Capturing Rock Damage and Environmental Forcings in Toppling Slopes: An Integrated Monitoring System in Bedretto

Rock slope toppling typically occurs in slopes with steep, deep-seated discontinuities and involves large unstable rock masses that may transform into catastrophic secondary failures. Understanding the long-term weakening processes of such slopes remains challenging due to limited subsurface access and the lack of continuous deformation monitoring under diverse external forcings. To address these limitations, this study implements a comprehensive, tunnel-based multi-parameter monitoring system in the toppling zone intersected by the first 500 meters of the Bedretto Tunnel in Ticino, Switzerland.

The system integrates high-resolution (~0.5 m) distributed fibre optic sensors for strain and temperature monitoring along the tunnel with GPS measurements of 3D surface displacements. In-tunnel hydraulic sensors installed, in both stable and critical zones, continuously capture changes in pore water pressure, tunnel inflow dominated by fractures, and groundwater origins through high-frequency recordings of pressure, temperature, and electrical conductivity. Meteorological stations at the slope toe and toppling crown measure rainfall, air temperature, snow depth, and humidity. Complementary manual snow water equivalent measurements support a degree-day model to estimate surface infiltration onsets and volumes.

Initial results from early 2024 suggest that structural orientation primarily controls deformation patterns. While reversible strain correlated with periodic temperature fluctuations is evident, strain variations become more dynamic after precipitation events, particularly intensified in the highly fractured ductile hinge zone. These observations are reinforced by hydrological evidence, which shows gradual seasonal inflow trends near toppling boundaries punctuated by intermittent inflow spikes in response to rainfall and snowmelt events. The findings provide insights into the coupled hydromechanical and thermomechanical processes driving damage accumulation within large toppling slopes. Long-term data collection and integration with historical records aim to pinpoint the primary drivers of deformation variability. As data monitoring efforts continue and more weather events are captured, the results will support the development of modelling toppling failure evolution and contribute to a deeper understanding of rock slope weakening mechanisms.