At 10 o’clock on November 19, after 123 days of excavation, the section between the railway station and the middle air shaft for Dalian Metro Line 5 was opened for two-way transport, which was undertaken by the Urban Rail Transit Engineering of China Railway First Group, marking the start of complete operation for the shield tunnel between the railway station and the South Suoyuwan Station, the control project of the whole line, seven days ahead of schedule.
The shield tunnel between the Railway Station and the South Suoyuwan Station for Dalian Metro Line 5 was completed.
The undersea tunnel project set “five new records in the industry”: the first large shield undersea tunnel in karst stratum in the world, the large shield tunnel with the longest distance to hard rock stratum in China, the largest-diameter subway undersea tunnel in China, the most fully functional domestic large-diameter slurry balance shield machine in the world, and the first large-diameter slurry shield machine with normal pressure cutter head to pass through the karst caves.
Workers assemble large shield segments.
Tunnel construction was faced with four major problems which could be characterized by “long, huge, high and dangerous.” First, the tunneling distance is long in the high-strength hard rock stratum, and the shield machine needed to continuously work through the hard rock stratum as long as 2,882 meters. Second, the environmental risks are huge. The large shield machine passes through important buildings and traffic facilities such as waterways, docks, etc.; besides, the project is located among limestone, diabase and calcareous slate, with high compressive strength of rocks as high as 118 MPa, which becomes a great safety risk. Third, the tunnel is deeply buried and the water pressure is high, with the maximum head pressure at 0.5 MPa, equivalent to the pressure of three people standing on the area of an egg. Fourth, as the tunnel crosses 1,538 meters of strongly developed karst area, more than 1,000 karst caves, large or small, were discovered in exploration, with the largest cave recording 29.8 meters high, which were difficult to detect and deal with.
Workers assemble segments in the narrow space of the section.
To ensure high-quality tunnel construction, China Railway First Group adopted new technologies and innovative management methods. First, in collaboration with China Railway Engineering Equipment Group, it developed “the smartest shield machine in China”—“Haihong” air cushion slurry balance shield machine. Second, the “drilling plus CT scanning” method was adopted to find out the distribution position and scale of more than 1,000 karst caves and implement grouting. Third, the BIM plus GIS three-dimensional dynamic simulation management platform was developed. Fourth, an information intelligent system was established to realize the double guarantee of safety and quality for management. Fifth, bid data was harnessed to summarize, analyze and apply the tunneling parameters. Sixth, a software for the tool change management and analysis system was developed.
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