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  Are ground settlements really always permanent? Something strange happens in the soft ground section of the Vedeggio – Cassarate Tunnel

  The Vedeggio-Cassarate road tunnel is part of the new Transportation Plan of the city of Lugano (PTL), in the southern part of Switzerland. A section of about 200 m was excavated in soft ground, which presents a very heterogeneous sequence of quaternary glacial lake and fluvial sediments, with artesian groundwater horizons at many different independent levels with pressures reaching up to 20 m water column above the ground surface. After completing the inner lining, which includes a full sealing membrane, the overall water pressure was quickly restored to the levels measured before the work had started and the amount of settlement was reduced at the same time (uplift of the ground), which in some cases reached up to 40% of the maximum deformations measured. The paper will present a possible explanation of this strange phenomenon, which was observed over the whole area of the tunnel’s stretch of soft ground.

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