ABSTRACT:

The aim of this paper is to study the mechanical behavior of a real pillar located in an abandoned gypsum mine in San Lazzaro di Savena (Bologna, Italy) through numerical simulations using a continuum to discontinuum hybrid approach. Continuum numerical simulations based on a Mohr-Coulomb constitutive model cannot represent the observed failure mechanism and estimated limit strength of mine pillars, supporting the need to properly account for their real 3D geometry and rock mass structure. A hybrid 3D FEM/DEM method has been applied to obtain a more realistic mechanical response of a gypsum pillar subjected to a vertical uniaxial load.

1 INTRODUCTION

The analysis of the mechanical response, failure mechanism and limit strength of mine pillars is a key point for the risk management in underground mine operation and decommissioning. Nevertheless, these analyses are usually performed through oversimplified approaches which do not take into account real 3D geometry and rock mass structure.

The aim of this work is to study the behavior of a real pillar located in an abandoned gypsum mine in San Lazzaro di Savena (Bologna) through numerical simulations using a continuum to discontinuum approach.

The 3D geometry of the pillar has been reconstructed by close-range terrestrial laser scanning (TLS). Structural analyses of the TLS point cloud and detailed field discontinuity surveys allowed the characterization of the pre-existing rock joints. Intact rock mechanical properties have been also evaluated through extensive laboratory testing.

The complex 3D geometry and structural pattern of the pillar suggest to go beyond a typical continuum approach. Thus, a hybrid FEM/DEM method, which allows the transition from continuum to discontinuum through the simulation of cracks nucleation and propagation, has been used. By means of a specific numerical code (ELFEN), the pillar behavior has been simulated from the laboratory test scale to the real in situ scale and geometry. The constitutive model, integrating Rotating Crack Model and Mohr Coulomb failure loci, was calibrated on the laboratory experimental results and in situ observation of real failure crack patterns.

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