Investigation of a Limestone Pillar Failure Part 1: Geology, Laboratory Testing and Numerical Modeling

Summary A pillar failure at shallow depth of overburden, featuring the recent formation of subvertical open cracks in the rock was observed. An extensive laboratory test program including Brazilian tests, uniaxial and triaxial compression tests for obtaining strength and deformation characteristics of the limestone was executed. Strength from single and multiple failure triaxial compression tests on intact rock and from tests on small scale rock mass specimens were obtained. Classification of the rock mass was conducted for use with the Hoek-Brown strength criterion. Numerical analysis shows that the strength of the rock mass exceeds by far the applied stress, suggesting a stable pillar. This typical rock engineering approach to assess rock mass stability is shown to be inadequate.