Twin super-large diameter slurry TBMs, developed by China Railway Construction Heavy Industry Corporation Limited (CRCHI), were launched on May 16th from opposite directions in Ningbo and Zhoushan for the Jintang subsea tunnel of the newly-built Ningbo-Zhoushan Railway.

With a total length of 135 meters and a maximum excavation diameter of 14.57 meters, the TBMs named “Dinghai” and “Yongzhou” are adorned with the motifs of the “Divine Dragon.”

The Jintang subsea tunnel of the Ningbo-Zhoushan Railway stretches from Yinzhou District in Ningbo City in the west to Jintang Town in Zhoushan City in the east, spanning a total length of 16.18 kilometers, of which the TBM section is 11.2 kilometers long, with a maximum buried depth of 78 meters.

The tunnel undercrosses the 100,000-ton Jintang main navigation channel, using two TBMs that start excavation towards each other from Ningbo and Zhoushan respectively, ultimately docking at the bottom of the sea with an accuracy requirement of an error not exceeding 20 millimeters.

This marks the world’s first case of subsea docking and disassembly of super-large diameter shield machines.

In view of the complex construction characteristics of subsea tunnels, the R&D team of CRCHI has implemented several innovative designs for the shield machine, such as the heavy pressurized cutterhead design, 70 disc cutters, and more than 100 tons of weight added compared to the conventional cutterhead.

There is a reduction in cutter spacing, and an increased number of disc cutters. The disc cutters wear an intelligent monitoring system which has been developed and applied. This will enhance the cutterhead’s wear resistance and rock-breaking ability, ensuring complete tunnelling efficiency.

The shield machine also uses a guidance system with high control precision and advanced technology acting as the “eyes” for the tunnelling equipment. It is equipped with special features such as advanced geological forecasting and probe grouting reinforcement.

These allow for advanced detection and reinforcement of undesirable geology in front of the shield machine to ensure the precision and safety at the point of the docking under the sea.

The Ningbo-Zhoushan Railway project spans about 77 kilometers and has a design speed of 250 km/h. Upon the completion, it will effectively promote the development of Yongzhou City and accelerate the construction of the Ningbo metropolitan area.