Widespread surface subsidence measured with satellite SAR interferometry in the Swiss alpine range associated with the construction of the Gotthard Base Tunnel

- InSAR employed to measure surface subsidence above a 57 km long tunnel in the Alps.
- Significant movements with values ranging from 1 to 12 mm/year detected.
- Results available for sectors where there is no information from other techniques.
- Results important to assess the hazard and calibrate models.
- Effect of ground-water drainage on the dynamic of large deep-seated landslides investigated.

Drilling deep tunnels in alpine rocks might induce surface settlements of a few centimetres because of groundwater drainage and associated pore pressure reduction. Settlements of this order of magnitude are sufficient to pose a potential threat to the integrity of any large concrete structure such as arch dams located above the tunnel and an accurate survey of surface deformation before, during and after construction is of high importance. We present the spatial and temporal evolution of surface subsidence measured with satellite SAR interferometry associated with the construction of the 57 km long Gotthard Base Tunnel in Switzerland. Significant deformations of 1 to 12 mm/year were detected between 2003 and 2010 with ENVISAT ASAR data above the tunnel on villages and sparsely vegetated alpine slopes where no displacement was recorded between 1992 and 2000 with ERS-1/2 SAR data. Our results, available also for sectors where there is no information from any other surveying technique, are important not only to assess the hazard posed on any large concrete structure but also for the development and calibration of numerical models - to be employed to simulate the expected surface deformation before and during the construction works - and to study the effect of groundwater drainage on the dynamic of large deep-seated landslides.