On December 2, the 7th ITA Tunnelling Awards 2021 revealed that the Dalian Metro Line 5 project (“A Large-diameter Shield Tunnel Engineering Project Through Karst Strata in a Sea Area”) constructed using CREG slurry TBM “Haihong” had won the “Project of the Year” category
The CREG (China Railway Engineering Equipment Group Co., Ltd.) slurry TBM excavated the Dalian Metro Line 5 subsea tunnel from Railway Station to Suoyu Bay South Station. Launched on January 18, 2018, the TBM successfully broke through on January 10, 2021, an event that marked a remarkable achievement in terms of overcoming the significant challenges posed when tunnelling through karstic strata under a seabed using a large diameter shield machine.
The tunnel construction between Railway Station and Suoyu Bay South Station posed four unpredictable challenges, thought of as unprecedented by industry experts. The first was the long tunnelling distance through high-strength, hard rock stratum, which meant that the TBM had to continuously advance for 2882m. The second was the host of environmental risks the TBM encountered, for example, the machine had to pass beneath buildings and transportation facilities such as the channel and wharf. Not only did the rock have a high compressive strength – with the maximum of 118MPa – but there were also weathered and fault zones and uneven, soft and hard strata, scattered through the limestone, diabase and calcareous slate.
The third challenge the TBM faced was the high water pressure caused by the large buried depth, with the maximum of 0.5MPa. The TBM had to pass through a 1538m long area of strong karstic development. More than 1000 various karst caves were found during exploration with a maximum height of 29.8m.
The TBM was suitably specified and configured and can adapt to unfavorable geology such as a karst cave, fault fracture zone, upper soft, and lower hard stratum. CREG optimized the cutting tools, as they would be frequently damaged by the complex geology. As a result, the excavation rates successfully increased from 60m per month to 90m, and then to 120m, finally exceeded 200m per month, creating an excavation record for a large diameter TBM tunnelling through seabed hard rock strata in China.
After completion of Dalian Metro Line 5, a north-south urban ‘fast track’ will be formed in the city, which will shorten the time from Suoyu Bay to Railway Station from more than 30 minutes to less than 3 minutes, alleviating the ground traffic pressure and building a new Dalian City of “one bay with two banks”.
This is another world-class innovation project involving CREG, after the project “The Mechanized Method with Large Section Horseshoe Shape EPB TBM First Applied in Loess Mountain Tunnel” won the ITA Tunnelling Awards 2018 in the “Technical Project Innovation of the Year” category.