Reasonable overburden thickness for underwater shield tunnel

A reasonable overburden thickness is of importance for the stability of underwater shield tunnels. Based on the analysis of existing theoretical methods, this paper presents a modified method for the estimation of the minimum overburden thickness during underwater shield tunnelling. As the existing methods neglect the effects of grouting pressure, the modified method takes into account the grouting pressure and the hardening of grouting mortar. The modified method is compared with existing methods based on a practical underwater tunnelling project of Beijing Subway Line 14. Parametric analysis of the proposed method considering the dimension of the tunnel, the geological condition and the grouting behavior is performed. The results show that tunnel diameter, friction angle and cohesion of soil, and grouting pressure have significant impacts on the results of modified methods. The results of this study can provide a reference for similar projects.