Ningbo Jintang Ocean-crossing Tunnel Project

Φ 14.57m CRCHI Slurry-Shield TBM

Project Year: 2024

Project Overview

Project Summary

  • Location:

    • The tunnel is located beneath the Jintang Waterway between Ningbo and Zhoushan.

    • Total length: 16.18 kilometers.

  • Significance:

    • The tunnel is currently the longest underwater high-speed rail tunnel in the world, with the Undersea Tunnel section measuring 11.21 km.

  • Tunneling Machines:

    • Two Slurry-Shield TBM, each machine has an excavation diameter of 14.57 meters, a length of 135 meters, and weighs 4,350 tons.

  • Tunneling Operations:

    • The “Yongzhou” TBM excavates 4,940 meters from west to east.

    • The “Dinghai” TBM excavates 6,270 meters from east to west.

    • Both TBMs will eventually meet under the sea, with a centerline misalignment of no more than 2 cm, even after traversing high water pressure zones and complex geological formations.

Construction Difficulties

  • Geological condition:

  • The tunnel primarily passes through soft soils, including silt, silty clay, and fine sand, as well as strongly weathered tuff, tuff breccia, and other rock formations.

  • The strata are heterogeneous, featuring both soft and hard layers, such as silty clay, gravelly soil, and tuff.

  • The weakly weathered tuff and tuff have compressive strengths of up to 72 MPa and 165 MPa, respectively.

  • The project is exposed to risks from tides and typhoons, with high and fast-moving sea waves.

  • Tunnelling Condition for “Dinghai” TBM:

  • The maximum water depth in the tunnel's marine section is 39 meters, with a maximum burial depth of 86 meters.

  • The tunnel will experience a maximum water pressure of approximately 0.84 MPa.

  • The tunnel has a large excavation diameter, making alignment and construction particularly difficult.

  • Difficulties in alignment and TBM docking due to complex and heterogeneous geology, as well as the challenges of underwater topography.

Jello-Mud Results for “Dinghai” TBM

Jello-Mud Injection for Shield Protection:

  • During pressurized entry into the tunnel, Jello-Mud is used to fill the annular space around the shield to form a protective ring around the shield body.

  • Jello-Mud provided excellent barrier effects and ensures sustained protection, especially during long-duration pressurized entry operations.

  • The method is particularly effective when there are extended shutdown periods during pressurized entry, as it provides long-lasting shielding.

  • Pressurized and Normal-Pressure Entry Operations:

    • In the project, pressurized entry work was carried out at the 171st ring, with a shutdown time of 20 days.

    • Normal-pressure entry work was done at the 209th ring and 243rd ring, with shutdown durations of 3 days and 4 days, respectively.

    • Jello-Mud’s highest held-pressure recorded in the slurry chamber at 171st, 209th, and 243rd ring are respectively 4.35 bar, 3.87 bar, and 3.63bar

  • Theoretical Grouting Calculation:

    • The theoretical annular gap between the outer diameter of the shield (14,520 mm) and the excavation diameter (14,570 mm) is calculated to be approximately 2.28 m³ of Jello-Mud per meter of the shield.

    • The project plan specifies that the shield will be wrapped with Jello-Mud to create a 5-meter-wide ring.

    • Therefore, the total theoretical grouting volume required is 11.4 m³ per meter of tunnel, which is injected through 4 reserved grouting ports located at the top and sides of the shield.

This method ensures a continuous protective barrier around the shield, enhancing structural stability and soil pressure resistance during the tunnelling process.

Illustration of annular protective Jello-Mud ring around the shield