TBM/EPB for building the Xian Metro

In the historic city of Xian famous for the Terracotta Army the 26.4 km long Metro Line 1 is under construction. It runs from north to south through the centre of the city. In contract section 12 two identical tunnelling machines (TBM/EPB) from Robbins, with 6.20 m cutterhead diameter, are driving 2 parallel, roughly 2.3 km long tunnel bores. In the process 4 railway stations produced in advance by cut-and-cover have to be passed through. Lifts and settlements must on no account exceed 15 mm in order to  protect structural damage to the historic buildings that must be undertunnelled. The 2 TBM...