June 9th saw the 15.53m diameter slurry TBM “Mawan” manufactured by China Railway Engineering Equipment Group Co. Ltd. (CREG) successfully break through into the reception shaft on the right bore of Shenzhen’s Mawan Subsea Tunnel project. The project has a 2063m long TBM drive, including a subsea section of 1100m, which is crucial on the entire project.
During boring, “Mawan” overcame four major construction challenges. The first being the long distance alignment of complex ground conditions, including 50% mix ground and 34.15% of full-face hard rock, which meant the TBM had to bore through a significant stretch of high-strength rock. The second challenge was the complex terrain in the subsea section which can tend to cause TBM floation and deviation from the designed route, combined with the risk of severe cutter wear and the subsequent need for cutter changes. The third issue was the large overburden, with the tunnel located at a depth of more than 40m under the seabed, with a maximum water pressure of 5bar and a maximum rock strength of 193MPa. The fourth was the large cross-section with an outer diameter of the segmental ring of over 15m.
To operate under such challenging conditions, “Mawan” was designed with multiple innovative technologies to ensure construction progress and safety. The best monthly advance recorded was 172m in the mixed ground and a best daily advance of 10m, which according to CREG sets a new record for the daily advance of large-diameter subsea TBM in China.
The Shenzhen Mawan Subsea Tunnel is expected to be put into operation in 2024. Once in operation it will play an important role in expanding the city’s urban development and transport interconnectivity in the Guangdong-Hong Kong-Macao Greater Bay Area.