ABSTRACT
An existing single-tube road tunnel of a highway network in an urban area is operated in bidirectional traffic. To enhance the safety level for the operation, a new safety gallery is planned to be constructed approximately 30 meters parallel to the existing tunnel. Cross-passages will connect the existing tunnel and the planned safety gallery. The infrastructure is constructed in soft soil conditions. Furthermore, the construction method must ensure the operation without interruption in peak hours and minimize disruption of the traffic. To fulfil these conditions, the advancement of the safety gallery and the cross-passages will be conducted independently from the existing structure. As a pre-support measure for the tunnelling in soil conditions, a pipe umbrella will be utilized. Only the connection between the cross-passage and the tunnel demands work to be performed from inside the existing structure and therefore night closure of the tunnel. The pipes of the final stage of the pipe umbrella will advance into the reinforced concrete of the outer shell of the tunnel. This allows the advance to continue as long as possible from the cross-passage, while minimizing the work from the inside of the tunnel. The challenges in the planning process consisted of identifying a suitable solution in soft soil conditions within the small cross sections and defining a construction process that minimizes the impact on the existing tunnel, which is under operation at the same time.
