In order to consider the presence of cracks in an abandoned gypsum pillar in numerical simulations, a hybrid method FEM/DEM, which allows the transition from continuum to discontinuum, was assumed. By means of a specific numerical code (ELFEN), this approach has been calibrated involving both physical quantities introduced by fracture mechanics and numerical aspects in order to support this hybrid method. Furthermore, the approaches FEM and FEM/DEM have been compared, showing advantages and disadvantages through experimental tests carried out to characterize geomechanical response of the pillar. The interaction domain has been calculated thanks to the implementation of both methods. The meaning of determining this domain is related to the evaluation of failure limit when a coupled system of loads (normal and tangential force and momentum) is acting on pillars. An application to a case study of an abandoned gypsum mine interacting with building in San Lazzaro di Savena (Bologna) is shown.
The choice of this pillar is related to its complex and redundant joint's system, its reduced section and its location. In fact, it was possible to obtain its topography by TLS to furnish a detailed geometrical for the simulation. In the following figure the mine system and the selected pillar is shown.
A series of laboratory tests permitted to obtain failure parameters to be inserted both in constitutive model for the continuum approach (FEM) than for the crack propagation model for the discontinuum approach (FEM/DEM).
A coupled system of loads acting on pillar P7 has been simulated. In particular, 3D numerical simulations have been run to calculate an interaction domain represented by normal and tangential force and momentum. Also for the 2D FEM/DEM approach an interaction domain has been built thanks to a simplified solution by choosing two representative sections of pillar P7. In the following the numerical calibration of the continuum and hybrid approach is shown.
