Camaras e pilares

Fracture process in pillars
J.-R.Pastarus
Tallinn Technical University, Tallinn, Estonis

ABSTRACT: The paper deals with fracture process in the pillars of Estonian oil shale mines. The study is based on field observations, theoretical investigations and numerical modeling. The analysis based on elaborated hypotheses and the Mohr-Coulomb’s failure criterion. For numerical modeling, the two-dimensional FLAC-code was used. Analysis showed that the failure criterion is satisfied in the inclined section, if the normal stress occurs on the top of a pillar. The failure criterion is satisfied in the vertical section, if the normal and shear stresses occur on the top of a pillar. The pillar is stronger under the first type of the stress state. Method is applicable in solving the rock mechanics problems. 1 INTRODUCTION Pillar design concerns matching pillar strength with pillar loading conditions to establish the dimensions that guarantee the pillar behavior as required. Despite structural simplicity and detailed knowledge of rock behavior obtained over the past years, pillar design has changed very little (Parker 1993). Consequently, the need of theoretical investigations and practical applications of the pillars behavior in Estonian oil shale mines are of interest in rock mechanics and phenomena of fracture. The main aim of this work is elucidation of the basic mechanism of the fracture and elaboration of the design methods for pillar. The study is based on field observations, theoretical investigations and numerical modeling on PC. If one knows from tests how a pillar or rock sample fails, one can develop a good hypothesis for the failure mechanism. It is important to notice that pillar loads vary from place to place within a mining block, depending mostly on the extent of the roof sags at each place. The analysis based on elaborated hypotheses and Mohr-Coulomb’s failure criterion allows estimation of the pillar strength depending on the type of the failure. For