Innovative Triple-Circular Pipe Roofing Machine to Support Sanya Estuary Tunnel

A new triple-circular pipe roofing machine, named “Lucheng,” has been developed to advance the Sanya Estuary Passage Project in Hainan Province, China. The tunnel will provide a critical connection between the Sanya Central Business District and the Phoenix Coast Unit. With a cross-section of 18.4 m by 18.4 m, construction will rely on 12 pipe roof sections that serve as both temporary support and permanent structural elements.

The tunnel alignment passes through highly variable and water-saturated ground. The strata include quartz sandstone, fault breccia, gravelly sand, and silty clay, with softer upper layers overlying extremely hard formations with high compressive strength. This combination presents challenges for stability, water control, and excavation safety. To address these conditions, the engineering team has adopted an innovative “pilot-tube guided, multi-segment pipe-jacking” method designed for large tunnel faces in complex geology.

The machine incorporates several specialized technologies. These include a multi-posture combinable system to adapt to different excavation angles, a portal thrust system with adjustable orientation, a combined guidance and deviation correction system for high precision, and a shaped portal sealing system for groundwater control. Developed over four years, the equipment introduces significant advances in construction efficiency and operational safety. Its application is expected to reduce risks commonly associated with undersea tunnels in mixed ground conditions.