Investigation of a limestone pillar failure - Part 1: Geology, laboratory testing and numerical modeling

A pillar failure at shallow depth of overburden, featuring the recent forma tion of subvertical open cracks in the rock was observed. An extensive labo ratory test program including Brazilian tests, uniaxial and triaxial compre ssion tests for obtaining strength and deformation characteristics of the l imestone was executed. Strength from single and multiple failure triaxial c ompression tests on intact rock and from tests on small scale rock mass spe cimens 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 s table pillar. This typical rock engineering approach to assess rock mass st ability is shown to be inadequate.