Abstract: To overcome the challenges of low construction efficiency, high variability in surrounding rock conditions, and fault-induced water inrush risks in high-head, large-section diversion tunnels in Southwest China, a series of targeted technical innovations were developed. Three-dimensional geological modelling combined with real-time surrounding-rock classification enabled the creation of a graded equivalent elastic resistance coefficient system, which guided lining optimization. As a result, Class II/III floor lining thickness was reduced to 30 cm, and adjustments to reinforcement spacing—along with denser anchoring in Class V sections—achieved an 8% reduction in steel usage. Construction efficiency was significantly improved through new techniques, including a hydraulic lifting trolley (precision ±5 mm) and a bottom-arch sliding formwork system (flatness <5 mm), which together increased lining installation speed by 40%. Parallel excavation of the upper and lower tunnel sections further boosted monthly advance rates by 50%, shortening the overall construction schedule by three months. For the Fx1 fault zone, a double-layer pipe-shed system combined with high-pressure grouting reduced water inflow by 90%, while the use of a single-side-wall pilot tunnel method cut convergence by 80%, ensuring safe passage through the 214 m high-risk segment. Monitoring results show that surrounding-rock deformation has remained stable and lining stresses have stayed within safe design thresholds. These outcomes provide a strong technical reference for similar diversion-tunnel projects across Southwest China. 

Key words: Hydropower Station, Water Diversion Tunnel, Surrounding Rock Classification, Lining Optimization, Construction Methods