The pipe roofing method is one of the widely used excavation support techniques for conventional tunneling. It is to install steel (or fiber glass) pipes in a canopy shape around the area to be excavated and then to excavate the soils under the protection of the pipe roof. This paper presents the optimization of the pipe roof design for the Gongbei Port tunnel excavation which represents the largest single tunnel excavation in China. The preliminary design proposed to use a pipe roof consisting of steel pipes with two different diameters which brought serious construability issues. During the construction phase, the contractor optimized the design of the pipe roof by using pipes with a uniform diameter, while adjusting the pipe layouts and optimizing the jacking and receiving plan. The new pipe roof design significantly improves the constructability, as well as reduces the construction cost and shortens the construction duration. The Gongbei Port tunnel construction expands the conventional tunneling technique by using an unprecedented large pipe roofing system along a curved tunnel alignment, and the optimization of the pipe roof design provides valuable case history experience for future projects.
The pipe roofing method is one of the widely used excavation support techniques for conventional tunneling. It is also referred as "Steel Pipe Umbrella" , "Steel Pipe Canopy" , "Umbrella Arch Method" , "Long-Span Steel Pipe Fore-piping" , or "Pipe Roof Umbrella"  in the literature. It is to install steel (or fiber glass) pipes in a canopy shape around the area to be excavated and then to excavate the soils under the protection of the pipe roof. The pipe roofing method was firstly used in Japan in 1982 and then widely used as an excavation support technique for shallowly buried underground excavations . Recent decades have seen many successful case history projects using pipe roof as an excavation support worldwide. The case history experience showed that under the protection of the pipe roof, the disturbance from the excavation to the ground can be significantly reduced and the ground movement can typically be controlled within 2 cm while the deformation of the pipe roof is smaller than 0.5 cm .