The Cerentino landslide, with a volume of approximately 65-80 million m3 and located in Vallemaggia Valley in Canton Ticino, Switzerland, has been intensively studied for over 40 years. A possible technical solution to reduce the effects of the Cerentino landslide could be the construction of a long drainage gallery with drainage boreholes drilled from below the landslide body. A deep borehole at a proposed gallery alignment was drilled in order to verify the feasibility of such a mitigation scenario and to characterize the hydro-mechanical material properties of the landslide mass and displacement zones. This borehole is equipped with pore pressure and in-place inclinometer sensors together with fiber optic strain and temperature monitoring system.
In order to reach the drilling targets, the completed borehole to be equipped with a monitoring system had to survive the local deformations for as long as possible. This is why distributed fiber optic sensing was selected: two Hydro & Geo sensing cable loops were pulled down the borehole respectively at 120 m and 230 m depth. The Hydro & Geo sensing cable is able to measure strain and temperature with a distance accuracy of 1 m all along the borehole and because of its construction the same cable is able to survive shear movements of the order of 10-20 cm.
The Hydro & Geo sensing cable has been installed in 2017 and is still measuring correctly after 3 years in operation, despite the large deformations. Measurements are carried out manually at regular intervals using a DiTeSt reading unit.