Karst structures in heterogeneous lithological units as a potential geo-engineering hazard factor for mining and civil infrastructures

The planning of civil engineering infrastructures and the exploitation of mineral resources in lithologically and structurally heterogeneous carbonate-dominated rock assemblages should take into account associated complex karst structures as potential geohazards. A recent study on the Paleocene-Eocene sedimentary succession outstandingly exposed in the Anhovo quarry (Outer NW Dinarides, Slovenia) points out the occurrence of paleokarst structures that are the result of localised dissolution processes along phreatic channels. These fluid flow pathways follow the directional anisotropy provided by a complex network of lithological matrix/clasts contacts in a matrix-rich depositional unit of ancient, large-scale submarine landslides (mass transport deposits; MTDs), which is in turn originated by specific sedimentary and post-sedimentary processes. Among primary sedimentary processes, down-slope gravitational transport favoured the lithological disaggregation and mixing of slide blocks and clasts into a marly-silty matrix, which later played an important role in controlling subsequent diagenetic processes on such exhumed MTDs. In this framework, groundwater flow followed different lithological and structural contacts, and block/clast boundaries, allowing the formation of contact karst structures, consequently providing favourable conditions for the formation of geomechanical labile systems in heterogeneous lithological units. The complex “worm-like” network of such phreatic channels, with certain anatomical features defined by the shape and orientation of structures and slide block/clast contacts, represents a zone potentially prone to gravitational collapse. The presented results suggest that the correct interpretation of synsedimentary structures, backed up by e.g. georeferencing of the contacts and the orientation of the slide blocks axes, allows us to identify or predict potential geomechanically weak areas of the quarry slopes where landslides could well be activated, and thereby contributes to better, more efficient decision-making on issues related tosafe mining and/or civil engineering practices.