A multicriteria approach to karst subsidence hazard mapping supported by weights-of-evidence analysis
Résumé
Soil subsidence/collapse is a major geohazard occurring in karst regions. It occurs as suffosion or dropout sinkholes developing in the overburden overlying karst. Less frequently it corresponds to a breakdown of karst void ceiling (i.e., collapse sinkhole). This hazard can cause significant engineering challenges. Therefore decision-makers require the elaboration of methodologies for reliable predictions of such hazards (e.g., karst subsidence susceptibility and hazards maps, planning strategies, priority areas for detailed investigations).
This study aims at developing a methodological framework for the evaluation of potential conditioning factors controlling the occurrence of sinkholes in a context of limestone karst: potential conditioning factors are first determined based on underlying physical processes for different geological contexts (barren and mantled karsts). Then the relevance of each factor is evaluated against a set of representative karst subsidence locations using the weight-of-evidence theory and relevant factors are tested for independence. Relevant and independent factors are finally weighed and combined together (i.e., superimposed) to achieve karst subsidence susceptibility models. The best model (i.e., the one showing the highest predictability) is determined by a receiver operating characteristic (ROC) curve analysis, which is performed using a set of independent and representative karst subsidence locations.
The method is applied to one case study where mantled karst setting prevails (Val d'Orléans, south of Paris). Results show higher susceptibility in mantled karst with significant role of the overburden lithology (presence/absence of low-permeability layer) and position of the karst piezometric surface within the overburden. The limited area of barren karst shows a low susceptibility.
Although this approach was developed for a specific karst context, it can easily be replicated in other karst contexts (e.g., interstratal karst, chalk or evaporitic karsts) which are known to be highly susceptible to karst subsidence even if some of the conditioning factors will be different.