By 1st June 2016, the gripper TBM by CREG "Yongji" (CREC TBM 188) which was applied to Lot 4 of Yinsong Water Supply Project, Jilin has created an excavation record of 1226 meters in May, setting a new high of monthly advance for the three TBMs by three different suppliers that are used for three lots of the project respectively.
Lot 4 is the most complicated section among the overall project. Since its launching on 1st June, 2015, the 8.03m diameter machine has undergone a sequence of unfavorable geological zones including the existence of karst cavity and cave, variable surrounding rocks, uneven strata and frequent occurrence of water inflow. Over the past year, "Yongji" has crossed 8 fault fractured zones, 4 areas where external resistance falls dramatically and 53m-long full face carbonaceous slate. The largest scope of impact by fault zone reaches up to 200 meters wide. Throughout the course, the machine has overcome numerous challenges such as low strength surrounding rocks, tendency to collapse, weathered rocks stuck on cutterhead, gripper slipping and difficult steering.
Despite numerous geological challenges, "Yongji" has managed to present an impressive performance. CREG’s rich construction experience and project-specific proposal are key factors to the astonishing success. Designs like segmented cutterhead and multiple muck inlets ensure outstanding rock breaking capacity and efficient mucking. The back-up and TBM support system have adopted Wirth know-how which guarantees smooth logistics and little intervention between different procedures. Thanks to the optimized designs, the first dressing cutters sustain availability for 800 meters. To lower the risk of collapse in Class IV-V surrounding rocks, the installed ring beams as temporary support has been applied and so far more than 1800 pieces have been in place. Nevertheless, the advancing speed of "Yongj"i in this type of geology has maintained 20 meters on average. What’s more, the installation of advance tunnel forecast system using induced polarization method also contributes to safe tunneling.