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Theses

Quantitative risk assessment in rockfall-prone areas

Abstract : Rockfalls are a common type of fast moving landslide, corresponding to the detachment of individual rocks and boulders of different sizes from a vertical or sub-vertical cliff, and to their travel down the slope by free falling, bouncing and/or rolling. Every year, in the Alpine environment, rockfalls reach urbanized areas causing damage to structures and injuring people. Precise rockfall risk analysis has therefore become an essential tool for authorities and stakeholders in land-use planning.To this aim, quantitative risk assessment (QRA) procedures originally developed for landslides have been adapted to rockfall processes. In QRAs, rockfall risk for exposed elements is estimated by coupling the hazard, exposure and vulnerability components. However in practice, the estimation of the different components of risk is challenging, and methods for quantifying risk in rockfall-prone regions remain scarce. Similarly, the few studies which so far performed QRAs for rockfall assume stationary, precluding reliable anticipation of the risk in a context where environmental and societal conditions are evolving rapidly and substantially. Moreover, rockfall risk remains - as for most of natural hazards - always defined as the loss expectation. This metric offers a unique risk value, usually inconsistent with short/long term constraints or trade-offs faced by decision-makers.On this basis, this PhD thesis therefore aims at (i) reinforcing the basis of QRA, (ii) assessing the effect of environmental changes on rockfall risk, and (iii) proposing method for quantifying rockfall risk from measures of risk alternative to the standard loss expectation. In that respect, we propose a QRA procedure where the rockfall risk is quantified by combining a rockfall simulation model with the physical vulnerability of potentially affected structures and a wide spectrum of rockfall volumes as well as release areas. The practicability and interest of this procedure is illustrated on two real case studies, i.e. the municipality of Crolles, in the French Alps, and the Uspallata valley, in the central Andes mountains. Similarly, the effect of environmental changes on rockfall risk is considered by comparing rockfall risk values in different land-use and land-cover contexts. Last, we implement in our procedure on an individual basis two quantile-based measures, namely the value-at-risk and the expected-shortfall, so as to assess rockfall risk for different risk-management horizon periods. All in all, this PhD thesis clearly demonstrates the added value of QRA procedure in the field of rockfall, and reinforces its basis by implementing analytical, statistical or numerical models. The resulting panel of risk maps, also proposed under non-stationary contexts, are of major interest for stakeholders in charge of risk management, and constitute appropriate basis for land-use planning and prioritizing of mitigation strategies.
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Manon Farvacque. Quantitative risk assessment in rockfall-prone areas. Earth Sciences. Université Grenoble Alpes [2020-..], 2020. English. ⟨NNT : 2020GRALU001⟩. ⟨tel-02860296⟩

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