Zhejiang's largest-diameter GIL underground utility tunnel fully energized

The construction team works on the GIL system in Shaoxing, Zhejiang province. [Photo provided to chinadaily.com.cn]

The Jinghu Road underground utility tunnel in Shaoxing was fully energized on June 5 after its last four 220-kV transmission lines were connected to the grid.

As Zhejiang province's largest-diameter tunnel and the first to use a Gas-Insulated Metal-Enclosed Transmission Line (GIL) system, the project marks a major step toward smarter, denser, and more reliable urban power grids. It also sets a clear model for city planning and land use.

Stretching nearly 2.75 kilometers and buried 15 meters deep, this "underground artery" brings together electricity, gas, telecom, and sewage lines. State Grid Shaoxing Power Supply Company initially introduced the GIL system in the province to overcome common challenges with high-voltage cables — such as heat, insulation, and difficult repairs.

The GIL's gas-insulated, fully enclosed metal design offers higher capacity, lower energy loss, greater stability, and a longer life than traditional cables. It also works reliably regardless of rain, snow, lightning, or temperature changes, making the city's high-voltage grid safer and more resilient.

Installing GIL equipment requires a dust-free environment and extreme precision. The construction team compared the process to assembling Lego blocks in a clean underground space. To ensure dust-free conditions, they built temporary sealed shelters inside the tunnel.

Workers wore special suits and cleaned each GIL component repeatedly until surface particles met strict standards before assembly. The entire tunnel required thousands of high-precision splices.

A schematic diagram of the Jinghu Road underground utility tunnel. [Photo provided to chinadaily.com.cn]

Once operational, the tunnel is guarded by eight intelligent inspection robots, described as its safety stewards.

Powered by an intelligent maintenance system, these robots perform three key tasks automatically: reading meters, inspecting equipment surfaces, and taking infrared temperature measurements. Working 24/7, they detect risks, monitor the environment, and flag abnormal data.

Now in service, the tunnel solves the long-standing "road zipper" problem — repeated digging and repaving. It improves use of underground space, frees up valuable land above ground, and supports Shaoxing's vision of a low-carbon, smart, and efficient modern city.