Holistic Thermal Assessment and Control Of The Artificial Ground Freezing For The New Underground Station "Museum Island " in Berlin-Paper

Paper

Pdf Summary

The Museum Island station was constructed beneath Berlin’s Spree Canal, the historic Castle Bridge and nearby buildings as part of the U5 metro extension. A 106 m-long platform hall was excavated around two existing TBM tunnels under a temporary ground-freezing system, primarily in Berlin sands, with glacial till below. The frozen ground mass was approximately 106 m long, 26 m wide and 12 m high.<br /><br />About 10 km of freeze pipes were supplied by three ammonia chillers with a combined capacity of 1.3 MW. The brine distribution system allowed operators to switch cooling among pipe groups, run intermittent freezing and reverse flow to control freezing near the shafts. The ground reached the required frozen condition in about 80 days, followed by a 420-day maintenance period.<br /><br />Roughly 2,000 temperature sensors, supported by a web-based 3D visualization system, tracked temperature changes across the frozen mass. Daily evaluations combined sensor data with finite-element thermal calculations. During excavation, automated analyses estimated frozen-ground thickness and average temperature in key sections, allowing operators to adjust freezing in response to heat from excavation, shotcrete application and concrete curing. These methods provided evidence that project safety requirements were being met.<br /><br />An active thawing system used heat from the district heating network to thaw the ground in 89 days, rather than allowing natural thawing to take around a year. The project demonstrated the value of extensive instrumentation, redundant systems, validated thermal models and close cooperation between the client, contractor and technical specialists. It also showed that tunnel excavation using an advancing-dome method can be carried out safely within frozen ground.

Keywords

Museum Island station

Berlin U5 metro extension

ground freezing

tunnel excavation

Spree Canal

temperature sensors

ammonia chillers

frozen ground

thermal monitoring

district heating thawing