Observed deformation behavior of Gongbei Tunnel of Hong Kong-Zhuhai-Macao Bridge during construction

The excavation of shallow buried tunnels with super-large section in coastal water-rich strata with complex geological conditions faces a lot of risks. The surrounding soil is easy to be disturbed during excavation, causing the ground deformation. The new method of "freezing-sealing pipe-roof for pre-support" can effectively control the surface settlement caused by the excavation construction. The change of surface displacement during tunnel excavation using this method is mainly affected by the factors such as the ground loss caused by tunnel excavation, expansion of frozen soil and floating effect after tunnel excavation unloading. The rules of tunnel crown displacement, horizontal convergence and ground deformation are investigated based on the in-situ observation. The displacements of the tunnel crown and the corresponding surface are consistent. In the longitudinal direction, the crown and ground surface move up in the middle section and move down in the sections at both sides near the working shafts. Under the influence of layered excavation disturbance, the inward deformation of the soil at both sides of the tunnel leads to the increase of horizontal convergence, and the maximum horizontal convergence is 15.72 mm, which is about 0.8% of the transverse span of the tunnel. The new freezing-sealing pipe-roof method can solve the problem of water leakage in the water-rich strata, and greatly reduce the internal deformation of the tunnel. However, the problem of surface heaving caused by soil freezing and the surface settlement after soil thawing still require great attention.