Nanjing Subway Line 4 Yangtze River-Crossing Project

Φ 11.64m CRCHI Slurry-Shield TBM

Project Year: 2024

Project Overview

Project Summary

Project Overview:

  • The Nanjing Metro Line 4 Phase II river-crossing tunnel spans the Yangtze River’s main navigation channel, with a total length of 3,062 meters.

Overburden Depths:

  • TBM Launch Location: Overburden is approximately 26.8 meters

  • River crossing: The deepest overburden is approximately 55 meters.

  • Receiving end: Overburden is approximately 34 meters.

  • Significance:
    This is the deepest river-crossing metro tunnel in the Yangtze River Delta region.

  • Geological Conditions:

    • The tunnel construction crosses a variety of soil layers, including silty clay, fine sand, medium-coarse sand, and gravel.

    • About 700 meters of the tunnel needs to pass through moderately weathered mudstone and sandy rock layers.

Construction Difficulties

  • Launch Portal

    • The overburden is approximately 26.8 meters.

    • Located in a layer of fine sand, clay, and an artesian aquifer.

  • Construction Risks:

    • The soil layers are prone to liquefaction due to the disturbance caused by shield tunnelling.

    • Complex geological layers between the groundwater, surface water, and the soil.

    • At the launch portal, risks include water and sand inflow at the tunnel face and ground settlement.

Jello-Mud Result

  • Stable pressure is established at the tunnel entrance.

  • During the sequential opening and closing of the reserved holes in the portal, Jello-Mud is fully extruded without any gas or liquid leakage.

  • Jello-Mud exhibited void-filling, sealing, and water proofing capabilities

  • Contractor was able to save on costs compared to using high-cost tail-seal grease to seal the entrance ring

  • For more information on how Jello-Mud assisted in lubrication and settlement control in this project, please contact us for more details.

Comparison to Traditional Launch Seal Method for a ф11.64 TBM

  • Traditional Method

    • Hs1 + Hs2 + Hs3 sealing material

      • 1t water + 4t of Hs1 + 4t of Hs3 + 10t of Hs2

      • 600% Fill

      • Takes 4-5 days to complete the launch seal

      • Pipe blockage when excessive fill, portal leakage when insufficient fill

  • Jello-Mud Method

    • Sodium based bentonite + BSP 70 = Jello-Mud

      • 2.4t Bentonite + tens of litres of BSP 70

      • 163% Fill

      • Takes Half of a day to complete the launch seal

      • No blockage or leakage observed when filled adequately

Site image of surplus Jello-Mud exiting through launch seal, a good indicator that Jello-Mud has formed a complete seal and blocked off soil and water ingress.

Site image of the shell body after advancing 1 ring. No leakage was observed.