Evaluation of the stability of underground cavities in calcarenite interacting with buildings using numerical analysis

Soft and highly porous rocks such as calcarenites are very common in all Mediterranean region. Due to their porous calcareous structure these rocks are prone to water induced weathering mechanisms. Natural onshore and inland underground cavities are evidence of such phenomena. The collapse of cliffs and underground cavities is usually the long-term result of a complex hydro-chemo mechanical process taking place at the micro-scale. Experimental results mainly give evidence of: (a) a marked and instantaneous reduction in strength and stiffness for these porous rocks when macro-pores are filled with water, (b) a slow successive reduction in strength and stiffness occurring in the long-term due to dissolution processes; (c) a more pronounced weakening of the rock material as a consequence of wetting and drying cycles. In the present work a methodological path to cope with deterministic assessment of the stability of natural and anthropic caves will be presented. The following steps will be adopted: (i) experimental study: execution of an experimental campaign to identify the physics of the processes taking place at both the micro-scale and the macro-scale; (ii) theoretical study: extend the concept of strain hardening-non mechanical softening to the time evolution of c-fi reduction; (iii) numerical study: present the 3D numerical results of a real case-study showing the capability of the proposed methodology to cope with risk assessment in complex geomechanical situations concerning weathering, as for underground cavities.