## 1 Introduction  
With the increasing complexity of the underground construction environment, the construction technology is becoming more and more complex and difficult. Shallow-buried underground excavation, as a major underground construction method, has an important role in tunnel engineering and its development relies on an auxiliary construction method. Among them, pre-supporting method is widely applied in shallow-buried underground excavation, because of simple technology and low cost. The pipe-roofing method is a primary method of pre-supporting. As the complexity of underground environment increases, it is difficult to meet the requirements of project quality with only one auxiliary method, especially in the construction of large cross-section tunnel with a rich aquifer. Therefore, the combination of pipe-roofing method and different innovative methods have been carried out to ensure the safety of construction, which is proposed by many scholars. As is known, combining a variety of engineering methods to realize the complementary advantages of the system is an effective way to solve engineering problems. Some successful applications related to the pipe roofing method are as follows: ESA (endless self-advancing method), FJ (front jacking method), RBJ (roof-box jacking method), Okumura R&C method, TULIP method [1], SR-J method [2],SR-JR method [3], New Tubular Roof method [4], etc. These pre-supporting methods provided good construction condition for excavation, but exposed the weakness of water sealing, especially in long distance curved pipe-jacked projects. However, the Freeze-Sealing Pipe Roof (FSPR) method as a new shallow-buried underground excavation technology can solve this issue well. In order to minimize the impact of transportation caused by construction in the Gongbei Tunnel in the Hong Kong-Zhuhai-Macau Bridge, shallow excavation is applied in the port line tenders with a length of 255 m. However, it is difficult to provide a good condition for the open-cut method, and the excavation part of the tunnel lies between soft soil and medium soft soil. Moreover, it is wasteful to construct with shield method in such large cross section and short-distance road tunnel. Therefore, shallow excavation scheme with pipe-roof method was adopted. A conventional water sealing method is to use sealing latch between steel pipes, but the water sealing effect of pipe-roofing cannot be guaranteed for such curve pipes. Therefore, the artificial ground freezing method was applied to ensure water sealing as an environmental method, compared with general slurry injection technology. The Freeze-Sealing Pipe Roof (FSPR) method is an auxiliary method combining the pipe roof method and artificial freezing method [5], where the steel pipe roof mainly plays a role in load bearing and the frozen soil curtain mainly plays a role in water sealing. FSPR makes full use of the advantages of the pipe roof method and artificial ground freezing method. On one hand, FSPR has little effect on the surrounding environment [6], on the other hand, the advantage of adaptability, controllability and strong sealing property of the freezing method can be fully used to solve the water sealing problem between steel pipes. FSPR, as a shallow-buried underground excavation method was first applied in the Gongbei Tunnel in the Hong Kong-Zhuhai-Macau Bridge [7; 8]. Only a few researches have undertaken in this field. [PERSON] briefly studied the mechanical properties between frozen soil and steel pipes and the interaction between them [9; 10; 11]. A similar method has been applied in few projects, which have only appeared in China and Germany [5], where frozen soil curtain mainly played a role in load bearing, which is essentially different from the method applied in the Gongbei Tunnel. There is an obvious difference between the pipe shed method and pipe roof method. Steel pipes are mainly regarded as load bearing structures in the pipe shed method, yet frozen soil is mainly regarded as a load bearing structure in the pipe roof method.