After 13 months of tunneling in Shaanxi Province, China and overcoming geological challenges, CREG’s horseshoe-shaped EPB TBM completed its bored excavation for Mengxi-Huazhong coal transportation railway tunnel on 26 January 2018.
The single-bore double-track TBM tunnel is about 3.056km long. The TBM with a horseshoe shape profile of 10.95m high and 11.9m wide mined through geology consisting of new loess, loess, sand and silt, passing beneath the junction of the Mu Us Desert and the Loess Plateau. The application of horseshoe-shaped EPB TBM in such geological conditions not only minimizes the risk of collapse but also increasezs construction efficiency. The designed maximum boring speed is 60mm/min and the average monthly speed is 200 to 300m.
The EPB machine with a cutterhead rotation of about 1.08rpm and a maximum torque of 3044kNm, features a tapered shield and two symmetric screw conveyors for muck transfer. The cutterhead is composed of nine small cutting wheels which could rotate either simultaneously or independently in different directions. In the event of shield machine rolling, several cutterheads would rotate in the same direction in order to generate a counter torque for the shield machine to rectify the deviation.
Geological conditions presented significant demands for the machine. In a region where geology where water is very little, muck discharge became quite difficult for screw conveyor. The solution was to change the ratio of soil conditioner, extending the mixing period, adjusting grouting positions and adding cutterhead grid to cope with the problem of blocky soil. To deal with the challenge of mining through stiff to hard clayey silt, overcutting is used to ensure steady progress of the machine.
Despite the various problems in the course of tunneling, the machien, after launch on 29 October 2016, achieved peak monthly rate of 308.8m in March 2017 and a best advance of 11 rings or 17.6m/day on 7 August 2017. On 1 April 2017, its total bored length exceeded 1000m. On 25 August, it was more than 2000m. On 3 January 2018, it was more than 3000m.
This breakthrough represents a milestone as the first horseshoe-shaped EPB TBM drive for railway tunnel in the world. It provides valuable scientific data and experience for the application of “specialty-type TBM” on tunnels featuring soft ground.
The horseshoe-shaped EPB TBM differs from traditional circular machines not only in section but also in construction methods. When the machine is applied to soft ground, the tunnel space utilization could be improved for 10% to 15% in comparison to circular cutting.
What worth particular mention is that the big horse-shoe shaped machine is equipped with a café shop where the construction crews could have a rest refresh themselves.
CREG has always been adhering to the innovation-driven strategy. While making breakthroughs in conventional TBMs one after another, the company has developed a series of new products including horse-shoe shaped TBM, Rectangular TBM, and U-shape TBM. With its quality products and successful completion of various projects both at home and abroad, CREG has established a reputation as being among the leading TBM suppliers of the world.