Recently, as the massive cutterhead began to rotate slowly once again, the right tube of the composite TBM shield machine for the Huanlegu Station to Jiuquhe East Station section (hereinafter referred to as the Huan-Jiu section) of Phase II of Chongqing Rail Transit Line 15, constructed by the Fifth Company of China Railway 11th Bureau Group, was successfully launched, marking the achievement of dual-tube launching for the tunnel in this section and important progress in the project's construction.

Launch site

The strata traversed by the Huan-Jiu section tunnel are mainly moderately weathered sandy mudstone and sandy mudstone formations. The tunnel depth in this section ranges from approximately 8.9 meters to 85.7 meters, and the surrounding rock grades of the strata traversed range from Grade III to Grade VI.

Since Huanlegu Station is a mined station, after the breakthrough of the section between Jinshansi Station and Huanlegu Station, the project team adopted a scheme of pushing the composite TBM shield body through the station without excavation. Due to the tight schedule, the conventional method of laying steel plates with rollers underneath for the pass-through could not meet the construction progress requirements and required large quantities of steel plates, rollers, and other materials. To reduce the pass-through time and lower the costs of personnel, machinery, and materials, the project department pooled collective wisdom, convened special seminars and expert demonstration meetings, and adopted a "stepping pass-through" scheme, using 4 sets of vertical jacking cylinders plus 2 sets of horizontal telescopic cylinders in coordination for propulsion. The front ends of the telescopic cylinders are connected to the composite TBM shield body, and the rear ends are connected to the launching cradle. While halving the manpower input, the propulsion speed increased from 30 meters per day to 50 meters per day, greatly improving pass-through efficiency.

In addition, the Huan-Jiu section tunnel is located in the central urban area of Chongqing, passing through multiple important buildings and residential areas. To ensure a smooth launch, the project team vigorously carried out labor competitions, continuously optimized the construction organization design, reversed the schedule, refined and decomposed construction tasks, conducted advance surveys of pipelines and buildings along the route, actively organized on-site exploration with relevant departments, and promptly coordinated the processing of construction permits, laying a solid foundation for the subsequent high-quality, efficient, and safe tunneling of the composite TBM shield machine.

Construction of ancillary structures at Huanlegu Station

It is reported that Chongqing Rail Transit Line 15 is the first urban express rail line in Chongqing. The line is divided into Phase I and Phase II construction, and Jiuquhe East Station, the terminus of the Huan-Jiu section, is the "intersection point" of the Phase I and Phase II projects. The successful launch of the right tube of the Huan-Jiu section this time lays a solid foundation for the later linked operation of the two phases. Upon completion, it will efficiently connect Chongqing's western industrial parks, effectively alleviate congestion in the central area of Chongqing's main urban districts, and promote the integrated high-quality development of the main urban metropolitan area.