In-situ monitoring behaviors of middle wall of large-span multi-arch tunnel

Considering the special condition of the six lanes large-span multi-arch tunnel in the Wanping Expressway, and choosing some representative cross-sections of Wujiazhuang Tunnel, their inner middle-wall's internal forces of the three-layer vertical middle-wall are monitored during the construction. Based on the monitoring data, and considering the interactive influences of different construction stages, the internal forces of the inner middle-wall are analyzed; and the mechanical characteristics during the construction are obtained. Then the safety performance of the Wujiazhuang Tunnel's inner middle-wall is evaluated. It is shown that the inner middle-wall's internal forces are affected by the different excavating sequences, especially in the stage of low bench excavations, however, the inner middle wall remains stable during the multi arch-tunnel construction.