Strategy for the permanent technical solution under the Lake Mälaren in the Stockholm Bypass Project
The tunnels in the Stockholm Bypass Project connect the northern and southern part of this Nordic city passing through several regional fault zones and subsea passages. For instance, the passage under the Lake Mälaren, Sweden’s third-largest freshwater lake, and the regional fault zone in the Fiskar fjord constitutes one of the most challenging parts in this project. The uncertainties in this subsea passage are high, and originate from limited information about the rock cover, the rock quality in the fault zone, water leakage and the existence of time-dependent geological processes that with time may lead to changes in the load acting on the support. These aforementioned factors affect the selection of the technical solution for the permanent rock support in the tunnels and the loads that it should be designed for. In this paper, we address these questions by discussing which factors that govern the selection of the technical solution in the regional fault zone for the permanent rock support in the tunnels under the Lake Mälaren.