Abstract:

The analysis of the overburden thickness of subsea tunnels is closely related to the safety and economy in the design process. Taking Jiaozhou Bay Subsea Tunnel in Qingdao as background project, the authors establish finite element seepage models for this drill and blast tunnel with 4 different overburden thicknesses. The authors focus on the inflow water volume, seepage velocity, pore water pressure and grouting zone parameters during the excavating process in the f3-1 fault fracture zone. Conclusions drawn are as follows: 1) Park formula coincides with FEM inflow results; 2) The most serious seepage area will occur at the arch springing if the overburden is thick; serious seepage will occur at both arch springing and crown if the overburden is thin; 3) The pore water pressure gradient of the wall and the floor increases as the overburden thickness increases, while the pore water pressure gradient of the crown is just on the contrary, and the pore water pressure gradient will remain almost stable when the overburden thickness is over 22 m; 4) Both reliability and economy should be taken into consideration when appropriate thickness and permeability value are selected, and the grouting zone thickness of 4～6 m and the permeability of 1×10-7～2×10-7 m/s are proposed for the project.

Key words: subsea tunnel, overburden thickness, fracture zone, seepage, grouting zone, finite element method