On September 19, the 1# downstream and 2# upstream main tunnels of the Shizishan Tunnel of the Central Yunnan Water Diversion Project were safely and smoothly holed through, with cumulative excavation of the entire section exceeding 21 kilometers. This marks a key breakthrough in the construction of the Shizishan Tunnel of the Central Yunnan Water Diversion Project and provides favorable conditions for the subsequent construction of the remaining works.

The Shizishan Tunnel is located in Binchuan County, Dali Prefecture, with a total length of 29.42 kilometers. It is one of the key control projects in the construction of the Central Yunnan Water Diversion Project. China Railway 18th Bureau Group is responsible for the construction task of 21.172 kilometers. The maximum buried depth of the tunnel is 728 meters. The drill-and-blast method is adopted with a configuration of "4 adits + 1 main tunnel," and the cross-section type is horseshoe-shaped. The engineering geological conditions of the tunnel are complex and variable, with Class IV and V surrounding rock accounting for 70%, and a maximum buried depth of 601 meters. It passes through unfavorable geological sections such as high geothermal zones, sections with risks of mud and water inrush, and soft rock deformation, posing high safety risks. In particular, the water inflow at the working face is large, and the interior of the tunnel presents a "Water Curtain Cave" condition, making construction difficult and technical requirements high.

On September 19, the 1# downstream and 2# upstream main tunnels of the Shizishan Tunnel of the Central Yunnan Water Diversion Project were safely and smoothly holed through.

According to Liu Junfeng, technical director of the Shizishan Tunnel Project Department, in response to the unfavorable geological problems, the project team adhered to the principles of "prevention first, combining prevention and control" and "investigate whenever in doubt, excavate only after investigation," proactively took measures to prevent problems before they occur, established a "QC" team, conducted "brainstorming," pooled wisdom, carried out comparative analysis, formulated plans, and repeatedly verified them, thereby arriving at reasonable and economical treatment methods and efficiently and safely passing through the high-risk, high-difficulty unfavorable geological tunnel sections. For special geological sections, the project team adopted excavation and lining simultaneously in lining construction, used traveling hydraulic trestles and advanced longitudinal sliding formwork technology for the invert, and adopted construction techniques such as an automatic pouring system for the side walls and crown, thereby ensuring project progress and excavation quality.

Xu Gang, head of the Shizishan Tunnel Project Department, stated that next the project department will closely focus on the main tone and core goals of project construction—"ensure safety, ensure quality, respect objective laws, carry out scientific construction, and proceed as quickly as possible"—continue to carry out labor competitions, vigorously promote the spirit of labor, the spirit of model workers, and the spirit of craftsmanship, work closely with all participating parties, overcome difficulties, and go all out to advance project construction. It will strengthen the construction organization of the critical path of the Shizishan Tunnel and make the final sprint toward the early holing-through of the entire tunnel. At the same time, the project department will strictly manage environmental protection and soil and water conservation, strengthen preventive measures, improve soil and water conservation measures, minimize the impact of construction on the environment, and comprehensively build a green model project.

The Central Yunnan Water Diversion Project is a landmark project among the 172 major water conservancy projects for water conservation and water supply determined by the State Council. It is also the largest and most heavily invested water resource allocation project in Southwest China and the largest water diversion project under construction in China. After the project is completed, the water-receiving areas will involve 34 water-receiving sub-districts in six prefectures and cities along the main water conveyance canal, benefiting a land area of 36,900 square kilometers, with approximately 11.12 million people directly benefiting.