Assessing karst hazards in urbanized areas. Case study and methodological considerations in the mantle karst from Zaragoza city (NE Spain)

Mantle karst environments can be analyzed by means of historical, geophysical and geomechanical approaches with the objectives of avoiding urban development in hazardous areas or to establish guidelines for foundation design. Nevertheless, geophysical and geomorphological techniques can show complexities in interpretation in urban domains. In order to analyze their limits and resolutions, historical approaches, geophysical surveys and field inspection are here combined with the analysis of building and construction problems in urbanized sectors. The particular case study presented is a sinkhole affecting three different domains: an agricultural area, an uncultivated plot and an urbanized zone where surficial karst evidences affecting streets, roads and buildings are observed. The results obtained permit to analyze the noises from urban environments for both magnetic and electromagnetic (multifrequency) techniques, and the limitations of ground penetrating radar (GPR) survey in agricultural areas with clayey soils and subhorizontal conductive layers. The comparison and evaluation of different approaches and geophysical techniques in the three domains permit to define an efficient routine in order to characterize surficial evidences, structural changes in underground materials, and changes in their geophysical characteristics.