S21-Berlin â€“ Design and Underwater Construction of a Covered Construction Pit without Direct Accessibility from AboveÂ-Video

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Video Summary

The presentation describes the M-Dash construction pit in Berlin, part of the S21 railway project. Because a previous water inrush showed that the existing jet-grouted cutoff could not be trusted, the team flooded the pit and excavated underwater rather than risk dewatering. Structural measures included steel cleats and reinforced underwater concrete to resist uplift, plus a massive underwater strut to support diaphragm walls.<br /><br />A remotely operated, electro-hydraulic excavator was lowered into the pit and controlled from the surface. It used interchangeable tools to excavate soil, remove the blinding layer and expose grout columns, while pumps and a treatment plant separated soil from water. Divers supported the work but stayed clear during excavation for safety.<br /><br />After excavation, crews installed a leveling layer and poured the underwater concrete base in separate sections, followed by the strut. The speakers emphasized that successful execution depended on careful safety planning, adequate site space and flexible cooperation among all project partners.

Keywords

M-Dash construction pit

Berlin S21 railway project

underwater excavation

remote-controlled excavator

underwater concrete base