Three-dimensional effects of multiple voids behind lining on the mechanical behavior of tunnel structure

Multiple voids often exist simultaneously behind the tunnel lining, which can seriously threaten the stability of a tunnel's structure. To explore the three-dimensional effects of multiple voids behind the lining on structural mechanical behavior, we conducted a quality evaluation of the concrete lining in a railway tunnel based on model tests and numerical analyses. The effects of the void area and distribution on the structural stress, internal force, and contact pressure of the lining were explored and summarized. Results reveal the following: (1) the direction of the maximum principal stress of lining structural elements within the void region gradually changed to a longitudinal distribution along the tunnel; (2) the structural internal force between each void increased as the distance between voids decreased; (3) the structural contact pressure between each void increased significantly when the distance between voids was less than half of the void's diameter.