“U-shape”: First Shield Machine for horseshoe-shaped Cross Sections
On 17 July 2016 the workshop acceptance was completed by the project owner for the world’s first U-shape (horseshoe shape) TBM, which is manufactured by CREG (China Railway Engineering Equipment Group Co., Ltd). Starting at the end of October 2016, the TBM will be used to bore the Baicheng tunnel of the Mengxi railway project, connecting the west area of Inner Mongolia and Central China.
The single tube Baicheng railway tunnel with a maximum depth of 81 m is 3345 m long. The whole alignment of the tunnel runs in a straight line, of which the maximum track gradient is 5 ‰. The Baicheng tunnel is located in the north of the Chinese Shaanxi Province, where in the crossing strata silty sand, sandy loess and fine sand are distributed.
U-shape Tunnel Boring Machine for the Baicheng Tunnel
The cutting cross section of the U-shape TBM is 10.95 m high and 11.90 m wide. Compared to a circular TBM the design and manufacture of the horseshoe shape cutter head is much more challenging due to the complex machine structure at the cutter head and the approach to cut the ground with several partly overlapping cutting wheels. The U-shape machine adopts a tapered shield and two symmetric screw conveyors for muck transfer. The cutterhead is composed of seven small cutting wheels which can rotate either simultaneously or independently in different directions. In the event of rolling, several cutter heads would rotate in the same direction in order to generate a counter torque for the shield machine to rectify the deviation.
When the machine is applied to soft soil tunnelling the tunnel space utilization could be improved up to 20 % compared to circular cutting. The U-shaped TBMs are very suitable for traffic tunnels in soft ground conditions. CREG improves the multi-cutting-wheel technology which is also used for the rectangular pipe jacking machines step by step and extends the capability of this technology to harder ground conditions.