Damage Report of the Construction Phase of a Suburban Railway Tunnel at the Airport of Munich, Southeastern Germany

In southeastern Germany, the new suburban railway tunnel “S-Bahntunnel Erdinger Ringschluss” was under construction from 2018 to 2021 at the airport of Munich. This 1800 m long cut-and-cover tunnel was predominantly built in highly water-saturated quaternary loose soils of the Munich gravel plain. The construction pit system used on site was composed of 20 m deep cast-in-situ concrete diaphragm walls and a 1.40 m thick non-anchored underwater concrete slab. Protected by the surrounding diaphragm walls and the concrete slab, the internal tunnel shell should be raised. On 30 July 2020, however, a damage occurred in the drained tunnel construction pit of section 17. During the execution of a horizontal pilot core drilling DN 350 through the southern 80 cm thick diaphragm wall, which should have connected the construction pit to the adjacent inverted siphon building 15 South, a massive entering of quaternary highly water-saturated loose soils into the construction pit could be observed just within a few seconds. Only a few tens of minutes later, a collapse sinkhole developed around the inverted siphon building 15 South, due to the continuous removal of soil material from the building ground. The danger area had to be secured and the construction work to be stopped. How did it come to this massive entering of loose soil material into the construction pit? What measures have been taken to stop the soil material and to stabilize the area of collapse? How did the damage affect the subsequent construction work? This paper provides an insight.