Complementarity of Empirical, Analytical and Numerical Techniques for Assessing the Stability of a Natural Cave System in the Coastal Cliffs of Las Grutas (Río Negro, Argentina)

Abstract

Coastal caves developed in weak and heterogeneous cliffs constitute complex geomechanical systems in which lithological variability, structural discontinuities, groundwater seepage and marine erosion interact. Their stability assessment is particularly challenging in urbanised coastal and touristic attractive environments, where local failures may affect infrastructure and public safety. This study presents an integrated assessment of a natural cave system in the coastal cliffs of Las Grutas, Río Negro, Argentina. Field observations, structural mapping, geomechanical characterisation and UAV-based three-dimensional reconstruction were combined with empirical classifications, analytical roof-stability methods, and two- and three-dimensional hydro-mechanical numerical modelling. Parameter uncertainty was further explored through probabilistic sensitivity analyses. The results show that the different approaches provide complementary rather than directly interchangeable information. Empirical methods identify sectors with high geomechanical susceptibility, whereas the analytical assessment clarifies the roof-failure mechanisms associated with cavity geometry and stratification. Numerical modelling highlights the stabilising influence of three-dimensional stress redistribution while showing that groundwater flow and discontinuities control the localisation of deformation and the development of potential failure zones. The analyses also indicate that groundwater conditions exert a major influence on the calculated stability margins. Overall, the cliff system remains globally stable under the steady-state hydraulic and monotonic loading conditions considered, although local instability and progressive degradation may develop where basal weakening, seepage and unfavourable discontinuities interact. The study demonstrates the value of critically integrating empirical, analytical and numerical approaches and provides a transferable framework for the assessment and management of naturally cavernous coastal cliffs.