Since the beginning of this year, the General Command of the China Railway Central Yunnan Water Diversion Project has consistently adhered to a goal-oriented approach, fully allocated all resource elements, coordinated participating units to seize the golden construction period, fought the construction battle, and advanced the Phase I and Phase II supporting works of the Central Yunnan Water Diversion Project with high quality and efficiency.
　　On July 15, the No. 2 pipe-jacking working shaft of the waterfall park water replenishment branch line of the Kunming section of the Phase II supporting works of the Central Yunnan Water Diversion Project, constructed by the Third Company of China Railway Seventh Group, was successfully poured, marking the start of pipe-jacking construction in the Kunming section of the Phase II supporting works. The Kunming Construction Section 2 of the Phase II supporting works has a total length of 36.8 km, including 7.8 km of pipe-jacking works. To ensure the smooth pouring of the ** pipe-jacking shaft, the project construction unit applied high standards and strict requirements throughout foundation pit excavation, foundation treatment, cushion pouring, rebar tying, formwork installation, and pipe-jacking shaft pouring, strictly following the design scheme and safety technical disclosure, achieving first-piece standardization and model guidance, and accumulating experience for subsequent pipe-jacking construction.
　　On July 19 and 20, the Laoyingwo Tunnel on the Cangling Branch Line of the Chuxiong Construction Section 2 of the Phase II project and the interval between the No. 1 downstream main tunnel control section and the No. 2 upstream main tunnel control section of the Wanjia Tunnel in Chuxiong Bid Section 1 of the Phase I project, constructed by China Railway Eighth Group, were successfully holed through 30 days and 139 days ahead of schedule respectively.
　　The Laoyingwo Tunnel has a total length of 2,059 meters. The traffic conditions at the tunnel portals are poor, the terrain and geological conditions along the route are relatively complex, the overburden of the tunnel body is thin, and the surrounding rock of the entire tunnel is dominated by Class IV and Class V surrounding rock, with squeezing and crumpling phenomena and significant influence from groundwater activity, making construction difficult.
　　The interval between the No. 1 downstream main tunnel control section and the No. 2 upstream main tunnel control section of the Wanjia Tunnel consists entirely of underground tunnels with large burial depth, with a maximum burial depth of 562 meters in the interval. The geological conditions are complex and variable, and Class IV and Class V surrounding rock are widely distributed within the interval, accounting for 90% of the entire interval length. In addition, faults in the interval are densely developed and large in scale, groundwater activity is strong, fractures are filled with gypsum, and the risk level of surrounding rock deformation and failure is high, making large-scale collapse, roof fall, water and mud inrush highly likely, with great construction difficulty and high risk.
　　Facing these challenges, the project department of China Railway Eighth Group adhered to the principle of technical schemes first. Through on-site exploration, review of relevant specifications, and special meetings, it formulated scientific and reasonable construction schemes. During construction, it always followed the construction principles of "advance pipe forepoling, strict grouting, short advance, weak blasting, strong support, and frequent measurement," used a combination of advanced geological forecasting and advanced horizontal drilling to detect the geological surrounding rock and groundwater distribution ahead in advance, and adjusted construction methods in a timely manner, greatly reducing construction risks. Based on the in-tunnel construction techniques and characteristics, it carried out technological innovation and small improvements to increase construction efficiency, and actively summarized its work, completing and publishing 11 patent applications and 2 construction technology studies. The application of these innovative achievements improved construction efficiency, accelerated project progress, and enhanced safety and quality.