Swiss Re Mythenquai: excavation pit and steel injection ring

The existing Mythenschloss, which was built in the 1980s using the cut-and-cover method, had to be dismantled for the new "Lake" replacement building. The existing diaphragm wall had to be re-supported so that the four floors of the underground car park, including the ground slab, could be dismantled. An innovative steel bracing ring ensured the stability of the 15-meter-deep excavations during deconstruction. This spanned the entire excavation of 70 x 90 meters and ensured that the diaphragm wall was supported. The forces acting on the diaphragm wall were transferred via longarins into solid steel vertical beams. These transferred the forces to the diaphragm wall and the ground slab. As the ground slab had to function as a sprout slab at all times, it was dismantled in stages and replaced by a new, deeper ground slab.

Due to the location directly next to Lake Zurich, the deconstruction was carried out almost completely below the groundwater level, which we lowered by 15 meters using vacuumed small filter wells within the diaphragm walls. Around 480 buoyancy anchors were installed to cope with the uplift pressure at the site close to the water. The underground connecting corridor to the existing buildings was constructed using sheet pile walls and jetting.