Fault zones along the Yangtze River crossing and countermeasures against risks in shield-driven tunneling for the 3rd West-to-East Gas Pipeline

Shield-driven tunneling may involve certain risks due to geologic conditions. The middle section of the 3rd West-to-East Gas Pipeline crossing the Yangtze River encounters 56 faults in shield-driven tunneling. The maximum width of fault is 14 m, and most of these faults have widths at 1-10 m. These faults mostly contain veins of quartz crystals with distribution widths not more than 30 cm. With uneven distribution of geologic conditions and significant water contents, these fault zones may suffer ground subsidence because of overbreak. Since crystals in quartz veins are characterized by lower volumes, high strength and significant contrast in strengths with surround matrix, it is not easy to identify quartz veins during drilling. Consequently, drilling operations in these formations may encounter disc jamming, severe abrasion and instability of matrix. With consideration to complex geologic features encountered in shield-driven tunneling for the Yangtze River crossing and previous experiences in shield-driven tunneling, together with understanding to relevant facilities, specific countermeasures are proposed. In addition, specific requirements for the shield machinary, discs and cutting devices are raised for the first time. Relevant research results may provide valuable references for operations and selection of shield machinary in rock formations in China.