The super-large diameter slurry TBM "Chunfeng" successfully broke through the Chunfeng Highway Tunnel, the first "single-bore double-deck" motor vehicle tunnel in Shenzhen, which has been significant to the construction of tunnels in complex strata with large diameters, long distances, high water pressures and multiple fault zones in China.

This Φ15.8m TBM is 135m long and weighs about 4,800 tons, whose total power exceeds 11,500kW. The Shenzhen Chunfeng Highway Tunnel has a total length of 5.08km with the 3.6km-long section excavated by the TBM, which is characterised by the "large diameter", "difficult construction", "high risk", "innovative technologies", etc.

· Lots of building structures above ground: The TBM needs to bore under the built-up Shenzhen Luohu district. There are lots of risk sources along the alignment, including the municipal pipelines, bridges, Metro Line 1 and 9, Buji River and high-rise buildings. Combined with the maximum overburden of 49m, the strict requirements for tunnel settlement control and equipment performance are put forward.

· Complex strata: The TBM mainly goes through the "upper soft and lower hard" and hard rock strata, among which the section in hard rock strata accounts for more than 80% with the strength of the surrounding rock up to 173MPa. There are 11 fault zones in the TBM-bored section. The tunnel is adjacent to Shenzhen River along which the minimum spacing is about 35m.

· Tight curve radius: The minimum horizontal curve radius is 750m in the TBM-bored section. When a super-large diameter (over 15m) TBM bores in a tight radius curve, it usually brings complex problems. For example, the tunnel axis is prone to deviate from the design axis.

During the TBM type selection, design and manufacturing, CREG fully take complex strata into consideration so that this machine integrates many innovative technologies, including atmospheric cutter changing technology, cutter status online monitoring technology and slurry circulation system with high-efficient muck discharge technology. The TBM is equipped with the double crushing muck treatment system, which means the muck is treated in stages by increasing the allowable particle size of the grid and installing two crushers inside and outside the slurry chamber. With this technology, the blockage occurrences in the slurry chamber and slurry discharge pump in fractured and "upper soft and lower hard" strata are reduced so as to improve the construction efficiency.

The breakthrough of the Chunfeng Highway Tunnel provides a useful reference for the tunnel construction in complex geological conditions by the super-large diameter TBMs and improves the tunnel construction level in China. With the completion and opening of the Chunfeng Highway Tunnel in future, a three-dimensional traffic corridor of "Chunfeng Overpass + Chunfeng Highway Tunnel" will be formed, which will play an important role in alleviating traffic congestion in the area, promoting the integration of Shenzhen and Hong Kong and improving the traffic capacity of the road network with new quality productive forces.