Effect of pillar size and joint dip on stability of porous limestone cellars

Abstract

Pillars play an essential role in the stability of an underground cavity. Their most important parameters are the dimensions, material parameters, condition, and joint geometry. This research investigates the impact of geometrical horizontal cross section and joint’s dip angle on the stability of the pillar, which affects the stability of cavities. The chosen study site is in a cellar system in Budapest, Hungary. According to the laboratory and on-site investigations, the cellar’s host rock is porous limestone with a low strength but a massive rock mass with few discontinuities. In some of the previously investigated cellar systems the edge of the pillars was cut because of space requirements. Therefore, this study aims to determine the effect of such geometrical changes on the stability of the cellar. A 25 m2 room with a single square-based pillar was used to model the stability. Material parameters were determined through various laboratory tests such as UCS, triaxial, and discontinuity shear strength tests, as well as rock mass classification. Three-dimensional finite element software (RS3) was used to evaluate the stability of the studied pillar. Overall, this study provides valuable insights into the factors that influence stability of pillars in underground cavities and highlights the importance of carefully considering these factors when designing, verifying, and constructing support systems for underground structures.