
National Natural Science Foundation of China (Grant No. 42201482) and Joint Fund Project of the Liaoning Provincial Natural Science Foundation (2024).  
Not applicable.  
The data presented in this study are available on request from the corresponding author. The data are not publicly available due to their complexity.  
Sincere thanks are given to [PERSON] for reading this work.  
The authors declare no conflicts of interest.