Published : 2026-01-07
The Mawan Undersea Tunnel, officially opened to traffic on 21 January. It is the largest diameter undersea shield tunnel in China and also first undersea tunnel in Shenzhen.
Reviewing the construction process of the Mawan Undersea Tunnel, four major challenges had to be overcome.
To achieve high-quality construction, China Railway Engineering Equipment Group (CREG) specially developed the custom-built Mawan shield tunnelling machine. What is so special about it?
A custom-built shield tunnelling machine
The Mawan Undersea Tunnel is located in the Nanshan District of Shenzhen. It is divided into two parts: a surface road and an underground road. The underground road is classified as a city expressway, with two-way, six-lane passage, a design speed of 80 km/h, and the underground tunnel has a total length of 6,280 metres.
The Mawan shield tunnelling machine was custom-built for the construction of the Mawan Undersea Tunnel, with an excavation diameter of 15.53 metres, equivalent to a five-storey building, a total length of about 140 metres, and a weight of 4,650 tonnes.
The section constructed by the shield tunnelling machine has a total length of 2,063 metres. During the excavation process, it was necessary to cope with the four major challenges of being "long, difficult, deep, and large".
The first is "long". The geological structure of the Mawan Undersea Tunnel is complex, with 34.15% being full-face hard rock. The maximum strength reaches up to 193 megapascals.
The equipment had to excavate a long distance through high-strength rock formations, which tested the rock-breaking capability of the cutterhead, while also resulted in the frequent replacement of cutter tools due to wear and tear.
"Difficult" refers to traversing complex submarine terrain, with 50% of the rock layers being of uneven hardness. This could easily cause the upper part of the shield to cut too quickly, leading to an upward tilt in the overall posture of the shield tunnelling machine, thus deviating from the preset trajectory.
As for "deep", this refers to the subsea tunnel being located more than 40 metres underwater, with a maximum water pressure of 500 kilopascals, resulting in high construction risks.
The final challenge, "large", refers to the tunnel's cross-section. Its segment outer diameter is 15 metres, making it the nation's largest diameter subsea tunnel at present. This placed extremely high demands on equipment performance and construction techniques.
Mawan pioneered patented technology to meet challenges
To meet the four major challenges, firstly, the Mawan utilised a pioneering patented technology for installing disc cutters, which improved force distribution and greatly increased their service life.
At the same time, the Mawan was equipped with a real-time cutter tool status monitoring system, which could detect the rotational status and wear condition of the disc cutters. This could also provide real-time feedback with image information of the excavated rock strata, comprehensively enhancing its sensing and perception capabilities.
On the other hand, the Mawan has a designed load-bearing pressure of 10 kilograms per square centimetre, equivalent to the pressure experienced by an ordinary person diving 100 metres without any auxiliary equipment. This is achievable because the Mawan's maximum thrust reaches 25,000 tonnes, its total installed power exceeds 11,500 kilowatts, which is even 10% higher than the total traction power of a Fuxing bullet train.
The Mawan Undersea Tunnel is a key demonstration project for the connectivity and transport infrastructure of the Greater Bay Area. After its completion and opening to traffic, it will effectively improve the external road network structure of Qianhai.
This tunnel connects the port-related freight traffic of Nanshan Port Area, reduce the pressure of surface freight traffic in the Qianhai area, and also facilitate passenger transport connecting the Mawan and Chiwan areas with other areas like Dachan Bay, achieving the separation of passenger and freight traffic, and further expanding the city's development space.
