Key techniques for the largest curved pipe jacking roof to date: A case study of Gongbei tunnel

The Gongbei tunnel, as a part of the Zhuhai Connection highway and Hongkong-Zhuhai-Macao Bridge project, is currently being constructed in Zhuhai, China. To guarantee the tunnel traversing under the Gongbei Port, a combination technology of curved pipe jacking roof for ground support and ground freezing for waterproof is applied. This jacked pipe roof, comprised 36 steel pipe strings of 1620 mm diameter with 355-358 mm gap between adjacent strings, has been faced with various challenges for design and construction due to the site conditions of multiple soft soil and high underground water pressure. These challenges include risks of excessive soil deformation, possibility of path deviation, excessive jacking force, leaking of pipe joint and failure of jacking machine gasketed launch and reception devices. This paper provides an overview of this project, summarizes the most challenging aspects they faced and introduces the relevant techniques applied during construction.