Application of optimized support system-based large deformation control technology in plate suture zone tunnels: a case study of the China–Laos railway

The Luang Prabang Suture Zone, characterized by its unique amalgamation of terranes from varied microcontinents, exhibits distinct metamorphic and paleogeographic histories, impacting the stability of infrastructure such as tunnels. This study addresses the challenges posed by complex tectonic stress patterns and the inherent weakness of rock masses in the suture zones, particularly influencing the China–Laos Railway tunnels. We conducted comprehensive tests, including tectonic stress assessments, rock strength measurements, tunnel loosening zone evaluations, and primary support stress analyses. Our findings reveal that the predominant crustal stress pattern, σ H > σ h > σ v , promotes thrust fault development, with significant deformations observed in carbonaceous slate exhibiting lump structures at suture boundaries. These deformations are primarily manifested through asymmetric sidewall squeezing, exacerbated by the expansion of surrounding rock loosening zones. In response, we propose a novel active control technology, verified through field application. This involves optimizing tunnel cross-sections, refining excavation techniques, employing a strategic long–short bolt system, and enhancing the stiffness of primary supports. Our research not only provides practical solutions for tunnel stability in similar complex geological environments but also extends the theoretical understanding of such geological settings. Future work will focus on refining these innovative control technologies for broader application in challenging tunneling scenarios.