A sinkhole susceptibility zonation based on paleokarst analysis along a stretch of the Madrid-Barcelona high-speed railway built over gypsum- and salt-bearing evaporites (NE Spain)

This paper presents a methodology for producing sinkhole susceptibility zonations along linear infrastructures based on the analysis of the subsidence and dissolution features exposed in the adjacent cuttings and the distribution of karstic depressions. The proposed approach have been applied to a 24 km long stretch of the high-speed Madrid-Barcelona railway built on halite- and glauberite-bearing evaporites of the Tertiary Zaragoza Gypsum Formation. More than 100 km of this railway line have been built over salt-bearing Tertiary evaporites and trains run at a cruising speed of 300 km/h. The susceptibility assessment has been restricted to the sections located in karstic depressions (2.98 km) and trenches excavated in the ground (13.93 km). A low susceptibility has been assigned to the sections built on thickened alluvium of the Huerva fluvial system (0.5 km) and those in which the evaporites exposed in the cuttings do not show evidence of dissolution or subsidence (3.52 km). A total of 4.5 km have received an intermediate susceptibility. The cuttings in these sections show sagging structures, cavities above the railway roadbed, irregular rockhead or shallow alluvium-bedrock boundary. A high susceptibility has been assigned to a total of 6.59 km. These correspond to cavities and collapse structures that reach the railway roadbed (3.61 km) and karstic depressions generated by interstratal karstification and subsidence (2.98 km). The paleokarst and geomorphic evidence in these sections reveals that cavities, either air- or sediment-filled, do exist beneath the railway. The distribution of the karst features and susceptibility zones seems to be controlled to a large extent by the lithostratigraphy of the bedrock; wedging out of the evaporites to the SE and increase in the proportion of halite and glauberite to the NW. The proposed zonation could be used as the basis for the selection of the stretches where further investigations and the application of mitigation measures would have a better cost/benefit ratio. (C) 2008 Elsevier B.V. All rights reserved.