Multi-source data analysis for conceptual modelling of slow landslide mechanisms: Application to the Pianello hillslope in the Daunia Appenines

A thorough diagnosis of landslide processes at the slope scale is the prerequisite for the design and implementation of effective and sustainable mitigation measures. This paper describes the advanced application of the first, phenomenological stage of an already published stagewise methodological approach for landslide hazard assessment. The presented application aims at deriving the conceptual model of landslide mechanisms through the integration of different thematic models built upon big sets of cross-disciplinary, multi-source data, while providing the systematization and fine-tuning of the previously proposed methodology. The employed workflow is particularly apt to be implemented through digital tools that would boost the process of conceptual and numerical modelling of landslides and other geotechnical processes, particularly in complex geo-hydro-mechanical contexts.

The methodology is applied to an urbanised site in the Southeastern Apennines, the Pianello hillslope in the town of Bovino, a prototype case representative of many other sites affected by ancient slow-moving landslides in structurally complex formations. The slopes are characterized by a complex geo-structural and hydro-geological setting, and by a highly heterogeneous, heavily tectonised soil, composed of fractured rock layers embedded in a predominant clayey matrix.

For the test site, low shear strength, both intrinsic and induced by previous shearing, and high piezometric heads, are recognized as internal factors predisposing the slope to failure. Besides the erosion exerted by the stream at the toe of the hillslope, the reactivation of existing landslides is ascribed to porewater pressure oscillations at depth, induced by high cumulative rainfall over a seasonal timescale. Thanks to the integration of different models and data, the study highlights that the interplay between predisposing and triggering factors influencing the landslide activity is strongly related to the complexity of the geo-hydro-mechanical setting. The insight into deep slow-moving landslide processes acquired through this advanced application of the methodology to the prototype case of the Pianello hillslope can be easily generalised to many other cases in similar geo-hydro-mechanical contexts.