Redundancy and coherence of multi-method displacement monitoring data as key issues for the analysis of extremely slow landslides (Isarco valley, Eastern Alps, Italy).

The paper describes the study of two extremely slow, active-continuous, deep-seated landslides located in the Isarco Valley (Eastern Alps, Italy): a Multiple Rotational Rock Slide (MRRS) and partial reactivation of a Deep-Seated Gravitational Slope Deformation (DSGSD). Both landslides interact with viaducts on the E45 highway. Extensive multi-method field investigation, monitoring of surface and subsurface displacements and limit equilibrium stability analyses were adopted to fully characterize slope dynamics. In order to overcome the limitations due to the systematic errors affecting each single monitoring system and analysis method, an operative framework based on redundancy and coherence tests was introduced to check the reliability of the data and results. In this framework, the geological and geotechnical models of the investigated slopes were progressively refined. This allowed assessment of the type of interaction between the slopes and the highway viaducts. • Study of large, composite and extremely slow landslides requires extensive multi-method monitoring of displacements. • Systematic errors affecting the measurements may mask the actual rate of movement. • Redundancy and coherence tests of monitoring data as a tool to check reliability of data and results. • The reliability of displacement monitoring is crucial to analyse large extremely slow landslides. [ABSTRACT FROM AUTHOR]