Large slow rock-slope deformations affecting hydropower facilities

Abstract

<p>Large-scale creeping landslides are widespread in alpine areas. Associated long-term, slow deformations threaten urban settlement, railways, main roads and hydropower facilities, on which our society is strictly dependent. Over the next decades, the continuous growing of the global population, the resulting increase in the urbanization (also closer to hazard-prone areas), and the climate change (e.g. melting of alpine glaciers) will increase these interactions and the related risk. Nevertheless, assessing the vulnerability of different types of elements at risk to this kind of hazard is not obvious, especially when hydropower structures (including dams, tunnels, penstocks, etc.) are involved. Large rockslides complexity often results in a variety of different evolutionary trends, making their forecasting and risk reduction a challenge. While catastrophic collapse can cause huge instantaneous damages, slow movements along long periods may lead to progressive damage of structures and infrastructures.<br>In the alpine and pre-alpine areas of Lombardia (Central Italian Alps), slow rock-slope deformations affect an area of 750 km2, threatening more than 10 km2 of urban areas and about 100 km of penstocks or tunnels related to hydropower facilities. Here we focus on the Mt. Palino slope (Valmalenco, Italian Central Alps), that is affected by a complex, apparently long-lived DSGSD (Deep seated Gravitational Slope Deformation) with a relief exceeding 1000 m. The slope hosts hydropower facilities and a tourist resort. In order to recognize dominant processes and their possible evolution (internal deformation, low-rate steady activity, progressive behaviour, seasonal effects) for better risk assessment and mitigation, we investigated the volume and depth of displaced rock mass and the possible localization of deformations along a basal shear zone. <br>Geomechanical and geomorphological surveys, seismic tomography, deep borehole logs and monitoring data (borehole instrumentation, precise levelling, topographic and GB-InSAR) allowed recognizing different sectors with different evolutionary stage and activity degree. The DSGSD which affect the entire Mt. Palino was probably active before the last LGM (Last Glacial Maximum), while only the northern slope sector is now considered as active. We recognized multiple nested phenomena faster than the main mass, identified as large rockslides. They are suspended over the valley floor and may evolve into fast rock avalanches. One of them is located in correspondence with the hydropower penstock, causing differential deformation to the structure. Borehole evidence of localization along cataclastic shear zones was found, motivating a petrographic geomechanical characterization of both rock masses and shear zone samples. Integrated 3D analysis of different information permitted to reconstruct displacement patterns, long-term mechanisms and the controlling factors of possible future evolution. </p>

Slope-Scale Evolution Categorization of Deep-Seated Slope Deformation Phenomena with Sentinel-1 Data

“…Due to the compound behavior related to multiple causal factors and the long-term evolution of these phenomena, the characterization of DsGSD deformation represents a challenging issue. Considering the extremely slow or very slow deformation trend, on-site monitoring is rarely used, apart from specific cases of point-wise ground-based measurements along sensitive infrastructures [47,48]. In such a context, the application of spaceborne DInSAR techniques proves to be a sustainable solution to remotely monitor and characterize these slow-moving phenomena, allowing us to measure ground surface displacements over large areas with millimeter precision [20,44,49].…”

Damage to anthropic elements estimation due to large slope instabilities through multi-temporal A-DInSAR analysis

“…In this mountainous area, DsGSDs are, by extension and gentle morphology, the ideal site of numerous inhabited centres and other strategic infrastructures, often exposing the anthropic structures and infrastructures to more or less severe damage. Damage can vary from slight effects, in urban areas without damage or crack to building walls, up to notable wall cracks and fractures (Di Martire et al 2016), or road network interruption (Cignetti et al 2019), up to cases where the decommissioning of a strategic work occurs (Barla 2018;Spreafico et al 2020). An in-depth characterization of DsGSDs evolution, focusing on the higher strain domains, is a key element to recognize the urbanized areas more susceptible to damage, which is actually poor investigated both in risk management and land-use planning.…”