Study on Pre-reinforcement Schemes for a Shield Tunnel Passing under the Pile Foundation of an Urban Viaduct

In this paper, the pre-reinforcement schemes for the pile foundations of an urban viaduct before shield construction are systematically analyzed on the basis of a shield-driven running tunnel passing under the existing urban viaduct, and four reinforcement schemes are put forward: namely the pre-reinforcement scheme with sleeve valve grouting pipes, the pre-reinforcement scheme with isolation piles, the pre-reinforcement scheme with sleeve valve grouting pipes + isolation piles, and the pre-reinforcement scheme with sleeve valve grouting pipes + isolation piles + additional pile foundations. Then, the design idea of each pre-reinforcement scheme is introduced in detail and the refined three-dimensional numerical simulation calculation is performed for four pre-reinforcement schemes. The results show that the pre-reinforcement scheme with sleeve valve grouting pipes alone and that with isolation piles alone have limited effect; the pre-reinforcement scheme with sleeve valve grouting pipes and isolation piles can desirably control the horizontal displacement, vertical settlement and differential settlement of piers and abutments, with good reinforcement effect; the pre-reinforcement scheme with additional pile foundations has limited contribution to settlement control, and so with a low cost performance.